NAS-NS-3060 NUCLEAR SCIENCE SERIES National Academy of Sciences-National Research Council Published by Technical Information Center, Office of Information Services UNITED STATES ATOMIC ENERGY COMMISSION COMMITTEE ON NUCLEAR SCIENCE D. A. Bromiey, Chairman, Yals University C. K. Reed, Executive Secretary, National Acacemy of Sciences Victor P. Bend, Brookhaven National Laboratory Gregory R. Choppin, Floride State University Herman Feshbach, Mamachusetts Institute of Technology Russell L. Heath, Aesrojet Nuciear Co., inc. Bernd Kahn, National Environimental Ressarch Center, EPA Jossph Wenaser, Brookhsven National Lashoritory Sheldon Woltf, University of California Medical Center Members-at-Large John R, Huirengs, Univentity of Rochaster G. C. Phillips, Rice University Alexander Zucker, Osk Ridgs Nationa! Laboratory Liaison Members John McElhinney, Navsl Ressarch Laborstory William S, Rodney, Nationsl Science Foundation George Rogoms, U. S. Atomic Energy Comm:siion Subcommittee on Radiochemistry Gragory R. Choppin, Chairman, Flovida State University Raymond Davis, Jr., Brockhaven National Lalworatory Glon E. Gordon, University of Maryland Rolfe Herber, Rutgers University John A. Miskel, Lawrence Radiation Laboratcry G. D. O’'Keiley, Osic Ridge National Laborstory Richerd W, Perking, Pacitic Northwast Laborstory Andraw F. Stehney, Argonne Nations! Laboritory Kurt Wolfsherg, Los Alamos Scientific Laboritory NAS-NS-3060 AEC Dstribution Category UC -4 pr—rrmsmemees st N Q) T 4 € i - This repoel was prepared a8 an sccount of work ’ sponsored by the United States Government. Nether ,’ the United States nor tha United 3tales Atomic Energy | Commission. nor any of their employesss, not sny of | theif con*ractors, 3UBCORTIACION., of lhell ¢mMployses, f makes a y wartanty, express or implied, or assumes sny | legal liab 'ty v responsibiity for the accuracy. com- [ platenass o usfulness of any iaformation, sppafsius, ; product of p.ocess duclowd. o reprewnts that its we | would not infr.ngs privately owned rights. | e i —emb it s, = il — e Aottt =t e RADIOCHEMISTRY OF NEPTUNIUM by G. A. Burney and R. M. Harbour Savannah River Laboratcry E. I. du Pont de Nemours § Co. Aiken, South Carolina 9801 Prepared for Subcommittee on Radiochemistry National Academy of Sciences - National Research Council Issuance Date: December 1874 Published by Technical Information Center, Office of information Services UNITED STATES ATOMIC ENERGY COMMISSION This paper was prepared in connection with work under Contract No. AT(07-2)-1 with the U. S. Atomic Energy Commission. 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Onh W uligs, Tommer s " Foreword The Subcommitiee on Radiochemistry 1s one of a number of jubcommutiees working under the Committee on Nuclear Scence within the National Academy of Sciences-——Nanional Research Council. its members represent government, industrial, and university laboratornies in the areas of nuciear chemistry and analytical chemistiy. The Subcommittee has concerned itself with those area: of nuclear science which involve the chemust, such as the collection and distnbution o radiochemical procedures, the radiwochemical purity of reagents, the piace o! radiochenistry in college and university programs, and radiochemistry in environmental science. This series of monographs has grown out of the need for compilations of radiochemical mnformation, procedures, and techniques. The Subcommittee has endeavored to present a series that will be of maximum use to the working scientist. Each monograph presents pertinent information required for radiochemical work with an indivafual element or with a specialized technue, Experts in the particular radiochemical technique have written the monographs. The Atomic Energy Commission has sponsored the printing of the series. The Subcommittee is confident these publications will te useful not only to radiochemists but aiso to research workers in other fields such as physics, b-ocliemistry, or medicine who wish 10 use radiochemical techniques to soive specific problems. Gregory R, Choppin, Chairman Subcommitiee on Radiochemistry II1. II1. IV. VI. VII. VIII. CONTENTS General Review of the Inorganic and Analytical Chemistry of Neptunium . . . . . . . General Review of the Radiochemistry of Neptunium . . . . . . . . . . . . . .. Discovery and Occurrence of Neptunium Isotopes and Nuclear Properties of Neptunium . Chemistry of Neptunium . . . . . . . A. Metallic Neptunium . A.1 Preparation . e e e s e A.2 Physical Properties . . . . . . . A.3 Chemical Properties . . . . Alloys and Intermetallic Colpoxnds . Compounds of Neptunium . . .. Neptunium Ions in Solution . D.1 Oxidation States . Oxidation-Reduction Reactlons . Disproportionatior of Neptunium . Radiolysis of Nepiunium S>lutions . Hydrolysis of Neptunium . ., . Complex Ion Formation . o0 w FPUUU LN Preparation of Neptunium Samples for Analys:s A. Neptunium Metal and Alloys . . B. Neptunium Compounds . . . . . C. Biological and Environmental Salples v e s Separation Methods . A. Coprecipitation and PrecipitatLon. - e v e B. Solvent Extraction . . . . . . . c e e C. Ion Exchange . . . . . . . .. D. Chromatography . . . . . . . . . E. Other Methods . Analytical Methods , . . A. Source Preparation and Radione.ric Hethods . B. Spectrophotometry . . . . e e C. Controlled Potential Coulo-etrr e e D. Polarography . . E. Titration Page 12 12 12 12 14 14 16 20 2 d- 24 24 29 31 33 39 39 39 40 41 41 54 104 107 109 109 114 119 . 121 - 123 IX. CONTENTS (CONTINUED) F. Emission Spectrometry . G. Gravimetric Methods . H. Spot Tests I. Mass Spectrouetry . . J. X-Ray Fluworescence Spectronetry . K. Neutron Activation . . . L. Other Methods . Radiocactive Safety Considerations . . . . . . . . Collection of Procedures A. Introduction . . B. Listing of Contents . . . . Procedure 1. Separation of Np by TTA Extraction . Procedure 2. Separation of Np by TTA Extraction . Procedure 3. Determination of “’Np in Samples Containing U, Pu, and Fission Products .. Procedure 4. Determination of Np . . . Procedure 5. Determination of Small Aununts of Np in Fu Metal . Procedure 6. Determination of Np in Sauples Containing Fission Products, U, and Other Actinides . Procedure 7. Detzmination of Np in Sanples of U and Fission Products . Procedure 8. Extraction Chronmtographic Separation of ***Np from Fission and Activation Pro- ducts in the Determination of Micro and Sub-microgram Quantities of U . boe e Procedure 9. Separation of U, Np, Pu, and Am by Reversed Phase Partition Chromatogr:aphy .o Procedure 10. An Analytical Method for Using Anion Exchange Procedure 1i. Separation of U, Np, and Pu Using Anion Exchange Procedure 12. Separation of Ir, Np, and Nb Using Anion Exchange 2 ”Np 132 134 134 134 138 141 145 150 185 158 161 163 165 167 169 171 References . CONTENTS (CONTINUED) Procedure Procedure Procedure Procedure Procedure Procedure Procedure Procedure Procedure Procedure Procedure Procedure Procedure 13. 14. 15. 16. 17. 18. 19. 20. 21, 22. 23. 24, 25. Separation ¢. Np and Pu by Anion ¥ .change . . Separation of Np and Pu by Cation Exchange . . Separation and Radiochcsinal Determination of U and Transuranium Elements Using Barium Sulfate The Low-Level Radio*heulcml Determination of 2*’Np in Environmental Sampl:es . Radiochemical Procedure for the Separation of Trace Amounts of 2*’Np from Reactor Effluent Water . Determination of Np in Urine Determination of 7 Ray Spectrometry . . . . . Spectrophotometric Uetermx- nation of Np . . . . Microvolumetric Commlexonetrxc Method for Np with EDTA . Photometric Determination of Np as the Peroxide Complex Separation of Np for Spectrographic Analysis of Impurities . . . . Photometric Determlnatxon of Np as the Xylenol Orange Complex . . Analysis for Np by Cantrolled Potential Coulometry -4 - "Np by Gamma 173 175 176 179 184 186 189 193 197 199 209 RADIOCHEMI!STRY OF HEPTUNIUM* by G. A. Burney and R. M. Harbour Savannah River Laboratory E. I. du Pont de Nemours § Co. Aiken, South Carolina 29801 I. GENERAL REVIEW OF THE INORGANIC FND ANALYTICAL CHEMISTRY OF - NEPTUNIUM J. J. Katz and G. T. Seaborg, The Chemistry of the Actinide Elements, Chap. V1, p 204-236, John Wiley and Sons, Inc., New York (1957). C. F. Metz and G. R. Waterbusy, '"The Transuranium Actinide Elements," in I. M. Kolthoff and P. J. Elving (Ed.), Treatise on Analytical Chemistry of the Elements, Volume 3, Uranium and the Actinides, p 194-397, John Wiley and Sons, Inc., New York (1962). "Neptunium," in P, Pascal (Ec¢.), Nowveau Traiile de Chimie Minerale, Vol. XV, Trcnsuraniens, p 237-324, Masson et Cie, Paris (1962). "tleptunium,' in P. Pascal (Ec¢.), Nouveau Traite de Chimie Minerale, Vol. XV, Trcnsuraniens (Supplement), p 1-94, Masson et Cie, Paris (1962). B. B. Cunningham and J. C. Hindman, "The Chemistry of Neptunium,' in G. T. Seaborg and J. J. Katz (Ed.), The Actinide Elements, p 456-483, Vol. 14A, Chap. 12, McGraw- Hill Book Co., New York (1954). *The 1nformation contained in this article was developed during the course of work under Contract AT(07-2)-1 with the U, S. Atomic Energy Commission. 6. 10. 11. 1z, 13. 14, 15. J. C. Hindman, L. B. Magnusson, and T. J. LaChapelle, "Chemistry of Neptunium. The Oxidation States of Nuptunium in Aqueous Solution," in C. T. Seaborg, J. J. Katz, and W. M. Manning (Ed.), The Iransuranium Elements, p 1032-1038, Vol. 14B, McGraw-Hill Fook Co., New York (1949). J. C. Hindman, L. B. Magnusson, and T. J. LaChapelle, "Chemistry of Neptunium. Absorption Spectrum Studies of Aqueous Ions of Neptunium," in G. T. Seaborg, J. J. Katz, and W. M. Manning (Ed.), The 'ransuranium Elements, p 1039-1049, McGraw-Hill Book Co., New York (1949). L. B. Magnusson, J. C. Hindman, and T. J. LaChapelle, “"Chemistry of Neptunium. First Preparation and Solubili- ties of Some Neptunium Compounds in Aqueous Solutions,' in G. T. Seaborg, J. J. Katz, and W. M. Manning (Ed.), The Transuranium Elements, p 1097-1110, McGraw-Hill Book Co., New York (1949). S. Fried and N. R. Davidson, '"The Basic Dry Chemistry of Neptunium,™ in G. T. Seaborg, J. J. Katz, and W. M. Manning (Ed.), The Transuranium Elenents, p 1072-1096, McGraw-Hill Book Co., New York (19493). C. Keller, The Chemiatry of the Transuranium Elemaenta, p 253-332, Verlag Chemie, Germany (1971). G. A. Burney, E. K. Dukes, and H. J. Groh, "Analytical Chemistry of Neptunium,"™ in D. C. Stewart and H. A. Elion (Ed.), Progrees in Nuclear Energy, Series IX, Analytical Chemiatry, Vol. 6, p 181-211, Pergsmon Press, New York (1966) . J. Korkisch, Moderm Methods for the Separation of Rarer Metal Ions, p 28-196, Pergamon Pre:«s, New York (1969). J. Ulstrup, '"Methods of Separating the Actinide Elements,”™ At. Energy Rev. 4(4), 35 (1966). A. J. Moses, The Analytical Chemis:ry of the Actinide Elements, MacMillan Co., New York [1963). A. D. Gel'man, A. G. Moskvin, L. M. Zaitssv, and M, P. Mefod'eva, "Complex Compounds of Transuranides,” Israel Prozram for Scientific Translations (1967), translated by J. Schmorak. 16. P. N. Palei, "Analytical Chemistry of the Actinides," translated by S. Botcharsky, AERE-LIB/TRANS-787., [See also J. Anal. Chem. USSR 12, 663 (1957)]. 17. Gmeling Handbuch der Anorgar iachen Chemie, Volume g, Transurane, Part C (1972). 18. Gmelins Handbuch der Anorgarischen Chemie, Volume 8, Trangsurane, Parts A, B, and D (1973). 19. V. A. Mikhailov and Uy. P. Movikov, '""Advances in the Analytical Chemistry of Neptunium (A Review)," J. Anal. Chem. USSR 25, 1538 (1970). 20. V. A. Mikhailov, Analyticai Chemisiru of Neptunium, John Wiley & Sons, New York (1973). 21. B. B. Cunningham, "Chemistry of the Actiaide Elements," in Amnual Rev. Nuel. Sci. 14, 323 (1964), 22. K. ¥W. Bagnell, The Actinide Elements, Elsevier Publishing Co., London (1972). II. GENERAL REVIEW OF THE RADIOCHEMISTRY OF NEPTUNIUM E. K. Hyde, "Radiochemical Separations of the Actinide Elements,” in G. T. Seaborg and J. J. Katz (Ed.), The Actinide Elaments, Chapter 15, National Nuclear Energy Series, Div. IV, Vol. 14A, McGraw-Hill Book Co., MNew York (1954). E. K. Hyde, "Radiochemical Separstions Methods for the Actinide Elements," Intermational Confererece on the Peaceful Uses of Atomic Emergy, 2nd Gemeva, 7, 281 (1955). M. Page "Separation and Purification of Neptunium," in Transuraniens, p 249-272, Masson et Cie, Paris (1962), ITI. DISCOVERY AND OCCURRENCE OF NEPTUNIUM Neptunium was discovered in 1940 by McMillan and Abelson.! They bombarded a thin uranium foil with low-energy neutrons and showed that the 2.3-day activity tha: was formed was an isotope of element 93 produced by the nu:lear r2actions: 2320 (n,y) 233U x> itNp - It was shown in 1941 that the decay product of 23°Np was 2%9pu.2 239Np is produced in large quantities as the intermediate in the nuclear reactor production of 23%-y, but because of its short half-life it is used only as a tra:er. Wahl and Seaborg® discovered the long-lived isotope 2*7Np in 1942. It was produced by the nuclear reactions: 30 (n2n) P30 geg 33N The first weighable quantity of 2?7Np (v45 ug of NpOz) was isolated by Magnusson and .aChapelle in 1944." These workers were the first to measure the specific a:tivity of 2?’Np. As a result of these reactions, Np is produced in relatively large quantities in nuclear rzactors fueled with natural U. When fuels entiched in 23%0 and 235U are used in nuclear reactors, the following reactions are increasingly important. 233U (n,yv) 2330 (n,y) v T‘g';"f 23inNp Since about 1957, the U. S. Atomic Energy Commission has recovered and purified bhyproduct Np in its production facilities. 237Np is used as target for the production of 22%pu, an isotope in demand for fueling radioisotopic power sources. ’ 233Np (n,v) 23%Np -2-_-%-&0 238, The half-life of 2?’Np is very short compared to the age of the earth. Therefore, it is found only in trace quantities in U minerals where it is formed cont:nuouslv by neutron reactions described previously.® It vas found that the abundance of 23”Np in a sample of Katanga pitchtlende was 2.16 x 10”'2 atoms per atom of 2%, while that of 2%Pu was 3.10 x 10°'? atoms per atom of 23%.7 IV. [1SOTOPES AND NUCLEAR PROPERTIES OF NEPTUNIUM The known isotopes and celected ruclear properties of Np are listed in Table 1. The radioaralytical chemist works mostly with long-lived %?"Np and short-lived 2?°Np and 23°Np. The decay schemes of these most important isotopes of Np are presented in Figure 1. Thermal neutron cross sections and resonance integrals for Np isotopes are shown in Table 2. Mass Nember Half-1ife n" 7] 25 133 238" 257 240" 240 11 a sf e a w EC = 4.6 nin 50 min 15 min 35 min 4.40 day 386.1 day 22 hr >5000 yr 2.14 x 10° yr 2.12 day 2,35 day 7.5 min 67 min 16 mla ISOTOPES OF MEPTURIUN®:® Specific A=tiviey 1.031 xapt* 4.5 x 10" 3.945 1 10" 3.514 2 10" 1.3 x 10'* $.117 x 10'* 2.815 x 10" 5.114 x 10" 3.397 z 10" 1.564 a2 10" 5.744 x 10" 5.160 2 10! 2.595 = 10" 1.0a2 x 10'* spoatansous fissiom alpha decay slectroa caspture decay f~ = ssgatrom decay TABLE 1 ode of® Mecyy sf a(>0.5) BC(<0.5) BC{0.97) a(0.03) EC(n0.99) a("0.01) EC ec a(? 2 107%) EC a(<10” ") £’ a(~10" 1) EC(0.48) A°(0.52) a 1 sf (5 n 10°'Y) L af(<® x 10°'") - 10 - Lecay Enmrgy (We¥V) . - 6.66 a " 6.0 a = 6.28 E, = 5.53 E’., = 0.8 . " 5.095(4%) 5.015(831) 4.925(12%) 4.064(1Y) g- " 0-518(601) 0.36(408) - 4.786(42%) 4.760(01) 4. 764 (SV) 4.661(5.5%) 4.634(6%) g- " 1.25(4a5%) 0.26(54\) EY = 1.027(231) 0.945(261) a- " 0.713(™) 0.437(aab) 0.393(13%) 0.332(204) E’V « 0.278[130) 0.220012%) 0.106(214) g - 2.18(52%) 1.60(31%) g~ - 0.89(100%) El' = 1.3 Methods of Preperation :".i - ll". I'Iu(’.sn) 1% (p,4n) 13%)(a,50) 138%(d,9m) 13%y(d, 5n) V%4, ) 3% (d, 4n) 1¥%(4, 3n) "’I.l[d,ln) M%y(4, ) '“U{d,n) '.’“[I,h) "'U[d,‘n) "% in,m) "y(e, v’ T3y (s--decay) I an(x-decay) 21 T"P [. ..',) 13 .“[d . h) "’U(G.'P) " %(n,T) 1% (B-decay) 218 (d-fl) " pa(a-decay) ’..U(B-fl.flyl 'I.uru'p] '..u(ulpl 237y, 52 (0.02°4) (52 / . 11/ (0.5%) 459 (60%) 4636 . N6"%) 4592 L7786 (L2%) (22%) 4708 4803 (15%) Sein Emergy . ond [heVi 4815 (12%) parity 4o 4865 (1] 28 52} 3G ——— Q2e) 2 192 166 %2 o2 108 e | /D) 86 et §2- 69— we- 57 w2 8 Energy (navi 556 2 =S - 8083 - L9122 T o~ 18 noy 85 t817s ”»sn 7y 765 2% Pu Enargy Spin and fardy 3o rg )fia Spin ond patity 7 1B L7 ] WH- $f2l-: mia N Uk W2« Vo Vi Figure 1. Decay Schemes of the Most Imgartant Neptunium Isotopes, 2*’Np, 23®Np, and 2?3Np.B*!° TABLE 2 CRUSS SECTIONS AND RESONANCE INTEGRALSY FOR NEPTUNIN. 1SOTOPES® Neuwtron Capture Fis:ion Mass Number c(n,n lp.n I¢ i E_{ 2&9_,_2__!3}_ 234 900 235 1a8d 236 2,800 237 185 600 0.02 0 0.0013° 1,424 238 1,600 600 2,070 800 23¢ 35¢ (to **"™wp) s 25¢ (ro 2"'Np) Cross-sections expressed in barms, 10~ “cal. J. #. Landrum, R. J. Nagle, M. Lininer, UCRL-S1263 (1972). For neutrons with the fission spectrum. For 3 MeV neutrons. For "reactor neutrons', 2 Y ke TR V. CHEMISTRY OF NEPTUNIUM A. METALLIC NEPTUNIUM A.1 Preparation Np metal was first prepared by Fried and Davidson in 1948 by the reduction of S0 ug of NpF, with Ba vapor at 1200°C.'! A similar method was used by Westrum and Eyring.'? Reduction of NpF. by excess Ca metal with iodine as a booster'? !? was used to produce multigram quantities of Np metal, A.2 Physical Properties Pure Np is a silvery ductile metal with a melting point of 637°C. The metal undergoes three allotropic modifications below the melting point. The physical properties ure summarized in Table 3. - 312 - L. TABLE 3 PHYSICAL PROPERTIES OF NEPTUNIUM METAL3®+17:1¢ Appearance: Silvery white (slowly c¢cated with oxide in dry air at room temperature) Melting Point: 637°C Boiling Point: 4175°C (extrapolated frcm vapor PIgssure measurements of liquid Np' ') Heat of Vaporization: AH 1800°K = 94.3 kcal/(g-atom) Properties of Various Allotropic Modifications: & 8 v Transition temperature to next higher phase, °C 280 577 637 Density, g/ca’ (at T°C) 20.48 19.40 18.04 Crystal Structure Orthor- Totragonal Cubic hoabic Stephens?'! determined the pressure-temperature relationship for Np. The specific heat (Cp) of Np is high. The Dulong and Petit value of 3R is reached at 140°K and 7.093 cal/(mol-°"K) st 27°C.?' The high specific heat can be entircly accounted for by the very high electronic contributions. No magnetic ordering in a-Xp occurs down to 1.7°K.°? - 18 - A.3 Chemical Properties Np is a reactive metal. The potential for the couple Np » Np” + 3¢ is 1.83 volts. Metallic Np is slowly covered with a thin oxide layer when exposed to dry air at sbout 20°C, and rapid oxidation to NpO; occurs at higher temperatures especially in moist air. Hydrogen, halogens, phosphorus, and sulfur react with Np metzl at elevated tempuratures. Hydrogen rescts to form the hydride at relatively low temperatures. Np forms intermetallic compounds of intermediate solid solutions with U, Pu, Be, Al, B, Cd, Ir, Pd, and Rh. Np dissolves readily in HCl at room temperature and H250, at elevated temperature. The behavior of Np toward various solutions is given in Table 4. 8. ALLOYS AND INTERMETALLIC COMPOUNDS Complete phase diagrams are reported for Np-Pu and Np-U.?3728 Complete miscibility has been reported betveen y-Np and y-U and between y-Np and L-Pu. Np is a unique elenent because of its extremely high solubility in both a-Pu and 8-Pu, The intermetallic compounds of Np with Al and Be (NpAl,, NpAl:, NpAl,, and NpBe;;) are prepared directly by reducing NpFi with an excess of metallic Al or Be. The borides (NpB;, NpBw, NpBs, and NpB,;) and the intermetallic corpounds NpCdg and NpCd:2 are obtained directly from the elcments.2?”2% Several - 14 - TABLE 4 BEHAVIOR OF Np METAL IN VARIOU:; SOLUTIONS'?® Observations Solution Concentration (M) Initial After 4 days H,0 Very slowly atta:ked He1? 1.5 Immediate vigoroas Completely dissolved reaction 6 131 " 12 1y tE HNO 4 2 No visible reaction Some turbidity, hydrated oxide 8 " e 15.7 " No resction- clear solvent H250.,% 2.25 Slow reaction No reaction- clegr solvent 9 1" " 18 No noticesble resction v (H,000H% 2 Slight initial reaction- Soms turbidity ceased hydrated oxide a " ” 16 No visible reaction No resction- clear solution HC10, Conc. Rapid dissoluticn " vhen hested HyPOs Conc. Rapid dissoluticn when heated HSO yNH Rapid dissoluticm " when heatad Conc. HNGy - Dissolution whey refluxod " trace HF 2. At ambient temperature, - 18 - compounds with noble metals, such as NpPt; and NpPts, have been prepared by hydrogen reduction of NpO: at 1300°C in the 0 presence of platinum.?® Alsc, Erdmann’! used the same method 10 prepare several other compcunds, Nplr,, NpPdi, and NpRhj. (.. COMPOUNDS OF NEPTUNIUM Compounds of Np for the III, IV, V, VI, and VII oxidation states have been prepared. The solubilities anc compositions of some of the compounds have not been verified because they were initially determined with small amounts of Np shortly after discovery and therefore may be semi-quant:.tative. Where studies have been made with larger amounts of neptunium, i.e., oxalates and peroxides, more quantitive data is available. Numercus Np compounds, such as nitrates, chlorides, and possibly thiocyanates, are readily soluble in s>lvating organic solvernits such as diethyl ether, hexone, TBP, ani other acid- containing solvents saturated with water. Investigation of compounds containing trivalent neptuniuwas has been limited because of the instability of Np(Ill) in aqueous solution in the presence of atmospheric oxygen. Np(III) is produced under hydmgen {on a platinum catalyst), by electro- chemical reduction and with rongalite, NaHSO:.(H;0‘2H,0., Mefod’eva ¢t al.’? have prepared several Np(ll1l) compouncis from solution with protection from oxygen. All the reagent solutions and water were - 16 - purged with pure argon. The precipitation and subsequent operations (centrifugation and washing) were conducted with a layer of benzene over the solution. The solids were washed with acetone or ether and dried in a strear of argon. Np(III) oxalate was prepared, but it was appreciably oxidized in a few hours. The solid was brown and was in the fo:rm of tetragonal prisms. Np(III) phenylarsonate is rose-lilac colored with the composition Np2 (CeHsAsO3) 3°nH20 when well dried; the compound is stable for a long period at room temperature. Np(III) salicylate and grayish- lilac Np(IIl} fluoride were also precipitated under controlled conditions. Two complex double sulfates of Np(III), KsNp(S04)s and NaNp(SO.)2°-nH20, were precipitated. In the dry form, these salts were stable to oxidation during prolonged storage even at increased temperature, Only one solid compound of Np(VII), Co(MH3)¢NpOs-3H20, has been reported.’? Compounds of Np(IV), (V), and (VI) are shown in Tables 5 and 6. Table 5 includes compounds produced in aqueous solution, and Table 6 includes compounis produced by other motliods. -17 - TABLE 5 NEPTUNIUM COMPOUNDS PRECIPITATED FROM AQUEDU!: SOLUTION Composition Compound Color __of Solution NpO; (OH) x~aq Black NaOH - NaNO, pHS5 9 Np(IV) hydroxide Srown green 1M NaDH -~ IM NaNO, Np(V) hydroxide Green IM NaQH - dilute ammonia {NH4 ) 2NpP209 Brown 1M N4, OH - 0.5M (NH,);50. Np(IV) peroxide Purple 2.5M HND, - 6.5M Hy0, NpF,+XH,0 Grayish 0.3 HCY - Iilac 0.3M HF (srgon atm) NpF .+ *XH;0 Green 1M HNO, - IM HF NHNpF -+ Green IM HF - 0.01M NH.F KNpaFe Gresn dM HF - 1N KF LaaNpF 3 XH0 Np(IV) iodate Tan Srown IM HC1 - 0.1M K10, Np(111) oxalate Brown Npl(C204);°6H0 Grean 0.14 H;C;0., - M IND, NpO:C;0.H*7H,0 Green NpO2C 04 3,0 Grey green L"“;Cfl. Tan H,D KgNpO2 (C0y) Greenish blue H,0 - 0.M K00, CaNp0; (CO») )y Greenish bluse H,0 ENpO, (CaH 03 )« Green 0.°M 4,380, - 0.0™ NaNO, . M NaC;1,0; Np(HPO, ) 2=XI;0 Green IM HC1 - 0.5 HyPO, KaNp (50. 1, Bluish lilac 0.3 HC1 - sat K250 - 0.2V N;50. NaXp(S0.) ;*nmi20 Blue 0.3M HC]1 - st K50, - 0.2 H,;S0, Np(CgligAs0,y); Green 0.1M CHsAsOH; - 0.5M HND, NpO2CeHy AsO 0.D8M CyllsAnDH; - 0.5M HNOD, [ Q) 2 (CoHla@fy) N2t 6 to BM \ND, NpiND,y ), So.ubility(mg Np/1) Dissolves in elithar acid or base Stod 17 e 120 28 1: 13 11 13 100 Refsronce 33 2 37 n » 32 40 41 42 43 32 32 TABLE 6 OTHER NEPTUNIUM COMPQUNDS Compound Color Lattice Symmetry Reference Npil; Cubic 47 NpH, Hexagonal 47 NpO, Green Cubic 48,49 Np20s Dark brown Monoclinic 49a Np10Os Dark brown Orthorhombic 50,51 NpOjy+H,0 Red brown Orthorhombic 47 A large wmber of termary and polynary oxides of Np(VII), Np(VI), Np(V), and Np(IV) with glkali metals and alkaline earth matale are knoum. Also, sindilar compournds are reported with thgzrare earths, other actinides, and alements in Groups 4 to 7. NpN Black Cubic 53 NpF Purple LaF, 54 NpF, Green 55 NpFe Orange Orthorhombic 52,56 A large number of fluoro ocompourde of alicali or alkagline earth metals with Np(IV) and fluoride -have baem reported; a few such compounda with Mp(V) and Np(VI) aleo are reported.®? NpO:F Green Tetrajonal s7 NpOF Green Rhombohedral 58 NpO,F 2 Pink 57 NpCl, Green 11 NpCl. Orange brown 11,58 NpOC); Orange 59 NpBr) Green 60 NpBr. Dark red 61 Npl, Brown 62 NpS Cubic 63,64 NpaSs (4 di fferent 63,64 structures) NpsSs Orthorhombic 63,64 Np2Ss Tetrngonal 63,64 NpS) Mono:linic 63,64 - 19 - D. NEPTUNIUM IONS IN SOLUTION D.1. Oxidation States Neptunium exists in the (II1I), (IV), (V), (VI), and (VI1I) oxidation states in aqueous solutions. The heat of formation, the entropy of the individual ionic species, and simple methods of preparation are listed in Table 7. The first four of these oxidation states exist as hydrated ions in the absence of complexing agents. Np(VII) is stable only ir alkaline solutions; reduction to Np(Vi) occurs in acid solutions. The singly charged, hydrated neptunyl ion, [NpOz(H20)51+, is the most probable oxidation state in solution. Because Np02+ hydrolyzes only at pH >7, disproportionates 3nly at high acid concentrations, and forms no polynuclear complexes, it is stable compared to the other pentavalent actinides. The standard potentials and formal electrode potentials in IM HC10, of pairs of neptunium ions are shown in Table 8. The formal oxidation potentials for Np couples in various IM solutions are given in Table 9, with the hydrogen electrode in the stated medium as the reference. The change in the potentials in 1.0M HSO. as compared to 1M solutions of HC10,, HC1, and HNO3 indicates strong complex formation cof Np“* with sulfate ions. ~ 20 ~ TABLE 7 MEPTUNIUM TONS IM AQUEOUS SOLUTIIM®**! Heat of Formation AHye ek Oaidation State Ionic Form Color (kcal/mol) .3 Np(H,0) {* Blus violet -127 . Np(Hg0)3* Yellow green -132.5 *5 NpO;(H;0); Gresn -231 *6 NpO, (HyM)2* Pink or red -208 '™ o +7 m! Green a. J. C. Hiochey, J. . Cobble. Imorg. Cham. 4, 992 (1970). R. Brandr, J. W, Cobble. J. C. Brown in HClO.. Incrg J. C. Sullivan and A. J. Zielen. . Chaw. 2, 912 (1970). Inorg. - 21 Mual. cal Simple Mathous of Preparscion Entropy Hree®K ~atom-"K)] 3.5 D 2) -8 1) 2) 3) - o:-.z'J 1) ) B 1) 1) — )] Np(>T11] « Hy/Pr Electrolytic reduction Np'T O Np(V) + 502 Np(v) ¢ I-(5M HC1) Np** « NGy (heat) Np(¥1) +« stoichiouetric I° Np(V1) +« NH,0H Np{<¥1) - HC1O0, (evaporate) Hp£¢\'l) « Ag(IL}0 (or BrO;, Ca ") Nissolutlon of chermally prepared LIyNpO¢ In dllute alkalis NP(V[) « otone [or Xel,,K;Sp0,, periodate) in 0.5 to 3.5 MDH Chen'. Latters I, 927 (1969). TABLE 8 STANDARD AND FORMAL REDOX POTENTIALS OF PAIRS OF NEPTUNIUM IONS** Standaid Formal Poten- Potenticls tials in 1M Electrode Process (volts) HC10, (voits) Np = Np** + 3e- -1.856 -1.83 2Np + 3H,0 = Npy0y + 6H* + Se- -1.420 - Np20y + Ha0 = 2NpO, + 2H* + 2e- -0.96 - Np;03 + SH,0 = 2Np(OH), + 21I* 2e- -0.921 - Np?* = Np** 4 e- -0.152 0.1S5 Np'* + 2H,0 = NpO, + 4H* + e- 0.337 - Np'* + 4H20 = Np(OH,) + 4H* + e- 0.391 - Np’* + 2H20 = NpO} + 4H* + 2e- 0.451 0.447 Np(OH), = NpO3 + 2H,0 + e- 0.530 - NpO; = NpO3 + e- 0.564 - Np“* + 2H,0 = NpO3 « 4H" + e- 0.749 0.739 NpO2 = NpO3* + e- 1.149 1.137 2Np{OH)% = Np3Os ¢ 2H,0 + 2H* + 2e- 1.219 - 2NpOz + Ha0 = NpaOs + 2H* + 2e- 1.283 - Np20s + H,O0 = 2NpO,3 + 2H* 2e- 1.310 - NpO; ¢ H,0 = NpOy ¢+ 2H' + e- 1.9¢8 - Np'* + 2H,0 a NpO3* + 4H* + 3e- - 0.677 Np*® ¢ 2H0 = NpO3* + aH" + 2e- - 0.938 - 22 - TABLE 9 REDOX POTENTIALS OF NEPTUNIUM (IN VOLTS AT 25°C) ?*¢¢°°° 1.0M HC10, -0.477 -1.137(¢-1.236)% | - 0.739 -0.155 | +1.83 NpO3* NpO$ e Np* b Np¥ e Np | -0.938 ] -0.677 1.0M HC1 -0.437 ~o-1ass | -0.737 -0.137 | 1.87 NpO3* NpOf —— — Np** Np3: Np | -0.936 ] -0.670 1.0M stfl'n -1.084 -0.99 +0.1 Nlfl%t—_—.——.— Nw; pri‘ _-NPS"' | ~1.04 1.02M HNO, -1.138 Npo3* Np03 1.0M NaOH -0.48 -0.39 +1.76 +2.25 NpOz (OH) 2 ——-———-—-NwQOH e e Np (U*{) I e rerinee Np fOH) 5 --————-Np (-0.43) 0.582 5 Np(VII) ———— Np(VI) a. Standard potential® b. According to the half-reaction NpOi~ + e~ + H,0 = Np02~ + 20H"%9 the dependance of E; on the OH™ concentration is expressaed by7°: Eo = 0.600 + 0.059 ¢ log [OH-]"" - 23 - The current-voltage curves for oxidation-reduction reactions of Np in aqueous solutions are shiown in Figure 2, D.2. Oxidation-Reduction Reactions Table 10 lists reagents and conditions; necessary to change oxidation states for Np ions. For cases wiere only one electron is t-ansferred, e.g., Np' /Np*" and Np0,*/Np022", the establish- went of redox equilibrium is rapid. Redox reactions that involve forming or rupturing of the neptunium-oxygen bond, e.g., Np“*/Npoz’ and Np“*/NpOzz*. have a slower reaction rate. Rate constants (k) and half-conversicn periods of the redox reactions in IM acid solutions at 25°C are given in Table 11. D.3. Disproportionation of Neptunium Only the Np(V) oxidation state underjoes appreciable disproportionation. The reaction 2Np02+ + 40" -'Np"+ + Np022+ + 2H20 shows that disproportionation of Np(V) is favored by high acid concentrations. Because Np"+ and NpOaz* form more stable complexes than the NpOg‘ ion, the disproportionation of Np(V) is promoted by the addition of complexing agents. The equilibrium constants, K, for various acid solutions are listed in Table 12 where Np (1V VI Np(V) - 24 - LR L T T 1 r 1 1 v v °r T 1 Np{IV)«=— Np(V) 100 ¢ Np{V)—e= Np(VI} — No{ M)=a—Npl1v) o MOV F==—RptVI) ~o—0 q Np{IV) —e= Np(V) x —— (01) —e=Np(1V) Current, mA o8 5388388 -0.2 -0A4 -08 -0.8 -0 1.2 -1A4 -1.6 -1.8 -2.0 Volts Figure 2. Current-Voltage Curve for Redux Reactions of Neptunium." - 25 - i KW © Apitet} ) ~ Npir) W - Npor) o3 = apIn) Wpivr) - i) Wpdye) -~ Ppn Nplvt) = Vil Npdd} - Wpivl) wp(vl) - WpVIL} Np(VEt) = Wp(vis s0f feriadate WOC1, MOBy "0, L R, -y 0.0m W, - » W L « A, B, s mselrmt - " " e, & m, [ .1 el b U 1.5 8 18" set, X .50 MW 2.8 n"\ e, .73 = ol b, A0, ., ) "o W, ) D, $ s 9wy L e 10 e g, 2.8 ¢ 10N Yy e Iha MY 0.1% 8,5,0, (B N 2.5 2 18 N O.IW 1.5 % 40 "W %p o .5 a [0 ™™ % 2w 18 ' W " s s i "wy S ow 1o 'wowDt O 1Y TOW D% te W R - 26 - sl saus BasBea 4% 3ILSIJITINT 2UE 3 3 s s " 53 20 Yyry 2 M T Yary fost Tosy LY 1Y) Yeory Tost A renversion ia W e ?ase 1fa Y2 Yprs Yy % e e Y Y fant S T =1} atn A .- o maw 20 e I mas M ms -‘z- " : m-fl'-’:' " l'“l“ o“--"nr ™ . ' el = W x 8 ".'h. ’.“"*v .Q"--"-.‘u- » ¢ ¥ l* ‘ - 5 v Wy 3.i e T . n Wiy ~ Wb =5 . m"s-r-m = ! :”".c spp™iive it sty gt VP et Psil Aol Tl o« a Byt eyt 'fi E TER, Ut o ¢ ‘v "ty st in ey popsd™ |1, b b L IRV = T s pnptf ) pom | LIt - b T Y gt i W] I (1) M W CUMEOTEN ICASIN W %€ St MUNITOM TR e AED MamA &5 Mgt T MMM o s, =20, : _,yE, -, % -t $ 4 ¥, 3 e, = WMy, w3k, v WRE, x WA, ;.3 e, ¥ s, i " ek, i -y ¥ s, » -, e ., 5P ek, 3 gg ® ¥ $. 00 0T 90, v 2 T W TR D e b S S it } 3 v ¥ HE A !l By ¥ 5% & 3 B, o+ F b i"?}" Sy £ B %, b o €00 2% &, vy " ‘*:‘-‘v"vl'l, “*’-’.‘L'?‘;‘, % ¢t 37 3 By t # &) 8 iy tit;i e 5 B ¢+ 2 e & % ‘;i‘,‘. " * i ¥ ¢ 5 # vk epF’ 8, 58 ks syt ‘;"l’. rw,‘ ¥ Mflj*‘ Ll ol - » et i3 . - ;b B t e 50 ’l ‘i t . om ' s ] et 5 Wierplemh biavgy AR IBEYS » . * ¥ e 4 ez v 4 e e bl - Ay > W TABLE 12 EQUILIBRIUM COMSTANTS FOR DISPROIPORTIONATION OF Mp(V) IN VARIOUS ACID SOLUTIONS AT 25°C 3 Solution ? IN HC10, 4 x 107 S.34M HCIO0, 0.127 8.67M HCIO, 200 IM H,S0, 2.4 x 1072 1.86M H;S0, .16 a. K » v vi * 2 (Np(V)) . 28 - The reverse reaction vt Np** « Np022* + 2H0-ws2Np);* + 4n"® takes place rapidly in weakly acid solutions. The rate constant in IM HC10, is 2.69 (M.min) !.?* D.4. Radiolysis of Neptunium Soluticns The radiolysis of Np(VI) by self-radiation of ?*’Np causes reduction to Np(V} with & rate constant of (3.1 $0.2) x 10°® sec” ! (0.5 to 1.7M HC10,) and a radiolytic reduction yield (G) of 6.4 ions/100 ev.””" 7" Compared to other hexavalent actinides, Np(VI) has a much lower rate of radiolytic reduction. For the *°Co irradiation of 0.1M Np(VI) in 1.1M HCIO., G = 3.4. The radiolytic yields for rudiolysis of Np solutions (saturated with atmospheric oxygen) exposed to a ~ | MeV 9231 3re shown in Table 13, Np(V) has a compara- electron beanm’ tively high stability to radiolysis. Np(IV) is oxidized to Np(V). When 2%°Np is prepared by neutron irradiation of uranyl salts, 80 to 90% of Np is in the tetravalent state.'? - 29 - TABLE 13 RADIOLYSIS OF NEPTUNIUN SOLUTIONS [N AN ACCELERATED 1-MeV ELECTRON Radiolytic Acid Con- Yield G centration {ramber of lons ion Acid ) per 100 eV) NpO$* ~ NpD,* HC10, 0.018 4.45 0.80 $.76 0.126 $.7 0.? 6.7 1.§ 4.7 3.4 1.9 HNO, 0.08 8.2 H2S0, 0.86 3.0 Np** < NpO,* H250, 0.8 2.1 0.5. Hydrolysis of Neptunium The hydrolysis of a metal ion is a special case of complex formation with OH™ ijon. Hydrolysis consists of the transfer of a proton from a coordinated water molecule to a water molecule in the outer sphere, ¢.3., Np(H20)4"" + H O = [Np(OH) (H;0)7]*" + Hy0" with K, - mgw“u,ohl” (Hy0]" [Np(H20) 4] The most recent and extensive hydrolytic studies of Np were made by A. 1. Moskvin.®?! Hydrolys.s constants, K, are listed in Table 14 for Np(1V), (V), and (VI).* The tendency for Np ions in dilute acid solutions to undergo hydrolysis increases with increasing ionic potential (d) where d = Z/r, Z is the ionic charge, and r is the ionic radius. Thus, the tendency to undergo hydrolysis increases in the order: ’+ wt NpO2* Np®® »>Np023* »Np022* 5NpO. Neptuwnium (I1I) Np(III) exists in aqueous solutions as Np(H20)e’*. The chloride and bromide complexes cf Np(III) have been studied spectroscopically in concentrated LiCl and LiBr solutions (see Table 15). - 33 - TADLE 18 COWPLEINS OF NEPTUNIWN IR AQUEOUS SOL JTION'*® cmim Lissme Moched” £°c} Madmm Speciey _ 'c.l-:::::_b Refereace npt Quleride spec 3 Cemc LiC1 wpC1** f - 2.42 “ "l.’ b -40 Brexide pex n Camc Libw fphe* # - 48 » Rpber, * hy - 6.54 p"* Qularids disea 20 1.00 MC10, w1 ** B, - 0,04 ” w1 By -0.24 mpCiy* By -0.4 -t n 1.0M NC10, 8, -0.3 20 dlaem » 2.0 ACI0, 8, +0.04 " By ~-0.1& dista ;-] 4.0 HC10, . AL - 5.10 Pl B, - 0.10 Flueride fex 20 4.0M HC10, NpP'* B, 402 02 npFi* Ba + 7.57 WpF,* By - 8.9 NpP, By 211 Ritrste dista 0 1.0M HC10, NpfwD,) "t B, +0.M4 B9 wp (0, §* By * 0.08 Np(NO,),* By -0.120 -t s 1.0M HC10. B, + 0.38 20 dista 0 2.0M KCIO, B, +0.34 ) dirtn 23 4. KCIO, g, -0.15 Y| Ba - 0.7 Hydronide pet 0.1 to ™ K10, npOH'* By ~I1.7 % » SulfsLe dista B 2.0M HC10, [Np(so 1 Br + 2.43 93 Np(SD.) 2 B; + 147 -f s 3.04 NaClO« By + 2.49 9 By ¢ .57 tex 2 4.0W NCIO, g, +2.70 92 By + 4,26 Oxalsts sol 5 - [Np(CA0e) %" 8, -« 8.5} 95 Mp(CyOu) s 6:r -I17.8% INp(Ca0a) 01" By +23.96 [Np(CsON )4 )" A +27.4D sol b 1.0M KC1O, 8y =~ 7.40 %% By *1%.82 8y =19. 48 dista » 1.0M HC10, B, +~0.19 8, sl14.42 fermats pac - 0.1 to 0.3 NgOOCH "Wp(HO0),]" By » 2.7 u Acetate len, ouf - 0. D4 e, cl [Np(AC)]?* 8 - Lol 27 (AC7) [Np(AC),)?* B + 478 [Mpeacy,)* B: +7.49 Mp(AL). Be » 0.87 [Np(AC)s]" & 1.9 (Mp(AC)4)*” Ay 4.7 [eprAC)s)*” Br 174 {ep{AC)a]*- Be 20,2 a. dists, distriimiies sessyyeusats: iea, \om exchange: spec, spactrophotwme'ry; emf, eloctromotive force. redon, eaf with redox slectrode; pH, pH methed. b. Stabtlity comstasts ars givem as logarithre to base 10 of the equilibrium : emstants. Per the resctiom of s cation N with Higmeds L, the canstamt X ond § mre d¢ fingd a3 l.-l.-fih—-l.-%l.-%m. Therefore B = K Lg, By = [,E,K,, ®c. Table 15. Cortinued Log of b Tamperaturs Equillbrium Cation __ Liggd = ethod” ("c) Mod | um Spec Les Constant RAsfsrence Np** 8-k dists <5 0_1M NH,C10. Np(OX), E. +4%.20 98 wminolimate ox-) 5,7-Dichloro- dintn 2% 0.1IM NHLC10 Np(DCD ' & B. +46.0% 98 i-hypdroxy- quisolinats o) Ethylens- dismn 21 0.5M (HCL) Hp (EMTA) 8, +26.% 9 dismine- tetrascetate (EDTA)" " Thenoyl - distn 21 0. 1N HNO, Np(TTA , A0+ 5,18 100 triflvore acetcoate (oTeA)t” tiethylene- lex IN HC104 Rp(DTPA) g - 29.79 101 trimmine- peataacatite (DTPA) *~ NpO,* Chloride fex 2L 1.0M HC1 NpaC. 8; -0 102 distn 2L 4. 0M HCI10, A, - 2.82 91 [NpOsCEs]” By - 1.5% Nitrats lax 2.0W MC10. NpD, N, B, - 0.1% 102 distn 25 4.0M HC10. B, - 1.6 91 [NpO3 N0y 417 g, - 1.4 Hydroxide mf Lo M 1ND, NpD,OH B, = 5.1 74 spac By » a 86 Suifite iex [NpO; 'S0 A, » 2.13 103 [NpO '50503 " 8, + 1,00 Sicarbonate iex NpD, (187004} By, + 2.4} 103 Tnalete Llex 0.05M NH.CIO. [¥po, 'C304) ] B, - 4.0 194 g, + 7.3% Acetats pec NpO; (1L} A, = 1.3% 105 [AC)™ [NpO, 'AC}, 1" fA; + 1.80 spec 1.5M NHLCID, #, + 1.08 B, =« !1.5% 8-hydroxy- spec 7 0.1M Mi.ClO, NpO; (O1) A, + 8.32 106 quimolinate (ox) " [NpOy ‘OX) 1aq]” A, +11.50 Glycolate spec 2% 0. 1M NH.CIO Np, (GLYC) 9y «1.51 107 (GLYC) "~ Lactate spec 25 0. LM NHWC10W NpO, (LACT) By =~ i.75 107 (LACT) " jex 0.2M MHLC10. [NpOy LACTY,;)" #, - 2.20 10% da. distn, distribution ssasuressnts; iex, lon exchangs; spéc, ipect -ophotoleiry; effl, electrfomotive force: redox, enf with redoxy eloctrode:. pH, pH sethod. 5. Stability constants ure given as logarithm to base 10 of the equ librium comstants. For the resction of a cation M with ligands L, the constant K az! A are defined ax: l,-h-#flrl.-%h-%-u. Thersfore By = KL, By = K;L;Ky, etc. . A H* wpf” e, 3. divga, J1ut/ibntljcs SPSEIGERrLs . (¢, s1th reder clociraje: pR, p agthed —hnd a-hpdroxy - | sabmtyrate (W19}~ Tlnru.- (TaRY) "' Citrate cmy ™ Acetyl acotommte [AR) Thaaslytira flusress ol anst e (TTA) " Digthylisus . trimmee. pont aacet sl e (oTPa;t” nitrile- Triacetpls oy’ fehyloes - digmine . totrascetate Ayt hiorids Sitrate ¥luor i de wilate Juglate Melote wifsta upehns” L "pec wper distm dists 1 Toblg 14. Tamporutwrs ) % % Cont | nued gl- 0 2 % MLCLO, G 1IN MLClO0. 0.1 MLCID. 0. 1N WLULIO, o 1IN WMLClo, 0 4N WALC10. -l NCI0, o MM NCL, - N0, 1 W Kio. 1 Om wio. t 4m w1, 1.7 saClO. —Sweiey Tipd; MHIBA) [Mg0, MIBA),]" (Mgl MIBA) |- NgO, (HTART) {¥p0, (YART) ]~ (w0, (TamT)" (g0, (YART), )" (Wpo, CITR) |- {mgo, (CTTR) )" Mgl (AR) | WOy (AR)y]" g0, CITA) [, (YA, ] (MgG , (DTPa} ]~ (0, OITR) |- (mp0, (orray |~ g0, EWTR) |7 sgn, (e9TA) )" 1Ny L1 [ 21)° [mlf'l]l. [%pa,f)* L T Mg, %0, lul(”-lll"- Wl g0 {Wp0,(Ce0a),]"" (W, (C)]" Wpo, (ALY, {Wpc,(aC),)" [Tyt 901" (9t ,(90.),}" P otabi ity coaniants are gives as logarithe vo base 10 of the squilibriun coly 'ats. Yor the resciion nof o calioh W with ligands L, Thy cowstant & and # ore defind as: M solare A, 0,8y, . - Efl-h-. 8 -m. oc. By =« B8,y wir. Lag i B, iy ., s} L - 2.17 « 3.07 = 3.33 -« 3 32 « 347 « &§.08 - 7.00 -« 1.0 « §.40 . 5.08 « 7.1 - 0.8 - 0.13% - D.9R -~ 0.68 = 308 » 8.27 s 1.90 v« .7 - 6.0 - 408 «2.1a . 4,00 « 6.0 » 2.1 - 4.23 .« 8.0 « 1.9 -« §. 24 et nn 111 il L5 n s 1 L1a ” L5 1ls a2 u? Lie ok enchaige: spic. spictiraphotaintiry: ol , eleciraisd ive forve. redcs, eaf Neptunium (IV) Np(IV), which exists as Np(Hz0)s"* in aqueous solution, forms strong complexes with most anions. Analogous to U and Pu, Np(IV) forms negatively charged chloro and nitrate complexes in concen- trated HCl and HNOy; these complexes are sorbed on anion ex- changers. Np(C204)2 is soluble in dilute (NH&)200y solution in- dicating that the carbonate complexes, which have not been studied in detail, are more stable than the oxalate complexes.' Definitive studies of the nature arnd composition of peroxide complexes in solution have not beern made. A purple-gray Np(lV) peroxide precipitate is formed by uddition of H20;to a solution of Np(IV) in nitric acid. From the stability constants .isted in Table 15, the following series of ligands were arranged according to in- creasing strength of the complexes formed by addition of the first ligand to Np*': C10,~ 99.7% by barium sulfate from strong sulfuric acid solutions containing potassium salts and hydrogen peroxide. This causes a separation from most other elements. Np was separated by dissolution of the barium sulfate and reprecipitation fros concentrated sulfuric acid containing chromic acid; Np(IV¥} was nct carried with the Ce, Ba, and La. The Np in the supernatant was reduced to Np(IV} with hydrogen peroxide and again coprecipitated with barium sulfate. After the precipitate was filtered, ??’Np vas determined by gamma comting of the filter.'?’ The method has been further modified'?" and also applied to a wide variety of environmental and biological samples'?® (Procedure 15, p176). Hydroxides. Insoluble hydroxides coprecipitate all oxidation states of Np except Np(VII).*3:,127-12% Ganerally, the trivalent and tetravalent states are carried most effectively. The choice of reagent for precipitation depends on the composition of the solution. Strong bases are used when the solution contains cations that are amphoteric (Al, Pb, Zn) or when the solution contains organic complexing ligands. When the solution contains cations that form ammine complexes or are insoluble in strong base (Cu, Co, Ni, Ca, Mg), ammonia is used as precipitant. - 44 - Other Inorganie Coprecipitants. Np(IV) is coprecipitated with bismuth phosphate and the double sulfate of lanthanum and potassium. Coprecipitation with lanthanum potassium double sele- nate gives results siniiar to those described for the double sulfate but does not have any advantages.!®® The pentavalent cations of the transuranium elements are coprecipitated with potassium uranyl tricarbonate.®'’! Dupetit and Aten'’? described the coprecipitation of tetrava- lent actinides with thorium peroxide and uranium peroxide. Neptunium is completely carried by thorium peroxide, but results were poor with uranium peroxide. This was attributed to the presence of Np(V). Other less common carriers for Np(IV) include thorium and lanthanum oxalates and zirconium, thorium, and ceric iodates. Other Organic Coprecipitantg. Zirconium phenylarsonate and zirconium benzenesulfinate are specific for coprecipitation of the tetravalent ions from solution. The t::ansuranium elements are separated from other cations and from cach other by a series of oxidation-reduction steps similar to those outlined for zirconium phosphate. '?*’ Kuznetsov and Akimova'?" have proposed a number of organic reagents for concentrating the tetravalent cations of the trans- uranium elements from very dilute solutions. Np(IV) and Pu(lV) form hexanitrato species in nitric acid-nitrate salt solutions, - 45 - and these cations are coprecipitated with the nitrate precipitates of heavy organic cations. Of the reagents studied, butylrhodamine was the most effective organic cation. In concentrated nitrate solutions, U(IV), TR(IV), and Ce(IV) coprecipitate with Np(IV) and Pu(IV). Other coprecipitation was with quaternary ammonium bases, dimethyl dibenzyl ammonium, and benzylquinolium compounds. Excellent separation from rare earths, iron, chromium, manganese, and copper was attained.'?? With many organic reagents containing sulfonic groups, tetravalent elements form soluble cyclic salts that are coprecipi- tated with precipitates formed by the cation of a ba. 'c dye (arsenazo) and the cyclic organic reagent. Compared to the organic nitrates above, the precipitation is more complete but less sejective. t 3¢ Np(VI) is carried with sodium uranylacctate. Precipitation. Precipitation of macro quantities of Np is seldom used as an analytical or radiochemical method. If other cations that form insoluble compounds are present, these must be separated first. When the solution is relatively free from other ions, a method such as alpha counting is usually more rapid and offers less health hazard. A number of Np compounds have low solubilities in aqueous solution; however, indefinite stoichiometry or necessity for calcination to the oxide limits the usefulness of direct gravimetric determination. - 46 - Hydrozxides. No information is available on Np(III) "hydroxide," probably because it is rapidly oxidized even in an inert atmosphere. Np(IV) is precipitated from mineral acid solutions by sodium, potassium, and ammonium hydroxides as the¢ hydrated hydroxide or hydrous oxide. The brown-green gelatinous solid is difficult to filter; it is easily redissolved in mine:al acids. No formal solubility studies are reported, but the solubility in 1M NaNO; - IM NaOH is <1 mg/l. Np(V) "hydroxide'" is green. The solubility in dilute ammonium solution is 0.18 g/1; in 1M NaOH, 0.017 g¢/1; and in 2.2M NaOH, 0.014 g/1.%> There was speculation in the early iterature’® that Np(V) might precipitate as NH4NpO3;*:H;0 or an analogous sodium compound as well as NpO;(OH)*H;0; however, the exact nature of the precipitate has not been confirmed. Np(VI) is precipitated as dark brown (NHs)2Np207°H;0 with exces: ammonia from mineral acid solution; the solubility is given as 25 mg Np/l.35 When sodium hydroxide is the precipitant, a bi;rown compound with reported composition NazNp207*xH;0 is precipitated. Studies on the variable composition of the uranates leave some question as to the composi- tion of the neptunates given above.'?’ Fluorides. Grayish-lilac colored Np(IIl) fluoride is pre- cipitated by adding a dilute HCl solution of Np(III) containing Rongalite to a solution of ammonium fluo:ride or hydrofluoric acid in dilute hydrochloric acid while sparging with argon. The dry compound was quite stable to oxidation.'* Np(IV)} fluoride hydrate - 47 - is precipitated when hydrofluoric acid is added to an acid solution of Np(IV). Ammonium Np(IV) pentafluoride precipitates as a bright-green granular solid when hydrofluoric acid is added to a solution of Np(IV) containing NH," ions. A similar precipitation in the pre- sence of potassium ions yields a bright-green precipitate that X-ray diffraction indicates is KNp2Fs. Tie supernatant IM HF - 0.01M NH., from precipitation of the ammonium salt contained 1.1 mg Np/l two hours after precipitation; th2 solubility of the potassium salt was 1.7 mg Np/1 after 16 hours in 0.5M H.,SO, - 0.5M K,50, - 2M HF.?® A double fluoride precipitate of La and Np with an approximate composition LaNpF;o*xH;0 is obtained by adding hydrofluoric acid to an acid solution o equivalent amounts of La®" and Np“*. The solubility of the salt in water was 4 mg/;.3g Rubidium neptunyl(V) fluoride was prepared by injecting a chilled ~C. 1M HNO; solution of NpOz+ into a chilled solution of "12M RbF at 0°C. The gray-green precipitate was washed with small amounts of water, methanol, and acetone fullowed by air drying.HB Oxalates. Brown Npz(C204)3°nH20 (n ~11) is precipitated by adding oxalic acid containing Rongalite irto a dilute acid solution of Np(1I1l) also containing Rongalite. The compound is appreciably . . . A % oxidized within a few hours. 2 - 48 - After valence adjustment to Np(IV) with ascorbic acid,"® bright-green Np(C204)2°6H20 is precipitated from solutions originally containing 5 to 50 g of Np(IV), (V), or (VI) in 1 to 4M HNO3y by the addition of oxalic acid. Tie solubility varies as a function of the concentration of nitric acid and oxalic acid (Figure 3). At oxalic acid concentrations ncar 0.1M, the solu- bility varies between 6 and 10 mg/l as the nitric acid concentra- tion is varied between 1 and 4M. The solutility is very dependent on maintaining all the neptunium in the tetravalent state, Significant separation from a number of cations is attained. The salt (NHy)«[Np(C204)4]® (NHy)2C204°xH20 has bec.. isolated.??? The soluble aqueous complex was cooled to 0°C to remove excess ammonium oxalate. Ethyl alcohol addition produced an oily, dark- green liquid that yielded dark-green crysta.s when treated with 96% ethanol. Green neptunyl (V) oxalate (Np0,C,04H*2H20) is precipitated when a solution of Np(V) in 1M HCl is treated with a 10% solution of oxalic acid in tert-butanol. ! Neptunyl(VI) oxalate (Np02C;0,°3H20), a grayish-green crystalline solid, is precipitated from 2M HNO3; - 0.05M KBrO, containing 20 to 40 g Np/l1 by adding oxalic 3cid until the solution is "0.3M H2C204."? The solubility in 0.5M HNO3 - 0.023M H,C,0. increased from 0.5 to V1.5 g Np/l1 over the :emperature range 0 ;o 20°C. In IM HNOjy at 14°C, the solubility varied from “3.8 to - 49 - Solubiiity of Np Oxalate, mg/¢ 100 - Temperoture: 23°C ' '| HNO, Con:eniration, M"fi o /’ 0.37 ] - -4 A oas & .64 10— - g - _-2.83 ] - 376 _| x i 1. 1111 ll l i i J _J . i.Ll 0.0 0.} 1.0 Oxalic Acid, M Figure 3. Solubility of Np(IV) Oxalate - 50 - “0.75 g Np/l as the oxalic acid concentration varied from 0.002M - to 0. 15M. Peroxide. Np(IV) peroxide is precipitated from solutions containing Np(IV), (V), or (VI) in >3M HNO; by the addition of hydrogen peroxide.'"® The higher valence states are rapidly reduced to Np(IV), and gray-purple neptunium peroxide precipitates. The precipitation does not progress through the highly colored, soluble peroxy complexes that are characteristic of plutonium peroxide. Two crystalline forms were prepared depending on the acidity of the precipitation solution. The solubility is reported as a function of the concentrations of nitric acid and hydrogen peroxide. A minimum solubility of “10™“M neptunium occurred in solutions 1.5 to 2.5M HNOj; and 4.5M H:02. T7The solubilities were not readily reproducible at nitric ac.d concentrations of <2.5M. Iodates. Precipitation of Np(IIl) iodate has not been reported. Np(IV) iodate, a tan-brown solid, is precipitated when HIO3 or KIOs is added to a dilute mineral acid solution. The solubility in IM HCI - 0.1M HIO3 is 0.8 g/1; in 1M HCl1 - 0.1M KIO,, 0.08 g/1.°% These solubilities appear to be high, possibly because some Np was in higher oxidation states. Acetate. Rose-colored NaNpO; (C2H30:)3 is precipitated when a sodium acetate - sodium nitrate solution is added to a dilute sulfuric acid solution that has been heated to 90°C in the pres- ence of potassium bromate to give NpO22*. The solubility is 0,1 g/1 in 0.5M H2S04 - 0.07M NaNOs - 2M NaCzH;0,.°*% - 51 - Carbonates. No simple carbonates of Ny (III) and Np(1V) are reporied. A light-colored precipitate of Np (V), KNpO2COs, is precipitated by addition of solid alkali carbonate (to about pH 7) to a solution of Np(V) made by reduction of Np(VI) with iodide ion."? Phosphate. A green gelatinous precipitate, Np(HPO,):*xH.0, is formed when phosphoric acid is added to Mp(IV) in hydrochloric or nitric acid. The solubility in IM HCl - 0.5M HsPO, is 56 mg/l, and the solubility in IM HNO; - 1M H;P0, is V134 mg/1."° Sulfates. Mefod'eva and Gel'man?? report precipitation of Np(III) as the complex sulfates KsNp(S04)4 iand NaNp(SOs)2+nH20. Np(III) is produced in dilute hydrochloric and sparged with argon at ~50°C using Rongalite reductant. In the dry form, the complex sulfates are stable to oxidation even at increased temperature.®? Np(IV) is crystallized from hot concentrated sulfuric acid as a bright-green compound, presurably Np(SO4)2°*:tH20. The solubility is 16 g Np/1. Sulfuric acid solutions of lip(V) and Np(VI) have becn reported, but no data are given on solubility.?® Although not reported, it is expected that Np(IV) commpounds analogous to Pu(IV) compounds could be precipitated from a solution containing sulfate salts, alkali metal ions, and Np(IV). Other Compounds. Several Np(IV) chloride complex salts have been prepared. Yellow Cs:NpCl; was precipi:ated by mixing solutions of Np(1V) and CsCl in 2 to 1IM HCl and saturating the resulting - 52 - solution with hydrogen chloride. The solubility in “10M HCl is <0.0IM and increases to v1.4M in VIM HC1.'"! A similar compound, [(C2Hs)«N]2NpCle, was precipitated by adding tetraethylammonium chloride in 12M HC1 to Np(IV) in 8 to 12M HCL.'*? Several other complex salts of Np(V) and Np(VI) have been reported. Yellow [(CzHs)uN]2Np02Cl, was precipitated by the same procedure used for the Np(IV) salt,'*? and Cs;NpOCls (bright yellow), (PhyAs) NpOCls (bright yellow), Cs3NpOCl, (turquoise), and Cs;Np02Cl, (dark yellow) were made by variations of the same pracedure.*® The phenylarsonate and salicylate of Np(IIl) have been reported. > They are quite stable at ambient temperature when dry. - 53 - B. SOLVENT EXTRACTION Solvent extraction of Np from aqueous solution into immiscible organic solvents is probably used most often for separation because of its rapidity, simplicity, and reliability. Solvent extraction of Np is usually made from nitrate systems. Generally the effi- c.ency and specificity are decreased from chloride systems; other systems, such as fluoride, sulfate, and phosphate, form complex ions with neptunium, and extraction is inhibited. There are examples of both ion association extraction and chelate extraction among the solvent extrac:ion systems for Np,'*“»1%% In chelate systems, compounds such as TTA, cupferron, acetylacetone, and 8-hydroxyquinoline replace coordinated vater from neptunium ions and form neutral, almost covalent, cheilate compounds that are soluble in such organic compounds as hydrocirbons. In ion associa- tion systems, several mechanisms are possible by which uncharged, extractable compounds are formed by electrostatic attraction between oppositely charged ions. In one ion association system, an oxygen-containing organic compound such as ether is coordinated to Np(IV), and the complex cation is associated with nitrate ions to give an uncharged extractable species. Ion association solvents commonly used for Np extraction include TBP, hexone, diethylether, isocamyl alcohol, pentaether, and dibutyl carbinol. For solvents such as hexone and diethylether, which forz coordination complexes with actinide nitrates, the order of extractability of the various - 54 - oxidation states is usually (VI) > (IV) > (III1) and (V), with the last two states generally considered to be nonextractable. The (IV) oxidation state is poorly extracted Ly diethylether but is extracted into hexone and dibutyl carbinol. For TBP and chelating agents, which form coordination complexes with the metal nitrates, the stable oxidation state giving the strongest complex is usually extracted most efficiently. The tendencies of the actinides to form complexes is (IV) > (VI) > (III) and (V). Thus, TBP, TTA, and other complexing agents usually extract the (IV) state most effectively. An exception (Table 17) is lip(IV)-TBP; however, these exceptions may be the result of the instability of the oxidation state in the aquebus solution. Groh and Schlea!“® and Schulz and Benedict® have reviewed production-scale neptunium processes, including solvent extraction. Chelate Syetems. A large number of 5>i-functional reagents that form strong coordination complexes wvith metal ions have been investigated, These complexes are more soluble in nonpolar organic solvents, such as benzene or CCl,, than in the aqueous phase. Of these compounds, the fluorinated 8-diketone, 2- thenoyltrifluoroacetone (TTA) has been most widely used for extrac- tion of Np in radiochemical and analytical applications.!'*7.1%%® Many variations include TTA extraction as a part of the total separation scheue before the analysis of Np or the determination of its oxidation states,127,132,149,150 - §5 - orsands These 198 TBP-kerosene 0.5M TTA-xylene Diethyl ether Hexone TABLE 17 VYARIATION OF EXTRACTION COEFFICIENTS WITH OXILATION STATE Aqueous Phase Np(IT1) MNp(IV) _Np(¥) Np(VI) _Pu(III) Pu{iv) _Pu(¥l) Am(I11} Am(VI) PYRTEN 3.0 0.13 11.0 0.014 1.5 2.% 0.08 IM HNO» 10°* to* 10" 107? 10t 1ot 0.004 107 oM HNO» 0.1 0.3 4.6 P 1M HNO;-sat 1.2 NEi ND 0.5M4 HNO3-11.1N 0.14 1.7 9.8 NHoNDy 6 1O, 0.3 1.7 3.5 >100 - 56 = Some data for the extraction of Np and other cations into 0.5M TTA in xylene for a range of nitric acid concentrations are given in Table 18. Shepard and Meinke have compil:d a useful set of TTA extrac- tion curves showing extraction as a function of pH for a number of elements.!%? The data show that by judicious pH control, TTA extraction is useful to separate neptunium from many other elements. Basically, the TTA method depends on quantitative reduction of Np to the highly extractable tetravalent state while inter- fering ions are stabilized in inextractable oxidation states. (Procedures 1 and 2, p 138 and 141). Neptunium in 1M HNOy or 1M HCl is rapidly and completely reduced with ferrous sulfamate, hydroxylamine hydrochloride-potassiim iodide, or hydroxylamine hydrochloride-ferrous chloride. Np(IV) is extracted into the TTA, and Pu(I1I) and U(VI) remain in the aqueous phase. If no inter- fering cations are present, the extract can be evaporated directly for counting. The efficiency of separation from other alpha emitters 1s verified by alpha pulse height analysis. Fe(I11), Zr(1V), and Pa(V) are strongly extracted from 1M HNO,, but separation is attained by stripping the Np(IV) from the TTA-xylene into 8M HNO;. Trivalent actinides and lanthanides do not interfere. Sulfate, phosphate, oxalate, and chloride, if present in the aqueous phase, ar: complexed with Al’* before extraction to prevent interference. - 57 - TABLE 18 149 EXTRACTION COEFFICIENTS FOR VARIOUS IONS INTO 0.5M TTA-XYLENE Extraction Coefticient __Ion_ HNOs (M) at 25°C Np(I1I) 1.0 <3 x 107" Np (IV) 1.0 1 x 10" 8.0 <1 x 10-2 Np (V) 0.8 <5 x 107" Np (VI) 0.8 <1 x 107} Pu(IIl) 1.0 1 x10°° Pu(IV) 1.0 1 x 10" 8.0 <1 x 10 2 Pu (V) 1.0 <1 x 107" Pu(VI) 1.0 4 x107° UvI) 1.0 3 x 103 Fe(Il) 1.0 <1 x 107°? Fe(III) 1.0 375 Ce(lII) 1.0 1 x 10°° Ce(1V) 1.0 1 x 10? Zr (IV) 1.0 1 x 107 8.0 250 Am(III) 1.0 1 x Lo~? Al(III) 1.0 1 x 10720 Na 1.0 1 x 10729 Nb (V) 1.0 4 x 107} Th (1V) 1.0 3.) - 58 - The relative standard deviation for :he analysis is 12%, The nominal decontamination attained from plutorium is 10? to 104.1512152 gome data on the extraction of Np from sulfate and perchlorate systems with TTA have been given by Sullivan and Hindman, ?3 TTA extraction preceded by a LaFy coprecipitation cycle has also been described.!5'"!*® Np has been separated from numerous special materials where a combination of methods including TTA extraction was used. Holcomb'37 has described a method for separating 17 gamma-emitting radionuclides, including 23%Np, from heavy water moderator by TTA solvent extiaction and anion exchange. The individual nuclides were determined ty gamma counting and gamma spectrometry. 8-Hydroxyquinoline forms the following chelates with Np: Np(CoHgNO) ¢ with Np(IV) and H[NpOa{(CeHgNO),] with Np(V). Extrac- tion of a number of elements as a function of pH into 0.1M 8-hydroxyquinoline in CHCl; is shown in l‘igure 4. The trivalent actinides extract only at pH 4-6, and at this pH appreciable hydrolysis of the metal cation occurs. *’ Np(IV) cupferron is extracted almost quantitatively into chloroform from 1M HC1 and is back extracted in BM HCl,'S®® Separation with acetylacetonate has been reported for U and Pu and probably has application for Np. - 59 - FIGURE 4. T e ' Patvi| INotv) Cmim ActmD ramf \Paiv) 5 2 s0f- ] ! Am{IIl) ). "7 0 2 4 6 8 10 12 4 pH | - Percentage Extraction of Tracer Quantities of Ac(iIl), Am{III), Cm(111), CF(IILX), Np(IV), and Pa(V) with 0.1M 8.Hydroxyquinoline /CHC1, and of Ra({II) with 1.0M 8-Hydroxyquinoline/CHCly [u = 0.1M (Na, NH,, H)C10,, 25°C]. [C. Keller and M. Mosdzelenski, Radiochim. Aota. 7, 185(1967) Supplemented]. - 60 = Extraction of plutonium dibenzoylmethane or salicylate has been reported.159'15° Neptunium dibenzoylmethane is unstable in aqueous solution, so Pu and U, which form extractable complexes, can be separated. 33,181 Chmutova et al. extracted Pu(IV) from 3M HNCiy with a chloroform sclution of N-benzoylphenylhydroxylamine; H0,2%, Am(III), (V), 162 and fission products (except Zr and Nb) do not extract. Np(IV) is strongly extracted from 1 to 4M HNO; and 1 to 6M HC1 with 4-benzoyl-3-methyl-1l-phenyl-pyrazolin-5-one; under the same conditions, Np(V) and (VI) are not extracted.!®’ Np is ex- tracted at pH 9 to 10 with l-nitroso-2-napthol in n-butanol and isopentancol and is separated from U and Pu.'®" Ion Association Systems. The TBP-HNOs system is a useful system for large-scale processing but is not widely used for quantitative analytical separation., TB’> forms an organic- soluble coordination complex with the metal nitrate, generally of the type M(NOs3),*2TBP.'®> Increasing the nitrate concentration by adding nitrate salts of Al or Ca favors ext::action. Other factors that affect the extraction include complexing ions, reagent purity, free TBP concentration, temperature, and mi>ing time. A summary of the early work with TBP has been given by Geary.'®® The physical and chemical properties of TBP as an extracting agent have been summarized by McKay and Healy.!®’ Other discussions of the use of TBP are in References 168-170. Extraction coefficients - 61 - for many elements for a variety of aqueous solutions and TBP concentrations have been reported by Schneider and Harmon;l“' data are shown in Table 19. Np(VI) is almost completely separated from Al(III), Am(III), Cr(III), Fe(Il), Fe(III), Na(I), Zn(I1), and many other cations in one stage of TBP extraction. Separation of Np from Pu and U involves either oxidation of Np to the (VI) state for extraction and subsequent stripping of Np(V), or stabilization of inextract- able Np(V) followed by extraction of Pu and U. The following sequence of extractability has been found for the various oxidation states of the actinides: M(IV) > M(VI) >> M(III) > M(V). For the tetravalent actinides the sequence is Pu(IV) > Np(1V) > U(1IV) > Th(IV), while among the hexavalent actinides the extractability decreases with increasing atomic number: U(VI) > Np(VI) > Pu(VI)'®® (Figures 5 ard 6). The tetravalent and hexavalent actinides ar: extracted from HCl solutions with similar relative distribution coefficients as from nitric acid but exhibit no maxima. Lower d:.stribution coef- ficients are observed for extraction from perchloric acid solutions because of weak complexing by the perchlorate ion. Strong complexing agents, such as, S042~, P0,?", and F-, reduce the extractability of all actinides appreciably; however, cations such as Al that form quite stable complexes with these anions partially negate the deletericus effect on actinide extraction. Distribution - 62 - Ton Am(III) Al Ca Co(1I) Cr(IIl) Cu(II) Fe(II) Fe(III) Mg Na Ni(II) Np(1V) Np(VI) Th Pa Zn Ru Zr Nb Rare earths Pu(IIIl) Pu(1V) Pu(VI) u(Iv) uqvI) HNO» TABLE 19 EXTRACTION COEFFICIENT DATA FOR TBP!*® Extraction Coefficient Solution _TEP_(%) At 25°C 4.0M HNOj 30 0.013 4.7M 15 0.0003 4.7M 15 0.0003 2.14M Co(NO,) , 60 0.002 3.0M HNO> 100 0.0001 3.0M 100 0.0004 4.7M 15 0.005 2.0M 12.5 0.003 4.7 15 0.0003 2.0M 12.5 0.003 3.0M 100 0.00006 4.0M 30 3.0 4.0M 30 12.0 4.0M 30 2.8 4.0M 50 2.8 2.0M Zn(NO3)2 12.5 0.0001 2.0M HNO3 30 0.15 2.0M 30 0.09 2.0M 30 0.03 2.0M 30 0.02 5.0M 20 0.012 5.0M 20 16.6 5.0M 20 2.7 4.0M 25 10 4.0M 25 23 2.0M 30 0.26 - 63 - Cistribution Coefficiens 0‘! 1 l 0 S 0 13 HNOy, mole /.t Figure 5. Distribution Coefficients for tre Extraction of Tetravaient Actinides by 19 vol % _ TBP-Kerosene from Nitric Acid Solutfon.'*? L4 1 1ilzd c 7 Distribution Coefficient » (( ( 10 31 0 aud L a2 1taiul -t | L ° o ) Ky s HNOy, mol /2 Figure 6. Distribution Coefficients for the Extraction of Hexavalent Actinides by 19 vol % . TBP-Kerosene from Nitric Acid Solutifon.’®® - 65 - coefficients for Np(V) and trivalent actinides are appreciably lower'’! than for tetravalent and hexavalent actinides. For NpOy": NpO2" gy ¢ N0 oy ¢ TBP o = [NpO2 (NOS)*TBP] For analytical applications with small volumes, equilibrium is attained in less than five minutes with good mixing. The extraction properties of many >ther organophosphorus compounds have been studied; however, f@w separation methods for Np have been defined. Higgins et al, working with the butyl series found the order to be phosphate ((RO)3P0) < phosphonate (R(R0)2P0O) < phosphinate (R2(RO)PO) < phosphine ox:.de (RyP0O). 172 The distribution coefficients for the extraction of some tetravalent and hexavalent actinides with various trialkyl phosphates are given in Table 20. Burger!’*+17% and Petrov et aqZ!’%® found that electronegative substituents in the alkyl chain, such as, chloride and phenyl, strongly depressed the extraction. Siddall’? found that increasing the length of the alkyl chain in the phosphate series made little difference for up to eight carbon atoms for tetravalent and hexavalent actinides., The effect of branching the alkyl chain is to increase the extraction of U, Np, and Pu, but to strongly depress extraction of Th, The extraction mechanism of these compounds is generally the same as that for TBP, but the solvation number is not - 66 - TABLE 20 DISTRIBUTION COEFFICIENTS FOR THE EXTRACTION OF TETRAVALENT AND HEXAVALENT ACTINIDES WITH 1.9M TRIALtYL PHOSPHATE/ n-DODECANE FROM 2M HNO, AT 30°C’* Distribution Coefficients? Extractant Th Np(IV)? Pu(IV)® JOVI) Np(VD)Y Pu(vI) Tri-n-butyl phosphate 2.9 3.2 16.1 26 15.6 3.5 Triisobuty! phosphate 2.4 2.7 11.8 22 15.9 3.4 Tri-n-amyl phosphate 2.9 4,2 15.6 32 19.3 4.1 Triisoamyl phosphate 4.2 4,7 17.8 34 18.9 4.4 Tri-n-hexyl phosphate 3.0 3.6 15.6 38 20.0 4.5 Tri-n-octyl phosphate 2.4 3.4 15.3 33 15.7 3.9 Tri-(2-ethylhexyl) phosphate 2.5 4.3 25 58 23 5.7 Tri-(2-butyl} phosphate 0.45 4. 28 42 20 4.6 Tri-(3-amyl) phosphate 0,22 3. 18.1 49 22 5.0 Tri- (3-methyl-2-butyl) phosphate 0.18 3.0 24 47 25 5.4 Tri-(4-methyl-2-amyl) phosphate 0.047 3.5 22 38 24 4.9 a. For tracer amounts of the given elements. b. The aqueous phase contains 0.01M Fe(NHz2S0y)2. ¢. The aqueous phase contains 0.0lM NaNO,. d. The aqueous phase contains 0.0IM (NH,),Ce(NO,),. - 67 - necessarily the same for all elements.'’? A method with mono{2-ethylhexyl]orthophosphoric acid in contact with 12M HC1 + 0.1M hydroquinone has been effective for separating Np(IV) from U(VI), Pu(III), Am(I[I), Cm(I1I}), and trivalent rare earths. The K value for Np([V) is ~103, and for the other cations,™107!; thus, separation is attained by a single contact followed by multiple scrubbing of the organic phase.!’’ K. Kimura'’® has determined the acid dependency of the distribu- tion coefficients for many elements extracted by 50 vol% bis(2-ethylhexyl)orthophosphoric acid (HDEHP from HC1l solutions (Figure 7). These data offer the basis for separating Np from many cations, The distribution coefficients of Am(IIl), Pu(IV), Np(V), and U(VI) in HDEHP from HNOj; are given in Figure 8.'7% The dis- continuity in the Np(V) curve at high acid concentrations is prcbably due to disproportionation of Np(V) into Np(IV) and Np(VI), both of which are more extractable than Np(V]. Np(V) in dilute nitric acid has been separated from U(VI), Pu(1V), and Th(IV) by HDEHP extraction; however, there was evidence that a few percent of the Np(V) was reduced to Np(lV) and not 80 Kosyakav et all’? used separated by a single extraction.! HDEHP to purify Am(III) from other actinides in higher valence states and to accomplish their mutual separa:ion. Am(IIl), Pu, and U were extracted from 0.01IM HNO; after stabill:ation of Np in the - 68 - S rFedl L * »t "\'f" 1 - ‘1' fll kl_LLL‘L ] el wdl Rl L Agdl cdld ndb Sall e Sb Tell 14 b 1t 1 j MNEL» -p\.: jr"s hjr e» 4 ik I N Y- r 4 L E - 4 <4 -4 r bt = dE N M T e L Redf O8]l Ir '“‘R]L"KJ. - ”] "h.»Tfij»'E L At T =1 [ | o {leaml\m ][ \T11] L "‘l" J:—\ja.‘-‘Jjfl/t\4r(”n-p\j, p 4 ) 1t 4 4 L . [ b p Aok i A 2 x .2 & el oo d i &oa *klnngfig.‘.‘||.|h_. 14 L ~ DFP values hasing on Duts of [MF Peppard et at - CAB Dataor CA Blake et a. =Tl Dataof T Ishimori. “*EN Dataof £ Nehamuri S Scrubbing [ . ) T v e -y L v T ey -y }‘.‘ C. - fiq- mi P--i- &1 E.{ 3 m u t'\ } 4 el - P \ 1F 4 4k 4+ < - - 4 ] 9 b F 4} 't b 4 F - o 4 -+ Lan 2 Bl 11 g bl 41;.1 i, ] i N - v T ey - ch{ - Pei\ A=l C={t O ) b 1k { . b 45 4% - ]- 1 } 4t s ey {4 {t ] 3 it { 00101 1 10 41 4} 4 L 4t » i, s Fuy Aredhin i A . 4 Lotk il Figure 7. Extraction of Elements frcm HC1 Solution by 50% HDEHP in Toluene as a Function cf Acid Concentration.!?® - 69 - Log [HNOs] Figure 8. Extraction of Various Actinides into 0.5M HDEHP (isooctane diluent) from HNO; Solutions.179 - 70 -~ pentavalent state with sodium nitrite. HNp(V) was then oxidized to Np(VI) and extracted with HDEHP. Np(Y'I) was reduced to Np(V) and recovered from the organic phase by vashing with 0.1M HNOs. Am was back-extracted from the HDEHP with 3M HNO; and Pu was reduced to Pu(III) and recovered by back extraction with 3M HNOs- U(VI) was recovered by back extraction w.th IM (NH,)2 CO,. Chudinov and Yakovlsv' ~° extracted !J and Fu from Np(V) with HDEHP as a preliminery step in the colorimetric determination of Np(IV) with Arsenazo(III). Peppard et al!?’,1®! studied the ex:raction of several actinides by mono-2-ethylhexylphosphoric acid (HM:HP) from HCl solutions (Figure 9). The distribution coefficien: for Np(IV) in 12M HC1 was v10?, 10" times larger than the non-:etravalent species studied. Gindler et al.!®? used this method to purify 2®Pu for fission counting. The Np(IV) can be returned to the aqueous phase by addition of TBP to the organic phase, re;ulting in a great reduction in the distribution coefficien:. Kosyakov et al.!’? determined the distribution coefficients of Am(III), Np(V), Pu(IV), and U(VI) in H,MEHP from nitric acid (Figure 10). They are generally higher for the same aqueous conditions than those for HDEHP. White and Ross'®? have written a general review of the extractive properties of tri-n-octylphosphine oxide (TOPQ). - 71 - HCI, M Figure 9. Extraction of some Actinide Cations into 0.48M H,MEHP in Toluene as a Function of HC1 Concentration.!”’ - 72 - 6 ° I T T T S.OT—\\- PullY) —_ ——— 4.0 — e Np(X) 3.0 s— — o u(xn g 2.0 — - wd '.»0 P el N\ sl 0 Am(I) — -'.O . \ g 2.0 l 1 | 1 ~-1.0 -0.% 0 0.5 1.0 t.og [HNO,] Figure 10. Extraction of Various Actinides irto 0.2M H,MEHP (Isooctane diluent) From HNOs; Solutions.!’? « 73 . Extraction data for Np and other actinides into TOPO have been summarized by Weaver and Horner.!'®" Extraction with methyl isobutyl ketone (hexone) is based on the solvent power of hexone for the covalent nitrates of the (VI) oxidation states. Hexone was used for large-scale prccessing of irradiated nuclear fuels (''redox" process) but has been supplanted by other solvents both in plant and laboratory applications. A two- cycle extraction system for the separation of neptunium from uranium-fission product mixtures has been given by Maeck.'®’ Hexone extraction of Np(VI) from acid-deficient ALI(NO,),; was followed by TTA extraction. Excellent separation from U, Pu, Ru, and Zr was attained. Also, Np has been separated from Pu and La. Np(VI) and Pu(VI) were produced by oxidition with KBrdi; both were extracted into hexone from an A1{NJi); solution. Back extraction with an aqueous sodium nitrite soluticn yielded Np(V) and Pu(IIl), neither of which is soluble in hexone. The hydroxides were precipitated and dissolved in nitric acid, and ferrous sulfamate war added to give Np(IV) and Pu(III). Np was extracted into a solution of tributylamine in hejone, leaving the Pu in the aqueous phase.’?? Extraction coefficients for ions :nto hexone from several different aqueous compositions are shown in Table 21. Diethylether quantitatively extra:ts hexavalent Np, Pu, and Am from salted solutions containing a strong oxidant (Table 22).'%S - 74 - TABLE 21 EXTRACTION COEFFICIENTS OF VARIOUS SOLUTES INTO HEXONE AT 25°C!*? Extraction Solute” Salting Agent (M) NGy~ (M) HNOy (M) Coefficient Na* A1(NOs)s 1.3 4.0 0.1 0.02 AlY 1.3 3.9 0.0 <0.0001 Cr 03~ 2.0 6.1 1.7 pH 0.011 crt 2.0 6.1 0.1 0.0003 yt* 1.3 4.4 0.5 2.1 Am®* 1.95 6.35 0.5 0.0018 tip** 1.3 1.4 0.5 1.5 Np3*t 1.5 5.0 0.5 <0.001 Np** 0.7 2.6 0.5 1.7 HNO s 1.0 5.4 0.4 0.82 NOs~ 1.5 4.5 0.0 1.1 Cs* 1.0 3.5 0.5 0.009 Zr-Nb 1.0 .25 0.25 0.01 Ru 1.0 1 0.10 0.10 e 1.3 da.1 0.20 0.12 F.p.b 1.4 ‘.6 0.4 0.10 Fe** NH,NO 8 £.2 0.2 0.004 Fe* 8 §.2 0.2 0.0005 Pu'’ 11.1 11.6 0.5 1.7 Put* 11.1 11.6 0.5 9.8 put” 11.1 11.6 0.5 0.14 put”’ A1(NO,s ), 2.0 6.3 0.3 50.0 us* Al (NO3)3 0.5 1.8 0.3 0.1 1.0 3.3 0.3 2.0 2.0 6.3 0.3 30.0 NH NO, 4.3 4.6 0.3 0.18 8.7 9.0 0.3 2.0 11.0 il 3 0.3 14.0 a. Concentration of all solutes is 2 g/: b. Gamms-emitting fission products after 144-day cooling period. - 75 - TABLE 22 EXTRACTION OF NEPTUNIUM, PLUTONIUM, AND AMERICIUM INTC VARIOUS SOLVENTS % Extracted Solvent Aqueous Phase Np (IV)E Rp (V) Mp (VD) Pu (I1I1) Pu (VI} Am_(VI) Ethyl ether iIM HNOjy; sat NH NO, a 100 6M HNOy 9 17 32 70 9M HNO, 17 65 12 89 Dibutyl G HNO, 17 23 il 8 carbinol 7 co M HNO, 23 48 49 35 DBBP,S 30% 4M HNO, 91 7™M HNO, 15 0BE,d 85% 2.4M Ca(NOy)2; 0.6M HNO, 11 5.4M Ca(NO3s)z; 0.0SM HNO, 0.3 41 a. High efficiency; no value given. b. Np(IV) unstable in HNOy. ¢. Dibutyl-butyl phosphonate, DBBP. d. Dibutyl ether. DBE, +ith 15% CCls. - 76 - Other elements that extract strongly are Ze(IV), Au(1Il), and Sc(IIl); P, Cr(V1), As(V), Hg(II), TI1(I1Il), Th(IV), and Bi(III) are partially extracted. After back-extriction with dilute acid, ferrous ion and urea or hydrazine are added to reduce Np(VI) to Np(V); NH(NOy is added for salting. A second extraction with diethylether further separates Np(IV) from U(VI).127.18¢ Distribution data for several of the actinides, including neptunium,as a function of nitric acid concentration into dibutyl carbitol are reported.’®’,18%® Arine extractants, including long-chain alkyl or aryl primary, secondary, and tertiary amines, and quaternary amine salts react with acids to form an ion-association complex which is soluble in the organic phase. The mechanism is illustrated with a tertiary amine: * + A” » RyNHY - RaNorg) * M (aq) * A (aq) A (org) A~ may be either a simple anion or the an:on of a complex metal acid. The complex may undergo a further reaction with another anion in a manner analogous to anion exchinge. +* - *RaNH == B org) * * (aq) RaNH === A org) * B (aq) The higher amines are excellent extractants for Np(IV), Pu(IV), and U, The advantage of amines over orgarnophosphorus compounds is the greater stability to radiation and hydrolysis in radioactive solutions. The amines are usually dissolved in an organic - 77 - solvent (xylene, benzene, or chloroform). Tco achieve rapid phase separation and to prevent formation of a third phase during extraction,a small amount (3 to S vol¥) of a long chain aliphatic alcohol is added to the organic phase. The relative extractroility of Np in nitrate solution is Np(IV) > Np(VI) > Np(V), although the selectivity depends on the structure of the umine and the composi- tion of the aqueous phase. The extractive power of the amines in nitrate and chloride solutions varies in the order quarternary ammonium > tertiary > secondary > pri-ary"’; from H,SO0, solutions, the sequence is reversed. The distribution coefficient of tetra- valent and hexavalent actinides from HCl and HNJ, acid solutions decreases in the sequence Pu > Np > U > Ps > Th. Keder et al.'®® have reported distribution coefficients for several actinide elements (more than one oxiijation state) from nitric acid solutions with tri-n-octylamine (TOA) diluted with xylene (Figures i, 12, and 13). The tetravalent ions show a second power deperdence on the amine concentration, indicating that the extracted complex involves two amine molecules. Extraction of Np(IV) md Np(VI) with trilaurylamine (TLA) from nitric acid is reported.'*!.!*? @ review of liquid-liquid extraction with high molecular weight amines has been publi:ned, '?’? Np(IV) has been separatea from U(VI), Pu(III), Am(Ill), and fission products by extraction of Np(IV) into tri-iso-octylamine - 78 - ot i L1114 O 2 4 & & 10 12 M Agqueows HNO,, M Figure 11. The Extraction of the Quadravalent Actinide Nitrates by 10 vol % TOA {n Xylene.'®? - 79 - 0 0 .0 L+ -+ 1 111 ] O 2 &4 6 8 W0 12 14 Aquecwus HNO,; M Figure 12. The Extraction of the Hexavalent Actinide Nitrates by 10 vol £ TOA in Xylene.'®* i B ‘ — 0! = -— A -3 D 0 —?_ 3 and ra |°“" / ":_.." - 10" J ] 1 o 2 4 S 8 10 12 14 Agueous HNQO,, M Figure 13. The Ext-action of Pentavalent and Trivalent Actinide Kitrates by 10 vol % TOA in xylene.'®® - 81 - (TIOA) in xylene from aqueous 5M nitric acid solution containing ferrous sulfamate. For further separation, the neptunium-bearing organic solution was scrubbed with 5M HNO, containing ferrous sulfamate. Final purification of lp was achieved with a TTA extraction.!?*»!%% 23N, hag been separated from 2*’Am by extraction with TIOA.'®* Np(IV) was extracted i > 20) from 0.1 to 10M HNOy with 0.1M tetraheptyl ammonium nitrate in xylene. The K was >2000 in IM HNO;.''” pistribution data for a large number of clements in quaternary smmonium compounds from various solutions have been determined, and a proceclure for separating Np and Pu with thix system has been reportexl.'®® Keder'®® has reported the distribution coefficients from tetra - and hexavalent Np, Pu, and U from HC] solutions into TOA (Figures |4 and 15). Pu(lV) is much more extractable than Np(1V) and U(IV) under the same conditions, and the hexavalent actinides are more extractable than the tetravalent in this system. Np(IV) and Pu(IV) were strongly extracted from sul furic acid by the primary amine "Primene” JM-T in xylene. In general, the order of extraction of Np(IV) and Pu(IV) from sulfate solution was primary >> secondzry > tertiary amine.’®® Many more proce- dures for acine extraction have been reported for U and Pu, and these methods also offer potential for Np separation.*t.'??,79! Mixred Extraotoite (diluents;. The term synergism is used to denote enhanced (or depressed) extraction of metals by mixed extractants (diluents) as compared to extraction by each extractant * Registered tradename of Rohm and liaas Co. - 82 - “ A 10 / 1.0 ' 0" 10~ 0~? Efium ® lip () . -2 0~ 10 ¢ () 0o 2 4 3 o 0 HCI. N Figure 14. Extraction o U(IV) and Np(IV) ’ by 10X TOA and Pu(IV) b ’1‘.01 TOA from HC! Solutions. - 8% - i *E 10 - ~ - - - o el D 'oo P - - 3 o - puone —g w! E- — aud unf 0 2 4 8 S 10 HCi, W Figure 15. Extraction of Hexavalent U, Np, and Pu from HC1 Solution with 1.0X TOA in Xylene.!?? (diluent) taken separately. The rang» of phenomena described under the term synergism is diverse, :omplex, and not completely understood. A review of this subject is given by Marcus,'’?® Although the subject has received considerable attention, only a few examples are reported for Np. Lebedev et al.?°? have reported a procedure to determine ?“’Am through its daughter product *Np in solutions containing large quantities of curium and fission products. 0.1M ]l-phenyl-3-methyl-4-benzoyl-pyrazolon-5 (PMBP) and 0.25M tributylphosphate (T3P) in benzene were used to separate Np(IV® from Zr, Nb, Cs, Ce, \m and Cm in 0.5M HNO, and IM H4PO,. More than 99% of the Np was extricted with <0.1% of other elements. The 2“’Am was determined by measurement of the gamma activity of the extracted ?Np. Taube?®? has discussed the influsnce of polarity in two- component diluent mixtures of chloroform, benzene and carbon tetrachloride on the extraction of Np(IV) and Np(VI) complexes with several phosphate and amine extractants. The results are inter- preted in terms of the size of the complex species, the diluent structure, dipole interaction between complex and diluent, and other factors. Figures 16 and 17 show tne effects of variation of diluent mixtures on the dis*ribution of Np{IV) and (VI) into TBP and tetrabutylammonium nitrate from nitric acid. - 85 - @*———LHC1 3 /CeHp—m | T T T Qo ¥ "l!‘l' Distribution Coefficient 0.2 Od‘ 0.6 0.8 1.0 Mole Froctions of Diluens Figure 16. Neptunium Extraction with TBP frrom 5M HNO; into Diluent Mixtures.?’? o I - " Distribution Coefficient o - 0 0.2 04 0.6 08 1.0 Moie Froctions of Dilvents Figure 17, Distribution Coefficients for Np(Iv) Extraction with 10-2M Tetratwutyl- Ammonfum Nitrate from 3M HN(, Using Mixtures of Different Diluents,2°? - A7 - C. ION EXCHANGE Many variations of ion exchange are used for separating Np from other ions. Np ions in dilute mineral acids with no strong complexing ions are sorbed by strongly acidic cation exchange resins, such as sulfonated polystyrene. In general, the ability of cations to be sorbed on cation exchargers increases with increasing charge and decreasing hydrated radius., Thus, the order of sorbability on cation exchangers for Np is Np(IV) > Np(III) > Npoz2+ > Np03. All Np species are sorted at low acid concentra- tions and eluted with high voncentraticrs of mineral acids; elution of NpOZ proceeds first and Np(IV) s last. Some anions form neutral or anionic complexes with c¢ifferent oxidation states of Np, so that Np may be eluted by this mechanism. Both Np(V) and Np(VI) are slowly reduced to Np(IV) by common organic base resins. For this reason and because cation exchange of Np(IV) cffers limited selectivity in the separation from other multivalent cations, this method has not been used widely for analytical applications. Anion exchange is one of the techniques most used for separation of Np in analytical and process applications. The method is simple to perform and yields excellent separation from many other elements, including most of the fission products. lon exchange has been the subject ¢f many reviews., The books of Helfferich,?°" Samuelson,?°® Anphlett,?’® and Rieman anc Walton?®? are good references to the theury and applications of ion exchangers. Other reviews of ion exchange include Massart,2°°® 10 h,299,211 Korkisc and Faris and Buchanan. Anion Exchange. Np(1V) forms anionic nitrate and chloride complexes that are strongly sorbed by anion resins; the anionic species provide separation from the cations of many other elements. The hexavalent state of the actinides al:io form strongly sorbed anionic chloride complexes. Greater sep:iration of Np is attained from most other elements in the nitrate system than in the chloride system. The distribution coefficients o many elements over a wide range of nitric acid and nitrate concentrations have been reported. Data are given in Figure 13, In a typical anion exchange cycle, a sample containing Np is adjusted to 7 to 8M HNOy for optimum sorption of Np(NO3)e?~ ions, and 0.01 to 0.05M ferrous sulfamat: is added to ensure that all Np(V) and Np(VI) is reduced to Np(IV). The solution is heated to 55°C for 30 minutes or treated with sufficient sodium nitrite to react all the sulfamate and oxidize excess Fe(II) to Fe(III); this treatment is necessary to prevent excessive gassing in the resin bed. The resin is washed with strong nitric acid to remove Zr, Ru, Pa, Fe, Al, rare earths, U, transplutonium elements, and most other cationic contaminants. Th(IV) and Pu(1V) are not separated; however, washing with 5 to 15 bed volumes of S to 6M HNOy-0.05M ferrous sulfamate-0.05M hydrazine reduces Pu(IV) to _OG- N0 ADE. - WO ADDORPTION FROM Oi-H R 1Oy B ADD. - SLIONT ADGORTFTiON Figure 18. Sorption of the Elements from Nitric Aciczl §olut1’ons by Strongly Basic Anion Exchange Resins.?! Pu(IIl), which is removed from the column. Washing with 84 HC1 removes Th. The Np is eluted with 0,.3M HNO;. Cross-linking and particle size of the resin greatly influences the separation from other cations as well as elution of the Np. !32»213-215 Macroporous anion resin is superior to gel-type anion resin for separation of Pu from Np.2!®*3 A number of similar procedures with variations in acid concentration and substitution of semicarbazide or aminoguanidine for hydrazine have been reported. The separation of tracer amounts of Np(VI), Th(IV), Am(III), and Pu’IV) in nitric acid by anion exchinge has been reported.2!® The feed was ad:iusted to 7.2M HNO;-0.054 NaNO; at 50°C to yield Np(VI) and Pu(IV). After sorption on "Jowex" 1-X4 resin, the column was washed with 7.2M HNO,; to elute Am(III} and Np022+, then with 4M HNO3 to elute Th(IV), and finally with 0.35M HNO, to elute Pu(IV). Other work with macro quantities of these cations has shown incomplete separation of Np probably because of some reduction to Np(IV). Also, Th(I[V) and Pu(IV) were not completely separated. The separation o Np from fission products in 7.SM HNOy using ascorbic acid reductant is reported by Ichikawa.2?!? Radiochemically pure Np has been p:repared for production of high purity metal with one nitrate anion exchange cycle and two chloride anion exchange cycles successively.?!'® The distribution coefficients of miuny elements over a wide range of hydrochloric acid concentrations have been reported. - 9] - These data are used to design separation systems for chloride anion exchange (Figure 19).’2"21’ Np, Th, and Pu are separated by chloride anion excharige by sorbing the anionic chloro-complexes of Np(IV) and Pu(IV) in 8 to ]J2M HCl. Pu(IIl) is eluted with NHyI in 8M HC1, NH20H-NH,I in 12M HCl or Fecl, in 8M HCl; Th is 156,429 pictribution not retained; and Np is eluted with 0.3M HCL. data for 65 elements on "Dowex" 1-X8 from 2 to 17.4M acetic acid in water have been reported??! (Figure 20), Examples of several separations including U and Np are given. Distritution data for 60 elements on cation exchange resin from 1 to 17.4M acetic acid in water have also been reported.22? With Np(VI) in 7.9M HC,H;0,, equilibrium was not reached even after 40 hours of mixing. A method to separate and determine Np, Pu, U, Zr, Nb, and Mo in mixed fission products by anion exchange with HC1-HF solutions d.??? Trace quantities of Np have been separated has been develope from macro amounts of Zr and trace amounts of Nb by elution with HC1-HF solutions.?2" Also, HC1 and HF solutions have been used to separate U, Pu, and Np from each other ard from alkali metals, alkaline earths, rare earths, trivalent actinides, Al, Sc, Ac, Th, Y, and N1 (Figure 21).%%2% (Controlled elution with a series of solvent mixtures was used to separate Np, Pu, Zr, Nb, Mo, Te¢, Te, and U from fission products.?2¢ The chloro complexes were sorbed on anion resin and sequential washes with 12M HC1-NH,OH-NH,I (Pu), 10M HC1-Aq H:02 (Np), 9M HCi-Aq H;0, (Np and Zr), 9M HCl-ethanol (1:i, 2r), 6M HCl-ethanol (1:1, Nb), ethanol-1M HCl1(4:1, Te)}, * Registered Trademark of Dow Chemical Co. - 92 - »26- [l " ods. - MO ADSORPTION Q¢ c A HCLeR i, ods. - SLIGHT ADSORPTION N 12 & HC! {0350g1) sir.ods. - STRONG ADSORPTION O, » ¢ LOS OISR, COLFT., D, Figure 19. Sorption of the Elements from Hydrochloric Acid Selutions by Strongly Basic Anion Exchange Resins, ?!® W 14 l'.’.r-lltl _M 4 A i r R AFYd ER 2 .+It.__ ——— 3 - [L W.H..hd NqAIL - . —— . — L - et ety B i) 1= v v " - = - ™ < # faads ] e 44 LD - m.irdmn ..mm- hf fl.lrla\rdl._r “H . 5 ® Eoo i By Fet m : «B J .r;\blllh- v : . "y 41 Y ] M*TL r“o —— E“-. TH. lfi + -« o r’L‘.a.!T.rn “:-!I»PIOII@IL aE. “ i — Al — H.O..L.L i e 5 —= T S . i 5 ~ddli .4 o - ..l\.‘“’&| - IdNEL E ¥ N |4..4.|+I¢_|1 *I.l.dl w IFIII.TL. | w.. e | . IIFHH...L | I » JJwI.Tfl[ T*.l’tfl..llnsl lrl.mn...l.wL I.._ 4 b —— gl ey - g + - bt et fiw.nla.nupl 21 -t l|.l.”||fl|L A i o e ~ bj 1 m — w 1T Sorption of the Elements from Acetic Acid Solutions by an Anion-Exchange Resin22} Figure 20. Figure 21. 5 T T 1 1 Igg HC! 4% om HeI-0.09M NH,) ~ < 50° &M HCI-0.1M HF O ( - SN NCIUIM WY B tined 0.5M HC - 1M HF - tle- N . o e § 3 merns N [50° — g v O ! ;z b ’b - : o« 4 \ ofi—i‘g‘“fij 10 i ”t;_—-] Eivent Volume, column volumis Uranium-Neptunium-Plutonium Separation by Anion Exchange ("Dowex" 1-X10, <400 Mesh, 0.25 cm? x 3 cm Column) 223 - 9% - othanol-6M HC1(4:1, Mo), O.IN HCI(W1), and 4M HNO, (Tc). Other literature has included a study of the elution charac- teristics of Np, Pu, U, Pa, and 2r in HC1, INO,, and H,SO. systems with "Dowex''-2 an’on resin. Fquilibrium data were given for cach acid from 0.1V to concentrated, and possible separations based on equilibrium daza were summarized.??’ Fquilibrium data were given for a number of elements including Np in 0.1 to 30N H,PO. with “Dowex'-2 resin. Separation of Np from Cs and Te was attained, but data were erratic.??® Np has hcen separated from Pa by elution with 12M HC1-0.5M IIF with Pa eluting first.”'" Separation has also been achieved by clution with SN HCl from anion resin, in which case Np eclutes firse. ??? Np(IV) has heon sorbed quantitatively on "“Dowex’-1 from 0.IM Na;00, and eluted with NH,C1 or dilute HC1.??? Np(VII) forms stable alkaline solutions as the 5p0s'- ion. Novikov 22 al.?'! studied the anion exchange hehavior of this soluble complex as a possible basis for separation from other clements. The sorption was irreversible for all experiments; this was attributed to the reduction of the Np(\Vll) by the resin. An anion exchange method using the nitrate system has been reported for removal of Np before spectrochemical determination of cationic impurities?’? (Procedure 23, p 200). In several reported instances, anion exchanje resin exploded or ignited after use in nitric acid or strong ni:rate solutions.??? These accidents are thought to be due to nitration of the skeleton of the exchange resin, leading to the spontaneous reaction in the presence of heat. Anion exchange resin in the nitrate form should not be stored in the dry state, and temperature should be carefully controlled at <60°C when used in stronj nitric acid. The nitric acid concentration should be <8.5M, and flow to the column shculd not be interrupted, particularly wihen high levels of radioactivity are in the column. Cation Exchange. Sulfonic acid type resins have had limited applications for Np separations because both Np(VI) and Np(V) are reduced slowly by the resin.’'" Several separations have been reported for the pentavalent state of Np. Y. A, Zolotov and D. Nishanov??® reported the separation of Np from U, Pu, and fissior products by elution of Np(V) ahead of U(VI) with 1M HNO, from a cation resin in the hydrogen form. Np was initially oxi- dited to the hexavalent state with bromate. Separation of Np depended on reduction to Np(V) by the resin. Also, cation exchange Las been used for partial separation of Np from Pu(IV), Th(IV), and Zr(1V). Np was oxidized to Np(V) in dilute nitric - 97 . acid before sorption on the resin, but a few percent of the Np(V) was reduced to Np(IV) by the '"Dowex"-50W re«in and was not separated from the other cations,?3?® The distribution coefficients for many of the elements were determined in 0.1 to 12M HBr with ''Dowex"-5C resin. Conditions for separation of U(VI) and Np(IV) and separation of Np(IV) and Pu(III) were given (Figures 22 and 23). Mary other separation methods for Np could be devised from the distribution data (Figure 24).%%7 Np and Pu have been separated by elution from cation resin with HF after reduction to Np(IV) and Pu(IIl) with S0,.%2%® Np(IV) was eluted first with 0.02M HF?}?, and then Pu(IIIl) was eluted with 0.5M HF. Also, Np was separated from Pu by cation exchange with HBr followed by TTA extraction.2?“? Pressurized elution development chromatography on cation resin at 70 to 90°C with a-hydroxyisobutyric acid has been very useful for separation of trivalent actiride elements both in the labora- ! Although no specific tory and with macroscopic quantities,?" separations of this type for Np are reported, the method is useful for highly radioactive solutions. Distribution data for many of the elements on "Dowex'.50 resin over a range of hydrochloric acid concentrations and also over a range of perchloric acid concentrations have been reported (Figures 25 and 26).%%° - 98 - A - - . —‘I -4 -~ ug— Sample L. L 9M HBr 2 \Np(w) utvi} r | ] Concentration (arbitrary units) o 4 O 1 &o___ J‘_ @j O 2 4 6 8 10 Column Volumes Figure 22. Separation of U(VI) and Np(IV) by Cation Lxchange ("Dowex* 50-X4 0.2 cm® x 2 om Column, 25°)2 3 T T 1 - € 2 _9M HBr - 0.2M HF :‘ e ettt ...J £ 3 Pu(OI} Np{IV) 2 f!_ I+ — : v o e B e 0 4 8 12 [ Column Volumes Figure 23. Separation of Pu(lll) and Np(IV) by Cation Exgl;gnge ("Dowex" 50-X4, 0.28 cm? x 3 ¢m Column, 60°) - 99 . - 001 - Figure 24. = R &Ko ot o0 Lx} toghsll |l 2o« @ NAR R Ll \B+ a0 He ah Kot Rt e ptl) i3 ol o W8 Elements from HBr Solutions by a Cation Exchange Sorption of the Resin.2?? 101 (Y =71 4 g'L-. -4 E)' ] - 1 b b -3} P NO, 113 ELEMENT ao # b e I %2 i - prewen 0reee “TT""'{ t:h-_-hfl = - oy .V—’ P '.hy - »!‘u +—| & Padl b 3 PO, - ét l 4 —i—- — - P \h‘- ‘e asane s ot el v [ ; pood BT e T e ] - i »" '..,u..\ '!’ ' -y ] =< B__?.__.,___,..‘ - T [ L -y Ry, P ‘ A yIr hu 4 m n 1 g«l Qlwd 8t Sy 8, QIiey 4(! Clemed & ot telo o rer man nr i - —— —_——— — 11— i 4 8,4t 8,41 &« L OB st \ T . dewwew |lotcwin]|ozmn 0. beapend ;A Abeamag r;iA L‘ o1 a1, ‘_IAIL al s Al 2 2 3 a1 4 R4 el L T e a ey P _1r_1 ity Figure 25, Sorption of the Elemen}g from HC] Solutions by a Cation Exchange Resin. - 201 - " v Y P - ELEmEnT - o, » T N ANQ p OXiDATHON _ - %tl'f-«—« - i l 4 0O 4 & 7 MOLARITY HCK, LOG OISTR, COEFF ~ o v 800 400 eh e Figure 26, Sorption of the Elements from HC10, Solutions by a Catfon Exchange Resin.??® Inonganioc Ion Exchangera. Inorganic exchangers have been largely superseded by synthetic resins principally because of higher capacities and more useful physical characteristics of the synthetic resins. However, inorganic exchangers have the advantage of greater resistance to radiation damage. The distri- bution coefficients of 60 cations, including Np, on hydrous zirconium oxide, zirconium phosphate, zirconium tungstate, and zirconium molybdate have been measured.?“? Shafiev et ai.?"? have studied the separation of Np, Pu, and Pm on zirconium phosphate. Np(V) is not retained while trivalent elements are readily eluted with IM HNO);. Pu(IV) is eluted with 0.5M HNO, containing reducing agents such as ferrcus sulfamate or hydro- quinone. Zirconium phosphate does not change the oxidation state of Np{V). The sorption of Np, Th, and U from HNO,, H-S0., and HF solutions on ammonium molybdophosphate (AMP) columns has been determined.?*"*2*5 The sequence of sorption is Np(IV) > Th(IV) >> U(VI) >> Np(VI) > Np(V). These same workers demonstrated the separation of Th, U, and Np using columns loaded with AMP,6?%% Tsuboya et al.2'” demonstrated conditions in a HNOy system for separating Np(IV) and U(VI) with a tung:tic acid exchanger; Np(IV) is much more strongly retained than U(V) from 0.5 to 2N HNO,. - 103 - D. CHROMATOGRAPHY Extraction Chromatography. Extrac:ion chromatography has been applied to the separation of Np, Pu, Am, and U with 100% TBP sorbed on diatomaceous silica. The diatomaceous silica was initially exposed to dimethylsilane vapor, then treated with TBP, and used as the stationary phase. Nitric acid, with and without ing 9 reducing agents, was used as the mobile »hase. Other workers?" used this system for a similar separation of Np and found that modifications were required to prevent reduction of Np{VI) to Np(V) and to improve separation from some fission products. Eschrich?3® used the same system to determine the oxidation states of Np by eluting with 0.5 to 2M HNO;. The order of elution was Np(V), Np(1V), and Np(VI). It is probablz that some reduction of Np(VI) occurred. 239Np was separated from fission procucts and U on a column of TTA sorbed on glass powder.?®! The chromatsgraphic method gave much more effective separation than batch extraction; recovery was adequate so that isotopic dilution was not necessary. However, two column separations were necessary to s:zparate Np frrm .r. Wehner et al. 252 have also reported separition cf *3’Np from fission and activation products on Poropak-Q impregnated with TTA~0-xylene. Some workers have used "Kel-F"* or '"Teflon"** powders coated with an organic extractant as the stationary phase for extraction * Registered tradename of M. W. Kellogg Co. **Registered tradename of Du Pont. - 104 - chromatography separations. ''Kel-F'" powder :oated with trilaurylamine nitrate has been used to separate Np from U, Pu, and fission products. The feed was adjusted to 2M HNO; - 0.1M Fe(SO3NH;), and passed through the bed. After the column wa:; washed with IM HNO, containing Fe(SO3NH2)2, thc Np was eluted with H2S0, - HNO,. The method is very selective for Np(IV) and has yielded chemically pure ?2?°Np when the weight ratio of U to Np was >10!% in the feed?5? The separation requires one to two days. A similar method was developed for the coseparation of Np and Pu from U.%%" Paper Chromatography. Paper chromatography Rf values for elements Ac through Am in many mixtures of either HNQ3; or HCl with methanol, ethanol, and butanol have been determined by Keller.2%® It was necessary to reduce Np(VI) to Np(V) or (IV) before starting the separation because Np(VI) is slowly reduced in the column rcsulting in poor separation of the bands. Neptunium(IV) was separated from Th(IV) with 12M HCl-butanol and >8M HNO3-butanol mixtures. Also, good separation of Np(IV) from U(VI) was attained with >1M HCl-butanol; Np(V) was separated from U(VI) with 2M HCl-ethanol as developer. Clanet?®® measured the R¢ values for elements with atomic numbers 90 through 96 in mixtures of mineral acids with alcohols and discussed analytical applications, Rg values for Np(1V), (V), and (VI) have been reported for paper treated with TOA using 0.5M HNO; developer solutions - 105 - - ae Al i ke AN fatcas containing LiNOy, NH4NO,, or A1(NOj3)3;. The valuzs are well separated for the different oxidation states of Np and for the different actinides, 2%’ Rg values were also obtained for paper treated with solutions of tetrabutylhypophosphate in acetone- water (20:1) using developer solutions of nitric and perchloric acid.?5? Twelve fission and neutron capture isotopes including 23°Np, have been separated from irradiated uranium with aquecus hydro- filuoric and methylethyl ketone-hydrofluoric acid mixtures as developers.?5? Thin Layer Chromatography. Rapid separation of different valence states of Np from each other and from cther actinide elements by thin layer chromatography on "Teflcn"-40 powder saturated with 0.IM tetrabutylhypophosphate solution has been demonstrated.?%® a8 Chromatography. Effective separation of the transuranium elements by gas chromatography of their chloriies has been demonstrated.?®® The volatile chloride complexes were synthesized at A500°C by adding Al,Clg vapors into the carrier gas. The experiments were carried out in glass capillary coluans maintained at 250°C with less than one microgram of each actinide. Cm, Am, and Pu were eluted in order of decreasing atonic number in about the same position as lighter lanthanide elements in a similar experiment. The retention times of Np, U, and Pa are much - 106 - shorter; it is postulated that the tetrachlorides of these elements are produced. The chromctogram is measured by collecting fractions of Al;Cle condensate at the exit of the column. The actinide hydroxides are carried with La from strongly basic sclution and separated from Al. Then the actinide is deposited, and the alpha spectrum is measured with a surface barrier detector and multi- channel pulse height analyzer, E. OTHER METHODS Volatilization. Separation of more-volatile Np{IV) chloride from Pu{lIII) chloride and other less voletile chlorides has been reported.?%!+2%2 The actinide chlorides were prepared by passing carbon tetrachloride vapor at 650°C over mixtures of plutonium- neptunium oxides or oxalates. The nepturium chloride sublimate was collected with a separation factor of "3 x 10° for Np initially containing 4% Pu; the yield was 96%. Tle method is useful for obtaining quite pure Np where a quantitative separation is not required. NpFe is quite volatile, intermediate between UFg &and PuFg. Separation was attained from UF¢ by co-scrption of the hexafluo- rides on NaF. Then the NpF¢*NaF complex was reduced, and the UFg desorbed. After refluorination, the NpF¢ was desorbed,?®? Electrophoresis. Clanet?®® has developed an electrophoretic nethod on cellulose acetate membranes to separate the charged species formed by elements with atomic numbers 50 to 86 in 1 to - 107 - 12M HC1 and HNO;. Mobility curves have beer obtained for the acid concentration range for both acids. A large number of potential separations of these elements and the solution conditions are tabulated, Some of the separations of Np irclude Np(IV) or (V) from U(VI); Np(IV) from Pu(IV) or (VI); Np(1V), (V), or (VI) from Am(ZiI) and Cm(III); and separation of the c¢xidation states of Np. Electrodepcaittion. Although electrodeposition has been used to prepare mounts for radiometric measurement, electrolysis has not been used as a separation method. There has been one report that U, Pu, and Np were separated by electrolysis from HNO, by varying the pH. Optimum conditions were stuted as current density 750 to 1000 mA/cm? with a plating time of 2 to 3 hours and solution volume of 20 to 30 ml. Np is completely deposited at pH > 9, and Pu and U are completely deposited at pH <6 und pH <3, respectively.?®* Other workers using different media for electrolysis have been unsuccessful in separating Np from other ac:inides. Although partial separation from a number of common cations has been attained, no useful separation method has been reported. Miscellatecus. An analytical schewme has beern described which yields sequential separation of the elements including Np remaining after neutron exposure of 1 mg of a fissile dlement.”** The products were separated and isolated for determination of isotopic abundance by mass spectrometry using solvent extraction, ion exchange, extraction chromatography, and precipitation methods, - 108 - VIII. ANALYTICAL METHODS A. SOURCE PREPARATION AND RADIOMETRIC METHODS Counting. Because counting methods are more se.sitive than chemical or spectrochemical methods, they are the primary methods for identifying and quantitatively determining Np. The two most common Np isotopes are 2'’Np and *?’Np. ?*7vyp is usually determined by alpha counting its two major alpha transitions at 4.781 and 4.762 MeV. If ?'"Np has decayed for a period of about 6 months or longer, it can be determined by gamma ray spectroscopy of its 2''pa daughter. If ?3’Np is separated from 2''Pa which has an B86.6-keV gamma ray, the 2Y'Np 86.6-keV gamma ray can be counted directly. 239Np is determined by gamma counting its gaima transitions at 228 and 278 kev.'® The gross alpha activity of 2'’Np can be determined with a proportional counter or plastic scintillation counter. If other alpha-emitting nuclides are present, an alphu pulse height analysis with a surface barrier detector allcws a determination of the percentage of the total alpha counts attributable to 2*7Np, Liquid scintillation counting can be us«d to determine gross alpha activity with almost 100\ efficiency ard in wmany cases can be used to determine *’’Np in the presence of other alpha-emitting nuclides. The energy resolution in liquid scintillation is 600 KeV as compared to IS5 KeV for surface barrier detectors. Gamma-ray spectrometry with either a Mal scintillation detector or a Ge(Li) detector may be used o determine ?*?Np. For 2’*Np gamma rays (228, 278 KeV), the energy resolution of a typical coaxial Ge(Li) detector (about 1.0 KeV) is much better than for Nal (about 20 KeV). The efficien:y of such Ge(lLi) detectors relative to a 3 x 3 in. Nal dete:tor is 3 to 15% for the 1.23-MeV gamma ray. Ge(Li) low-energy photon detectors (LEP) have an energy resolution of 0.5 KeV with lower efficiency. An a-y coincidence method for determinating **’Np was * The resolving time of developed which increased selectivity.?® the coincidence system was taken as 8 x 1(~% sec. A radioactivation method was developed to increase the > The activation product is sensitivity for determining *3’Np.?® short-lived ?°’Np which is determined by counting its 1.0 MeV gamma ray. To obtain maximum sensitivity the Np should be purified before and after neutron irradiation. A summary of the sensitivity and sel:ctivity of radiometric and radioactivation methods for determiniig Np is presented in Table 23, In summary, alpha counting is the most convenient method for 2*’Np, and gamma spectrometric methods are preferred for 23®Np and ?*°Np. Because of the continuing advancements in nuclear radiation detection systems, the sensitivity, precision, and accuracy of the radiometric methods discussed above could be - 110 - SERSITIVITY AND fllflmn oF TALE 13 MADISNITRIC S0 AABIOACTIVATION RETHODS CETCRNTRAIVE REPTURIUN®®S® Perainsibles tmowmr is Yorms of Seasitivily of Interforing —— Isstape athed Nt had El omamt » p weight Activity 1) 1c* trammtry lo-' aCl ll'~ (’l) ,Iol (1000 LeV) v (»100) »19' " - g.1 ' e e -- 2.1 l!l- » - | st 189) "y Radioactl- 107" ug [wjgh L 1 10’ e 10° wmtion by fimm of ) disy 1 y-mpec- o/ (ca’-s0e) ] ey 308 _ tram of 1np) Ochar >100 . ol eumed s rnr nyewl FP - Fissiea Product 11 - Stebier isstopes Durstisa of Amalyuin 10 ts &0 &0 to 200 17 to &0 5 to &0 14 10 180 improved with available advanced instrumentation, Scurce Preparation. Direct evaporation is the simplest method for preparing sample aliquots for counting. The disadvantage for alpha pulse height analysis is the thickness of the deposit, which results in self absorption of the alpha particles. If a surfactant such as tetraethyleneglycol (S0 ug/cnz) is added to the aqueous solution, t:he Np solution is evaporated from a film rather than a drop resuiting in a more 267+26% The surfactant po.ymerizes on heating homogeneous deposit. and burns up when ignited. The diluted sample is transferred to & suitable counting plate, e.g. stainless stee] disk, and slowly evaporated to dryness to prevent spattering. The direct mount is flamed to dull red heat, cooled, and coated with a thin layer of collodion solution, and the Np is counted. Electrodeposition has been widely used to prepare high-quality sample mounts for precise alpha counting. The procedure is extremely useful when samples contain a mixture of alpha emitters that need to be resolved. Electrodeposition results in excellent sample mounts from organic solutions that evaporate very slowly or leave large amounts of residue and from aqueous solutions that contain large amounts of dissolved solids. Np and other actinides can be deposited from a variety of electrolytes and under several conditions. Graves?®? described - 112 - a semiquantitative method for depositing 237Np from Li onto Pt. Ko?7? reported a method for quantitative deposition of Np from 0.2M HC10, - 0.15M NH4COOH, and Mitchell?’! used NH,CI - HCl to obtain a yield of 94%. Some systems used by other workers?’2 27" are formic acid-ammonium formate, ammonium coxalate, ammonium acetate, ethanol, isopropanol, and NH,C1l witl uranium carrier. Donnan and Dukes?’°® developed one of the fastest procedures for quantitative depositions by combining Mitchell's method with uranium carrier addition. 23°U is added as a carrier in three increments to the NH,Cl electrolyte to ensure quantitative vield; only 20 minutes deposition time is required. An average recovery of 99.8% with a relative standard deviation of #0.2% (n = 10) was obtained with Pu. Similar results were obtained with Np. Resolution of 20 keV is achieved consistently with electro- deposited mounts and a silicon surface-barrier detector. ® reviewed electrodeposition procedures Parker and Colonomos?®’ and described two new methods. One is a co-deposition method for alpha-spectrometry, and the other for preparation of carrier-free layers as fission detectors. In the co-depcsition method with uranium carrier, ??’Np was deposited quantitatively in 10 min at 1700 V with stainless steel as the cathode. In other recent work, Np was deposited quantitatively from ammonium oxalate or ammonium acetate solution or mixed ammonium - 113 - 277-280 A)cohol is an oxalate-ammonium chloride electrolyte. excellent plating medium for aqueous and organic samples. Methods have been reported for ethanol, isopropanol, and alcohcl saturated with ammonium chloride.2®'~2%% peposition from sulfuric, hydrochloric, perchloric, and oxalic acid has been reported by Palei.?®* The effect of variables on the quantitative de¢position on Np and other actinide elements has been reported by other authors.?®%5'286¢ Other methods which have a lower efficiency but yield sources with excellent resolution include vacuum sublimation and electro- spraying.2%%°29! poth electrodeposition and ¢lectrospraying have several disadvantages. These methods take a longer time than evaporation and require special equipment including a specially designed electrolytic cell for electrodeposition, high voltage equipment, and special capillary with a needle electrode for electrostatic spraying.?%® B. SPECTROPHOTOMETRY Although different oxidation states of Np have sharp absorption bands, spectrophotometric analysis has had limited use because radiometric procedures are more sensitive. Further, alpha contain- ment is required for the spectrophotometer, anu operation within a glove box is tedious. Generally, procedures used for other actinides can be applied to the determination. Np is adjusted to a single oxidation state, and the concentration is calculated from the molar extinction coefficient and the absorption of the - 114 - sclution at the proper wavelength. When more than one oxidation state is present, appropriate equations may be fcrmulated for the concentration of each component,???2 Absorption Bande. Important absorption bands and molar extinction coefficients of the different oxidation states are listed in Table 24. Most of the sharp bands can be used for qualitative or quantitative work even though they only obey Beer's Law over a limited concentration range. The best band to use for analysis of Np(IIll) is at 786 my tecause this band obeys Beer's Law. The strongest bands for Np(IV) (960 mu, 723 mu) do not obey Beer's Law, but they can be used with appropriate calibration and constant slit width. The strongest band for Np(V) (at 980 mu in 1M HNO,) does obey Becr's Law;2?® a high- resolution monochromator (e.g., a double-grating monochromator) should be used. Cauchatier' and coworker:;2°® have developed a method for determining Np in irradiated nuclear fuels by measuring the Np(V) band in IM HNO3. The pentavaleat state is produced by adding hydrazine to a Np(V)-Np(VI) mixture obtained after evaporation of the nitric acid solution. Correction for Pu(VI) is necessary. The most useful band for Np(VI) is at 1.23 um; Colvin developed a method using this band for measurements in nitrate solution.??? In this method, Np is oxidized to the hexavalent state with sodium dichromate, and then the acidity is adjusted to 1 to 2M, The absorbance is measured at 1.23 um - 118 - TABLE 24 [MPORTANT ABSORPTION PEAKS OF NEPTUNIUMZ®?-297 Absorption Band (my) Molar Extinction Coefficient Np (111) 5524 44.5 607724 25.8 661%:4 30.5 7862+ 44 (50 to 60°C) 849 25 9910 27 1363 39 Np(1V) 500° n15 50494 22.9 590.59»9 16.1 600° n 7.5 715004 n 3.7 723b 127 74374 43.0 8oo® 21 g25%:9 245 960P 162 975° n32 Np (V) 4284 1.1 617029 22 v617°29 18 980” 395 990° n]180 Np (V1) 4767 6.4 5572 6.8 1223554 a5 1230%+9 a3 Np(VII) 412° 1370 +40 618¢ 382 +10 a. 1M HC10, . b, 2M HC10w. c. 1M HNO». d. Obeys Beer's Law. €. KOH Solution. - 116 - against a reference HNOs solution that i:; the same HNJ3; concentration as the sample. The method has a relative standard deviation of *0.5% at 3 g/. A number of ions, including Pu, do not interfere when present in amounts ten times that o:® the Np. A study on heavy water solutions of neptunium salts in wh:ch numerous well-defined bands were found in the region 1.2 to 1.8 um is reported by waggener.3?° Color Complexes. Spectrophotometri: methods for Np lack sensitivity. Furthermore, the position of the band extinction coefficients are affected by some anions and by the Np concen- tration. These disadvantages are partially overcome when color complexcs that have very high molar extinction coefficients are used, A method with arsenazo III [1, 8-dihydrcxynapthalene-3, 6-disulfonic acid-2, 7-bis(azo-1) benzene -2-arsonic acid] is reported. %1393 The intensity of the s:able green complex of Np(IV) and arsenazo III is measured a: 665 mu. The color forms instantaneously, and its intensity is constant over the concentration range 4 to 6M HNO3;. The molar extinction coefficient at 665 mu is ~10°. Chudinov and Yakovlev separated U(Iv), Pu(lv), and Th(IV), which form colored complexes, from Np02+ by extraction with di-2-ethylhexylphosphoric acid (HDEHP) in carbon tetrachloride. After extraction, Np is reduced to Np(IV), and arsenazo III is added. The lower linit of detection is 0.04 ug/ml, and the relative accuracy is between 1 and 7%. - 117 - Bryan and Waterbury?®? separated Np from U and Pu by extrac- tion with tri(iso-octyl)amine (TIOA) before determining the arsenazo III complex. They found that of 45 ¢lements teste, only Pd, Th, U, Pu, and Zr interfered. The reclative standard deviation was between 7.2 and 1.1% in 200-mg samples of 8.5 tn 330 ppm of Np. (Procedure 20, p192.) Novikor et al. have studied the color complex of Np(IV) with Arsenazo M.*%“ At 664 my the molar extinction coefficient is 1.18 % 10% in 7M HCl and 9.5 x 10" in 0.SM HC1. Thorin was used by scveral workers to analyze Np.’'%%*306 The absorbance is measured at 540 mu against a reference solution not containing Np. The molar extinction coefficient measured with a Beckman DU spectrophotometer is 14,500. The precision of the method at the 95% confidence limits is *2.1% for 0.63 ug of Np/ml. Chudinov and Yakovlev used extraction to separate Np from U and Fu interferences. The thorin method has also been automated®®’ with the Technicon AutoAnalyzer, and the precision has been improved. Np reacts in weakly acidic solution (pHv2) with xylencl orange to form a colored complex with an abscrbance maximum at 550 mu and molar extinction coefficient of 5.5 x 10“.%%% Xylenol orange is three times more sensitive than thorin but only one-half as sensitive as arsenazo I[{Il as a reagent for Np(IV). The greatest - 118 - advantage of xylenol orange is that uranyl ions do not interfere. Fe(III), 2Zr, Th, and Bi interfere. Np(IV) forms a color complex with quercetin that is stable in the pH range 3 to 7 and obeys Beer's Law over a concentration range 0.4 to 4.0 ug/ml. The molar extinction coefficient is 2,3 x 10* at 425 mu. This method requires an extensive purification to remove cations and traces of organic impurities.’°’ The color complex of Np(V) and arsenizo IIl exists over a narrow pH range and was studied by Chudinov ind Yakovlev.3'? A method with the green-colored complex of Np(V) and chlorophosphonazo ' Chemical separation IIT was also Jeveloped by these workers.®: or masking agents are required for a nurber of elements. Chudinov has studied spectrophotometrically the interaction of 12 organic dyes of different types with Np02+.3’2 He concluded that the most promising reagents for pentavalent neptunium are 1-(2-pyridylazo) resorcinol (PAR), arsenazo Ill, and chlorophosphonazo III. With PAR, the molar extinction coefficient is 4.3 x 10" at 510 mu. C. CONTROLLED POTENTIAL COULOMETRY Determination of Neptuniwm Conzentration. Alpha counting is generally superior to coulometry for determining less than a few micrograms of Np; however, controlled poteiitial coulometry is an accurate and precise method for determininj; Np above the 10-ug level.?!'? The electrolysis cell contains a platinum electrode at which the Np(V/VI) couple is titrated in 0.5M H2S0,. First, - 119 - the Np is oxidized to Np(VI) with Ce(IV), the Np(VI) and Ce(IV) are electrolytically reduced to Np(V) and Ce(IIl), and then Np(V) is coulometrically oxidized to Np(VI). The integrated current in the last step is used tc calculate the concerntration of Np. The standard deviation ranged from 6% for 7 ug to 0.05% for about i mg of Np. As little as 2 ug was detectad. Elements which significantly interfere are Au, Pt, Hg, Tl, and Cl1 ; Pu and Pd cause only slight interference., Stromatt's method was used successfully with a gold electrode instead of a platinum electrode to eliminate the Pt/Pt(OH)2 reaction repo:-ted by'Fulda*"“ Fulda obtained a precision of *0.6% for 6 mg of Np. In another application of Stromatt's method, the precision was 0.1% (n = 8) for 9 mg of Np. Also, Buckingham®!® demonstrated a ccefficient of variation for the coulometric method of *0.8% for neptunium oxide and *1.1% (n = 11) for neptunium nitrate solutions. Delvin and Duncan’'® used the same method in the presence of 7 used nitrate with H;50, electrolyte. Plock and Polkinghornegl coulometry to analyze solutions of dissolved alloys for both U and Np without prior chemical separation. Propst?!® has reported a coulomteric method for Np using a conducting glass electrode in a thin-layer electrochemical cell. Organic contaminants interfered and were removed by bisulfate fusion before coulometry. - 120 - Determination of Oxidation States. This method applies to the (IV), (V), and (VI) states and was reportel by Stromatt.>!? The analysis depends on the fact that Np(IV) is not cxidized, nor is Np(V) reduced at a significant rate at a plitinum electrode in IM H S0, electrolyte. The procedure is: (1) 1 potential is applied at the controlled potential electrode to reduc2 Np(VI) to Np(V); (2) Np(V) is electrolytically oxidized to Np(VI); (3) Ce(IV) is added to oxidize Np(IV) to Np(VI); (4) excess Ze(IV) and Np(VI) are electrolytically reduced to Ce(IlI) and Np(V); and (5) Np(V) is electrolytically oxidized to Np(VI). Np(VI) is determined in the first step. The difference between the integrated currents for the first and second titrations corresponds to Np(V), and the difference between the integrated currents for Step S and Step 2 corresponds to Np(IV). Determination of Oxidation-Reduction Poteiatial. The potential for the Np(V)/(VI) couple was measured in sulfaric, perchloric, and 2 The potential in HCl nitric acids with a platinum electrode.’ was not obtained because of reduction of Np(VI) by chloride. The inability of the method to measure irreversible couples, such as Np(IV)/(V), is a serious limitation. The potential for the Np(III)/(IV) couple was obtained with a mercury electrode. D. POLAROGRAPHY Alternating current polarography with square-wave or pulse polarographs has been applied to determine small concentrations - 121 - of Np. Slee and others’’* have reported an analytical method with square-wave polarography to determine Np la Pu after pre- liminary separation from Pu by TTA extraction. Np is back- cxtracted from the TTA into 10M HNO,. After several evapora- tions with nitric acid and wet ashing with mixed nitric and perchloric acid (to oxidize organic material)}, the final per- chlorate residue is taken up in | ml of HC1. I wmi of SM hydroxyl- amine hydrochloride is added, and the solution is evaporated to reduce the volume to 0.5 xl. Then, 0.5 ]l of IM EDTA is added; the solution is adjusted to pH 5.5 to 6.5 with several drops of ammonia and diluted to S ml. Exactly 2 =]l of the dilution are transferred to a polarographic cell and sparged with nitrogen. The Np peak is recorded at about -0.8V against the mercury pool electrode on the square-wave polarograph. Theri an accurately measured aliquot of a standard Np solution prepared in EDTA is added to the cell, and the Np concentration in the original solution is calculated from the increase in pesk height. Interference from the oxidation of chloride ions is decreased by adding EDTA to shift the half-wave potential of the Np peak. The potential for the reduction of the EDTA complex is about 700 mV more negative than for the reduction of neptunium ions; therefore, the peak is shifted well away from the anodic oxidation of chloride ions and is well defined. The authors report precision of *2% and *10% for concentration ranges of 500 and 25 ppm, respectively. Cauchetier ¢t al.?*® reported a method which mskes use of the Np(IV)-Np(i11) couple for determining Np in solutions of irradiated nuclear fuels and ?’'Np targets. Np is reduced electrolytically to Np(1V), and the polarogram is taken. An aliquot of standard Np is added to the cell, and the procedure is repeated. The method was used to analyie solutions with a Np content >20 mg/L containing Pu, U, Fa, Ni, Cr, and fission products, with a precision of 2\, Polarography and other methods were used to compare the chemistry of U, Np, and Pu by Kraus, ¢t al.’?! Jenkins used a manua)l polarograph to study the nature and stability of EDTA complexes with Np(II1) and Np(IV).’2? Np(II1) and (IV) were studied in chloride and perchlorate media by Hindman and Kritchevsky.®?? Np was included in a review of electrochamistry of the & actinides by Milner.'?" The sulfate complexes of Np(1V) were studied polarographically by Musikas.®?’ E. TITRATION Potentiometric. 10- to 100-mg quantities ¢f Np were determined by redox titration.’?® Cc(IV) is used to tityate Np(V) to Np(VI), and iron(Il) perchlorate was used to titrate Mp(VI) to Np(V). The methods can be used successively on the same sliquot of sample if HNOy is present (to give the required ceric oxidation potential) and chloride ion is absent (it would be oxidi:ied to chlorine). - 123 - Stoppered weight burets were used for adding reagents, and a platinum-calomel system was used to detect the end points. Relative standard deviations for a single determination were 0.15% for ferrous titers and 0.59% for ceric titers. Complexomstrio Titration. Np(IV) is titrated with a solution of EDTA at pH 1.3 to 2.0 with xylenol orangu as iniicator. The reaction of Np(IV) with EDTA is stoichiometric and the color changes from bright rose to light yellow at equal molar concentrations. The error for determining 1 to 4 mg of Np i3 1 to 2%, Np(IV) is produced in 0.01 to 0.05M HC1 with hydroxylamine reductant. Fe’®, Zr'*, Pu", Th“’. and ascorbic acid interfere. Reasonably large amounts of alkali, alkaline-earth, rare earth elements, Zn’*, cd?*, co?*, Cr'*, Mn?*, Ni?*, and UO,2" do not interfere.’2® Chronopotentiometric. There has been little analytical chemistry done in molten salts, and so “ar the only useful results have been obtained from electroanalytical methods. Np(IV) was determined quantitatively in molten LiC1-K(1 eutectic at 400 to 500°C with an accuracy of +4%. %27 F. EMISSION SPECTROMETRY Np has a line-rich emission spectra with the more-sensitive lines at 4154.5, 4098.8, 3999.5, and 3829 X.%29732% Qther methods are more useful for quantitative determina:ion of Np than the spectrochemical method, which is generally used only for analyses of impurity elements. To prevent interference by the numerous spectral lines of Np, a chemical separation is usually made, or the carrier distillation method with gallium sesquioxide is used. - 124 - A quantitative method for determinatior of impurities in Np 232 is reported by Wheat (Procedure 23, page 200). The method is 7% The neptunium a modification of one reported by Ko for Pu. oxide is dissolved in HNOs, reduced to the tetravalent state with hydrazine and sulfamic acid, and then sorbed on anion exchange resin. Two cycles of anion exchange are used to separate Np. The second effluent is evaporated to dryness to decompose hydrazine. The residue is made water soluble with aqua regia, ‘evaporated to dryness, and dissolved in 6M HCl containing Co as the internal standard for the spectrographic anaiysis. The coefficient of variation for a single determination of a number of common metal ion impurities ranges from 9 to 24%. For a 50-mg sample, the minimum concentration of impurities that car be analyzed is 0.5 to 10 ppm. G. GRAVIMETRIC METHODS Precipitation of Np for yravimetric determination is not a useful method. 1If other ions which form insoluble salts are present, these must be separated first. When the solution is relatively free from other ions, alpha counting or some other method is usually more rapid and offers less health hazard. A number of Np compounds have low solubilities in aqueous solution; however, indefinite stoichiometry or necessity for calcination to the oxide limits the usefulness of direct gravimetric determination. Often the small quantity or low concentration of neptunium precludes the use of gravimetry. - 125 - Hydroxide. Np(IV) is completely precipitatod from mineral acid solution by Na, K, or NH,OH as the hydrated hydroxide or hydrous oxide. The brown-green gelatinous solid that forms is difficult to filter but is easily redissclved in acids. The solubility in IM NaNO, - IM NaOH is <0.,1 sg/t. Np(V) "hydroxide’ 1% green; it is somewhat more soluble in a2 sodium nitrate-sodium hydroxide solution. Np(VI) is precipitated as dark brown (NH4) 2Np209+H20 with excess NH,OH from minersl acid solution.®? Fluorides., Np(IV) is precipitated f:rom mineral acid solution as green hydrated NpF, by adding excess H°. The compound dissolves readily in reagents which complex fluorid: ion, such as Al’* or boric acid. When K or NH.F 1is used as tho precipitant, the green double salt KNp,Fy or NH NpFs is produced. Peroxides. Purple Np(IV) peroxide is precipitated when a large excess of H,0, is added to a strongly acidic solution of Np(IV}, Np(V), or Np(Vl), because peroxide rapidly reduces Np to the tetravalent state. Reduction is much slower in dilute mineral acid. Np(IV) peroxide always incorporates some of the anion into the crystal and may have different crystalline forms depending on the acid contentration of the supernatant. Np is separated from many cations by precipitation of neptunium peroxide. '® Oralates. Green Np(IV) oxalate hexiahydrate is precipitated from dilute acid solution with oxalic acid. Because quantitative precipitation is not attained for Np(V) >r Np(VI), a reducing - 126 - agent, such as ascorbic acid, is used to ensure complete reduction to Np(IV). A granular, easily-filtered precipitate is produced under controlled conditions.“® (NHy)WNp(C204)« and NpO2HC20, have also been precipitated from Np(1V) and Np(Y) solution. Todate. Light tan Np(IV) iodate is precipitated from dilute mineral acid by adding excess potassium iodate.’'® Carbonatae. The double carbonate of Np(V), KNpO,CO,, is produced by adding potassium bicarbonate to a dilute acid solution of Np(V), until the resulting solution is 0.IM in bicarbonate. The solution is heated at 90°C for 3 to 4 hours to produce the light tan double salt."’® Acatate. Sodium neptunium(VI) dioxytriacetate, NaNpO; (C2Hy02) s, 1s pink by transmitted light and pale green by reflected light. Np is oxidized in dilute acid with KBrO; at $0°C to Np022*. Sodium neptunylacetate is precipitated by adding an equal volume of 4M NaNOy - 4M NaC,Hs0; solution.3® Phosphate. Np(IV) di(monohydrogenphisphate) hydrate [Np(HPO,) ;- XH,0], a pale-green gel, is precipitated by adding phosphoric acid to a dilute acid solution of Np(IV).>® H. SPOT TESTS Spot tests for determining oxidation states of Np and Pu were obtained for 36 organic and inorgani: reagents commonly used in paper chromatography.??! The tests we:e made on Whatman No. 1 - 127 - paper which was treated with 2M HC1 in descenling chromatography for 12 hours to remove traces of Fe, Mg, and Ca, The paper was treated with two successive 24-hour washings by migration with twice-distilled water. Because of hazards of these alpha emitters and the high sensitivity of radioactive measurement K very sensitive spot tests with an identification limit of less than 1 ug of actinide were selected. Observations were pade in white and ultravioclet light for both acidic and basic media with each reagent. First the acidic media was allowed to dry; then ammonia was added and evaporated. A standard scale ¢f colors was used for comparison. In most cases, a color reaction was obtained with less than 1 ug of actinide, but the colur was the same for all oxidation states of both Np and Pu. Diphenylcarbazide gives a color reaction with Np(VI) but not Np(V); however, Pu(VI) gives the same color :reaction. In acid solution, sodium alizarinsulfonate or arsenazo give a color with Pu(IV) and Pu(VI), but no color with Np(V) and Np(VI). Four of the reagents, chromazural-S, arsenazo, 4,2-pyridyl-azo-resorcinol, and pyrocatechol, give fluorescent spots under ultravioclet light with all oxidation states of Pu and Np; kojic acid fluoresces only with Pu(III). The oxidation states of Np and Pu were characterized from color reactions on chromatograms and electrcpherograms.?®® - 128 - The tetravalent states give characteristic colors with alizarin, arsenazo-I, and thorin-I; however, diphenylcarbaiide was used for the hexavalent state. I. MASS SPECTROMETRY f ?*’Np were determined with a mass Subnanogram quantities o spectrometer by Landrum, et al.’''? The instrument was a double- focusing, 60-degree sector type, with a 12-inch radius. The source chamber contained a tantalum filament (from whick the sample was volatilized) and a rhenium filsment (on which gaseous species were ionized). After mass analysis, the ionized Np atoms were collected in a Faraday cup. The method uses isotopic dilution with 235Np or preferably 2%®™Np. This method is much more rapid than neutron activation, and the sensitivity is at least ten times greerer. The standard deviation for 0.1 to 0.5 nanogram of Np was 1 to 2%. Isotope dilution with 27?Np has also been applied to determine ?3’Np, 3?3 Spark source mass spectrometry is useful for less quantitative measurements of many elements including Np; however, it is most often used for determining cationic impurities in Np and other actinides.?3" J. X-RAY FLUORESCENCE SPECTROMETRY The ease of production and simplicity of the X-ray spectra produced for elements of high atomic numter allow mixtures of - 129 - actinides to be analyzed by X-ray fluorescenc: spectrometry with considerable precision and accuracy. Either s3o0lid cr liquid samples can be analyzed by the internal standard technique. Mixtures of U, Np, and Pu were analy.ced at razios as high as 1:1:1; results were comparable to standard counting. U, Np, and Pu in any combination of two elements were analyzed at ratics as high as 1:8 without seriously affecting ac:uracy. However, at ratios of 1:10, low results of 5 to 7% were n>tained for the element present at lower concentration. The principal L series X-ray emission lines of elements with atomic numbers 92 through 96 are given by Kofoed.33® Novikov et al.?%® used X-ray fluorescence to determine microgram amounts of Np in pure solutions or in solutions containing Pu. The sensitivity was 0.2 to 0.3 ug of Np. The relative standard error in determining 1 ug Np was 5%, and the analysis, including sample preparation, required 30 to 40 minutes. The Ka) and Ka, X-ray energies for Np, Pu, and Am were measured by Nelson, et al.?3’ K. NEUTRON ACTIVATION Neutron activation was used to determine subnanogram quantities of 2?7Np.??? The unknown sample was irradiated with another Np sample of known Np content and comparable weight in the same average time-integrated neutron flux. After irradiation, - 130 - the 2?®Np was determined by gamma spec:rometry. Conventional radiochemical separation methods were used. Isotopic dilution with mass quantities of 237Np served t» determine chemical recovery. L. OTHER METHODS Gamma counting 239Np, the decay product of 2%3am, has been used to determine 2"%Am in solutions containing large amounts of Cm. The ratio of the equilibrium amount of “3**Np to the amount of **3Am was determined by separating (by TTA extraction) and analyzing (gamma counting) 239Np trom samples in which **3am and zasz were known to be in secular equilibrium. The method was compared to determining °“’Am by the isotope dilution-mass spectro- metric method. The precision of the mz2thod was 7% at the 95% con- fidence limits (n = 16) for sample alijuots that contained 0.1 to 5 ug of °“?Am.?® A similar approach sas reported by Lebedev et al.?°? 233pa, the daughter of 2°’Np decay, has more-abundant gamma rays, which are easier to measure than 237Np. Cofield??® used this as a basis for determining ?3’Np-2?%Pa in human lungs by in vivo gamma spectrometry with a large Nal scintillation detector in a low-background counting chamber. The neutron capture cross section of 2%%U was measured by analysis of 23%Np produced [2*%U(n,y)?%% & 239%p] . The procedure uses isotope dilution with 237Np to determine chemical yield, TTA extraction for separation of Np ard U, electrodeposition for - 131 - Np source preparation, and gamma counting’“’ fo: analyses. Characteristic isomer shift ranges have besn measured fcr several valence states of Np using MUssbauer resonance of the 5$9.54-keV gamma ray of ??'Np. They exteard from about -6.8 cm/sec to +5 cm/sec for the individual oxidation scates of +7 to +3 and are clearly defined.?“'’?“? The isomer shift charact.ristic of each oxidation state is useful for study of bonding in Np compounds. Dunlop and Kalvius have also made . . . . L1a significant contributions,*! IX. RADIOACTIVE SAFETY CONSIDERATIONS The Np isotopes emit high-energy alpha particles, medium- encrgy beta particles, and low-energy gamma ravs. The tendency of Np tu concentrate in the bones with a biological half-life of 7.5 x 10* vears makes ingestion the primary hazard to personnel. Studies of the distribution of ?’’Np in animal tissue showed 131 60 to 80% of the Np was Jeposited in the bone-. Studies have also heen made of the inhalation, pulmonary absorption, gastro- intestinal absorption, and short-term retention of ?*’Np in rats,?"? Because 2?7Np (T, = 2.14 x 10°y) is the only isotope of Np which is available in weighable amounts, it presents the only serious hazard. The radiati-n hazard is small due to the low specific activity of ?’Np and the low energy of its gamma radiation. Table 25 lists body burdens and maximum permissible concentrations of Iy 2375%p and ?'*N\p for continuous occupational erposure. In - 132 - handling large quantities of ?*’Np, standard gloved-boxes maintained at a negative air pressure with respect to the laboratory air’“® should be considered for containment. Criticality is no problem for ?*’Np because the bare critical mass for a sphere of density 20.45 g/m’ is 68.6 kg.'"® TABLE 25 HEALTH HAZARD DATA FOR NEPTUNIUM [SOTOPES®** Maximum Permissible Concentration for Max Permissible 40-hr Week (uCi/cc) Isotope Organ Body Burden (uCi:' Water Air 2379p (sol.) Bone 0.06 9 x 10°% 4 x 10712 Kidney 0.1 2 x 107 7 x10°!2 Total Body 0.5 4 x 107 2 x 107! Liver 0.5 6 x 107% 2 x 107! GI(LLI) 9 x 107% 2 x 1077 (insol.) Lung 1071° GI (LLI) 9 x 107" 2 x 1077 23%p (sol.) GI(LLI) 4 x 1077 8§ x 1077 Bone 30 100 4 x 107 Kidney 40 200 7 x 10°¢ Total Body 70 300 1073 Liver 100 500 2 x 1073 (insol.) GI(LLI) 4 x10°* 7 x 107 Lung 2 x107° - 133 - X. COLLECTION OF PROCEDURES A. INTRODUCTION The procedures are divided into three categories: ® Procedures for extraction, extraction ch:omatography, iion exchange, and carrier precipitation or some combination of these nathods with highly radioactive samples. Most of these methods utilize alpha counting (alpha pulse height analysis), gamma spectroscopy, or possibly isotopic dilution. The method of determination is not detailed for all procedures. e Procedures used for environmental and biological samples. e Miscellaneous procedures for quantitative determination, including absorption spectrometry of color complexes, coulometry, and gamma spectrometry. B. LISTING OF CONTENTS Procedure Author Title cr Method Page 1 Moore!"® Separation ¢f Np by TTA Extraction 138 2 Dorsett!®! Separation of Np by TTA Extraction 141 3 Smith?*’ Determination of Z3INp in Samples Countaining U, Pu and Fission Products 145 4 Landrum?®“® Determination of Np 150 5 Slee et al,’?° Determination of Small Amounts of Np in Fu Metal 155 - 134 - Procedure 6 10 11 12 13 14 15 Author Schneider?!?"* Maeck et q/.!®" Wehner et al.?2°? Eschrich?"® Roberts?!" Nelson et ai.22° Holloway et al.®?“ Jackson et al.3“? Zagrai et al.?3? Si11l23,12“,125 Title or Method Determination of Np in Samples Containing Fission Products, U and Other Actinides Determination of Np in Samples of U and Fission Products Extraction Chromatographic Separation of ?’?Np from Fission and Activation Products in the Determi- nation of Micro and Submicregram Quantities of U Separaticn of U, Np, Pu, and Am by Reversed Phase Partitior Chromatography An Analytical Method for 237Np Using Anion Exchange Separaticn of U, Np, and Pu Using Anion Exchange Separaticn of Zr, Np, snd Nb Using Anion Exchange Separation of Np and Pu by Anion Exchange Separation of Np and Pu by Catiorn Exchange Separation and Radiochemical Determination of U and Transuranium Elements Using Barium Sulfate - 135 - Page 158 161 163 165 167 169 171 173 175 176 Procedure Type 16 17 18 Type 19 21 22 23 24 II III Author Taylor?®? Perkins! 33 Butler’®! Granade?s? Bryan et al.}'%? Sairnov- Averin et al.’?® Novikov et al.?'*? Wheat?3?2 Ermoloev et aql.3°%* Title or Method The Low-Level Radiochemical Determination of 2*’Np in Environmertal Samples Radiochemical Procedure for the Separ:ition of Trace Amounts of 2¥Np from Reactor Eiifluent Water Determina:ion of Np in Urine Determination of 2¥'Np by Gamma Ray Spectrometry Spectrophotometric Determination of Np Microvolumetric Complexo- metric Mathod for Np with EDTA Photometi'ic Determination of Np as the Peroxide Complex Separation of Mp for Spectrographic Analysis of Impurities Photometric Determination of Np as the Xylenol Orange (omplex - 136 - Pfl‘fi 179 184 186 189 193 197 199 201 204 Procedure 25 Author Stromatt?!? Title or Method Analysis for Np by Controlled Potential Coulcmetry - 137 - 206 Procedure 1. Separation of Np by TTA Extraction F. L. Moore!“® Outline of Method Np is separated from fission products, U, Pu, transplutonium elements, and nonradioactive elements by extraction into thenoyltrifluoroacetone (TTA). After separation, an aliquot 1is suitably prepared for either alpha counting of ?3?’Np or gamma counting of *"Np. Reagents (C.F. Chemicals) e HCl, IM ® HNO,, 10M e Hydroxylamine hydrochloride (NH,OH+*HCl1l) solution, 5SM, Dissolve 69.5 g of reagent in 200 ml of distilled water and warm if necessary for dissolution. e FeCl , v2M. Dissolve 40 g of reagent-grade FeCl;<*4H;0 tetrahydrate in 100 ml of 0.2M HCl. Store in a dark glass stoppered bottile, ® 2-Thenoyltrifluoroacetone-xvlene solution, “0,5M, Dissolve 111 g of compound in one liter of reagent- grade xylene. Equipment e Extraction vessel with mixing device e Hot plate e Micropipets e Stainless steel counting plates e Counting plate heater ® Meeker burner - 138 - ® Asbestos board e Sample carrier ® Alpha proportional counter (or gamma counter) Pretreatment If interferences may be present in salution with the Np tracer, Np is adjusted to Np(IV) and carried on 1 mg of La pre- cipitated as the hydroxide. The hydroxide precipitates are dissolved in IM HNOs, and LaFs is precipitated to carry Np(1V). The fluoride precipitates are dissolved in a few drops of 2M Al1(NOs)s and dilute HC1. While the extraction of Np(IV) from HNC, is usually very effective, HCl should be used whenever possible because there is a greater tendency to form extractable Fe(III) ion in the HNOj3; system. It is desirable to measure the chemical yield if much chemistry is employed. A 2?7Np spike is vseful for determining 239yp recovery; 2¥°Np may be used for determining 2’’Np yield. Procedure 1. Pipet a suitable aliquot of the sumple intc a separatory funnel or other extraction vessel. 2. Adjust the solution to 1M HC1 - 1M NH,OHeHC1 - 0.25M Fe(Cl,. KI may be used as a reductant in place of FeCl,. 3. Mix the solution for 5 min at amb: ent temperature. 4, Add an equal volume of 0.5M TTA and mix for 10 min. 5. Allow the phases to separate; then remove the aqueous phase and discard it. - 139 - ~4 Nash the organic phase by mixing with an equal volume of IM HC]1 for 3 min. Allow the phases to sepa-ate and discard the aqueous wash. Strip the Np from the organic phase by mixing with an equal volume of 10M HNOy for 2 min. (If the aqueous strip is too high in gamma activity for alpha measurement, the last traces of radioactive Zr and Pa may be removed by a 5 min re-extraction of the 10M HNO, strip solution with an equal volume of TTA. Ordinarily, the small amount of Fe in the TTA causes negligible self absorption in counting, and the TTA extract is mounted directly on the counting plate. If Fe is a problem, excellent separation is attained by stripping the Np into 10M HNO,. A suitable aliquot of the TTA extrict or the 10M HNO; strip is prepared by conventional nethods for either 237 alpha counting for *’’Np or gamma :ounting for “’°Np. - 140 - Procedure 2. Separation of N? by TTA Extraction R. S. Dorsett!?® Outline of Method Np is determined in the presence of Pu, U, fission products, and other alpha-emitting nuclides by extraction into thenoyltrifluoro- acetone (TTA) followed by alpha counting of the TTA. The analysis consists of three parts: (1) the pre-extriction step in which acid and oxidation state are adjusted, (2) the extraction in which Np is quantitatively extracted into 1TA, and (3) the mounting and alpha counting of the TTA extract. When additional purifi- cation is required, the Np is stripped fron the TTA, acid and oxidation state are adjusted, and a second extraction is done. The precision of the method is dependent on the type and quantities of interferences. The interferences caused by sulfate, phosphate, fluoride, and oxalate ions are eliminated by addition of Al1(NO;3), which complexes these ions. A coefficient of variation of 2% is obtained with relatively pure solutions. Reagenta ¢ Hydroxylamine hydrochloride (NH,0OH*HCl1), 1M, is prepared by dissolving 69.5 g of C.P. grade compound and diluting to one liter. e (NaNO:), 1M, is prepared by dissolving 69 g of C.P. grade comgcund and diluting to one liter, e 2-Thenoyltrifluoroacetone-xylene, 0.5M, is prepared by dissolving 111 g of the compound in one liter with C. P. xylene. - 141 - ¢ Ferrous sulfamate {Fe(NHS0,4)2]), 2M, is prepared by dis- solving iron powder in an excess of sulfamic acid with minimum heating. The solution |s filtered after dis- solution. ® Aluminum nitrate [Al1(NOjy):], 2M, is prepared by dis- solving 750 g of C.P., grade compound and diluting to one liter, e (HNO3) nitric acid solutions are prepared as required from C.P. grade stock. e Collodion solution, 0.5 mg/ml, is prepared by dissolving S00 mg of collodion in one liter of 1-to-1 ethyl alcohol- ethyl ether. Equipment e Centrifuge cones (with caps) e Vortex mixer ® Micropipets ®» Stainless steel counting plates e Counting plate heater ® Meeker burner ® Asbestos board e Sample carrier ® Alpha proportional counter e Alpha pulse height analyser Pretreatment Fluoride method. When it is not known what impurities are present in the solution, Np(Pu) can be carrier precipitated with La(OH) . The hydroxide is dissolved in HNOy, and La is - 142 - reprecipitated as the fluoride. The fluoride precipitate con- taining the actinides and lanthanides is dissolved in Al(NOs)i and dilute HNOj;, and this solution is extra:ted with TTA. Np in Tributylphosphate (TBP). 1f Np :s present in TBP or other organic extractants, it is stripped w:th dilute HNO, ("0, 1M) and then analyzed by the procedure. Separation of Np and U. Acid control is very important for this separation. In the analysis of low-level Np solutions that contain large quantities of U, the prcblem is complicated because 237Np and 2°“U have the same alpha energies. Also, the specific activity of 2%*U is 10 times greater than 2?’Np. An accurate analysis is assured by (1) close control of :he extraction acidity, (1 +0.1M}, (2) a double extraction cycle, and (3) in extreme cases, a fluorophotometric determination of U conternt of the final TTA extract. Proaedure 1. Pipet 10® to 10" dis/min alpha of ?*'Np into a 15-ml centrifuge cone. e Add sufficient water or HNO; so that at the end of Step 3 the acid is 1M. Mix. 3. Add 1 ml of 2M Fe(NH2S03)2 solution., Mix and let the solution stand for 5 min. 4. Add 3 ml of 0.5M TTA in xylene, and mix for 5 min in a vortex mixer. S. Allow the phases to separate; then renmove the aqueous phase and discard it. Add 4 ml of IM HNO, to the organic phase, and mix for 2 min in the vorte) mixer. - 143 - 10. 11. 12, If the alpha activity due to Pu and U is <10? dis/min, proceed to Step 9. If the alpha activity is >103, proceed to Step 7. Remove the aqueous phase from St2p 5 and discard it. Add 1 ml of 8M HNO; to the organic phase, and mix for 5 min in the vortex mixer. Discard the organic phase. Repeit-Steps 2 through 5. Turn on the counting plate heater, heat to 175° to 190°C, ad place a clean stainless steel counting plate on the heater. Pipet an aliquot from the organi: phase that contains ~10? dis/min Np, and add it dropwise to the plate. Rinse the pipet twice with xylene, and add both rinses to the plate. Heat the plate until dry. Heat the plate over a Meeker burier flame until the plate is a dull red color. Place the »’late on an asbestos board to cool. When the plate is cool, add 1 drap of coilodion to cover the surface. Allow the plate to dry several minutes before counting. - 144 - Procedure 3. Determinatfon of 2?°Np in Sanples Containing U, Pu, and Fission Products H. L. Smith®"7 Introduction The procedure for determining ??°Np arfords excellent decon- tamination from milligram quantities of U, the fissi m products obtained from 10!? fissions, and Pu. The decontamination factor for Pu is about 10"“. An initial fuming with H,SO, is required to ensure exchange between the 23’Np tracer employed and 2?°Np, and also to complex U(VI). If the sample is a dissolved U foil, HNOj; must be added before the fuming step to convert U to the VI oxidation state. Np(IV) and (V) are carried by LaFi precipitations in the presence of Zr and Sr holdback carriers. The preciritations provide decontamination from the activities of Zr and Sr a: well as from U. LaF3 scavenging with Np in the VI oxidation state decontaminates from the lanthanides and partially from Pu. The chemical yield is about 50%, and eight samples can be analyzed in one day. Reagents @ La carrier: 5 mg La/ml, added as La(NO;),. 6H>0 in H,0 ® Sr carrier: 10 mg Sr/ml, added as Sr(NOi).. 4H,0 in H,0 @ 2r carrier: 10 mg Zr/ml, added as ZrOCl; in H,0 e 2?'Np standard solution: 5,000 t> 10,000 courts/(min-ml) in 2 to 4M HC1 or HNO, - 145 - e HCl: O0.1M; 2M; concentrated ® H2S50,: concentrated e HNO,y: concentrated e HyBO,;: saturated solution @ HF: 1:1 H,0 and concentrated HF e HI-HCl: 1 ml 47% HI + 9 ml concentrated HCl ® HF-HNO;: equal parts by volume of 2M solutions ® NHOH*HCl: 5SM (or saturated) e KMnO,: 10% solution e MNH,OH: concentrated e 'Dowex'" 1-X10 anion exchange resin: 100 to 200 or 200 to 4N0 mesh, slurry in H,O* Procedure Step 1. Pipet 1 ml of ??’Np standard into a clean 125-ml erlenmeyer flask, and then pipet in the sample. Wash down the sides of the flask with a little H;0, add 1( drops of concentrated H2S04,** and evaporate nearly to dryness on a hot plate. (No harm is done if the solution is permitted to evajorate to hard dryness.) Step 2. Dissolve the residue by boilirg briefly in & minimum of 2M HCl. Transfer the solution to a clear. 40-ml Pyrex centrifuge * The resin is supplied by thc Bio-Rad Laboratories, Richmond, Calif., who purify and grade the resins nianufactured by the Dow Chemical Co. ** If the sample has been obtained from more than the equivalent of 50 mg of soil, do not add any H,S0, since CaSO, will pre- cipitate and carry Np to some extent. - 146 - tube; wash the fla... once wit H;0, and transfer the washings to the tube, The volume of solution shou.d be 5 to 10 ml. (Ignore any small residue.) Step 3. Add 5 drops of La carrier and 3 drops of Zr hold- back carrier. Add 2 drops of NH,OH*HC] for each ml of solution, stir, and let stand for a few minutes. Add HF dropwise until the yellow color of the solution disappear: and the solutio. becomes cloudy (LaF3). Centrifuge. Remove anc¢ discard the supernate. Wash the precipitate with 1 to 5 ml of HF-HNOj;. Step 4. Dissolve the precipitate by slurrying with 3 drops of saturated HiBO3; and adding 3 drops of concentrated HCl. (Ignore any small residue.) Add 3 ml of 2M HCl and precipitate La(OH), by adding about 1 ml of concentrated NH,OH. Centrifuge, and discard the supernate. Wash the precipitate by boiling it briefly with several milliliters of H,0. Centrifuge and discard the supernate. Step 5. Dissolve the precipitate in about 5 ml of 2M HC1. Reprecipitate LaF; by adding 10 drops of HF; centrifuge, and discard the supernate. Wash the precipitate with 1 ml of HF-HNO,. If the precipitate volume is greater thin 0.2 ml, repeat the hydroxide and fluoride precipitations until the volume of LaF, precipitate docs not exceed 0.2 ml. - 147 - Step 6. Dissolve the fluoride precipitate in 1 drop each ..f saturated H3BO; and concentrated HNO,y. Add 10 drops of KMnO,, and allow to stand for 5 min. Add 2 drops of HF, and allow the solution to stand for a few mirutes. Centrifuge, and transfer the supernate to a clean centrifuge tube, Wash the precipitate with 1 m]l of HF-HNOj3, centrifuge, and add the supernate to the previous one. Discard the precipitate. Step 7. Add 2 drops of La carrier to the sclution, stir. centrifuge, and transfer the supernate to i clean centrifuge tube. Wash the precipitate with ] ml of HIF'-HNO,, add the washings to the previous supernate, and di:scard the precipitate. Step §. Add 5 drops of NH,OH¢HC1 and 2 drops of ZIr carrier, and let stand for a few minutes. Add 2 drops of La carrier, stir well, centrifuge, and discard the supernate. Wash the prec pitate with 1 ml of HF-HNO,, centrifuge, and disczrd the supernsatc. Step 9. Repeat Steps 6 and 7. Stepr 10. Add 5 drops of NH,OH*HCl ard 2 drops ot S hold- back carrier, and let stand for a few minuttes. Add 2 drops of La carrier, stir well, centrifuge, and discard the supernate. Wash the precipitate with 1 ml of HF-HNOj;, centrifuge, and discard the supernate, - 148 - Step 11. Dissolve the precipitate with 1 drop of saturated H3BOy and 10 drops of concentrated HCL. Pass the soluticn through a ""Dowex" 1-X10 anion exchange column, 3 c¢n x 3 mm, and wash the column with 1 ml of concentrated HCl. The Np, now in the IV oxidation state, is sorbed on the column. If necessary, remove Pu from the column with HI-HCi.* Add approximately 1 ml of 0.1M HC1 to the reservoir of the column. §iscard the first 2 drops that come off the column, and then collect approximately 0.25 ml in a clean, dry centrifuge tube. Use no air pressure when eluting the Np. Pick up the solution in a transfer pipet and evaporate by stippling on a 2.5 cm Pt plate. If possible keep the deposit within a 1.3 cm circle. Flame the sample to dull red in a burner, mount with double-sided Scotch tape in the center of an Al plate, and o- and B-count on 3 successive days,*~ * The procedure should remove 95% of the Pu initially present in the sample. If, at this point, there remains enough Pu to interfere with the determination of the Np yield, that is, more than 1% of the Np tracer, Pu may be removed more efficiently in the following way: Allow 1 ml of HI-HCl solution to drip through the column with no added pressure. Wash the column with several ml of concentrated HC1l, and discard the effluent, which contains Pu in the III oxidation state, and proceed with the rest of Step 11. One elution step such as the one just described removes 99.5% of the Pu. ** Alpha-counting: The sample is counted in a 7.5 cm i.d. methane- flow proportional counter with a loop ¢node, operated in the a-plateau region. Beta counting: The sample is placed on the third shelf of a methane-flow proporticnal counter with a window thickness of 4.8 mg/cm?’. An absorber (about 5 mg Al/cm?), placed on the first shelf, stops soft tetas and alphas. The individual counts are corrected to t,, using a half-life of 56.6 hr, and are then averaged. - 149 - Procedure 4. Determination of Np J. Landrum?“® Outline of Method After the sample is dissolved, the vo.ume is reduced by evaporation. Np and other hydroxides are precipitated with 50% NaOH to separate Al. The precipitate is di.ssolved in concentrated H71, and Np is separated from many impuriti.es by chloride anion exchange. Further separation is attained by performing in order: TTA extraction, cupferron extraction, and chloride anion exchange. The plate for counting is prepared by electrolysis. Reagents e 50% NaOH e La carrier, 5 mg La/ml (as La(NO;)3*6H,0 in H,0) e Concentrated HCI1 ® 55% HI solution ® HCl pas @ Bio-Rad AG 1 x 8, 50 to 100 mesh resin e 10M HC1 - 0.S5M HI e 5M HC1 e IM HC1 ® 0.4M Thenoyltrifluoroacetone (TTA) in xylene e 6% Cupferron e CHCl, e Saturated NH,Cl solution e Concentrated NH,OH - 150 - Procedure 1. To the sample add about 3 x 10° alpha counts/min ?°®’Np stan- dardized tracer. Add "2 mg of La’* carrier and 2 ml $5% HI (no inhibitor), and boil the sclution until the volume has been reduced to about 10 ml. Transfer to a 40-ml cone. Add suffi- cient 50% NaOH to dissolve any Al that may be present. Heat in a water bath, centrifuge, and discard the supernatant liquid. Wash the precipitate with 10 ml of 10M NaOH. Again heat, centrifuge, and decant. Wash the precipitate thoroughly with 30 ml of H0 (to remove most of the Na* salts), centrifuge, and decant. Dissolve the precipitate in 10 ml of concentrated HCIl. Add 2 drops of 55% HI (no inhititor). Cool and saturate the solution with HCl gas. (If white salts precipitate, centrifuge them and decant.) Pass the solution through a "Dowex" 1-X8, 50 to 100 mesh column, 6 mm I.D. by 11 cm, pretreated with concentrated HCl - 0.5M HI. Discard the effluent. If 23%Pu is to be measured, save the effluent and note the time of Np-Pu separation. Wash the column with 15 ml of 10M HC1 - 0.5M HI, and collect the wash with the effluent. Elute the Np with three 5-ml portions of SM HCl, and allow a minute or so between elutions. Collect the eluate in a 125-ml Erlenmeyer flask. Add 2 drops HI, and boil to neer dryness. Transfer to a 40-ml cone with 1M HCl. Add IM HCl to make approximately 15 ml. - 151 - 10. 11. 12. 13. Add 10 ml1 of 0.4M TTA in benzene, toluene, or xylene, and equilibrate for 30 min. Soparate the layers by centrifuging, and transfer the organic layer into a clean 40-ml cone. Repeat the oxtraction with 5 ml of 0.4M TTA for 10 min. Combine t:he organic fractions. Discard the aqueous fraction, Wash the organic with 5 ml of IM HC1l for 2 min. Centri- fuge, and discard the aqueous. Back-extract the Np by equilibrating the TTA with 2 ml of SM HCl for 10 min. Separate the layers as before, and transfer the aqueous to a clean cone. Repeat the extraction with 1 ml of 9M HC1 for S min. Combine the aqueous phases. To the combined aqueous phases, add 2 drops of 6% cupferron and 5 ml of CHCl;. Ejuilibiate for 30 sec. Discard the CHCl; (lower layer). Add 5 ml of CHCl; and repeat the extraction. Again discard the CHCl3. This step is designed to remove trou>lesome Nb activity. Transfer the solution to a 125-inl Erlenmeyer flask, add 1 ml concentrated HNO,;, and boil to near dryness. Add S ml of 9M HCl1 and 1 ml of concentrated fo:rmic acid. (CAUTION: The reaction between HNO; and formi: acid may be violent if too much HNOs is present.) Warm the solution until the HNOj3 has been destroyed. This step oxid:zes U(VI) and reduces Np(1IV). Add 5 ml of fresh concentrated HC1l (final HCl concentration should be >10M, use HC1 gas if necessary). Pass the solution through a '"Dowex" 1-X8, 50 to 100 mesh, 6-mm I.D. x 5 cm column, pretreated with 10M HCl. Wash the column with 5 ml of 10M HCl, Discard the effluent and wash, - 152 - 14, Elute the Np as in Step 6, but with 10 ml of 5M HCI. Collect in a 125-ml Erlenmeyer flask. 15. Repeat Steps 7, 8, 9, and 10. (TTA extraction) 16. Examine on a Nal detector for gammi contemination. If the sample is radiochemically pure, plate the sample. Electroplating Boil the solution from Step 10 to near dryness. Add 1 ml of saturated NH,Cl and one drop of methyl red indicator, and adjust acidity with NH,OH and 1M HCl so that one drop of IM HCl turns the solution red. (Volume should be 3 to 4 ml.)] Transfer the solution to an electroplating cell fitted with a Pt wire anode and a 1-in.- diameter Pt disc cathode. Pass approximately 1.5 amps through the cell for 15 min. Add 1 ml of concentrated NH,OH to the cell while electrolysis is in progress. Continue plating for another 15 to 30 sec. Remove the solution from the cell, and check it for activity in a well counter. If appreciable activity is present, repeat the plating procedure without the addition of NH4Cl. Dismantie the cell, flame the Pt disc to a dull red, and alpha count for chemical yield. Gamma and beta count for 2?°Np and 2?%Np. Notes 1. Using this procedure, Np is separated from solutions whose contents underwent 10!° fissions (one week previous) and up to one gram of dissolved soil. CGamma-ray spectroscopy showed no activities other than 2?Mp and 2*°Np, - 153 — 2. 10 to 12 hours is required for six samples. 3. The yield for this procedure is 30 to 60%. - 154 - ocedure 5. Determination of Small Amounts of Np in Pu Metal L. J. Slee, G. Philllps &nd E. N. Jenklns32?® Outline of Method Pu metal is dissolved in HC1l. The Np (10 to 2000 ppm) is parated from Pu by TTA extraction and determined with a square- ve polarograph. Reagents Distilled water HNOs, analytical-reagent grade Hydroxyamine hydrochloride (NF2OH-HCl) solution, SM TTA solution, 0.5M in xylene: Dissolve 28 g of 2- thenoyltrifluoroacetone (TTA) in 200 ml of pure xylene, filter, and dilute with xylene to 250 ml. Ferrous chloride (FeCl,) EDTA solution: Dissolve 37 g o2f discodium ethylenediamine- tetraacetate (EDTA) in distilled water, adjust to pH 7 with ammonia solution, and dilute to 100 ml. Procedure 1. Weigh 300 mg of Pu metal accurstely. 2, Add S ml of distilled water and then slowly add 0.5 ml of 10M HCl. When the reaction subsides, add 1 ml of 10M HCl and 2 ml1 of 5M NH;OH*HCl1 and warm the solution. 3. Dilute to 10 ml with distilled water, add 250 mg of FeCl,, allow 5 min for oxidation state adjustnent. 4. Transfer quantitatively to an extraction vessel, and add S ml of 0.5M TTA. Stir for 10 minutes, allow the phases to separate, and remove the organic phase. - 155 - 10, 11. 12. 13. 1‘30 15. 16. 17. 18. Repeat the extraction with 5 ml of 0,5M TTA, Combine the organic phases in the extraction vessel, add 1 ml of IM HCl, and stir for 1 min (to remove entrained Pu. Remove the aqueous phase. Add 5 ml of 10M HNO,, and stir for 10 min to strip the Np. Remove the aqueous phase into a clear vessel, and repeat Steps 7 and 8. Evaporate the 10M HNO3; to ~3 ml and then add 5 ml of analytical-grade concentrated HNOj, Evaporate to 1 ml, and repeat evaporation with two more 5-ml portions of concentrated HNO,. Add 3 ml of analytical-grade perchloric acid (606%) and more concentrated HNO3 and evaporate to complete wet oxidation of organic matter. Heat until solid perchlorates remain but do not bake. Dissolve the residue in 1 ml of warm 6M HCl and 1 ml of water, Add 2 ml of 5M NH,OH*HCl and evaporate slowly to “}.5 ml. Add 0.5 ml of 1M EDTA and 4 to 7 drops of ammonia to adjust pH to 5.5 to 6.5. vilute to 5.0 ml, and mix thoroughly. Transfer 2.00 ml to a polarograph cell, and de-aerate with N, (pre-saturated with water) for 3 min, Record the Np peak at about -0.8 V apainst the mercury- pool anode on the square wave polarojyraph. Add 0.2 ml of a standard Np solution prepared in EDTA so that the original peak height is upproximately doubled. Deduce the Np concentration of the or-iginal solution from - 156 - the increase in peak height. Interference from the oxidation of chloride ions is decreased by adding EDTA to shift the half-wave potential of the Np peak. The precision is *2 and #10% for concentrations of 500 and 25 ppm, respectively. ~ 157 - Procedure 6. Determination of Np in Sample Containing Fission Products, U, and Other Actinides A. Schneider!®® Introduction This procedure describes an analytical solvent extraction method for separating Np from Pu, Am, Cm, U, Th, and fission products using tri-iso-octylamine (TIOA) and thenoyltrifluoroacetone (TTA). Np is separated from Pu, Am, Cm, and fission products by extraction of Np(IV) into the amine from HNO,; containing a reducing agent. Further purification is obtained by stripping Np from the amine with dilute HCl anil then extracting the Np into TTA, Reagents e 5M HNO, ® 3M [Ferrous Sulfamate], Fe(NH2S0:): ® 5.5M [hydrazine], N:H, ® 10 Vol% tri-isooctylamine (TIOA) in xylene e IM HCl1 ® 5M [hydroxylamine hydrochloride] (NH20H=HC1) @ 0.5M TTA in xylene Procedure 1., To a 5-ml extraction vial add 1.5 ml of S5M HNO; and a glass-covered magnetic stirring bar. 2. Pipet the sample (not to exceed 200 uR) into the HNO, and stir. - 158 - Add 3 drops 2M Fe(NH;S03); aad 1 drop of 5,5M NaHs. Stir and allow to stand for 5 min at room temperature. Add 1.0 ml of 10% TIOA in xylene and stir for 3 min to produce an emulsion. Allow he phases to separste. Separate the phases, and discard the aqueous. Transfer the organic phase fiom the original vial to a clean vial containing 1.5 ml of SM HNO,, 3 drops of Fe(NH2S03)2, and 1 drop of N;H,. Stir for two minutes, allow the phases to separate, and discard the aqueous phase. Transfer exactly 0.75 ml of the organic phase to a clean vial containing 2.5 ml of IM HCl and 1.5 ml of xylene. Rinse the 0.75-ml pipet in tle xylene phase of the new vial. Stir for 3 min and allow the phases to separate. Discard the organic phase. Transfer exactly 2.0 ml of the aqueous HC1l phase to a clean vial. Add 3 drops of 5M NH;OH*HCl and 3 drops of 2M Fe(NH2S03)2. Stir and heat at 65°C for 3 min. Remove from the bath, and let stand for 3 min. Add 1.0 ml of 0.5M TTA in xylene. Stir for 4 min to give a complete emulsion. Allow the phases to zeparate. The organic phase contains the purified Np. This phase is mounted for alpha counting for measurament of 2%7Np. Notes 1. The presence of fluoride, sulfate, uxalate, and phosphate lower the extraction coefficiznt of Np(IV) into TIOA; Chloride ion does not interfere. 7The deleterious effect of these anions is circumvent:d by reducing the sample size or by adding Al ion. - 159 - ta For U-tree samples, the combined system yields 96 *2% recovery. For U-bearing samples, the recoveries are dependent on the amount of U taken., 7The extraction conditions are reproducible, and for control analyses the recovery factnrs are included in the calculations. In routine use, the combined extraction system achieves a separation from common fission products (Ce, Ru, Nb, Zr, Cs and St) of about 1 x 10° and a Pu separation factor of S to 50 x 10°, Control of the method for samples of unknown composition is maintained by spiking a portion of the sample solution with 2?’Np or ??’Np and evaluating the recovery of the spike. An alpha pulse height analysis may be necessary if large amounts of Pu are initially present in the sample. - 160 - Procedure 7. Determination of Np in Samples of U and Fission Products W. J. Maeck ; G. L. Booman, M. C. Elliott, and J. E. Rein'®® Introduction This procedure describes a method for sezparation and determination of Np in solutions of U and fission products using methyl isobutyl ketone and thenoyltrifluoroa:etone (TTA) extractants. Np is oxidized to the hexavalent state and quantitatively extracted as a nitrate complex into methyl isobutyl ke:one from an acid- deficient AI1(NOs)s solution containing tetrapropylammonium nitrate. Np is stripped from the ketone with 1M HCl containing reductants and then quantitatively extracted into TTA-xrlene to complete the separation. Reagentsa @ Al(NOy}; salting solution: Dissolve 1050 g of A1 {NOjy) 3*9H20, add 135 ml of concentrated NH,OH with mixing, and cool to 50°C. Add S0 mi of 104 tetrapropylammonium hydroxide reagent, and stir the solution until all solid is dissolved. Dilute the solution to one liter with water. ¢ Reducing-strip solution: IM HI - (.5M NH,OH10%. An alpha scintillation counter is used for gross counting, and a Frisch-grid chamber, 256-channel analyzer system is used for pulse height analysis. - 162 - Procedure 8. Extraction Chromatographic Separatior of 2°°Np From Fission and Activation Products in the D:tfirmination of Micro and Subinicrogram Quantities o H. Wehner, S. Al-Murab, and M, Stoeppler?3? Introduotion This procedure describes extraction chromatographic separa- tion of 2*°Np from fission and activation products after neutron irradiation. The system is Poropak-Q resin impregnated with TTA-xylene. It is suggested that radioactive samples are more easily analyzed with extraction chromatography than with TTA extraction. Raeagents ® Poropak-Q resin, 100 to 120 mesh ® 0.4M TTA in xylene (=mall amount of n-pentane added) e 2M HCl1 e IM FeCl: e 3M NH,OH yield hexavalent U, Np, and Pu. 2. Wash the packed column with ~10 ¢>lumn volumes of ~VvIM HNO, at relatively high flow and pressure to remove any air and nonsorbed TBP. 3. Add the sample volume (not greater than 1/10 of the total column volume and containing a macimum cf 1 mg TBP- extractable species per 100 mg of silaned Hyflo Super-Cel) at a flow of 0.4 to 0.8 ml/(min-cn?). - 165 - 4. Wash the column with 1.7M HNO, to remove (in order) Am(IIT), Cr(VI), and Pu(VI). S. After Pu(VI) elution, switch to 1.7M HNOy - 0.1M N;H. wash., (Np is reduced to Np(V) and elutes immediately, and U(VI) is removed.) Note If U, Np, and Pu are present, no oxidation step is required. The feed is adjusted 0.7M HNO, - 0.02M Fe(SO3NH2), to yield Pu(III), Np(IV), and U(VI), and the same composition wash solution is used. The order of elution is Pu(IIl), Np(IV), and U(VI). - 166 - Procedure 10, An Analytical Method for 2*7lp Usiny Anfon Exchange F. P. Roberts2?!" Outline of Method This method separates Np from Pu, U, An, Cm, and fission products by anion exchanpge in HNO; solutions to permit ?*"Np estimation by gamma spectrometry. The sample is spiked with 23'Np tracer to permit yield corrections and loaded onto a small column of "Dowex" 1-X4 (100 to 200 mesh) resin from 8M HNOjs containing Fe (NH2SO3)2 and semicarbazide. After washing with 30 to 40 column volumes of 4.5M HNOy containing Fe(NH2SOs); and semicarbazide, the Np is eluted with dilute HNOy containing 0,005M Ce(SOs)2. Np recovery is “95% with a Pu decontamination factor of 5 x 10°. Decontamination factors from U, Am, Cm, and gross fission products are all >10*. Uranium at concentrations up to 180 g/% in the feed does not interfere. The Pu decontamination factor can be increased 10 to 100 by following the HNO3; wash with L2M HCl - 0.IM NH.I. Np is then eluted with 6.5M HCl - 0.004M HF. The method is appli- cable to samples containing high salt concentrations. Reagenta (C.P. Chemicals) e Concentrated HNOj, e "2M Fe(SO3NH:)2 ¢ Semicarbazide ® zasz tracer Materials e 'Dowex" 1-X4, 100-200 mesh e Glass colum, 0.3 cm x 7 cm with 10-m]l reservoir ~ 167 - e Counting equipment Proocedure 1. Adjust an aliquot of sample to w8V HNO, with concentrated HNO 4, 2. Add an equal volii.e of 8M HNOy - 0.02 Fe(NH;S03), - 0.2M semicarbazide and mix. 3. Add ?’’Np tracer (“10° dis/min). 4. Pass the adjusted sample through the column at 3 to 6 drops/min. 5. Rinse the reservoir several times with a few drcps of. 8M HNO,, pass through the column, and discard. 6., Pass 15 to 20 ml of 4.5M HNO; - 0. IM semicarbazide - 0.01M Fe(NH2503) 2 through the column at J§ to 6 drops per minute {(Pu fraction). 7. Pass 2 m]l of 8M HNO3 rinse through the column. 8. Elute the Np with 2 ml of 0.005M Ce(SO4)2 in 0.25M HNO,. Catch the eluate in a 2-ml volumetric flask. 9. Mount an aliquct of the Np product on a Pt disc for alpha counting and alpha energy analysis. (The yield is determined by comparative counting of the 0.23 MeV 23°Np gamma from the disc with that of a standard °?°Np disc.) - 168 - Procedure 11. Separation of U, Np, and Pu Using Anion Exchange F. Nelson, D. C. Michelson, and J. H. Holloway*?? Cutline of Method This method utilizes anion exchange .n HC1 for separating U, Np, and Pu from '"1~n-adsorbable" elensents which include alkali metals, alkaline earths, trivs!=i1t actiiides, rare earths, and a number of other elements such as Al, Sc, Y, Ac, Th, and Ni. Sorption of the uranides by anion =xchangers from HCI solutions can occur in either the +4 or +6 oxidation states but not in the +3 or +5 states. In this pracedure, U is sorbed as +6, while Np and Pu are sorbed in the +! oxidation state. Pu is selectively reduced to Pu(III) and elut:d, while U®* and Np** remain sorbed. The latter are then eluted in separate portions with HCl - HF mixtures. Reagents (C.P. Chemicals) ® 9M HC1 ® 9M HC1l - 0.05M NH,I e 4M HC1 - 0.1M HF e O0.5M HC1 - IM HF Materials e '"Dowex" 1-X10, -400 mesh anion resin e Column, 0.6 cm I.D. and 12 cm in length, with heating device. e Resin bed, 0.28 cm? x 3 cm long. ® Plastic test tubes - 169 - ® "Teflon" evaporating dishes @ Plastic transfer pipettes Procedure 1. Evaporate sample to near drynmess. 2. Add 1 ml of 9M HC: - 0.O0SM HNO3 and heat for 5 min. Do not boil. 3. Heat column to 50° and maintain throughout elution. 4, Pretreat resin bed with 3 column volumes of 9M HC1. Use air pressure to obtain flow of G.& cm®/min. S. Pass sample through resin bed a: 0.8 cm/min. 6. Wash bed with 4 column volumes of 9M HCI. 7. Wash bed with 8 coiumn volumes of 9M HC1 - 0.05M NHuI fPu fraction). 8. Wash bed with 4 coiumn volumes of 4M HC1 - {O,1M HF (Np fraction). 9, Wash bed with 3 column volumes c¢f 0G.5M HC1 - IM HF (U fraction). 10. Regenerate the column with 3 column volumes of SM HCI. The total time for the column operation is about 80 min. - 170 - Procedure 12. Separation of Zr, Np, and Nb Using Anion Exchange J. H. Holloway and F. Nelson?2" Qutline of Method This procedure is used to separate trace amounts of Np and Nb from micro-amounts of Zr. It makes use of ¢he fact that Zr(IV) in HCl - HF media at high HCl concentrations is essentially non- sorbable by anion exchange resin under conditions where Np(VI) and Nb(V) are strongly sorbed. Keagents ¢ OM HC: - IM HF - Cl; ¢ ©OM HC1 - IM HF ¢ O.5M HC1 - 1.0M HF e 4M HNOj3; - 1M HC1 - 0.2M HF Matertale e '"Dowex' 1-X10, -400 mesh anior resin ¢ Column, 0.9 cm I.D. x 12 cm ir length containing 2 ml of resin e '"Teflon" evaporating dishes ¢ Plastic transfer pipettes e Plastic test tubes ® Chlorine gas Prceedure 1. Dissolve the sample, and evaporate it to near drymness. 2, Add 1 ml of 6M HCI - 1M HF - Cl,, and warm. 3. Transfer the sample to a plastic tube and bubble Cl: gas through it for ~3 min. - 171 - 4. Chlorinate the resin, and add it to the column. 5. Wash the bed with 2 column volumes {4 ml) of 6M HC1l - IM HF - Cl,. Then pass the sample through the bed. (Control the flow with air pressure at 0.8 cm/min. When the sample has passed, wash with arn additional 3.5 column volumes of 6M HC1 - IM HF - Cl; (Zr fraction). 6. Wash with 3 column volumes of 0.5M HCl - IM HF to elute Np. 7. Wash with 3 colummn volumes of 4M FENOs - IM HCl - 0.2M HF to elute Nb. 8. Regenerate with 3 column volumes of 6M HC1 - IM HF - Cl,. The total time for the column operation is 'v30 mir., Procedure 13. Separation of Np and Pu by Anion Exchange N. Jackson and J, F. Short3"? Outline of Method This procedure describes separation of macro amounts of Pu and Np. It is based on the fact that Pu(IIl) is not sorbed on anion exchange resin, while Np(IV) is strongly sorbed at high HC1 concentrations. The valence adjustment is don2 before sorp- tion on the column by dissolving the hydroxides in a concentrated HC1 solution that has been saturated with NH4I. The Np is removed from the column with 2 M HCl. The separation is quantitative and complete, Procedure The purification of 2.3 g of Np?37 from approximately 50 mg of Pu??? was then undertaken. The Np and Pu were precipitated as hydroxides, centrifuged, and dissolved in 210 ml of concentrated HC1 saturated with NH,I. The solution was allowed to s*and for 30 min and poured onto a Deacidite FF*anion column 20 cm long and 2.5 cm diameter, while a flow rate of 1 ml/nin was maintained. The first 200 ml of effluent were pale blue [Pu(IIl)]. The column was then washed with 100 ml of concentrated HCl, and wash was collected separately. No activity was found in a drop collected at the end of the washing. The Np was eluted with 2M HC1l. It was possible to follow the dark green band of the Np down the column, and the first 4C ml of eluate was included with the concentrated HCl wash. All the Np *Deacidite is supplied by Permutit Co. Ltd., England. - 173 - was collected in the next 50 ml of eluate. No activity was found in any eluate after this stage. Some f-y a:tivity was detected on the glass wool at the top of the resin column and was assumed to be ??'pa, the daughter of Np2'7, - 174 - Procedure 14. 5Separation of Np and Pu by Cation Exchange V. D. Zagrai and L. {. Se!'chenkov?’? Cutline of Method Np(IV) and Pu(liI) are adsorbed on the cation resin MUl or KU2 from 0.25M HCl solution after reduction with SO, at boiling water temperatures. Np is eluted with 0.02M HF, and Pu stripped with 0.5M HF. Procedure 1. To 6 to 8 m1 © 2,25N HC1 containing ug awounts of Np and Pu, add a >ut half of the resir in the hydrogen form required to fill the plerigluss column (1 mm diameter x 90 mm high) and 1 to 2 m! of water. 2. Pass SO, gas through the solution vigorously for 15 to 20 min, while the solutions heating on 2z boiling water bath, 3. Allow the solution to cool to room temperature, and transfer the resin to the column with a pipette. Plug the top of the column with cotton, and pass the remaining solution through the column. 4. Wash the resin with i0 m) of 0.25 ¥ HCl, followed by 10 ml of H20. S. Elute the Np into a Pt disk or a "Teflon" beaker with 40 to 60 ml of 0.02M HF. 6. Elute the Pu with 4 to S mi of 0.5 HF. - 175 - Procedure 15. Separation and Radfochemical Determination of lsl 4]|lf1d the Transuranium Elemerts Using Barium ulfate C. W. si'l!!l,llb'lls Introduotion Large trivalent and tetravalent ions are precipitated with BaS0, while monovalent and divalent cations sre not precipitated. This procedure outlines the separation of U and transuranium elements both from other elements and from each other. The oxygenated cations of the hexavalent state are too large to fit into the BaSO, lattice and are not carried. The BuSO, precipitate can be alpha counted directly with 92% counting efficiency, or the radionuclides can be electrodeposited for alpha spectrometry. Reagents and Equipment o Concentrated H;SO. o (.P, K3SO. e Concentrated HNO, e Concentrated porchloric acid (HC10.) e C.P. KNO, C.P. potassium dichromate (KCr;0y] ® 30V hydrogen peroxide (H;0;) Erlenmeyer flask ¢ Centrifuge and special tubes o Counting supplies and equirment -~ 176 - Procedure S. 6, 10. Add 3 g of anhydrous K;SO, 2 ml of concentrated H;SO., 6 drops each of concentrated HNOj and HC10,, and 2.00 ml of 0.45% solution of BaCl,*2H;0 (5 ng of Ea) to the solution containing the elements to be precipitated in a 250-m] Erlenmeyer flask and evaporate until fumes of H2S0, appear. (If there is any question about removal of organic matter, add HNO, and/or HCiO, and re-svaporate. Heat the solution over a blast burner with swirling until the excess H2S0, and HC)O, are volatilized and a clear pyrosulfate melt is obtained. Cool the melt, add 2 al of concentrated H;SO,, and heat to boiling or until the pyrosulfate melt is dissolved. Do not volatilize much H,;S0,.. Cool and add ~10 mg of solid K;Cr;0,, and mix to ensure complete cxidation of Np. Do not heat because Pu will be oxidized and the excess dichromate will be theraally decomposed. Cool to "40°C and add ~20 m1 of water; boil for 1 minute, Cool, centrifuge, and wash the prccipitate: the Np and U are in the supernate. Add 0.5 ml of 30V H;0; and 2.00 m] of 0.45% BaCl; to the supernate, and evaporate until fumes of H;5%0. appear to reduce any Pu that may have followed the Np. Heat the H,S0. to hoiling, cool for } minutes, and add V0 g of Kjf Fe(NH2503),, and let stand for S min. Transfer to a 100-ml plastic tube, 3add 5 ml of concentrated HF, stir, and let stand 5 min. Centrifuge, and discard the liquid phase. Dissolve the precipitate in 20 vo 50 ml of IM HC1, and dilute to 75 ml with IM HCI. Add 5 ml of concentrated HF, stir, and ler stand for 5 min, Centrifuge and discard the liquid phase. Repeat Steps 5 through 7. Transfer the precipitate to a 50-ml beaker containing 3 ml of concentrated HC10.,, and evaporate to dryness. Dissolve the residue in 20 ml of 1M HCl1 by boiling. Cool the solution and dissolve 0,25 g of Fe(NH,;S0s),. Transfer the solution to a 125-ml separatory funnel and mix., Add 20 ml of TTA in benzene, and extract for 10 min. Discard the aqueous phase. - 184 - 12, 13. 14. 15. 16. Note Wash the organic phase with three 20-ml portions of IM HC1 for 5 min each. Discard the aqueous solutions. Back-extract the 2%?Np with 10 ml of BM HNO; for 10 min. Place the aqueous in a 50-ml beaker containing 3 ml of concentrated HC10,, and evaporate to dryness under a JAeat lamp, Cool the beaker, add 5 ml of 8M HNO;, and heat to boiling. Dilute the solution to a measured volume and analyze by gamma counting. The analysis requires 6 hours, and tle yield is >90%, - 185 - Procedure 18. Determination of Np in Urine F. E. Butler?’’ Outline of Method Urine is wet ashed with HNO,; and H;02 to destroy organic matter. The salts are dissolved in 8M HCl and extracted with TIOA (tri-isooctylamine). The Np is then back extracted, and the alpha activity is determined by direct planchetting and counting on low background solid-state counters. A variation of the procedure provides for sequential deter- mination of actinides in biological and environmental samples. Pu, Np, and U are extracted from 8M HCl to TIOA. The residual 8 HCl containing Th, Am, Cm, Bk, Cf, and Es are extracted from i2M HNO3 to DDCP (dibutyl N, N-diethylcarbamyl phosphonate}. The actinides of interest are back-extracted sequentially for quanta- tive determinations. Preparation of Sample Urine collected in polethylene bottles is transferred to an Erlenmeyer flask with concentrated HNO; (20) ml of acid per liter). Acid is added to the urine in the polyethylone bottle to remove the Np, which may be adsorbed on the walls of the container. The acidified sample is evaporated to dryness, and the residue is wet ashed with HNOj and H;0,. Nitrates are met:uthesized to cnlorides by evaporation to prevent interference with Pu (1iI) removal. - 186 - Reagents and Equipment The liquid anion exchanger, TIOA (Bram Chemical Cc.) is diluted to 10 vol % with Xxylene and washed with half its volume of 0.1M HC1 before use. The alpha-detection equipment are 2l solid-state counters. The counters are equipped with detectors *hat have an active area of 350 mm? and ure capable of accepting l-in. stainless steel planchets. All other reagents used in the procecure are prepared from analytical grade chemicals. Froccdure 1. Wet ash urine with HNO3; and H,0,; then add 19 ml of 8M HCI to the white salts twice and evaporate the solution to dryness each time. Z. Dissolve the salts in freshly prepared 8M HC! - 0.05M NH4I (50 ml of acid/250 ml of urine in sample), and heat to com- plete solution. 3. Transfer a 50-ml aliquot of the solution witk 25 ml TIOA-xylene into a separatory funnel and shake for 1l min. (For urine samples of 250 ml or less, rinse the flask twice with 10 ml of 8M HC1, and add the rinses to the funnel.) 4. Drain and store the aqueous (lower) layer for Pu, Th, Am, Cm, and Cf analysis. 5. Rinse the organic phase with 25 ml of &M HCl - 0.05M NH.I at 80°C and shake for 1 min. Discard the rinse solution or com- bine with solution stored for other actinide analysis. - 187 -~ 10. Add 25 ml of 4M HC1 - 0.02M HF to the funnel and shake vigorously for 10 sec. Drain the Np strip to a i00-ml breaker. Repeat a second time and combine the two 25-ml solutions. Discard the organic phase or strip with 0.IM HC]l for uranium analysis. Cvaporate the Np strip to dryness. Wet ash with HNO, and H;0;. Rinse sides of breaker with 4M HNO3; and evaporate solution to dryness. Add 1 ml 4M IINO; and transfer solution to stainless steel planchets and evaporate to dryness under an infrared lamp. Complete transfer with 3 rinses of 4M HNO;. Flame the dried planchet tc dull red, cool, and count on low- level solid state alpha counters. Calculation: Np activity on planchet is determined as follows: total count - Bkfll_ (t)(counter cff.) dis/(min-planchet) where: Bkgd. = counter background (3 to 10 counts/Z24 hr) t = counting time in minutes counter eff = counter efficiency as a fraction {normally 0. 30) The sensitivity of this analysis is 0.02 * 0.01 dis/ min-sample). The recovery efficiency is determined by adding a known amount of Np standard to an aliquot of urine sample and following the same procedure for analysis. - 188 - Procedur2 19. Determination of 237Np by Gamma Ray Spectrometry W. 0. Granade?? Introduction A gamma spectrometric method was develored that allows for the rapid determination of Np in process solttions containing fission products. The method is unaffected Ly highly salted, 217 corrosive, or organic media. Np is determined by gamma spectrometry using a thin lithium-drifted germanium [Ge(Li)] semi- conductor detector to resolve the 86.6-keV 2?’Np gamma ray. Apparatus The detector system consists of an Ortec model 3113-10200, low-energy photon detector with cooled FET przamp and a resolution of 900-keV full width at half maximum (FWHM) at 86.6-keV. A 4096-channel pulse height analy:zer is used for the sccumulation and storage of the gamma sjpectra. The data are read onto magnetic tape or printed out directly from a high-spee digital printer. Datz reduction is performed using an IBM 360 .:system and FORTRAN programs developed to calculate nuclide abundanccs from multi- channel gamma ray spectra.® Procedure Calibration. ?%*Pa, the daughter of 2?™Mp, has a 0.017 abundant gamma ray at B6.6-keV that interfere: with the mcasure- ment of the 2?’Np gamma ray of the same erergy. 227Pa also has 4 0.34 abundant gamma ray at 311.9-keV that ir not associated with a 2?’Np gamma ray. In order to determine the 2??Pa :ontribution - 189 - to the 86.6-keV 2?7Np photopeak, a pure stancard solution of 233pa is required. 2?%Pa is purified by passing an equilibrium solution of 23’Pm-anp throveh a diatomaceors earth column which sorbs *3%a. The 2%¥%a is eluted, and the 2°'Np contaminant level is determined by alpha counting (??°Pa does not decay by alpha emission). Aliquots of *'?Pa are pipetted into a standard gamma counting geometry. A series of counts of the 2?3Pa are made to determine the ratio of gamma counts at the 86.6-keV peak to counts at the 311.9-keV peak. The ratio is used to calculate the 2?%pa contribution to the total counts detected at the 86.6-keV peak. The efficiency of the Ge(Li) detector for 86.6-keV gamma rays is determined by calibration with known gamma standards between 43.5 and 511.6-keV. Araiyeis The standards and sample are counted in a holder which ensures a reproducible geometry at 2 cm. The deadtime correction (always <20%) was found to be accurate to <1%. The gain setting of the amplifier is adjusted to provide a peak width of 7 to 10 channels (FWiiM) to allow reliable integration of the photopeak area. For a Gaussian distribution, 99% of a peak area is contained in 2.1 x FwliM. Therefore a peak area of 24 channels is used with a gain setting giving 10 channels FWHM. The net counts per minute of ?*’Np is calculated by subtractin p P Y g the Compton background and the 2?%pa contribution from the 86.6-keV - 190 - total photopeak area. The contribution of underlying Compton background is assumed to be linear over the peak arca. An average of the counts from 4 channels on each side of the peak is used to determine the background correction. For an analyvsis above the determination limit (the relative standard deviation is less than 10% of the measured value), the peak area minus the background should be greater than?: o[- 2ae] 12. The absolute disintegration per minute value of *’'N\p is obtained by dividing the net counts per minute hy the product of the gamma ray abundance (photon/disintegration) and the detector efficiency at 86.6-keV. A comparison of 2'’Np results obtaincd by gamma spectrometry and TTA extraction® agreed within 3%. An aliquet of 1.06 x 103 alpha dis/(min-ml) z"Np standard solution was e¢xtracted using TTA. A standard geometry sample was made from the TTA [orpanic) phase and one from the aqucous phase. The resulting gamma count- ing showed that 97% of the ??'Np had been extracted into the TTA phase. Close agreement between the two mithods demonstrated the reliability of the gamma pulse height analysis. Samples can be counted in organic media with no adverse offects. A lower limit of detection of 1 x 10° d/m/ml at a conficdence level of 95% was determined from a series of counts using : diluted standard ?°7Np solution. - 191 - Refarence 1. R. V. Slates. GELI 2 and SPAV 2, Fortro: Programs to Caleulate liuclide rAdundances from Huitiarnel Garwma Ray Spactra. USAEC Report DP-1275 (1971). s a M. A. Kakat and E. K. Dukes, /. Szdioaniilve. Cier. <, 109 (1970). 3. F. Rider. Seciaciod Anciytival ¥etnodr Jor Furex Frococss tontreic. USAEC Report KAPL-890 (1953). wr - - 192 - Procedure 20, Spectrophotometric Determination of Np R. G. Bryan and G. R. Waterbury®?? Outline of Method Np is measured spectrophotometricallyr as the arsenazo III complex after separation from Pu and impurity elements by liquid- liquid extraction. U is removed first by extraction from 4M HCl into triisooctyl amine (TIOA)}-carbon tetriachloride, while Np(IV) and Pu(I1l) are stabilized in their nonexiractable oxidation states by Fe(ll) and ascorbic acid. Then Np(IV) is extracted from 84 HCl1 into TIOA and back-extracted into 0.1M HC1l. The Np-arsenazo IIl complex is formed in 6.1M HCl, and the absorbance is measured at a wavelength of 665 nm. Heagente ® Arsenazo IIl, 0.2% [i,8-dihydroxynapthalene -3, 6-disulfonic acid-2, 7-bis {azo-2)-phenylarsonic acid]. Dissolve 1 g of arsenazo Il in 500 ml of water containing two KOH pellets. ® Ascorbic acid, 5%. Dissolve 6 grams of ascorbic acid in 120 m]1 of 8M HC1. ¢ Carbon tetrachloride, (CCl,) reagent grade. e HCl, 12M, reagent grade. e HCl, 8M, 4M, and 0.1, & Np stock solution. Dissolve high purity Np metal in 12M KCl. ® Phosphoric acid, (1,P0,) 15.9M, reragent grade. ® KOH, pellets, reagent grade. - 193 - ® Reducing solution, 5% ascorbic acid and 0.5% Fe(II) ion in 4M HCl. Dissolve 2.5 gy of ascorbic acid and 1.75 g of Fe(NH2S03)2 in 50 ml of 4M NCI. @ Tri(iso-octyl)amine-xylene (TIOA in xylene), 5%. Dissolve 31 ml of TIOA in 500 ml of reagent-grade xylene. e Tri(iso-octyl)amine-carbon tetrachloride (TIOA-CCl,), S%. Dissolve 31 ml of TIOA ir 500 ml of CCl,. Equipment ¢ Extractors (see figure in Reference 302). e Laboratory glassware (beakers, pipets, syringes, and volumetric flasks). e Spectrophotometer, Beckman model DU or equivalent, with matched fused-silica cells having l-cm light paths. Pretreatment The sample of metal or alloy is inspected, and extraneous material is removed. Cutting oil is removed by washing with methyl chloroform. For each Pu metal sample, take two accurately weighed portions, each not greater than 200 mg and containing less than 60 ug of Np. Make duplicate determinations on each sample, on a solution containing a known quantity of WNp, and on the reagent blank solution. - 194 - Procedure 1. 10. Place each accuratcly weighed sample in a glass extractor and add 1.5 ml of 12M HCl. When the sample has dissolved, add 1 ml of the reducing solution and 2.5 ml of water. Prepare reagent blank solutions by adding 1 ml of reduc- ing solution and 4 ml of 4M HCl to each of two extractors. Prepare known Np solutions by adding an aliquot of standard Np solution that contains an amount of Np approximately equal to that expected in the sample and 1 ml of reducing solution to each of two extractors. Dilute the solutions to 5 ml with 4M HCI. Add 5 ml of TIOA-CCl, to ecach of the solutions prepared in previous steps, mix the phases for 2 min, and then allow the phases to separate for 1 min. Separate the TIOA-CCl., layer and discard. Repeat Steps 4 and 5. Add S ml of 12M HCl and 10 ml of TIOA-xylene to each extractor, mix the phases for 5 min and allow the phases to separate for 1 min. Remove the aqueous phase con- taining the Pu. Wash the inside of the extractor with 5% ascorbic acid-81 HCl, mix the phases for 2 min, and allow the phases to separate for 1 min. Remove the aquecous phase. WNash the inside of the extractor with B8M lHCl. Mix the phases for 2 min, and allow to separate for 1 min. Remove the aqueous phase. Add 4 ml of 0.1M HC] to each extractor. Mix the phases for 3 min, and allow to separate for 1 min. - 195 - 11. 13. 14. 15, Remove the aqueous phase into a 25-ml volumetric flask containing 0.6 ml of H3PO,, 1 ml of 5% ascorbic acid- 8 HC1l, and 12.7 m]l of 12M HCI. Repeat Steps 10 and 11, Add 2.5 ml of 0.2% Arsenaz> III solution to the volumetric flask, and dilute to 25 ml with water. Stopper and mix the contents of the f'ask, Measure the absorbance of the solution in cells having l-cm light paths at a wavelength of 665 nm. Np, ppm = Ab = Ak As = Wk = (As-Ab) (Wk, ug of Np) (Ak-Ab) (sample wt in grams) absorbance of blank absorbance of known Np solution absorbance of unknown sample ug of Np in known N solution Relative standard deviations range between 7.2 and 1.1% in measuring 8.5 to 330 ppm of Np in 200 mg samples. Of 45 elements tested only Pd, Th, U, and Zr cause serious interference, but only if present in concentrations greater than 0.8%. However, initial extraction from 4M HCl into TIOA removes some U, and Th is not significantly extracted from HC. solution. Also, H,4PO, complexes up to | mg of Zr without affecting the analysis., HF and HNO; cause low results unless removed by volatilization. The method tolerates the intense radioactivity from quantities of 2)8py as large as 100 mg. - 196 - Procedure 21. Microvolumetric Complexonetric Method for Np with EDTA A. P. Smirnov-Averin, G. S. Kovalenko, N. P. Ermoloev, and N. N. Krot'?® Outline of Method Np(IV) 1is titrated with a solution of EDTA at pH 1.3 to 2.0 with xylenol orange as indicator. The ireaction of Np(IV) with EDTA is stoichiometric, and the color changes from bright rose to light yellow at equal molar concentriations. The determination takes approximately two hours; the erro: is *(0.03 mg. Reagents and Equipment HC]l, reagent grade Test solution, 10 mg Mn?® and 50 mg NH,OH10. Centrifuge the precipitate, and discard the solution. Add 10% NaCl in 4M HCl1 dropwise until the precipitate is dissolved. - 197 - 5. Add 1 to 1.5 ml of 4M HC! containing 50 mg of NI20H*HCl per ml, and heat the solution for 20 min on a boiling water bath. 6. Cool the solution, dilute to ~1J0 ml with water, and add 1 to 2 drops of 0.1% xylenol orange. 7. Titrate with 2 x 1073M EDTA fronr a microburet until the cclor changes from rose to brigit yellow. Notes 1. HCl solutions are preferred in >rder to reduce all the Np to the tetravalent state with NH0H*HCl. Ascorbic acid is not suitable, since its decomposition products interfere with the titration. 2. Doubly charged readily hydrolyzable ions (Mn**, Ni2*, U022%), which do not interfere with the titration, are used as carriers. 3. Np can be determined with an error of $0.03 mg in the presence of large amounts of alkali, alkaline earth, and rare carths elements, Mn2*, Zn2?*, cd?*, Pb?*, Cr?* (up to 20 mg), Ni?*, Co?* and U022*. Anions which are scparated by strong base precipitation include NO;~, Q1,000™, SO04?™, C2042", Cr,0,2", and EDTA*". Pu is reduced to Pu(III) and does not interfere up to 2 mg. Zr**, Th**, and Fe®® interfere because they are cotitrated with Np(1V). - 198 - Procedure 22. Photometric Determination of Hp as the Peroxide Complex Yu. P, Novikov, S. A. lvanova, E. V. Bezrogova, and A. A. Nemodruk??? Outline of Method Np(V) forms an intensely colored complex in alkaline solutions (pH >8). The ratio of Np(V) to H0; in the complex is 1:1; the molar absorptivities of the complex at 430 and 370 nm are 5010 2210 and 7950 £350, respectively. The method is highly selective for Np. Peagents and Eq': . ent e NaOH, CP gradc ® "202, CP grade e Spectrophotometer and cells. Procedure 1. Add the dilute acid (HNO,;, HCl1l, or hHClQ,) solution, 2.5 ml containing 5 to 50 ug of Np into a test tube. N Adjust to Np(V) by adding 0.1 ml of 30% H,0,, and keep in a boiling water bath for 10 min. 3. Cool the solution, and add 0.1 ml of 0.5M H,0,. 4. Neutralize to pH 1 to 3 with Na0l, and add an extra 1 ml of 4M NaOH. 5. Dilute to exactly 4 m}l with water, and mix thcrcughly. 6. Measure the absorbance in a 1 cm cell at 430 or 370 nm realtive to a blank. 7. Determine the Np content using a calibration curve. -~ 199 - Notes 1. Np(V), but not Np(IV) or Nu(VI), gives a color reaction with H-0,. The stability of the colored Np(V) peroxide complex increases as the pH is increased. In 0.IM NaCOH solution, the absorbance remrins unchanged for two hours. Increasing the H,0; concentratiol to >7 x 107°M does not change the ahsorbance. At higher H202 concentrations, the time for constant absorbance increases. When the solution contains U, 7 to 10 mg of (NHs4)2HPO, is added before the NaOH. Great2r amounts of the phosphate reduce absorbance of the Np(V) complex. Fluoride reduces the absorbance of the Np(V) peroxide complex. Tartrate, carbonate, and sulfate ions to 0.1M have no effect. When iron is present, Fe(OH).; precipitates and is removed by centrifugation. Up to 300-fold amounts of Fe do not interfere. Four-fold amounts of Pu do not interfere. - 200 - Procedure 23. Separation of Np for Spectrographic Analysis of Impurities J. A, Wheat??? Outiine of Method Np compounds are dissolved in concentratec¢ HNOj, and the solution is heated to dryness. The residue is dissolved in dilute HNO3, and Np oxidation state adjustment is made with NzH. and sulfamic acid. The hexanitrato anionic complex of Np(IV) is sorbed on strong base anion resin; the cationic impurities are not sorbed by the resin. The cycle is rzpeated, and the effluents are evaporated and baked at 400°C. The residue is dissolved in 6M HCl, and the cationic impurities are determined by emission spectroscopy. Reagents and Equipment ® Double-distilled HNO; e "Dowex" 1-4 100 mesh e Hydrazine (N2Ha) @ Sulfamic acid e Cobalt solution ® Small glass column ® Spectrograph Procedure 1. Dissolve 50 mg of sample in concentrated HNO,, and evaporate to dryness. 2. Dissolve solid residue in 2 ml of 0.35M HNO, and add one- fourth ml of 11M aqueous solut.on of N,li,. Wait at least 30 min for valance adj'::ment. - 201 - 3. Add one-half ml of 3M sulfamic acid and 2.5 ml of 16M HNO,, and mix the solution. 4. Pass the adjusted solution thraugh a 3 ml bed of !JU-mesh "Dowex" 1-X4 resin at <3 ml/(min-cm?®), and collect the effluent. 5. Wash the resin with 10 ml of BM HNO;, and combine the effluent with that from Step 2. 6. Elute Np from the resin with 0.35M HNO;, and condition the column with 8M HNO; for rease. 7. Evaporate the sorption and was: effluents tc dryness, and repeat Steps 2 through 6. (99.96% of the Np was removed with two cycles of aniin exchange). 8. Evaporate the sorption and wasi effluents from Step 7 to dryness and bake at 400°C t> expel hydrazine. 9. Dissolve the residue in 1 ml of aqua repgia, and evaporate to dryness. 10. Dissolved the last residue in | ml of GM HCl containing 100 ug of Co, which serves as in internal standard. 11. Evaporate two hundred uf of th:2 solution to dryness on top of a 1/4-inch-diameter flat-top electrode. 12. Excite the sample for 30 sec bs a 10-amp dc arc using a large Littrow spectrograph in the 2500 to 3500 A wavelength region. The slit width is 10 ym, and a two- step neutral filter 100%/35% is inserted in the slit. SA-2 emulsion is used. Because of the relatively large volume of reagents used, a reagent blank should be carried throuzh the procedure. Doubly distilled HNO3; was used. - 202 - Recovery was 88 to 106% for all elements except Ni which was 65%. The coefficient of variation for a single determination of the several elements varies from 9 to 24% with an average of 17%. The precision is affected by large volumes of reagents and incomplete removal of cationic impurities from the resin column. The method was applied to determination of Fe, Cr, Ni, Mn, Cu, Al, and Mg. - 203 - Procedure 24. Photometric Determination of Np as the Xylenol Orange Complex N. P. Ermoloev, G. 5. Kovalenko, N. N. Krot, and V. J. Blokhin3%® Outline of Metnod Np(IV) reacts in weakly acidic solution {pH “2) with xylenol orange to form a color complex with an absorbance maximum at 550 nm and molar extinction coefficient of 5.5 x L0°. Xylenol orange 15 three times more sensitive than thorin but only one-half as sensitive as Arsenazo I11 as a reagent for Np{IV). The greatcst advantage of xylenol orange compared to thorin and Arsena:zo III is the relatively minor interference of U. Reagents and Equipment e HCI e 30% KOH @ Test solution, 10 mg Mn?* and 50 mp of Ni;0t=1C] per ml ® 100 mg NI;0H*HC] per ml in 7N {IC] ® M NH, Ol ® 0.05% xylenol orange e pli meter ® Spectrophotometer ® Centrifuge tubes Frooedure L. Add sclution containing S to 0 ug of NXp to a centrifuge tube, and dilute to § to 8 ml; then add 30% KOM until pil >10. fe Add | @l of test solution contnining 10 mg of n®® and 50 mp of NN;ON-ICLl int: the contrifupe tube. - 204 - Mix and centrifuge the precipita:e. 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