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REVIEW OF THORIUM RESERVES IN .
GRANITIC ROCK AND PROCESSING
OF THORIUM ORES
K. B. Brown
F. J. Hurst

D. J. Crouse
W. D. Arnold

CENTRAL RESEARCH LIBRARY
DOCUMENT COLLECTION

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OAK RIDGE NATIONAL LABORATORY
operated by
UNION CARBIDE CORPORATION
for the
U.S5. ATOMIC ENERGY COMMISSION

   
L L e L b g L o s R e b L L L it b et ettt il otk b

 
ORNL-3495

Contract No. W-Th4OS5~eng-26

CHEMICAL TECHNOLOGY DIVISION

Chemical Development Section C

REVIEW OF THORIUM RESERVES IN GRANITIC ROCK @
AND PROCESSING OF THORIUM ORES |

K. B. Brown D, J. Crouse
F. J. Hurst W. D. Arnold

Paper presented at Thorium Fuel Cycle Symposium,
Gatlinburg, Tennessee, Dec. 5-7, 1962

Date Issued

MDY 72 1961

o S5 o D

 

 
iii

CONTENTS

ABSETACE & & ¢ 4 ¢ ¢ o o ¢ s s o e o 2 o s s & s s e
Introduction .+ + « o & ¢ o o o o o o o s o o o o o o
Recovery of Thorium from Monazite c o 4 e o 4 e e e
Recovery of Thorium from Blind River Ores c e e s e
Processing Thorite Ores © o o s & ¢ s e & & & & o o

Thorium Recovery from Granite s s s s 6 & o & 8 + @
5. 1 Conway Granite s 8 & & & B 8 8 & & ¢ ® e & » @

5.2 Granites from Maine, Massachusetts, Rhode Island
Other Low-Grade Thorium Sources e e e e e e e e e
Conc lusions . - . . - ® . . . - - . e . . - . . - .

Acknowledgments e s s s s e e s 8 s s s e e s e s .

References . « o o o o s s ¢ o o o o ¢ o o s s o o o

 

 
REVIEW OF THORTIUM RESERVES IN GRANITIC ROCK
AND PROCESSING OF THORIUM ORES

 

K. B. Brown D. J. Crouse
F. J. Hurst W. D. Arnold

ABSTRACT

Methods for treating monazite ore to recover thorium
are reviewed. Recovery by solvent extraction with amines
is particularly attractive because it is economical and
provides high recoveries and efficient separations of the
thorium, uranium, and rare earths. Amine extraction is
also easily adapted to processing western thorite ores
and for by-product thorium recovery from Blind River
uranium ores. Solvent extraction with organophosphorus
acids can also be used for processing some ores.

Since the reserves of high-grade ores are limited,
studies are being made of granitic rock as a long-range
source of thorium. These rocks comprise an appreciable
fraction of the earth's crust. The thorium content and
response to acid leaching were determined for samples
from many major granitic bodies in the United States,
and estimated costs for recovering thorium (and uranium)
from these granites are presented. Of principal interest
is the Conway granite of New Hampshire, which has been
studied extensively. This formation contains tens of
millions of tons of thorium recoverable at costs below
$100/1b. The cost of thorium recovery from most granites
should not be prohibitive in power production pending
development of a successful thermal breeder reactor.
Other low-grade sources of thorium, such as sublateritic
soils and volcanic rocks, show less promise than granitic
rocks on the basis of studies conducted to date.

1. INTRODUCTION

The past and current demands for thorium have been satisfied chiefly
from monazite, although significant amounts have been recovered in the
last few years as a by=-product of uranium milling operations in the
Blind River area of Canada. Recently, a large reserve of relatively
high-grade thorite ore has been discovered in the Lemhi Pass area of

Idaho.1 These ores have not been exploited as yet owing to the small

current market for thorium.

 
The monazite, thorite, and Blind River (when thorium is recovered
as a by-product of uranium) ores are easily processed to yield low-cost
thorium products. Ores of this type which are already known, and those
expected to be discovered in the future, comprise a sufficient low-cost
reserve to initiate a large-scale, thorium-reactor power industry. On
the other hand, when production of power over a very long period of time
is considered, the known and predicted reserves of low-cost thorium are
limited. Eventually it will be necessary to process low-grade sources
at higher cost. From the long-range standpoint, granitic rocks are
especially interesting as a potential low-grade source since they are
known to contain most of the thorium in the earth's crust.

This paper describes the processing methods which are available for
recovering thorium from both the high and low-grade sources. Particular
attention is given to estimation of the costs of recovering thorium (and
uranium) from different grades and types of granitic rock. General dis-
cussions are presented concerning the amounts of thorium available from

this source within different cost ranges.

2. RECOVERY OF THORIUM FROM MONAZITE

Monazite mineral is usually obtained as a relatively high-grade
concentrate from physical beneficiation of fine-grained beach or alluvial
sand. It consists principally of the phosphates of rare earths and
thorium, the thorium concentration ranging typically from 3 to 9% (as
metal). Much lower concentrations of uranium (0.1 to 0.5%) are also .
present. (An excellent review of monazite processing methods was made
by Wylie.g) The mineral can be decomposed with concentrated sulfuric *
acid or caustic solutions at elevated temperatures, and both methods are
used commercially. Chlorination of the ore to produce ThCl, has been
studied with some success,E-LL but the process has not been applied on a
commercial basis.
In the alkaline process, as developed at Battelle Memorial Institute,5
the finely ground monazite is digested with concentrated caustic solution

at 140°C and leached with water to remove phosphate. The metal hydroxides

are dissolved from the residue with 37% hydrochloric acid, and the thorium

and uranium are coprecipitated by neutralizing the liquor to pH about 6

 

 
-

with sodium (or ammonium) hydroxide. Further addition of caustic pre-
cipitates the rare earths. The thorium-uranium precipitate is redis-
solved in nitric acid, and the elements are separated by tributyl phos-
phate (TBP) extraction. Several variations of the alkaline process are
used in industry.

In the acid process, the monazite sand is digested at 200 to 220°C
with 93 to 96% sulfuric acid and the digestion product dissolved in water.
Many methods of treating the resulting liquor to recover and separate
thorium, rare earth, and uranium products have been investigated and
described in the literature., In a process developed at Ames Labora-
tory,T’8 the elements were partially separated by stepwise precipitation
with ammonium hydroxide, and the thorium and uranium concentrates were
then redissolved in nitric acid and purified by TBP extraction. Sub-

9

sequently, a modified process” was developed, which included coprecipi-

tation of the thorium and rare earths with sodium oxalate, conversion of

the precipitate to hydroxides by digestion with caustic (which liberated

the oxalate for recycle), calcination to oxidize cerium, redissolution

of the calcine in nitric acid, and TBP extraction and partitioning to

give thorium, cerium, and mixed rare earth products. Other separation
schemes utilizing oxalate precipitation, sulfate precipitation, etc.,

have been proposed by other workers.g’lo-15

More recently, a versatile solvent extraction method, utilizing
long-chain alkylamine extractants (Amex process) was developedlu"17
for recovering thorium, uranium, and rare earths from the acid digest
liquors. This method is described here in greater detail since the
information is more recent and the processes appear to show advantages
over the older ones. In addition, they are applicable to all currently
known thorium sources and are not restricted to monazite.

The relative extraction power of the amine reagents for thorium and
other metal values is strongly dependent on the amine type and alkyl
structure. By proper choice of amine, the thorium, uranium, and rare
earths can be extracted and efficiently separated from each other and

from phosphate in consecutive extraction cycles. Figure 1 shows one

arrangement of a three-cycle flowsheet for treating a monazite acid di-

gest liquor. In the first cycle, thorium is extracted with a primary

 

 
 

UNCLASSIFIED
ORNL-LR-DWG 75603

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Th PRODUCT
; ACID DIGEST LIQUOR )
| ThO2-6 G/L |____1 » PRECIPITATION
| RE20O3-35 G/L )
| U30g-0.2 G/L THORIUM THORIUM
| PO4-25 G/L EXTRACTION STRIPPING o _

$04-130 G/L t l A NOg3, Cl, OR COj
RNH2 U PRO+DUCT

 

 

»{ PRECIPITATION

 

 

 

 

 

\ I l

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

URANIUM URANIUM
EXTRACTION STRIPPING ] ~
t Cl OR CO3_
R3N OR RpNH RARE EARTHS
, PRODUCT
NaCl r— — — —
l | PRECIPITATION
¥ Y | l .
DOUBLE SULFATE RARE EARTHS RARE EARTHS .
PRECIPITATION EXTRACTION STRIPPING
‘If J | NO3~, CI”, CO5,
RARE EARTHS RNH» OR HSOy4
PRODUCT

Fig. 1. Flowsheet for the Amine Extraction of Monazite Liquors.

 

 
amine, such as Primene JM, in kerosene diluent. (Descriptions of re-
agents and suppliers are given in refs 16 and 21.) A number of reagents,
including nitrate, chloride, and carbonate salt solutions, can strip the
thorium from the solvent phase. The choice of optimum stripping agent
depends on several factors, including the type of product desired.
Uranium is recovered from the first cycle raffinate by extraction with

a tertiary amine, or preferably, an N-benzyl-branched-alkyl secondary
amine. The rare earths are then recovered by extracting with a primary
amine or, alternatively, by adding sodium chloride or sodium sulfate to
the second cycle raffinate to precipitate the rare earth sodium double
sulfate. 1In bench-scale, mixer-settler demonstrations of this flowsheet,
thorium and uranium recoveries were greater than 99.5%. Typical thorium
products contained more than 98% thorium oxide, less than 10 ppm of
uranium, less than 0.2% of rare earth oxides, and less than 0.1% of
phosphate. This product would require further purification in a TBP
extraction cycle to produce nuclear-grade thorium oxide., However, by

ad justing flowsheet conditions it may be possible to eliminate the need
for TBP purification. The rare earth extraction flowsheet has not been
demonstrated in continuous equipment. Batch tests showed that rare
earth products only slightly contaminated by phosphate and other metals

are obtainable.

5. RECOVERY OF THORIUM FROM BLIND RIVER ORES

In the past few years large tonnages of uranium-thorium ores have
been treated in the Blind River district of Canada for uranium recovery,
although many of the mills are not now active. Until recently, no pro-
vision was made for recovering thorium as a by-product from the Blind
River ores. However, Rio Tinto Dow, Ltd., is now operating thorium re=-
covery plants at two uranium mills, and solvent extraction is used for
thorium recovery.18 The particular extractant used has not been announced.
The use of di(2-ethylhexyl)phosphoric acid in hydrocarbon diluents for ex-
tracting thorium from these liquors was studied and found promising, pro-
vided that the iron in the liquor is reduced to the ferrous state prior

12,19-20

to extraction. Long-chain mono-alkylphosphoric acids, which are

somewhat similar extractants, can also be used. With both of these

 
extractants thorium is usually stripped from the solvent with 3 to 8 M
sulfuric acid to give a thorium sulfate precipitate.

Amine extraction of the Blind River liquors was also studied with
considerable success. In this case, reduction of the iron is not re-
quired., Both uranium and thorium can be recovered and separated cleanly
by a two-cycle amine extraction process, - using a tertiary amine to
extract uranium in the first cycle and a secondary amine to extract thorium
in the second. Also, thorium can be recovered from effluents from the ion

1 -
exchange circuits presently used for uranium recovery. 2,1T,22-25

Here,

a primary amine is used if the ion exchange effluent contains nitrate
(added for the nitrate elution of uranium from the resin) since nitrate
interferes severely with secondary amine extractions of thorium. If
chloride elution of uranium is practiced, a secondary amine can be used
for the thorium extraction step. Pilot plants using amine extraction have

25,26

been operated successfully at two mills.

4, PROCESSING THORITE ORES

Ores from the Powderhorn and West Mountain districts of Colorado and
from the Lemhi Pass area of Idaho, which contain thorium principally as
the thorite or phosphothorite mineral, have been successfully treated by
a sulfuric acid—amine extraction flowsheet.27 Thorium recoveries greater
than 90% were obtained by leaching with relatively large amounts (200 to
600 1b per ton of ore) of sulfuric acid. The thorium was recovered as a
relatively pure concentrate by extracting with a primary amine, stripping
with sodium chloride solution, and precipitating thorium from the strip

solution with sodium oxalate or soda ash.

5. THORIUM RECOVERY FROM GRANITE

Although the reserves of high-grade thorium and uranium ores are
appreciable, they are limited with regard to the needs of a long-range

nuc lear power economy.l’28’29

Consequently, if the development of com-
petitive nuclear power is highly successful, the supply of high-grade
fissile and fertile materials could change fairly rapidly from one of
plenty to one of scarcity. Although it is conjectural as to just when

this will occur, eventually the world will be entirely dependent on low-
 

grade ores for its nuclear fuel supply. For long-range planning of reactor
development programs, it is important to know how much uranium and thorium
the earth can supply and at what cost in support of a successful nuclear
power economy. It is obvious that the large expenditures of money for
reactor development should be aimed at supplying man's power requirements
for a very long time rather than for a relatively short one.

The large military demand for uranium in recent years created a sig-

28,29

nificant amount of information on low-grade uranium reserves, in-
cluding the outlining of several million tons of uranium in Chattanooga
shale, recoverable for $40 to $60 a pound. Since comparable information

on reserves and recovery costs for low-grade thorium ores was virtually
nonexistent, a program was initiated at Oak Ridge National Laboratory (ORNL)
in 1959 to extend the knowledge in this area. After preliminary tests,

and discussions with a number of geologists,* it was decided to place

ma jor emphasis on granitic rocks as a thorium source. Low-grade placers,
fossil placers, and other types of ore will probably also yield significant
amounts of thorium in the future. However, it is knownBO-38
granitic and related igneous rocks comprise a large fraction of the earth's
crust and contain, on an average, about 12 ppm of thorium and about a
quarter as much uranium. It is also known that some granite formations
contain larger concentrations of thorium. It may be considered that if
thorium (plus uranium) could be recovered from granites at costs commen-
surate with the commercial production of power, the nuclear fuel require-
ments could be satisfied for a very long period of time. This possibility

39

was previously proposed by Brown and Silver, who described results from
cursory leaching tests on several granites and conjectures as to recovery
costs. The potential importance of granitic rock as a source of nuclear
fuels was also discussed by Weinberg,l'LO who dubbed the process "burning

the rocks."

 

*
An informal meeting on thorium (and uranium) reserves was held at ORNL on

February 29-March 1, 1960, and attended by the following: H. H. Adler,
A. L. Benson, D. R, Miller, R. S. Nininger, J. M. Vallance, and Jack
Vanderryn of the U.S. Atomic Energy Commission; J. C. Olson and George
Phair of the U.S. Geological Survey; J. J. W. Rogers of Rice University;
E. D. Arnold, K. B. Brown, C. F. Coleman, D. J. Crouse, F. L., Culler,

W. K. Ergen, A. T. Gresky, J. A. Lane, H. G. MacPherson, and A. M,
Weinberg of ORNL.

 

 
The program at ORNL has been aimed at obtaining much more extensive
information on the availability, properties, and grades of different types
of granites and more definitive estimates of their processing costs. To
implement the program, a subcontract was established with the Geology De-
partment of Rice University, under the direction of Professors J. A. 5.
Adams and J. J. W. Rogers, to collect samples from many large and dispersed
eranite formaticns, to determine their thorium content and, where possible,
their micromineralization.Ll Many of these samples were evaluated at ORNL
as to their amenability to processing, 2 and the process believed best
suited for treating granites, within the limits of present knowledge,
involves crushing and grinding, leaching with sulfuric acid, countercurrent
decantation to separate the leach liquor from the ore tailings, solvent
extraction recovery of the metal values from solution, and finally, neutra-
lization of the waste streams with lime. All the unit operations employed
have been reduced to practice at various places within the domestic metal-
lurgical industry, and this simplifies the estimation of costs. Other
process operations, such as preconcentration of the thorium minerals by
gravity or magnetic separation, are being considered, but only cursory
tests have been made at this time.

With assistance from mining and metallurgical consultants,* preliminary
estimates were made of the recovery costs, covering all the steps from
ore development and mining to production of the final product ( thorium
oxide concentrate). These costs ranged from $3.97 to $5.35 per ton of
granite, variations within this range depending on differences in assumed .
ore/waste ratios for different formations and variations in acid consumption

*x
for different granites (Table 1). *

 

*Cost estimates were made in cooperation with A. H. Ross and Associates
of Toronto, Canada, who, in turn, received advice on mining operations
from prominent metallurgical companies. Estimation of capital costs
for mining were made by C. C. Huston and Associates, Toronto, Canada.

%*The costs given are for open-pit mining to depths of one or possibly
several thousand feed. They are not intended to represent costs that
would be incurred in, for example, mining most of the earth's crust to
depths of several miles.
Table 1. Estimated Costs for Treating Granite

Assumptions: Treatment of 100,000 tons of granite per day
10 year amortization
149, annual return on capital investment

 

Processing Costs
($/ton granite)

 

Mining 0.45-0.90
Milling
Crushing to pregnant liquor recovery 0.57
Pregnant treatment to product 0.11
Sulfuric acid plus lime™ 0.95-1.88
Other chemicals 0.10
Total direct operating costs 2,18-3.56
Overhead 0.29
Contingency .31
Amortizationb 0.50
Return on investmentb 0.69

Total 2.97=5.35

 

a . : i
Based on sulfuric acid at $20/ton and lime at $18/ton. Assumes
use of a countercurrent leach and recycle of the solvent extrac-
tion raffinate to the countercurrent decantation circuit.

bBased on capital costs of $35,000,000 for mining and $145,000,000
for milling.

A summary of test results with a variety of granites from various
locations in the United States is shown in Table 2. It is apparent that
there are a number of large granitic bodies that contain much more than
the average concentration of thorium., The thorium recoveries are moder-
ately low from several samples, ranging from 30 to 40%, whereas other
samples have responded better, giving recoveries of 45 to 60%, and some
have given recoveries of 65 to 80%. The Conway granite from New Hamp-

shire responded unusually well to acid leaching. Uranium recoveries are

 

 

 
 

Table 2. Estimated Costs for Recovering Thorium and Uranium from Various Granites

Conditions: =48 or -100 mesh ore® leached & hr at room temperature with
2 N HsS04; 60% pulp density (130 1b of HoSO, per ton of ore)

 

 

Head Recovery in . \
Conc. (ppm) Leaching (%) Coniz;ition Reizsziitggst
Granite Source Th U Th U (1b H-S0,/ton ore) (3 per 1b Th+U)
Boulder Batholith, Colorado (A) 8 2 ks 20 70 590
Minnesota 12 n Lo 20 110 L70
Philipsburg Batholith 12 3 35 30 60 450
Washington 16 3 55 20 60 2Lho
Boulder Batholith, Colorado (B) 20 5 ks 25 50 220
Enchanted Rock Batholith, Texas 19 L 60 15 90 210
Dillon Tunnel, Colorado 22 8 4s L5 65 170
Colorado Lo 5 35 15 70 160
Pikes Peak, Colorado 24 L 65 25 85 150
Cathedral Peak, California 23 10 50 Ls 35 140
Boulder Batholith, Colorado (C) 33 6 ks 25 35 130
Owl's Head Granite, N, H.d 19 L 75 80 4o 120
Lebanon Granite, N, H.d 30 5 70 45 35 95
Silver Plume, Colorado® ok 2 35 25 60 70
Boulder Creek Batholith, Colorado 76 L 50 50 40 55
Missourid ho 19 80 75 4o 45
Conway Granite® ™ 14 8o 68 60 30

 

aSubsequent tests with Conway and Pike's Peak granites showed that much coarser grinds (-20 mesh) could be used
without loss of thorium leaching efficiency.

bCalculated by subtracting the residual free acid (by the method of Ingles) in the leach liquor from the head
acid.

“Assumes direct mining costs of $0.68/ton in each case.
¢l eached at 50% pulp density (195 1b of H-50, per ton).

e
Average test results for two samples.

01
11

almost always significantly lower than those for thorium. The variations
in thorium (and uranium) recoveries are apparently due mainly to differences

31,36,41,43-45

in mineralization. The soluble thorium fraction seems to

be associated with unidentifiable interstitial material and such minerals
as thorite, apatite, allanite, etc., whereas the insoluble fraction is
probably tied up in minerals such as zircon and monazite, which are almost
inert to the acid leach.

Estimated recovery costs ranged from $400 to $500 per pound of Th+U
for an average-grade granite such as the Minnesota or Philipsburg samples,
to about $30 for higher grade, more amenable samples. Although the re-
covery costs from average or somewhat greater-than-average grade granites
are high, it has been estimated that they would contribute 2 or 3 mills/
kwhr to power costs, assuming future development of an efficient thermal
breeder reactor (Fig., 2). Such costs should not be prohibitive when de-
mands for large amounts of power become unavoidable. The bulk of the cost
is for inventory charges on the fertile fuel since make-up charges are
relatively low. No inventory charge is made against the fissile inventory
in this estimate since it is assumed that, for a breeder reactor with a
reasonably short doubling time, the value of the excess fuel produced

would approximately balance the inventory charge.
5.1 Conway Granite

The higher-than-average radioactivity in the Conway granite of New
Hampshire was reported in 1946 by Billings,51 but no quantitative measure-
ments were made of the thorium and uranium concentrations. Until recently,
only a few thorium analyses were available. Four samples by Hurley ~ ranged
32 to 67 ppm in thorium concentration, averaging 5l. Flanagan gg.gl.,u7
reported an average thorium concentration of 70 ppm in 16 samples from the
Redstone Quarry at Conway, N. H. Analyses of samples from scattered lo-
cations in the Conway formation by Rice University geologistsu1 and by
Butler of the U.S. Geological Survey48 indicated that the thorium concen-
tration in the main mass of the Conway granite might be expected to average
close to 50 ppm. In view of the attractiveness of the Conway granite from

the standpoint of thorium content and process behavior, recent studies at

ORNL and Rice University have centered principally on this material.

 
12

UNCLASSIFIED
ORNL-LR-DWG 76075

 

 
 
  
     
   
   

          
   

 

 

 

10
- THERMAL BREEDER
| ASSUMPTIONS:
| ““FERTILE TINVENTORY - 150 kg/MwE TOJAL
11% ANNUAL CHARGE ON FERTILE INVENTORY
| 50% UTILIZATION OF FUEL
‘ 80% LOAD FACTOR -
i | 30% EFFICIENCY - HEAT TO ELECTRICAL N\
| INVENTORY
CHARGE .
1 |
= B
5 —
4
| \
E — FUEL MAKEUP
= | CHARGE
O
O
d L
o
L
0.1 b—
1 p—
|
| -
0.01LL L1 1] Lot Lotaatld |
5 10 100 1000

RAW MATERIALS COST ($/1b Th)

Fig. 2. Effect of Raw Material Cost on Power Reactor Fuel Charges,

 

 
13

The Conway granite is part of the Central White Mountain magma series,

which occurs largely in the White Mountains and in smaller outlying areas

L49-52

Figure % outlines the major rock types in the cen-

52

in New Hampshire.
tral White Mountain magma series as mapped by Billings and modified in
certain areas by geologists at Rice University. The major rock unit is
Conway granite, which is relatively continuous and extensive, having out-
crop areas totaling about 300 square miles. Other significant rock types
are the Mount Osceola granite (which is distinguished from the Conway
with difficulty in the field), the porphyritic quartz syenite, and the
syenite. The outcrop areas for these rocks total about 100, 28, and 7
square miles, respectively. During the summer of 1961, over 500 field
determinations of thorium were made in the area by Adams, Rogers, and
coworkers of Rice University. They used a portable transistorized gamma-

1208

ray spectrometer that counts the 2,62-Mev gamma of T A statistical

h1,5%

analysis of these data checked by laboratory radiometric and chemical
analyses, indicates that the accessible surface of the Conway granite
contains 56 + 6 ppm of thorium as an average, with few samples containing
less than 40 or more than 100 ppm (Table 3). The average thorium content
for the Mount Osceola granite, the porphyritic quartz syenite, and the
syenite were 43, 38, and 23 ppm, respectively. The Mt. Osceola granite,

although less extensive and less concentrated in thorium than the Conway

granite, still represents a sizeable thorium reserve.

Table 3. Major Rock Types and Thorium Contents in the

Central White Mountain Batholith

 

 

Average
Number Thorium Area
of Content (square
Rock Type Stations (ppm) miles)
Conway granite 214 56 307
Mt. Osceola 98 L3 100
Porphyritic quartz syenite 28 38 28

Syenite 19 23 7

 

 

 
1k

UNCLASSIFIED
ORNL-LR-DWG 75605

71° 00
+ 44°45'

  
  
  
   

71° 45'
+ 44°15'

4 44°00'
74° 00'

+ 44°00'
75° 45'

[T7] CONWAY GRANITE [F] PORPHYRITIC QUARTZ SYENITE
SYENITE [ MT. OSCEOLA GRANITE

Fig. 3. Rock Types in Central White Mountain Batholith.

A, B, and C show locations of drill sites.

 

 
r-

-

~&

15

A number of the outcrop measurements taken on the side of mountains
representing over several hundred feet of natural relief showed no de-
pendence of thorium concentration with depth. However, to obtain more
definite information on the deep and less-weathered material, three
1-1/8-in.-dia drill cores were taken during the summer of 1962 at lo-
cations A, B, and C, shown in Fig. 3. Core A (off the Kancamagus Highway)
and core B (at Diana's Baths area) reached a depth of 600 ft. Core C
(in the Mad River area) reached a depth of 500 ft. As shown in Table I,
analysis of the cores at 5-ft intervals by a field gamma-ray spectrometer
revealed a rather constant thorium concentration throughout the core.ul’55
Physical observation of the cores indicated typical Conway granite through-
out, with the exception of a relatively large dike in the Mad River core
at the 300-ft level. However, the dike rock was less than 0.5% of the
total drilled. On these bases, Adams and Rogers estimated a minimum
indicated reserve of 21 million tons of thorium (computed as the metal)
in the outer 600 ft of the main Conway granite. There is a probability

of at least twice this amount and possibly several times this amount by

going to greater depths.

Table 4. Thorium Content of Conway Granite Cores

 

a
Thorium Concentration® (ppm)

 

 

Core A

Depth (Kancamagus Core B Core C

(ft) Highway) (Diana's Baths) (Mad River)

0-100 54 54 69
100-200 52 55 70
200-300 51 48 76
300-400 L7 56 67
400~500 56 58 76
500-600 68 64

 

a . . .
Average of radiometric measurements taken at 5-ft intervals.

 

 
16

Over a dozen samples from widely scattered locations in the Conway
formations were evaluated with regard to thorium recovery. The thorium
concentration in the samples ranged from 36 to 106 ppm, averaging 58,
or practically the same as that indicated by the radiometric field data.
A range of 52 to 85% (or an average of 72%) of the thorium was dissolved
by the sulfuric acid (2 N) leach (Table 5). The uranium content of the
samples ranged from 6 to 14 ppm and averaged l1l. The uranium recoveries
were lower than those for thorium, averaging 56% and ranging from 26 to
75%. Acid consumption was relatively high, ranging from 55 to 111 lb per
ton or an average of 85 1b/ton. Estimated recovery costs ranged from “
$25 to $89 per pound of Th+U recovered and averaged $57. The data in
Table 5 were obtained from testswith outcrop samples. However, recent
leaching tests with drill core samples showed no significant variation in
thorium leachability with depth in the formation. Consequently, no im-
portant change in process amenability is expected for granite mined to a

depth of at least 600 ft.

5.2 Granites from Maine, Massachusetts, Rhode Island

Granitic rock samples from southwestern Maine and from Massachusetts
and Rhode Island were, on the average, considerably above the earth's
crustal average in thorium content.L'Ll For example, 22 samples from south-
western Maine ranged from 11 to 78 ppm in thorium concentration, averaging
28; nine samples from Massachusetts ranged from 9 to 38 ppm, averaging 19;
four samples from Rhode Island ranged from 16 to 64 ppm, averaging 32. A
number of these samples were tested with respect to process amenability
and, in general, have responded well.)"L2 Pending further study, granites

from these areas could represent attractive large-tonnage thorium sources.

6. OTHER LOW-GRADE THORIUM SOURCES

Other potential low-grade sources, including bauxites, sublateritic

41,h2

soils, and volcanic rocks, have been studied briefly. For one or
more reasons, including, for example, low thorium content, relatively small
tonnages available, poor recoveries in leaching, and high acid consumption,

none of these sources appear as attractive as granitic rock for long-range

thorium production.

 

 
Table 5. Estimated Costs for Recovering Thorium and Uranium from Conway Granite

Conditions: =48 mesh or -100 mesh ore leached & hr at room
temperature with 2 N HsS04; 50% pulp density

 

 

Head Recovery in d )

EEEE;—LBBEA -ESESEEEE—Q%l Conéziption ReizszT;tggsta

Sample Location Th U Th U (1b H-50,/ton ore) (% per 1b Th+TU)
North Conway Quadrangle, N.H. 50 13 60 26 93 T5
Crawford Notch Quad., N.H. 48 12 52 39 109 89
Plymouth Quad., N.H. 54 12 8Lk 73 80 Ll
North Conway Quad., N.H. 56 7 55 51 66 70
Plymouth Quad., N.H. o 12 8Lt 60 60 38
Franconia Quad., N.H. 76 1k 58 50 T2 46
North Conway Quad., N.H.b 70 1k 78 60 80 38
North Conway Quad., N.H. L5 6 67 49 93 5
Crawford Notch Quad., N.H. 52 12 67 65 111 62
Ossipee Lake Quad., N.H. 106 13 82 75 80 25
Mt. Ascutney, Vt. 36 6 80 49 55 72
North Conway Quad., N.H. L6 10 85 61 77 5%
Mt. Chocorua Quad., N.H. 51 8 81 69 86 52

 

a
Assumes direct mining costs of $0.68/ton in each case.

bAverage results for 5 samples from the Redstone Quarry, Conway, N.H.

 

 

L1
18

T. CONCLUSIONS

Although the amount of information on thorium reserves has increased
considerably during the last few years, exact relationships between their
extent, thorium concentration, and treatment costs cannot be drawn in
most cases., Nevertheless, for current consideration of a nuclear power
economy that includes a thorium fuel cycle, several reasonable assumptions
can be made. As to the thorium supply, for example, it may be assumed
that there is a sufficient amount of low-cost thorium to start a large-
scale thorium fuel reactor industry. Further, it is possible that larger
quantities will be found and that they can support the industry for an
. appreciable time. As these low-cost reserves are depleted, sizeable re-
serves at moderate costs are attainable from the relatively high-grade
Conway granites or others of equivalent or nearly equivalent quality.

By accepting lower-grade granites, immense reserves should become avail-
able, and they could supply a nuclear power industry for a very long time
and at nonprohibitive costs, pending the development of successful breeder
reactor systems, It should also be noted that the granite reserves de-
scribed here are located in the United States, and there is every reason
to expect that granites of relatively high thorium content, possibly sur-
passing that of the Conway granite, will be found in many other parts of
the world.

With regard to processing methods, those currently available for
treating the high~grade thorium ores are acceptable from the standpoint
of both operation and economics. Although future improvements can be
expected as a natural outcome of advancing technology, they will probably
not be large or dramatic. The present methods for processing low-grade -
sources are essentially the same as those for the high-grade ores and are
also technologically and economically acceptable. Owing to greater room
and incentive for improvement, larger future advances in these processes
are more probable.

With respect to costs, sizeable reductions are not likely to be at-
tained by modifying present unit operations or by replacing a single unit
operation with another, unless this considerably improves recoveries.

Significant savings might eventually result from combinations of com-

pletely new developments such as atomic-blast mining and crushing, in

situ leaching, bacterial leaching, etc. v

 

 
~—

19

8. ACKNOWLEDGMENTS

The authors wish to express their appreciation to members of the
U.S. Geological Survey who furnished several of the granitic rock samples
examined in the initial studies. Chemical analyses were by the ORNL
Analytical Division, and the radiometric analyses at ORNL were made by
S. A. Reynolds of that division. Thanks are also extended to Professors
J. A. S. Adams and J. J. W. Rogers and coworkers Mary-Cornelia Kline,

Keith Richardson, and Abraham Dolgoff for their energetic and capable

efforts under subcontract 1491,

 

 
10.

11.

12.

15.

L4,

15.

16,

17.

20

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