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Патент USA US3036891

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United States Patent 0
_‘
aasassi
Patented May 29, 1962
1
2
3,036,881
Still another object of the invention is to provide a
catalytic method for promoting the oxidation of uranium
in a carbonate solution with air, oxygen gas, and hypo
CATALYZED OXIDATION OF URANIUM IN
CARBONATE SOLUTIONS
Warren E. Qliiford, San Francisco, Calif., assignor, by
mesne assignments, to the United States of America as
represented by the United States Atomic Energy Com
chlorite oxidizing agents.
One other object of the invention is to provide a car
bonate leaching process employing hypochlorite oxidiz
ing agent for the more economical leaching of lower
valent uranium compounds and minerals from solids.
A further object of the invention is to provide catalyz
10 ing agents for promoting the oxidation of lower valent
The invention relates, in general, to the processing of
uranium ionic species and/or uranium compounds in
uranium in a carbonate solution and, more particularly,
a carbonate solution.
to improved methods of catalyzing the . oxidation of
A still further object of the invention eiseto provide 8.
uranium in a carbonate solution.
catalyzed oxidation carbonate leaching process for im
Aqueous solutions of alkaline carbonates are used ex 15 proving the recovery of uranium from ores containing
tensively for leaching uranium from various solids such
uranium in lower valent oxidation states.
as ores and residues in a variety of recovery and puri?ca
Other objects and advantages of the invention will
tion processes. The carbonate solutions are alkaline and
become apparent by consideration of the ‘following de
contain variable ratios of carbonate and bicarbonate ions
scription.
dependent on operating pH conditions. In such a solu 20
The starting material in the present process may com
tion hexavalent uranium is complexed by the carbonate
prise uranium oxides such as U303, U02, lower valent
ion to form uranyl tricarbonate ion, UO2(OO3)3-4, as
hydroxides such as U(OH)4 or primary~secondary urani
the soluble species; however, at least a part of the uranium
um minerals such as carnitite-uraninite ores, all of which
mission
No Drawing. Filed May 23, 1957, Ser. No. 661,264
9 Claims. (Cl. 23-145)
in such ores and residues often occurs in a lower valent
oxidation state which does not readily produce a species
'which is soluble in such leach solutions. Also, the
uranium may be partially reduced by contact with steel
processing equipment or other etfective reducing agent
during mining or preliminary processing.
For example, if a uranium mineral such as pitchblende,
uraninite or co?inite is present in the ore the carbonate
leach solution does not eifectively dissolve all of the
available uranium since the lower valent states, especially
the tetravalent, does not dissolve in the solution or react
to produce insoluble hydrous oxides or hydroxides on
contact with the ore. Under other process conditions in
which the leach solution contains an excess of CO3=
and the OH“ is buffered out with H003“, a soluble tetra
may contain uranium in oxidation states lower than the
hexavalent and particularly the uranous and mixed
uranous-uranyl states. Residues obtained in other proc
esses and having generally similar characteristics may
likewise be processed. Solutions or other materials con
taining lower valent uranium compounds can likewise be
converted to the carbonate form and the oxidative proc
ess of the invention applied thereto. The ore materials
or other solid, if necessary, ‘are ?rst subjected to grind
ing and screening to provide the proper particle size to
render the uranium content accessible to the leaching
solution. 'Customarily, particle sizes in the vicinity of
minus 100 mesh are adequate; however, with certain
ores, e.g., limestones, grinding to nominally minus 325
mesh may be required.
Solutions are converted to the
valent uranium carbonate may ‘be produced; however,
carbonate form by adding Na2CO3 or NaHCO3 thereto.
this complex is very unstable if the OH— concentration 40
In accordance with the invention, the iinely divided
increases during processing and uranium can be lost
source material is disposed in equipment adapted for
from the solution by precipitation as U(OH)4 at an in-,
heating, agitation, and the introduction of reagent solu
appropriate time in the procedure. In conventional prac
tions and gases if air or 02 is to ‘be employed as the
oxidant. The solid is then contacted at elevated tem
This
tice, procedure
uranium ores
is not
mayalways
be oxidized
effective,byentails
roasting
additional
'in
peratures with an aqueous alkaline carbonate solution
operations and equipment, and cannot be applied to
under catalyzed oxidizing conditions to selectively leach
solutions. Chemical oxidation may be slow and reagent
uranium therefrom. In the event that vanadium is pres
cost high.
ent some vanadium is also leached; however, most other
The present invention is predicated on the discovery 7
materials which are present in ores and residues are not
leached to any great extent.
50
valent states of uranium in such a solution with the
More particularly, carbonate solutions containing from
that certain metallic ions catalyze the oxidation of lower
oxygen in air, 02, and also by hypochlorite. Such catal
ysis is made more effective by the provision of superior
operating conditions and combinations of reagents in
oxidizing uranium contained in carbonate solutions in
general, and is equally effective in oxidizing uranium pres- a
ent in solid materials during leaching operations thereby
‘preventing the formation of insoluble lower valent hy
droxides in such solutions and speeding up as well as in
about 4 to 10% of sodium carbonate and/or from about
0.25 to 7% of sodium bicarbonate are generally used.
Certain very favorable ratios and regent concentration
limits of the reagents and concurrent pH conditions will
be set forth hereinafter.
For the purposes of the invention catalytic quantities
of compounds of certain metallic elements are added to
the solution to provide ionic oxidation states of the
creasing the amount of uranium leached thereby. Sub
metals which effectively promote the oxidation of the
sequently, the carbonate solution may be processed for 6 uranium in the solution. In theory the ions of any ox
the recovery of uranium by various procedures includ
idation-reduction couple above OHr-air and UO2-—
ing processes as conventionally practiced, e.g., in the do
UO2(CO3)3—4 could act as a catalyst; however, it is found
mestic mining industry.
‘experimentally that some substances meeting that quali
Accordingly, it is an object of the invention to pro
?cation and which will oxidize reduced uranium com
‘vide a catalytic process for promoting the oxidation of Ga 5 pounds when introduced in the oxidized state are not
lower valent uranium compounds in an alkaline carbonate
effective when introduced in the reduced state. These
solution.
materials
include PbO-PbOg, Fe(CN)(,-4---Fe(CN)6-3
Another object of the invention is to provide a cata
and Hg——HgCl2. These materials therefore cannot be
lyzed air oxidation method for use in the carbonate
have in a catalytic fashion.
>
leaching of uranium containing solids to improve the
Ionic species corresponding to the oxidation states
recovery of uranium therefrom.
of the following couples produced by the addition of
8,036,881
3
4
solutions by reducing agents such as Na2S2O'4, Zn and
ammonia, and Zn and cyanide. Treatment with 0.2%
sodium amalgams ?nely dispersed in solutions at about
appropriate compounds to carbonate solutions are cata
lytically active in oxidation with 02 or air: C+ +--Co+++;
V+4—V+5; Tl+-—Tl+3; and Mn+2—Mn+4 or possibly
25° C. also precipitates the uranium as a hydrous oxide.
Mn+3--Mn+4 on consideration of the oxidation poten
tials. The ions of the couple Cu+--Cu++ are very eifec
Necessary conditions and procedures for obtaining
bene?cial results in accordance with the teachings of
the invention will be apparent from the following descrip
tion of systematic experimental studies of various op
tive for the indicated purpose. Moreover, the catalytic
eifect of the Cu species is greatly enhanced on addition
of ammonia to the system and the Cu catalysis is also
effective when using hypochlorite (or C12) as the oxidant.
Consideration of the various couples indicates that suit
able couples require, as a minimum, that the oxidation
erating conditions.
At the outset, the distinctive behavior of various ad
ditive agents with reference to oxidative leaching was ex
potential be above the OH--air couple and about equal
plored using a standard procedure. wherein various
to or greater than the H2O2—HO2'— couple consistent
with the view that oxygen reduction which is concurrent
taining 0.5M Nazcoa and 0.5M NaHCO3, in contact with
with uranium oxidation proceeds stepwise through perox
ide. The potentials of the foregoing couples are dis
closed, for example, in chapter IV,, under “Oxygen” of
amounts of the agent were added to a leach solution con
15 5 g./liter of U308 at a temperature of 90° C., with air
blown at a standard rate therethrough and for a standard
time period. A number of control runs with no additive
were made to serve as standard, giving a range of 20 to
“The Oxidation States of the Elements and Their Po
30% of the U303 being dissolved. From the results,
tentials in Aqueous Solutions,” by Wendell M. Latimer,
published by Prentice-Hall, Inc., 1938. The above-indi 20 tabulated below, the materials can be classed as in~
hibitors, as having no effect, as being oxidants, or as
cated catalytic species are produced on the addition. of
being catalysts.‘ The di?erentiation between the latter
compounds such as KMnO4, MnO‘Z, MnSO4, CuSO4,
is made on the basis that catalytic agents improve the
Cu2O, CuCl2,TlNO3, and V205 in amounts ranging from
leaching when either the oxidized or reduced form of
0.1 mg./liter for the more effective catalysts such as
the copper couple to a few grams/ liter of the less e?ective 25 the agent is introduced, while oxidants improve the leach
ing onlywhen the oxidized form is added generally in
materials as discussed further hereinafter.
much larger amounts than is required for catalysis.
'In practice, leaching is conducted at temperatures
TABLE I
Agent (Inhibitors)
Percent
Agent (No Effect)
Leached
25 g./1_ FeSO4 ______ .; ___________ -.
Percent
Leeched
1
5 g./l. Na indigodisulionate ____ __
25 g./l. Pyrogallolm?
_.
1
5 gJl. Na diphenylamine p-sul»
25 g,/l. NH1OH~HCL_
-_
3
.._
6
5 g./l, SnClz-ZHzO .............. __
5
5 g./1. Quinhydrone-..
20
ionate _______________________ __
20
5 g./l. Na 1-10 phenanthroline
monohydrate.
_
20
25
30
30
25
15
20
Agent (oxidants)
Percent
'
.25M H201 ..................... -_
___
.
.
Agent (Catalyst)
Percent
Leeched
.
Leeched
100
55
100
.
30
.
.
5 g./l.
-
75
v
5 g./l. P
-
20
5 g. .
5 ELI].
-
100
5 g./l. 011504515120“
_
100
5 g /l.
..
25
8.5 gJl. OHSOA’SHZO +NH4OH_
100
5 gJl.
_
50
5 all. C1120 ____ _.'_____________ __
70, 85
5 g./1.
_
100, 90
5 g./l. CoO1z-6Hq0 _____________ --
55
5 g./l.
_
100
5 g./l. OOOln-GH; +NH4OH
45
5 g./l.
5 gJl. Hg __________ ._
8 g./l. NaC10(Purex)_. _
_
_
100
20
85
5 g./l. TIN
5 g.[l.
45
60
above about 80° C. and preferably at about 90° C. toob
I A standard procedure and experimental apparatus was
5
employed for a more complete elucidation of the oper
tain maximum rates and degrees of dissolution. The
oxidant, if air or 02, is bubbled continuously through the
agitated mixture, if hypochlorite, is added incrementally
'
ating conditions‘using U308, U02, .ulraninite and other
ores.
300 m1., of leach solution. was disposed in a ‘500
C12 gas should be
7 ml. 3-neck'flask and the system‘ purged with the test gas
leach solution by a variety of conventional ?ltration or
‘desired level and solid containing uranium equivalent to
1 g./liter of solution was added. Copper and other
675 catalysts were added as solids-or solutions, e.g., CuSO4
or at the beginning of the leaching.
equivalent to the hypochlorite and other strong oxidizing 60 (air, 02, or N2) and a bubbling ?ow of about. 10 mL/min.
of the gas was continued during the experiment with
agents should produce similar results.
Following leaching, the uranium is separated from the’ . ,Oontmuous stirring. I Thetemperature was brought to the
centrifugation processes. The uranium can’ be'precipi
tated from leach solutions containing vanadium as a syn
thetic carnotite by acidi?cation to a pH of about
solutions. ' Samples were taken hourly and uranium de
6 from which the uranium and vanadium can be obtained a. V
termined’ ?uorinietrically. '
as U02 and V205 by standard processes. The uranium
can also be recovered and puri?ed from such solutions
‘
l"
compositionof U03 (Shattuck) at'1100°' C. yielding a
A. stock quantity of UaOs'was prepared by the de
by adsorption on a strong base anion exchange,’ resin 7 0' material whose X'-ray diffraction pattern‘ agreed with
that given in ASTM 'data card No. 4-0518. The U02
such as Dowex 1 followed by selective elution as .dis
closed in the copending application of Richard ‘H. Bailes
et -a1., Serial No. 362,122, ?led June 16, 1953, which
issued as Patent No. 2,864,667 on December 167,‘ 1958. '
Was also obtainedfrorn S. W.’ Shattuck _Co., lot No.
10054:and, yielded 'X-rayzdifr'raction data typical of pre
pared UO2. j ;Uraninite labeled “'Urananite (Pitc'hblende)”
Uranium is also precipitated ‘from such carbonate leach" 75 from theGreat Bear» Lake area and analyzing 50% U303
3,036,881
5
6
was obtained from Wards. The ores, all ground to —l00
mesh, tabulated below were also used. It is to be ex
substantial amounts of sodium salts were used to leach
U308 at 90° C. air bubbling with other conditions and
results tabulated below:
pectedpthat lots of di?erent origins and different meth~
ods ‘of preparation will vary in behavior; however, re
sults with identical lots will be self-consistent and ac
TABLE V
‘curately indicate consistent trends in the several varia
tions of the process described hereinafter.
TABLE II
_
10
Ore
Percent Percent Percent Percent
V205
Monticello N o. 27__________________ __
ACM Grey Special ________________ __
0. 16
0.96
0.06
trace
Garwood & Gerlock No. 10453 _____ ._
0. 43
1. 35
Big Buck No. 10521-___'_____'_ ______ __
0.38
0.03
CaCOa
V
leached
per
hour
Analyses of Tested Ore
3 8
Fraction U305
Conditions
.5M Na2CO3—.5M NaHCO3, 25 mg./1. Cu ___________ ._
0.14
.5M NazCO3—.5M NaHCO3, 25 mg./1. Cu, AM Na1SO4_
0.14
.9M Na2CO3-—.1M NaHOO; _________________________ _-
0.035
.9M NtizCOr-JMI NaHCOa, .41“ NaNO; ___________ -_
0. 040
Fe
6.16
92.8
2. 90
0. 26
9. 96
0. 40 .
1. 68
0.28
As may be seen therefrom, variations in ionic strength
have little, if any, eifect on leaching rates.
EFFECT OF COPPER CATALYST CONCENTRATION
Leach rate variations with various copper catalyst con
centrations, added as CuSO4 solution, were determined
EFFECT OF SOLID CONTENT IN SOLUTION
The effect of variations in the amount of solid source
using two different leach solution compositions, with both
air and N2 bubbling at 90° C. to leach U308 with the
results tabulated below:
material present in the solution was determined using
25 mg./liter of Cu added as CuSO4 at 90 C. air bubbled
yielding the maximum leaching rates with the leaching
solutions as tabulated below:
TABLE
25
TABLE VI
Fraction UaOs Leeched Per Hour
Fraction U309 leached per
hour
Conditions
'
1 g./1. max.
2 g./1. max.
.5M NazCOz-—.5M NaHCOa ____________ __
0.14
.'5M NazOO3—.5 NaHCO3, .lM NHQOHH
0. 30
0.31
.9M NélzC 03——.1M NaHCOa ____________ _-
0. 23
0. 24
Air
Air
0. 15
As anticipated the initial leaching rate, i.e., the max.
rate, is directly proportional to solid content within ex
perimental error; however, since the relative rate of
leaching was essentially independent of the solid content
the remainder of the experiments were done using solid
It will be seen from the foregoing that the leach rate
equivalent to 1 g./l. of U308. That the absolute rate
increased with increasing Cu catalyst concentration in
of leaching does not fall off as rapidly as might be ex
all cases although the power dependence is considerably
pected may be due to the fact that surface area (to
less than one. The remarkable effectiveness of the cat
which the rate should be proportional) does not decrease 45 alysis on air oxidation with even very small amounts of
as rapidly as the volume (to which the weight is pro
Cu is apparent. Under N2 the dependence on Cu ap
portional). The large increase in extraction rate using
pears to be approaching the ?rst power at low Cu con—
ammonia is apparent therein.
centrations. Under air the dependence is much less even
correcting for direct air oxidation which might be oc
TEMPERATURE EFFECT
50 curring simultaneously. Note that at 25 mg./l. On the
0.5M Na2CO3—0.5M Natl-I003 solutions catalyzed
with Cu(lCuSO4) with and without ammonia were used
‘to leach U308 at 70 and 90° C. with air bubbling and
with the results tabulated below:
TABLE IV
Conditions
rate under N2 is much lower than under air even ‘when
the latter is corrected for air oxidation. This observa
tion can only .be explained by the formation of oxidizing
species other than cupric in the air ‘blown system. The
55 obvious explanation is the formation of peroxide in the
reoxidation of cuprous ion or copper metal if, during the
catalytic reaction, the cupric state is reduced to that ex
Fraction U508 leached per
hour
tent.
Various mechanisms are possible to explain the results
90° C
70° C
O. 019
0.009
25 rug/11. ou ............................ _-
0.14
0.043
25 mgJl. Cu+.1M NHAOH _____________ -.
0.29
0. 074
60 although simple mechanisms alone cannot explain the
data, i.e., that the rategunder air (corrected for meat
ialyzed direct air oxidation) is
.10
65
The results indicate that leaching at temperatures as
-
.0364‘?
times that under N2 instead of twice or four times which
may be explained by simple mechanisms.
C. is much more preferable so that the remainder of the
experiments were done at 90° C. At temperatures above
EFFECT OF INCREASED O2 CONCENTRATION
70
80° C. the leaching rate increases at a rapid rate.
U
303
was leached under standard conditions described
EFFECT OF IONIC STRENGTH
V low as 70° C. are uneconomical and that leaching at 90°
above at 90° (3.; however, 02 was bubbled through the
leach solution of the character and with the results tab
ulated below. The results of comparable operations
tion pairs in one of the members of which was included 75 with air are included for comparison.
Since pH changes in a CO3=-—HCO3- system result in
large changes in ionic strength, controlled leach solu
3,036,881‘
8
mainingconstant, CO3: concentration and pH are inter
related. The change in ratio of 0.5M Na2CO3-—0.5M
TABLE VII
H003‘ to‘ 0.9M Na2CO3-—0.1M'NaHCO3' corresponds
Fraction
Conditions
U303 Leached
Per Hour
to a pH change from 9.9 to 10.9 or a‘factor of 10 in
OH- concentration. The bene?ts'to be derived’ from
Air
operating with CO3=/-HCO3— ratios givinga'pI-I near
10.9, i.e., a practical range of about pH 10.5 to 1121 being
02
indicated, are obvious.
.5M NazCOa-.5M N aHCOa ____________________ __
0.01
0.04
.5M Na2CO3-5M NaHCOa, 2.5 mgjl. Cu“, ____ __
0.11
0.12.
NH4OH _______________________________________ -_
0.165
0. 17
.9M NazC03-——.1l\/I NHHCOx, 2.5 mgJl. Cu ...... _-
0.19
0.23
.5M N22C0$——.5M NaHCOg, 2.5 mgJl. Cu+.1M
.
.
.
CATALYTIC ENHANCEMENT ‘VITH COMPLEXING
10
'
AGENTS
'
Leaching solutions of constant 0.5M NagCO3--0.5M
NaHCOa composition with various complexing agents
present were used to leach U303 at 90° C. with air bub
It will be noted that the use of 02 increased the leach
ing rate slightly; however, the increase is no more than
which can be accounted for by the expected increase in
normal uncatalyzed oxidation. The use of 02 produces
no increase in the rate of catalyzed oxidation and leach
bling with the results tabulated below:
TABLE X
Fraction
ing.
Conditions
> U305 Leeched
Per Hour
EFFECT OF VARYING TOTAL CARBONATE SPECIES
CONCENTRATION
25mg./l. Cu __________________________________________ __
25 rug/l. Cu +.1M NH4OH_____
____
25 mg/l. Cu + .lM Pyridine__..
...1
‘Pairs of catalyzed leaching solutions having two dif
ferent ratios of CO3=/HCO3- at two different total con
centrations were used to leach U308 at 90° C. with air
25 mg/l. Cu +.1M NaCN ____________________ __
-.__
0.017
25 mg./l. Cu as C11(NH2CH2CHzNH2)2(NO3)2 ________ __
0. 16
bubbling under standard conditions with the results tab
ulated below:
TABLE VIII
It will be observed thatammonia greatly increased
the rate while pyridine and ethylenediamine have a slight
bene?cial e?ect. Cyanide had a strong adverse eifect
Fraction
explainable by the fact that CN- complexes the cuprous
U303 Leached
state so strongly that reoxidation cannot take place and
r
Conditions
Per Hour
the catalytic cycle is blocked. The ammonia undoubt
.5M NagCOs-JSM NaHCOg, 25 mgJl. Cu ____________ __
0.14
.25M NazCOa—-.25M NaHCOa, 25 mg/l. Cu_-
0.14
.9M NarCO3—.1M NaHOOS, 25 mg./l. Cu.-.
.45M Na2CO3--.05M NaHCOg, 25 mgJl. Cu__
0.14
0. 29
0.17
_
_
edly converts the copper to a more e?ectiveionic species
having different charge characteristics and more favor
able oxidation-reduction potentials than those present in
0.23
0.16
the absence of ammonia.
‘
,
COPPER-AMMONIUM CATALYSIS VARIABLES
-It will be noted that a CO3=/=HCO3— ratio of 1, the
(1) Concentration of catalyst: Pairs of
indicated change in total carbonate species concentration
‘
produced no change in the leaching rate. At a ratio of
9, the rate fell 0E considerably indicating that the leach
0.5M Na2CO3—-0.5M NaHCOa
solutions containing diiferent amounts of Cu(CuSO4)
ing rate is critically and increasingly dependent on the
HCO3- concentration in the range of 0.05M to 0.1M
with and without ammonia added were used to leach
UaOa-at 90° C. and with air bubbling, with the results
tabulated below:
than it is in the range of 0.25M to 0.5M. Also, the rate
TABLE. XI
at 0.45M OO3=—0.05M HCO3— is higher than at 0.5M
CO3=-0.5-M HCO3" even though the total concentra
tion of carbonate species as well as HCOg'" is lower.
These facts indicate that the variations noted are attrib—
utable to pH variations and not to ionic strength or total
carbonate concentrations, a deduction which is con?rmed
hereinafter.
Fraction U305 Leached Per Hour
Conditions _________ __
.5M NazOOg
.5M NaHCOa .5M NaHCO3——
Ratio
EFFECT OF VARYING pH
Pairs of solutions with varying amounts of @801
catalyst with ratios of 1:1 and 9:1 of CO3=/HCO3"
were used to leach U308 at 90° C. in’ air and N2 with the
results
tabulated below:
.
'
a
_
a.
55
TABLE IX
Fraction U30, Leached Per Hour' j 1
Conditions _________________ __ .5M NazCO1-1 jfiM N211CO3- j;Ratio
.5M NaHOOa .lM NaHCOa
V
As may be noted the rate of leaching increases much
more rapidly with increasing Cu(NH3)4++ concentration
than'with Cu. (ionic species) alone, though the depend
ence is still less than'?rst power. .The enhancement ef
fect of ammonia. may be quite speci?c for copper since
60 in similar e'irperimentswith Cot+ and 0.1M NH4OH
' ‘the rate was only 0.021 ‘as’ compared to 0.020 for no
.
.
0. 074
0.12
.
0.11
0.185
5 mg /l. Ou(air)
0. 14
0.23
0. 036
0. 0s
2. 2
' 0.10
0.14
1. 4
25 rug/l. ou(N2)___
-- >
125 mg./l. 011(Nz) ___________ -_
»
1. 62
catalyst as above.
1. 68
(2) NH4OH'concentration'e?ects: Solutions contain
ing 0.5M Na2CO3'—'0.5M NaHCO3 and equivalent
1. 64
65
,
r
'
amounts of Cu (25 mg.)?w.ere usedv to leach U308. at
90° C. with air bubbling withthe'results tabulated below:
It will be noted that'increasing the ratio of
'
'
from 1 to 9 increased the rate. of leaching ‘in all'cases. 70
'
r
'
TABLE
r
' '
"
'
V
XII
'
1
'
'
Fraction U308
Conditions
When the ratio was changed to 0.11 the’, leachingrate
was lower. The leaching rate ratios. under 'air?are re
markably constant indicating the complete elfectiveness .
of even very small amounts of Cu catalystunder vthe’
‘
Leached Per
.
Hour
intimation;..;.l._r;_...--_rV
0.29
,25M NH1OH___ _____ .5 _____ __
0. 29
indicated conditions. With total carbonate- species re— 75'.
3,038,881
10
It will be observed that increasing the ammonia con
Various ores were leached for 6 hours at 90° C. with
centration from 0.1M to ‘0.25M had no effect. The
air bubbling with the results tabulated below. Control
possibility that the catalytic couple is
runs using a standard oxidant are included for com
parison.
TABLE XV
Ore Leaching Results
Percent U305 Leaehed
.5M NazOOa
.9M NagCOrJM NaHCOs
.5M NaHCOa,
.IM NH40H
Ore
600 mgJl.
N0. Cat. 25 mg./l. Cu
KMnOl
25 mgJl. Cu
67
65
77
78
.
AOM Grey Special _______________ __
47
66
47
89
63
90
58
96
Garwood and Gerlock No. 10453....
74
86
94
94
is therefore doubtful since the ammonia concentration
As may be noted the copper-ammonia catalyzed aerat
would effect the potential of such couple thereby aifect
ed leaching is at least as good if not superior to any
ing the leaching rate. This circumstance may indicate
other tested. The results with the indicated ores would
25
that the catalytic couple involves a mixed ammonia-car
be further improved with ?ner grinding in accordance
bonate complex, e.g., Cu(NH3)2+—Cu(NI-I3)2CO3. It
with conventional practice.
is apparent that ammonia concentrations lower than
0.1M should also be effective, e.g., 0.025 or 0.050 and
above.
'
HYPOCHLORITE OXIDATION AND LEACHIN G
While copper catalyzed aeration oxidation leaching,
30
especially with ammonia, is very economical and at least
CATALYTIC LEACHING OF OTHER SOLIDS
as good as any other, the required equipment may some
times be more complex and engineering costs are some
Carbonate solutions were used under control and var~
ious catalyzed conditions to leach U02, uraninite and
what greater than using standard chemical oxidants.
various ores at 90° C. with either air or 02 bubbling
and‘ with the results tabulated below:
35 Permanganate has generally been found most elfective
TABLE XIII
found that hypochlorite oxidation is quite rapid and ef
?cient and, moreover, is also improved by copper catal
ysis. The equivalent reagent cost of hypochlorite is less
in conventional practice.
U02 Leaching Results
Fraction U02
Leaehed Per
Hour
Conditions
.5M NaiCO;—-.5M NaHOO3—air ____________________ __
.5M N a2O03-—.5M N aHCO3+25 n1g./l. Ou-air ______ __
NH4OH-air
___
____ __
40 than with permanganate.
For example, a 25% excess of
hypochlorite over the stoichiometric amounts required to
oxidize 0.0037M U02 gave 100% leaching with a car
bonate leach solution in 6 hours at 90° C. Variables in
hypochlorite leaching were studies as follows:
0. 038
0. 040
.5M N azCO;-.5M NaHOOa+25 mgJl. Ou+.1M
However, it has now been
45
HYPO CHLORITE CONCENTRATION
0. 083
.5M N &2CO3—.5M NaHOO3+25 mgJl. Cu+.1M
The effect produced by varying the hypochlorite con
centration was determined by leaching U03 solid with
0.5M Na2CO3—0.5M NaI-ICO3 solutions at 90° C. N2
The improved results were similar to those obtained 50 atmosphere with aqueous hypochlorite added in the
with U308, i.e., Cu catalysis improved leaching and the
amounts and with the results tabulated below. The NZ
improved leaching is enhanced at higher pH and in the
atmosphere is employed to eliminate air oxidation effects
presence of ammonia. Moreover, the use of 02 also .
which would complicate interpretation of results. In
yielded a more pronounced enhancement in the present
55 actual practice air atmosphere could be used thereby ob
case than with U308 supra.
taining enhanced results and additional economics.
Uraninite was leached similarly to the U02 above with
the following results:
TABLE I i [
NH4OH+O2 _______________________________________ __
0.165
.9M N azCO3—.1M NaHCO3+25 mgJl. Cu-air ______ ._
,
0. 050
.
TABLE XIV
_
.
60
Uraninite Leaching Results
Conditions
Fractions .Uraninite Leached
Per Hour
-
Flrst?w“
'
h.
Last 40%
0
GT
Fraction U0,
on 1 Ions
MZ‘E‘ESIPQ‘
16.7 m1./1.5% N aCl0r___
6.7 m1./1.5% NaClO_____
65
0, 83
0. 46
.
.
.
As may be noted the rate of leaching increases with
0 20
0 085
goglgllr/llgffjfl'gfiiij::::::::"I:
0:38
0:087
tween ‘0.5 and 1.0). The lower apparent rate may be
25mgJ1- Cu+-1M N1140H——air ----- --
0-46
0-105 ,
due to disproportionation of C10_ into Cl‘ and C1O3-.
As may be observed copper and copper-ammonia
increased ClO- but with a low power dependence (be
70
TEMPERATURE
catalysis gave successively higher leaching rates over the
6.7 ml. of 5% NaClO was added to 0.5M
'control as above with U308 and U02. The catalytic
Na2CO3——0.5M NaHCOg
"effect appears to'be most pronounced during dissolu
tion of the initial 60% of the uranium.
75 solutions and the solutions were employed to leach U02
3,036,881
11
explanation is apparent.
below:
EFFECT ‘OF pH ON HYPOCHLORI'I‘E LEACHING (U305)
TABLE XVII
U308 was leached with 1M total carbonate species con
centration at different pH values with a carbonate leach
solution containing 6.7 ml. of 5% NaClO at 90° C. in
N; as with U02 with the results tabulated below:
TABLE XPG
Fraction U09
Conditions, ° C.
12
sults with the same lotrof U308 and U02 for which no
solid at 70 and 90° C. in N2, with the results tabulated
Leached Per
Hour
0. 46
0.25
10
Fraction UaOs
Conditions
As in air oxidation lowering the temperature decreases
Leaehed Per
Hour
the leaching rate signi?cantly and it is therefore preferred
to operate in the range of 80° C. to above 90° C.
15
CATALYSIS
Various possible catalytic agents were added to 0.5M
Na2CO3—-0.5M NaI-ICO'3 solutions with 6.7 ml. of NaClO
present which solutions were used to leach U012 at 90°
C. N2 atmosphere with the results tabulated below: '
TABLE XVIII
0.45
.5M NaHC03—.5M N81200:; _________________________ __
0. 32
Note that the rate in 1M NaI-ICO3 is substantially greater
than with 0.5M Na2CO‘3-—'0.5M NaHOO'a (and similar
reasoning is applicable as with U02.
20
OVRE LEACHING WITH HYPO‘CHLORITE
Various carbonate solutions with 6.7 ml. NaOlO were
used to leach various ores for 6 hours at 90° C. with
Fraction U02
Conditions
1M NaHCO3 ___________________ _; ___________________ __
Leeched Per
Hour
0. 46
25 mgjl. Cu __________________________________________ _.
0.60
.004M Mn“...004M Fe(ON)-4
0. 46
0.43
25
air blowing (oxidation) with the results tabulated below:
TABLE XXII
Percent U303 Leeched
Ore
As above Cu(C‘uSO4) ‘exerts a pronounced catalytic ef 30
feet. The fact that cupric materials should exert about
1M HCOr
.5M CO3—.5M H003
.QM CO3"
.lM H003
the same absolute effect as in air is reasonable since the
Monticello N0. 27 ______________________ _-
reoxidation of the reduced copper species is not the slow
step in the catalytic cycle, hence the character of the
Big Buck No. 10521...
47
58
ACM Grey Special _______ __
93
____________ __
91
____________ __
oxidant makes little difference.
'
81
____________ __
Garwood & Gerlock No.
35
EFFECT OF pH VARIATION
10453 ______ _, _________________________ __
Under ‘the observed conditions, the pH dependence
Leach solutions of varying carbonate species content
noted above ‘apparently does not apply; however, the re
and containing 6.7 ml. of 5% NaOlO were used to leach
sults are explainable on the basis that air-oxidation leach
U02 at 90° C. and with an N2 atmosphere with the
ing increases with increasing pH and that this e?ect is
40
results tabulated below:
dominant. in any event it can be seen that leaching as
above is comparable to that achieved with 0.600 g./l. of
TABLE XIX
Conditions
Fraction U01
Leached Per
Hour
KMnO4, or copper-ammonia catalyzed air oxidation leach
ing. The amount of hypochlorite is cheaper as chlorine
45 than the amount of KMI‘LOL; required to obtain equivalent
, recovery. Moreover, a far less objectionable contaminant
is introduced into the system. 7 7
1M NaHCO; ________________________________________ __
1(i.e.:l:.75)
.5M NaHCO3-—.5M NazC03 _________________________ __
0.46
While there have been described in the foregoing what
may be considered to be preferred embodiments of the
Also the leaching rate was greater in 1.0M NaI-ICOa 50 invention, modi?cations _may be made therein without
departing from the teachings of the ‘invention and it is
than in the ‘0.5M Na2CO*3-—-0.5M NaHCO3 solutions.
intended to cover all such as fall within the scope of
These results are contrary to those obtained with air oxida
tion but are reasonable in the present case, since the
the appended claims.
Cl2—-OlO~ potential becomes more favorable for U02
oxidation with decreasing pH and the tendency of C10" 55
to disproportionate into 01- and 0103* is less.
What is claimed is:
j
’
'
'
'
,
1. In a process for leaching uranium from a solid con
taining uranium in hexavalent and lower oxidation states,
the steps comprising contacting said solid with a carbonate
EFFECT OF HYPOCHLORITE CONCENTRATION (UaOs).
leach solution containing catalytic amounts of the ionic
The eifect of varying ClO‘" concentration on the leach
species of copper in the presence of'aminonia at a tem
ing of U from U308 was studied by adding two diiie'rént 60 perature of above aboutj80° C., and simultaneously add
"ing anroxidizing agent torsaid solution vto oxidize and
amounts of 5% NaClO to 0.5M NagCO3——0.5M NaHCO3
solution in contact with U308, at 90° C. in an N2 atrnosl '
,dissolve the‘ uranium" from said solid.
7
7
L 2. A process for recovering ‘uranium from a solid con
phere under the conditions and with the results tabulated
taining
uranium in hexavalent and lower valent states
below:
TABLE XX
65 comprising reducing said solid to Ia particle size of below
about v--100 mesh, contacting said solid with a carbonate
,leach solution containing, ammonia together with catalytic
Fraction U508
Conditions
Leeched Per
Hour
6.7 ml./l. 5% NaClO ________________________________ __
2.2 1nl./l. 5% NaClO _________________________________ __
7'
0. 32
.
0. 22
'
amounts of ionic’ species ‘of copper at a temperature of
above about 80° C., simultaneouslyadding an oxidizing
.70 agent to said solutionto oxidize and, leach the uranium
fronfsaid ‘solid to, produce a carbonate leach solution con
taining hexavalent uranium, and recovering uranium from
the leach solution.
>
i j
' >
'
It is interesting to note that the leaching rate with;
3. 'A process for, recovering uranium from a solid _con
U308 is less than with U02 with the same NaClO‘con
centration. This is the reverse of the ‘air oxidation re .75 taining uranium in hexavalent and lower 'valent states
3,036,881
13
14
comprising reducing said solid to a particle size of below
about -—100 mesh, contacting said solid with a carbonate
leach solution containing catalytic amounts of ionic
about ~10!) mesh, contacting said solid with a carbonate
leach solution having a pH in the range of about 10.5 to
species of copper in the presence of ammonia at a tem
of ionic species of copper at a temperature of above about
perature of above about 80° C., simultaneously adding
at least one oxidizing agent selected from the group con
sisting of air, 02 and hypochlorite to said solution, said
11.1, containing ammonia together with catalytic amounts
80° 0., simultaneously providing an oxidizing agent in
said solution to oxidize and leach the uranium from said
solid to produce a carbonate leach solution containing
carbonate solution having a ratio of CO3=/HCO3"- con
hexavalent uranium, and recovering uranium from the
centrations yielding a pH in the range 10.5 to 11.1 with
leach solution.
said air and O2 oxidants and a HCO3" concentration of 10
9. The process as de?ned in claim 8 wherein said
about 1M with said hypochlorite oxidant to oxidize and
carbonate leach solution is at a temperature of about
leach the uranium from said solid to produce a carbonate
90° C.
leach solution containing hexavalent uranium, and re
covering uranium from the leach solution.
4. The process as described in claim 3 wherein said 15
oxidizing agent comprises air.
5. The process as described in claim 3 wherein said
oxidizing agent comprises air and said temperature is
about 90° C.
6. The process as de?ned in claim 3 wherein said 20
oxidizing agent comprises 02.
7. The process as de?ned in claim 3 wherein said
oxidizing agent comprises hypochlorite.
8. A process for recovering uranium from a solid con
References Cited in the ?le of this patent
UNITED STATES PATENTS
2,813,003
Thunaes et al _________ __ Nov."12, 1957
OTHER REFERENCES
Brown: Preliminary Investigation of Carbonate Leach~
ing ACCO-36, Oct. 15, 1953, declass. Sept. 23, 1955,
pages 5-32 relied on.
Proceedings of the International Conference on the
Peaceful Uses of Atomic Energy, Aug. 8~20, 1955, vol.
taining uranium in hexavalent and lower valent states 25 8, pages 8, 9, 18-22, 28 and 32-37.
comprising reducing said solid to a particle size of below
AEC Document RMO-2621 June, 1956, pages 1-27.
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