Nov. 29, 1966 A. V. HENRICKSON 3,288,570
PROCESS FOR THE SELECTIVE RECOVERY OF
URANIUM, ZIRCONIUM AND MOLYBDENUM
Filed Aug. 16, 1963 2 Sheets-Sheet 1
1000 LBS. PREGNANT
CARBONATE LIQUOR
25 LBS. U30a
10 LBS. Mo
2.5 LBS. Zr
t 4 LBS. NaOH----~..-ADJUST pH TO 10
t
PRECIPITATE Zr(C03)2
BY DIGESTING AT 195°F
~
FILTER AND WASH---.....-Zr PRODUCT
~ 2.45 LBS. Zr
9 LBS. NaOH------il..-- PRECIPITATE
YELLOW CAKE
t
FILTER AND WASH---.......-. U30a PRODUCT t 25 LBS. U30a
.15 LB. Zr
57 LBS. H2S04 ----...,.,- ACIDIFY TO pH 1.5
~
ABSORB Mo ON CHARCOAL----40...-BARREN EFFLUENT
18 LBS. NaOH---...... -E~~~E I
10 LBS. HCL ----~.,..- ADJUST pH TO pH 7
t
14 LBS. CaCI 2------..,.- PRECIPITATE CaMo04
t FILTER AND WASH ---~~- Mo PRODUCT
10 LBS. Mo
INVENTOR.
ANGUS V. HENRICKSON
BY
5~ o-d;:t?o=
ATTORNEYS
Nov. 29, 1966 A. V. HENRICKSON 3,288,570
PROCESS FOR THE SELECTIVE RECOVERY OF
URANIUM, ZIRCONIUM AND MOLYBDENUM
Filed Aug. 16, 1963 2 Sheets-Sheet 2
NoOH---PRECIPITATE
YELLOW CAKE
pH II
t
FILTER a WASH t
YELLOW CAKE
PRODUCT
40 LBS.
PREGNANT CARBONATE
25 LBS. U30S _-------;"'-8.5 LBS. H2S04
15 LBS. Mo
48 LBS. H2S04 t .3 LB. NoCIO -~,.--ADJUST TO pH 3.5
TO PRECIPITATE
URANYL MOLYBDATE
t
DIGEST 6 HRS. AT 25°C t FILTRATE
FILTER - NO WASH---25 LBS. U30S---~ t I LB. Mo
PRECIPITATE
25 LBS. U30a
14 LBS. Mo
t
14 LBS. NoOH ----11,.._ DISSOLVE Mo
t
DIGEST I HR. AT 80°C t PRECIPITATE
FILTER - NO WASH~ 25 LBS. U30S t .02 LBS. Mo
FILTRATE
14 LBS. Mo
t 3 LBS. HCL--~,.-ADJUST pH TO 8.0
t
18 LBS. CoCI2--- PRECIPITATE COM004 t FILTER AND WASH
t
COM004 PRODUCT
2 INVENTOR.
ANGUS V HENRICKSON
BY
S~.-r?~
ATTORNEYS
United States Patent Office 3,288,570
Patented Nov. 29, 1966
1 2
that the presence of zirconium during charcoal adsorption
of molybdenum seriously poisons the charcoal against
molybdenum adsorption and thus renders such .adsorption
prohibitive in its presence. Uranium can be precipitated
5 directly from ,the pregnant strip carbonate solution with
sodium hydroxide or it can be precipitated after destroying
the carbonate; however, such precipitation also precipitates
zirconium as zirconium hydroxide and this compound
ends up as an impurity in the yellow cake.
Accordingly, it is an object of this invention to provide
a process for the selective recovery of uranium, zirconium
and molybdenum from composite ores in which they exist
together.
It is another object of this invention to provide a process
15 for the selective recovery of uranium, zirconium and
molybdenum existing together in ores having a high content
of carbonaceous or organic material, such as, lignite
ores.
It is still another object of this invention to provide a
20 process for the selective recovery of the metals uranium,
zirconium and molybdenum from carbonate solutions in
general and from carbonate liquors and leach solutions
formed by treatment of carbonaceous ores.
It is a further object of this invention to provide a
25 process as stated which is commercially feasible and which
produces the metals in a form meeting standard requirements
of purity.
The above objects of the invention are accomplished
by a process in which zirconium is first selectively re-
30 covered from a carbonate solution containing the three
metals, followed by selective separation of uranium and
molybdenum. The process includes two modifications.
In accordance with modification (1) of the process of the
invention, in step (1) zirconium is precipitated as the
35 carbonate by adjusting the pH of the carbonate strip liquor
to a point just below the incipient precipitation of uranium
and the precipitate recovered by filtration. In step
(2) uranium is removed from the filtrate of step (1)
containing uranium land molybdenum by precipitation as
40 yellow cake followed by filtration. In step (3) molybdenum
is removed from the filtrate of step (2) byadsorption
on charcoal and recovered by stripping from the
charcoal and precipitation from the stripping solution as
calcium molybdate.
!5 In modification (2) of the invention, after step (1')
in which zirconium is precipitated as basic zirconium
carbonate as above, in step (2') the filtrate of step (1')
is treated by pH adjustment and heating to precipitate
50 the molybdenum as uranyl molybdate, followed by filtration.
The filtrate from step (2') is treated to recover
uranium not used in step (2') as yellow cake for the main
stream recovery. In step (3') the molybdenum is dissolved
from the precipitate of uranyl molybdate of step
55 (2') and recovered from the solution as a calcium molybdate
precipitate. The precipitated uranium of step (2')
which remains after molybdenum is dissolved out is converted
to yellow cake and re-cycled to maintain sufficient
percentage of uranium in the pregnant carbonate for the
60 succeeding precipitation of uranyl molybdate.
An improvement of the process comprises the oxidation
of molybdenum to its highest valence state before its recovery.
A further improvement of modification (2),
the uranyl molybdate precipitation procedure, includes
65 the treatment of the precipitate of step (3') containing
sodium diuranate and some zirconium hydroxide, with
sulfuric acid at the required pH value to separate the zirconium
from the uranium. The separation can alternatively
be accomplished by completely dissolving both the
70 sodium diuranate and the zirconium hydroxide at pH 1
and separating the two compounds by re-precipitating the
zirconium as the basic sulfate.
3,288,570
PROCESS FOR THE SELECTIVE RECOVERY OF
URANIUM, ZIRCONIUM AND MOLYBDENUM
Angus V. Heul'ick§on, Goli[len,Colo., assignor, by mesne
assignments, to Susquehanna Western, Inc., Denver,
Colo., a corporation 01' Wisconsin
Filed Aug. 16, 1963, Ser. No. 302,627
19 Claims. (el. 23-328)
This invention relates to a method for the selective re- 10
oovery of uranium, zirconium land molybdenum from
,composite ores containing these metals ,together; more
particularly, it relates to the process for the selective recovery
from relatively low grade carbonaceous minerals
of the metals uranium, molybdenum and zirconium existing
together in the minerals.
The inve'htion is illustrated by its application ,to carbonate
strip liquors resulting from the treatment of lignite
ores by conventional processes. More specifically, the
invention is illustrated by its application to the selective
recovery of uranium, zirconium and molybdenum from
carbonate strip liquors resulting from solvent extraction
of carbonate leach liquor of lignite ore. The invention
is not limited in its application to carbonate strip liquor so
formed but is applicable to carbonate strip and leach
liquors of the three metals in general. Likewise, it is not
limited in its application ,to strip or leach liquors but can
be applied to carbonate solutions in general containing
the three metals, and particularly ,to liquors formed by
leaching ores with alkali metal carbonates and bicarbonates.
The process of the invention is particularly useful for
,the selective recovery of uranium, zirconium and molybdenum
from ores associated with various carbonaceous
materials, for example, coal, lignite, oil shale and others.
It is illustrated herein by its application to lignite ores.
Ore grade uraniferous lignite exists in commercial
quantity in Montana and the Dakotas. Experience has
shown ,that uranium recovery from -lignite ores has a
marginal profit potential using available recovery processes,
and that burning the ore before leaching ·offers the
best possibility for processing. The ore contains sufficient
carbonaceous materials to support combustion and the
residue is more susceptible than the ore to treatment with
an aqueous leaching solution, such as, a strong mineral
acid or an alkali metal carbonate. The ash contains
molybdenum and zirconium in addition to uranium, and
the separation of these elements from the uranium is
necessary in order to meet yellow cake specifications.
These specifications include a limit for molybdenum of
.6% of the UaOs, and will include a limit for zirconium
of 2% of the UaOs. Aside from the fact that molybdenum
and zirconium must not contaminate the yellow
cake, their separation and recovery in saleable form would
increase the income from the process and contribute to
its commercial feasibility.
There are a number of disadvantages attendant to the
selective separation of uranium, molybdenum and zirconium
from carbonate leach or strip liquors in which
they exist together. For example, it is known that zirconium
can be precipated free of uranium through pH
control. Unfortunately the required pH range (2.5-3.5)
results in uranium loss as uranium molybdate if molybdenum
is present because this compound is insoluble in
the same pH range. It would be possible to remove the
molybdenum from the leach liquor by charcoal adsorption
before solvent extraction of the uranium, but this would
require a large installation and high capital cost in order
to treat approximately 250 gallons per minute, the approximate
rate of treatment required for commercial feasibility.
Further, as will be pointed out hereinafter, it is known
3,288,570
:3
The detailed description of the operation of the process,
including both modifications, is presented herein in
conjunction with the flow sheets of Figs. 1 and 2, Fig. 1
being the flow sheet for modification (1) 'and Fig. 2
being the flow sheet for modification (2), that is that
feature of the invention which is applied to the filtrate
remaining after removal of zirconium as zirconium carbonate
from the ,carbonate strip liquor. The flow sheets
are based on reagent requirements for 1000 lbs. of pregnant
carbonate liquor, the liquor on which the first flow
sheet is based on 'containing 25 lbs. U30 a, 10 lbs. Mo
and 2.5 lbs. Zr and the liquor upon which the uranyl
molybdate precipitation fluw sheet is based containing
25 lbs. U30 a, 15 lbs. Mo and originally 2.5 lbs. Zr. The
flow sheets are based on actual examples using the respective
modifications of the process. Results obtained
utilizing the described process steps of the two modifications
are included.
As used herein in the specification and claims, the
expression "carbonate solution" includes carbonate liquors,
carbonate leach solutions and carbonate solutions
in general irrespective of how they are formed. The
term "solution" includes leach liquor, strip Hquor, slurry,
etc.
The strip carbonate liquor used for the examples
presented herein was obtained by acid leach of lignite ash
followed by solvent extraction of uranium, zirconium
and molybdenum with a tricapryl amine solution in kerosene
and stripping the metals from the solvent with sodium
carbonate. The invention, of course, is not limited
in its application to a strip carbonate liquor formed in
4
A solution of sodium hydroxide is preferable for the
pH adjustment to flake caustic because it tends to minimize
localized precipitation of sodium diuranate. Any local
precipitation which does occur during addition of sodium
5 hydroxide must be allowed to re-dissolve completely before
the temperature is increased, otherwise separation
from uranium will be poor.
The pH of the pregnant carbonate strip liquor before
adjustment was close to 8. At this pH value about 30%
10 of zirconium could be precipitated merely by heating.
By increasing the pH to 10 about 90% of the zil'conium
was precipitated. Under normal operating conditions it
was found that a pH between 9.5 and 10 was satisfactory
for maximum precipitation of zirconium, this pH being
15 slightly below the point of incipient precipitaton for
uranium. The strip liquor used is typical of that obtained
from lignite ash produced from uraniferous lignite ores
from Montana and the Dakotas.
In order to thoroughly test the zirconium carbonate
20 precipitation step, a series of three precipitations were
made at pH values of 8.6, 9.5 and 10.0 to determine
what effect pH has on the completeness of precipitation
and to determine the purity of the precipitate. The pregnant
carbonate was spiked with zirconium and molyb-
25 denum to the desired concentration. The pH in each
test was adjusted with sodium hydroxide and the solution
heated to 95° C. and digested for 1 hour. The slurry
was then cooled to about 50° C. and filtered. The precipitate
was washed twice with water, dried and assayed
30 for zirconium, uranium and molybdenum. The date obtained
is tabulated in Table 1.
TABLE I
Test No. pH
Vol.
Sol.
ee.
Zr
Assay
g.fl. Mo
U30S
Wt.
Zr
ppt.
Zr
Assay,
Percent Mo
U30 S
Pereont
Zr
ppt.
------1--------- -----------------------
L________________ 8.6
2_________________ 9.5
3_________________ 10.0
250
250
500
6.4
2.5
3.1
42.7
23.4
22.4
11. 2
13.2
13.9
.96
1. 22
2.92
48.9
49.0
49.4
.06
.07
.29
.04
.01
.08
28.7
89.5
98.3
It will be noted that good precipitation was obtained
at a pH range of 9.5 to 10 from the solutions used in the
test, this being at a point just below the incipient pre-
45 cipitation of uranium. Also, separation from uranium
and molybdenum was excellent. These tests showed conclusively
that optimum results are obtained when the pH
used is just below the incipient precipitation of uranium.
A temperature range between 80° C. and boiling is pre-
50 ferred for the zirconium carbonate precipitation step.
Removal of zirconium from carbonate solution by the
above described procedure provides a solution which can
then be processed directly for separation of uranium and
molybdenum by either modification of the process, that is,
55 with either the uranyl molybdate precipitation modification
or the charcoal adsorption modification. This is
illustrated by the examples given below.
The charcoal adsorption modification of the process
(No.1) is performed as follows:
In step (2) the filtrate of step (l), containing uranium
and molybdenum, was treated with 5 grams of sodium
hydroxide per liter of solution plus .15 gram for each
gram of U30 a per liter. Since the solution was already
at the point of incipient uranium precipitation this pro-
65 vides sufficient sodium hydroxide to precipitate Na2U207
plus 5 grams per liter in excess. The precipitated yellow
cake was filtered and washed in the standard manner as
the main stream recovery product. The precipitation of
yellow cake is, of course, conventional procedure and the
70 amount of sodium hydroxide used is calculated as follows:
In order to reduce the solubility of uranium to less
than .05 gram per liter in a 10% sodium carbonate
solution the free hydroxide concentration must be greater
than 0.1 molar. 5 grams per liter is 0.125 molar. The
75 additional 0.15 gram for each gram of U30 a per liter is
this manner but is equally applicable to carbonate strip
or leach liquors in general. The lignite ash was produced
fmm uraniferous lignite ores representative of those from
Montana and the Dakotas.
The first step of both modifications of the process comprises
the removal of zirconium from the strip carbonate
liquor by precipitation as the basic carbonate and is described
as follows: It has been found that the zirconium
carbonate complex is unstable at higher temperatures. At
about 85 ° C. it tends to lose C02 ,and precipitate from
solution as a basic carbonate. l1he basic carbonate precipitated
in this manner is quite stable and does not redissolve
to any significant extent on cooling. This instability
at higher temperatures provides a method for its
removal from carbonate solutions and separation from
both uranium and molybdenum.
Essentially, quantitative precipitation is obtained by
adjusting the pH with sodium hydroxide to a point just
below incipient precipitation of uranium and then di- 60
gesting near boiling for about an hour. Accordingly, the
pH of the pregnant carbonate strip liquor was adjusted to
about 10, a point just below that of incipient precipitation
of uranium in the particular solution, with a 50%
solution of sodium hydroxide. The solution was heated
to 195° F. and digested for 1 hour. Zirconium carbonate,
precipitated in quantitative amount, was filtered and
washed with water. The above procedure for recovering
zirconium was used for the examples which follow.
The pH is measured at 25 to 30 degrees centigrade in
order to get accurate readings. At higher temperatures
the readings are subject to considerable error, even
though the temperature compensator of the instrument is
set correctly, because of the increased activity of the sodium
ion.
3,288,570
5)
required to form the precipitated sodium diuranate. The
amount of sodium hydroxide used will, of course, vary
with recovery requirements and the carbonate concentration
of the solution. Other alkaline metal hydroxides,
such as, lithium and potassium hydroxides, may, of course, 5
be used for the precipitation of the yellow cake.
Step (3) comprises the recovery of molybdenum from
the filtrate of step (2) by adsorption on charcoal followed
by elution and precipitation from the eluate. The filtrate
of step (2) was acidified with sulfuric acid to a pH of 1.5. 10
A pH range between about 1 and 2 is preferred. At this
point if reduction of molybdenum to molybdenum blue
had occurred, enough sodium chlorate was added to oxidize
the molybdenum. Sodium hypochlorite or other suit- 15
able oxidizing agent may be used. The soluticJll was then
heated to approximately 120° F. and passed through a bed
of charcoal at a preferred rate equal to 7.2 grams of
molybdenum per hour per kilogram of charcoaL The
6
filtered and washed with .1 percent calcium chloride
solution.
Percentage recoveries of all three metals above 97 were
consistently achieved with the above described process.
Reduction of molybdenum to molybdenum blue may
occur during acidification of the yellow cake filtrate. The
reason for this is not definitely known but it is probably
due to reaction with oxidizable residual organic material
coming from the solvent extraction circuit. Approximately
.3 pound sodium chlorate per pound molybdenum
is required for the oxidation.
The schematic flow sheet of FIG. 1 for the above procedure
gives estimated relative reagent requirements for
each step.
A final test was made following the entire procedure
of modification (0 given above using strip carbonate
liquor spiked with molybdenum and zirconium, the liquor
being made by treatment of lignite ash from North Dakota
ore. The results obtained are given in Table II.
TABLE II
.01 .005 2.88
22.61 .05 .05
.02 14.00 .008
22.64 14.06 2.94
Assay, percent or g./1. Content, graIns
Product 'Nt. or Vol.
U,O, Mo Zr
Head Sample __________ 1,000 23.48 13.94 3.12
Zr and U,Os, ppt.:
Zr ProducL_______._ 5.84 .29 .08 49.4
Yellow Cake_______ 28.06 80.58 .19 .17
Yellow Cake_______ 1,170 .024 11.95 .008
Filtrate _
23.48
Mo
13.94
Zr
3.12
U30S
.05
£9.85
.10
Distr., percent
Mo
.04
.36
99.60
Zr
98.30
1. 65
.05
Nil
Nil
99.1
.9
93.3 _
Nil
Nil
Nil _
• DOS _
.13
.02 9.56
.02
Nil 7.38 Nil
Nil 1. 43 Nll
Nil .02 Nil
Nil .03 Nil
Nil .06 Nil
Nil 7.38 Nil
Nil 7.44 Nil
Nil .007 Nil
Nil
Nil
Nil
Nil
Nil
.028
<.008
.22
.28
.55
78.4
44.1
.041
78.4
14.3
<.001
.006
.006
<. 001
<.001
<.001
<.001
<.001
94
100
100
100
100
Mo Precipitation
(Fraction 10) _
Precipitate_____________ 16.90
Filtrate________________ 184
Mo Adsorption (800 cc.
yellow cake filtrate) 0 _
Fraction L _ 100 .006 <.005 Nil
Fraction 2_ _ 100 .023 <.005 Nil
Fraction 3_ _ 100 .027 <.005 Nil
Fraction L _ 86 .025 <.005 Nil
Fraction 5_ _ 200 .025 <.005 Nil
Fraction 6_ _ 93 .025 <,005 Nil
Fraction L _ 100 .024 <.005 Nil
Wash 8_________________ 100 .027 .117 Nil
Wash 9_________________ 48 .006 2.71 Nil
Mo Elution: 10 _
11 _
12 _
13 _
14 _
flow was maintained through the bed until the molyb- Recoveries and analyses of products produced in andenum
broke through. A preferred pH range for the other representative test run of modification (1) of the
solution is between about 1 and about 2. 50 process are given in Table III.
TABLE IlL-RECOVERY AND ANALYSIS OF U30S, Mo AND Zr PRODUCTS
Product Percent
Recovery
U,Gs
Analysis, percent
1110 Zr
Yellow Cake (U30S) _
:Molybdenum ppt. _
Zirconium ppt. _
99.85
97.50
9S.30
80.58
.006
.29
.19
44.70
. 08
.17
. 003
49.4
The molybdenum was eluted from the charcoal with
two Normal (8%) sodium hydroxide solution at a rate
equal to 1;2 a column void column per hour. Other bases
which form a soluble molybdate can be used to strip the
molybdenum, such as, potassium or ammonium hydrox- 65
ide. An excess of stripping solution sufficient to give a
terminal pH above about 8 is preferred.
Molybdenum was recovered from the sodium hydroxide
eluate by precipitation as calcium molybdate. The sodium
hydroxide eluate from the charcoal adsorption was 70
acidified with hydrochloric acid, a pH of about 7 being
preferred. To this solution was added 1.4 pounds of anhydrous
calcium chloride per pound of molybdenum in
solution. The solution was agitated for one hour at ambient
temperature and the precipitated calcium molybdate 75
As the data in Tables II and III show, the process
provides percentage recoveries of each of the three
meDals above 97. The metals were in a state of purity
meeting AEC requirements. The eflluent from the charcoal
adsorption step is suitaible for recycling to the
solvent extraction feed stream. The charcoal loading
obtained by this procedure was 18%, operating with
a column two feet deep at an adsorption rate of 7.2 gms.
Mo/hr.lkg, of chaI1coal at 120° F. The consumption
of chemicals, induding the chemicals used for stripping,
based on a concentration of 25 grams of U30 a and 10
grams Mo per liter, were well within feasible economic
limits for .a commercially operating flow chart.
The alternate procedure, or the uranyl molybdate precipi,
tation modification of the process, modifiication (1),
3,288,570
7
is descr1bed in detail as follows, with reference to the
flow chart of FIG. 2.
Step (1') of this modification is identka1 with step
(1) of the modification of the process described above,
that is, zirconium was precipitated as the carbonate and
removed from the strip liquor as such in the same manner
as in modification ,( 1) described above. Results for the
recovery of zirconirum ·as carbonate (step 1) are given
in Tables I, II and III :above.
In step (2') the pregnant corbonate liquor filtrate
!from the ziI'conium oarbonate precipitation was cooled
to 25 ° C. or lower and neutralized with sulfuric acid
to a pH of about 3.5 measured with a pH meter at
25° C. A pH within ±.5 of 3.5 is used. Uranyl molybdate
was precipitated. It should be lemon yellow in
color. If it is olive green or~dark colored an oxidant
such as sodium hypochlorite or sodium chorate is
added until la lemon yellow co10>r is obtained indicating
complete oxidation of molybdenum. The complete oxidation
of molybdenum before precipitation of uranyl molybdate
is preferred. The slurry was agitated for about four
hours at 25 ° C. in order to permit completion of crystal
growth of the uranyl molybdate 'and to obtain complete
precipitation. It was then filtered.
Yellow cake was precipitated tlJrom the filtrate with
sodium hydroxide 'at a pH of about 11 in accordance
with s1Jandard procedures to provide ,a pure recovery
product whkh met AEC specifications in all respeots.
Step (3') comprises the separation of molybdenum
from the precipitate of step (2'). In step ,(3') the uranyl
molybdate precipitate was agitated with sodium hydroxide
for lh, hour ,at 80° C. to dissolve the molybdenum.
A pHa:bove ,about 10 is preferred. The molybdenum
goes into solution as sodium molybdate and the uranium
is converted to insoluble sodium diuranate. The sodium
diuranate was ·filtered and washed with one replacement
of w,ater. The molybdenum was recovered from the
filtrate by precipitation as calcium molybdate by adjusting
the pH between about 7 and 8 with hydrochloric
acid and adding calcium chloride. About 25% excess
'calcium chloride is required to complete the precipitation.
The soLution was agitated about one hour at ambient
temperatures land filtered with washing of the calcium
molybdate pre:cipitate.
The yellow cake remaining after remo",al of molybdenum
from the uranyl molybdate precipitate is dissolved
in sulfuric ·acid and recycled for the succeeding precipitation
of ruranyl molybdate. This uranium cycle is necessary
in order to maintain Ian excess of uranium in the
uranyl molybdate precipitation. The amount of uranium
in the recycle will be proportional to the molybdenum
precipitated. The uranyl molybdate compound precipitated
under the ,given condition approximates the
formula U03·2Mo04•
Results obtained by pmctice of the above describe.d
uranyl molybdate precipitation modification of the process
are presented in Table IV.
TABLE IV
8
adsorption runs were made under different conditions.
All three runs were made with acidified yellow cake
filtrate. Run No.1 was not oxidized prior to adsorption,
Run No.2 was oxidized with .3 gram sodium chlorate per
5 gram of molybdenum and Run No.3 was operated 7.5
bed volumes on unoxidized feed then the feed of this
latter run was oxidized as in Run No. 2 to determine
if the charcoal would recover and determine conclusively
if oxidation is beneficial. Run No. 1 operated 7.0 and
10 9..7 bed volumes gave effiuents assaying 1.90 and 1.57
gm. Molliter, respectively, while Run No.2 operated up
to 16 bed volumes never gave effiuents assaying more than
.005 gm. Molliter. Run No. 3 demonstrated that the
charcoal does recover, as the effiuent of the run operated
15 7.5 bed volumes assayed .59 gm. Molliter before oxida-
- tion and a rU~Bperated 8.6 bed-volumes after oxidation
gave an effiuent assaying only .15 gm. Molliter. The
results of these runs demonstrated the desirability of
oxidizing the molybdenum prior to ,the charcoal adsorp-
20 tion step. It is preferable to perform the oxidation prior
to the uranyl molybdate precipitation step.
An improvement in the uranyl molybdate precipitation
modification of the process comprises the separation of
J'esidual ziI'conium from the recycle uranium in the
25 sodium diuranate precipitate resulting from the separation
of molybdenum from uranyl molybdate (step 3').
In the sodium hydroxide treatment to, dissolve molybdenum
both uranium and any zirconium which is present
remains undissolved in the precipitate. The uranium is
30 in the form of sodium diuranate and the zirconium is
present as zirconium hydroxide. The precipitate was
treated with sulfuric acid at a pH of about 3 or 3.5 and
digested at about 80° C. at which point the zirconium
hydroxide remained insoluble and sodium diuranate was
35 dissolved. Alternatively, separation was accomplished
by completely dissolving the precipitate at pH 1 and reprecipitating
zirconium as the basic sulfate with sulfuric
acid.
It is seen from the above description that a process has
40 been provided for the selective recovery of the metals
uranium, zirconium and molybdenum existing together
in their ores, including carbonaceous ores, and in carbonate
solutions in general, including carbonate leach
and strip liquors. The method provides metals in a state
45 of commerical grade purity, and is economically feasible.
Although the invention has been illustrated and described
with reference to the preferred embodiment thereof,
it is to be understood that it is in no way limited to the
details of such embodiments, but is capable of numerous
50 modifications within the scope of the appended claims.
What is claimed is:
1. The process of selectively recovering uranium,
zirconium and molybdenum values from carbonate solutions
containing said values which comprises: adjusting
55 the pH of the pregnant carbonate solution to a point not
in excess of that slightly below the precipitation point of
uranium for the solution to precipitate zirconium from
Tcst Product Wt.orVol.
Assay, Percent or
g./l.
Content, gms. •• Distribution,
Percent
U30, Mo U30, Mo UsO, Mo
---------.1----1------------------
Head Sample___________________ 250 mL _
Uranyl Molybdate Filtrate 310 cc _
Yellow Cake 6.34 gm _
Calcium Molybdate Filtrate____ 270 cc _
Calcium Molybdate 8.51 grn _
45. so
IS. 27
81. 31
.006
nil
13.8
.93
.39
.12
33.54
11.45
5.68
5.18
.002
nil
3.45
.29
.025
.032
2.86
52.2 9.1
47.6 .8
.2 1. 0
89.1
As the results of Table IV show, total recoveries of
uranium and molybdenum were obtained in percentages
of 99.8 and 89.1, respectively. The purity of the metals
met AEC requirements.
In order to investigate the advantage of oxidizing
molybdenum before the charcoal adsorption step, three 75
the carbonate solution as the carbonate and separating the
precipitate of zirconium carbonate from the remaining
solution thereby forming a second solution; precipitating
uranium from said second solution by adding to said
second solution an excess of an alkali metal hydroxide to
precipitate uranium as alkali metal diuranate, separating
10
tion by adjusting the pH of the carbonate solution to a
point slightly below the precipitation point of uranium
for the solution and digesting the liquor at a temperature
between about 80° and the boiling point of the liquor to
5 precipitate the zirconium as carbonate, separating the
zirconium carbonate precipitate from the remaining solution
and thereby forming a second solution; adjusting
the pH of said second solution to between about 3 and
about 4 to precipitate uranyl molybdate, separating the
10 last precipitate from the remaining solution and thereby
forming a third solution; precipitating uranium from said
third solution by adding to said third solution an excess
of an alkali metal hydroxide to precipitate uranium as an
alkali metal diuranate; separating the last precipitate from
15 the remaining solution; treating said uranyl molybdate
precipitate with an alkali metal hydroxide at a pH of
about 10 or above to dissolve the molybdenum from the
uranyl molybdate precipitate and convert the uranium to
sodium diuranate thereby forming a fourth solution; re-
20 cyling the uranium from the uranyl molybdate precipitate
for succeeding precipitation of uranyl molybdate; adjusting
the pH of said fourth solution to between about 7
and 9 and recovering the molybdenum therefrom as
calcium molybdate.
12. The process of claim 11 in which the molybdenum
is oxidized before recovery.
13. The process of claim 11 in which the sodium
diuranate precipitate is treated with sulfuric acid at a
pH between about 3 and 4 to selectively separate residual
30 zirconium and uranium.
14. The process of claim 11 in which the sodium
diuranate is treated with sulfuric acid at a pH of about
1 to completely dissolve the precipitate and residual
zirconium is selectively separated from uranium in the
35 filtrate by precipitation as the sulfate.
15. In the process for the selective recovery of
zirconium, uranium and molybdenum values from carbonate
solutions, the improvement which comprises first
separating zirconium from the other two metals by
40 adjusting the pH of the carbonate solution to a point
slightly below the precipitation point of uranium for the
solution, adjusting the temperature of the solution to
between about 80'° and its boiling point to precipitate
zirconium carbonate and separating the precipitate from
45 the remaining solution.
16. In the process for selectively recovering zirconium,
uranium and molybdenum values from carbonate liquors
by which zirconium and uranium are selectively recovered
leaving the molybdenum contained in a basic leach liquor,
50 the improvement which comprises adjusting the pH of the
leach liquor to between about 1 and 2 and adsorbing the
molybdenum on charcoal.
17. In the process for selectively recovering uranium,
zirconium and molybdenum from carbonate leach liquors,
55 by which zirconium and uranium are selectively recovered
leaving molybdenum contained in a basic carbonate
leach liquor, the improvement which comprises
oxidizing the molybdenums, adjusting the pH of the carbonate
solution to between about 3 and about 4 to precip-
60 itate uranyl molybdate, treating the precipitate with
sodium hydroxide to dissolve the molybdenum and recovering
the molybdenum from the filtrate.
18. The process for the selective recovery of zirconium,
uranium and molybdenum values from carbonate solu-
65 tions which comprises adjusting the pH of the carbonate
solution to a point slightly below the precipitation point
of uranium for the solutions, digesting the solution at a
temperature between about 80° C. and the boiling point
of the solution to precipitate zirconium carbonate and
70 separating the precipitate thereby forming a second solution
containing uranium and molybdenum; precipitating
the uranium by adding to said second solution an excess
of an alkali metal hydroxide to precipitate uranium as
an alkali metal diuranate and separating the last precip-
75 itate from the remaining solution thereby forming a third
SJ
the precipitate of the last precipitation from the remaining
solution and thereby forming a third solution; adjusting
the pH of said third solution to acidic and adsorbing
molybdenum from said third solution on charcoal.
2. The process of claim 1 in which the molybdenum
is eluted from the charcoal and recovered from the
eluate.
3. The process for selectively recovering uranium,
zirconium and molybdenum values from carbonate solutions
formed from composite ores containing said values
which comprises: adjusting the pH of the pregnant carbonate
solution to a point not in excess of slightly below
the precipitation point of uranium for the solutions to
precipitate zirconium as a precipitate of zirconium carbonate,
separating said zirconium carbonate precipitate
from the remaining solution and thereby. form a second
solution; precipitating uranium from said second solution
by adding to said second solution an excess of an alkali
metal hydroxide to precipitate uranium as alkali metal
diuranate, separating the precipitate of the last precipitation
from the remaining solution and thereby forming
a third solution; adjusting the pH of said third solution
to acidic, separating the molybdenum from said third
solution by passing the solution through charcoal to
adsorb the molybdenum on ,the charcoal; eluting the 25
molybdenum from the charcoal; and recovering molybdenum
from the eluate by precipitating it as an insoluble
compound.
4. The process of claim 3 in which the molybdenum is
oxidized before adsorption on charcoal.
5. The process of claim 3 in which the carbonate
solution is digested at a temperature between about 80°
C. and the boiling point of the solution during the
precipitation of zirconium carbonate.
6. The process of claim 3 in which the pH of said
third solution is adjusted to between about 1 and 2 for
adsorption of the molybdenum on charcoal.
7. The process of claim 3 in wllich molybdenum is
recovered from said eluate as calcium molybdate and the
pH of said eluate is adjusted to a point between about
7 and 9 for precipitation of the calcium molybdate.
S. The process for selectively recovering uranium,
zirconium and molybdenum values from carbonate solutionscontaining
said values which comprises precipitating
the zirconium from the carbonate solution as the
carbonte by adjusting the pH of the pregnant carbonate
solution to a point not in excess of slightly below the
precipitation point of uranium for the solution, separating
the precipitate of zirconium carbonate from the
remaining solution and thereby forming a second solution;
precipitating molybdenum and some of the uranium
from said second solution as uranyl molybdate by adjusting
the pH of said second solution to between about 3 and
4, separating the precipitate from the last precipitation
from the remaining solution and thereby forming a third
solution; precipitating uranium from said third solution
by adding to said third solution an excess of an alkali
metal hydroxide to precipitate uranium as alkali metal
diuranate; separating the precipitate of the last precipitation
from the remaining solution; selectively dissolving
molybdenum from said uranyl molybdate precipitate at
a pH of about 10 or above, separating the precipitate of
the last precipitation from the remaining solution; and
thereby forming a fourth solution; and recovering molybdenum
from said fourth solution.
9. The process of claim 8 in which the uranium remaining
after separation of molybdenum from said uranyl
molybdate precipitate is recycled for succeeding precipitation
of uranyl molybdate.
HI. The process of claim 8 in which molybdenum is
oxidized before precipitation of uranyl molybdate.
H. The process for selectively recovering uranium,
zirconium and molybdenum values from carbonate solutions
of composite ores containing said values which comprises
precipitating zirconium from the carbonate soluI
3,288,570
15 Clegg et a1.: Uranium Ore Processing, September 1958,
pages 223-224.
BENJAMIN R. PADGETT, Primary Examiner.
CARL D. QUARFORTH, Examiner.
M. J. SCOLNICK, Assistant Examiner.
OTHER REFERENCES
3,078,141
3,180,703
12
an alkali metal hydroxide to precipitate uranium as an
alkali metal diuranate; dissolving molybdenum from the
uranyl molybdate precipitate with an alkali metal
hydwxide at a pH of about 10 to form a fourth solution
containing molybdenum; 'and recovering molybdenum
from said fourth solution as calcium molybdate.
References Cited by the Examiner
UNITED STATES PATENTS
2/1963 Koble 23-14.5
4/1965 Ableson et a1. 23-19 X
:n
solution containing molybdenum; adjusting the pH of
said third solution to between about 1 ,and 2 and adsorbing
the molybdenum on charcoal; stripping the molybdenum
from the charcoal with an alkali metal hydroxide
at a pH between about 7 and 9 and recovering molyb- 5
denum from the eluate of the stripping step by precipitation
as calcium molybdate.
19. The process for the selective recovery of zirconium,
uranium and molybdenum values from carbonate solutions
which comprises adjusting the pH of the carbonate 10
solution to a point slightly below the precipitation point
of uranium for the solution, digesting the solution at a
temperature between 80° C. and the boiling point of the
solution to precipitate zirconium carbonate and separating
the precipitate thereby forming a second solution containing
uranium and molybdenum, oxidizing the molybdenum
in said second solution; adjusting the pH of said
second solution to between about 3 and about 4 to precipitate
uranyl molybdate and separating the precipitate
thereby forming a third solution; precipitating uranium 20
from said third solution by adding to said third solution
r*8֭mo��0�on:none;mso-layout-grid-align:none;text-autospace:none'>in three stages, indicating the complete feasibility
of the recovery of uranium from the acid percolatioI} leach
liquors. Additional evaluation tests of amine solvent
extraction from the standpoint of operability and reagent
C:onsumption conclusively demonstrated that the recovery
of uranium by this method is entirely feasible from reagent
consumption standpoint and that it produces yellow '
cake from acid percolation leach liquors meeting all requirement
specifications.
Alkaline percolation leach
The use of alkali metal and ammonium carbonates as
agglomerating and leaching agents in the overall process
was extensively tested. As set forth below, ammonium
carbonate is the preferred leaching agent from a commercial
standpoint; however, tests demonstrated that alkali
metal carbonates, such as, sodium carbonate and bicarbonate,
are highly effective. Other alkali metal carbonates,
such as, potassium ,carbonate and bicarbonates are opera- 60
tive for the process.
Table IV above presents results of a representative test
in which sodium carbonate and sodium bicarbonate were
used as agglomeration and leaching agents in the process.
The results in Table IV indicate the stability of the 65
nodules formed. This is supported by flow rates, slump
value and absence of gassing. Although sodium bicarbonate
was added it is obvious that sodium carbonate alone
can be used. The definition of sodium carbonate and ammonium
carbonate as used in the claims includes either 70 ---------_------'----'------'------'--
the carbonate alone or the combination of sodium carbo- As seen from Table VI, uranium extraction from the
nate and bicarbonate. Although the wetting agent "Aero- four lignite samples ranges from 74.4% to 90.2%. The
sol OT" and the flocoulating agent "Separan" were used lower extractions were obtained in 'accelerated tests with
in the test and it has been found that their use is bene- lower dilution and shorter leach time, so over-all extracficial
in some cases, their use is not critical and the process 75 tions would probably be in the 85% to 90% range for
3,288,569
13
completed leach tests. Sample A, the most typical of the
available ore supply, gave 87.2% uranium extraction, and
41.2% zirconium extraction. An optimum leach rate in
time is estimated to be a maximum flow rate of I-bed
volume every 8 hours for a total 'Continuous leach time
of five or six days.
The ore was agglomerated with a solution of ammonium
carbonate and sufficient cure time was allowed for
complete evaluation of CO2 gas. Flow rates, obtained
were more than sufficient for mill use, in which a flow
rate of 10 gal./sq. ft.!{lay (l-bed volume/8 hours) is
adequate.
The uranium was precipitated from the ammonium
14
destroy ammonia. Tests showed conclusively that a high
percentage of ammonia can be recovered quite easily
from the liquor and from the tails by raising the pH and
steam sparging, and that there is no apparent chemical
5 destruction of the ammonium compound to destroy the
ammonia. Tests performed by percolating an ammonium
carbonate solution through a percolation leach system
for four days with no ore in the system showed that
ammonia losses by volatilization are all within 1%, well
10 within the limits of experimental error. Ammonia material
balances on ammonium carbonate percolation leach
tests of samples of various lignites are given in Table
VII.
TABLE VII.-AMMONIA BALANCE ON AMMONIUM CARGONATE
PERCOLATION LEACH TESTS
4
7
8
Ammonia Added, Amnlonia Recovered,
lb,fton lb,fton NH,
Guin (+)
Sample or Loss (-) Percent
Agglom- Leach Total Liqnor Tail Total lb./ton ore
eration
---- --------------
A-(1) ______ 51 554 605 486 86 572 -33 -5.
A-(2) ______ 60 173 233 170 67 237 +4 +1.
B ___ "______ 11 393 404 293 83 376 -28 -6.9
C __________ E __________ 27 235 262 211 49 260 -2 - None 401 491 405 51 456 -35 -7.1
carbon~te leach liquor in accordance with the flow sheet
shown in FIG. 2. Ordinarily, if ammonium carbonate
'solution containing uranium is boiled 'and sparged with
steam, the ammonium carbonate is volatilized and uranium
precipitates as U03; however, the presence of organic
compounds in lignite leach liquor prevents the precipitation
of uranium by this simple method, probably because
of the formation of complex ,compounds. In accordance
with the process of the invention, a small
amount of a strong oxidizing agent was added to the
solution after boiling off the ammonium carbonate and
the pH raised to 12 with lime. This precipitates the
uranium completely as a low grade material containing
organics as well as some gypsum and a small amount of
calcium carbonate. The addition of lime has the added
advantage of liberating any ammonia which is present in
the liquor as a non-volatile compound such as ammonium
sulfate. The uranium precipitate was then calcined to
produce a uranium 'Concentrate assaying approximately
5% U30 8• The oxidant used to complete uranium precipitation
was sodium hypochlorite; however, other strong
oxidizing agents can be used. This may not be necessary
for all leach solutions.
In order to test the effect of an oxidizing agent in the
precipitation of uranium, duplicate precipitations were
made on similar solutions at pH 12. The first was a
control run, and the second contained the equivalent of
.2 gram sodium hypochlorite per liter. Recovery of
U30 8 in the control test was 77.5% compared to 100%
in the test containing hypochlorite. The tests showed the
effectiveness of an oxidizing agent for this ore; however,
for other ores an oxidizing agent may not be required.
Other tests indicated a preferred pH range of about 10
to 12 for conducting the precipitation. Tests indicated
that reagent consumption for the overall process is favorable
as respects economic commercial utilization of the
process.
Information as to the grade of the concentrate was
obtained from several lime precipitation tests using varying
grades of liquor. The tests showed that the concentrate
meets required specifications.
The economic feasibility of the ammonium carbonate
leaching system depends largely upon the recovery and
re-use of ammonia in the same sense that sodium must
bere-used in leaching with sodium carbonate. Three
possible ways in which ,ammonia can be lost in a percolation
leach process are (l) in the leach liquor, (2) in
the solid tails, and (3) a chemical att~ck which would
The material balances given in Table VII indicate that
all of the ammonia from an ammonium carbonate percolation
leach can be recovered. These test results demon-
30 strate that (1) lignite ores can be readily agglomerated
into nodules for ore beds from which uranium can be successfully
leached by ammonium carbonate percolation
leaching, (2) uranium can be recovered from the leach
solution at low cost as a concentrate capable of further
35 treatment to produce specification grade yellow cake and
(3) ammonia can be recovered from solution and residues
by heating and lime addition to drastically reduce reagent
cost.
40 If selective recovery of uranium, molybdenum and zirconium
from the carbonate strip liquor is required, this
can be acomplished by a process disclosed in copending
application Serial No. 302,627 filed in the U.S. Patent
Office on August 16, 1963 entitled "Process for the Selec-
45 tive Recovery of Uranium, Zirconium and Molybdenum."
It is thus seen from the above description that the invention
provides a process for the percolation leaching of
carbonaceous ores of uranium and other ores which is
commercialIy feasible. The process broadly includes the
50 steps of nodulizing the carbonaceous ore and removing
uranium from the nodules by percolation leaching. An
important feature of the invention which makes possible
the percolation leaching of carbonaceous ore is the nodulizing
procedure by which nodules are formed which are
55 sufficiently stable and porous to permit leaching in an ore
bed with the required leaching agent. The nodules are
made by cascading the ore particles accompanied by spraying
the cascading ore with a water base mixture which
preferably includes a portion of the leaching agent and
60 may include an agglomerating agent, such as, wetting a!ld
flocculating agents. The nodules must be cured under
high humidity conditions. The nodules are formed into
a bed in the percolation leach step. Percolation leaching
may be performed with either an acidic or basic agent.
65 Preferred basic agents for uranium leaching are alkali
metal carbonates and bicarbonates and ammonium carbonate
and bicarbonate. Preferred acids are dilute solutions
of strong mineral acids, such as sulfuric acid. Ammonium
carbonate is the preferred basic leach agent and
70 sulfuric acid is the preferred acidic leaching agent.
The acid leach is preferably performed at a pH between
about 1 and 2. Uranium is recovered from the acid leach
liquor by conventional solvent extraction processes.
Uranium is recovered from the ammonium carbonate
75 leach liquor by boiling off the ammonium carbonate £01-
3,288,569
2,982,602
M. J. SCOLNJCK, Assistant Examiner.
References Cited by the Examiner
UNITED STATES PATENTS
5/1961 Sherk et al. 23-14.5
OTHER REFERENCES
Clegg and Foley, Uranium Ore Processing, AddisonWesley
Co., 1958, pp. 115-136, 153-169, 197-199, 301,
393-394.
70 BENJAMIN R. PADGETT, ,Primary Examiner.
CARL D. QUARFORTH, Examiner.
16
14. The process of claim 12 in which the alkaline leaching
agent is a material from the class consisting of alkali
metal carbonates and bicarbonates and ammonium carbonate
and bicarbonate.
15. The process of claim 14 in which the leaching agent
is sodium carbonate.
16. The process of claim 14 in which the leaching agent
is ammonium carbonate.
17. The process of claim 16 in which uranium is re10
covered from the leach liquor by boiling off ammonium
carbonate followed by precipitation of the uranium with
lime.
18. The process of claim 17, in which the uranium is
precipitated at a pH between about 10 and 12.
19. -The process of claim 17 in which an oxidizing agent
is added to the solution after removal of ammonium carbonate
to aid in the precipitation of uraniuIIl.
20. The process for the recovery of metals selected
from the group consisting of uranium, zirconium and
20 molybdenum from ores of said metals contained in carbonaceous
material which comprises: agglomerating the
material into porous nodules sufficiently porous and stable
to permit percolation leaching with an ammonium carbonate
solution; forming a percolation leach bed of the
25 nodules; percolation leaching the metal from the nodules
with an ammonium carbonate leach solution; boiling the
leach solution to remove ammonium carbonate therefrom
and recovering the ammonia for re-use; precipitating the
metal from the soluton with lime at a pH of between
30 about 10 and 12; and calcining the precipitated metal to
purify it.
21. The process for the recovery of metals selected from
the group consisting of uranium, zirconium and molybdenum
from ores of said metals contained in carbonaceous
35 material which. comprises: grinding the material to fine
particles; cascading the particles in the presence of moisture
to form porous nodules; curing the nodules in a humid
atmosphere; forming a percolation leach bed from the
nodules while moist; and percolation leaching the metal
40 from the ore in the nodules with a leaching agent.
22. The process of claim 21 in which said particles are
sprayed with a portion of the leaching agent during cascading.
23. The process of claim 22 in which the nodules are
45 cured in an atmosphere of high relative humidity.
24. The process for the recovery of metals selected
from the group consisting of uranium, zirconium and
molybdenum from ores of said metals contained in
50 carbonaceous materials which comprises: grinding the
material into small particles; cascading the particles
to form porous nodules while adding thereto from
10 to about 60 percent of a leaching agent based
on the weight of the material; curing said nodules in an
55 atmosphere in which the relative humidity is from about
80 to 100 percent; forming said nodules into a bed; and
percolation leaching the metal from the nodules with said
leaching· agent.
15
lowed by raising the pH of the solution to between about
10 and 12 with lime. A small amount of a strong oxidizing
agent is added to aid the precipitation. The ammonia
removed in the recovery process is recovered and re-used.
The precipitated uranium is calcined to produce a urani- 5
um concentrate assaying approximately 5% UgOs. The
material balances for the sulfuric acid and ammonium
carbonate leach processes show that reagent consumption
is favorable for commercial requirements.
.The broad process is not restricted to the recovery of
uranium from carbonaceous ores as the invention applies
to the nodulizing of carbonaceous materials containing
ores of metals in general for the purpose of removing the
metals by percolation leaching, regardless of the percolation
leaching reagents and procedures peculiar to the metal 15
being recovered. This feature is illustrated by the per-
·centageyields oCzirconium and molybdenum recovered
in the leach liquors even though the leaching was directed
to the recovery of uranium.
Although the invention has been illustrated and described
with reference to the preferred embodiments thereof,
it is to be understood that it is in no way limited to the
details of such embodiments, but is capable of numerous
modifications with the scope of the appended claims.
What is claimed is:
1. The process for the recovery of metals selected from
the group consisting of uranium, zirconium and molybdenum
from ores of said metals contained in carbonaceous
material which comprises: agglomerating the ore-containing
material to form porous nodules; forming a percolation
leach bed of the nodules; leaching the metal from
the nodules by percolation leaching with a leaching agent;
and recovering the metal from the leach liquor.
2. The process of claim 1 in which a portion of the
leaching agent is added to the are during agglomeration.
3. The process of claim 1 in which the nodules are
cured without drying under high relative humidity conditions.
4. The process of claim 2 in which the nodules are
cured without drying under high relative humidity conditions.
5. The process of claim 1 in which an agglomeration
agent is added to the ore during the agglomeration step.
6. The process of claim 5 in which the agglomeration
agentis a wetting agent.
7. The process of claim 5 in which the agglomeration
agent is a flocculating agent.
S. The process for the recovery of metals selected from
the group consisting of uranium, zirconium and molybdenum
from ores of said metals contained in carbonaceous
material which comprises: forming porous stable nodules
of rthe ore-containing carbonaceous material; forming
a percolation leach bed of the nodules; and percolation
leaching the metal from the nodules with acid leaching
solution.
9. The process of claim 8 in which the acid is sulfuric
acid.
10. The process of claim 9 in which the uranium is recovered
from the leach liquor by solvent extraction. 60
11. The process of claim 8 in which the leaching step
is performed at a pH of less than about two.
12. The process of recovering metals selected from the
group consisting of uranium, zirconium and molybdenum
from ores of said metals contained in carbonaceous mate- 65
rial which comprises: forming the ore-containing carbonaceous
material into stable, porous nodules; forming a
percolation leach bed of the nodules; percolation leaching
the metal from the nodules with an alkaline leaching solution;
and recovering the metal from the leach liquor.
13. The process of claim 12 in which a portion of the
leaching agent is added during forming of the nodules and
the nodules are cured without drying under high relative
humidity conditions.