Method for solution mining of uranium ores

In the solution mining of uranium ores using an aqueous ammonium carbonate leaching solution containing hydrogen peroxide and/or molecular oxygen as oxidant, permeability of the ore formation during the leaching operation is maintained or improved by including a small amount of alkali metal silicate dissolved in the leaching solution. The silicate also improves the stability of the oxidant in many instances.

DESCRIPTION 
TECHNICAL FIELD 
The present invention relates to processes for the solution mining of 
uranium ores and more particularly to such processes which maintain the 
permeability of the uranium ore formations. 
BACKGROUND ART 
With the increasing use of nuclear power plants for the production of 
electricity in the United States, uranium ore deposits have become an 
increasingly valuable natural resource. Even though there are extensive 
uranium deposits distributed throughout the Western United States, many of 
these are located at too great a depth from the surface and/or are of too 
low concentration to be mined economically by conventional open pit or 
shaft mining techniques. Especially for such ore sources where 
conventional mining techniques are uneconomical or where they present 
severe ecological or esthetic problems, solution mining has been proposed 
in many instances. 
In a typical solution mining situation, a central production well can be 
drilled into a permeable uranium ore formation and a plurality of 
regularly spaced injection wells drilled around the production well. To 
start production, a leaching solution is pumped into the ore formation 
through the injection wells. The solution moves through the formation 
dissolving the uranium compounds in the ore as it passes toward the center 
of the ore formation from which it is removed by means of the production 
well. The leaching solution containing the dissolved uranium is then 
pumped to an extraction treatment zone where the leaching solution is 
treated to separate the uranium compounds. 
Several solution mining (in-situ leaching) processes have been suggested. 
For example, the solvent most frequently used for leaching has been an 
acid or carbonate solution. The uranium is then removed from the leaching 
solution by ways such as (1) adjusting the pH of the solution to neutral 
or basic pH to precipitate out the uranium, (2) separating the uranium 
compounds by ion exchange or (3) concentrating the uranium by 
liquid-liquid extraction. 
Many in-situ leaching operations employ an alkaline carbonate leaching 
solution containing an oxidizing agent. The carbonate can be present as an 
ammonium or sodium salt or mixtures thereof. Ammonium ions are preferred 
in many instances because they are less likely to interfere with 
permeability of the ore formation. 
Because uranium in the 4+ valence state is insoluble in water, an oxidant 
is needed to oxidize it to the 6+ valence state, which is soluble in the 
form of a carbonate complex. The basic chemistry of this method of 
extraction is shown by the following equations: 
EQU UO.sub.2 +1/2O.sub.2 .fwdarw.UO.sub.3 ( 1) 
EQU UO.sub.3 +H.sub.2 O+3CO.sub.3.sup.-- .fwdarw.UO.sub.2 
(CO.sub.3).sub.3.sup.4- +2OH.sup.- ( 2) 
The hydroxyl ions produced in reaction (2) tend to cause formation of 
insoluble uranium compounds, especially when sodium ions are also present. 
The -OH ions can, however, be readily removed by reaction with bicarbonate 
ions which favorably affect the equilibrium of the solubilizing reaction 
as well as prevent precipitation of insoluble uranium compounds such as 
sodium uranate. Thus, it is usually preferred to use carbonate leaching 
solutions containing enough bicarbonate to react with hydroxyl ions formed 
in the manner of reaction (2). 
Though many oxidizing agents have been suggested and tried for this use, 
hydrogen peroxide and molecular oxygen (O.sub.2) are especially desirable 
for this use because they and their decomposition products--O.sub.22 and 
H.sub.2 O--are completely non-polluting and thus ecologically acceptable. 
Hydrogen peroxide is preferred, however, because it can be introduced as a 
liquid that contains oxidant in highly concentrated form, whereas the 
concentration of injected oxygen gas is highly limited by its solubility. 
As a consequence, the liquid oxidant is less likely than a gas to cause 
vapor locking within the ore body. Even when the hydrogen peroxide does 
decompose in contact with the ore, the O.sub.2 produced is likely to be 
well distributed over a wider portion of the ore body in the form of quite 
small sized bubbles which further contribute to an even more thorough 
distribution of oxygen solubilized in leach solution. Thus, there is 
greater potential for increasing the reaction rates for solubilizing the 
insoluble uranium compounds in the ore. 
The chemistry of uranium leaching is less well characterized for hydrogen 
peroxide than for oxygen. Conceivably, by analogy with equation (1) above, 
the reaction may be: 
EQU UO.sub.2 +H.sub.2 O.sub.2 .fwdarw.UO.sub.2.sup.++ +2OH.sup.- 
However, uranium in the 6+ valence state is known to form peroxy addition 
compounds such as UO.sub.6.sup.--, and it is entirely likely that one or 
more peroxy compounds are involved in the overall chemistry. Suffice it to 
say, however, that H.sub.2 O.sub.2 is a potential oxidant either as 
H.sub.2 O.sub.2 or as a latent source of O.sub.2. 
The use of either molecular oxygen or hydrogen peroxide in alkaline 
carbonate leaches may contribute to the tendency of the formation to 
become less permeable as the leaching process proceeds. Diminished 
permeability greatly increases the time required to leach out an ore body. 
Thus, the use of hydrogen peroxide and/or molecular oxygen as the oxidant, 
along with other factors such as the particular cations in the leaching 
solution, the type of clay, the electrostatic charges on the clay 
particles and pressure drop between the injection and production wells, in 
some instances appear to cause loss of permeability. 
The problem of maintaining permeability of an ore body during leaching is 
not a new one. For example, in U.S. Pat. No. 3,309,140, Gardner et al 
propose the addition of polyacrylamide to an acidic leaching solution 
containing sodium chlorate as an oxidant. U.S. Pat. No. 3,567,427 mentions 
that hydrogen peroxide can be effective for the disaggregation of certain 
clay minerals, which suggests that hydrogen peroxide might be troublesome 
in applications such as solution mining where disaggregation is to be 
avoided. These references obviously do not, however, address themselves to 
the problem of maintaining permeability in the presence of hydrogen 
peroxide. De Vries in U.S. Pat. No. 3,908,388 discloses the use of the 
reaction product of a non-aqueous slurry of alkali metal silicate with an 
alkyl amide to insolubilize the alkali metal silicate for the purpose of 
stabilizing sand and thus to maintain oil permeability. Also, Peeler in 
U.S. Pat. No. 2,968,572 employs similar amides to insolubilize aqueous 
alkali metal silicates for soil stabilization in the presence of ground 
moisture. However, the problem contemplated there was oil permeability, 
not water permeability. Furthermore, no oxidant was present in the system 
and higher silicate concentrations were used. 
Several other U.S. patents disclose the use of many other agents for 
gelling or setting alkali metal silicates to make them useful for soil 
stabilization, e.g., the following: . 
U.S. Pat. No. 583,166 Portland cement 
U.S. Pat. No. 3,288,040 Alkali metal hexafluorosilicate 
U.S. Pat. No. 3,558,506 Methyl C.sub.1-3 acylates. 
The use of alkali metal silicates for the purpose of soil stabilization has 
heretofore apparently been limited to systems in which the alkali metal 
silicate was admixed with an extraneous agent for the purpose of gelling 
or solidifying the dissolved silicate. 
DISCLOSURE OF THE INVENTION 
According to the present invention there is provided in a process for the 
solution mining of a uranium ore formation where an aqueous carbonate 
leaching solution containing an oxidant is passed through the ore 
formation to dissolve uranium from the formation therein and the solution 
is withdrawn from the ore formation enriched in uranium, the improvement 
comprising: passing through the ore formation an aqueous ammonium 
carbonate leaching solution having a pH of 7-10, and which has dissolved 
therein an oxidant selected from the group consisting of hydrogen 
peroxide, molecular oxygen and a mixture thereof and an alkali metal 
silicate. 
The process of the invention is applicable generally to the use of ammonium 
carbonate leaching solutions which contain either hydrogen peroxide or 
molecular oxygen as an oxidant. When hydrogen peroxide is used, the 
process is likely to involve both species of oxidant since the hydrogen 
peroxide undergoes decomposition in contact with the ore. Such 
decomposition is probably catalytic in nature, can be quite extensive and 
may be virtually complete in some instances. 
As used herein, the term "ammonium carbonate leaching solutions" means 
aqueous solutions of NH.sub.3 and CO.sub.2. Such solution will ordinarily 
have an initial pH, i.e., prior to injection into the ore formations, of 
7-10. Although the concentration of NH.sub.2 and CO.sub.2 may vary widely 
within those pH limits, the leaching solution will ordinarily be comprised 
of from 0.5 to 20 grams per liter of ammonium carbonates, basis either 
--CO.sub.3 or -HCO.sub.3. From 1 to 10 grams per liter are preferred. Such 
solutions are prepared most easily by sparging NH.sub.3 and CO.sub.2 into 
water until the desired concentrations of chemical reactants are reached 
and then adjusting the pH by the addition of more NH.sub.3 to raise the pH 
or CO.sub.2 to lower pH. They can, however, also be made by dissolving the 
solid carbonates in the water and then adjusting pH in the same manner 
only altering the proportions of the solid carbonates. Typically, an 
ammonium carbonate leaching solution will contain from about 10 to 15 
grams of carbonate compounds per liter of solution, e.g., 10 grams of 
ammonium bicarbonate and 0-5 grams of ammonium carbonate. 
The concentration of hydrogen peroxide in the leaching solution is only one 
factor that impinges on successful solution mining of uranium bearing 
ores. Other economic or technical parameters associated with the 
particular formation being treated, such as pH, particle size and 
temperature, may be more important and may even be overriding 
considerations. Ordinarily, however, the aqueous leaching solution will 
contain 0.1-10 grams H.sub.2 O.sub.2 per liter and preferably 0.2-2 grams 
H.sub.2 O.sub.2 per liter. 
Hydrogen peroxide suitable for use in leaching solutions used in the 
invention is available commercially in aqueous solutions containing from 
10 to 90% by weight H.sub.2 O.sub.2, any of which can be used in the 
invention. As used in accordance with the invention, hydrogen peroxide has 
very little effect on pH of the leaching solution and therefore need not 
ordinarily be a factor in adjusting pH of the leaching solution. These 
H.sub.2 O.sub.2 solutions may in some instances contain one or more 
stabilizers to inhibit decomposition such as those which are disclosed in 
U.S. Pat. Nos. 2,872,293; 3,122,417; 3,387,939; 3,649,194; 3,691,022; 
3,687,627 and 3,869,401. However, the use of such stabilizers is not 
essential to the practice of the invention. 
It has been found that only a very small concentration of alkali metal 
silicate per liter of total leaching solution is needed to reduce loss of 
permeability within the formation significantly. The minimum effective 
concentration of silicate is highly subjective to the formation being 
treated and its particular physical and chemical characteristics. However, 
ordinarily at least about 0.1 and preferably at least about 0.2 gram of 
alkali metal silicate will be used per liter of total leaching solution. 
However, more significant effects are produced if at least about 0.5 gram 
per liter is used. An optimum concentration of alkali metal silicate 
appears to be 0.5-1.5 grams per liter. Even through higher concentrations 
of alkali metal silicate (e.g., up to 5 g/l) may be used, no further 
advantage with respect to permeability was apparent from such use. 
Furthermore, the use of higher concentrations in some instances will 
significantly increase the incidence of gelling the silicate which will 
cause a loss in permeability of the ore formation. However, it has been 
found that leaching solutions containing as high as 10 grams of NH.sub.3 
-CO.sub.2 per liter and even higher and the preferred 0.5-1.5 grams of 
silicate per liter resist gellation for quite long periods of time. 
Suitable alkali metal silicates include silicates of sodium, potassium and 
lithium, of which sodium is preferred. The silicates must, however, be 
stable aqueous solutions which contain no appreciable amount of 
particulate silica. Transparent solutions which exhibit little, if any, 
Tyndall effect, are uniformly suitable with respect to stability against 
loss of permeability induced by gellation. Suitable aqueous sodium 
silicate solutions are available having SiO.sub.2 :Na.sub.2 O weight 
ratios of from 1.90 to 3.25 and containing from 27.0 to 36.0% wt SiO.sub.2 
and from 8.7 to 19.4% wt Na.sub.2 O. Sodium silicate solutions of this 
type are alkaline and have a pH range of between 10 and 13. 
In preparing leaching solutions for use in the process of the invention, no 
particular order of mixing is needed.

The invention is exemplified and can readily be understood by reference to 
the examples which are set out hereinbelow. 
DEFINITIONS AND ABBREVIATIONS 
ABC=ammonium bicarbonate=NH.sub.4 HCO.sub.3 
AC=ammonium carbonate=(NH.sub.4).sub.2 CO.sub.3 
NH.sub.3 -CO.sub.2 or "carbonate" refers broadly to aqueous leach solutions 
of NH.sub.3 and CO.sub.2 containing ammonium carbonate, ammonium 
bicarbonate or mixtures thereof. 
"Goal flow" or "goal flow rate" refer to a predetermined flow rate to be 
maintained during a run (within the capabilities of the pump being used) 
to pump leachate from the bottom of a leach column. 
"Companion Run" refers to side-by-side comparative column leaching runs. 
"Leach" refers to the solution fed from the inlet reservoir to the top of 
the leach column. 
"Leachate" refers to the solution pumped from the bottom of a leach column 
after passing through the ore bed. 
The terms "silicate", "sodium silicate", "sil.", and "NaSiO.sub.3 " may be 
used interchangeably. All weights or concentrations are on the basis of Du 
Pont Sodium silicate, Grade F or Grade No. 9 diluted to the same solids as 
Grade F. Both Grades have an SiO:Na.sub.2 O weight ratio of 3.25. 
EXPERIMENTAL APATUS AND PROCEDURE 
1. Apparatus 
Two parallel leaching systems were set up, each having (1) an inlet 
reservoir for fresh leaching solution, (2) a leach solution feed pump on 
the outlet of the inlet reservoir communicating with (3) a leaching column 
containing a fixed bed of finely divided uranium ore having a depth in 
most cases of about 2.5-10 cm, (4) a peristaltic leachate pump on the 
outlet of the leach column discharging into (5) a leachate reservoir. The 
vapor space in the tops of the leach columns, the leachate reservoir and 
inlet reservoir were each manifolded to a gas collection burette so that 
any O.sub.2 gas release in the system could be measured. 
2. Procedure 
(1) Pack leach columns with ore charge resting atop a glass wool plug on a 
coarse fritted glass disk. Tamping was generally not required to prevent 
voids; 
(2) Charge inlet reservoirs with one liter of leaching solution with 
ingredients being added in the following order: NH.sub.4 HCO.sub.3 and/or 
(NH.sub.4).sub.2 CO.sub.3, sodium silicate solution and H.sub.2 O.sub.2 
solution; 
(3) Pump leaching solution into leach columns to permeate to bottom of ore 
bed and continue pumping rate; 
(4) Activate leachate pump and establish as nearly as possible a 
predetermined leach flow through both systems. Pump speeds were recorded. 
3. Ore Characteristics 
A. A high-uranium ore containing 0.85% wt U and about 21% wt CaCO.sub.3 
from a South Texas site. Material was dry (1-1.4% wt H.sub.2 O based on 
drying loss at 110.degree. C.) and free flowing. 
B. A weakly mineralized ore of sandy consistency containing only about 
0.03% wt U rich in pyrite also from South Texas. Material was sufficiently 
wet (12-14% wt H.sub.2 O) that it did not flow freely but was easily 
spooned into the leach column. 
C. A very weakly mineralized ore containing less than 5 ppm by weight U. 
Material was dry and free flowing. 
4. Methods of Determining H.sub.2 O.sub.2 Loss During Leaching 
A. By Gas Collection 
As described above, manifolded flexible tubing conveyed all O.sub.2 gas 
released by H.sub.2 O.sub.2 decomposition from the leach column, the inlet 
reservoir and the leachate collection reservoir into an inverted gas 
collection cylinder. The percent of H.sub.2 O.sub.2 decomposed (% 
converted to O.sub.2) after a time (t) in which a certain volume (liters) 
of leachate, containing a certain concentration of H.sub.2 O.sub.2 was 
collected, was computed as follows: 
##EQU1## 
The collected gas volume was converted to STP by multiplying the observed 
volume by 0.9. This conversion factor was based on the finding that when 
1.8 g of H.sub.2 O.sub.2 was contacted with three different ores and the 
released gas collected by displacement of water, the following relation 
was obtained: 
##EQU2## 
B. By Titration 
Assuming that the H.sub.2 O.sub.2 in the inlet reservoir is stable, the 
H.sub.2 O.sub.2 lost solely to leaching can be measured by titrating a 
grab sample from the column. This was generally done by collecting at the 
end of a run (without interrupting flow) a 100 cc sample of leachate at 
the same flow rate (mostly 5 cc/min) as used during the run. Then 20 cc 
aliquots of the 100 cc sample and of the leach in the inlet reservoir were 
titrated by standard iodimetry: 
##EQU3## 
Unless otherwise stated, analysis of "H.sub.2 O.sub.2 lost by titration" 
is by titration of a grab-sample rather than of the collected leachate. 
EXAMPLE I 
This example illustrates both the effect of a leaching solution containing 
H.sub.2 O.sub.2 in reducing permeability of an ore body and the reversal 
of that effect by adding aqueous sodium silicate to the leaching solution. 
Using Ore A, a control leach solution containing 10 g ABC/l, 2.5 g AC/l and 
1.2 g H.sub.2 O.sub.2 /l (pH 8.7) was pumped through a 50 g ore bed 
contained in a 42 mm ID column, at 10 cc/min. After 20-30 minutes, the 
column began to plug, and by 50-60 minutes it was only possible to pump 
from the bottom of the ore bed about 5 cc/min, even though the outfall 
pump rate was substantially increased. Stirring the wet bed with a spatula 
did not improve permeability. 
In a companion set of two runs, it was found that silicate essentially 
prevented this loss of permeability. With 3 g/l of silicate (Du Pont Grade 
F) in the abovedescribed leach solution, a flow rate of 10 cc/min was 
easily maintained over a 65-minute period, to collect 650 cc of leachate. 
Using no silicate in the companion run, it took 98 minutes to collect 620 
cc of leach, even though the outlet pump was at a much higher speed. 
EXAMPLE II 
In a series of tests, permeability of the ore bed was examined as a 
function of H.sub.2 O.sub.2 in the leaching solution, pH and silicate in 
the leaching solution. One hundred grams of Ore C were extracted in 
companion 42 mm leaching columns using a basic leach solution containing 
10 g ABC/l +2.5 g AC/l adjusted to pH 8.6 with NH.sub.3 or to pH 10.2 with 
NaOH. Goal flow rate was 5 cc/min. The results are given in Table 1. 
TABLE 1 
______________________________________ 
Cumulative 
Basic Leach 
Running Modifications 
Times, Column Leach Flow Rate, cc/min 
Min. Column A.sup.(1) 
B.sup.(2) 
Column A Column B 
______________________________________ 
0-60 as is as is 5 cc/min at 
Similar 
(no H.sub.2 O.sub.2) 
(no 25 rpm pump 
H.sub.2 O.sub.2) 
speed 
60-68 as is as is 12.8 cc/min 
Similar 
(no H.sub.2 O.sub.2) 
(no at 58 rpm 
H.sub.2 O.sub.2) 
68-108 1.8g H.sub.2 O.sub.2 /1 
1.8g Slowed to 
Similar 
H.sub.2 O.sub.2 /1 
4-5 cc/min 
at &gt;110 rpm 
also 
108-144 1.8g H.sub.2 O.sub.2 /1 
added 3.6 cc/min 
6.1 cc/min 
3g at 50 rpm 
at 50 rpm 
NaSiO.sub.3 / 
1 
(Example 
III) 
______________________________________ 
.sup.(1) Leaching solution pH 8.6 
.sup.(2) Leaching solution pH 10.2 
Summary of Results: 
With no H.sub.2 O.sub.2 in either formulation, the pump setting needed to 
pull 5 cc/min from the bottom of the columns was close to the 20-25 rpm 
used to maintain an inlet feed of 5 cc/min to the columns, indicating only 
a small resistance to flow. With a modest increase in pump speed, the rate 
quickly rose to 12.8 cc/min. 
At both pH 10.2 and 8.6 the addition of H.sub.2 O.sub.2 during the runs 
caused a very noticeable loss in the rate at which leach solution could be 
pulled through the columns. A further indication of permeability loss was 
shown by the reading of a vacuum gauge at the outlet of the column being 
leached at pH 8.6, which showed only 0.6 in. during the period when no 
H.sub.2 O.sub.2 was in the leach. However, the vacuum gradually increased 
to 20-21 in. of mercury during the 40-minute leach period after H.sub.2 
O.sub.2 was added. 
Note in the last 36-minute time period that the addition of silicate to the 
pH 10.2 leach solution caused a marked improvement in leach flow as 
compared to the pH 8.6 leach containing no silicate. 
In another similar run (using one column), the vacuum at the outlet of the 
column rose to 16.8 in. over a 40-minute period. As the NH.sub.3 -CO.sub.2 
leach containing 1.8 g H.sub.2 O.sub.2 /l was pumped from the bottom of 
the column at an average rate of 4.0 cc/min, the pump speed had to be 
increased from 23 to 130 rpm (85 rpm after 7 minutes). Then 3 g 
NaSiO.sub.3 /l was added to the leach and pumping was resumed for 60 
minutes to pump 298 cc of leach (5.0 cc/min). During this time the vacuum 
decreased from 18.5 to about 13.5 in. as the pump speed also gradually 
decreased to about 70 rpm. The leach flow was interrupted for ten minutes, 
and during an ensuing 15-minute flow period, an average 6.3 cc/min flow 
rate was obtained as the pump speed fell to 42 rpm and the vacuum fell to 
about 7 in. 
EXAMPLE III 
In this test series, the adverse effect of H.sub.2 O.sub.2 on permeability 
and its prevention by use of sodium silicate addition were demonstrated on 
Ore B using a basic leach containing 4 g ABC/l+4 g AC/l. The results are 
given in Table 2. 
TABLE 2 
__________________________________________________________________________ 
Basic Leach Leach Flow Rate 
Pump Speed 
Length of Run 
Modifications cc/min rpm 
Run No. Min. Column A 
Column B 
Column A 
Column B 
Column A 
Column 
__________________________________________________________________________ 
B 
1 (Control) 
Run, 60 min 
None -- 2.83 -- 58 -- 
(no H.sub.2 O.sub.2) 
2 (Control) 
Run, 90 min 
None -- 2.89 -- 58 .fwdarw. 64 
-- 
(no H.sub.2 O.sub.2) 
Stand overnight. 
3 (Control) 
Run, 60 min 
Add 1.80g 
-- 1.67 64 .fwdarw. 119 
H.sub.2 O.sub.2 /1 
Recharge columns 
with fresh ore. 
4A (Control) 
Run, 110 min 
with 1.80g 
-- 1.27 -- 115 after 
-- 
H.sub.2 O.sub.2 /1 & no 20 min 
sil 
4B (Example III) 
Run, 110 min 
-- with 1.80g 
-- 2.76 -- 58 .fwdarw. 110 
H.sub.2 O.sub.2 /1 plus over 110 
1g sil/1 min 
Stand for 49 min; 
no flow. 
5A (Control) 
Run, 40 min 
with 1.80g 
-- 0.87 -- 115 -- 
H.sub.2 O.sub.2 /1 & no 
sil 
5B (Example III) 
Run, 40 min 
-- With 1.80g 
-- 2.77 -- 100 
H.sub.2 O.sub.2 /1 plus 
1g sil/1 
__________________________________________________________________________ 
EXAMPLE IV 
In a series of tests, the effect of the following variables upon 
permeability was studied: (1) adding H.sub.2 O.sub.2 with and without 
silicate; (2) discontinuing silicate addition; and (3) effect of adding 
silicate after permeability has been diminished. Two comparison runs were 
run at a goal flow rate of 10 cc/min on Ore A using a basic leach 
containing 10 g ABC/l+2.5 AC/l. 
In two comparison runs, Columns A and B were first flushed with 500 cc of 
peroxide-free basic leach for 50 min. A flow of 10 cc/min was easily 
maintained well below a pump speed of 100 rpm. When 1.20 g H.sub.2 O.sub.2 
/l was added to the leach solution to Column A, and pumping from the 
column was resumed for 30 minutes, the outlet pump speed had to be 
increased to 345 rpm during this period to be able to maintain an overall 
flow rate of close to 10 cc/min. However, this same flow rate could be 
obtained in the companion column (B), in which the peroxide-containing 
leach also contained 3 g/l of sodium silicate, at a pump speed of only 92 
rpm. When the silicate was removed from the leach being fed to Column B, 
facile flow (at 10 cc/min) was maintainable for an additional 2 hours, at 
the end of which the run was terminated. These runs show not only that 
silicate is beneficial in preventing loss of permeability, but also that 
the beneficial effect is sustained for a substantial period of time after 
silicate is removed from the leaching solution. 
In a similar companion set of runs, partial plugging was induced by pumping 
through 320 cc of a silicate-free basic leach solution containing 1.20 g 
H.sub.2 O.sub.2 /l for 56 minutes, as a result of which flow diminished to 
below 5 cc/min even though pump speed was increased to 350 rpm. When 3 g/l 
of sodium silicate was added to the leach, flow rate did not improve as 
the next 210 cc of leach was pumped through the ore. However, when pumping 
was interrupted for 72 minutes, it became possible to pump 1000 cc of 
leach through the ore bed over an 80 minute period at about 12.5 cc/min at 
a pump speed of only about 85 rpm. In the companion control run, where 
silicate was not added, the 72-minute standing period caused only a 
temporary relief from plugging. Over the subsequent 80-minute period, flow 
was less than half the 12.5 cc/min rate of the silicate run even though 
pump speed was up to about 425 rpm. 
The second experiment indicates that permeability, even after being 
partially lost during leaching with a peroxide-containing ammonium 
carbonate solution, can be restored if silicate is added to the leach 
subsequent to the loss. Furthermore, this experiment suggests that such 
restoration of permeability is best effected by interrupting the flow of 
leach for a period of time after the ore has been permeated with a 
relatively small quantity of silicate-containing leach. 
EXAMPLE V 
In a series of tests, the following effects were examined: 
(1) Loss of permeability with peroxide leach 
(2) Use of silicate to prevent loss of permeability, and 
(3) Use of silicate to restore permeability once lost. 
Table 3 is a running log of comapanion leach experiments using the basic 
leach 4 g ABC/l+4 g AC/l (equivalent, by calculation to 2.28 g NH.sub.3 /l 
and 4.06 g CO.sub.2 /l) +1.80 g H.sub.2 O.sub.2 /l, and 100 gram charges 
(in the 42 mm I.D. columns) of ore A. Information on permeability is given 
by the "Leachate Flow Rate" column in Table 3 in conjunction with data on 
pump rpm's below in the text. Information on H.sub.2 O.sub.2 lost during 
leaching is based on O.sub.2 loss (last column in table). 
TABLE 3 
__________________________________________________________________________ 
COLUMN LEACHING OF ORE A 
EFFECT OF SILICATE AND STABILIZER ON STABILITY AND PERMEABILITY 
BASIC LEACH: 4 g ABC/1 + 4 g AC/1 + 1.80 g H.sub.2 O.sub.2 /1 
LEACH- 
VOL ATE 
LENGTH LEACH- 
FLOW 
OF ATE RATE 
RUN pH ADDITIVES cc cc/min 
RUN NO. MIN A B A B A B A B 
__________________________________________________________________________ 
6A & B (Control) 
90 8.6 
8.6 None None 455 
450 
5.1 
5.0 
7A & B (Control) 
60 8.6 
8.6 None None 135 
100 
2.2 
1.7 
8A & B (Control) 
37 8.6 
8.6 None None 25 
22 
0.67 
0.59 
Stand overnight, no flow 
9A (Control) 
9B (Example) 
50 8.6 
8.77.sup.(1) 
None 4 g/l Sil.sup.(2) 
52 
160 
1.0 
3.2 
Stand overnight for 62 min, no flow. 
10A (Control) 
10B (Example) 
35 8.6 
8.77 
None 4 g/l Sil 
35 
208 
1.2 
5.9 
Let stand 156 min., then add silicate to A and run A alone for 
next 74 min. 
11A (Example) 
74 8.77 
-- 4 g/l Sil 
-- 111 
-- .75.sup.(3) 
-- 
Let stand 272 min., then run B alone for next 30 min. 
12B (Example) 
30 -- 8.77 
-- 4 g/l Sil 
-- 162 
-- 5.4 
Let stand over weekend, then run A alone for next 41 min. 
13A (Example) 
41 8.77 
-- 4 g/l Sil 
-- 336 
-- 8.2 
-- 
14A & B (Example) 
36.5 8.77 
8.77 
4 g/l Sil 
4 g/l Sil 
150 
150 
4.1 
4.1 
15A & B (Example) 
100 8.77 
8.77 
4 g/l Sil 
4 g/l Sil 
415 
418 
4.2 
4.2 
__________________________________________________________________________ 
.sup.(1) pH after silicate and H.sub.2 O.sub.2 added; note small pH 
raising effect of silicate. 
.sup.(2) Sodium silicate with SiO.sub.2 *Na.sub.2 O = 3.25. Source Du Pon 
Grade F. 
.sup.(3) Excluding the first 3 minutes, where flow rate was 19.3 cc/min. 
The following can be concluded from these data 
Permeability gradually diminished over the 187 minutes (Control Runs 6-8) 
for the ammonium carbonate/bicarbonate leach containing H.sub.2 O.sub.2 
and no silicate, even though the pump speed had increased to &lt;110 rpm. 
However, permeability was largely restored when 4 g/l of silicate was 
added to the leach (Example 9B). In this regard, compare the 35-minute and 
50-minute running periods of Runs 10 and 9, but note that a no-flow or 
rest interval (62 min) was needed after the silicate-bearing leach was 
added during the 50-minute period. The 5.9 cc/min rate (Example Run 10B) 
was obtained at a pump speed of 62 rpm; the comparative 1.22 cc/min rate 
(Control Run 10A) was obtained at 115 rpm. 
When silicate was then added to the silicate-free column that had been used 
in Control Run 9A, there was a marked improvement in permeability. Note, 
however, (Example Run 11A) that permeability was not improved immediately. 
Other experiments indicated that 30-60 minutes (and possibly less) was a 
sufficient interlude between first introducing the silicate-bearing leach 
and resuming flow. 
EXAMPLE VI 
The following tests were carried out to determine the effectiveness of low 
levels of sodium silicate addition to the leaching solution. 
In two companion runs using 100 gram charges of Ore C, one ore column was 
leached with a solution containing 4 g ABC/l+4 g AC/l+1.8 g H.sub.2 
O.sub.2 /l, the other with the same solution fortified with 0.2 g/l of 
sodium silicate. Leachate was pumped from both column outlets using the 
same pump rpm. The leach containing 0.2 g/l of silicate flowed noticeably 
better, about 1.3 times faster than the leach containing no silicate for 
the first 80 minutes, and increasing to 1.44 times faster during the next 
120 minutes. 
When the leachate containing no silicate was then enriched with 0.5 g/l 
sodium silicate, the flow improved to the point that it was as good as, or 
slightly better than, the leach containing 0.2 g/l of sodium silicate. 
In another 60-minute comparative run, leach containing 1 g/l of sodium 
silicate flowed easily at 5 cc/min at pump settings of 45-65 rpm. With no 
silicate the average flow over this period was only 3.6 cc/min, even 
though the pump speed was increased from 65 to 118 rpm during the run. 
EXAMPLE VII 
Because of interest in using sodium as well as ammonium carbonates, tests 
were conducted in which the ammonium ion was replaced in part or 
completely by sodium. 
Table 4 summarizes companion runs using different leaches containing 1.80 g 
H.sub.2 O.sub.2 /l and 100 gram charges of Ore C in the 42 mm I.D. column. 
A goal leach flow-rate of 5 cc/min using a pump having 0-120 rpm range was 
attempted. 
The ore had been sieved to -12+80 mesh, but the particles were soft (to 
finger crushing) and clay-like in appearance. When wetted in the column, 
the larger pieces seemed to lose their particulate identity and the wetted 
plug seemed to be a fairly uniform, sandy, clay-like aggregate. 
TABLE 4 
__________________________________________________________________________ 
SILICATE AND PERMEABILITY IN COLUMN LEACHING: EFFECT OF Na.sup.+ VS 
NH.sub.4.sup.+ IN LEACH 
ADDITIONS LENGTH 
RUN.sup.(1) g/l NaSiO.sub.3 
TO ADJUST pH 
pH OF RUN, 
LEACH FLOW RATES.sup.(6) 
NO. BASIC LEACH 
A B A B A B MIN A B 
__________________________________________________________________________ 
16 4 g NH.sub.4 HCO.sub.3 /l + 
0 1.0 None None 8.6 8.65 
60 3.6 cc/min 
OK, at 45-65 
4 g (NH.sub.4).sub.2 CO.sub.3 /l at 65 .fwdarw. 118 
rpm 
rpm 
17 4 g NH.sub.4 HCO.sub.3 /l + 
1.0 1.0 H.sub.2 SO.sub.4 
NaOH 7.0 9.6 
70 OK at 38-66 
3.6 cc/min at 
4 g (NH.sub.4).sub.2 CO.sub.3 /l rpm 80-110 rpm 
18.sup. (2) 
4 g NH.sub.4 HCO.sub.3 /l + 
1.0 1.0 5 g/l 
None 8.6 8.6 
140 OK at 22-43 
Flow gradually 
4 g (NH.sub.4).sub.2 CO.sub.3 /l 
Na.sub.2 SO.sub.4 rpm slowed to 3.5 
cc/min at 110 
rpm 
19.sup.(3) 
4 g NH.sub.4 HCO.sub.3 /l + 
1.0 -- None -- 8.6 -- 57 OK at .about. 32 
-- 
4 g (NH.sub.4).sub.2 CO.sub.3 /l rpm 
20 4 g NH.sub.4 HCO.sub.3 /l + 
1.0 1.0 0.60 g/l 
4.3 g/l 
9.0 9.6 
110 OK at 35-118 
OK at 35-68 
4 g (NH.sub.4).sub.2 CO.sub.3 /l 
NH.sub.3 
NH.sub.3 rpm.sup.(7) 
rpm 
21 4 g NH.sub.4 HCO.sub.3 /l + 
1.0 1.0 1.1 g/l 
3.0 g/l 
9.0 9.6 
40 OK at 25-80 
OK at 25-49 
4 g (NH.sub.4).sub.2 CO.sub.3 /l 
NaOH NaOH rpm rpm 
22.sup.(4) 
8 g (NH.sub.4).sub.2 CO.sub.3 /l 
0 2.0 None None 8.78 
8.80 
A:130 Fell off 
OK at .about. 25 
B:60 2.6 cc/min 
rpm 
during last 
60 min at 
117 rpm 
23.sup.(2),(5) 
8 g (NH.sub.4).sub.2 CO.sub.3 /l 
0 2.0 None None 8.78 
8.80 
110 Fell to 2.2 
OK at .about. 30 
cc/min at 
rpm 
111 rpm 
during last 
80 min 
24 8 g (NH.sub.4).sub.2 CO.sub.3 /l 
2.0 2.0 None None 8.78 
8.80 
140 OK at .about. 25 
OK at .about. 25 
rpm during 
rpm 
last 100 
min 
25 8 g (NH.sub.4).sub.2 CO.sub.3 /l 
1.0 1.0 4.7 g/l 
13.8 g/l 
10.0 
10.0 
40 OK at 55 
1.2 cc/min at 
NaOH NH.sub.3 rpm 111 rpm 
26 4 g NH.sub.4 HCO.sub.3 /l + 
1.0 1.0 3.9 g/l 
3.85 g/l 
9.6 9.6 
70 OK at .about. 25 
1.3 cc/min at 
4 g (NH.sub.4).sub.2 CO.sub.3 /l 
NH.sub.3 
NaOH rpm 110 rpm 
27 4 g NH.sub.4 HCO.sub.3 /l + 
1.0 1.0 3.9 g/l 
3.85 g/l 
9.6 9.6 
60 OK at .about. 25 
1.2 cc/min at 
4 g (NH.sub.4).sub.2 CO.sub.3 /l 
NH.sub.3 
NaOH rpm 110 rpm 
28 4 g NH.sub.4 HCO.sub.3 /l + 
1.0 1.0 13.8 g/l 
5.05 g/l 
10.0 
10.0 
90 OK at .about. 25 
1.5 cc/min at 
4 g (NH.sub.4).sub.2 CO.sub.3 /l 
NH.sub.3 
NaOH rpm 114 rpm 
29 8 g (NH.sub.4).sub.2 CO.sub.3 /l 
1.0 1.0 9.3 g/l 
4.7 g/l 
10.0 
10.0 
110 OK at .about. 
OK at 
NH.sub.3 
NaOH 25-35 rpm 
25-35 rpm 
30 10 g NaHCO.sub.3 /l + 
0 2.0 None None 8.78 
8.95 
60 1.3 cc/min 
1.5 cc/min 
at .about. 110 
at 95 .fwdarw. 
113 
and then 
rpm 
&lt; 0.1 cc/min 
31 5 g NaHCO.sub.3 /l + 
0 1.0 None None 8.75 
9.02 
130 OK at 20-45 
3.0 cc/min at 
0.25 g Na.sub.2 CO.sub.3 /l rpm .about. 111 rpm; 
then down to 
0.3 cc/min 
32 10 g NH.sub.4 HCO.sub.3 /l + 
3.0 3.0 NH.sub.3 
NaOH 8.6 10.2 
70 OK at 23-77 
1.4 cc/min at 
2.5 g (NH.sub.4).sub.2 CO.sub.3 /l rpm; mostly 
115 rpm after 
at 54 15 
__________________________________________________________________________ 
min 
.sup.(1) Brackets denote runs using same ore charge. 
.sup.(2) After standing 2-3 days after previous runs. 
.sup.(3) After standing 90 min, after previous run. 
.sup.(4) Prior to this, leached with 600 cc of H.sub.2 O.sub.2 --free 
leach at 5 cc/min. 
.sup.(5) Prior to this, leached with 965 cc of H.sub.2 O.sub.2 --free 
leach at 5 cc/min. 
.sup.(6) "OK" means a 5 cc/min flowrate is maintainable at the pump speed 
(rpm's) indicated. 
.sup.(7) Flow improved greatly (only 30-56 rpm needed) for last 40 minute 
of this run, which followed a 44min noflow interlude. 
The data in Table 4 show the following. 
(1) Without silicate, permeability decreased during column leaching. 
Silicate in an NH.sub.3 -CO.sub.2 -H.sub.2 O.sub.2 leach improved 
permeability (Runs 16, 22 and 23). 
(2) Silicate improved permeability throughout the pH range 7-10 normally 
associated with in-situ uranium leaching. Some effect was seen even when 
total NH.sub.3 was &gt;10 g/l (e.g., Run 28). 
(3) In Runs 30 and 31 using a sodium carbonate/bicarbonate leach, silicate 
did not improve permeability. (Note, however, that inherent permeability 
using the sodium-based leach was also less than that of ammonium-based 
leach cited in the table.) 
(4) In most runs where a substantial concentration of NaOH (e.g., 3.85-5.05 
g/l) was added to the leach to raise a pH to 9.6 or 10.0, the beneficial 
effect of silicate on permeability was lost (See Runs 17 and 25-28). In 
fact, these caustic-fortified leaches seemed to cause even poorer 
permeability than silicate-free leaches containing no caustic. (Compare 
these last cited runs with Runs 16, 22 and 23.) 
In a minority of runs (Runs 21 and 29), however, the caustic fortification 
did not seem to interfere with permeability. Furthermore, note, in Run 18, 
that the addition of 5 g/l of Na.sub.2 SO.sub.4 caused no apparent loss in 
permeability. The conclusions to be drawn from these observations are 
that, for purposes of improving permeability in a carbonate leach 
containing H.sub.2 O.sub.2, 
(a) silicate is decidedly beneficial in an NH.sub.3 -CO.sub.2 system in a 
pH range at least as broad as pH 7-10, 
(b) that silicate may be beneficial in a carbonate leach containing both 
NH.sub.4.sup.+ and Na.sup.+ as counterions for carbonate and bicarbonate, 
and, 
(c) that carbonate/bicarbonate leaches containing only Na.sup.+ counterions 
appear to cause more permeability loss than silicate-containing NH.sub.3 
-CO.sub.2 formulations whether or not they contain silicate. 
EXAMPLE VIII 
In this series of tests, a comparison was made between the use of H.sub.2 
O.sub.2 as oxidant, both with and without silicate, and NaClO.sub.3 as 
oxidant without silicate. 
Test Conditions: 
Two companion runs at goal flow 5 cc/min. 
Basic Leach: 4 g ABC/l+4 g AC/l; pH 8.6 
Column A: 3 g NaSiO.sub.3 /l+1.8 g H.sub.2 O.sub.2 /l 
Column B: 10.8 g NaClO.sub.3 /l 
Ore: 100 g/column, containing about 0.85% uranium 
TABLE 5 
__________________________________________________________________________ 
ORE PERMEABILITY: HYDROGEN PEROXIDE VS SODIUM CHLORATE 
VOL. Uranium 
RUN. OXIDANT & LEACHATE 
LEACH FLOW % LOSS 
Extracted.sub.2 
RUN TIME 
pH ADDITIVE cc RATE, cc PUMP SPEED 
BY O.sub.2 
Mg.sup.(1) 
NO. MIN. 
A B A B A B A B rpm A B A B 
__________________________________________________________________________ 
33 80 8.72 
8.6 
H.sub.2 O.sub.2 + 
NaClO.sub.3 
400 
400 5.0 5.0 23-112 
23-34 
113 -- 221 
187 
3 g/l Sil 
34 70 8.72 
8.6 
H.sub.2 O.sub.2 + 
NaClO.sub.3 
398 
398 5.0 5.0 .about. 54 
.about. 32 
98 -- 79 
41 
3 g/l Sil 
35 120 8.72 
8.6 
H.sub.2 O.sub.2 + 
NaClO.sub.3 
600 
600 5.0 5.0 .about. 50 
.about. 50 
96 -- 127 
69 
3 g/l Sil 
25 Flush with 150 cc of basic leach and let stand overnight, no 
flow. 
36 170 8.6 
8.6 
H.sub.2 O.sub.2 
NaClO.sub.3 
850 
850 5.0 5.0 49-85 
25-30 
92 -- 100 
41 
only 
Let stand 75 min, no flow. 
37 140 H.sub.2 O.sub.2 
NaClO.sub.3 
700 
700 5.0 5.0 38-101 
22-24 
93 -- 95 
31 
38 50 only 192 
195 3.8 3.8 115 .about. 15 
-- -- -- -- 
7.5 Flush with basic leach (68 cc). 
Stand over weekend, no flow. 
39 60 H.sub.2 O.sub.2 + 
H.sub.2 O.sub.2 
250 
238 4.17 
4.0 20-73 
23-&gt; 85 
67 67 -- -- 
0.5 g/l 
only 
Sil 
40 60 H.sub.2 O.sub.2 + 
H.sub.2 O.sub.2 + 
210 
134 3.5 2.2 20-112 
21-114 
-- -- -- -- 
0.5 g/l 
1 g/l 
Sil Sil 
Let stand 70 min, no flow. 
41 150 H.sub.2 O.sub.2 + 
H.sub.2 O.sub.2 + 
740 
745 4.9 5.0 25-40 
40-75 
52 63 -- -- 
0.5 g/l 
1 g/l 
Sil Sil 
__________________________________________________________________________ 
.sup.(1) Determined by dibenzoyl methane colorimetry. 
Summary of Results: 
The following conclusions can be drawn from the data in Table 5. 
Loss of permeability is not associated with all oxidants. Note the 
excellent permeability with sodium chlorate, Runs 33-37B. On the other 
hand, the preceding examples showed that H.sub.2 O.sub.2 -containing leach 
in contact with ore caused loss of permeability. Furthermore, note from 
the gas collection data in Runs 33-37A that virtually all the H.sub.2 
O.sub.2 decomposed to O.sub.2 gas during passage over the ore bed. Thus, 
it would appear that the loss of permeability is occasioned by H.sub.2 
O.sub.2 and/or the attendant oxygen resulting from decomposition of the 
H.sub.2 O.sub.2 in contact with the ore. 
Runs 33-35 clearly show that a silicate fortified peroxide leach is also 
freely flowing. Both the chlorate and peroxide-silicate leaches flowed 
freely for 270 minutes, requiring on the average a pump speed of well 
below 50 rpm's. It is interesting to note here that the beneficial effects 
from silicate were sustained for a substantial period of time after 
silicate was removed from the leaching solution. However, the beneficial 
effects gradually fell off after silicate was removed from the leaching 
solution. See Runs 36A-38A following Runs 33A-35A. Compare especially the 
50-minute running period in Runs 38A, B. 
Though (non-plugging) chlorate is also a potential oxidant for solution 
leaching of uranium ore, it does suffer from the disadvantage of producing 
far more environmentally objectionable reaction products, such as chlorite 
and chloride ions. Furthermore, it is a less effective oxidant for 
leaching uranium as shown by the data in the last column. This was so even 
though twice as many moles of chlorate than H.sub.2 O.sub.2 were used, 
i.e., 0.101 vs. 0.053 moles/liter of each. 
EXAMPLE IX 
It was noted that when a leachate containing 10 g ABC/l+2.5 g AC/l+3 g 
sil/l was allowed to stand one or more days, a slight but quite noticeable 
haze or light cloudiness developed which indicates gelling of the 
silicate. This was even more noticeable by the Tyndall effect from a beam 
of light. After fortifying with 1.2 g H.sub.2 O.sub.2 /l, this aged 
solution was pumped through 50-100 g ore beds, which resulted in a marked 
loss of permeability for Ores B and C after less than 3 hours of leaching. 
There is no such loss when freshly made solution free of gellation is 
used. 
EXAMPLE X 
Following up on the findings of Example IX, the gellation stability of a 
number of leach compositions having varying salt contents was observed 
with respect to variations in silicate content. Hellige Turbidimeter data 
for the several leaches are given in Table 6 below: 
TABLE 6 
______________________________________ 
Gellation Stability 
A.P.H.A. TURBIDITY 
COM- UNITS.sup.(2) (ppm) 
POSI- LEACH AFTER 
TION COMPOSITION, g/l 
6 11 
NO..sup.(1) 
ABC AC SIL pH.sup.(1) 
DAYS DAYS 
______________________________________ 
1 -- 16 1.0 8.95 1.3 -- 
1A -- 16 1.0 8.40 -- 2.2 
2 -- 8 1.0 8.90 nil 0.2 
2A -- 8 1.0 8.20 -- 0.3 
3 -- 4 1.0 8.90 0.1 nil 
3A -- 4 1.0 8.20 -- nil 
4 8 8 1.0 8.80 1.3 1.2 
4A 8 8 1.0 8.20 -- 0.95 
5 4 4 1.0 8.80 0.70 nil 
5A 4 4 1.0 6.60 -- 0.1 
6 4 4 0.5 8.80 0.3 nil CLEAR 
6A 4 4 0.5 7.00 -- nil 
7 4 4 2.0 8.85 0.95 0.6 
7A 4 4 2.0 7.20 -- 1.2 
8.sup.(3) 
8 8 1.0.sup.(3) 
8.80 1.2 0.9 
8A.sup.(3) 
8 8 1.0.sup.(3) 
7.20 -- 1.2 
9.sup. (3) 
4 4 1.0.sup.(3) 
8.80 1.2 1.4 
9A.sup.(3) 
4 4 1.0.sup.(3) 
7.30 -- nil 
10.sup.(3) 
4 4 2.0.sup.(3) 
8.80 1.7 1.4 
10A.sup.(3) 
4 4 2.0.sup.(3) 
6.80 -- 0.4 
11 10 2.5 3.0 8.55 very gel on 
cloudy 
bottom 
of beaker 
12 10 2.5 3.0 8.55 very gel on 
cloudy 
bottom 
of beaker 
______________________________________ 
.sup.(1) For A series, each numbered sample was split at 6 days and the A 
series portion was adjusted downward with H.sub.2 SO.sub.4. Thus, only th 
last 5 days of the 11day readings (last column) were at the lowered pH fo 
A series solutions. 
.sup.(2) These values are from calibration curve supplied by Hellige for 
SiO.sub.2, and do not necessarily represent the actual ppm of SiO.sub.2 i 
these leaches. 
.sup.(3) From an aged (many months old) lab supply of sodium silicate tha 
had sediment on the bottom. All other runs used silicate from a new drum 
of Du Pont Grade F sodium silicate. 
During this work it was observed that cloudiness (and thus, gelling) of 
leach solutions could be completely avoided by using 2.0 g/l or less of 
silicate in a solution not too concentrated in salts, e.g., 10 g/l. Within 
the range pH 7-8.95, it didn't seem to matter much where the pH was. At pH 
10 and above, silicate is inherently free from gelling because of 
solubilization by base. 
Overall, for the clear solutions, the only suggestion of possible or 
incipient gelling, as manifested by somewhat higher turbidity readings, 
was for compositions containing high leach salt content (Compositions 
Number 1, 1A, 4, 4A, 8 and 8A), high silicate (Compositions 7, 7A and 10) 
or aged silicate (Compositions 8-10). 
Fortunately, the salt and silicate concentrations giving apparently 
non-gelling leaches coincide with the concentrations which are highly 
useful for leaching and prevention of permeability loss. 
EXAMPLE XI 
In this Example, extended runs were carried out which illustrate that 
silicate may in some instances be effective to stabilize the H.sub.2 
O.sub.2 solution from decomposition. 
In a companion run using 100 gram charges of Ore C, a 5 cc/min flow rate, 
and a basic leach containing 10 g ABC/l+2.5 g AC/l+1.80 g H.sub.2 O.sub.2 
/l (pH 8.2), the comparison tested the difference in adding or not adding 
3 g NaSiO.sub.3 /l to the leach. The run was for 330 minutes, and 
permeability loss was prevented by prior screening so the ore contained 
-12 +80 mesh particles. The results can be summed up as follows: 
______________________________________ 
Loss of O.sub.2 in cc/min 
Serial Time Without With 
Segments Silicate Silicate 
______________________________________ 
First 30 min -- -- 
2nd 100 min 2.4 1.05 
3rd 100 min 2.65 1.15 
4th 100 min 3.05 1.05 
TOTAL - 330 min 2.80 1.26 
Stand overnight -- -- 
with no flow 
100 2.35 0.95 
______________________________________ 
The O.sub.2 loss for the 330 minutes corresponded to an 84% loss of H.sub.2 
O.sub.2 in the leach when the leach contained no silicate; only 37% when 
the leach contained silicate. 
These results showed that silicate not only improved H.sub.2 O.sub.2 
stability during leaching, but also seemed to prevent an increase in 
instability with time.