CA1112459A - Composition and method for solution mining of uranium ores - Google Patents
Composition and method for solution mining of uranium oresInfo
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- CA1112459A CA1112459A CA290,337A CA290337A CA1112459A CA 1112459 A CA1112459 A CA 1112459A CA 290337 A CA290337 A CA 290337A CA 1112459 A CA1112459 A CA 1112459A
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Abstract
ABSTRACT
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 improved by inclusion of a small amount of alkali metal silicate dissolved in the leaching solution.
The silicate also improves the stability of the oxident in many instances.
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 improved by inclusion of a small amount of alkali metal silicate dissolved in the leaching solution.
The silicate also improves the stability of the oxident in many instances.
Description
FIELD OF T~E II~ NTION
_, . .
The invention is concerned with the solutlon mining of uranium ores and particularly with maintaining the permeability o~ the uranium ore formations upon treatment with oxidative leaching solutions.
BACKGROUND OF THE INVENTION
.
With the increasing use of nuclear power plants ~or the production of electricity in the United States, uranium ore deposits have become an increasingly valuable natural resource. Lven though there are extensive uranium deposits distributed throughout the Western United States, many o~ 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 co~ven-tional 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 ~ormation and a plurality o~ regularly spaced in~ection wells drilled aro~nd the production well. To start produc-tlon~ a leachin~ solution is pumped into the ore ~ormation through the in~ection wells. The solution moves through the formation dissolving the uranium compounds in the ore as ~t passes toward the center of the ore ~ormation ~rom which it is removed by means of the production well. The leaching ~olut,ion cont;aining the dissolved uranium is then pumped to a~ extraction treatment zone hhere the leaching solution is treated to separate ~he uraniwQ compounds~
5~
Several ~olution mining (in-situ leaching) pro-cesses have been suggested. For example, the ~olvent 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 (l) ad~ust~ng the pH of the solution to neutral or bas1c pH to precipitate out the uranium, (2) separating the uranlum compounds by ion exchange or (~) 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 ion~ are pre-- ferred in many instances because they are less likely to interfere with permeability o~ the ore ~ormation.
Because uranium in the 4+ valence state is insolu-ble 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 equat~ons:
(l) UOz + 1/2 2` ~U09
_, . .
The invention is concerned with the solutlon mining of uranium ores and particularly with maintaining the permeability o~ the uranium ore formations upon treatment with oxidative leaching solutions.
BACKGROUND OF THE INVENTION
.
With the increasing use of nuclear power plants ~or the production of electricity in the United States, uranium ore deposits have become an increasingly valuable natural resource. Lven though there are extensive uranium deposits distributed throughout the Western United States, many o~ 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 co~ven-tional 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 ~ormation and a plurality o~ regularly spaced in~ection wells drilled aro~nd the production well. To start produc-tlon~ a leachin~ solution is pumped into the ore ~ormation through the in~ection wells. The solution moves through the formation dissolving the uranium compounds in the ore as ~t passes toward the center of the ore ~ormation ~rom which it is removed by means of the production well. The leaching ~olut,ion cont;aining the dissolved uranium is then pumped to a~ extraction treatment zone hhere the leaching solution is treated to separate ~he uraniwQ compounds~
5~
Several ~olution mining (in-situ leaching) pro-cesses have been suggested. For example, the ~olvent 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 (l) ad~ust~ng the pH of the solution to neutral or bas1c pH to precipitate out the uranium, (2) separating the uranlum compounds by ion exchange or (~) 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 ion~ are pre-- ferred in many instances because they are less likely to interfere with permeability o~ the ore ~ormation.
Because uranium in the 4+ valence state is insolu-ble 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 equat~ons:
(l) UOz + 1/2 2` ~U09
(2) UO3 + H20 ~ 3 C03 - ~ U02 ( ~3 ) 3 + 20H
The hydroxyl ions produced in reaction (2 ) tend to - cause formation o~ insoluble uranium compounds, especially when sodium ions are also present. The -OH ions can, how-ever, be readily removed by reaction with bicarbonate ~ons which favorably a~fect the e~uilibri~l o~ the solubilizing reaction as well as pre~ent precipitation of insoluble uranium compounds such as sodium uranate. Thus, it is usually pre~erred to use carbonate leaching solutions ~0 containing enough blcarbonat~ to react with hydroxyl ions formed in the manner of reaction (2).
Though many oxidlzing agents have been s~ggested and tried for this use, hydrogen peroxlde and molecular oxygen (2) are especially desirable ~or this use because they and their decomposition products -- 2 and H20 -- are completely non-polluting and thus ecologically acceptable.
Hydrogen peroxide is preferred, however, because it can be introduced as a ll~uid that contains oxidant in highly concentrated form, whereas the concentratlon of in;ected oxygen gas is highly limited by its solubility. As a consequence, the liquid oxidant is less likely than a gas to cause vapor lockin~ within the ore body. Even when the hydrogen peroxide does decompose in contact with the ore, the 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 o~ oxygen solubilized in leach solution. Thus, there is greater potential for increasing the reaction rates for solubil~ 7~ing the insoluble uranlum compounds in the ore.
The chemistry of uranium leaching i5 less well characterized fcr hydrogen peroxide than for oxygen. Con-ceivably, by analogy with equation (1) above, the reaction may be:
U0z ~ H202 ~ UO2+~ ~ 20H
However, uranium in the 6+ valence state is known to form peroxy addition compounds such as U& ~, and it is entirely likely that one or more peroxy co~pounds are involved in the overall chemistry. Suffice it to sa~, however, that H202 ls a potential oxldant either as H202 or as a latent source o~ Oz.
g The use of either molecular oxygen or hydrogen peroxide in alkaline carbonate-leaches m~y contribute to the tendency of the formatlon to become le3s 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 &nd/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 lnjection and production wells~ in some instances appear to cause loss of permeability.
BRIEF DESCRIPTION OF THE INVENTION
It has now been found that in the solution mining of uranium ores using ammonlum carbonate solutions (as defined hereinbelow) containing ~22~ 2 or mixtures thereo~ a8 oxidant, the tendency of the formation being treated to become less permeable during the leaching process can be overcome by including in the leaching solution a very small concentration 3f sodium silicate.
DISCUSSION OF THE PRIOR ART
The problem of maintain~ng permeability o~ an ore body during leaching is not a new one. For example, in U.S. Patent 3,309,140, Gardner et al propose the addition of polyacrylamide to an acid~c leaching solut~on containing sodium chlorate as an oxidant. U.S. Patent 3,567,427 mentions that hydrogen peroxide can be effective for the disaggregation of certain clay n~nerals9 which suggests that hydrogen peroxide might ~e troublesome in applications such as solution mining where disaggregation is to be avoided.
These references obvlously do not, however, address S~
themselves to the problem of maintaining permeability in the presence of hydrogen peroxide. De Vries in U.S. 3,908,388 discloses the use of the reaction product of a non-aqueous slurry of alkal~ metal æilicate with an alkyl amide to insolubilize the alkali metal silicate for the purpose of stabilizing sand and thus to maintain o11 permeability.
Also, Peeler in U.S. 2,968,572 employs similar amides to insolubilize aqueous alkali metal silicates for so~l stabilization in the presence o~ ground moi~ture. However, the problem contemplated there was oil permeability, not water permeability. Furthermore, no oxidant was present ln the system and higher silicate concentrations were used.
Several other U.S. patents disclose the use o*
many other agents ~or gelling or setting alkali metal sili-cates to make them useful for soil stabilization, e.g., the ~ollowing:
U.S. 583,166 Portland cement U.S. 3,288,o40 Alkali metal hexafluorosilicate U.S. 3,558,506 Methyl Cl 3 acylates-Thus, the use of alkali metal siIicates for the purpose of80il 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 solidify-ing the dissolved silicate.
DETAILED DESCRIPTION OF THE INVENTION
The process of the in~ention is applicable generally to the use o~ ammonium carbonate leaching solu-tions 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 exten~ive and may be virtually complete in some instances.
As used herein, the term "ammonium carbonate leaching solutions" means aqueous solutions of NH3 and COz.
Such solution will ordinarily have an initial pH, i.e., prior to in~ection into the ore formations, of 7;10. m ough the concentration of NH3 and CO2 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 =C03 or -HCO3. From 1 to 10 grams per liter are preferred. Such solutions are prepared most easily by sparging NH3 and C02 into water until the desired concentrations of chemical reactants are reached and then ad~usting the pH by the addition of more NH3 to raise the pH
or C2 to lower pH. They can, howe~er, also be made by dissolvin~ the solid carbonates in the water and then ad~usting pH in the same manner only altering the propor-tions of the solid carbonates. Typically, an ammoniumcarbonate leaching solution will contain from about 10 to 15 grams o~ 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 economlc or technical parameters associated with the par-ticular formation belng treated~ such as pH, particle size and temperature~ may be more importan~ and may even be overriding considerations. Ordinarily, however, the aqueous leaching solution wlll contain 0.1-10 grams H202 per liter and preferably O.2-2 grams H202 per liter.
Hydrogen peroxide suitable for use ln the inven-tion is available commercially in aqueous solutions con-taining from 10 to 90% by weight H202, any of which can be used in the invention. As used in accordance with the invention, hydrogen peroxide has very little effect on pK
of the leaching solution and therefore need not ordinarily be a factor in adjusting pH of the leaching solution. These H202 solutions may in some instances contain one or more stabilizers to inhibit decomposition such as those which are disclosed in U.S. Patents 2,872,2~3, 3,122,417, 3,387,939,
The hydroxyl ions produced in reaction (2 ) tend to - cause formation o~ insoluble uranium compounds, especially when sodium ions are also present. The -OH ions can, how-ever, be readily removed by reaction with bicarbonate ~ons which favorably a~fect the e~uilibri~l o~ the solubilizing reaction as well as pre~ent precipitation of insoluble uranium compounds such as sodium uranate. Thus, it is usually pre~erred to use carbonate leaching solutions ~0 containing enough blcarbonat~ to react with hydroxyl ions formed in the manner of reaction (2).
Though many oxidlzing agents have been s~ggested and tried for this use, hydrogen peroxlde and molecular oxygen (2) are especially desirable ~or this use because they and their decomposition products -- 2 and H20 -- are completely non-polluting and thus ecologically acceptable.
Hydrogen peroxide is preferred, however, because it can be introduced as a ll~uid that contains oxidant in highly concentrated form, whereas the concentratlon of in;ected oxygen gas is highly limited by its solubility. As a consequence, the liquid oxidant is less likely than a gas to cause vapor lockin~ within the ore body. Even when the hydrogen peroxide does decompose in contact with the ore, the 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 o~ oxygen solubilized in leach solution. Thus, there is greater potential for increasing the reaction rates for solubil~ 7~ing the insoluble uranlum compounds in the ore.
The chemistry of uranium leaching i5 less well characterized fcr hydrogen peroxide than for oxygen. Con-ceivably, by analogy with equation (1) above, the reaction may be:
U0z ~ H202 ~ UO2+~ ~ 20H
However, uranium in the 6+ valence state is known to form peroxy addition compounds such as U& ~, and it is entirely likely that one or more peroxy co~pounds are involved in the overall chemistry. Suffice it to sa~, however, that H202 ls a potential oxldant either as H202 or as a latent source o~ Oz.
g The use of either molecular oxygen or hydrogen peroxide in alkaline carbonate-leaches m~y contribute to the tendency of the formatlon to become le3s 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 &nd/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 lnjection and production wells~ in some instances appear to cause loss of permeability.
BRIEF DESCRIPTION OF THE INVENTION
It has now been found that in the solution mining of uranium ores using ammonlum carbonate solutions (as defined hereinbelow) containing ~22~ 2 or mixtures thereo~ a8 oxidant, the tendency of the formation being treated to become less permeable during the leaching process can be overcome by including in the leaching solution a very small concentration 3f sodium silicate.
DISCUSSION OF THE PRIOR ART
The problem of maintain~ng permeability o~ an ore body during leaching is not a new one. For example, in U.S. Patent 3,309,140, Gardner et al propose the addition of polyacrylamide to an acid~c leaching solut~on containing sodium chlorate as an oxidant. U.S. Patent 3,567,427 mentions that hydrogen peroxide can be effective for the disaggregation of certain clay n~nerals9 which suggests that hydrogen peroxide might ~e troublesome in applications such as solution mining where disaggregation is to be avoided.
These references obvlously do not, however, address S~
themselves to the problem of maintaining permeability in the presence of hydrogen peroxide. De Vries in U.S. 3,908,388 discloses the use of the reaction product of a non-aqueous slurry of alkal~ metal æilicate with an alkyl amide to insolubilize the alkali metal silicate for the purpose of stabilizing sand and thus to maintain o11 permeability.
Also, Peeler in U.S. 2,968,572 employs similar amides to insolubilize aqueous alkali metal silicates for so~l stabilization in the presence o~ ground moi~ture. However, the problem contemplated there was oil permeability, not water permeability. Furthermore, no oxidant was present ln the system and higher silicate concentrations were used.
Several other U.S. patents disclose the use o*
many other agents ~or gelling or setting alkali metal sili-cates to make them useful for soil stabilization, e.g., the ~ollowing:
U.S. 583,166 Portland cement U.S. 3,288,o40 Alkali metal hexafluorosilicate U.S. 3,558,506 Methyl Cl 3 acylates-Thus, the use of alkali metal siIicates for the purpose of80il 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 solidify-ing the dissolved silicate.
DETAILED DESCRIPTION OF THE INVENTION
The process of the in~ention is applicable generally to the use o~ ammonium carbonate leaching solu-tions 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 exten~ive and may be virtually complete in some instances.
As used herein, the term "ammonium carbonate leaching solutions" means aqueous solutions of NH3 and COz.
Such solution will ordinarily have an initial pH, i.e., prior to in~ection into the ore formations, of 7;10. m ough the concentration of NH3 and CO2 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 =C03 or -HCO3. From 1 to 10 grams per liter are preferred. Such solutions are prepared most easily by sparging NH3 and C02 into water until the desired concentrations of chemical reactants are reached and then ad~usting the pH by the addition of more NH3 to raise the pH
or C2 to lower pH. They can, howe~er, also be made by dissolvin~ the solid carbonates in the water and then ad~usting pH in the same manner only altering the propor-tions of the solid carbonates. Typically, an ammoniumcarbonate leaching solution will contain from about 10 to 15 grams o~ 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 economlc or technical parameters associated with the par-ticular formation belng treated~ such as pH, particle size and temperature~ may be more importan~ and may even be overriding considerations. Ordinarily, however, the aqueous leaching solution wlll contain 0.1-10 grams H202 per liter and preferably O.2-2 grams H202 per liter.
Hydrogen peroxide suitable for use ln the inven-tion is available commercially in aqueous solutions con-taining from 10 to 90% by weight H202, any of which can be used in the invention. As used in accordance with the invention, hydrogen peroxide has very little effect on pK
of the leaching solution and therefore need not ordinarily be a factor in adjusting pH of the leaching solution. These H202 solutions may in some instances contain one or more stabilizers to inhibit decomposition such as those which are disclosed in U.S. Patents 2,872,2~3, 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 i5 not essential to the practice of the invention.
It has been found that only a very small concen-tration of alkali metal silicate per liter of total leach-ing solution is needed to reduc~e loss of permeability within the formation signi~icantly. The minimum effective conce-tration of silicate is highly sub~ective to the formation being treated and its particular physical and chemical characteri~tlcs. However, ordinarily at least a~out 0.1 and preferably 0.2 gram of alkali metal silicate wlll be used per liter of total leaching solution. However, more signi-~icant effects are produced if at least about 0.5 gram per liter is used. An optimum concentration of alkali metal sllicate appears to be 0.5-1.5 gram per liter. Even though hi~her conccntrations of alkali metal ~licate (e.g.~ 5 g/l) may be uscd, no further ad~antage wlth re~pect to perme-g ability was apparent from such use. Furthermore, the use OI` -higher concentrations in some inst~lces will signiflcan~ly ~ -increase the incidence of gelling the silic~te which will cause a loss in permeability of the ore ~ormation. However, it has been found that leaching solutions containing as high as 10 grams of NH3-CO2 per liter and even higher and the pre~erred 0.5-1.5 gram of silicate per liter resist gellation for quite long periods oP time.
Suitable alkali metal silicates include silicates of sodium, potassium and lithium, of which sodium is pre-ferred. The silicates must, howe~er, be stable aqueous æolutions which contain no appreciable amount of particulate silica. Transparent solutions which exhibit little, if any, visible Tyndall effect, are uniformly suitabl~ with respect to stabili~y against los~ of permeability induced by gella-tion. Suitable aqueous ~odium silicate solutions are available having Si02 :Na20 weight ratios of from 1.90 to 3.2~ and containing from 27.0 to 36.o% wt Si02 and from 8.7 to 19.4~ wt Na20. Sodium silicate solutions of this type are alkaline and ha~e a pH range of between 10 and 13. The addition o~ sodium silicate in these amounts has only a small e~ect in ele~ating pH of the leaching solution.
In preparing l~aching solutions for the purpose of the invention~ no particular order o~ mixing is needed.
The in~ention is exemplified and can readily be understood by reference to the examples which are se~ out hereinbelow.
DEFINITIONS AND ABBREVIATIONS
ABC = ammonium bicarbonate ~ NH~HCO3 3 AC = ammonlum carbonate ~ (NH4) 2C03 NH3-CO2 or "carbonate" refers broadly to aqueous leach solutions of NH3 and CO2 containing ammonium carbo-nate, ammonium bicarbonate or mixtures thereof.
"Goal flow" or "goal flow rate" refer to a pre-determined flow rate to be maintained during a run (within the capabilities o~ 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.
"Ieach" refers to the solution fed from the inlet reservoir to the top o~ the leach column.
"Leachate" refers to the solution pumped from the bottom o~ a leach column after passing through the ore bed.
The terms "silicate"~ "sodium silicate", "sil- It~
and "NaSiO3" may be used interchangeably. All weights or concentrations are on the basis o~ Du Pont sodium silicate, Grade F or Grade No. 9 diluted to the same solids as Grade F.
Both Grades have an SiO:Na20 weight ratio o~ 3.25.
EXPERIMENTAL APPARATUS 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 ~eed pump on the outlet o~ the inlet reservoir communicating with (3) a leaching column contain-ing a fixed bed o~ ~inely divided uranlum ore having a depth {n most cases o~ about 2.~ 10 cm, (4) a peristaltlc leachate pump on the outlet of the leach column discharging into (5) a leachate reser~oir. The ~apor space in the tops o the leach columns, the leachate reservoir and inlet reservoir were each mani~olded to a gas collection burette so that any 2 gas release in the system could be measured.
2. Procedure (1) Pack leach columns with ore charge re~tlng atop a glass wool plug on a coarse fritted glass disk. Tamping was generally not required to preYent voids;
(2) Charge inlet reser~oirs with one liter of leaching solution with ingredients being added in the following order: NH4HCO3 and/or (NH4)2CO3, sodium silicate solution and H202 solution;
(3) Pump leaching solution into leach columns to permeate to bottom of ore bsd and cont~nue pumping rate;
It has been found that only a very small concen-tration of alkali metal silicate per liter of total leach-ing solution is needed to reduc~e loss of permeability within the formation signi~icantly. The minimum effective conce-tration of silicate is highly sub~ective to the formation being treated and its particular physical and chemical characteri~tlcs. However, ordinarily at least a~out 0.1 and preferably 0.2 gram of alkali metal silicate wlll be used per liter of total leaching solution. However, more signi-~icant effects are produced if at least about 0.5 gram per liter is used. An optimum concentration of alkali metal sllicate appears to be 0.5-1.5 gram per liter. Even though hi~her conccntrations of alkali metal ~licate (e.g.~ 5 g/l) may be uscd, no further ad~antage wlth re~pect to perme-g ability was apparent from such use. Furthermore, the use OI` -higher concentrations in some inst~lces will signiflcan~ly ~ -increase the incidence of gelling the silic~te which will cause a loss in permeability of the ore ~ormation. However, it has been found that leaching solutions containing as high as 10 grams of NH3-CO2 per liter and even higher and the pre~erred 0.5-1.5 gram of silicate per liter resist gellation for quite long periods oP time.
Suitable alkali metal silicates include silicates of sodium, potassium and lithium, of which sodium is pre-ferred. The silicates must, howe~er, be stable aqueous æolutions which contain no appreciable amount of particulate silica. Transparent solutions which exhibit little, if any, visible Tyndall effect, are uniformly suitabl~ with respect to stabili~y against los~ of permeability induced by gella-tion. Suitable aqueous ~odium silicate solutions are available having Si02 :Na20 weight ratios of from 1.90 to 3.2~ and containing from 27.0 to 36.o% wt Si02 and from 8.7 to 19.4~ wt Na20. Sodium silicate solutions of this type are alkaline and ha~e a pH range of between 10 and 13. The addition o~ sodium silicate in these amounts has only a small e~ect in ele~ating pH of the leaching solution.
In preparing l~aching solutions for the purpose of the invention~ no particular order o~ mixing is needed.
The in~ention is exemplified and can readily be understood by reference to the examples which are se~ out hereinbelow.
DEFINITIONS AND ABBREVIATIONS
ABC = ammonium bicarbonate ~ NH~HCO3 3 AC = ammonlum carbonate ~ (NH4) 2C03 NH3-CO2 or "carbonate" refers broadly to aqueous leach solutions of NH3 and CO2 containing ammonium carbo-nate, ammonium bicarbonate or mixtures thereof.
"Goal flow" or "goal flow rate" refer to a pre-determined flow rate to be maintained during a run (within the capabilities o~ 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.
"Ieach" refers to the solution fed from the inlet reservoir to the top o~ the leach column.
"Leachate" refers to the solution pumped from the bottom o~ a leach column after passing through the ore bed.
The terms "silicate"~ "sodium silicate", "sil- It~
and "NaSiO3" may be used interchangeably. All weights or concentrations are on the basis o~ Du Pont sodium silicate, Grade F or Grade No. 9 diluted to the same solids as Grade F.
Both Grades have an SiO:Na20 weight ratio o~ 3.25.
EXPERIMENTAL APPARATUS 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 ~eed pump on the outlet o~ the inlet reservoir communicating with (3) a leaching column contain-ing a fixed bed o~ ~inely divided uranlum ore having a depth {n most cases o~ about 2.~ 10 cm, (4) a peristaltlc leachate pump on the outlet of the leach column discharging into (5) a leachate reser~oir. The ~apor space in the tops o the leach columns, the leachate reservoir and inlet reservoir were each mani~olded to a gas collection burette so that any 2 gas release in the system could be measured.
2. Procedure (1) Pack leach columns with ore charge re~tlng atop a glass wool plug on a coarse fritted glass disk. Tamping was generally not required to preYent voids;
(2) Charge inlet reser~oirs with one liter of leaching solution with ingredients being added in the following order: NH4HCO3 and/or (NH4)2CO3, sodium silicate solution and H202 solution;
(3) Pump leaching solution into leach columns to permeate to bottom of ore bsd and cont~nue pumping rate;
(4) Acti~ate leachate pump and establish as nearly as possible a predetermined leach flow through both systems.
Pump speeds are recorded.
3, Ore Characteristics A. A high-uranium ore containing o.85% wt ~ and about 21% wt CaC03 from a South Texas site. Material was dry (1-1.4~ wt H20 based on drying loss at 110C) and free flowing.
B. A weakly mineralized ore o~ sandy consistency containing only about 0.0~% wt U rich in pyrite also from South Texas. Material was su~ficiently wet (12~14~ wt H20) that it did not flow freely but was easily spooned into the leach column.
C. A very weakly mineralized ore containing less than
Pump speeds are recorded.
3, Ore Characteristics A. A high-uranium ore containing o.85% wt ~ and about 21% wt CaC03 from a South Texas site. Material was dry (1-1.4~ wt H20 based on drying loss at 110C) and free flowing.
B. A weakly mineralized ore o~ sandy consistency containing only about 0.0~% wt U rich in pyrite also from South Texas. Material was su~ficiently wet (12~14~ wt H20) 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 Determinin~ H202 Loss Durin~, Leach~ng A. By Gas Collection As described above, n~ifolded flexible tubing conveyed all 02 gas released by II~02 decomposition from the 45~
leach col~ the inlet reservoir and the leachate collec-tlon reservoir into an inverted gas collection cylinder.
The percent of H202 decomposed (% converted to 02 ) after a time (t) in which a certain volume (liters) of leachate, containing a certain concentration of H202 was collected, was computed as follows:
CC 02 collected converted to STP
liters of leachate x g H202/l leach x 3~-~-x 2 The collected gas volume was converted to STP by multiplyin~
the observed volume by 0.9. This conversion factor was based on the finding that when 1.8 g of H202 was contacted with three dif~erent ores and the released gas collected by displacement of water, the following relation was obtained:
Stoichiometric 0? from equation 2H202 >2H~0 ~ 0~ , O 9O~O 03 se~ved 02 re ea~ed B. By Titration Assuming that the Hz02 in the inlet reser~oir is stable, the H202 lost solely to leaching can be measured by titrati~g a grab sample from the column. This was generally done by collecting at the end of a run (without interrupt-ing flow) a 100 cc sample of leachate at the same flow rate (mostly 5 cc/min) as used during the run. Then 20 cc ali-quots of the 100 cc sample and of the leach in the inlet reservoir were titrated by standard iodimetry:
% H2O2 lost _ ~ e~t~~eservOi-rGTitb Sam~le Titr~
Unless otherwise stated, analysis of "H2G2 lost by titration" i3 by titration of a grab-sample rather than of the collected leachate.
EX~LE I
. .
This example lllustrates both the effect of a leaching solution containing II202 in reduc:lng permeability of an orc body and the reversal of that effect by addlng - l? -24~9 aqueou~ sodium silicate to the leaching ~olution.
Using the ore A, a leach solution containing 10 gABC/l, 2.5 g AC/l and 1.2 g H22/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 out-fall 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 leach, a flow rate of 10 cc/min was easily maintained over a 65 mlnute period, to collect 650 cc of leachate. Using no silicate in the companion run~ it too~ 98 minutes to collect 620 cc of leach, even though the outlet pump was at a much hlgher speed.
EXAMPLE II
In this series of tests, permeability of the ore bed was examined as a ~unction of H202 in the leaching solution, pH and silicate in the leaching solution. -One hundred grams o~ Ore C were extracted in companion 42 mm leachlng columns using a basic leach containing 10 g ABC/l + 2.5 g AC/l adjusted to pH 8.6 with NHs or to pH 10.2 with ~aOH. Goal flow rate wa~ 5 cc/min. The results are given in Table 1.
g Cu~ulative Running Basic Leach ~difications Leach Flow Rate cc/min in. Column A(l) Column B( ) Column A Column B
o-60 as is as is 5 cc/min at Similar (no H20z) (no H202) 25 rpm pump speed 60-68 " " 12.8 cc/min Similar at 58 rpm 68-108 l.&g H202/l 1.8g H202/l Slowed to Similar 4-5 cc/min at ~ 110 rpm 108-144 " Also added 3.6 cc/min 6.1 cc/min 3g NaSiO3/l at 50 rpm at 50 rpm - (l)Leachlng solution pH 8.6 - (2)Leaching solution pH 10.2 Summary of Results:
With no H202 in either formulatlon, the pump 2Q 6etting 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 H202 caused a very noticeable loss in the rate at which leach 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 o.6 in. during the period when no H202 was in the leach. However, the vacuum gradually increased to 20-21 in. of mercury during the 40-minute leach period after H202 was added.
....
Note in the last 36-minute time period that the addition of silicate to the p~ 10.2 leach 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 NH3-CO2 leach containing 1.8 g H202/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 NaSiO3/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-mlnute flow period, an average 6.3 cc/min flow rate was obtained as the pump speed ~ell to 42 rpm and the vacuum fell to about 7 in.
EXAMPLE III
In this test series, the ad~erse e~fect of H202 on permeability and its prevention by use of sodium silicate addition were demonstrated on Ore B using a basic leach conta~ning 4 g ABC/l + 4 g AC/l. The results are g~ven ~n Table 2.
m oo 0 ~ , 1~- g ¢ ~ 0 O 0~ 1 0 ~1 u~ ~ ~o m ~ ~ ' ~; V N C~J
O ~
~C~ ¢
~ O
V ~J N ~1 ~1 0 CU . ~ ~
~1 m o~
I
tl~ I I I ~ N .C N
~1 ~0 ~ ~0 b~
O V ~ ~ ~ ~N
C) q-l bD O bD O
~ q~ ~ ,_ O ~ O
1~ ~ ¢ O 0~ 0 C~ ao 0~3 0 = ~ S~ N ,r: N -O ":50 ~0~ ~0 O ~ ~N ~ ~ ~rt ~ ~N
~} bD ~ h ~ a '' ~ ~ ~
o ~ a) 0 o o ~ O O OO bD h ~1 ~ :~ O
~ ~ ~ h ~t ~ ~ o ~
o P; Pl 'I '`J ~ ~ ,,~
~.
4~
EXAMPLE IV
In this series of tests, the e~fect of the follow-ing ~ariables upon peImeability was studied: (1) adding H202 with and without silicate; (2) discontinuing silicate addition; and (3) ef~ect of adding silicate after perme-ability 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 compariæon runs, columns A and B were first flushed with 500 cc of peroxide-free bas~c 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 H202/l was added to the leach 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 wh~ch 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 bene~icial in preventing loss of permeability, but also that the beneficial ef~ect is sustained for a substantial period of time after silicate ~s remQved from the leaching solution.
In a similar comp~ion set of runs~ partial plugging w~s lnduced by pumping through 320 cc of silicate-free leach containing 1.20 g H202~1 ~or 56 minutes, as a result of which fl ow diminished to belo~ 5 cc/r~n 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 ~or 72 minutes, lt became possible to p~np 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 t~mporary relie~ 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 experintent indicates that permeability, even after being partially lost during leaching with a peroxide-containing am~lonium 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.
EX~IPLE V
-In this series of tests, the following effects were examined:
(1) Loss of permea~ ty with peroxide leach (2) Use o~ silicate to prevent loss o~ permeability, and (3) Use o~ silicate to restore permeability once lost.
Table 1 is a running log of comp~lion leach experiments uslng the basic leach 4 g ABC~ 4 g AC/l (equivalent, by calculation to 2.28 g NH3/l and 4.o6 g COz/l) + 1.80 g H202/l, and 100 gram charges (ln the 42 mm I.D. colu~ns) of ore A. Information on permeability is glven by the "Leachate Flow Rate" column in Table 3 in con~unction with data on pu~p rpm's below in the text.
Information on Hz02 lost during leaching is based on Oz loss (last column in table).
~l ~ ~ o ~ ~ ~
~ ~ ¢1 ~ ~ ~ C~ ~ ~
o ~i ~ x ~:J F~ O O C~J O 0 h I C~l ~ ~ ~C) ~ .
~ N c) ¦ Lf~ Ir~ U'~ C~l ~1 ¢~ ~ ¢1 ~
~ ~ h O X
~ ~ ,1 m ", x ~ h O ~; ~¢~ o ~0 -i ~ ~ ~o~ g ¢ ~ ~,,`m a) ~
E~ c~; ~ ~ cd h I ,~
q O ~; O .-1 R
m ~ ~ ~ O ~ h C~
C ~ C~ ~ a:~ co 0 ~ 0 1~ ~3 ~ ., v~ ~ ~D ~ ~D bO ~D t~a ~D ~D C- CU I a) E4 H ¢ h h E~ oP P ~ ~ ~
~i ~ 0 ~ O ~ ~ ~
~ o~ O ~1 P~
~Z~5~
~ r ~
H ~ O
~i~ 5 ~
~ r~ J ~ ~ O ~li r ~ ¢ ~ ~
u~ ~ rl ~ ~ ~ ~ h ~-~ C3 a~ ~ ~1 ~3 S
~~; O ~ H~ C) O +~ ~I
P~ X ~ ~ ~
~ O X
The ~ollowing can be concluded ~rom these data:
Permeability graduaIly diminished over the 187 minutes (Runs 6-8) for the ammonium carbonate/bicarbonate leach containing H202 and no silicate, even though the pump speed had incr~ased to < 110 rpm. However, permeability was largely restored when 4 g/l of silicate was added to the leach. In this regard, compare the 35-minute and 50-minute running periods of Runs 10 and 9, but note that a no-~low 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 ~Run lOB) was obtained at a pump speed of 62 rpm; the comparative 1.22 cc/min rate (Run lOQ) was o~tained at 115 rpm.
When silicate was then added to the silicate-free column that had been used as a control in Run 9, there was a marked improvement in permeability. Note, however, (Run 11) that permeability was not ~mproved 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.
EXA~LE_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 con-taining 4 g ABC/l ~ 4 g AC/l ~ 1.8 g II202~1, the other with the same solution fortified with O.2 g~l o~ sodium silicate.
Leachate was pumped from both col~ outlets using the s~me pump rpmO ~he leach containin~ 0.2 g~l of silicate flow~d ~0 noticeably better, about 1.3 tlnles faster th~l the leach containing no silicate for the first 80 minute~, 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 impro~ed to the point that it was as good as, or ~lightly better than, the leach containing 0.2 g/l of sodium silicate.
In another 60-minute comparative run, leach con-taining 1 g/l of sodium silicate Mowed easily at 5 cc/min at pump settings of 45-65 rpm. With no silicate the average flo~Y over this period was only 3.6 cc/min, e~en though the pump speed was increased from 65 to 118 rpm during the run.
E ~ ~LE 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 companlon runs using different leaches containing 1.80 g H202/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 ha~ing 0-120 rpm range was attempted.
The ore had been sieved to -12+80 mesh, but the particles were so~t (to finger crushing) and clay-like in appearance. When wetted in the column, the largel pieces seemed to lose their particulate identity and the wetted plug seemed to be a fairly uniform, sandy, clay-like ~ggre~ate.
~ ~ u~ o _~ ~1 ~ ~o l,~ N
i~ ~ rl 0 ~
P. ~ O ~ ~1 C~ ~ I ~ P-~3: O S~ 0 ~ h IO h O h O h ~3 CIC) 0 ~ ~ 1 0 0 N
~i ¢ C) OC)W~P~
1--1 C) L~ h ~ ~ 0 ~ o ~ , V ~ ~ h O h O h O h O S'l O hE' ~J ~ ~r) ~1 ~ .~ O
Z ~ ~ :Z O O O t- O C) ~
H ~ ~D ~-- ~ (~ ~ ~
~ ~0 ~ a~ 00 +~d 0 O~ ao I cr o~ 0 E~; ~:
o~ ~ ¢I~D O ~ ~ ~' E~ oo ~ 0 a) ~ ~ ~
:~ Iq ~
1~ ~ V2 ~ 5 o~ g ~ oo~
¢ Yi ~ E~
E~ ~ O
~ Q ~ ~ ~1 ~ EO~ ¢ a) ~ Q~ w~ ~
~ ~ ~ ~10~ ~
~1 ~ ; o~
:~; I I O o o 5 O O O
o m~ i CU
H
~ ~;
~ ~ Cl~ ¦ O ~ ~i ~_i ~ O
P~
~ ~Or) O
~ ~: O N ~ -- N
t~ C~
¢ ~ ~ ~ -V
H H
~q ~ ~0 W
,_ r~l CU
~ ~O t- ~ ~ O ~ ~U
L,~ 4S9 r~
E-'¦ ~ u S. t) ~ ~ h ~11\
1 ~ O C~ O ~
O h O h ~ r~/ ~1~1 ~1~1 ~1~ 0 CU
r~ C~J ~
~ o ~d ~ ~ ? ~ ~
r, 5: ~ o ~ R~ C~ ~ X ~
c~> 1~C-) ~ ~00 0 ~ ~ ~3 0 0 h O h O h O ~J
~i .~
:~i E~ O O O O O O O
H ~ ~ ; J
+~,, ~ o . ~
.. ~ 1 0o o~ O ~ ~D O O
+ ~ 0 ) ~0 ~ CJ~ O ,~
O O R ¦ 0 00 V ¢ t- t- O ~D ~ O O
E~ 0 co ~0 ~ 0 ~0 ~ ~ ~ a~
m . ~ l2 ~~o~ )0~ 0O~ ~o~
P~ H C~ ~; J Z~;
¢ Q ~
. EO~ ~ ~ 0 O ~ ~ ~
V
H ~ ¦ 0 0 0 0 0 0 0 ~ H O O O O O O
~ \ ¢ O C~
¢ ~ o = - ~o = = ov r~ c~ (~1 o ru tu E~ ¢ ,_ V ^
H r-~l H H
cn ¢ bO - - bD bD '~ ~
~q ~
r-l C~l ~_ ,~ . ~ ~ 1~ ~ ~ ~ a~
_ !'~ C -1 C ~ C ~ ~ 9 1~ C) L~
~ Lf~ fl 7 s ~ . ~ L~
,i ~d h ~ ~ O ~1~1~1 h fi t L~ ~p, J I ~ ,, ~ , ,i ~ O ~
C
H ~ O ¦ ~ h .~ ~ ~
4. Methods of Determinin~ H202 Loss Durin~, Leach~ng A. By Gas Collection As described above, n~ifolded flexible tubing conveyed all 02 gas released by II~02 decomposition from the 45~
leach col~ the inlet reservoir and the leachate collec-tlon reservoir into an inverted gas collection cylinder.
The percent of H202 decomposed (% converted to 02 ) after a time (t) in which a certain volume (liters) of leachate, containing a certain concentration of H202 was collected, was computed as follows:
CC 02 collected converted to STP
liters of leachate x g H202/l leach x 3~-~-x 2 The collected gas volume was converted to STP by multiplyin~
the observed volume by 0.9. This conversion factor was based on the finding that when 1.8 g of H202 was contacted with three dif~erent ores and the released gas collected by displacement of water, the following relation was obtained:
Stoichiometric 0? from equation 2H202 >2H~0 ~ 0~ , O 9O~O 03 se~ved 02 re ea~ed B. By Titration Assuming that the Hz02 in the inlet reser~oir is stable, the H202 lost solely to leaching can be measured by titrati~g a grab sample from the column. This was generally done by collecting at the end of a run (without interrupt-ing flow) a 100 cc sample of leachate at the same flow rate (mostly 5 cc/min) as used during the run. Then 20 cc ali-quots of the 100 cc sample and of the leach in the inlet reservoir were titrated by standard iodimetry:
% H2O2 lost _ ~ e~t~~eservOi-rGTitb Sam~le Titr~
Unless otherwise stated, analysis of "H2G2 lost by titration" i3 by titration of a grab-sample rather than of the collected leachate.
EX~LE I
. .
This example lllustrates both the effect of a leaching solution containing II202 in reduc:lng permeability of an orc body and the reversal of that effect by addlng - l? -24~9 aqueou~ sodium silicate to the leaching ~olution.
Using the ore A, a leach solution containing 10 gABC/l, 2.5 g AC/l and 1.2 g H22/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 out-fall 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 leach, a flow rate of 10 cc/min was easily maintained over a 65 mlnute period, to collect 650 cc of leachate. Using no silicate in the companion run~ it too~ 98 minutes to collect 620 cc of leach, even though the outlet pump was at a much hlgher speed.
EXAMPLE II
In this series of tests, permeability of the ore bed was examined as a ~unction of H202 in the leaching solution, pH and silicate in the leaching solution. -One hundred grams o~ Ore C were extracted in companion 42 mm leachlng columns using a basic leach containing 10 g ABC/l + 2.5 g AC/l adjusted to pH 8.6 with NHs or to pH 10.2 with ~aOH. Goal flow rate wa~ 5 cc/min. The results are given in Table 1.
g Cu~ulative Running Basic Leach ~difications Leach Flow Rate cc/min in. Column A(l) Column B( ) Column A Column B
o-60 as is as is 5 cc/min at Similar (no H20z) (no H202) 25 rpm pump speed 60-68 " " 12.8 cc/min Similar at 58 rpm 68-108 l.&g H202/l 1.8g H202/l Slowed to Similar 4-5 cc/min at ~ 110 rpm 108-144 " Also added 3.6 cc/min 6.1 cc/min 3g NaSiO3/l at 50 rpm at 50 rpm - (l)Leachlng solution pH 8.6 - (2)Leaching solution pH 10.2 Summary of Results:
With no H202 in either formulatlon, the pump 2Q 6etting 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 H202 caused a very noticeable loss in the rate at which leach 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 o.6 in. during the period when no H202 was in the leach. However, the vacuum gradually increased to 20-21 in. of mercury during the 40-minute leach period after H202 was added.
....
Note in the last 36-minute time period that the addition of silicate to the p~ 10.2 leach 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 NH3-CO2 leach containing 1.8 g H202/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 NaSiO3/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-mlnute flow period, an average 6.3 cc/min flow rate was obtained as the pump speed ~ell to 42 rpm and the vacuum fell to about 7 in.
EXAMPLE III
In this test series, the ad~erse e~fect of H202 on permeability and its prevention by use of sodium silicate addition were demonstrated on Ore B using a basic leach conta~ning 4 g ABC/l + 4 g AC/l. The results are g~ven ~n Table 2.
m oo 0 ~ , 1~- g ¢ ~ 0 O 0~ 1 0 ~1 u~ ~ ~o m ~ ~ ' ~; V N C~J
O ~
~C~ ¢
~ O
V ~J N ~1 ~1 0 CU . ~ ~
~1 m o~
I
tl~ I I I ~ N .C N
~1 ~0 ~ ~0 b~
O V ~ ~ ~ ~N
C) q-l bD O bD O
~ q~ ~ ,_ O ~ O
1~ ~ ¢ O 0~ 0 C~ ao 0~3 0 = ~ S~ N ,r: N -O ":50 ~0~ ~0 O ~ ~N ~ ~ ~rt ~ ~N
~} bD ~ h ~ a '' ~ ~ ~
o ~ a) 0 o o ~ O O OO bD h ~1 ~ :~ O
~ ~ ~ h ~t ~ ~ o ~
o P; Pl 'I '`J ~ ~ ,,~
~.
4~
EXAMPLE IV
In this series of tests, the e~fect of the follow-ing ~ariables upon peImeability was studied: (1) adding H202 with and without silicate; (2) discontinuing silicate addition; and (3) ef~ect of adding silicate after perme-ability 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 compariæon runs, columns A and B were first flushed with 500 cc of peroxide-free bas~c 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 H202/l was added to the leach 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 wh~ch 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 bene~icial in preventing loss of permeability, but also that the beneficial ef~ect is sustained for a substantial period of time after silicate ~s remQved from the leaching solution.
In a similar comp~ion set of runs~ partial plugging w~s lnduced by pumping through 320 cc of silicate-free leach containing 1.20 g H202~1 ~or 56 minutes, as a result of which fl ow diminished to belo~ 5 cc/r~n 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 ~or 72 minutes, lt became possible to p~np 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 t~mporary relie~ 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 experintent indicates that permeability, even after being partially lost during leaching with a peroxide-containing am~lonium 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.
EX~IPLE V
-In this series of tests, the following effects were examined:
(1) Loss of permea~ ty with peroxide leach (2) Use o~ silicate to prevent loss o~ permeability, and (3) Use o~ silicate to restore permeability once lost.
Table 1 is a running log of comp~lion leach experiments uslng the basic leach 4 g ABC~ 4 g AC/l (equivalent, by calculation to 2.28 g NH3/l and 4.o6 g COz/l) + 1.80 g H202/l, and 100 gram charges (ln the 42 mm I.D. colu~ns) of ore A. Information on permeability is glven by the "Leachate Flow Rate" column in Table 3 in con~unction with data on pu~p rpm's below in the text.
Information on Hz02 lost during leaching is based on Oz loss (last column in table).
~l ~ ~ o ~ ~ ~
~ ~ ¢1 ~ ~ ~ C~ ~ ~
o ~i ~ x ~:J F~ O O C~J O 0 h I C~l ~ ~ ~C) ~ .
~ N c) ¦ Lf~ Ir~ U'~ C~l ~1 ¢~ ~ ¢1 ~
~ ~ h O X
~ ~ ,1 m ", x ~ h O ~; ~¢~ o ~0 -i ~ ~ ~o~ g ¢ ~ ~,,`m a) ~
E~ c~; ~ ~ cd h I ,~
q O ~; O .-1 R
m ~ ~ ~ O ~ h C~
C ~ C~ ~ a:~ co 0 ~ 0 1~ ~3 ~ ., v~ ~ ~D ~ ~D bO ~D t~a ~D ~D C- CU I a) E4 H ¢ h h E~ oP P ~ ~ ~
~i ~ 0 ~ O ~ ~ ~
~ o~ O ~1 P~
~Z~5~
~ r ~
H ~ O
~i~ 5 ~
~ r~ J ~ ~ O ~li r ~ ¢ ~ ~
u~ ~ rl ~ ~ ~ ~ h ~-~ C3 a~ ~ ~1 ~3 S
~~; O ~ H~ C) O +~ ~I
P~ X ~ ~ ~
~ O X
The ~ollowing can be concluded ~rom these data:
Permeability graduaIly diminished over the 187 minutes (Runs 6-8) for the ammonium carbonate/bicarbonate leach containing H202 and no silicate, even though the pump speed had incr~ased to < 110 rpm. However, permeability was largely restored when 4 g/l of silicate was added to the leach. In this regard, compare the 35-minute and 50-minute running periods of Runs 10 and 9, but note that a no-~low 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 ~Run lOB) was obtained at a pump speed of 62 rpm; the comparative 1.22 cc/min rate (Run lOQ) was o~tained at 115 rpm.
When silicate was then added to the silicate-free column that had been used as a control in Run 9, there was a marked improvement in permeability. Note, however, (Run 11) that permeability was not ~mproved 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.
EXA~LE_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 con-taining 4 g ABC/l ~ 4 g AC/l ~ 1.8 g II202~1, the other with the same solution fortified with O.2 g~l o~ sodium silicate.
Leachate was pumped from both col~ outlets using the s~me pump rpmO ~he leach containin~ 0.2 g~l of silicate flow~d ~0 noticeably better, about 1.3 tlnles faster th~l the leach containing no silicate for the first 80 minute~, 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 impro~ed to the point that it was as good as, or ~lightly better than, the leach containing 0.2 g/l of sodium silicate.
In another 60-minute comparative run, leach con-taining 1 g/l of sodium silicate Mowed easily at 5 cc/min at pump settings of 45-65 rpm. With no silicate the average flo~Y over this period was only 3.6 cc/min, e~en though the pump speed was increased from 65 to 118 rpm during the run.
E ~ ~LE 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 companlon runs using different leaches containing 1.80 g H202/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 ha~ing 0-120 rpm range was attempted.
The ore had been sieved to -12+80 mesh, but the particles were so~t (to finger crushing) and clay-like in appearance. When wetted in the column, the largel pieces seemed to lose their particulate identity and the wetted plug seemed to be a fairly uniform, sandy, clay-like ~ggre~ate.
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¢ ~ C>~3 t~l h I O~1) Q~ C) a) ~:) ~: O ~ C~O ~~ ~1 o\ r~
r~ ~, o ~ N V ~ a~ ~0 ~
r~ ¢ c~ o ~ ~ bD ~ r~l ¢ ~L~ ~ C~ ; O
c~ ~1 ~ , r~ r~
~ ~ z ,~ ;
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Fll ~ Ll~OH C~l ~ h h h h r-l C) (V ~ O O
h ~ ~ h h O r-l O
~r; ~ ~\ ~\ r-l ~J ~, ~ L~ ~O ~
- 2G ~
g The data in Table 4 show the following:
(1) Without silicate~ permeability decreased during column leaching. Silicate in an NH3-COz-H202 leach improved permeability (Runs 16, 22 and 23).
(2) Silicate improved permeability throughout the pH
range 7-1O normally associated with in-situ uranium leach-ing. Some effect was seen even w~en total NH3 was ~10 g/l ~ (e.g.~ Run 28).
(3) In Runs ~0 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 ~here a substantial concentration of NaOH (e.g., 3.8~-5.o5 g/l) was added to the leach to raise a p~ to 9.5 or 10.0, the beneficial e~fect of silicate on permeability was lost (See Runs 17 and 25-283. In fact, these caustic-fortified leaches seemed to cause even poorer permeability than silicate-~ree 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 addi-tion of 5 g/1 of Na2SO4 caused no apparent loss in per-meability. The conclusions to be drat~ ~rom these observa-tions is that, for purposes o~ improving permeability in a carbonate leach containing H202, (a) silicate is decidedly beneff clal in an NH3-CO2 system in a pH r.a~e at least as broad as pH 7-10, (b) that silicate may be beneficial in a carbonate leach containing both NH4 and Na+ as counterions for carbonate and blcarbonate, and, (c) that carbonate/bicarbonate leaches containing only Na+ counterions appear to cause more permeability loss than silicate-containing NH3-C02 formulations whether or not they con-tain silicate.
EXAMPLE VIII
~ .
In this series of tests, a comparison was made between the use o~ H202 as oxidant, both with and withou~
silicate, and NaCl03 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: ~ g NaSiO3/l + i.8 g H202/l Column B: 10.8 g NaCl03/l Ore: 100 g/column, containing about o.85% uranium ~J I ~ I t ~1 0 ~u~ ~
o u~ ~~
~ ~ o u~ N
U~ O
~ 1~ 0 ~ ~ æ j 0 :~ N O O :i' L~ 0 ~ ~ ~ ~ N ~ ~\
~ ~ ~ ~ V ~ N
P~
~ ~ U~ U~ o ~_ O~ ~1 .
Ei3 ~ ~1 ~ 0 ' i~ ~ L~
~ ~ I ;~ t-u~ ~3 ~ C o o O ~ o o U~ ~ Ir~ Lr~
:' a~
1~ 1: 1 O 00 0 0 0 0 L~ CO
E~ a~ o ~ o ~ o G~
~C ~ ~ rr~ 0 ~ ~I N
lS' ~0 ¢
~ ~ ~C) ~ Z~ . ~ I 0 0:~ 0 ~ O O O
E~ O ~ ¢ ~ Oo. co O N~ N
~ O O O ~ 0~ 0~ --`
.. ~ ~ ~1 ~ ~
~ ~ ~ ~
Z :~; ~ Z Z ~ O ~ O
~3 ,~
E~ u2 cq ~ ~ ~ o +~ +~ tr_~ o 0 1~ 0 ,,~ +~
~ N ~ N N ~ C
H O ~D O bl) O b~D C) o ~ O t) ~) O L~
N N ~'J N ~r~ N
O O ~ 0~ O u~
m ~ ~ .0 ~ ~ O
P ' ~U~
~ ~ N
¢ . . '. ,~
co co CO 1:4 CO, ~ F'. u~
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,.
L~ O O O t-- O
C~
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H ¢ ~
O O ~OU~ O~ rl O O
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R ~ D O C
~ o ¦ $ ~ ~_ Summary of Results:
The followlng conclusions can be drawn ~rom the data in Table 5.
Loss of permeability ls not assoclated with all oxldants. Note the excellent permeabillty with sodium chlorate~ Runs 33-37B. On the other hand, the preceding ex~mples showed that H202-containing leach in contact with ore caused loss of permeability Furthermore, note from the gas collection data in ~uns ~ 7A that virtually all the H202 decomposad to 2 gas during passage over the ore bed.
Thus, it would appear that the loss of permeab~lity is occasioned by H202 and/or the attendant oxygen resulting from deco~position of the H202 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 t~me after silicate was removed from the leaching solution.
Howe~er, the beneficial effects gradually fell off a~ter 6ilicate was removed ~rom the leaching solution. See Runs ~6A-38A following Runs 33A-35A. Compare especially the 50-~inute running period in Runs ~8A, B.
Though (non-plugging) chlorate is also a potential oxidant ~ solution leaching o~ uranium ore, it does suffer from the disadvantage of producing far more environ-mental]y ob~ectionable reaction products, such as chlorite and chloride ions. Furthermore~ it is a less effective ~0 oxidant for leaching uranium as sho~ by the data in the last column. This was so even though twlce as many moles of chlorate than H202 were used, i.e., 0.101 vs. 0.053 moles/liter o~ each.
EXAMPLE IX
It was noted that when a leachate conta~ning 10 g AB~ 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 whi^h indicates gelling o~ the silicate.
This was even more noticeable by the Tyndall effect ~rom a beam of light. After fortifying with 1.2 g H202/l, this a~ed 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~
EX~LE 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:
~ .
T~BLE 6~ i9 Gellation Stabillty A.P.H.A. ~y~BIDITy UNITS~) (ppm) COMPO$~TION ~ -1 1 AFTER
NO.~ ) ABC AC SI~ ~ 6 DAYS 11 ~AYS
1 --- 16 1.0 8.95 1.~
lA --- 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 ~A 8 8 1.0 8.20 --- 0.95 ~ 4 4 1.0 8.80 0.70 nil 5A 4 4 1.0 6.60 --- 0.1 LEAR
6 4 4 0.5 8.80 0.~ nil 6A 4 4 0.5 7.00 --- nil
~1 Ll~ L~
~ t4 ~
E~~:: E l D ~ ~ ~J
V H ~ h h .
~ E~ ¢ ~ *1 ~ ~
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~ ~ ~ ~4 0 ~O ~ O
m H I 0 0 h h ~` C~
\ ¢1 1~ * .~ r ~ ?
¢ ~ C>~3 t~l h I O~1) Q~ C) a) ~:) ~: O ~ C~O ~~ ~1 o\ r~
r~ ~, o ~ N V ~ a~ ~0 ~
r~ ¢ c~ o ~ ~ bD ~ r~l ¢ ~L~ ~ C~ ; O
c~ ~1 ~ , r~ r~
~ ~ z ,~ ;
H ) b0 LO O ~ " ~j u~ c~ o ~ o ~ ~ $ $
Fll ~ Ll~OH C~l ~ h h h h r-l C) (V ~ O O
h ~ ~ h h O r-l O
~r; ~ ~\ ~\ r-l ~J ~, ~ L~ ~O ~
- 2G ~
g The data in Table 4 show the following:
(1) Without silicate~ permeability decreased during column leaching. Silicate in an NH3-COz-H202 leach improved permeability (Runs 16, 22 and 23).
(2) Silicate improved permeability throughout the pH
range 7-1O normally associated with in-situ uranium leach-ing. Some effect was seen even w~en total NH3 was ~10 g/l ~ (e.g.~ Run 28).
(3) In Runs ~0 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 ~here a substantial concentration of NaOH (e.g., 3.8~-5.o5 g/l) was added to the leach to raise a p~ to 9.5 or 10.0, the beneficial e~fect of silicate on permeability was lost (See Runs 17 and 25-283. In fact, these caustic-fortified leaches seemed to cause even poorer permeability than silicate-~ree 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 addi-tion of 5 g/1 of Na2SO4 caused no apparent loss in per-meability. The conclusions to be drat~ ~rom these observa-tions is that, for purposes o~ improving permeability in a carbonate leach containing H202, (a) silicate is decidedly beneff clal in an NH3-CO2 system in a pH r.a~e at least as broad as pH 7-10, (b) that silicate may be beneficial in a carbonate leach containing both NH4 and Na+ as counterions for carbonate and blcarbonate, and, (c) that carbonate/bicarbonate leaches containing only Na+ counterions appear to cause more permeability loss than silicate-containing NH3-C02 formulations whether or not they con-tain silicate.
EXAMPLE VIII
~ .
In this series of tests, a comparison was made between the use o~ H202 as oxidant, both with and withou~
silicate, and NaCl03 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: ~ g NaSiO3/l + i.8 g H202/l Column B: 10.8 g NaCl03/l Ore: 100 g/column, containing about o.85% uranium ~J I ~ I t ~1 0 ~u~ ~
o u~ ~~
~ ~ o u~ N
U~ O
~ 1~ 0 ~ ~ æ j 0 :~ N O O :i' L~ 0 ~ ~ ~ ~ N ~ ~\
~ ~ ~ ~ V ~ N
P~
~ ~ U~ U~ o ~_ O~ ~1 .
Ei3 ~ ~1 ~ 0 ' i~ ~ L~
~ ~ I ;~ t-u~ ~3 ~ C o o O ~ o o U~ ~ Ir~ Lr~
:' a~
1~ 1: 1 O 00 0 0 0 0 L~ CO
E~ a~ o ~ o ~ o G~
~C ~ ~ rr~ 0 ~ ~I N
lS' ~0 ¢
~ ~ ~C) ~ Z~ . ~ I 0 0:~ 0 ~ O O O
E~ O ~ ¢ ~ Oo. co O N~ N
~ O O O ~ 0~ 0~ --`
.. ~ ~ ~1 ~ ~
~ ~ ~ ~
Z :~; ~ Z Z ~ O ~ O
~3 ,~
E~ u2 cq ~ ~ ~ o +~ +~ tr_~ o 0 1~ 0 ,,~ +~
~ N ~ N N ~ C
H O ~D O bl) O b~D C) o ~ O t) ~) O L~
N N ~'J N ~r~ N
O O ~ 0~ O u~
m ~ ~ .0 ~ ~ O
P ' ~U~
~ ~ N
¢ . . '. ,~
co co CO 1:4 CO, ~ F'. u~
E17 ~ u~
,.
L~ O O O t-- O
C~
~ l l l m ~ ¢l i i ~V~
æ~ ~
U~ a1 V~O .
~ ~I j cu .
P~ E3 N ,~
V~
li3 ~ O I , -:
~ ~ ~q ¦ N o i~ c.) N 15 ~ ~ c~
~ ~1 ~ c~l .
~1 ~ ~
~ ¦ O tD ~ O bO ~ O
,~:1 ~ O O
H ¢ ~
O O ~OU~ O~ rl O O
~1 ~ ~j Pkl D
R ~ D O C
~ o ¦ $ ~ ~_ Summary of Results:
The followlng conclusions can be drawn ~rom the data in Table 5.
Loss of permeability ls not assoclated with all oxldants. Note the excellent permeabillty with sodium chlorate~ Runs 33-37B. On the other hand, the preceding ex~mples showed that H202-containing leach in contact with ore caused loss of permeability Furthermore, note from the gas collection data in ~uns ~ 7A that virtually all the H202 decomposad to 2 gas during passage over the ore bed.
Thus, it would appear that the loss of permeab~lity is occasioned by H202 and/or the attendant oxygen resulting from deco~position of the H202 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 t~me after silicate was removed from the leaching solution.
Howe~er, the beneficial effects gradually fell off a~ter 6ilicate was removed ~rom the leaching solution. See Runs ~6A-38A following Runs 33A-35A. Compare especially the 50-~inute running period in Runs ~8A, B.
Though (non-plugging) chlorate is also a potential oxidant ~ solution leaching o~ uranium ore, it does suffer from the disadvantage of producing far more environ-mental]y ob~ectionable reaction products, such as chlorite and chloride ions. Furthermore~ it is a less effective ~0 oxidant for leaching uranium as sho~ by the data in the last column. This was so even though twlce as many moles of chlorate than H202 were used, i.e., 0.101 vs. 0.053 moles/liter o~ each.
EXAMPLE IX
It was noted that when a leachate conta~ning 10 g AB~ 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 whi^h indicates gelling o~ the silicate.
This was even more noticeable by the Tyndall effect ~rom a beam of light. After fortifying with 1.2 g H202/l, this a~ed 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~
EX~LE 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:
~ .
T~BLE 6~ i9 Gellation Stabillty A.P.H.A. ~y~BIDITy UNITS~) (ppm) COMPO$~TION ~ -1 1 AFTER
NO.~ ) ABC AC SI~ ~ 6 DAYS 11 ~AYS
1 --- 16 1.0 8.95 1.~
lA --- 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 ~A 8 8 1.0 8.20 --- 0.95 ~ 4 4 1.0 8.80 0.70 nil 5A 4 4 1.0 6.60 --- 0.1 LEAR
6 4 4 0.5 8.80 0.~ nil 6A 4 4 0.5 7.00 --- nil
7 4 4 2.0 8.85 o.95 o.6 7A 4 4 2.0 7.20 ___ 1.2
8(~) 8 8 1.0(3) 8.80 1.2 o.g 8A(~) 8 8 1-0(3) 7-20 --- 1.2
9(3) 4 4 1.0(3) 8;80 1.2 1.4 9A(3) 4 4 1.0(3) 7.30 ___ nil
10(~) 4 4 2.o(3) 8.80 1.7 1.4 lOA(3) 4 4 2.0(~) 6.80 --- 0.4
11 102.5 3.0 8.55 very gel on cloudy bottom o~ beaker
12 102.5 3- 8.55 very gel on cloudy bottorn o~ beaker .. .. . . .
( )For A series, each numbered~sample w~s split at 6 days and the A series portion was ad~usted downward with H2SO4.
Thus, only the last 5 days of the l;L-day readin~,s (last column) were at the lowered pH for A scrles solu-tions.
(2)These values are ~rom calibration cul~ve suppli.ed by I~elllge for SiO25 ~d clo no~ nec~ssarlly rcpr~sent the actual ~p;n of SiO~ .in t}~e.~.e le~ches.
(3)From an ~g~d ~m~ month~ old) lab ~upply o~ sodi~m silic~te ~hat had ~edinient on the bcttom, ~11 o~her r~u~s used sillc~ e ~rom a ne~ r~un 01' Du l'ont Grade F ,,o~iU~ qte.
During this work it was observed that cloudiness (and thus, gelling) Or leach solutions could be completely a~oided by using 2.0 gh 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, silicat~ is inherently ~ree ~rom gelling because of solubilization by base.
Overall, for the clear solutions, the only sugges-tion of posslble or incipient gelling, as manifested by some-what higher turbidity readings? was for compositions con-taining high leach salt content (Compositions Number 1, lA, 4, 4A, 8 and 8A), high silicate (Compositions 7, 7A and 10) or aged sllica~e (Compositions 8-10).
Fortunately, the salt and silicate concentrations giving apparently non-gelling leaches coincide with the con-centrations which are highly useful ~or leaching and preven-tion of pe~eability loss.
~XAMPLE XI
In this Example, extended runs were carried out which illustrate that silicate may in some instances be effectlve to stabilize the H202 solution from decomposition.
In a companion run us~ng 100 gram charges of Ore C, a ~ cc/min ~low rate, and a basic leach con~aining 10 g ABC/l + 2.~ g AC/l + 1.80 ~ H202/l (pH 8.2)~ the comparison tested the di~erence in adding ~r not adding 3 g NaSiO3/l to the leach. The run was for 330 minutes, and permeability loss was pre~ented by prior screening so the ore contained -12 +80 mesh particles. The results can be summed up as ~ollows:
1~2~59 ~ /min Serial Time Wlthout With ScF,ments Silicate Sillcate First ~0 min 2nd 100 min 2.4 1.05 3rd 100 min 2.65 1.15 4th 100 min ~.05 1.05 TOTAL - 330 min 2.80 1.26 Stand overnight ---- ----with no flow 100 2.35 0.95 me 2 loss for the 330 minutes corresponded to an 84% loss of H202 in the leach when the leach contalned no silicate; only ~7~ when the leach contained silicate.
These results showed that silicate not only improved H202 stability during leaching, but also seemed to prevent an increase in lnstability with time.
( )For A series, each numbered~sample w~s split at 6 days and the A series portion was ad~usted downward with H2SO4.
Thus, only the last 5 days of the l;L-day readin~,s (last column) were at the lowered pH for A scrles solu-tions.
(2)These values are ~rom calibration cul~ve suppli.ed by I~elllge for SiO25 ~d clo no~ nec~ssarlly rcpr~sent the actual ~p;n of SiO~ .in t}~e.~.e le~ches.
(3)From an ~g~d ~m~ month~ old) lab ~upply o~ sodi~m silic~te ~hat had ~edinient on the bcttom, ~11 o~her r~u~s used sillc~ e ~rom a ne~ r~un 01' Du l'ont Grade F ,,o~iU~ qte.
During this work it was observed that cloudiness (and thus, gelling) Or leach solutions could be completely a~oided by using 2.0 gh 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, silicat~ is inherently ~ree ~rom gelling because of solubilization by base.
Overall, for the clear solutions, the only sugges-tion of posslble or incipient gelling, as manifested by some-what higher turbidity readings? was for compositions con-taining high leach salt content (Compositions Number 1, lA, 4, 4A, 8 and 8A), high silicate (Compositions 7, 7A and 10) or aged sllica~e (Compositions 8-10).
Fortunately, the salt and silicate concentrations giving apparently non-gelling leaches coincide with the con-centrations which are highly useful ~or leaching and preven-tion of pe~eability loss.
~XAMPLE XI
In this Example, extended runs were carried out which illustrate that silicate may in some instances be effectlve to stabilize the H202 solution from decomposition.
In a companion run us~ng 100 gram charges of Ore C, a ~ cc/min ~low rate, and a basic leach con~aining 10 g ABC/l + 2.~ g AC/l + 1.80 ~ H202/l (pH 8.2)~ the comparison tested the di~erence in adding ~r not adding 3 g NaSiO3/l to the leach. The run was for 330 minutes, and permeability loss was pre~ented by prior screening so the ore contained -12 +80 mesh particles. The results can be summed up as ~ollows:
1~2~59 ~ /min Serial Time Wlthout With ScF,ments Silicate Sillcate First ~0 min 2nd 100 min 2.4 1.05 3rd 100 min 2.65 1.15 4th 100 min ~.05 1.05 TOTAL - 330 min 2.80 1.26 Stand overnight ---- ----with no flow 100 2.35 0.95 me 2 loss for the 330 minutes corresponded to an 84% loss of H202 in the leach when the leach contalned no silicate; only ~7~ when the leach contained silicate.
These results showed that silicate not only improved H202 stability during leaching, but also seemed to prevent an increase in lnstability with time.
Claims (11)
1. In the solution mining of uranium ores using an aqueous ammonium carbonate leaching solution having a pH of 7-10 containing an oxidant selected from the group consisting of hydrogen peroxide, molecular oxygen and mixtures thereof, permeability of the ore formation during the leaching operation is improved by the inclusion of a small amount of alkali metal silicate dissolved in the leaching solution.
2. The process of Claim 1 in which the leaching solution contains at least 0.1 grams alkali metal silicate, dry basis.
3. The process of Claim 1 in which the leaching solution contains 0.1-5 grams alkali metal silicate, dry basis, per liter.
4. The mining process of Claim 1, 2 or 3 in which the leaching solution contains 0.5-20 grams of ammonium carbonates.
5. The process of Claim 1, 2 or 3 in which the leaching solution contains 0.1-10 grams H2O2 per liter.
6. The process of Claim 1, 2 or 3 in which the alkali metal silicate is sodium silicate.
7. The process of Claim 1, 2 or 3 in which the ore formation is treated with silicate-containing leaching solution after it has been treated with a leaching solution containing no silicate.
8. A leaching composition for use in the solution mining of uranium ores having a pH of 7-10 comprising an aqueous solution in which is dissolved 0.5-20 grams per liter of ammonium carbonates, 0.1-10 grams per liter of H2O2 and 0.1-5 grams per liter of alkali metal silicate.
9. The composition of Claim 7 in which the solution contains 0.5-1.5 gram per liter of alkali metal silicate, dry basis.
10. The composition of Claim 7 in which the solution contains 0.2-2 grams H2O2 per liter.
11. The composition of Claim 7 in which the solution contains 5-15 grams ammonium carbonates per liter.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US73996776A | 1976-11-08 | 1976-11-08 | |
| US739,967 | 1976-11-08 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1112459A true CA1112459A (en) | 1981-11-17 |
Family
ID=24974518
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA290,337A Expired CA1112459A (en) | 1976-11-08 | 1977-11-07 | Composition and method for solution mining of uranium ores |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1112459A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN114000859A (en) * | 2021-10-25 | 2022-02-01 | 紫金矿业集团股份有限公司 | Mining device and mining method based on leaching mining method |
-
1977
- 1977-11-07 CA CA290,337A patent/CA1112459A/en not_active Expired
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN114000859A (en) * | 2021-10-25 | 2022-02-01 | 紫金矿业集团股份有限公司 | Mining device and mining method based on leaching mining method |
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