CA2270744A1 - Method for removal of gold by liquid-liquid extraction from gold-cyanide complex in aqueous solution - Google Patents
Method for removal of gold by liquid-liquid extraction from gold-cyanide complex in aqueous solution Download PDFInfo
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- CA2270744A1 CA2270744A1 CA002270744A CA2270744A CA2270744A1 CA 2270744 A1 CA2270744 A1 CA 2270744A1 CA 002270744 A CA002270744 A CA 002270744A CA 2270744 A CA2270744 A CA 2270744A CA 2270744 A1 CA2270744 A1 CA 2270744A1
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- gold
- cyanide
- solution
- complex
- liquid
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P10/00—Technologies related to metal processing
- Y02P10/20—Recycling
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- Manufacture And Refinement Of Metals (AREA)
Abstract
An improved method is provided for the liquid-liquid extraction of gold from an aqueous liquid containing gold-cyanide complex comprising the steps of providing an aqueous solution which comprises a gold-cyanide complex, contacting the solution with a quaternary ammonium hydroxide extractant resulting in the formation of an insoluble gold-quaternary ammonium complex, and recovering the gold-quaternary ammonium complex.
Description
BACKGROUND OF THE PRESENT INVENTION
The present invention is directed to an improved method for the separation of gold from an aqueous liquid containing a gold-cyanide complex.
The recovery of gold from gold-bearing ores has been generally accomplished by heap-leaching of the ore. In such a method, a pile of low grade ore is contacted (by spraying, trickling, pouring on, etc.) with an aqueous alkaline cyanide solution whereby the solution is caused to permeate through the ore. Water-soluble gold cyanide complexes (e.g., as defined by the formula [Au (CN) 4 ] -) are formed upon such contact, with the now-pregnant gold-cyanide complex-contairung leach liquor being recovered for separation of the gold.
This process is well described in the literature.
A number of methods have been employed in an attempt to separate the gold from the leach liquor. See, for example, U. S. Patent Nos. 2,753,258 (anion exchange resin); 3,215,524 (water-soluble aldehydes); 3,816,587 (reverse osmosis); 3,935,006 (activated carbon); 4,273,579 (metallic hydroxide); 4,289,531 (proteinaceous material); 4,372,830 (anion exchange resin); 4,528,166 (activated carbon); 4,540,435 (organic phosphorus and sulfur oxides); 4,762,556 (diallylamine polymer); 4,814,007 (guanidine reagent); 4,894,407 (organic oxides of sulfur and phosphorus on resin substrate);
5,019,162 (activated carbon); 5,023,060 (activated carbon); 5,073,354 (activated carbon); 5,156,825 (anion exchange resin); 5,158,603 (quaternary amine); 5,290,525 (activated carbon); and 5,643,456 (metal chelating polymer).
Such processes have not been altogether satisfactory. First, complexes of gold with cyanide are very stable and the gold is not easily separated therefrom. Once separated by means such as activated carbon or chelating or anion exchange resins, additional process steps must still be undertaken to separate the gold from this additional material. Such multi-step recovery processes are time-consuming, expensive, result in undesirable waste products, and are generally inefficient. A fiirtller disadvantage of such processes is that a cyanide-containing waste product is created upon recovery of the gold from the cyanide-containing leach liquor. It is desirable to avoid contaminating the environment with such cyanide-containing by-product or waste solutions. It is also frequently found that a high percentage recovery of the gold values from the solution cannot be achieved. As the price of gold decreases, it is all the more important to maximize the amount of gold removed from the leach liquor while minimizing the cost of such removal. It is also important to provide a gold product having the highest possible degree of purity to enhance the value of the final product in the marketplace.
OBJECTS AND SUMMARY OF THE PRESENT INVENTION
It is therefore an object of the present invention to provide a cost-effective process for the separation of gold from a cyanide-containing aqueous solution.
It is further an object of the present invention to provide a process for the separation of gold from a cyanide-containing aqueous solution which enables a high percentage of the gold to be separated.
It is still further an object of the present invention to provide a process for the separation of gold from a cyanide-containing aqueous solution whereby the amount of cyanide-containing waste products is reduced.
It is also an object of the present invention to provide a process for the removal of gold from cyanide-containing aqueous solution which enables a gold product of high purity to be produced with high efficiency and at minimal expense.
In accordance with the present invention, there is accordingly provided a method for the recovery of gold from an aqueous liquid containing gold-cyanide complex comprising the steps of (a) providing an aqueous solution which comprises a gold-cyanide complex;
(b) contacting said solution with a quaternary ammonium hydroxide extractant of the formula:
R' R3 +
N OH' RZ / ~ R4 wherein R' and Rz are C,o-,8 alkyl (preferably C,o_,4 alkyl), R3 is C,~
alkyl, and R4 is methyl, whereby a complex of said extractant with gold in said solution is formed; and (c) separating said complex formed in step (b) from said solution.
DETAILED DESCRIPTION OF THE PRESENT INVENTION
The present invention is directed to the use of a quaternary ammonium hydroxide extractant to separate gold from a gold containing aqueous cyanide solution by liquid-liquid extraction.
The quaternary ammonium hydroxide extractant which may be used in the method of the present invention is defined by the following formula:
R' R3 +
N OH-Rz~ \ R4 wherein R' and Rz are C,o_,8 alkyl, R3 is Cl_9 alkyl, and R4 is methyl.
Preferably, Rl and Rz are C,o_,4 alkyl, most preferably C14 alkyl.
Preferably, R3 is methyl.
Quaternary ammonium hydroxide compounds of the type employed in the present invention are known in the literature. See, for example, U.S. Patent Nos. 2,234,548; 3,169,983; 3,429,694;
3,506,828; 4,929,454; 5,399,762; and 5,559,155. However, none of such compounds have been used to separate gold from aqueous cyanide-containing solutions by solvent-solvent extraction.
Quaternary ammonium compounds have been previously taught for use in the separation of metals from aqueous solution as evidenced by U.S. Patent Nos. 3,194,652; 3,203,968; 3,238,127;
3,429,694; 4,289,530 and S,l 58,603. However, the teachings of such references do not encompass the use of the specific quaternary ammonium compounds of the present invention in the removal of gold front aqueous cyanide solutions in the manner claimed, especially in llllsllpporteCl forrll.
The present invention may be practiced as follows. A
quaternary ammonium hydroxide extractant of the present invention is admixed with au aqueous cyanide leach liquor prepared by the leaching of gold-bearing ore with an aqueous alkaline cyanide solution. Tlle extractant is permitted to remain in contact with the leach liquor for a period of time ranging from about 1 to 60 minutes, upon which gold in the leach liquor (in the form of [Au (CN) 4 ] -) will be extracted from the solution according to the following reaction scheme:
R ~ R3 .E
/
N OH- + [Au (CN) a ~ -' Rz / ~ Rn R' R3 +
\ N / [Au (CN) 4 ] - + OH
~. R
The resulting gold-bearing quaternary ammonium complex is insoluble in the aqueous leach liquor and forms a insoluble gold-bearing phase therein. Tlle insoluble gold-bearing phase may be recovered fiom the treated aqueous leach liquor by conventional means such as by decanting/filtration. Once recovered, the gold-bearing quaternary ammonium complex may be dried to remove bound water (i.e., at a temperature less than 100 °C.) to yield a waxy solid material. This material is then smelted or fired under conventional conditions and procedures (i.e., at temperature in excess of the melting point of gold) to recover the gold as substantially pure metal, with the quaternary ammonium complex being burnt off during the smelting step. Advantageously, a conventional flux such as borax may be added during the smelting or firing step to assist in the removal of impurities.
The process of the present invention enables gold of high purity to be obtained from the cyanide leach liquor at lower cost than has previously been possible. Cyanide by-product is also reduced due to the fact that the cyanide by-product which is extracted together with the gold is destroyed during the smelting process.
The quaternary ammonium extractant of the present invention may be admixed with the cyanide leach liquor in the form of a solution in a suitable diluent solvent in order to enhance the dispersibility of the extractant in the leach liquor. Suitable solvents which may be used in combination with the compounds of the present invention include but are not limited to water-immiscible organic solvents such as alcohols, xylene, methyl isobutyl ketone, etc.
Ethanol is a preferred diluent solvent. One skilled in the art can readily determine which diluent solvents may be employed. A 1:1 dilution (by volume) of extractant in the water-immiscible solvent is generally acceptable, although the degree of dilution is not critical and may suitably range from 1:10 to 10:1 (by volume). The extent of dilution is generally dependent upon the viscosity of the extractant at the conditions employed in order to achieve acceptable dispersibility of the extractant in the leach liquor.
The conditions of extraction of the gold from the cyanide leach liquor are not critical. The pH of the liquor will preferably range form about 7.0 to 10.5. Extraction temperatures within the range of from about 20 to 3 5 ° C. are generally employed, although temperatures within the range of about 20 to 25 °C. are preferred.
EXAMPLE
In order to demonstrate the advantages of the present invention, a quaternary ammonium hydroxide extractant of the following formula is provided:
R~ R3 +
~ N ~ OH-R2 / ~ Ra wherein R' and RZ are C14 alkyl, R3 is methyl, and R4 is methyl.
The extractant compound is diluted with an equal volume of ethanol on a volume basis and used to treat synthetic cyanide leach solutions. The conditions of extraction included cyanide concentrations of lg/1, gold concentration ranging from 10 to 50 mg/l, extractant concentrations ranging from 12 to 48 mg/1, extractant temperatures ranging from ambient to 3 5 ° C. , pH ranging from 8. 5 to 10.5, and iron and copper concentrations in the leach solution ranging from zero to 590 mg/1.
Experiments were carried out by contacting 170 ml of leach liquor with the diluted solution of extractant in a conical flask The above extractant in undiluted form is a light brown organic liquid.
Mixing of the respective phases was achieved by mechanically shaking the flasks in an incubator, which enabled the temperature to be controlled. Samples (10 ml) were taken after 5, 10, 30 and 60 minutes of shaking. The samples were immediately filtered through coarse filter papers to remove the insoluble extractant phase. The gold concentration of the aqueous phase was measured by atomic absorption analysis upon the removal of each sample.
In most experiments it was found that the extraction of gold after 5 minutes of contact was quite high. Depending upon the conditions of extractions (pH ranging from 8.5-10.5 and extraction temperatures ranging fiom ambient to 35 °C.), the degree of extraction of gold from the aqueous solution may but did not necessarily increase over time. For example, gold extraction after 5 minutes contact varied from 40% to 99 % with a mean value of 77%.
After 60 minutes, the degree of gold extraction ranged from 29% to 99.5 %, but the mean value increased to 83.9%, showing that the longer contact time was in general more effective. The presence of iron and copper in the leach solution did not adversely affect the extraction of gold from the solution. The above trials demonstrate that, even under the most adverse conditions, substantial recovery of gold is achievable. Under optimum conditions, substantially all of the gold is recovered.
Modifications and variations of the method may be undertaken by those skilled in the art upon practice of the claimed invention.
Such modifications and variations are intended to come within the scope of the invention defined by the appended claims.
The present invention is directed to an improved method for the separation of gold from an aqueous liquid containing a gold-cyanide complex.
The recovery of gold from gold-bearing ores has been generally accomplished by heap-leaching of the ore. In such a method, a pile of low grade ore is contacted (by spraying, trickling, pouring on, etc.) with an aqueous alkaline cyanide solution whereby the solution is caused to permeate through the ore. Water-soluble gold cyanide complexes (e.g., as defined by the formula [Au (CN) 4 ] -) are formed upon such contact, with the now-pregnant gold-cyanide complex-contairung leach liquor being recovered for separation of the gold.
This process is well described in the literature.
A number of methods have been employed in an attempt to separate the gold from the leach liquor. See, for example, U. S. Patent Nos. 2,753,258 (anion exchange resin); 3,215,524 (water-soluble aldehydes); 3,816,587 (reverse osmosis); 3,935,006 (activated carbon); 4,273,579 (metallic hydroxide); 4,289,531 (proteinaceous material); 4,372,830 (anion exchange resin); 4,528,166 (activated carbon); 4,540,435 (organic phosphorus and sulfur oxides); 4,762,556 (diallylamine polymer); 4,814,007 (guanidine reagent); 4,894,407 (organic oxides of sulfur and phosphorus on resin substrate);
5,019,162 (activated carbon); 5,023,060 (activated carbon); 5,073,354 (activated carbon); 5,156,825 (anion exchange resin); 5,158,603 (quaternary amine); 5,290,525 (activated carbon); and 5,643,456 (metal chelating polymer).
Such processes have not been altogether satisfactory. First, complexes of gold with cyanide are very stable and the gold is not easily separated therefrom. Once separated by means such as activated carbon or chelating or anion exchange resins, additional process steps must still be undertaken to separate the gold from this additional material. Such multi-step recovery processes are time-consuming, expensive, result in undesirable waste products, and are generally inefficient. A fiirtller disadvantage of such processes is that a cyanide-containing waste product is created upon recovery of the gold from the cyanide-containing leach liquor. It is desirable to avoid contaminating the environment with such cyanide-containing by-product or waste solutions. It is also frequently found that a high percentage recovery of the gold values from the solution cannot be achieved. As the price of gold decreases, it is all the more important to maximize the amount of gold removed from the leach liquor while minimizing the cost of such removal. It is also important to provide a gold product having the highest possible degree of purity to enhance the value of the final product in the marketplace.
OBJECTS AND SUMMARY OF THE PRESENT INVENTION
It is therefore an object of the present invention to provide a cost-effective process for the separation of gold from a cyanide-containing aqueous solution.
It is further an object of the present invention to provide a process for the separation of gold from a cyanide-containing aqueous solution which enables a high percentage of the gold to be separated.
It is still further an object of the present invention to provide a process for the separation of gold from a cyanide-containing aqueous solution whereby the amount of cyanide-containing waste products is reduced.
It is also an object of the present invention to provide a process for the removal of gold from cyanide-containing aqueous solution which enables a gold product of high purity to be produced with high efficiency and at minimal expense.
In accordance with the present invention, there is accordingly provided a method for the recovery of gold from an aqueous liquid containing gold-cyanide complex comprising the steps of (a) providing an aqueous solution which comprises a gold-cyanide complex;
(b) contacting said solution with a quaternary ammonium hydroxide extractant of the formula:
R' R3 +
N OH' RZ / ~ R4 wherein R' and Rz are C,o-,8 alkyl (preferably C,o_,4 alkyl), R3 is C,~
alkyl, and R4 is methyl, whereby a complex of said extractant with gold in said solution is formed; and (c) separating said complex formed in step (b) from said solution.
DETAILED DESCRIPTION OF THE PRESENT INVENTION
The present invention is directed to the use of a quaternary ammonium hydroxide extractant to separate gold from a gold containing aqueous cyanide solution by liquid-liquid extraction.
The quaternary ammonium hydroxide extractant which may be used in the method of the present invention is defined by the following formula:
R' R3 +
N OH-Rz~ \ R4 wherein R' and Rz are C,o_,8 alkyl, R3 is Cl_9 alkyl, and R4 is methyl.
Preferably, Rl and Rz are C,o_,4 alkyl, most preferably C14 alkyl.
Preferably, R3 is methyl.
Quaternary ammonium hydroxide compounds of the type employed in the present invention are known in the literature. See, for example, U.S. Patent Nos. 2,234,548; 3,169,983; 3,429,694;
3,506,828; 4,929,454; 5,399,762; and 5,559,155. However, none of such compounds have been used to separate gold from aqueous cyanide-containing solutions by solvent-solvent extraction.
Quaternary ammonium compounds have been previously taught for use in the separation of metals from aqueous solution as evidenced by U.S. Patent Nos. 3,194,652; 3,203,968; 3,238,127;
3,429,694; 4,289,530 and S,l 58,603. However, the teachings of such references do not encompass the use of the specific quaternary ammonium compounds of the present invention in the removal of gold front aqueous cyanide solutions in the manner claimed, especially in llllsllpporteCl forrll.
The present invention may be practiced as follows. A
quaternary ammonium hydroxide extractant of the present invention is admixed with au aqueous cyanide leach liquor prepared by the leaching of gold-bearing ore with an aqueous alkaline cyanide solution. Tlle extractant is permitted to remain in contact with the leach liquor for a period of time ranging from about 1 to 60 minutes, upon which gold in the leach liquor (in the form of [Au (CN) 4 ] -) will be extracted from the solution according to the following reaction scheme:
R ~ R3 .E
/
N OH- + [Au (CN) a ~ -' Rz / ~ Rn R' R3 +
\ N / [Au (CN) 4 ] - + OH
~. R
The resulting gold-bearing quaternary ammonium complex is insoluble in the aqueous leach liquor and forms a insoluble gold-bearing phase therein. Tlle insoluble gold-bearing phase may be recovered fiom the treated aqueous leach liquor by conventional means such as by decanting/filtration. Once recovered, the gold-bearing quaternary ammonium complex may be dried to remove bound water (i.e., at a temperature less than 100 °C.) to yield a waxy solid material. This material is then smelted or fired under conventional conditions and procedures (i.e., at temperature in excess of the melting point of gold) to recover the gold as substantially pure metal, with the quaternary ammonium complex being burnt off during the smelting step. Advantageously, a conventional flux such as borax may be added during the smelting or firing step to assist in the removal of impurities.
The process of the present invention enables gold of high purity to be obtained from the cyanide leach liquor at lower cost than has previously been possible. Cyanide by-product is also reduced due to the fact that the cyanide by-product which is extracted together with the gold is destroyed during the smelting process.
The quaternary ammonium extractant of the present invention may be admixed with the cyanide leach liquor in the form of a solution in a suitable diluent solvent in order to enhance the dispersibility of the extractant in the leach liquor. Suitable solvents which may be used in combination with the compounds of the present invention include but are not limited to water-immiscible organic solvents such as alcohols, xylene, methyl isobutyl ketone, etc.
Ethanol is a preferred diluent solvent. One skilled in the art can readily determine which diluent solvents may be employed. A 1:1 dilution (by volume) of extractant in the water-immiscible solvent is generally acceptable, although the degree of dilution is not critical and may suitably range from 1:10 to 10:1 (by volume). The extent of dilution is generally dependent upon the viscosity of the extractant at the conditions employed in order to achieve acceptable dispersibility of the extractant in the leach liquor.
The conditions of extraction of the gold from the cyanide leach liquor are not critical. The pH of the liquor will preferably range form about 7.0 to 10.5. Extraction temperatures within the range of from about 20 to 3 5 ° C. are generally employed, although temperatures within the range of about 20 to 25 °C. are preferred.
EXAMPLE
In order to demonstrate the advantages of the present invention, a quaternary ammonium hydroxide extractant of the following formula is provided:
R~ R3 +
~ N ~ OH-R2 / ~ Ra wherein R' and RZ are C14 alkyl, R3 is methyl, and R4 is methyl.
The extractant compound is diluted with an equal volume of ethanol on a volume basis and used to treat synthetic cyanide leach solutions. The conditions of extraction included cyanide concentrations of lg/1, gold concentration ranging from 10 to 50 mg/l, extractant concentrations ranging from 12 to 48 mg/1, extractant temperatures ranging from ambient to 3 5 ° C. , pH ranging from 8. 5 to 10.5, and iron and copper concentrations in the leach solution ranging from zero to 590 mg/1.
Experiments were carried out by contacting 170 ml of leach liquor with the diluted solution of extractant in a conical flask The above extractant in undiluted form is a light brown organic liquid.
Mixing of the respective phases was achieved by mechanically shaking the flasks in an incubator, which enabled the temperature to be controlled. Samples (10 ml) were taken after 5, 10, 30 and 60 minutes of shaking. The samples were immediately filtered through coarse filter papers to remove the insoluble extractant phase. The gold concentration of the aqueous phase was measured by atomic absorption analysis upon the removal of each sample.
In most experiments it was found that the extraction of gold after 5 minutes of contact was quite high. Depending upon the conditions of extractions (pH ranging from 8.5-10.5 and extraction temperatures ranging fiom ambient to 35 °C.), the degree of extraction of gold from the aqueous solution may but did not necessarily increase over time. For example, gold extraction after 5 minutes contact varied from 40% to 99 % with a mean value of 77%.
After 60 minutes, the degree of gold extraction ranged from 29% to 99.5 %, but the mean value increased to 83.9%, showing that the longer contact time was in general more effective. The presence of iron and copper in the leach solution did not adversely affect the extraction of gold from the solution. The above trials demonstrate that, even under the most adverse conditions, substantial recovery of gold is achievable. Under optimum conditions, substantially all of the gold is recovered.
Modifications and variations of the method may be undertaken by those skilled in the art upon practice of the claimed invention.
Such modifications and variations are intended to come within the scope of the invention defined by the appended claims.
Claims (6)
1. A method for the removal of gold from an aqueous liquid containing gold-cyanide complex comprising the steps of:
(a) providing an aqueous solution which comprises a gold-cyanide complex;
(b) contacting said solution with a quaternary ammonium hydroxide extractant of the formula:
wherein R1 and R2 are C10-18 is alkyl, R3 is C1-9 alkyl, and R4 is methyl, whereby a complex of said extractant with gold is formed in said solution; and (c) separating said gold-containing complex formed in step (b) from said solution.
(a) providing an aqueous solution which comprises a gold-cyanide complex;
(b) contacting said solution with a quaternary ammonium hydroxide extractant of the formula:
wherein R1 and R2 are C10-18 is alkyl, R3 is C1-9 alkyl, and R4 is methyl, whereby a complex of said extractant with gold is formed in said solution; and (c) separating said gold-containing complex formed in step (b) from said solution.
2. The method of claim 1 wherein each of said R1 and R2 are C10-14 alkyl.
3. The method of claim 2 wherein each of said R1 and R2 are C14 alkyl.
4. The method of claim 1 wherein said gold-cyanide complex is Au(CN)4.
5. The method of claim 1 wherein each of said R1 and R2 are C10-14 alkyl, and each of said R3 and R4 are methyl.
6. The method of claim 1 wherein said separated aqueous-gold-containing complex is smelted to recover said gold.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US6982498A | 1998-04-30 | 1998-04-30 | |
| US09/069,824 | 1998-04-30 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2270744A1 true CA2270744A1 (en) | 1999-10-30 |
Family
ID=29709271
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002270744A Abandoned CA2270744A1 (en) | 1998-04-30 | 1999-04-29 | Method for removal of gold by liquid-liquid extraction from gold-cyanide complex in aqueous solution |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2270744A1 (en) |
-
1999
- 1999-04-29 CA CA002270744A patent/CA2270744A1/en not_active Abandoned
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| FZDE | Discontinued | ||
| FZDE | Discontinued |
Effective date: 20020429 |