CA1102557A - Desorption of gold from activated carbon - Google Patents
Desorption of gold from activated carbonInfo
- Publication number
- CA1102557A CA1102557A CA272,439A CA272439A CA1102557A CA 1102557 A CA1102557 A CA 1102557A CA 272439 A CA272439 A CA 272439A CA 1102557 A CA1102557 A CA 1102557A
- Authority
- CA
- Canada
- Prior art keywords
- percent
- gold
- solution
- volume
- cyanide
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
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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
Landscapes
- Manufacture And Refinement Of Metals (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
Gold and/or silver are desorbed from activated carbon by contacting, at a temperature of about 80 to 160°C, with a solution comprising about 20 to 30 percent by volume of a water soluble alcohol and about 80 to 70 percent by volume of an aqueous solution of a strong base.
Gold and/or silver are desorbed from activated carbon by contacting, at a temperature of about 80 to 160°C, with a solution comprising about 20 to 30 percent by volume of a water soluble alcohol and about 80 to 70 percent by volume of an aqueous solution of a strong base.
Description
(`yanidation is conunonly employc~cl for extrac~ion of gold from its ores. In this process, the crush~d ore is disso]ved in a di.lute solution of sodi.um cyanide, or calcium cyanide, and a small amo~nt of lime, in tile presence of oxyyen, the gold dissolving in the form of the comp~.e~
Au(CN)2. Recovery of the gold has conventionally been accomplished by treatment of the resulting cyanide solution with zinc dust. Moxe recently, activated carhon has been found to be an efficient adsorbent on the gold cyani.de ]0 complex, and a vari.ety of processes based on this reaction have been d.e~l.oped. ~ffectiveness of these processes is, however, dependent on development of efficient means for desorbi~.g the gold from the loaded carbon. Stripping with hot caustic sodium cyanide soluti.on at atmospheric pressure : to desorb the gold, followed .by electrolysis to win the metal values, has been employed. However, this method has the disadvanta.~e that simultaneous strippincJ and electrolysis is slow. Elevated pressure has. aJ.so been employe~, so that:
the temperatu~:e of th~ caustic cyanide solution can be rai.sed to about 250~ without boiling, thereby accelerating tlle desorption rate. This technique, however, requires the use of a ho.i.ler-pressure reactor, which ma]ces the process more complicated.
: ~ recent innovation, described in U.S. patent application Ser.ial No. 551,941, filed March 19, 1975, employs caustic-alcohol-water mixtures, containing about 75 percent : alcohol by volume, a.t ambi.ent temperature and pressure for desorbing gold from activated carbon. This method is very cffective for de60rption of yo].d from activated carbon loaded ` 10 by treatment with synthetic NaAu(CN)2 solutions. I~owe~er, .it . . - . .
.
~-hl~ 7 has not been found to be effective for desorption of gold from activated carbon loaded by treatment with cyanide plant effluent5, particularly when the effluents contain the gold in the form of CaAu(CN)2, i.e., when the effluent is formed by treatment of ores with calcium or sodium cyanide and lime. Investigations have shown that there is a significant difference in the behaviour of sodium and calcium regarding carbon adsorption of gold, the aurocyanide complex being much more strongly adsorbed when calcium is employed as the cation. Since lime is generally employed to provide protective alkalinity in conventional cyanidation processes, an efficient process for desorption of the aurocyanide complex in the presence of calcium ion is essential for economi.cal recovery of gold by means of activated carbon adsorption. In addition, soluble extraneous matter, such as organics, silicates, and ferrous-iron salts, in the pregnant cyanide effluents may play a significant role in the desorption process.
According to the process of the present invention there is provided a process for desorption of metal cyanide complexes from the group gold, silver, or mixtures thereof, from activated carbon loaded by treatment with a leach solution containing cal-cium or sodium cyanide and lime comprising contacting the carbon with stripping solution consisting essentially of solution com-prising about 20 to 30 percent by volume of a water soluble alco-hol and about 80 to 70 percent by volume of a strong base, the operating temperature being about 70 to 160C. It has been found that the use of the elevated temperature provides a much more efficient desorption of the gold or silver, while at the same time permitting the use of a relatively low concentration of alcohol, whereby the economy of the process '.
5~i7 . . ~ -is subs~ln~ially improved. Recovery of the c~o]d or silver from the strippin~3 solution is readily accomplis}led by convelltiolla] mealls such as elect:rolysis.
Activateci carbon, suitable for use in the invention is a widely available material that is convelltionally used in adsoxption process, including yold adsorptioll. Typically, it wi11 have a particle size of about 0.15 to 2 mm and a total surface area of about G00-900i~12/y. It may be derivecl from any of a variety of sources sueh as eoal, petroleum chars, c~conut shell, or pulp mill blae~ ash, and is aetivated by eonventional means sueh as heatlng i.n a steam air mixture at a temperature of about 850C.
The aetivated carbon adsorbent is initially loe~ed by eonventional means, i.e., by eontaeting a gold-eyanlde and/or si].ver-eyanide solution, e.g., a eyanide plant effluent, with the aetivated earbon for a time suffieient to permit adsorption of a major amount of the gold-eyanide and/or sîlver-eyanide eomplex. This may be aeeomplished by any eonventional me~ans for eorltaetinc3 liquid3 wit:ll sol.id adsorbents, e.g., by passin~ the gold-cyanide and/or silver-cyallide soluLion throuyh a columnar unit conl:aininy a fixed bed of the aetivated earbon.
The ~old and/or silver are then desorbecl from the loaded earbon, aeeording to the proeess of the invention, by treatment with a solution eomprisiny a water soluble aleohel and an aqueous solution of a stron~3 base, at a temperature of about 80 to 160 DC. As discussed above, and illustrated in the examples below, this temperature range has been found to be essential to aehievement of effieient desorption of the gold, partieularly where the gold-cyanide solution is a ~', .
cyanide p~ant effluent formed by treatment: of ores witl calcium or sodium cyallide and lime.
l`he water soluble alcohol is prefera~ly a lower aliphatic alcohol such as methanol, ethanol, propanol, or isopropanol. As noted above, the use of an elevated temperature permits the use of a relatively small proportlon of alcohol, preferably about ~0 to 30 percel-t by volume of the stripping solution, thereby substantially improving the economy of the process.
The balance of the strlpping solution consists essent:ially of a water solution of a strong base. Sodium hydroxide is the preferred base, but potassium hydroxide may be used. The base is employed in an amount of about 1 to 2 percent by weight of the water solution, or an amount sufficient to provide the stripping solution with a pH of about 11 to 14, preferably about 13 to 14. Use of a high pH is essential since the activated carbon has a substantially decreased capacity for adsorption of tlle go:Lcl-cyarl;de complex at higher values of pH.
The strippiny solution may also contain a small amount of sodium cyanide, e.g., about 0.02 to 1 percent hy weight of the water solution, particularly where the stripping solution is recycled after removal of the desorbed -.
gold. Such recycled solutions often contain small amounts of sodium cyanide as a contaminant from the stripping operation. Alternatively, the sodium cyanide may be added to the stripping solution and may result in somewhat increased efficieny in some cases. It is not, however, an essential ingredient of the stripping solution.
l'he stripping operation is carried out by contactillg the loaded carbon with -the stripping solution of th~
invention, at tlle l-equired tempeLature. Again, contacting may be by any conventional means such as passing the stripping solution through a bed or column of the loaded carbon.
Optimum amounts and flow rates of the stripping solution will depend on the amount of yold and/or silver adsorbed on the loaded carbon, the composition of the gold-cyanide and/or silver-cyanide solution used for loading and specific composition and temperatures of the stripping solution and are best determined empirically. Generally, however, treatment of the loaded carhcl with about 5 to 30 bed volumes of stripping solution, at a flow rate of about 2 to 8 bed volumes of so].ution per hour givec good results.
Although the process of the invention has been found to be particularly effective for desorption of gold, it is also generally effective for desorption of silver, either alone or in combination with the gold.
The following examples will more speci~:ica1ly illustrate the practice of the .invention and the advantages obtained thereby.
xample 1 ~; In this example, a series o~ desorption tests was conducted on loaded activated carhon from a heap leach-carbon adsorption cyanide plant in which leaching was accomplished by means of calcium cyanlde solution containing sufficient lime to provide a pl-l in the range of 9-ll. The loaded carbon carried 235 or Au/ton and 35 oz ~g/ton.
Desorption ~as conducted in a vertical column 24 lnches in length and 2 inches in diameter, cantaining an ;~ 30 ~ 18 inch deep bed o the loaded carbon. The stripping 5~7 solution consisted of a water solution of 1 ~ercent NaOII and 0.1 percent NaCN and varying proportions of ethallol.
Nineteen bed volumes of the stripping solution were pumped upward through the carbon bed at a rate of 1 bed volume of solution per 15 minutes. Operating temperature was 80C.
Results shown graphically in Figure 1. It will be seen that an ethanol concentration as low as 20 percent gave near-maximum gold desorption. Results of such tests have in general shown a concentration of about 20 to 30 percent by volume of the alcohol to be optimum.
In this example, a series of desorption tests was conduct~l under conditions similar to those of Example 1, except that all strip solutions contained 20 volume percent of methanol as the alcohol component, and varying operating temperatures were employed. Results are shown graphically in Figure 2. It will be seen that the gold desorption is highly temperature dependent and that a temperature of about 80C or above is essential for efficiellt desorption. Temperatures above about 160C, however, have been found to result in minor, if any, add1tional improvement in deeorption efficiency.
. '"
' _7-. " ' ' ~
i :
-
Au(CN)2. Recovery of the gold has conventionally been accomplished by treatment of the resulting cyanide solution with zinc dust. Moxe recently, activated carhon has been found to be an efficient adsorbent on the gold cyani.de ]0 complex, and a vari.ety of processes based on this reaction have been d.e~l.oped. ~ffectiveness of these processes is, however, dependent on development of efficient means for desorbi~.g the gold from the loaded carbon. Stripping with hot caustic sodium cyanide soluti.on at atmospheric pressure : to desorb the gold, followed .by electrolysis to win the metal values, has been employed. However, this method has the disadvanta.~e that simultaneous strippincJ and electrolysis is slow. Elevated pressure has. aJ.so been employe~, so that:
the temperatu~:e of th~ caustic cyanide solution can be rai.sed to about 250~ without boiling, thereby accelerating tlle desorption rate. This technique, however, requires the use of a ho.i.ler-pressure reactor, which ma]ces the process more complicated.
: ~ recent innovation, described in U.S. patent application Ser.ial No. 551,941, filed March 19, 1975, employs caustic-alcohol-water mixtures, containing about 75 percent : alcohol by volume, a.t ambi.ent temperature and pressure for desorbing gold from activated carbon. This method is very cffective for de60rption of yo].d from activated carbon loaded ` 10 by treatment with synthetic NaAu(CN)2 solutions. I~owe~er, .it . . - . .
.
~-hl~ 7 has not been found to be effective for desorption of gold from activated carbon loaded by treatment with cyanide plant effluent5, particularly when the effluents contain the gold in the form of CaAu(CN)2, i.e., when the effluent is formed by treatment of ores with calcium or sodium cyanide and lime. Investigations have shown that there is a significant difference in the behaviour of sodium and calcium regarding carbon adsorption of gold, the aurocyanide complex being much more strongly adsorbed when calcium is employed as the cation. Since lime is generally employed to provide protective alkalinity in conventional cyanidation processes, an efficient process for desorption of the aurocyanide complex in the presence of calcium ion is essential for economi.cal recovery of gold by means of activated carbon adsorption. In addition, soluble extraneous matter, such as organics, silicates, and ferrous-iron salts, in the pregnant cyanide effluents may play a significant role in the desorption process.
According to the process of the present invention there is provided a process for desorption of metal cyanide complexes from the group gold, silver, or mixtures thereof, from activated carbon loaded by treatment with a leach solution containing cal-cium or sodium cyanide and lime comprising contacting the carbon with stripping solution consisting essentially of solution com-prising about 20 to 30 percent by volume of a water soluble alco-hol and about 80 to 70 percent by volume of a strong base, the operating temperature being about 70 to 160C. It has been found that the use of the elevated temperature provides a much more efficient desorption of the gold or silver, while at the same time permitting the use of a relatively low concentration of alcohol, whereby the economy of the process '.
5~i7 . . ~ -is subs~ln~ially improved. Recovery of the c~o]d or silver from the strippin~3 solution is readily accomplis}led by convelltiolla] mealls such as elect:rolysis.
Activateci carbon, suitable for use in the invention is a widely available material that is convelltionally used in adsoxption process, including yold adsorptioll. Typically, it wi11 have a particle size of about 0.15 to 2 mm and a total surface area of about G00-900i~12/y. It may be derivecl from any of a variety of sources sueh as eoal, petroleum chars, c~conut shell, or pulp mill blae~ ash, and is aetivated by eonventional means sueh as heatlng i.n a steam air mixture at a temperature of about 850C.
The aetivated carbon adsorbent is initially loe~ed by eonventional means, i.e., by eontaeting a gold-eyanlde and/or si].ver-eyanide solution, e.g., a eyanide plant effluent, with the aetivated earbon for a time suffieient to permit adsorption of a major amount of the gold-eyanide and/or sîlver-eyanide eomplex. This may be aeeomplished by any eonventional me~ans for eorltaetinc3 liquid3 wit:ll sol.id adsorbents, e.g., by passin~ the gold-cyanide and/or silver-cyallide soluLion throuyh a columnar unit conl:aininy a fixed bed of the aetivated earbon.
The ~old and/or silver are then desorbecl from the loaded earbon, aeeording to the proeess of the invention, by treatment with a solution eomprisiny a water soluble aleohel and an aqueous solution of a stron~3 base, at a temperature of about 80 to 160 DC. As discussed above, and illustrated in the examples below, this temperature range has been found to be essential to aehievement of effieient desorption of the gold, partieularly where the gold-cyanide solution is a ~', .
cyanide p~ant effluent formed by treatment: of ores witl calcium or sodium cyallide and lime.
l`he water soluble alcohol is prefera~ly a lower aliphatic alcohol such as methanol, ethanol, propanol, or isopropanol. As noted above, the use of an elevated temperature permits the use of a relatively small proportlon of alcohol, preferably about ~0 to 30 percel-t by volume of the stripping solution, thereby substantially improving the economy of the process.
The balance of the strlpping solution consists essent:ially of a water solution of a strong base. Sodium hydroxide is the preferred base, but potassium hydroxide may be used. The base is employed in an amount of about 1 to 2 percent by weight of the water solution, or an amount sufficient to provide the stripping solution with a pH of about 11 to 14, preferably about 13 to 14. Use of a high pH is essential since the activated carbon has a substantially decreased capacity for adsorption of tlle go:Lcl-cyarl;de complex at higher values of pH.
The strippiny solution may also contain a small amount of sodium cyanide, e.g., about 0.02 to 1 percent hy weight of the water solution, particularly where the stripping solution is recycled after removal of the desorbed -.
gold. Such recycled solutions often contain small amounts of sodium cyanide as a contaminant from the stripping operation. Alternatively, the sodium cyanide may be added to the stripping solution and may result in somewhat increased efficieny in some cases. It is not, however, an essential ingredient of the stripping solution.
l'he stripping operation is carried out by contactillg the loaded carbon with -the stripping solution of th~
invention, at tlle l-equired tempeLature. Again, contacting may be by any conventional means such as passing the stripping solution through a bed or column of the loaded carbon.
Optimum amounts and flow rates of the stripping solution will depend on the amount of yold and/or silver adsorbed on the loaded carbon, the composition of the gold-cyanide and/or silver-cyanide solution used for loading and specific composition and temperatures of the stripping solution and are best determined empirically. Generally, however, treatment of the loaded carhcl with about 5 to 30 bed volumes of stripping solution, at a flow rate of about 2 to 8 bed volumes of so].ution per hour givec good results.
Although the process of the invention has been found to be particularly effective for desorption of gold, it is also generally effective for desorption of silver, either alone or in combination with the gold.
The following examples will more speci~:ica1ly illustrate the practice of the .invention and the advantages obtained thereby.
xample 1 ~; In this example, a series o~ desorption tests was conducted on loaded activated carhon from a heap leach-carbon adsorption cyanide plant in which leaching was accomplished by means of calcium cyanlde solution containing sufficient lime to provide a pl-l in the range of 9-ll. The loaded carbon carried 235 or Au/ton and 35 oz ~g/ton.
Desorption ~as conducted in a vertical column 24 lnches in length and 2 inches in diameter, cantaining an ;~ 30 ~ 18 inch deep bed o the loaded carbon. The stripping 5~7 solution consisted of a water solution of 1 ~ercent NaOII and 0.1 percent NaCN and varying proportions of ethallol.
Nineteen bed volumes of the stripping solution were pumped upward through the carbon bed at a rate of 1 bed volume of solution per 15 minutes. Operating temperature was 80C.
Results shown graphically in Figure 1. It will be seen that an ethanol concentration as low as 20 percent gave near-maximum gold desorption. Results of such tests have in general shown a concentration of about 20 to 30 percent by volume of the alcohol to be optimum.
In this example, a series of desorption tests was conduct~l under conditions similar to those of Example 1, except that all strip solutions contained 20 volume percent of methanol as the alcohol component, and varying operating temperatures were employed. Results are shown graphically in Figure 2. It will be seen that the gold desorption is highly temperature dependent and that a temperature of about 80C or above is essential for efficiellt desorption. Temperatures above about 160C, however, have been found to result in minor, if any, add1tional improvement in deeorption efficiency.
. '"
' _7-. " ' ' ~
i :
-
Claims (12)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A process for desorption of metal cyanide complexes from the group gold, silver, or mixtures thereof, from activated carbon loaded by treatment with a leach solution containing calcium or sodium cyanide and lime comprising contacting the carbon with stripping solution consisting essentially of solution comprising about 20 to 30 percent by volume of a water soluble alcohol and about 80 to 70 percent by volume of a strong base, the operating temperature being about 70 to 160°C.
2. The process of Claim 1 in which said aqueous solution includes at least 20 percent by volume of water soluble alcohol.
3. The process of Claim 1 in which said stripping solution consists essentially of 20 to 30 percent by volume of a water soluble alcohol, and 80 to 70 percent by volume of an aqueous solution of a strong base, the operat-ing temperature being 80°C to 160°C.
4. The process of Claim 1 in which the activated carbon has been loaded by treatment with a leach solution containing calcium cyanide and lime in an amount to provide a pH of 9-11.
5. The process of Claim 1 in which the alcohol is methanol, ethanol, propanol, or isopropanol.
6. The process of Claim 1 in which the aqueous solution of the strong base has a pH of 13-14.
7. The process of Claim 6 in which the strong base is sodium hydrox-ide or potassium hydroxide.
8. The process of Claim 1 in which the stripping solution addition-ally contains 0.02 to 1 percent of sodium cyanide.
9. The process of claim 1 in which the operating tempera-ture is 80 to 93°C at ambient pressure.
10. The process of claim 1 in which the operating tempera-ture is 80 to 160°C in a slightly pressurized system.
11. The process of claim 1 in which said metal is gold.
12. The process of claim 1 in which said metal is silver.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US66094276A | 1976-02-24 | 1976-02-24 | |
| US660,942 | 1976-02-24 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1102557A true CA1102557A (en) | 1981-06-09 |
Family
ID=24651561
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA272,439A Expired CA1102557A (en) | 1976-02-24 | 1977-02-23 | Desorption of gold from activated carbon |
Country Status (3)
| Country | Link |
|---|---|
| AU (1) | AU513621B2 (en) |
| CA (1) | CA1102557A (en) |
| MX (1) | MX145047A (en) |
-
1977
- 1977-02-23 CA CA272,439A patent/CA1102557A/en not_active Expired
- 1977-02-23 AU AU22596/77A patent/AU513621B2/en not_active Expired
- 1977-02-24 MX MX16814677A patent/MX145047A/en unknown
Also Published As
| Publication number | Publication date |
|---|---|
| AU2259677A (en) | 1978-08-31 |
| AU513621B2 (en) | 1980-12-11 |
| MX145047A (en) | 1982-01-04 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |