CA1236308A - Process for hydrometallurgical extraction of precious metals - Google Patents
Process for hydrometallurgical extraction of precious metalsInfo
- Publication number
- CA1236308A CA1236308A CA000475205A CA475205A CA1236308A CA 1236308 A CA1236308 A CA 1236308A CA 000475205 A CA000475205 A CA 000475205A CA 475205 A CA475205 A CA 475205A CA 1236308 A CA1236308 A CA 1236308A
- Authority
- CA
- Canada
- Prior art keywords
- thiourea
- process according
- leaching
- adsorbent
- precious metals
- 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
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
- C22B11/00—Obtaining noble metals
- C22B11/04—Obtaining noble metals by wet processes
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
- C22B3/00—Extraction of metal compounds from ores or concentrates by wet processes
- C22B3/20—Treatment or purification of solutions, e.g. obtained by leaching
- C22B3/42—Treatment or purification of solutions, e.g. obtained by leaching by ion-exchange extraction
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
- C01G5/00—Compounds of silver
- C01G5/003—Preparation involving a liquid-liquid extraction, an adsorption or an ion-exchange
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
- C01G7/00—Compounds of gold
- C01G7/003—Preparation involving a liquid-liquid extraction, an adsorption or an ion-exchange
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
- C22B3/00—Extraction of metal compounds from ores or concentrates by wet processes
- C22B3/20—Treatment or purification of solutions, e.g. obtained by leaching
- C22B3/22—Treatment or purification of solutions, e.g. obtained by leaching by physical processes, e.g. by filtration, by magnetic means, or by thermal decomposition
- C22B3/24—Treatment or purification of solutions, e.g. obtained by leaching by physical processes, e.g. by filtration, by magnetic means, or by thermal decomposition by adsorption on solid substances, e.g. by extraction with solid resins
-
- 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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- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Organic Chemistry (AREA)
- Mechanical Engineering (AREA)
- Manufacturing & Machinery (AREA)
- Materials Engineering (AREA)
- Metallurgy (AREA)
- Geology (AREA)
- Geochemistry & Mineralogy (AREA)
- General Life Sciences & Earth Sciences (AREA)
- Life Sciences & Earth Sciences (AREA)
- Environmental & Geological Engineering (AREA)
- Inorganic Chemistry (AREA)
- Manufacture And Refinement Of Metals (AREA)
Abstract
Abstract A description is given of an economically interesting process for the hydrometallurgical extraction of precious metals from materials which contain said precious metals, by the use of thiourea as the reagent in an aqueous acidic medium, in which the leaching solution contains less than 7 g/l, preferably from 0.05 to 2.5 g/l of thiourea, and from 10 to 90% by weight of the thiourea are present in oxidized form, and a redox potential of from 250 to 500 mV prevails in the solution. The ad-sorption of the precious metal is effected by acidic ion exchangers or by active carbon from the slurry, and after the end of the leaching process said acidic ion exchang-ers or active carbons are separated from said slurry by means of the correspondingly coarse-meshed fabric.
Description
3~
Process for hydrometallurgical extraction of Precious Metals The invention concerns a process for the extraction of precious metals from materials, which uses,instead of the highly toxic cyanide, thiourea and simultaneously makes possible the processing of cyanide resistant ores.
The reserves of high-grade and easily processed gold and silver ores are constantly decreasing all over the world.
Therefore great efforts are being made to render poor materials which are difficult to treat usable for the extraction of precious metals. The low value contents of the initial substances demand, however, processes which make possible a high yield of the metals combined with low capital and operating costs and low energy input.
~36~
In recent works it has therefore been noted that when using thiourea as the reagent instead of cyanide, very short leaching times are possible. In this process very high thiourea concentrations are used. Thus T.Groenewald reports in ~Iydrometallurgy 1 (1976), 277-290, that when using 1.2 moles of thiourea (= 96 g/l) in the leaching solution, the gold can be extracted within one hour.
C.K. Chen et al. reported in Hydrometallurgy 5 (1980), 207-212, that the dissolution speed of gold and silver in a 1% thiourea solu-tion is more than 10 times as fast as in a solution containing 0.5% sodium cyanide. Lastly J.B. Hiskey also mentions in Proceedings from the 11 0th AIME Meeting, Chicago, Feb.22-26,1981,page 87, that in the gold leaching process the optimal concentration of the thiourea solution is between 80 to 100 g/l.
Due to the high concentrations of thiourea in the solutions and to the simultaneous presence of oxidation agents, considerable losses of thiourea have to be accepted, as a result of which the process has only occasionally been found useful in the technology of gold leaching.
Lastly in precious metals extraction heap leaching and the so-called pulp process have been introduced. These processes dispense with the separation of the leached residues from the solution containing the precious metals.
The extraction of the precious metals is done by adsorp-tion on granular adsorbentS such as ion exchangers or active carbon, which are added directly to the ore slurry (pulp). The separation of the adsorbents charged with the precious metals is performed by simple filtration using correspondingly wide-meshed fabrics, whereby the consider-able capital and operating costs for the separation of the ore residue from the solution are saved. On the other hand, all the added reagents are lost with the leached ore pulp. Therefore either low reagent costs or a lower reagent expenditure are the precondition for the use of the . .
3~1~
pulp process.
When leaching precious metals with cyanides, the pulp process has meanwhile found application on a world-wide scale, since with low reagent concentrations of e.g.
0.05% of sodium cyanide it is possible to work with economy.
But a great drawback to cyanide is the fact that only selected ore types can be processed. They have to be free of cyanicides, i.e. of all those substances which them-selve consume cyanide in an undesirable manner,and with-draw the cyanide from the precious metal leaching.
But a withdrawal of cyanide is inadmissible precisely in the pulp processes which in any case are operated with very low reagent concentrations, since thereby the basic precondition of their economical application is lost if larger amounts of cyanide have to be consumed.
The difficulties above can be overcome by the use of thio-urea, since it is far less susceptible to the cyanicide present,e.g.copper, arsenic, zinc et al.,than cyanide and in addition, it has the advantage of the higher dissolution speed for the precious metals concerned.
Yet despite these indisputable advantages, -thiourea wasonly used in practice in exceptional cases until the present time. The reasons for this are to be found in its sensitivity to oxidation, which leads to high consumption of the reagent and to a decreased yield of the precious metals concerned.
~3~
These mistakes were -triggered by the previous concept of wanting to increase the yield of precious metals by the use of ever-increasing reagent concentrations.
This often had precisely the opposite result, since wi-th increasing concentration,the chemically-conditioned consumption of thiourea was s-till further accelerated.
The oxidation of the thiourea which causes the loss of reagent takes place in several stages. As the last step in the reaction, elementary sulphur is released which leads to the passivation of the leaching goods.
Then attempts were made to keep the reagent loss within bounds by adhering to very low oxidation potentials of less than 160 mV. But the result of this was that the rate of dissolution of the precious metals was so greatly reduced that very high reagent concentrations had to be applied in order to obtain satisfactory time-space yields. However high reagent concentrations inev-itably mean high consumptions and/or they require addit-ional investments for installations and processes for the reextraction of the reagent from the leaching liquid.
The object therefore arose of developing a process for the hydrometallurgical extraction of precious metals which does not have the drawbacks described, but which leads to high yields of precious metals with economically acceptable losses of the reagent.
This object has been solved by the treatment of the initial material with thiourea in an aqueous acidic medium, in which the leaching solution contains from 0.01 to 7 g/l of thiourea in at least partially oxid-ized form, so that a redox potential of from 250 to 500 mV is adjusted against the Ag/AgCl electrode.
~2363~
It was wholly surprising that high rates of dissolution for the precious metals can also be achieved by very low thiourea concentrations in the reagent solution of from 0.07 to 7 g/l, but preferably Erom 50 mg/l to 2500 mg/l, with a specialpreEerence for from 100 mg/l to 1500 mg/l, when certain conditions are observed. Thus it is pre-ferable for from 10 to 90~ by weight of the thiourea present in the solution to be in oxidized form. Because of the low reagent concentration, these solutions are stable for days on end, without any loss of effective-ness and without harmful deposition of sulphur.
The oxidation of the thiourea is effected in the course of the leaching process by the influence of the oxygen in the air, by the presence of iron - III -ions or by the deliberate addition of small amounts of nitric acid, hydrogen peroxide, chlorine or other suitable oxidation agents. The optimum of the oxidized state of the thiourea is analytically supervised and is preferably adjusted to from 40 to 60 per cent.
Such partially oxidized solutions have high redox potentials of from 250 to 500 mV and also possess high rates of dissolution with values of up to ten times those which result from comparison with moderately or non-oxidized solutions having a correspondingly low redox potential.
In addition, such highly active solutions are stable for several days. By the addition of dosed amounts of reduction agents, for which preferably use is made of sulphur dioxide in the form of sulphites, the stability period can be still further extended, in that the oxidized thiourea is partially re-reduced into the in-itial reagent.
3~
The leaching process is carried out at approximately atmospheric temperature or at inc:reased temperature.
The ra-te of dissolution rises sha:rply when the temper-ature is increased.
As a further precondition for the inventive applica-tion of very low thiourea concentrations in precious metal leaching, i-t is necessary to undertake the adsorption of the leached precious metals in the slurry of the leaching material. For this puropose granular adsorpt-ion agents such as strongly acidic inorganic or organ-. ic cation exchangers, active carbon or ion exchangers of the thiol type are added to the slurry before, during or after the leaching. Preferably the adsorbents are added to the material slurry before or during the leach-ing process and after the ending of the adsorption process are simply separated by means of a wide-meshed sieve which allows the finely-milled material slurry to pass through it.
When these conditions are observed, the yield of precious metals can be substantially increased, while relatively brief leaching times are required. The precious metal contents of less easily soluble and complex ores or ther materials also have access in this way to the leaching process.
The separation of the precious metal from the adsorption agent is carried out according to the known processes, such as for example elution using concentrated thiourea solution, with subsequent electrolysis or cementation of the precious metal or with combustion of the adsorption agent.
The examples below are to explain the invention in more detail, but without restricting it thereby.
:~23~
Example 1:
1 kg of a gold ore milled to less than 100 em with a content of 1.5 g/t of gold was first stirred with 1.4 l of water. 100 ml of a mixture of 0.5 g thiourea, 3.5 g Fe-III-sulfate with 22.4% of trivalent iron as well as 4.5 g of sulphuric acid were added thereto. This mixture had reacted for 20 minutes at 40 C, whereby about 50% of the thiourea were oxidized. After the combination of the two mixtures, the acidic suspension was fur-ther stirred.
After 1 hour more than 95~ of the gold in the ore had already dissolved. 3 g of a thiol resin obtainable on the market (IMAC GT 73 from the Dualite firm) were then added to the ore slurry. In the course of the subsequent hour, the gold content sank in the dissolution phase from originally 1 to about 0.05 mg/l, caused by the adsorption of gold on the thiol resin. The separation of the leached ore pulp was performed,by means of screening thLough a fabric having 0.2 mm of mesh width, from the thiol resin.
The thiol resin can thereafter be used for further batches of the same type or it can be regenerated. Warm and concentrated thiourea solution has proved to be an efficient elution agent. In the present case for almost complete elution,it was sufficient to use 50 ml of a 5 thiourea solution of 60 C, which was then enriched to about 29 mg/l of gold, which corresponds to a total yield of 97% oE gold. The precious metal can be extracted there-from according to the conventional process by electrol-ysis or cementation with non-precious metals.
In an alternative modus operandi, the ion exchanger resin used as the adsorption agent can also be fired after repeated use, whereby the precious metal collects in the ash.
~2~i3~3 In a parallel test -the stated reagents were added direct-ly to the ore slurry without previous reaction. It has been found that for the equivalent yield of gold, more than 2 hours, i.e. more than twice the length of time, were necessary.
Example 2 In this example a dust containing iron oxide with 118 g/t of silver was used. 0.5 kg of the material were mixed in 1.5 l of water; the slurry was heated to 35 C and kep constantly at a pH value of about 2 by means of sulphuric acid. At this point the addition of 10 g of a strongly acidic cation exchanger was carried out (Amberlite 252) in order to adsorb the silver which was dissolving into solution during the subsequent leaching.
-For this purpose 1.5 g of thiourea were added dissolved in 20 ml of H20. At the same time the continuous dosing of a concentrated sodium pyrosulphite solution with a content of 120 g/l Na2So205 was performed in an amount of 8 ml/h, in order to adjust the oxidation potential of the solution to 350 mV.
After 30 min. practically the entire content of silver in the initial material had dissolved and had been ad-sorbed by the ion exchanger resin.
The separation of the resin from the leaching residue was effected by use of a sieve via a fabric with a mesh width of 0.2 mm.
The resin was then regenerated with 200 ml 1 M sulphuxic acid and was recycled for repeated use. The content of 525 mg/l of silver in the sulphuric acid corresponds to a yield of 89~. The known techniques such as for example the precipitation as sulphide can be used to extract the silver from the acidic solution.
Process for hydrometallurgical extraction of Precious Metals The invention concerns a process for the extraction of precious metals from materials, which uses,instead of the highly toxic cyanide, thiourea and simultaneously makes possible the processing of cyanide resistant ores.
The reserves of high-grade and easily processed gold and silver ores are constantly decreasing all over the world.
Therefore great efforts are being made to render poor materials which are difficult to treat usable for the extraction of precious metals. The low value contents of the initial substances demand, however, processes which make possible a high yield of the metals combined with low capital and operating costs and low energy input.
~36~
In recent works it has therefore been noted that when using thiourea as the reagent instead of cyanide, very short leaching times are possible. In this process very high thiourea concentrations are used. Thus T.Groenewald reports in ~Iydrometallurgy 1 (1976), 277-290, that when using 1.2 moles of thiourea (= 96 g/l) in the leaching solution, the gold can be extracted within one hour.
C.K. Chen et al. reported in Hydrometallurgy 5 (1980), 207-212, that the dissolution speed of gold and silver in a 1% thiourea solu-tion is more than 10 times as fast as in a solution containing 0.5% sodium cyanide. Lastly J.B. Hiskey also mentions in Proceedings from the 11 0th AIME Meeting, Chicago, Feb.22-26,1981,page 87, that in the gold leaching process the optimal concentration of the thiourea solution is between 80 to 100 g/l.
Due to the high concentrations of thiourea in the solutions and to the simultaneous presence of oxidation agents, considerable losses of thiourea have to be accepted, as a result of which the process has only occasionally been found useful in the technology of gold leaching.
Lastly in precious metals extraction heap leaching and the so-called pulp process have been introduced. These processes dispense with the separation of the leached residues from the solution containing the precious metals.
The extraction of the precious metals is done by adsorp-tion on granular adsorbentS such as ion exchangers or active carbon, which are added directly to the ore slurry (pulp). The separation of the adsorbents charged with the precious metals is performed by simple filtration using correspondingly wide-meshed fabrics, whereby the consider-able capital and operating costs for the separation of the ore residue from the solution are saved. On the other hand, all the added reagents are lost with the leached ore pulp. Therefore either low reagent costs or a lower reagent expenditure are the precondition for the use of the . .
3~1~
pulp process.
When leaching precious metals with cyanides, the pulp process has meanwhile found application on a world-wide scale, since with low reagent concentrations of e.g.
0.05% of sodium cyanide it is possible to work with economy.
But a great drawback to cyanide is the fact that only selected ore types can be processed. They have to be free of cyanicides, i.e. of all those substances which them-selve consume cyanide in an undesirable manner,and with-draw the cyanide from the precious metal leaching.
But a withdrawal of cyanide is inadmissible precisely in the pulp processes which in any case are operated with very low reagent concentrations, since thereby the basic precondition of their economical application is lost if larger amounts of cyanide have to be consumed.
The difficulties above can be overcome by the use of thio-urea, since it is far less susceptible to the cyanicide present,e.g.copper, arsenic, zinc et al.,than cyanide and in addition, it has the advantage of the higher dissolution speed for the precious metals concerned.
Yet despite these indisputable advantages, -thiourea wasonly used in practice in exceptional cases until the present time. The reasons for this are to be found in its sensitivity to oxidation, which leads to high consumption of the reagent and to a decreased yield of the precious metals concerned.
~3~
These mistakes were -triggered by the previous concept of wanting to increase the yield of precious metals by the use of ever-increasing reagent concentrations.
This often had precisely the opposite result, since wi-th increasing concentration,the chemically-conditioned consumption of thiourea was s-till further accelerated.
The oxidation of the thiourea which causes the loss of reagent takes place in several stages. As the last step in the reaction, elementary sulphur is released which leads to the passivation of the leaching goods.
Then attempts were made to keep the reagent loss within bounds by adhering to very low oxidation potentials of less than 160 mV. But the result of this was that the rate of dissolution of the precious metals was so greatly reduced that very high reagent concentrations had to be applied in order to obtain satisfactory time-space yields. However high reagent concentrations inev-itably mean high consumptions and/or they require addit-ional investments for installations and processes for the reextraction of the reagent from the leaching liquid.
The object therefore arose of developing a process for the hydrometallurgical extraction of precious metals which does not have the drawbacks described, but which leads to high yields of precious metals with economically acceptable losses of the reagent.
This object has been solved by the treatment of the initial material with thiourea in an aqueous acidic medium, in which the leaching solution contains from 0.01 to 7 g/l of thiourea in at least partially oxid-ized form, so that a redox potential of from 250 to 500 mV is adjusted against the Ag/AgCl electrode.
~2363~
It was wholly surprising that high rates of dissolution for the precious metals can also be achieved by very low thiourea concentrations in the reagent solution of from 0.07 to 7 g/l, but preferably Erom 50 mg/l to 2500 mg/l, with a specialpreEerence for from 100 mg/l to 1500 mg/l, when certain conditions are observed. Thus it is pre-ferable for from 10 to 90~ by weight of the thiourea present in the solution to be in oxidized form. Because of the low reagent concentration, these solutions are stable for days on end, without any loss of effective-ness and without harmful deposition of sulphur.
The oxidation of the thiourea is effected in the course of the leaching process by the influence of the oxygen in the air, by the presence of iron - III -ions or by the deliberate addition of small amounts of nitric acid, hydrogen peroxide, chlorine or other suitable oxidation agents. The optimum of the oxidized state of the thiourea is analytically supervised and is preferably adjusted to from 40 to 60 per cent.
Such partially oxidized solutions have high redox potentials of from 250 to 500 mV and also possess high rates of dissolution with values of up to ten times those which result from comparison with moderately or non-oxidized solutions having a correspondingly low redox potential.
In addition, such highly active solutions are stable for several days. By the addition of dosed amounts of reduction agents, for which preferably use is made of sulphur dioxide in the form of sulphites, the stability period can be still further extended, in that the oxidized thiourea is partially re-reduced into the in-itial reagent.
3~
The leaching process is carried out at approximately atmospheric temperature or at inc:reased temperature.
The ra-te of dissolution rises sha:rply when the temper-ature is increased.
As a further precondition for the inventive applica-tion of very low thiourea concentrations in precious metal leaching, i-t is necessary to undertake the adsorption of the leached precious metals in the slurry of the leaching material. For this puropose granular adsorpt-ion agents such as strongly acidic inorganic or organ-. ic cation exchangers, active carbon or ion exchangers of the thiol type are added to the slurry before, during or after the leaching. Preferably the adsorbents are added to the material slurry before or during the leach-ing process and after the ending of the adsorption process are simply separated by means of a wide-meshed sieve which allows the finely-milled material slurry to pass through it.
When these conditions are observed, the yield of precious metals can be substantially increased, while relatively brief leaching times are required. The precious metal contents of less easily soluble and complex ores or ther materials also have access in this way to the leaching process.
The separation of the precious metal from the adsorption agent is carried out according to the known processes, such as for example elution using concentrated thiourea solution, with subsequent electrolysis or cementation of the precious metal or with combustion of the adsorption agent.
The examples below are to explain the invention in more detail, but without restricting it thereby.
:~23~
Example 1:
1 kg of a gold ore milled to less than 100 em with a content of 1.5 g/t of gold was first stirred with 1.4 l of water. 100 ml of a mixture of 0.5 g thiourea, 3.5 g Fe-III-sulfate with 22.4% of trivalent iron as well as 4.5 g of sulphuric acid were added thereto. This mixture had reacted for 20 minutes at 40 C, whereby about 50% of the thiourea were oxidized. After the combination of the two mixtures, the acidic suspension was fur-ther stirred.
After 1 hour more than 95~ of the gold in the ore had already dissolved. 3 g of a thiol resin obtainable on the market (IMAC GT 73 from the Dualite firm) were then added to the ore slurry. In the course of the subsequent hour, the gold content sank in the dissolution phase from originally 1 to about 0.05 mg/l, caused by the adsorption of gold on the thiol resin. The separation of the leached ore pulp was performed,by means of screening thLough a fabric having 0.2 mm of mesh width, from the thiol resin.
The thiol resin can thereafter be used for further batches of the same type or it can be regenerated. Warm and concentrated thiourea solution has proved to be an efficient elution agent. In the present case for almost complete elution,it was sufficient to use 50 ml of a 5 thiourea solution of 60 C, which was then enriched to about 29 mg/l of gold, which corresponds to a total yield of 97% oE gold. The precious metal can be extracted there-from according to the conventional process by electrol-ysis or cementation with non-precious metals.
In an alternative modus operandi, the ion exchanger resin used as the adsorption agent can also be fired after repeated use, whereby the precious metal collects in the ash.
~2~i3~3 In a parallel test -the stated reagents were added direct-ly to the ore slurry without previous reaction. It has been found that for the equivalent yield of gold, more than 2 hours, i.e. more than twice the length of time, were necessary.
Example 2 In this example a dust containing iron oxide with 118 g/t of silver was used. 0.5 kg of the material were mixed in 1.5 l of water; the slurry was heated to 35 C and kep constantly at a pH value of about 2 by means of sulphuric acid. At this point the addition of 10 g of a strongly acidic cation exchanger was carried out (Amberlite 252) in order to adsorb the silver which was dissolving into solution during the subsequent leaching.
-For this purpose 1.5 g of thiourea were added dissolved in 20 ml of H20. At the same time the continuous dosing of a concentrated sodium pyrosulphite solution with a content of 120 g/l Na2So205 was performed in an amount of 8 ml/h, in order to adjust the oxidation potential of the solution to 350 mV.
After 30 min. practically the entire content of silver in the initial material had dissolved and had been ad-sorbed by the ion exchanger resin.
The separation of the resin from the leaching residue was effected by use of a sieve via a fabric with a mesh width of 0.2 mm.
The resin was then regenerated with 200 ml 1 M sulphuxic acid and was recycled for repeated use. The content of 525 mg/l of silver in the sulphuric acid corresponds to a yield of 89~. The known techniques such as for example the precipitation as sulphide can be used to extract the silver from the acidic solution.
Claims (15)
1. A process for hydrometallurgical extraction of precious metals from material which contains said metals by treatment with a leaching solution comprising thiourea in an aqueous acidic medium, wherein the leaching solution contains from 0.01 to 7 g/l of thiourea in at least partially oxidized form so that a redox potential is set of from 250 to 500 mV against an Ag/AgCl electrode.
2. A process according to claim 1, wherein the leaching solution contains from 0.05 to 2.5 g/l of thiourea.
3. A process according to claim 1, wherein the leaching solution contains from 0.1 to 1.5 g/l of thiourea.
4. A process according to claim 1, 2 or 3, wherein 10 to 90% by weight of the thiourea is in said oxidized form.
5. A process according to claim 1, 2 or 3, wherein 40 to 60% by weight of the thiourea is in said oxidized form.
6. A process according to claim l; wherein a granular adsorbent is added to a slurry of the materials of the extraction process.
7. A process according to claim 6, wherein said adsorbent is an organic cation exchanger.
8. A process according to claim 6, wherein said adsorbent is an ion exchanger resin of the thiol type.
9. A process according to claim 6, wherein said adsorbent is active carbon.
10. A process according to claim 6, wherein the material to be treated has a granular size smaller than that of the adsorbents.
11. A process for the hydrometallurgical extraction of precious metals from materials which contain said metals comprising:
leaching a material containing precious metal in an aqueous acidic medium containing 0.01 to 7 g/l of thiourea in an at least partially oxidized form effective to establish a redox potential of from 250 to 500 mV against an Ag/AgCl electrode.
leaching a material containing precious metal in an aqueous acidic medium containing 0.01 to 7 g/l of thiourea in an at least partially oxidized form effective to establish a redox potential of from 250 to 500 mV against an Ag/AgCl electrode.
12. A process according to claim 11, wherein said material, and said medium form a slurry and including a step of adding a granular adsorbent to said slurry.
13. A process according to claim 12, wherein said adsorbent is added prior to said leaching.
14. A process according to claim 12, wherein said adsorbent is added during said leaching.
15. A process according to claim 12, wherein said adsorbent is added after said leaching.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE19843407049 DE3407049A1 (en) | 1984-02-27 | 1984-02-27 | Process for the hydrometallurgical extraction of noble metals |
| DEP3407049.4 | 1984-02-27 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1236308A true CA1236308A (en) | 1988-05-10 |
Family
ID=6228945
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000475205A Expired CA1236308A (en) | 1984-02-27 | 1985-02-26 | Process for hydrometallurgical extraction of precious metals |
Country Status (5)
| Country | Link |
|---|---|
| AU (1) | AU566716B2 (en) |
| CA (1) | CA1236308A (en) |
| DE (1) | DE3407049A1 (en) |
| ZA (1) | ZA851489B (en) |
| ZW (1) | ZW2985A1 (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5342449A (en) * | 1990-12-11 | 1994-08-30 | Holbein Bruce E | Process for the decontamination of toxic, heavy-metal containing soils |
Families Citing this family (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CA1321077C (en) * | 1986-08-26 | 1993-08-10 | Lucia Rosato | Process for the recovery of silver from zinc plant calcines and neutral or low acid leach residues with thiourea |
| CA1337741C (en) * | 1987-07-23 | 1995-12-19 | Masaaki Matsuda | Process for recovery of gold using sulphur-containing acidic compounds |
| DE3801340C1 (en) * | 1988-01-19 | 1989-03-16 | Skw Trostberg Ag, 8223 Trostberg, De | |
| DE19715319C2 (en) * | 1997-04-04 | 2001-03-01 | Werner Fabian | Three-stage hydrometallurgical process for the metal separation of electronic waste, in particular from printed circuit boards and metal-containing plastic residues |
-
1984
- 1984-02-27 DE DE19843407049 patent/DE3407049A1/en not_active Withdrawn
-
1985
- 1985-02-26 CA CA000475205A patent/CA1236308A/en not_active Expired
- 1985-02-26 ZW ZW29/85A patent/ZW2985A1/en unknown
- 1985-02-27 ZA ZA851489A patent/ZA851489B/en unknown
- 1985-02-27 AU AU39219/85A patent/AU566716B2/en not_active Ceased
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5342449A (en) * | 1990-12-11 | 1994-08-30 | Holbein Bruce E | Process for the decontamination of toxic, heavy-metal containing soils |
Also Published As
| Publication number | Publication date |
|---|---|
| DE3407049A1 (en) | 1985-09-05 |
| AU3921985A (en) | 1985-10-31 |
| ZA851489B (en) | 1985-11-27 |
| AU566716B2 (en) | 1987-10-29 |
| ZW2985A1 (en) | 1985-09-04 |
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