CA1262050A - Process for extracting gold by decomposition of lead cyanide compound - Google Patents
Process for extracting gold by decomposition of lead cyanide compoundInfo
- Publication number
- CA1262050A CA1262050A CA000545177A CA545177A CA1262050A CA 1262050 A CA1262050 A CA 1262050A CA 000545177 A CA000545177 A CA 000545177A CA 545177 A CA545177 A CA 545177A CA 1262050 A CA1262050 A CA 1262050A
- Authority
- CA
- Canada
- Prior art keywords
- lead
- cyanide
- gold
- cyanide compound
- decomposition
- 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
- C22B11/08—Obtaining noble metals by cyaniding
Landscapes
- Engineering & Computer Science (AREA)
- Chemical & Material Sciences (AREA)
- Manufacturing & Machinery (AREA)
- Materials Engineering (AREA)
- Mechanical Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Manufacture And Refinement Of Metals (AREA)
Abstract
This invention relates to the extraction of gold from gold-bearing materials like ores, concentrates, tailings, municipal sewage and other materials.
The process consists of leaching the gold-bearing material with solid lead cyanide compound, which an be formed in-situ in the pulp by mixing soluble lead compounds like lead nitrate, lead acetate and other lead salts with commonly used cyanide reagents like sodium cyanide, calcium cyanide and potassium cyanide at a much lower PH than the PH to be used later in the actual leaching process for the decomposition of lead cyanide compound and generation of active CN- ions. Therefore the main innovation of this process lies in the fact that once solid lead cyanide compound has been added to or formed in the leach pulp it will be decomposed at a higher PH to produce more active "nascent" CN-.
The process consists of leaching the gold-bearing material with solid lead cyanide compound, which an be formed in-situ in the pulp by mixing soluble lead compounds like lead nitrate, lead acetate and other lead salts with commonly used cyanide reagents like sodium cyanide, calcium cyanide and potassium cyanide at a much lower PH than the PH to be used later in the actual leaching process for the decomposition of lead cyanide compound and generation of active CN- ions. Therefore the main innovation of this process lies in the fact that once solid lead cyanide compound has been added to or formed in the leach pulp it will be decomposed at a higher PH to produce more active "nascent" CN-.
Description
This inven-tion rela-tes -to -the e~-trac-tion of gold from gold-bearin~ ma-terials like ores, eoncen-tra-tes, -tailin~s~ municipal sewa~e and o-ther ma-terials.
The process consists of leachin~ the gold-bearing ma-terial with solïd lead cyanide compound, whieh can be formed in-si-tu in the pulp by mixing soluble lead compounds like lead nitrate, lead acetate and other lead salts with eommonly used cyanide reagents like sodium cyanide, calcium cyanide and po-tassium cyanide at a much lower PH than -the PH to be used later in the actual leaching process for the decomposition of lead cyanide compound and genera-tion of active CN ions. Therefore the main innova-tion of this process lies in -the fac-t that once solid lead cyanide eompound has been added -to or ~ormed in -the leach pulp it will be decomposed at a higher PH to produce more active "nascent" CN--.
Aeeording to -the present indus-trial praetiee many gold mills use lead nitrate or o-ther lead eompounds in much smaller amount than the amount of cyanide used, i.e. 0.1 -to o.L~ pounds of lead nitrate per ton of ore compared to 0.~ -to 2.0 pounds of eyanide per -ton of ore. The funetion of lead nitrate or o-ther lead eompounds here is to preeipitate any soluble sulfides or thiosulfa-tes -tha-t may be present and -thereby avoiding their harmful effee-ts on the eyanidation leaching process. The presen-t invention, however, proposes -the use of rela-tively inereased amount of lead nitrate or other soluble lead salts to form preeipitated lead eyanide eompound in the pulp whieh will be eventually deeomposed -to produee "nascentl' CN . The chemical reaction Pb(N03)2 ~ 2NaCN _~ Pb(CN)2 -~ 2NaN03 indicates the ratio of lead ni-trate to eyanide to be approximately 3.L~:l. The exae-t na-ture of the reaetion, however, has not been found ou-t.
One of -the rnain reagen-ts, besides cyanide~ in ~the commonly used cyanidation process is oxy~en. Because the solubility of oxy~en in water is very low, the availability of oxy~en in the pulp becomes the cri-tical fac-tor in the extraction of ~old by ordinary cyanida~tion leachin~ process. Leachin~ at a hi~her pulp density or of pulps con-tainin~ oxy~en consumin~
compounds can't be achieved in many cases due -to insufficient oxy~en available for cyanidation reaction itself. Therefore, it would be a tremendous advanta~e if one can find a cyanidation reaction, where oxy~en may not be a reactant or much less oxy~en is required than that in the presen-tly defined cyanidation reac-tion. It is to be noted that the previously used Bromo-Cyanide process for ~old -telluride ores did no-t require oxy~en for successful gold leachin~. At presen-t, however, -this process is obsolete. I have found, on the other hand, that leaching of ~old-bearin~ materials by the decomposition of solid lead cyanide compound a~t a hi~her PH than -the PH at which such compound can be formed may provide a cyanida-tion reac-tion where little or no oxy~en may be required. The followin~ test performed shows that lead cyanide compound can be formed at a lower PH
and can be decomposed at a higher PH -to produce active CN :
A) 10 c.c. of 0.~% NaCN solu-tion (.05 gm NaCN) was mixed wi-th - 30 c.c. of l.~o Pb(NO3)2 solution (.4~ ~m Pb(NO3)2) and then ~O c.c. water was added -to this mix-ture -to make a total volume of 90 c.c. solu-tion. Immedia~tely whi~te precipitate formed, which was thou~ht to be lead cyanide compound. The ~H of this solution was 7.5. The solution with ~the white precipitate in it was a~itated by a rotatin~ stirrer for a period of 40 minutes. The solution was -then -titrated for NaCN by the usual silver nitrate titration method. Amount of NaCN by -this titration was found to be nil indicatin~ no decomposition of the lead cyanide compound.
.; .
.. ...
135~
B) The same mixture of NaCN, lead ni-tra-te and water was formed. Bu-t this -time after the white precipi-tate was formed, lime was added to brin~ the PH up. PH after lime addition was 9 . 5 . The solu~tion was -then agitated for a period of 40 minutes in the same way as in A). After this a~itation the ti-tration for NaCN was 0. 9 pound NaCN per pound solu-tion. This indicates comple-te decomposition of of the lead cyanide compound at a hi~her PH compared to no decomposition at PH 7.5 in A).
The application of the present invention can now be illustra-ted by the following examples:
579 ~=ms of ~old ore from a deposi-t in Vancouver Island, British Columbia, was leached at a pulp densi-ty of 50% solids for 24 hrs.
Initial addition of NaCN at the star-t of leachin~ was 2 pounds per ton solution and the final ti-tration at the end of leachin~
was 0.831 pound per ton solution, which ~ave a cyanide consumption of 1.17 pounds per ton ore. The PH was maintained at 10.4 by addition of CaO ancl the CaO consump-tion was 3 . 89 pounds per ton ore. The feed assay of this sample was .06 oz. Au per ton ore and the leach residue assay was . 024 oz . Au per -ton ore ~ivin,~
a Au extrac~tion of only 60 percent. The ~rind size of feed was 74% minus lOO mesh.
This relatively lower extrac-tion at a finer size was unexpected, since the same ore sample at much coarser ~rinds of 100% minus 6 mesh, 30% minus 100 mesh and 48% minus 100 mesh ~ave Au ex-traction of 83, 82 and 83 percen~ts respec-tively under similar leachin,~
conditions. A possible conclusion was drawn tha~t the low reco~ery a-t -the finer ,~rind size of 7L~% minus lOO mesh could be due -to hi~her oxy~en consump-tion via surface adsorp-tion because of the lar~er surface area formed.
L~ _
The process consists of leachin~ the gold-bearing ma-terial with solïd lead cyanide compound, whieh can be formed in-si-tu in the pulp by mixing soluble lead compounds like lead nitrate, lead acetate and other lead salts with eommonly used cyanide reagents like sodium cyanide, calcium cyanide and po-tassium cyanide at a much lower PH than -the PH to be used later in the actual leaching process for the decomposition of lead cyanide compound and genera-tion of active CN ions. Therefore the main innova-tion of this process lies in -the fac-t that once solid lead cyanide eompound has been added -to or ~ormed in -the leach pulp it will be decomposed at a higher PH to produce more active "nascent" CN--.
Aeeording to -the present indus-trial praetiee many gold mills use lead nitrate or o-ther lead eompounds in much smaller amount than the amount of cyanide used, i.e. 0.1 -to o.L~ pounds of lead nitrate per ton of ore compared to 0.~ -to 2.0 pounds of eyanide per -ton of ore. The funetion of lead nitrate or o-ther lead eompounds here is to preeipitate any soluble sulfides or thiosulfa-tes -tha-t may be present and -thereby avoiding their harmful effee-ts on the eyanidation leaching process. The presen-t invention, however, proposes -the use of rela-tively inereased amount of lead nitrate or other soluble lead salts to form preeipitated lead eyanide eompound in the pulp whieh will be eventually deeomposed -to produee "nascentl' CN . The chemical reaction Pb(N03)2 ~ 2NaCN _~ Pb(CN)2 -~ 2NaN03 indicates the ratio of lead ni-trate to eyanide to be approximately 3.L~:l. The exae-t na-ture of the reaetion, however, has not been found ou-t.
One of -the rnain reagen-ts, besides cyanide~ in ~the commonly used cyanidation process is oxy~en. Because the solubility of oxy~en in water is very low, the availability of oxy~en in the pulp becomes the cri-tical fac-tor in the extraction of ~old by ordinary cyanida~tion leachin~ process. Leachin~ at a hi~her pulp density or of pulps con-tainin~ oxy~en consumin~
compounds can't be achieved in many cases due -to insufficient oxy~en available for cyanidation reaction itself. Therefore, it would be a tremendous advanta~e if one can find a cyanidation reaction, where oxy~en may not be a reactant or much less oxy~en is required than that in the presen-tly defined cyanidation reac-tion. It is to be noted that the previously used Bromo-Cyanide process for ~old -telluride ores did no-t require oxy~en for successful gold leachin~. At presen-t, however, -this process is obsolete. I have found, on the other hand, that leaching of ~old-bearin~ materials by the decomposition of solid lead cyanide compound a~t a hi~her PH than -the PH at which such compound can be formed may provide a cyanida-tion reac-tion where little or no oxy~en may be required. The followin~ test performed shows that lead cyanide compound can be formed at a lower PH
and can be decomposed at a higher PH -to produce active CN :
A) 10 c.c. of 0.~% NaCN solu-tion (.05 gm NaCN) was mixed wi-th - 30 c.c. of l.~o Pb(NO3)2 solution (.4~ ~m Pb(NO3)2) and then ~O c.c. water was added -to this mix-ture -to make a total volume of 90 c.c. solu-tion. Immedia~tely whi~te precipitate formed, which was thou~ht to be lead cyanide compound. The ~H of this solution was 7.5. The solution with ~the white precipitate in it was a~itated by a rotatin~ stirrer for a period of 40 minutes. The solution was -then -titrated for NaCN by the usual silver nitrate titration method. Amount of NaCN by -this titration was found to be nil indicatin~ no decomposition of the lead cyanide compound.
.; .
.. ...
135~
B) The same mixture of NaCN, lead ni-tra-te and water was formed. Bu-t this -time after the white precipi-tate was formed, lime was added to brin~ the PH up. PH after lime addition was 9 . 5 . The solu~tion was -then agitated for a period of 40 minutes in the same way as in A). After this a~itation the ti-tration for NaCN was 0. 9 pound NaCN per pound solu-tion. This indicates comple-te decomposition of of the lead cyanide compound at a hi~her PH compared to no decomposition at PH 7.5 in A).
The application of the present invention can now be illustra-ted by the following examples:
579 ~=ms of ~old ore from a deposi-t in Vancouver Island, British Columbia, was leached at a pulp densi-ty of 50% solids for 24 hrs.
Initial addition of NaCN at the star-t of leachin~ was 2 pounds per ton solution and the final ti-tration at the end of leachin~
was 0.831 pound per ton solution, which ~ave a cyanide consumption of 1.17 pounds per ton ore. The PH was maintained at 10.4 by addition of CaO ancl the CaO consump-tion was 3 . 89 pounds per ton ore. The feed assay of this sample was .06 oz. Au per ton ore and the leach residue assay was . 024 oz . Au per -ton ore ~ivin,~
a Au extrac~tion of only 60 percent. The ~rind size of feed was 74% minus lOO mesh.
This relatively lower extrac-tion at a finer size was unexpected, since the same ore sample at much coarser ~rinds of 100% minus 6 mesh, 30% minus 100 mesh and 48% minus 100 mesh ~ave Au ex-traction of 83, 82 and 83 percen~ts respec-tively under similar leachin,~
conditions. A possible conclusion was drawn tha~t the low reco~ery a-t -the finer ,~rind size of 7L~% minus lOO mesh could be due -to hi~her oxy~en consump-tion via surface adsorp-tion because of the lar~er surface area formed.
L~ _
2~
The presen~t invention was then applied to a higher grade ore from the same deposi-t at a much finer grind and at a much higher pulp densi-ty -to determine the need of oxygen availability in the following manner:
Ore sample taken - lOO gms Grind Size - 91~o minus lOO mesh 25 c.c. of 0.5~0 NaCN solution (.125 gm NaCN) was mixed with 25 c.c. of 1.5% Pbt-1~03)2 solu-tion (.375 gm Pb(N03)2). This 50 c.c. solution which gave immediate precipi-tate of lead cyanide compound was mixed with the above 100 gms ore sample -to give a high pulp density of 66% solids; also 15 washed carbon particles weighing 0.3 gm were added -to the pulp at -the start. The whole pulp was then leached for 22 hours. PH of the pulp (after the addition of the lead cyanide compound) was maintained at 10 to 11 by the addition of lime. The results of this leaching test by the decomposition of lead cyanide compound are shown below:
Feed Assay - o.lL~9 oz. Au per -ton ore Leach Residue Assay - 0.031 oz. Au per ton ore ~oaded Carbon Assay - 23 oz. Au per ton carbon NaCN -titra-tion at end of leach - 0.5 lb./ton solu~tion Percent Au Extraction - ~2~o The results of this ~test according to the present invention indicate that ~old can be leached successfully by -the decomposition of lead cyanide compound at a higher PH than the PH at which lead cyanide compound is stable and oxygen-requiremen-t may not be as high as in the ordinary cyanidation process.
. .
The presen~t invention was then applied to a higher grade ore from the same deposi-t at a much finer grind and at a much higher pulp densi-ty -to determine the need of oxygen availability in the following manner:
Ore sample taken - lOO gms Grind Size - 91~o minus lOO mesh 25 c.c. of 0.5~0 NaCN solution (.125 gm NaCN) was mixed with 25 c.c. of 1.5% Pbt-1~03)2 solu-tion (.375 gm Pb(N03)2). This 50 c.c. solution which gave immediate precipi-tate of lead cyanide compound was mixed with the above 100 gms ore sample -to give a high pulp density of 66% solids; also 15 washed carbon particles weighing 0.3 gm were added -to the pulp at -the start. The whole pulp was then leached for 22 hours. PH of the pulp (after the addition of the lead cyanide compound) was maintained at 10 to 11 by the addition of lime. The results of this leaching test by the decomposition of lead cyanide compound are shown below:
Feed Assay - o.lL~9 oz. Au per -ton ore Leach Residue Assay - 0.031 oz. Au per ton ore ~oaded Carbon Assay - 23 oz. Au per ton carbon NaCN -titra-tion at end of leach - 0.5 lb./ton solu~tion Percent Au Extraction - ~2~o The results of this ~test according to the present invention indicate that ~old can be leached successfully by -the decomposition of lead cyanide compound at a higher PH than the PH at which lead cyanide compound is stable and oxygen-requiremen-t may not be as high as in the ordinary cyanidation process.
. .
Claims
Claim 1 A process of extracting gold from gold bearing materials such as ores, concentrates, slimes, tailings, municipal sewage, beach sands and other materials comprising leaching by decomposition of solid lead cyanide compounds at a PH higher than 8.0 whereby a leaching pulp is created.
Claim 2 A process according to claim 1, where the lead cyanide compounds can be formed in-situ in the leaching pulp by adding compounds at a PH lower than 8.0, and then raising the PH higher for the decomposition of lead cyanide compounds and generation of active "nascent" CN- ions.
Claim 3 A process according to Claims 1 and 2, where the PH of the leaching pulp is raised higher after the lead cyanide compound has been added to or formed in the leaching pulp.
Claim 2 A process according to claim 1, where the lead cyanide compounds can be formed in-situ in the leaching pulp by adding compounds at a PH lower than 8.0, and then raising the PH higher for the decomposition of lead cyanide compounds and generation of active "nascent" CN- ions.
Claim 3 A process according to Claims 1 and 2, where the PH of the leaching pulp is raised higher after the lead cyanide compound has been added to or formed in the leaching pulp.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000545177A CA1262050A (en) | 1987-08-24 | 1987-08-24 | Process for extracting gold by decomposition of lead cyanide compound |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000545177A CA1262050A (en) | 1987-08-24 | 1987-08-24 | Process for extracting gold by decomposition of lead cyanide compound |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1262050A true CA1262050A (en) | 1989-10-03 |
Family
ID=4136324
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000545177A Expired CA1262050A (en) | 1987-08-24 | 1987-08-24 | Process for extracting gold by decomposition of lead cyanide compound |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1262050A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US7025942B2 (en) | 2001-03-13 | 2006-04-11 | Her Majesty The Queen In Right Of Canada, As Represented By The Minister Of Natural Resources | Control of lead nitrate addition in gold recovery |
-
1987
- 1987-08-24 CA CA000545177A patent/CA1262050A/en not_active Expired
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US7025942B2 (en) | 2001-03-13 | 2006-04-11 | Her Majesty The Queen In Right Of Canada, As Represented By The Minister Of Natural Resources | Control of lead nitrate addition in gold recovery |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKLA | Lapsed |