Specialized metallurgical processes – compositions for use therei – Processes – Free metal or alloy reductant contains magnesium
Patent
1996-06-12
1998-06-23
Simmons, David A.
Specialized metallurgical processes, compositions for use therei
Processes
Free metal or alloy reductant contains magnesium
75421, 75422, 75423, 75426, 75427, 75428, 75721, 75729, 75732, 75735, 75737, 75744, 210684, 210685, 210694, 423 25, 423 29, 423236, 423368, 423378, 423407, C22B 1100
Patent
active
057699259
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a process for eluting gold and/or silver which are adsorbed on activated carbon by direct elution or by elution with presoaking, the direct elution comprising bringing the carbon into contact with an eluent solution containing a cyanide and/or a base and optionally an organic solvent, in conditions such that the carbon is at least partially stripped, thus producing a gold-bearing and/or silver-bearing eluate, and the elution with presoaking comprising bringing the carbon into contact with a presoaking solution containing a cyanide and/or a base and optionally an organic solvent, so as to produce presoaked carbon which is more suited to being eluted and a spent presoaking solution, and bringing the presoaked carbon into contact with an aqueous or organic eluent in conditions such that the presoaked carbon is at least partially stripped, thus producing a gold-bearing and/or silver-bearing eluate, the presence of cyanide in the eluent solution or the presoaking solution being obligatory if one wishes to elute silver.
BACKGROUND OF THE RELATED ART
Many processes of this kind are already known, especially the Zadra process, the Zadra process under pressure and the Zadra process using organic solvents, all of which work by direct elution, and the AARL and Micron Research processes, which make use of presoaking before elution.
In the Zadra process (J. B. Zadra et al., 1952. A process for recovering gold and silver from activated carbon by leaching and electrolysis. U.S. Bur. Mines, Rep. Invest. No 4843) the eluent solution contains approximately 10 g/l NaOH and 1 g/l NaCN, although these concentrations can vary from one plant to another. The elution temperature varies between 80.degree. and 97.degree. C. and the duration between 48 and 70 hours. This process has the advantage of operating at atmospheric pressure at relatively moderate temperatures without any flammable solvent. The big disadvantage is the excessive duration.
In the Zadra process under pressure (J. R. Ross et al. Pressure stripping gold from activated carbon. Paper presented at the Annual Conference, Society Mining Engineers AIME, Chicago Ill., Feb. 26-Mar. 1, 1973, 14 pp.) an elution temperature higher than 100.degree. C. and an appropriate pressure enable the duration of the elution to be shortened to 24 or even 10 hours. However, this elution time is still relatively long.
Insofar as the Zadra process using organic solvents is concerned, the following conditions may be considered ideal: Zadra NaCN--NaOH eluent solution with 20% by volume of an alcohol such as ethanol; duration from 6 to 8 hours; temperature from 80.degree. to 90.degree. C. (U.S. Pat. 4,208,378 and H. J. Heinen et al., 1976. Gold desorption from activated carbon with alkaline alcohol solution; in: A. Weiss (ed.), World Mining and Metals Technology, vol. 1, A.I.M.E., New York, chap. 33, pp. 551-564). In this process the replacement of ethanol with a less flammable glycol is accompanied by an appreciable increase in the duration of elution (J. L. Fast: Glycol stripping. A viable option for recovering gold from carbon. Engineering and Mining Journal, 1987, pp. 48-49). Other solvents that can be employed are acetone and acetonitrile (F. Espiell et al., 1988. Gold desorption from activated carbon with dilute NaOH-organic solvent mixtures. Hydrometallurgy, 19, pp. 321-333).
In the AARL process the carbon is soaked in a solution containing 2-3% NaCN and 2% NaOH for 30 minutes and the actual elution is done with the aid of soft water of very high quality at 110.degree. C. The complete cycle takes from 10 to 11 h. (R. J. Davidson et al., 1977. Desorption of gold from activated carbon with deionised water. J. South Afr. Inst. Min. Metall., 77 (12); pp. 254 and R. J. Davidson et al., 1979. Further studies on the elution of gold from activated carbon using water as the eluant. J. South Afr. Inst. Min. Metall., 79 (19); pp. 437-495).
In the Micron Research process the carbon is presoaked with 0.5 to 1 bed volume of solution containi
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H.J. Heinen et al., "Gold Desorption from Activated Carbon with Alkaline Alcohol Solutions" pp. 551-563
John L. Fast., "Glycol Stripping a Viable Option For Recovering Gold from Carbon" Jun. 1987., pp. 48-49.
J.B. Zadra et al. "Process for Recovering Gold and Silver from Activated Carbon by Leaching and Electrolysis", 1952., pp. 1-32.
F. Espiell et al., "Gold Desorption from Activated Carbon with Dilute NaOH/Organic Solvent Mixture", 1988, pp. 321-333.
D.M. Muir et al. "Elution Of Gold from Carbon by The Micron Solvent Distillation Procedure"., 1985., 151-169.
R.J. Davidson et al., "The Elution ff Gold from Activated Carbon Using Deionized Water." Jul. 1977., pp. 939-946.
J. Richard Ross., "Extractive Metallurgy" Feb. 1, 1974.
R.J. Davidson et al., "Further Studies on the Elution of Gold from Activated Carbon Using Water as the Eluant"., Oct. 1979., pp. 437-445.
Ross, J. Richard, "Desorbing Gold from Activated Carbon" U.S. Pat. application 74/438906, Abstract, Feb. 1, 1974.
Harvey Sarah
Louis Pierre
Van Lierde Andre
Elve M. Alexandra
Simmons David A.
UM Enginerring S.A.
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