Hydrometallurgical process for recovering precious metals from anode slime

A process for the recovery of gold, silver, selenium and tellurium from a copper refinery anode slime containing these metals which comprises:

• treating a decopperized anode slime three times with stoichiometric proportions of about 4 to 9 M nitric acid and at a temperature between about 40.degree. to about 115.degree. C. for a period of at least 40 minutes to obtain a nitric acid leach solution containing at least about 95% by weight of the silver content, about 96% by weight of the selenium content and about 75% by weight of the tellurium content of the decopperized anode slime and to also obtain a nitric acid leach residue containing gold, arsenic, antimony, lead, silica, tin and other impurities present in the decopperized anode slime, denitrating and chlorinating the selenium, tellurium, lead, copper and other impurities-containing solution by liquid-liquid extraction with 5% to 100% by volume of neutral or basic organic solvent balanced with a hydrocarbon diluent as the organic extractant, 8 M or higher hydrochloric acid as the acidity adjustment solution and water as the stripping solution,
• separating tellurium from selenium, lead, copper and other impurities by liquid-liquid extraction using 5% to 100% by volume of a neutral or basic organic solvent balanced with a hydrocarbon diluent as the organic extractant, 4 M or higher hydrochloric acid as the scrubbing solution and 1 M or less hydrochloric acid as the stripping solution,
• precipitating selenium from the selenium-containing solution with sulfur dioxide at a temperature between about 35.1.degree. to 45.degree. C. and at a free acid content in the selenium-containing solution between about 3.5 to 5.4 M of the hydrochloric acid;
• precipitating tellurium from the tellurium-containing solution with sulfur dioxide at a temperature between about 10.degree. to 45.degree. C. and a free acid content in the tellurium-containing solution greater than 0.1 M of the hydrochloric acid;
• treating the nitric acid leach residue with stoichiometric proportions of aqua regia at an elevated temperature of between about 40.degree. C. to 110.degree. C. for a period of at least 1 hour to obtain an aqua regia leach residue containing at least 99.46% by weight of the gold content of the nitric acid leach residue,
• separating gold from arsenic, antimony, lead, tin, silica, platinoids and other impurities by liquid-liquid extraction at a temperature lower than 30.degree. C. with ether having a carbon content of 10 to 12 as the organic extractant and 2 M or higher hydrochloric acid as the scrubbing solution, and
• recovering gold from the gold-loaded organic extractant with stoichiometric proportions of oxalic acid at an elevated temperature of between 40.degree. to 100.degree. C. for a period of at least 3 hours.