Biological-acid leach process

A process for leaching copper from a chalcopyrite containing ore, comprising:

• (a) grinding the ore to a particle size of less than about 200 mesh;
• (b) mixing the ore with an aqueous leaching medium in an amount to obtain a mixture having 2% to 60% by weight of the ore, the leaching medium being acidified with sulphuric acid to a pH between about 1.5 and 3.0, and containing T. ferrooxidans bacteria, a bacterial nutrient, about 100 to 4,000 mg of dispersed silver per kilogram of chalcopyrite, about 10 to 30g/L dissolved copper, and about 2 to 25g/L thiosulphate;
• (c) agitating the ore and leaching medium mixture while simultaneously sparging with carbon dioxide enriched air;
• (d) maintaining the temperature between about 10.degree. C. and 40.degree. C., and the oxidation potential between about 0.54 to 0.66 volts, and periodically adding a sufficient amount of sulphuric acid to the mixture to maintain the pH between 1.5 and 3.0, so as to produce elemental sulphur rather than sulphuric acid from sulphide in the ore.