Cobalt and zinc extraction from Sikkim complex sulphide concentrate

Abstract

The lead concentrate produced from the complex sulphide deposit of Sikkim is not suitable for usual treatment processed like smelting due to high bismuth content. The present investigation has been carried out to study the amenability of the above concentrate towards leaching - both chemical and bioleaching. Bioleaching of the concentrate using Thiobacillus ferrooxidans in a 2 litre bioreactor resulted in about 39% extraction of both cobalt and zinc after 168 hours of leaching under the following conditions: pulp density 10%, pH 1.5, stirring speed 500 rpm, bacterial population 108 cells/ml, temperature 351 C and air flow rate 200 cc/min For chemical leaching different routes were tried like oxidizing roasting followed by acid leaching, direct sulphuric acid leaching, ammonia pressure leaching and ferric chloride leaching, Addition of lignin sulphonate as surface-active agent during sulphuric acid leaching significantly increased the recoveries of cobalt and zinc. Increasing the leaching temperature did not have significant effect on the recoveries, whereas acid concentration showed significant effect. At 140degrees C, 5 kg/cm(2) oxygen partial pressure, 2.5% (v/v) H2SO4 and 10% pulp density, 95% Co and 100% Zn could be extracted in 3 hours.