Microbial leaching of low grade chalcopyrite: difficulties arising due to jarosite and elemental sulpur deposition on ore surfaces: and a few suggestions to win over them

In biohydrometallurgical leaching of low grade chalcopyrite ore, the extraction rate is reduced due to deposition of jarosite or elemental sulphur on the ore surfaces. These deposits of basic ferric sulphate and demental sulphur are due to the bacterial activity of thiobacillus ferrooxidans on the pyrite ores. Sometimes the sulphur coating gets oxidized by more specific strain, thiobacillus thiooxidans, and the protective film of elemental sulphur is removed resulting in a higher metal relase. The leached residue is subjected to regrinding resulting in enhanced leaching. Regrinding brings fresh ore surfaces amenable to bacterial leaching. By successive regrinding the leached ore, 63.13% more copper recovery is obtained. The leached residue is washed with carbondisulphide and acetone. With carbondisulphide treatment, after four successive treatments a further release of 50.61% copper is obtained. With acetone, after two successive treatments a further release of 89.15% copper is obtained. This investigation shown that acetone is a more suitable solvent for removing the sulphur film from the ore surfaces compared to carbondisulphide. Desulphovibrio desulphuricans, a sulphate reducing bacteria have been utilized for the pyritization of precipitated basic ferric sulphate on the ore surfaces. The pyrite again becomes amenable to leaching by T. ferrooxidans. By this treatment a further recovery of 85.97% copper is obtained