Bacterial and chemical leaching of copper-containing ores with the possibility of subsequent recovery of trace silver

Abstract

This investigation compares bacterial leaching to chemical leaching to solubilize copper from a copper containing ore of the new site Northern Qarashoshaq in Zhylandy (Kazakhstan) which is currently under commercial development. From ICP-OES analysis, the bulk ore sample contains 1.5% of Cu and a trace level at 0.0024% of Ag. Phase analysis shows the main copper containing minerals are covellite, chalcocite, malachite, chrysocolla and chalcopyrite. According to X-ray diffraction analysis, silver is mainly presented as jalpaite (Ag3CuS2) minerals. Copper leaching was carried out by acidophilic bioleaching for comparison with extraction by chemical methods involving the addition of sulfuric acid and Fe3+ or only sulfuric acid in flasks, as well as column leaching tests to simulate heap leaching. Ag was extracted by cyanidation methods again in flasks as well as column leaching tests. Results showed that copper extraction is up to 95% when using bioleaching in the flask, 83% in the case of Fe3+ with sulfuric acid and 76% for sulfuric acid. Furthermore, subsequent extraction of Ag reaches 97% for bioleaching and 92% for chemical leaching. Column bioleaching tests showed an 82.3% yield of copper after 70 days of the experiment and a 70% of silver, whereas for chemical leaching the yield of copper is 66.8% and silver is 51%. In conclusion, this investigation demonstrated higher extraction for both copper and silver from the primary ore in the bioleaching sample compared to the chemical leaching sample. More silver was extracted in the bioleaching case as there was less copper remaining to compete for the cyanide anions.