CHEMICAL AND BIOLOGICAL LEACHING OF ENARGITE

Enargite (Cu3AsS4) was leached faster by bacteria in sulfuric acid med ium (pH 1.6) with added ferric sulfate than by chemical leaching at th e same or higher iron concentration. During chemical leaching with fer ric iron, the copper dissolution rate decreased from an initial value of 0.03% per hour to a value of 0.002% per hour. Enargite is oxidized to elemental sulfur and dissolved arsenic (As3+ and As5+). Less than 1 0% of sulfur is oxidized to sulfate. The arsenic and copper dissolutio ns observed in bacterial leaching experiments suggest the existence of a specific bacterial action on the leaching of enargite, demonstrated by the ability of bacteria to oxidize enargite at very low concentrat ion of dissolved iron and by the higher dissolution rate obtained in b acterial leaching compared to chemical ferric leaching.