Bioleaching of a chalcopyrite concentrate using an extremely thermophilic culture

The ability of an extreme thermophile to oxidise a concentrate comprising o f chalcopyrite (66%) and pyrite (11%) is described. A batch test at 70 degr eesC showed that a copper extraction of > 98% was possible. A series of con tinuous tests were carried out in a three-stage pilot plant. employing stan dard-design mechanically agitated and aerated tanks. The effect of residenc e time, feed grind and the mass transfer supply of oxygen and carbon dioxid e on bioleach performance were evaluated. The results showed that overall C u extractions of 95% could be obtained. However, compared to mesophilic and moderately thermophilic bioleaching bacteria, the extreme thermophiles app eared to be more sensitive to the solids concentration employed, which may also be related to the particle size of the feed solids. Levels of oxygen c onsumption approaching the maximum rates currently being employed in commer cial-scale bioleach tanks treating refractory gold pyritic concentrates cou ld be achieved. To maintain these high oxidation rates, it was important to ensure that the supply rate of oxygen and carbon dioxide to the reactors w as sufficient. The high copper extractions obtained in these tests showed t hat a process treating chalcopyrite concentrates using extreme thermophiles has the potential for further development and assessment for commercial ap plications. (C) 2001 Elsevier Science B.V. All rights reserved.