Copper bioleaching behaviour in an aerated heap

This is a case study of a field test carried out to correlate heap aeration with copper bioleaching. A 62,500-t portion of a production leach pad was monitored for oxygen levels, copper content, and bacterial activity at different heap heights during bioleaching. Different rates of forced aeration were applied to this test heap. There was a direct correlation between copper leached and oxygen consumed; the stoichiometry indicated partial oxidation of chalcocite to cupric ion and elemental sulphur. Oxygen levels in heap airspace were maximum near the bottom of the heap and decreased towards the top. This distinct oxygen gradient was due to oxygen depletion by bacteria as the air travelled upwards through the heap. Bacterial oxygen consumption in the heap, as measured by respirometer, accounted for the oxygen consumption profile when air flow rate and residual copper were taken into account. Extrapolating the oxygen consumption profile for the entire heap height was used as a direct measurement of Heap Oxidative Capacity, an indicator of copper bioleaching performance in an aerated heap. (C) 2001 Elsevier Science B.V. All rights reserved.