WHY CHALCOPYRITE IS DIFFICULT TO FULLY DISSOLVE

摘要

Most of the world's copper reserves exist as chalcopyrite. Hydrometallurgically the preferred approach is the acidic ferric sulphate dissolution route. Unfortunately this chemistry can also exhibit incomplete dissolution, often mistaken for passivation. The possible phase candidates for dissolution inhibition are examined, with most discussion focussed on elemental sulphur and jarosites. Phases such as polysulphides are rejected as candidates. The physical reality of metal-deficient sulphides is also questioned. A conceptual 4-stage model is proposed which explains all the general dissolution behaviour that is widely observed, i.e. that of an induction period and a parabolic rate curve that may or may not be followed by linear rate behaviour. The general conclusion is that thick over-layers of sulphur cause the initial parabolic behaviour, and a thin systemic sulphur layer is likely responsible for the rate-limiting step, even in the linear region. Depending upon solution conditions, either unhindered near linear dissolution may occur, or jarosite precipitation that will cause a second parabolic region. Sulphur formation remains a systemic phase in the context of heap bioleaching but is not a problem of any consequence for mixed culture systems unlike jarosites.