Oxidation of sulfide ore bodies; II, Oxidation mechanisms of sulfide minerals at 25 degrees C

Measurements of the single electrode potentials of sulfide minerals backed with basic understanding of their electrode behavior make it possible to clarify their oxidation or reduction mechanisms. The electrode potential of a sulfide mineral is controlled by the first-step reaction of the oxidation mechanism for the sulfide in an oxidizing solution, and by that of the reduction mechanism in a reducing solution. Sulfides of copper, lead, silver, iron, and zinc were studied. The results indicate that the direct oxidation of a simple sulfide mineral is a process in which the metal atoms move into the surrounding solution to become aqueous cations, accompanied by a step-wise decrease in the metal to sulfur ratio of the remaining solid phase. When solid sulfur is finally left over, it undergoes a series of reactions to be oxidized to sulfate ion. In case of reduction, sulfur atoms move out into the solution to become aqueous sulfide ions with a step-wise increase in the metal to sulfur ratio of the solid phase. To illustrate, the oxidation of chalcocite proceeds as (Cu/sub 2/S) - 1/ 5(Cu/sub 9/S/sub 5/ + Cu/sup 2+/)r - (CuS + Cu/sup 2+/) - (2Cu/sup 2+/ + S). The path of the stepwise oxidationmore » is not necessarlly the same as that of the step- wise reduction for a metal-sulfur system. In the case of disulfides of iron, namely pyrite and marcasite, ferrous ions and S/sub 2/ molucules appear to be released simultaneously upon oxidation. (auth)« less