Combined chemical and bacterial leaching of ultrafine ground chalcopyrite

The changes in surface properties and the leaching of chalcopyrite CuFeS2 after ultrafine grinding are examined. Surface area measurement and photoelectron spectroscopy (XPS) were used for characterization of the ground samples. A gradual decrease in the particle size, from 32 mu m, for as received CuFeS2, to 2 mu m, for the sample ground for 60 min, as well as increasing the surface area from 0.23 m(2) g(-1) to 2.68 m(2) g(-1) for equal samples was observed. Analysis of the XPS line of sulphur S2p electrons has shown the existence of sulphur in three different chemical forms: S2-, S-0 and S6+. The ground samples exhibited a greater proportion of higher oxidation states. The samples were chemically preleached with an acid solution of Fe(III) sulphate to an equal conversion degree (epsilon(Cu) = 25%), characterized and subsequently leached by the bacteria Thiobacillus thiooxidans. While the rate of chemical leaching is proportional to the increase in CuFeS2 surface area, the rate of subsequent bacterial leaching is limited by 15 min grinding. The different behaviour of the samples ground for a long time may be explained by differences in the chemical composition of surface layers.