COMBINED CHEMICAL AND BACTERIAL LEACHING OF ULTRAFINE GROUND CHALCOPYRITE

The changes in surface properties and the leaching of chalcopyrite CuF eS2 after ultrafine grinding are examined. Surface area measurement an d photoelectron spectroscopy (XPS) were used for characterization of t he 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 mi n, 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 o f sulphur S2p electrons has shown the existence of sulphur in three di fferent chemical forms: S2-, S-0 and S6+. The ground samples exhibited a greater proportion of higher oxidation states. The samples were che mically preleached with an acid solution of Fe(III) sulphate to an equ al conversion degree (epsilon(Cu) = 25%), characterized and subsequent ly leached by the bacteria Thiobacillus thiooxidans. While the rate of chemical leaching is proportional to the increase in CuFeS2 surface a rea, the rate of subsequent bacterial leaching is limited by 15 min gr inding. The different behaviour of the samples ground for a long time may be explained by differences in the chemical composition of surface layers.