THE LEACHING BEHAVIOUR OF VARIOUS ZINC SULPHIDE MINERALS WITH THREE THIOBACILLUS SPECIES

Abstract

The availability of high-grade specimens of sphalerite, wurtzite and marmatite prompted a comparative study of the leaching rates of these minerals in the presence of Thiobacillus ferrooxidans, T. thiooxidans and T. thioparus. In this preliminary study, samples of the finely-ground minerals, of equivalent surface area, were subjected to attack by populations of equal magnitude of each of the three bacterial species in shake flasks at 30 C. The microorganisms were acclimatised to the particular substrates. The results indicate that (1) Wurtzite is much more slowly degraded than marmatite or sphalerite by all three organisms. (ii) Marmatite is leached more rapidly by T. ferrooxidans and T, thiooxidans than sphalerite, in both the presence and absence of soluble iron. (iii) Iron-free synthetic zinc sulphide is leached more rapidly by T. thiooxidans than by T. ferrooxidans or T. thioparus. The hexagonal crystalline structure of zinc sulphide in wurtzite appears to be more recalcitrant to microbial degradation than the cubical form of sphalerite, and the substitution of iron for some of the zinc in the marmatitic form of zinc sulphide appears to greatly facilitate biodegradation.