DIRECT OBSERVATIONS OF BACTERIA AND QUANTITATIVE STUDIES OF THEIR CATALYTIC ROLE IN THE LEACHING OF LOW-GRADE, COPPER-BEARING WASTE

Abstract

Observations have been made of Thiobacillus ferrooxidans, Thiobacillus thiooxidans, and a high-temperature Sulfolobus- like microorganism attached to mineral-phase surfaces following various stages of leaching low-grade copper waste ore. Attachment in all cases is observed to be selective, that is bacteria attach only to sulfide-phase surfaces (principally CuFeS 2 and FeS 2 ), but attachment has been observed not to be a requirement for leaching to occur. The regularity of attachment is much less for T. ferrooxidans and T. thiooxidans than for the higher-temperature Sulfolobus- like microbe and this seems to be because of the absence of a flagellum in the case of the latter. Attempts to relate bacterial attachment on chalcopyrite surfaces to emergence sites of dislocations and related crystal defects which can cause local changes in surface stoichiometry (using the transmission electron microscope) are also described. Direct, systematic observations and comparison of surface degradation (corrosion) of FeS 2 and CuFeS 2 in sterile acid environments and inoculated acid environments clearly indicate a significant enhancement in leaching rate by bacteria. This bacterial catalysis is shown to be important in enhanced conversion rates by galvanic processes when FeS 2 and CuFeS 2 phase regions are in intimate (electrical) contact; and the implications of bacterial catalyzed galvanic conversion as it relates to sulfide dissemination in large ore bodies is briefly described.