Correlations between reaction rates and evolution of corrosion pits in bacterial leaching of pyrite

Abstract

In order to understand the influence of crystallographic orientation on the mechanism of pyrite bioleaching, single crystals of pyrite cut to expose plane orientations of {100}, {111} and {110} were studied. Differences in the reaction rates of the pyrite surfaces in the presence of Thiobacillus ferrooxidans have been observed. The microbial corrosion patterns generated on the surfaces were further used to study the leaching process. Surfaces with high sulphur/iron atomic ratios were observed to develop surface films and to generate elongated pits similar in shape to bacteria, but much larger than the bacteria cell dimensions. The dissimilarity of corrosion patterns observed on the surfaces of samples indicates a variation in cell–surface interaction from one crystal plane to the other. Subsequent correlation between the surface corrosion patterns associated with the dissolution process and the changes occuring in the leaching solution indicated that the most signficant aspect in the early stages of leaching is the recognition and subsequent attachment of the bacteria to active sites on the immediate surfaces. This initial process consequently controls the leaching progression and defines the type and evolution of pits occurring on the surfaces. The overall analysis indicates that the surface properties of pyrite may control the initial oxidation kinetics and the evolution of corrosion patterns in acid bacterial leaching.