Are bioleaching rates determined by the available particle surface area concentration?

Abstract

It is well known that pulp density and particle size determine the available surface area concentration and have an influence in the overall rate of bioleaching of minerals. As metal solubilization takes place through the surface area of the particles, it can be expected that different combinations of pulp densities and particle sizes giving the same surface area concentration would determine the same leaching rate. The objective of this work was to test this hypothesis on the effect of surface area concentration, pulp density and particle size of the biooxidation of a pyritic gold concentrate by the thermophilic Archaeon Sulfolobus metallicus in shake flasks. The gold concentrate was used at 2.5%, 5%, 10%, and 15% w/v pulp density and at four size fractions: 150–106, 106–75, 75–38 and –38 μm. Temperature was 68°C and the initial pH was 2.0. Results showed that the volumetric productivities of iron and sulfate depend not only on the surface area concentration but also on pulp density and particle size considered separately. These two variables not only determine surface area but also exert additional effects on the process, so the hypothesis was not confirmed. Maximum attained iron productivity was 1.042 g/l day with the 75–38 μm fraction at 5% pulp density. Maximum sulfate productivity was 4.279 g/l day with the 75–38 μm fraction at 10% pulp density.