Growth and activity of pure and mixed bioleaching strains on low grade chalcopyrite ore

The kinetics of iron and sulfur oxidation by selected bioleaching strains grown in simple chemically defined media have in some instances been studied exhaustively. However, there is very little available information on the growth and leaching kinetics of known bioleaching strains on low grade chalcopyrite ore. Eleven known bioleaching strains were shown to be capable of growing, although at a slow rate, on low grade chalcopyrite ore in pure culture. When the same eleven strains were added as a mixed inoculum and enriched on low grade ore at 28, 35, 45, 55 and 65 °C, the resultant mixed populations were shown to comprise both iron and sulfur oxidising microorganisms. Rates of iron and sulfur oxidation by mixed cultures generated at each temperature varied considerably. Fastest rates of iron and sulfur oxidation were observed at 65 °C. Dominant strains in the mixed cultures were determined using PCR-DGGE and included Metallosphaera hakonensis, Sulfolobus metallicus, Sulfobacillus thermosulfidooxidans, Acidimicrobium ferrooxidans, Acidithiobacillus caldus and Leptospirillum ferriphilum. Further development of methods to accurately quantify microbial growth and activity on low grade ore will likely help us understand the role of bioleaching microorganisms in heap bioleaching of low grade ore.