Abstract
Coupling of biotechnology and mineral processing arise from the depletion of high-grade ores. Acidithiobacillus ferrooxidans (A. ferrooxidans) is a chemolithotroph, gamma-proteobacterium, gram negative bacteria that has been used in biomining over the years due to its ability of bio mobilising valuable minerals and metals. In this study, the ability of A. ferrooxidans ability to modify and pre-concentrate base metal sulphides from Upper Group 2 (UG2) was investigated. Mesophile (37 degrees C) and thermophile (47 degrees C) A. ferrooxidans mixtures were cultured and used to condition UG2 run of mine sample for 4 h at a pH ranging from 7,5 to 7. The adherence of the bacteria to the UG2 run of mine (ROM) was confirmed with FTIR, XRD, XRF and XRD. Biomodification results suggested that Culture A significantly concentrated Cu, however Ni and S were not concentrated as desired, culture B showed the same effect at 4 h. Comparing the effect of culture, A to B, it was ruled that culture A had a high concentrating effect towards valuables (Cu, Ni, S and Fe which could be from sulphides or chromite) whereas culture B had a concentrating effect on the gangue elements such as Al, Si, Ca, Mg, and Cr. To study the effect of the bacteria on biomodification and surface oxidation, flotation was conducted. Cu grade and recovery obtained was 1.9 % and 87.33 % for mesophile and 1.44 % and 84.4 % for thermophile A. ferrooxidans, respectively. Whereas for Ni, thermophile A. ferrooxidans a higher grade of 1.35 % compared to 1.22 % obtained when mesophile A. ferrooxidans was used. It was concluded that mesophile and thermophile A. ferrooxidans could be used for the biomodification of chalcopyrite and pentlandite. But where selective flotation of chalcopyrite is desired, using mesophile would provide an effective process, whereas thermophile would provide optimum grade and recoveries for pentlandite. Nonetheless, to further optimize the bioflotation process, controlling conditioning time and pulp density was crucial for both mesophile A. ferrooxidans-bioflotation and thermophile A. ferrooxidansbioflotation these two factors were ruled as the most factors that majorly influence the grade and recoveries of Cu, Ni.