The potential use microorganisms in the

Biooxidation is a process by which the recovery of a metal is enhanced by microbial decomposition of the mineral, but the target metal is not necessarily solubilized. The biooxidation process results in the microbiological oxidation of the metal ores which contain metal compounds, in this case the metal values of interest remain in the solid residues in a more concentrated form. The aim of this project was to ascertain the potential biooxidation of gold ore from Bulawayo using a natural bacterial consortium. Additional objectives of the research were to investigate the effect of pH on the biooxidation process and to identify the bacterial consortium responsible. The biooxidation of the gold ore was investigated using the shake flask method in 250 ml Erlenmeyer. Two different types of inoculum were used to carry out the biooxidation. In one experiment, the gold ore was microbially oxidized using natural gold ore bacterial consortium. For the second biooxidation experiment, a selected pure bacterial consortium was inoculated to autoclaved gold ore. The selected consortium was established by enrichment of four mine samples (gold ore, mine dump ore, water from the drilling surface and a sample suspect acid mine drainage stream). The effect of pH on the biooxidation reaction was investigated by having a parallel biooxidation reaction regulated at pH 2 also containing the natural and selected consortium set up. Incubation of the flasks was carried out in a thermo-regulated orbital shake at 25 °C and 140 rpm. Aliquots were sampled from the biooxidation reactions every 48 hours and the biooxidation of the gold ore was measured in terms of solubilisation of preg-robbing substances (copper, zinc and iron) using Atomic Absorption Spectroscopy. The results showed an increase in the amount of preg-robbing substances being solubilised with time, hence the gold ore was being purified (biooxidized) thereby potentially increasing the subsequent gold extractable by cyanidation. The biooxidation rate of the pH controlled experiment was significantly faster than the biooxidation rate in the unregulated pH experiment. The increased rate of the pH controlled reaction can be attributed to the favourable environmental conditions created by the presence of H+ ions. The bacteria responsible for catalysing the microbial oxidation of the gold ore were presumptively identified as Acidithiobacillus spp, Leptospirillum spp and Sulfolobus spp.