Bioleaching of Lateritic Nickel Ore using Chemolithotrophic Micro Organisms(Acidithiobacillus ferrooxidans)

In this study, the recovery of nickel from a low grade ore was attempted employing a chemolithotrophic micro organism, a bacteria, named Acidithiobacillus ferrooxidans. The factors studies were pulp density of the ore for leaching and the effect of residence time on leaching of nickel from the ore at a constant total iron. The entire experiment was carried out at room temperature. The objective of the study was thus to calculate the amount of nickel leached or extracted from a low grade ore by bio leaching methods at different pulp densities of the ore as well as at different residence times. The first step in the procedure was the collection and activation of the bacterial strains of Acidithiobacillus ferrooxidans. The bacteria were raised in a culture of 9K+ media supplied with adequate calculated amount of nutrients and were shaken continuously in a shaker cum incubator to fully activate them. The activity and fully active conditions were determined by Ferrous Iron and Total Iron estimations. Pulp densities of 2%, 5%, 10% and 20% were prepared. For each residence time, 5 conical flasks were allocated for testing samples at 0 hour, 5 days, 10 days and 15 day and a control flask were prepared. Then the samples were analyzed by an Atomic Absorption Spectrophotometer at Regional Research Laboratory, Bhubaneswar for the percentage of nickel extracted from each sample of residence time and different pulp densities. The pH was maintained at around 1.5-2 for each sample for the optimum activity of the bacteria. The data obtained was tabulated and the required graphs were drawn to get the final result. The graphs were plotted between percentage of nickel extracted vs. residence time at various pulp densities and nickel extracted vs. pulp densities at various residence times. From the graphs, it was observed that the maximum nickel extraction was observed for a pulp density of 2% at 15 days. The percentage of nickel extraction decreases with increase in pulp densities for a particular residence time. The percentage of nickel extracted increases with the increase in residence time for a particular pulp density. The percentage of nickel extracted also depends a lot on the type of ore used, modifications made on the ore as well as on the activity of the bacteria. Higher is the activity of the bacteria, more is the extraction of nickel