Biohydrometallurgy for Cobalt and Nickel recovery from laterites: project BioProLat

Laterite ore deposits in Brazil and other tropical countries contain approximately 70 % of the world’s Ni and Co resources. High energy and/or reagent costs, accompanied by expensive equipment costs, are generally incurred when recovering Ni and Co via pyrometallurgy or high pressure acid leaching. Several acidophilic bacteria are able to use elemental sulfur as electron donor and couple the oxidation of sulfur to the reduction of molecular oxygen and/or ferric iron, and are thereby generating sulfuric acid and dissolving distinct Ni- and Co-bearing mineral phases partly via chemical reduction, e.g. Mn-oxides. Reductive bioleaching of laterites with acidophiles has been described for anaerobic as well as aerobic conditions. Stirred-tank bioreactor and percolation column laboratory experiments were carried out in the BioProLat project to test various samples from three different laterite deposits in Brazil and to optimize parameters including pH, temperature, aeration, and finding the most suitable bacterial consortium for the bioleaching of Ni and Co. Stirred-tank laterite bioleaching experiments starting at pH 1.5 under aerobic conditions with a consortium of different Acidithiobacillus thiooxidans strains resulted after 15 days in maximal extraction of 83 % Co and 83 % Ni, for 10 % (w/v) pulp density of a laterite sample. Column bioleaching with another laterite sample achieved 95 % Co and 66 % Ni extraction after one month. Eventually, the optimized process will be upscaled, transforming unexploited laterite ores and limonite stockpiles into valuable resources.