Reductive dissolution of ferric iron minerals: A new approach for bio-processing nickel laterites

► Over >70% of Ni contained in a limonitic laterite ore was successfully bioleached using an acidophilic bacterium ( Acidithiobacillus ferrooxidans). ► A novel approach was used, involving bio-processing of the mineral under anoxic conditions where the bacteria used the ferric iron minerals (predominantly goethite) present as alternative electron acceptors to oxygen, causing the mineral to be solubilised by a process of reductive dissolution, and releasing the associated Ni. ► Elemental sulfur was used as the energy source for the bacteria in this process. ► This represents a new area for biomining, where minerals are conventionally processed by oxidative dissolution. ► Successful demonstration of the process suggests that bio-processing of other oxidized metals ore may be feasible. Nickel laterites represent the major ore reserves of this base metal present in the lithosphere. However, processing these ores by conventional technologies involves considerable energy or reagent expenditure and consequently is less cost-effective than extracting nickel from sulfide ores. Biological options, using metal-complexing organic acids and mineral acids generated by fungi and bacteria, have been investigated but generally found to be ineffective in terms of extraction dynamics or yields. We have examined the possibility of using bacteria that can bring about the reductive dissolution of ferric iron minerals and thereby facilitate the extraction of nickel from a lateritic ore at relatively low (