Role of Aspergillus niger in recovery enhancement of valuable metals from produced red mud in Bayer process.

Annual worldwide growth rate of red mud (RM) as a hazardous waste has caused serious environmental problems for its disposal in the mining and metallurgy industries. Accordingly, the aim of this study was to investigate biological leaching of RM and recovery of metals using organic acids exerted by Aspergillus niger. Experiments using A. niger were conducted in batch cultures with a pulp density of 2% (w/v) RM under one-step, two-step and spent-medium bioleaching. Based on HPLC results, the major lixiviant was the secretion of organic acids (citric, gluconic, oxalic and malic) by A. niger. Leaching efficiency of metals in the one-step process was the highest and the amounts of leached metals were 69.8%, 60% and 25.4% for Al, Ti and Fe, respectively. The fungal leaching technique demonstrated an adequate recovery of metals, with an efficient and cost-effective means and respect to a reuse of RM for economic and environmental purposes.