Biological leaching of copper mine residues by Aspergillus niger

A study was initiated to determine the possibility of using the fungus Aspergillus niger for bioleaching and then identify and evaluate the parameters which affect this process. An oxidized mining residue containing mainly copper (724 mg/100g residue) was studied. Sucrose and mineral salts medium were initially used to produce citric and gluconic acids by A. niger without residue, After incubation for 15 days, the supernatant, containing the acids, was added to various concentrations of the residues (1, 5, 7, 10 and 15% w/v). Maximal removal of up to 60% of the copper was obtained for the 5% residue. Experiments then included growing the fungus in the presence of various concentrations of residue up to 15 days. These experiments showed that the pH decreased to around 3 within 10 days of incubation. Again, copper removal of up to 60% was found for all concentrations of residue. It was shown that gluconic and citric acids were the main acids produced. Other experiments using ultrasound as a pretreatment showed that 80% removal of the copper could be obtained for a 5% residue concentration. In conclusion, leaching of copper from a mining residue is technically feasible using A. niger. Further research must be performed to increase the economic feasibility of the process.