Bioleaching of copper mining residues by Aspergillus niger

A study was initiated to determine the possibility of using the fungus Aspe rgillus niger for bioleaching and then to identify and evaluate the paramet ers that affect this process. An oxidized mining residue containing mainly copper (7240 mg/kg residue) was studied. Sucrose and mineral salts medium w ere initially used to produce citric and gluconic acids by A. niger with va rious concentrations of residue (1, 5, 7, 10 and 15% w/v). Maximal removal of up to 60% of the copper was obtained for the 5% residue. These experimen ts showed that the pH decreased to around three within 10 days of incubatio n. Other substrates were evaluated including molasses, corn cobs and brewer y waste. Sucrose gave the best results for copper removal. followed by mola sses, corn cobs and brewery waste. Other experiments using ultrasound as a pre-treatment 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 pe rformed to increase the economic feasibility of the process.