Bioremediation of metal contamination.

A study was initiated to evaluate the use of the fungus Aspergillus niger for bioleaching and then to determine the effect of process steps, the tailings concentration and type of substrate. An oxidized mining tailing containing mainly copper (7240 mg kg(-1) tailings) was studied. A sucrose and mineral salts medium was initially used to produce citric and gluconic acids by A. niger at various concentrations of tailings ( 1, 5, 7, 10 and 15% w/v). Maximal removal of up to 60% of the copper was obtained for the 5% tailings when the organic acid supernatant was added to the tailings. In a single step process, A. niger was then grown in the presence of mining tailings at various concentrations. Maximum copper solubilization (63%) occurred with 10% mining tailings using sucrose as the substrate. Other substrates were then evaluated including molasses, corn cobs and brewery waste (10% mining tailings). Sucrose gave the best results for copper removal, followed by molasses, corn cobs and brewery waste. Other experiments using ultrasound as a pretreatment showed that 80% removal of the copper could be obtained for a 5% tailings concentration. In conclusion, leaching of copper from mining tailings is technically feasible using A. niger but further research will be required to increase the economic feasibility of the process.