Leaching of valuable metals from red mud via batch and continuous processes by using fungi

•Bioleaching of Ga, Ge, V, Sc, La, Eu and Yb from red mud was examined.•Spent medium process showed the best metal leaching performance in batch test.•A continuous bioleaching process by using filamentous fungi was studied.•Continuous leaching can reach a steady state at high red mud pulp densities.•Continuous leaching was cost effective comparing to acids leaching.

Bioleaching of valuable metals (Ga, Ge, V, Sc, La, Eu, Yb) from red mud was examined. Batch and continuous leaching experiments were deployed by using the filamentous fungi, Aspergillus niger. The leaching results showed that there was a strong negative relation between biomass and pH value. In batch leaching test, the best leaching performance was achieved under spent medium process at 2% pulp density. And in continuous leaching test, the system can reach a steady state at high red mud pulp densities (10%) with a pH value below 3.0. Comparing to organic and inorganic acids leaching, the continuous leaching mode which produces organic acids through glycometabolism by using A. niger is cost effective in a laboratory scale.