Bioleaching of spent Zn–Mn or Ni–Cd batteries by Aspergillus species

•Citric and oxalic acids were produced by Aspergillus spp. depending on nutrients.•Citric acid secreted by Aspergillus was effective for bioleaching of spent batteries.•A. tunbingensis KUC5037 was the most promising fungus for bioleaching. This research explores the recovery of metals from spent Zn–Mn or Ni–Cd batteries by a bioleaching using six Aspergillus species. Two different nutrients, malt extract and sucrose, were used to produce different types of organic acids. Oxalic acid and citric acid were shown to be the dominant organic acid in malt extract and sucrose media, respectively. In the bioleaching, the metal removal was higher in sucrose media than malt extract. All species, except A. niger KUC5254, showed more than 90% removal of metals from Zn–Mn battery. For Ni–Cd battery, more than 95% of metals was extracted by A. niger KUC5254 and A. tubingensis KUC5037. As a result, A. tubingensis KUC5037 which is a non-ochratoxigenic fungus was considered to have the greatest potential for improving the safety and efficiency of the bioleaching.