Bioleaching of indium from waste LCD panels by Aspergillus niger: Method optimization and mechanism analysis

Using Aspergillus niger (A. niger) to produce low-concentration organic acids is challenging for dissolving In₃O₂ from waste LCD (liquid crystal display) panels with high toxicity. In this study, three bioleaching approaches from the general and the optimized fermentation systems were investigated respectively to compare indium recovery effects and firstly clarified its bioleaching mechanism. The indium bioleaching efficiency can be improved from 12.3% to 100% by fermentation method optimization. Carboxy groups from organic acids and proteins were the critical substances to release H⁺ for leaching indium mainly competed with iron via reactions analysis. The effective components increased after optimizing, including the dissociative H⁺ concentration, the effective carboxyl groups for leaching metal oxides, and the output of oxalic acid. A. niger biomass prevented the contact between H⁺ and In₃O₂ and adsorbed In³⁺ adverse to indium recovery. The bioleaching effects of fermentation broth for indium can be further promoted by controlling bioleaching process parameters.