Conjoint bioleaching and zinc recovery from an iron oxide mineral residue by a continuous electrodialysis system

Many metal refining processes generate low-grade mineral residues that are typically stored on landfills and responsible for inefficient land-use. While being of environmental concern, residual metals contained in these wastes can become an interesting secondary resource. A novel bio-hydrometallurgical route for recovery of Zn from such waste residues to a highly pure resource is proposed. The use of microbiologically produced citric acid for extraction of Zn was optimized by varying the lixiviant pH and contact time so to achieve maximal Zn recovery against minimal co-extraction of Fe. Bioleaching with 0.2 M citric acid at pH 2.9 can extract 12.5 mg g−1 Zn from the iron oxide residue. Compared to inorganic acids commonly used in extraction and non-microbially produced citric acid, almost no iron was dissolved by the biogenic extractant. Hence, optimal selectivity in favor of Zn was achieved, especially at short contact times. Integration of bioleaching in a continuous percolating column to a coupled electrodialysis system could subsequently separate Zn from the leachate solution to a purity of 76 m%.