Leaching of Manganese Using Bio-solubilized Iron Reductant to Prevent Manganese Carbonate Formation

Abstract A mixed culture of metal-reducing microorganisms was used to dissolve iron, which was then utilized as a reductant to extract manganese in a 250 mL two-stage bioleaching system. In this two-stage configuration, CO 2 generation associated with microbial metabolism occurs in the iron-reduction stage, while MnO 2 reduction is confined to a separate manganese-leaching stage, thereby minimizing manganese carbonate formation. The results demonstrated that the two-stage system effectively maintained Fe 2+ availability, enhancing manganese dissolution while mitigating loss of manganese through manganese carbonate (MnCO 3 ) formation. In contrast, a single-stage bioleaching approach, where microorganisms directly reduced manganese oxides, led to significant MnCO 3 precipitation, reducing overall leaching efficiency. The two-stage process not only improved manganese recovery but also maintained a pH where Fe 3+ would precipitate. The two-stage system achieved a maximum manganese concentration of 1792 mg/L at pH 4.4 ± 0.8, significantly exceeding the single-stage biotic (928 mg/L) and abiotic (192 mg/L) experiments. Bio-solubilized iron and improved solid-liquid contact played a key role in enhancing manganese dissolution, demonstrating the effectiveness of the two-stage approach. To evaluate the scalability of this approach, a 19 L bench-scale bioleaching experiment was also conducted, producing manganese oxide precipitate with 93% purity, free of manganese carbonate. This study provides insights into a bioleaching strategy that addresses key limitations of previous approaches, supporting the development of a more practical and scalable manganese extraction process in the future.