Bioleaching behaviors of silicon and metals in electrolytic manganese residue using silicate bacteria

Electrolytic manganese residue (EMR) is a kind of solid waste generated along with the production of electrolytic manganese, with a high content of quartz and metals. The former can be used as silicon fertilizer for crops after activation, while the latter may cause harm to surrounding environment due to their toxicity. The aim of this study was to investigate the effects of bacterial on the activation of silicon and fixation of heavy metals in EMR by using microbe-mineral direct contact and indirect contact methods. Mixed cultures of Bacillus mucilaginosus (BM) and Bacillus circulans (BC) were used to achieve activation of silicon in EMR, and the leaching concentration of Mn, Co and Ni and their chemical forms in the leaching residue were also investigated. The results show that the microbe-mineral direct contact method has better performance for the activation of silicon in EMR with the available silicon in the leaching solution up to 163.27 mg L−1 than the indirect contact method. The metals (Mn, Co and Ni) remaining in the residue mainly exist as the stable state after bioleaching, with lower leaching concentration after bioleaching of 20 d. And the effect of silicon bacteria on activation of silicon and the fixation mechanism of metals including the effect of silicate and silicate bacteria is confirmed, and it is verified by the identification of metabolites and the analysis of chemical reaction process. This study investigates the treatment of EMR by using mixed silicate bacteria, and reveals the mechanisms of bacteria on the activation of silicon and fixaion of heavy metals in EMR. The bioleaching method not only provides silicon source for soil but also can realize the reclamation of EMR.