Bioleaching of Mn from manganese residues by the mixed culture of Acidithiobacillus and mechanism

BACKGROUND: Electrolytic manganese residues are the largest and most dangerous waste stream from the electrolytic manganese metal industry, and recovery of Mn from manganese residues is one of the main methods of recycling this waste. Bioleaching of electrolytic manganese residues for Mn extraction was investigated in this study. RESULTS: An extraction efficiency as high as 99.7% was achieved at 1% slag pulp concentration, 2320 mg L^-1 extraction concentration and 80% extraction efficiency was attained at 8% slag pulp concentration, indicating the application potential of bioleaching in Mn extraction from manganese residues. CONCLUSION: The extraction of Mn from manganese residues depended exclusively on the non-contact mechanism. The acidic dissolution of soluble Mn²⁺ induced by sulfur-oxidizing bacteria resulted in 91.9% Mn extraction, while the reduction dissolution of insoluble Mn⁴⁺ by iron-oxidizing bacteria caused 5.8% Mn extraction. The combined action of sulfur-oxidizing bacteria and iron-oxidizing bacteria assured the maximum Mn extraction. EDS and XRD analysis of bioleaching residues further demonstrated the bioleaching mechanism involved.