Solidification/stabilization of electrolytic manganese residue using phosphate resource and low-grade MgO/CaO

In this study, P-LGMgO (low-grade MgO and NaH2PO4·2H2O), P-CaO (CaO and NaH2PO4·2H2O), and P-MgCa (low-grade MgO, CaO and NaH2PO4·2H2O) were used for the solidification/stabilization (S/S) of electrolytic manganese residue (EMR). Relevant characteristics such as ammonia nitrogen and manganese stabilization behavior, unconfined compressive strength (UCS), probable S/S mechanisms, and EMR leaching test were investigated. The results demonstrate that using P-LGMgO had higher stabilization efficiency than P-CaO and P-MgCa for the S/S of EMR at the same stabilization agent dose. The stabilization efficiency of ammonia nitrogen and manganese in the EMR were 84.0% and 99.9%, respectively, and the UCS of EMR was 5.1MPa using P-LGMgO process after curing for 28 days when the molar ratio of Mg:P was 5:1 and dose of stabilization agent was 12wt%. In this process, ammonia nitrogen was stabilized by struvite (NH4MgPO4·6H2O), and manganese by bermanite (Mn3(PO4)2(OH)2·4H2O) and pyrochroite (Mn(OH)2). The leaching test results show that the values of all the measured metals on the 28th day were within the permitted level for the GB8978-1996 test suggested by China's environmental protection law and the concentration of ammonia nitrogen can be reduced from 504.0mgL(-1) to 76.6mgL(-1).