Electrolytic manganese residue disposal based on basic burning raw material: Heavy metals solidification/stabilization and long-term stability

Abstract

Solidification/stabilization (S/S) is an option for the treatment of electrolytic manganese residue (EMR). Basic burning raw material (BRM) could successfully solidify/stabilize EMR, though heavy metals S/S mechanism and long-term stability remain unclear. Herein, Mn2+ and NH4+ S/S behavior, hydrated BRM and S/S EMR characterization, Mn2+ long-term leaching behavior, phase and morphology changes for long-term leaching were discussed in detail to clarify these mechanisms. Mn2+ and NH4+ leaching concentrations as well as pH value in S/S EMR were respectively 0.02 mg/L, 0.68 mg/L and 8.75, meeting the regulations of Chinese standard GB 8978–1996. Long-term stability of EMR was significantly enhanced after S/S. Mn2+ leaching concentration, Mn2+ migration, Mn2+ cumulative release, Mn2+ apparent diffusion coefficient and conductivity of EMR reduced to 0.05 mg/L, 5.5 × 10−6 mg/(m2·s), ~ 9 mg/m2, 6.30 × 10−15 m2/s and 435 μs/cm. Mechanism studies showed that the hydration of BRM forms OH−, calcium silicate hydrate gels (C-S-H) and ettringite. Therefore, during S/S process, NH4+ was escaped as NH3, Mn2+ was solidified/stabilized as tephroite (Mn2SiO4), johannsenite (CaMnSi2O6) and davreuxite (MnAl6Si4O17(OH)2), and Pb2+, Cu2+, Ni2+, Zn2+ were solidified/stabilized by C-S-H and ettringite via substitution and encapsulation. This study provides a good choice for EMR long-term stable storage.