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.

Keywords: Ammonium; Basic burning raw material; Electrolytic manganese residue; Heavy metals; Long-term stable storage.