Immobilization of high concentrations of soluble Mn(II) from electrolytic manganese solid waste using inorganic...

Electrolytic manganese solid waste (EMSW) is a by-product of electrolytic manganese production and generally contains a high concentration of soluble Mn(II) (2000-3000 mg/L). Millions of tons of EMSW are stored in China, and the environmental pollution caused by manganese in this waste product is concerning. Unfortunately, little attention has been paid to the immobilization of manganese from industrial solid waste because manganese is absent from toxicological identification standards, and there is a lack of relevant quality standards in China. The objectives of this study were to immobilize soluble Mn(II) using chemical reagents, to analyze the immobilization mechanism, and to identify the most economical reagents. We investigated the immobilization degrees of soluble Mn(II) achieved by the reagents quicklime (CaO), carbonates (NaHCO₃ and Na₂CO₃), phosphates (Na₃PO₄, Na₂HPO₄, NH₄H₂PO₄, and Ca₁₀(PO₄)₆(OH)₂), and caustic magnesia (MgO) both individually and in combination. Our results showed that the use of 9% CaO+ 5% NaHCO₃, 9% CaO+ 5% Na₃PO₄, 10% MgO alone, or with 1-5% NaHCO₃ or 1-5% Na₂CO₃ can reduce the amount of Mn(II) leached to 100 mg/kg when the eluate pH was in the range of 6-9. The most economical reagent treatments were determined using K-means cluster analysis. Analysis of the immobilization mechanism showed that CaO + NaHCO₃ may be favorable for immobilizing soluble Mn(II) as precipitation and oxidation products because the addition of NaHCO₃ releases OH(-) and buffers the system.