Harmless Impact of Electrolytic Manganese Residue by Low Temperature Thermochemical Method with Carbide Slag

Abstract

This study introduced a low-temperature thermochemical method for the treatment of EMR in the presence of carbide slag (CS) to achieve an economical and efficient harmless effect. The experimental results indicate that, under suitable conditions, the NH₄⁺ and Mn²⁺ contents in EMR decrease notably with the increasing CS content, accompanied by an increase in pH value. Furthermore, the concentration of NH₄⁺ in EMR considerably decreases with the increasing liquid-to-solid ratio, eventually stabilizing. Similarly, the pH value first increases and then decreases, ultimately stabilizing. At a CS content of 12% and a liquid-to-solid ratio of 0.7, the leaching concentrations of NH₄⁺ and Mn²⁺ in EMR (127.7 mg/kg and 0.15 mg/L, respectively) fall below the standard detection limit (2 mg/L), with the pH measuring 8.26, meeting the conditions outlined in the GB 8978. NH₄⁺ is converted to NH₃, while Mn²⁺ is transformed into solid precipitates such as Mn(OH)₂, Mn₂O₃, MnO₂, Ca₃Mn₂O₇, and Ca₂MnO₄. The majority of manganese ions exist in trivalent or tetravalent states and remain stable over time. The cost of using CS as a reagent for treating 1 ton of EMR is merely $1.01. The high OH⁻ concentration provided by CS enables the effective removal of NH₄⁺ from EMR and the solidification of Mn²⁺ during thermal reactions.

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Wuhan University of Technology and Springer-Verlag GmbH Germany, Part of Springer Nature