Purification of Mn-Electrolyte Solution from Leaching of Zn-MnO2 Spent Batteries Using Cementation Technique

Abstract

This paper investigates the purification of a manganese electrolyte solution, produced by leaching spent Zn-MnO2 primary batteries, using cementation with metallic manganese powder. The battery paste, composed mainly of 59.98% Mn and 37.23% Zn, was roasted at 900 °C for 30 minutes to remove carbon and convert MnO2 to Mn3O4. After roasting, the composition changed to 63.65% Mn and 31.73% Zn. Ascorbic acid and sulfuric acid were used as reducing and leaching agents, respectively, at 70°C for 3 hours with a solid-to-liquid ratio of 1/20 g/mL and a stirring rate of 200 rpm. The resulting leachate solution contained Mn and Zn at concentrations of 16.5 and 9.2 g/L, respectively. Cementation with manganese powder was then used to remove zinc from the leachate solution. The effects of reaction temperature, time, stirring rate, and amount of manganese powder on zinc removal were investigated. The optimal conditions for zinc removal (98.4%) were found to be 60 °C, 600 rpm, and 20 minutes. Analysis of the cemented powder revealed a composition of 82% Zn and 17% Mn. Further investigation determined that using the ideal amount of manganese powder achieved a purification efficiency of 99.67%, reducing the zinc concentration in solution to 0.03 g/L.