Production of potassium manganate and barium manganate from spent zinc–MnO2 dry cells via fusion with potassium hydroxide

This work describes a route for extracting manganese and zinc from spent zinc–manganese dioxide dry cells via fusion of the electroactive components with potassium hydroxide to form potassium manganate (K 2 MnO 4 ) and soluble zincates. The fused mass was dissolved in aqueous KOH and the insoluble matter was separated. Under the best optimal conditions, 70–78 wt% of manganese was solubilized as K 2 MnO 4 whereas 30–44 wt% of zinc was solubilized as [Zn(OH) 4 ] 2− ions. Lead was the only minor component dissolved in detectable amounts. Manganese was isolated by a one-step precipitation procedure as barium manganate (BaMnO 4 ) or via crystallization of K 2 MnO 4 . Lead and excess barium were isolated as sulfate by adding K 2 SO 4 . Zinc was precipitated as hydroxide after neutralizing the alkaline solution with H 2 SO 4 . pH control is essential to avoid decomposition of manganate ions and for the sequential precipitation of leached elements. K 2 SO 4 was partially recovered as by-product after partial evaporation of the neutralized solution. • Zn–MnO 2 dry cells as a raw material for production of potassium manganate. • Over 70 wt% of manganese converted into potassium or barium manganate. • No interference of zinc and other elements in the separation step. • ZnO and K 2 SO 4 as by-products of the fusion process. • Lower generation of final wastes.