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

• Published in: Journal of power sources 2014-12, Vol.268, p.831-840
• Main Authors: da Rocha, Renan Azevedo, Quintanilha, Carolina Leão, Lanxin, Thayná Viana, Afonso, Júlio Carlos, Vianna, Cláudio Augusto, Gante, Valdir, Mantovano, José Luiz
• Format: Article
• Language: English
• Subjects: Alkaline fusion; Applied sciences; Barium manganate; Direct energy conversion and energy accumulation; Electrical engineering. Electrical power engineering; Electrical power engineering; Electrochemical conversion: primary and secondary batteries, fuel cells; Exact sciences and technology; Potassium manganate; Spent Zn–MnO2 dry cells
• ISSN: 0378-7753; 1873-2755
• DOI: 10.1016/j.jpowsour.2014.06.134

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 (K2MnO4) 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 K2MnO4 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 (BaMnO4) or via crystallization of K2MnO4. Lead and excess barium were isolated as sulfate by adding K2SO4. Zinc was precipitated as hydroxide after neutralizing the alkaline solution with H2SO4. pH control is essential to avoid decomposition of manganate ions and for the sequential precipitation of leached elements. K2SO4 was partially recovered as by-product after partial evaporation of the neutralized solution. •Zn–MnO2 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 K2SO4 as by-products of the fusion process.•Lower generation of final wastes.