Recycling manganese from spent Zn-MnO2 primary batteries

The cathode of spent Zn-MnO2 primary batteries is made up of mainly Mn3O4 and α-MnO2. Energy dispersive X-ray analysis of the cathode surface also shows the presence of zinc from the anode and chloride from the electrolyte. Manganese was recovered by precipitation, electrodeposition and anodization. X-ray diffraction measurements confirmed that the Mn3O4 material was recycled by chemical precipitation. The charge efficiency by electrodeposition was 85% at 25.0 mA cm−2. In the current density range studied, the potential/current density plots follow a Tafel-like relation. In the anodic process, the material oxidizes at the electrode/solution interface and precipitates to the bottom of the cell. Only a fraction corresponding to 20% of the charge density is deposited onto the electrode. This happens because Mn2+ oxidizes to Mn3+, which then suffers disproportionation.