Preparation of Zn-Mn ferrite from spent Zn-Mn batteries using a novel multi-step process of bioleaching and co-precipitation and boiling reflux

Synthesis of wide-application Zn-Mn ferrite soft magnetic materials using spent Zn-Mn batteries as starting raw materials has attained growing attentions in recent years. The multi-step series processes of reductive acid leaching and oxidative co-precipitation and high temperature calcination or hydrothermal reaction were generally utilized to carry out the conversion. In this work, a novel multi-step process of bioleaching and co-precipitation at 30 °C and boiling reflux at 100 °C, which was characteristic of low cost, environmental friendliness and energy saving, was attempted to accomplish the conversion for the first time. The results showed that synthesis of Zn-Mn ferrite using bioleaching liquor as a precursor was feasible. NaOH was the best coprecipitator for manufacturing the soft magnetic material from bioleaching liquor compared with NaHCO₃ and NH₄HCO₃. Higher pH value of the second co-precipitation at 13.0, higher total concentration of Mn^{2 +} + Zn^{2 +} + Fe^{2 +} at 2.0 mol/l and longer reflux time at 5 h were essential for greater magnetization and better crystallinity. Under optimum conditions, this novel multi-step process harvested soft magnetic material with highest saturation magnetization of 102 emu · g^-1, offering an alternative to convert spent Zn-Mn batteries into Zn-Mn ferrite.