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

• Preparing Zn–Mn ferrite soft magnetic material with bioleaching liquor was feasible.
• NaOH was the best for manufacturing soft magnetic material from bioleaching liquor
• Higher pH, greater total dose and longer reflux were needed for better magnetization
• The highest saturation magnetization of 102 emu · g − 1 was obtained by the novel process
• Process was characteristic of low cost, environmental friendliness and saving energy

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 Mn2 + + Zn2 + + Fe2 + 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.

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