Reductive acid leaching of spent zinc–carbon batteries and oxidative precipitation of Mn–Zn ferrite nanoparticles

The non-magnetic 8-mesh undersize material obtained by crushing, magnetic separation and sieving of spent zinc-carbon batteries assayed 23.9% Mn, 14.9% Zn, and 4% Fe. Reductive acid leaching of this material at a solid/liquid ratio of 1:10, and 60 °C with 2 mol dm− 3 H2SO4 and 0.39 mol H2O2 extracted 97.9% Mn, 98.0% Zn and 55.2% Fe after 60 min. The leach liquor composition was then adjusted to a Mn:Zn:Fe molar ratio of 1:1:4 suitable for producing MnZnFe4O8 ferrite powder by adding Mn(II), Zn(II) and Fe(II) sulfates. The effect of pH in the range pH 5–12 on the precipitation of Mn–Zn ferrite powder was investigated over 60 min using O2 gas flow rate of 1.3 dm3 min− 1 at 80 °C. The precipitated Mn–Zn ferrite at pH 12 were 20 nm particles that had a spinel structure. The saturation magnetizations of Mn–Zn ferrite powder (Mn1 − xZnxFe2O4) were determined to be 39–91 emu/g with various zinc contents (x = 0.2–0.8).