Oxidative precipitation of manganese with SO2/O2 and separation from cobalt and nickel

The oxidation of Mn(II) and precipitation as MnO2/Mn2O3 occurs spontaneously using SO2/O2 gas mixtures in the pH range 1–6 and temperature range 25–80 °C. The rate of Mn(II) oxidation with SO2/O2 is first order with respect to SO2 partial pressure up to 5.7% SO2 at 80 °C and half order with respect to [H+]. The rate of oxidation of Mn(II) is slow at pH<3 and increases rapidly at pH>4. Any Fe(II) is oxidised and precipitated before Mn(II). ncentrations of manganese (0.01 M) can be selectively oxidised and precipitated from cobalt and nickel solutions at pH 3–4 with less than 1% co-precipitation of cobalt and nickel in the laboratory batch tests. The selectivity of manganese precipitation at pH 3–4 is consistent with thermodynamic data for the Mn–Ni/Co–H2O systems.