Oxidative precipitation of manganese with SO 2/O 2 and separation from cobalt and nickel

Abstract

The oxidation of Mn(II) and precipitation as MnO 2/Mn 2O 3 occurs spontaneously using SO 2/O 2 gas mixtures in the pH range 1–6 and temperature range 25–80 °C. The rate of Mn(II) oxidation with SO 2/O 2 is first order with respect to SO 2 partial pressure up to 5.7% SO 2 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). Low concentrations 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–H 2O systems.