JOURNAL PAPER

Oxidative precipitation of Mn(II) from cobalt leach solutions using dilute SO₂/air gas mixture

N. Mulaudzi^{I, II}; T. Mahlangu^II

^IHydrometallurgy Division, Mintek, South Africa
^IIDepartment of Materials Science and Metallurgy, University of Pretoria, Pretoria, South Africa

SYNOPSIS

The use of SO2/air gas mixtures as an oxidant to precipitate Mn from Co(II) leach liquors was investigated. The effects of SO₂/air ratio, pH and temperature on Mn precipitation were evaluated. It was found that the use of SO₂/air gas mixtures resulted in significantly higher Mn precipitation kinetics compared to using air or pure O₂alone.
The SO2/air ratio was varied from 0% to 6% SO2 (v/v) in air and similar Mn removals were achieved at 0.75% to 3% SO₂at pH 3. The solution pH was varied from pH 2 to pH 4; Mn precipitation did not increase considerably from pH 2 to pH 3, but increased significantly at pH values higher than pH 3. Cobalt co-precipitation also increased as pH increased, with 1% Co co-precipitation at pH 3. An increase in temperature from 30°C to 60°C also increased Mn precipitation and 100% Mn precipitated at 50°C. Cobalt co-precipitation also increased significantly with an increase in temperature. An activation energy of 25 kJ/mol was calculated from the Arrhenius plot, which is an indication that the precipitation reactions were both chemically and diffusion controlled.
XRD analysis showed that Mn precipitated in the form of Mn₂O₃instead of MnO2 that was predicted from thermodynamic data. SEM and XRD analysis also revealed that the precipitate consisted mainly of gypsum or bassanite (99%), with the Mn containing phase (< 1%) distributed within the gypsum phase. The co-precipitated Co reported to the Mn phase.

Keywords: manganese precipitation; SO₂/O₂gas mixtures; cobalt solutions

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The work published in this paper is in partial fulfilment of an M.Eng Metallurgical Engineeringthesis from the University of Pretoria