Iron(II) oxidation by SO2/O2 in acidic media: Part II. Effect of copper
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The oxidation of 0.1 and 0.5 M Fe2+ with O2 and with SO2/O2 mixtures is compared in the presence of CuSO4 at 80°C. The SO2/O2 system oxidises Fe2+ at a faster rate than the O2 system, particularly at low concentrations of Fe2+. With O2, the rate is second order with respect to Fe2+ concentration, and is catalysed by Cu2+. But with SO2/O2, the rate is independent of Fe2+ and is inhibited by Cu2+. It is proposed that copper catalyses the oxidation of Fe2+ by O2 through a mechanism that involves the formation of ionic CuO2+ and H2O2 as the oxidant. In contrast, oxidation by SO2/O2 is catalysed by Fe3+ in a free radical mechanism involving peroxysulphate radical that is inhibited by Cu2+. The presence of the free radical scavenger hydroquinone also inhibits the oxidation of Fe2+ with SO2/O2, but has little effect on the oxidation with O2. It is shown that when high concentrations of Fe2+ and Cu2+ are oxidised by SO2/O2, the reaction is initially dominated by the O2 reaction mechanism, but is overtaken by the SO2/O2 reaction mechanism as Fe2+ is oxidised and the concentration of Fe2+ decreases. The results indicate that the SO2/O2 system would oxidise ferrous ions faster than O2 to achieve higher levels of Fe(III) in solution during ferric leaching of minerals.
|Publication Type:||Journal Article|
|Murdoch Affiliation:||Parker Cooperative Research Centre for Integrated Hydrometallurgy Solutions|
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