US EPA

1704341 

Journal Article 

Iron(II) oxidation by SO2/O-2 in acidic media - Part II. Effect of copper 

Zhang, WS; Muir, DM; Singh, P 

2000 

Yes 

Hydrometallurgy
ISSN: 0304-386X 

58 

2 

117-125 

WOS:000090012500003 

The oxidation of 0.1 and 0.5 M Fe2+ with O-2 and with SO2/O-2 mixtures is compared in the presence of CuSO4 at 80 degreesC, The SO2/O-2 system oxidises Fe2+ at a faster rate than the O-2 system, particularly at low concentrations of Fe2+ With O-2, the rate is second order with respect to Fe2+ concentration, and is catalysed by Cu2+. But with SO2/O-2, the rate is independent of Fe2+ and is inhibited by Cu2+. It is proposed that copper catalyses the oxidation of Fe2+ bq O-2 through a mechanism that involves the formation of ionic CuO2+ and H2O2 as the oxidant. In contrast, oxidation by SO2/O-2 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/O-2, but has little effect on the oxidation with O-2. It is shown that when high concentrations of Fe2+ and Cu2+ are oxidised by SO2/O-2, the reaction is initially dominated by the O-2 reaction mechanism, but is overtaken by the SO2/O-2 reaction mechanism as Fe2+. is oxidised and the concentration of Fe2+ decreases. The results indicate that the SO2/O-2 system would oxidise ferrous ions faster than O-2 to achieve higher levels of Fe(III) in solution during fenic leaching of minerals. (C) 2000 Elsevier Science B.V. All rights reserved. 

iron(II) oxidation; SO2/O-2; acidic media