The Oxidation of Fe(II) in Acidic Sulfate Solutions with Air at Elevated Pressures. Part 2. Influence of H2SO4 and Fe(III)

Abstract

The oxidation of ferrous ions in acidic sulfate solutions at elevated air pressures was investigated. The effect of the Fe2+ concentration, Fe3+ concentration, H2SO4 concentration, and partial oxygen pressure on the reaction rate were determined at three different temperatures, that is, T = 90, 70, and 50 °C. A second order of reaction in Fe2+ and a first order of reaction in O2 were determined, respectively. A slight inhibition by Fe3+ on the Fe2+ oxidation reaction was observed. The reaction is first order in Fe3+ in the kinetic term for the inhibition by Fe3+. Concentrations of H2SO4 up to 1 M result in a fractional negative order of −0.6; concentrations of H2SO4 above 1 M result in a zero order. One kinetic equation for the oxidation of Fe2+ was postulated, in which the order of reaction in H2SO4 is changed depending on the H2SO4 concentration. RFE2+ = −d[Fe2+]/dt = k[Fe2+]2PO2[H2SO4]c/(1 + A[Fe3+]), with c = −0.6 for [H2SO4] < 1 M, and c = 0 for [H2SO4] > 1 M. The activation energy was determined to be EA = 62.1 kJ/mol. The order c in H2SO4 is either −0.6 or zero, depending on the H2SO4 concentration.