Kinetics of oxidation of bivalent iron by chlorate

Abstract

Kinetics of Fe(II) oxidation by chlorate was studied in homogeneous systems (pH 1, HCLO4 and in heterogeneous systems involving precipitate of Fe(III) hydrolysis products (pH 1 to 5.5). The stoichiometry ( 6 Fe2+ : 1 ClO-3 : 6H+) as well as the rate equation (-d[Fe2+]/dt = kexp/.[Fe2+][ClO-3]) is the same in the two cases. Also the differences in the experimental activation energies and entropies for the two pH regions are insignificant. The [OH-]/[Fe3+] ratio passes a maximum during the spontaneous change of pH (pH0 5), whereas if the pH is maintained constant (pH 5) the ratio increases monotonically throughout the whole time interval followed. The balance of the Fe2+ and Fe3+ showed that part of the Fe2+ ( 10-3 mol l-1) was present during the reaction in the precipitate of the Fe(III) hydrolysis products, while part of the Fe3+ (5 . 10-3 mol l-1) existed outside this precipitate; the latter dropped by approximately two orders of magnitude only several tens of hours after the finishing of the Fe(II) oxidation.