Kinetics of Dissolution of Cobalt Oxides in Acidic Media

The kinetics of dissolution of cobalt oxides Co2O3 and Co3O4 in aqueous solutions of acids (H2SO4, EDTA(1)) is experimentally studied. Dissolution rate W increases with the temperature or the EDTA concentration. The reaction orders of dissolution for hydrogen ions in sulfuric acid and EDTA (dlogW/dpH = 0.5 +/- 0.1) and for anions (dlogW/dlog[An(-)] = 0.5 +/- 0.1) are determined. A specific feature of the dissolution kinetics in EDTA is a maximum in the dissolution rate of the cobalt oxides at pH -1. The activation energy of the process Ea is 70 kJ/mol in H2SO4 and 60 kJ/mol in EDTA. The modeling of the process shows that the CoOH+ ion is a surface particle controlling the dissolution rate in mineral acids and the CoHY- ion, in the complexone.