ABSTRACT

A simple flow-system was designed to study the dissolution of cobaltous oxide (CoO) at surface conditions (25° and 39°C, one atmosphere). Experiments were carried out using solutions with salinities less than 0.01m and pH's of 0.7-3.46. The dissolution was found to be controlled by surface reactions and has a reaction order of 0.67±0.05 with respect to hydrogen ion concentration. The integrated kinetic equation has the form [Co(H₂O)₆²⁺] =k₊/k_- [H⁺]^0.67(1-e^-Ak_t) where k₊ and k_- are reaction rates for the forward and reverse reactions, and were determined to be 1.05±0.26×10^-10 m^-2s^-1 and 7.25±1.20×10^-10 m^-2s^-1 respectively. CoO is not stable in acidic aqueous solutions under surface conditions. It gradually transforms into cobalt spinel (Co₃O₄) and which is effectively insoluble under our experimental conditions. A rate constant of 0.0038 day^-1 was estimated for the phase transition reaction (CoO→Co₃O₄) assuming a first-order reaction model.