DISSOLUTION KINETICS OF BARITE AND THE EFFECT OF CRO₄^2- ON DISSOLUTION

The toxic Cr(VI) as an environmental pollutant necessitates remediation if detected at sufficiently high concentrations. The immobilization of Cr(VI) prior to clean-up often involves reduction to Cr(III), however, alternative immobilization methods such as the co-precipitation of chromate with barium sulfate may be more effective in some circumstances. As an initial investigation into the processes involved in this immobilization strategy, the influence of CrO₄^2- adsorption on the dissolution of Barite was studied using atomic force microscopy (AFM). Experiments were carried out using freshly cleaved (001) surfaces of barite crystals exposed to aqueous solutions at a pH of 8.4 under constant flow through conditions in an AFM fluid cell. Movement of microscopic surface structures (e.g. steps) was the basis of measuring step speeds and rates of mineral substrate dissolution. Reaction rates were determined at different solution saturation indices with respect to both barite and Hashemite (BaCrO₄) phases. The substrate dissolution rates were similar when exposed to solutions at identical saturation states with respect to barite and hashemite phases. Thus presence of CrO₄^2- in solutions has an effect on the dissolution process, resulting in a coupled barite dissolution-hashemite precipitation reaction.