STEP VELOCITIES AND RATES OF DISSOLUTION AT DIFFERENT SATURATION INDICES AND VARYING IONIC RATIOS STUDIED DURING DISSOLUTION OF CELESTITE (SRSO4)

Dissolution kinetics of Celestite was studied using AFM (atomic force microscopy). Experiments were carried out on freshly cleaved 001 surfaces of the SrSO4 crystal at room temperature and at a pH of 5.0. In-situ AFM experiments were designed in a fluid cell system, which aided the understanding of the dissolution behavior under flow through conditions. On the basis of movement of microscopic surface structures (e.g. steps), step velocities and rates of dissolution were calculated as functions of different saturation indices of the solution flowing into the system. Similarly, rates were also calculated under conditions of varying ionic ratios (of the participating Sr2+ and SO42- ions) at a fixed saturation index. Step velocities and dissolution rates follow the trend of increasing order of magnitude with decreasing saturation indices. On the other hand, varying ionic ratios revealed an interesting effect on the anisotropic step kinetics suggesting varying roles of the two ions on varying step structures. Experiments also show etch pit morphologies and step distribution at different conditions.