PRECIPITATION OF STRONTIUM SULFATE IN AQUEOUS-SOLUTIONS AT 25-DEGREES-C

The spontaneous precipitation of strontium sulfate from equimolar supersaturated aqueous solutions was investigated under conditions of constant supersaturation. The stability diagram of the system was drawn and it showed a marked inverse dependence of the induction times on the solution supersaturation. At supersaturation ratios Omega greater than or equal to 8, the precipitation was homogeneous and a value of 88 mJ m(-2) was calculated for the precipitating strontium sulfate. The rates of precipitation showed a first-order dependence on the relative solution supersaturation. This order is consistent with a surface-controlled mechanism suggested in the literature. At higher supersaturations however (Omega greater than or equal to 8), the order increased to 4 suggesting prevalence of the nucleation process. The habit of the crystals formed included rhombohedral and hexagonal shapes irrespective of the solution supersaturation, within the range examined in the present work.