SPONTANEOUS PRECIPITATION OF BARIUM-SULFATE IN AQUEOUS-SOLUTION

The formation of barium sulfate scale in oil wells and in several industrial processes in which water supersaturated with respect to this salt is used, is often a serious cause of energy losses. The spontaneous precipitation in aqueous solutions containing relatively high barium and sulfate concentrations was investigated in the present work. In our experiments the supersaturation of the solutions was chosen so that an induction period preceded the onset of precipitation. In all cases the induction time was found to be inversely proportional to the solution supersaturation and the rates of the subsequent precipitation were higher the higher the solution supersaturation. The stability domain of the barium sulfate system was not affected by the barium: sulfate molar ratio which ranged from 0.01 to ca. 100. The dependence of the induction time on the initial barium concentration was linear and irrespective of the molar ratio of barium: sulfate the same slope was obtained. The slope may be related to the size of the critical nucleus. The kinetic data obtained suggested a surface-controlled, polynuclear mechanism. On the basis of this model a value of 86 mJ m-2 was obtained for the surface energy of the precipitating solid phase.