Impact of feeding policy and ion excess on particle shape in semi-batch precipitation of barium sulfate

Precipitation of barium sulfate from barium chloride and potassium sulfate was investigated concerning particle morphology depending on feeding policy, i.e. feeding sequence and feeding time, as well as the level of supersaturation and barium to sulfate ion ratio. Experiments were carried out in a semi-batch operated stirred tank reactor with single feed. Although precipitation of barium sulfate is well studied in literature, an explicit investigation of the dependence of morphology on semi-batch feeding policy is still missing. This work tries to fill this gap. To observe particle morphology SEM pictures were taken. A strong dependency on the feeding sequence was observed, giving different particle morphologies at the same supersaturation level. Also the feeding time had a strong influence for otherwise the same experimental conditions, giving dendritic particle shapes for high feeding rates, and cuboid-shaped particles for lower feeding rates. In all cases, particles grow with a characteristic morphology at specific experimental conditions defined by the supersaturation level, the ion ratio and the feeding policy.