Control of crystal morphology through supersaturation ratio and mixing conditions

Precipitation of sparingly soluble materials is an important unit operation in chemical industry, which is employed in the production of bulk and fine chemicals. So it is of good significance to investigate this process. Barium sulfate was selected as the study material. We present a result in this work that the crystal morphology in a liquid precipitation could be controlled through supersaturation ratio and mixing conditions. With different supersaturation ratios, the precipitation process could be comparted to four regions: the growth region, the grow-control transition region, the nucleation-control transition region and the nucleation region. In the growth region, the supersaturation ratio is quite low and the product is a big crystal with special crystalline form. In the nucleation region, the high supersaturation ratio causes the nanoparticle product. There are two different cases at media supersaturation ratio: close to the growth region snow-like crystals with branch orientation determined by the crystalline form are produced, which is the grow-control transition region; close to the nucleation region leaf-like crystals are produced, which is the nucleation-control transition region. The boundaries between the regions are roughly determined based on the experimental data. The mixing performance affects precipitation through its determination of the precipitation region existence. Poor mixing causes the coexistence of different regions and the generation of crystals with different morphologies. Finally, it is found that the mixing performance determines the monodispersity only while the supersaturation ratio determines the morphology of crystals in a precipitation process.