Crystallisation kinetics of ZnS precipitation; an experimental study using the mixed-suspension-mixed-product-removal (MSMPR) method

The precipitation kinetics of zinc sulfide were studied using a lab scale mixed-suspension-mixed-product-removal (MSMPR) precipitation reactor. The vessel was operated at different feed concentrations, molar ratios, stirrer speeds, pH-values, feed injection positions and residence times. Primary nucleation and volume average crystal growth rates as well as agglomeration kernel were determined. Relationships were found between the rates of the different crystallization steps on the one hand and supersaturation, stirrer speeds, pH-values, Zn2+ to S2- ratio, feed positions on the other. These show that larger crystals are obtained at high supersaturation, moderate stirrer speeds, small residence times, a pH-value of around 5 and high Zn2+ to S2- ratios. One should realize though that the applied MSMPR method is not the most optimal technique for examining fast precipitation reactions