Although crystallization process is optimized mainly with respect to the physicochemical properties, the mechanical properties such as the strength of crystal particles are the important factors in the industrial process because the crystallization usually follows the filtration process and the filtration time occupies relatively a long time in the whole processing time. In this study, the crystallization process of a sulfate which forms spherical agglomerate of primary crystal particles has been studied with particular attention to the effect of the operating conditions of crystallization on the filtation characteristics of crystal agglomerates.
The filtration characteristics were evaluated by the specific resistance calculated from Darcy's equation through the filtration experiments carried out under constant pressure drop. The compression ratio is also measured with a tapping method. It was found that the specific resistance has almost no correlation with the compression ratio, suggesting that the compression ratio is an inadequate parameter for the evaluation of the filtration characteristics. The specific resistance of agglomerated crystal is higher at a lower crystallization temperature and a higher mixing speed during crystallization. However, the amount of seed particles has no effect on the specific resistance.
The centrifugal filtration time under optimized conditions were compared with the filtration time under the condition employed in an industrial process. It was confirmed that the filtration time of the tested sulfate crystals can be reduced to a half by optimizing of the operating conditions of crystallization.