Growth Rate Dispersion of Sodium Perborate Crystals

A procedure to evaluate the growth rate diffusivity from seeded batch runs is reported. The experiments concerned the crystallization of sodium perborate from aqueous solutions. The crystal size distributions were satisfactorily simulated by assuming the inverse gamma function for the growth rate distribution. Values of the growth rate diffusivity in the range 2.3 to 4.1 . 10-13 m2s-1 were determined. A number of studies have shown that, when exposed to constant external operating conditions, different crystals of a given material and a given size may grow at different rates. This phenomenon is known as growth rate dispersion (GRD). Several authors (1) (2) reported that an individual crystal has a characteristic growth rate for a given driving force and maintains this growth rate during its growth. This assumption is the base of a model which is generally referred to as "constant crystal growth" (CCG). This work refers to a system for which crystal GRD has been assumed to be not negligible. It mainly aims at the evaluation the GRD of crystals from seeded batch crystallization experiments carried out in a lab-scale apparatus. The crystallization of sodium perborate (SPB) from aqueous solutions has been used as the case study.