Crystallization study of potassium sulfate-water system, metastable zone width and induction time measurements using ultrasonic, turbidity and 3D-ORM techniques

A batch cooling crystallizer was used to explore the solubility, metastable zone width (MSZW), induction time and crystallization kinetics of potassium sulphate-water as a model system. Three techniques were used: ultrasonic, turbidity and 3D-ORM probes. In the first step, the potassium sulphate solubility in water was measured over the temperature range from 15 to 35 °C by using a refractometer. In a second step, the MSZW was measured using different cooling rates for different solution concentrations by both ultrasonic and turbidity probes in order to compare between the two methods. The nucleation kinetics of the studied system was estimated based on approach the crystal growth rates were calculated from desupersaturation curve during seeded batch experiments. Finally, induction time measurements were achieved by means of a 3D-ORM and the effect of supersaturation degree and saturation temperature on measured induction time was investigated. Based on classical nucleation theory, the induction time data were used to calculate the surface tension.