Promoting effect of AlN foreign particles on crystallization of sodium sulfate decahydrate

Abstract

Crystallization is a major separation technology in chemical process engineering and wastewater treatment. The promotion of nucleation is a primary concern because it affects both product purity and separation efficiency. In this study, the effect of aluminum nitride foreign particles on the crystallization of sodium sulfate decahydrate was investigated. Also the influence of aluminum nitride foreign particles on kinetics and thermodynamics of sodium sulfate decahydrate nucleation was determined. Induction time, metastable zone width and solubility of sodium sulfate decahydrate in the aluminum nitride foreign particles were determined by the application of a turbidity monitoring technique in stable and uniform temperature conditions by drip titration method unlike the traditional polythermal and isothermal methods commonly applied in the unstable temperature conditions. In the presence of aluminum nitride foreign particles, induction time and metastable zone width decreased 30% and 13% respectively and solubility did not show significant changes. The experimental results were analyzed by empirical secondary nucleation model, classical nucleation theory and empirical Kashchiev heterogeneous nucleation model. It was found that the secondary nucleation model can better illustrate the influence of aluminum nitride foreign particles on nucleation. In the presence of aluminum nitride foreign particles, the surface tension decreased which results in lower induction time.