CRYSTALLISATION OF SODIUM SULFATE: SUPERSATURATION AND METASTABLE PHASES

Abstract

Crystallisation of sodium sulfate solutions by evaporation under controlled climatic conditions has revealed the existence of crystalline hydrated sodium sulfate salts not previously reported. The sodium sulfate phase crystallising and the concentration of the solution at the point of crystallisation depends on the climatic conditions (temperature and evaporation rate). During the rehydration of the anhydrous sodium sulfate phase, thenardite, another previously unreported phase was formed prior to the nucleation of the stable phase, mirabilite Na2SO4 · 10H2O. The addition of organic inhibitors changes both the crystallisation and the rehydration behavior in this system.