Continuous Double Recrystallization of Light Soda Ash into Super Dense Soda Ash

In this work, a new process is explored for the bulk densification of light soda ash. Advantages of the new process are that no (crystal) water needs to be evaporated and that a crystalline super dense soda ash is produced at atmospherical conditions. The so-called "mixed-solvent" process is based on the fact that the transition temperature at which monohydrous and anhydrous soda in contact with an aqueous solution are in equilibrium, can be lowered when a second solvent is applied. Continuous double recrystallization experiments were carried out in mixtures of water and ethylene glycol: first, light soda was recrystallized into monohydrate below the transition temperature, then the temperature was raised above the transition temperature, and monohydrate was converted into solid, anhydrous soda with a high bulk density. Values of up to 1400 kg/m³ were measured. Further, a significant amount of chloride was removed from the soda during the two recrystallization steps. The potential industrial applications of the double recrystallization process are described by Oosterhof et al. (patent application no. EP19980203963 19981124, 2000).