EXTRACTIVE CRYSTALLIZATION OF SALTS FROM CONCENTRATED AQUEOUS-SOLUTION

Extractive crystallization is considered as an alternative to evaporation in processes for the purification of raw salts. Purified concentrated salt solution is mixed with a selected solvent, and salt is forced to crystallize by the mutual solubility of water and solvent. After removal of the solid salt, the mother liquor of solvent, water, and residual salt is re-formed into a regenerated relatively dry solvent phase and a diluted aqueous phase by change in temperature and contact with additional concentrated solution. Both phases are directly recycled within the process, allowing creation of a continuous, industrially useful process. Solvents can be employed that are either miscible or immiscible with water. Process energy and capital requirements are shown to be substantially below those of conventional multieffect evaporation processes. Detailed examination is made for processes to produce NaCl and Na2CO3.