Method of crystallizing salts from aqueous solutions

Abstract

Method of crystallizing from aqueous solution an inorganic solute, whose solubility in water varies relatively litter with temperature such that crystallizing by adjustment of temperature results in low yield, such method comprising contacting a concentrated aqueous solution of the solute with a hydrophilic organic solvent at a temperature T.sub.1, T.sub.1 and the organic solvent being selected such that at T.sub.1 a water-rich phase is formed in which the ratio of solute to water is less than the ratio found in the incoming aqueous solution, resulting in formation of crystals of solute. The resulting wet, organic-rich phase is separated and dried by contact with a concentrated aqueous solution of the solute at T.sub.2. T.sub.2 differs from T.sub.1, preferably being less than T.sub.1 if the solute dissolves exothermically in water and preferably being greater than T.sub.1 if the solute dissolves endo- thermically in water. The resulting dried organic phase is recycled to the crystallizing zone. The resulting diluted aqueous solution is used to dissolve solid solute to provide the concentrated solution. In some cases the wet organic phase will separate into two phases at T.sub. 2, one solvent-rich phase and one water-rich phase, and the water-rich phase may then be treated to remove water from the process. A portion of the diluted aqueous solution may be employed to adjust the concentration of solution going to the crystallizing zone to the desired concentration.