GB785660A - Fractionating solution containing more than one solute - Google Patents

Abstract

<PICT:0785660/III/1> In a method of fractionating two or more solutes from a solution, solid and liquid phases of the solutes in a common solvent medium are established and the solid and liquid phases are moved countercurrent to each other, the common solvent being introduced into that end of the medium toward which the solid phase tends to move to provide a concentration gradient in the liquid phase of the solutes with respect to the common solvent, and solid phase enriched in one of the solutes is removed adjacent the place of introduction of the solvent while the liquid phase is removed from the end of the medium opposite that from which the solid phase is removed. A solution, saturated or at high concentration, of potassium persulphate and ammonium persulphate in water or in aqueous sulphuric acid, is introduced by an inlet 18 (Fig. 1), to a tube 16 which has a portion 10 cooled by cooling medium in a jacket 12 to initiate crystallization of the salts. Crystals may be removed from surface 10 by means of a scraper. Crystals of both salts form and settle down the tube 16, building up a loose mass of crystals which occupies the full height of tube 16. The solvent, i.e. water or aqueous sulphuric acid, is introduced by an inlet 19 and flows gradually upwards through the mass of crystals establishing a concentration gradient as it dissolves some of the descending salts, particularly ammonium persulphate which is more readily soluble. Crystals are constantly removed from the bottom of the mass through an outlet 21 while fresh crystals are supplied to the top of the loose mass. The crystals are removed by outlet 21 as a slurry, liquid being recirculated by a pump 30, and consist almost entirely of potassium persulphate. A solution of ammonium persulphate containing almost no potassium persulphate is removed by an outlet 11. Instead of introducing a solution of the two salts by inlet 18, the salts may be introduced in crystal form to the medium in tube 16, in which case the cooled portion 10 is not required. The lower end of tube 16 may be heated or cooled by circulating a medium through a jacket to maintain a temperature at which the difference in solubilities of the salts is most pronounced. Other salts mentioned which may be separated are barium and lead nitrates.