GB439287A - Improvements in or relating to the production of potassium sulphate - Google Patents

Abstract

In obtaining potassium sulphate from potassium chloride and sodium sulphate by the cyclic process described in Specification 410,830, the second glaserite producing step is effected by a multi-stage process; that is, a process in which the reactant is converted into the product indirectly through two or more stages involving the formation in the solid phase of an intermediate compound or series of such compounds. The first step may also be conducted as a multi-stage process, in which case, both steps may be combined as a counter-current flow process. According to a modification, the whole of the potassium chloride is added with sodium sulphate in the second step, and in the first step water alone is brought into contact with the solids from the second step, the amount of potassium chloride added in the second step being sufficient to cause solid potassium chloride as well as enriched glaserite to pass to the first step. Instead of potassium chloride impure materials containing substantial quantities thereof and also containing for example sodium chloride, may be employed. Temperatures not exceeding 55 DEG C., may be employed in the first and second steps. According to one example, which is conducted in a trough subdivided into twelve compartments. The first compartment is fed with solid sodium sulphate and a liquor is withdrawn therefrom. This liquor is worked up by evaporation to separate sodium chloride, followed or preceded by cooling to separate a mixture of potassium chloride and glasenite which is introduced with additional crude potassium chloride, as a solution into compartment 12. Further crude potassium chloride may be supplied to compartments 10 or 11. The solid phase moves successively from compartment 1 to 12 while the liquid phase moves in the reverse direction. Potassium sulphate is withdrawn from compartment 12. According to a second example, four stirred pots containing potassium chloride, sodium sulphate, potassium sulphate and water are provided, pot 4 being relatively rich in sodium salts and pot 1 in potassium salts. After stirring for 15 minutes at 30 DEG C., the solids and liquids are separated the liquors being transferred in the direction 1 --> 4 and the solids in the opposite direction so that liquid from 1 reacts with solid from 3 in pot 2 in the next cycle while the liquid from pot 4 and the solid from pot 1 are withdrawn from the system. The liquor from pot 4 is worked up by cooling and evaporation as previously described, the resulting mixture of potassium chloride and glasenite being returned to any of the pots 1--4. Potassium chloride and sodium sulphate are supplied to pot 4 and water to pot 1 and when steady conditions have become established pure potassium sulphate is withdrawn from pot 1. According to the Provisional Specification when carrying out the first example with impure potassium chloride it is preferable to bleed off some of the liquor circulating through the apparatus, e.g. from compartments 8 or 9, and add it to the liquor withdrawn from compartment 1.