GB403077A - Improvements relating to processes for the preparation, separation or purification of salts or salt solutions - Google Patents

Abstract

The preparation of salt solutions from solutions of two reacting salts is effected by the aid of a predetermined excess of a mass of mixed base exchangers containing mobile cations corresponding to the cations of the reacting salts, the mass being so graded that it contains solely cations of one kind at one end and only cations of the other kind at the other end, and the proportions of each cation in intervening portions of the mass varying gradually. To effect reaction, relatively small and equivalent quantities of the two salt solutions are passed through the mass alternately and slowly in opposite and appropriate directions (or the mass through the two solutions respectively). A pure solution of a salt may be obtained from solutions containing two salts by passage through a similarly graded mixed base exchanger, in which case the mixed solution is first brought into contact with that part of the base exchanger having the same proportion of cations as exists in the solution, the latter in its flow encountering progressively base exchangers containing increasing quantities of cations of the salt that is to be produced pure. In this case the base exchanger is regenerated by a part of the pure solution. The graded base exchanger may be produced by first completely saturating a mass thereof with cations of one kind or by selecting a mass containing solely cations of one kind and then passing slowly therethrough a solution of a salt containing cations of the other kind until the first traces of the cations in the solution introduced just begin to appear in the liquid leaving the mass. Alternatively base exchangers each containing cations of one kind may be mechanically mixed in varying proportions and be disposed in superposed layers to give the graded effect. When using cations of weak bases such as iron, the solution may be slightly acidified or the more acid boro-, chromo-, or zircono-hydrosilicates may be employed as base-exchangers, or aluminohydrosilicates combined with such more acid radicles. The base exchanger may be disposed in a vertical tube through which the solutions are passed; or in large scale operations rotating continuous filters may be caused to pass through the solutions, successive segments of the periphery of the filters being coated with mixtures of the two base exchangers in gradually varying proportions; or a battery of receptacles may be charged with the two base exchangers, the proportions of the two in successive receptacles varying gradually and the solutions being passed through the battery in opposite directions. In one example, potassium nitrate solution is obtained by passing alternately in opposite directions through a graded mixture of calcium and potassium zeolites solutions of calcium nitrate and potassium chloride. Calcium chloride solution is also produced. In a second example potassium cyanide solution is obtained similarly from solutions of sodium cyanide and potassium chloride, using a graded mixture of sodium and potassium artificial zeolites. In a third example, copper acetate solution is obtained from solutions of slightly acid sodium acetate and copper sulphate using a graded mixture of sodium and copper zeolites. In a further example, crude potassium chloride containing sodium chloride is purified by passage through a graded mixture of sodium and potassium glauconite. The Specification as open to inspection under Sect. 91 comprises also the following subject matter:--The production of sodium sulphate solution by passing water containing calcium sulphate in suspension through a body of sodium glauconite the upper end of which has been admixed with finely ground gypsum. Sea water is then passed through in the reverse direction to regenerate the glauconite. This subject-matter does not appear in the Specification as accepted.