GB351271A - - Google Patents

Abstract

In the production of potassium nitrate by the double decomposition of potassium sulphate and calcium nitrate, double salts such as syngenite (K2SO4, Ca SO4, H2O) and potassium pentacalcium sulphate (K2SO4, 5 Ca SO4, H2O) ar formed as byeproducts. This disadvantage is avoided in a cyclic process in which potassium chloride, nitric acid, ammonia and carbon dioxide are the raw materials and potassium nitrate and ammonium chloride the products, whilst gypsum is added and its calcium and sulphuric acid kept in circulation. The process comprises the following steps: (i) stirring a solution of ammonium chloride and carbonate (obtained in (v)) with gypsum (obtained in (iii)) and separating the precipitated calcium carbonate; (ii) adding potassium chloride to the liquor from (i), treating with ammonia and separating potassium sulphate; (iii) treating a mixture of the calcium carbonate and potassium sulphate with nitric acid to produce gypsum and potassium nitrate, the former being separated and the latter obtained by evaporating the solution; (iv) separating part of the ammonium chloride in the liquor from (ii) by cooling; (v) neutralizing the remaining liquor from (iv) with carbon dioxide to produce the starting material of (i). In a modification, steps (i) and (ii) are combined, the ammonium chloride-ammonium carbonate solution being successively stirred with gypsum and potassium chloride and treated with ammonia, and the mixture of potassium sulphate and calcium carbonate so formed treated as in (iii), In another modification the greater part of the potassium nitrate is separated from the liquor of (iii) by cooling instead of evaporation, and the mother liquor is used for dissolving further quantities of potassium sulphate for treatment with calcium carbonate and nitric acid.