GB494556A - Improvements in the manufacture and production of alkali metal hyposulphites - Google Patents

Abstract

Alkali metal hyposulphites are produced by reacting solutions of heavy metal, e.g. zinc, cadmium or iron, hyposulphites with alkali metal amalgam. The heavy metal separates in part in metallic form, and is partly dissolved in the mercury, and partly dispersed in the aqueous solution. Unreacted heavy metal hyposulphite remaining dissolved in the solution may be precipitated by alkali hydroxide, carbonate, sulphite or other suitable agent. The two precipitates may be removed consecutively or simultaneously. Sodium and potassium amalgams are specified, the amalgam produced by the electrolysis of common salt with mercury as cathode being advantageously used. The amalgam is preferably used in stoichiometric excess, e.g. from about 5-15 per cent excess. The process may be carried out continuously by leading the amalgam and solution countercurrently through a trough or tube. The aqueous solution escapes over an overflow, and the mercury, which may contain unused alkali metal in addition to the heavy metal, through a syphon. The heavy metal set free may be reconverted to hyposulphite, for example, by treatment with sodium bisulphite. The mercury liberated is re-used for the preparation of the amalgam. In an example, sodium amalgam is run, in an atmosphere of nitrogen, into zinc hyposulphite solution at 35 DEG C.