GB639855A - Improvements relating to processes for the manufacture of alkali metal hydroxides, sulphur dioxide and sulphuric acid - Google Patents

Abstract

Alkali metal hydroxides, e.g. NaOH, KOH and LiOH, and sulphur dioxide are made by reacting a metallate (i.e. the chemical combination derived from the hydroxide of a polyvalent metal, which forms an insoluble sulphide in alkaline solution, in which one or more hydrogen atoms are replaced by an alkali metal) with an alkali metal sulphide, to form an alkali metal hydroxide and a sulphide of the metal of the metallate, and separating and roasting the metal sulphide to form sulphur dioxide and the metal oxide, which may be used together with alkali metal hydroxide thus produced to form the metallate. Metals specified are zinc, copper, lead, nickel, tin, iron and manganese. The alkali sulphide may be made by reducing with coal or coke an alkali sulphate which may contain the metal of the metallate as impurity or may be purified by crystallization prior to the reduction. The metallate may be formed by dissolving the metal oxide or hydroxide in aqueous caustic alkali solution. In the case of the zincate, purification may be effected by adding alkali sulphide in stoichiometrical amount to precipitate impurities as sulphides, and after removal of impurities further alkali sulphide may be added to precipitate zinc sulphide. The caustic alkali formed may contain some alkali sulphide by adding excess of the latter to the metallate. In a modification, alkali sulphide is reacted with a metal capable of forming a metallate or an oxide or hydroxide thereof and water.