GB464834A - Process for the manufacture of caustic soda - Google Patents

Abstract

Sodium hydroxide or solutions thereof are obtained by a process comprising the following steps: (1) the reaction between sodium chloride and barium hydroxide in aqueous medium at a temperature not exceeding 40 DEG C. to form basic barium chloride which is removed from the reaction mixture; (2) the evaporation, with or without carbonation or sulphation, of the mother liquor from step (1), to remove as solids the remaining barium content and the sodium chloride. The reaction of step (1) may be conducted in an aqueous alcoholic medium, e.g. a methanol-water mixture, or in an aqueous ammoniacal medium. The evaporation of step (2) may be followed by cooling, or flash evaporation may be employed, if desired, in several stages with intermediate removal of solids. The mother liquor from step (1) may be carbonated prior to evaporation, the resulting barium carbonate being calcined and returned to the process as oxide or hydroxide. Alternatively, the liquor may be evaporated to obtain a mixture of barium hydroxide and sodium chloride for return to the process. Preferably at least a part of the basic barium chloride is worked up for return to the process. For example, the basic chloride may be treated with water or aqueous ammonia to produce solid barium hydroxide. For complete barium recovery, the liquor remaining after the removal of the solid barium hydroxide is carbonated, the resulting barium carbonate being calcined for return to the process. Preferably, the liquor is made ammoniacal prior to carbonation or ammonium carbonate is employed. The sodium hydroxide solution obtained may be further purified in known manner from sodium chloride and/or may be worked up into solid sodium hydroxide.