GB443101A - Improvements in and relating to the manufacture of sodium carbonate - Google Patents

Abstract

Anhydrous sodium carbonate is obtained by evaporating solutions thereof at atmospheric or reduced pressure, the transition temperature of the reaction Na2CO3.1H2O --> Na2CO3 + H2O being lowered by the addition to the solution to be evaporated of a readily soluble compound or compounds of the alkali metals other than acid salts and compounds which form mixed crystals with sodium carbonate, and the amount of such addition being sufficient to lower the transition temperature to below the temperature at which the concentration is effected but not so great that separation of the additional substance or substances takes place. Alternatively, hydrated sodium carbonates are converted into the anhydrous form by heating them, at atmospheric or sub-atmospheric pressure, in suspension in water to above the transition temperature, with evaporation if required, in the presence of the above additional substances present in the above defined amount. Suitable alkali metal compounds are sodium chloride, sodium hydroxide and potassium hydroxide. Light soda ash may be converted into heavy soda ash by converting the light soda ash into sodium carbonate monohydrate which is then converted into the anhydrous salt as described. According to an example, light ash containing sodium chloride is introduced into a liquor containing sodium carbonate and 16,4 per cent of chloride. The mixture is digested at 80--90 DEG C. until the light ash is converted into monohydrate when the temperature is raised to 106 DEG C. The resulting anhydrous carbonate is removed by centrifuging and the mother liquor which has the same composition as that originally employed, is returned for use in further conversions. When commercial sodium carbonate containing chloride is used, the process may be commenced with the addition of the minimum necessary amount of sodium chloride, the liquors being allowed to become enriched in the course of continuous operation.