Physicochemical Foundations of an Energy and Resource Efficient Combined Technology for Processing of Soda Ash Production Wastewater

Abstract

The production of soda ash by the Solvay method is accompanied by the formation of wastewater, much of which is the distiller liquid containing up to 100 g/L calcium chloride and up to 50 g/L sodium chloride. A highly efficient electrochemical method was proposed to treat the distiller liquid to form calcium hydroxide, sodium hydroxide, and hydrochloric acid. The proposed process consists of two stages. At the first stage, the distiller liquid is treated with alkali to produce calcium hydroxide and a filtrate containing sodium chloride. At the second stage, the filtrate is processed in a membrane electrolyzer to obtain solutions of sodium hydroxide and hydrochloric acid. It was shown that the process of treating the distiller liquid with alkali should be carried out at a CaCl₂ : NaOH molar ratio of 1 : 1.25. The processing of the filtrate in the membrane electrolyzer makes it possible to obtain sodium hydroxide at a concentration of up to 4320 g/L and hydrochloric acid at a concentration of 148 g/L.