Study on the removal of SO42− and Ca2+ from potassium chloride brine via a method combining calcium chloride and carbon dioxide

Abstract

Purification treatment is needed to control the concentration of SO₄²⁻ and Ca²⁺ in brine to solve the problem of low electrolysis efficiency for the electrolysis of KCl solution in the chlor-alkali industry. However, the traditional barium method to remove SO₄²⁻ faces the problem of high cost and environmental pollution. Herein, inexpensive and environmentally friendly anhydrous calcium chloride was used as the precipitant to replace barium chloride. The conditions for SO₄²⁻ removal at room temperature were optimized by studying the precipitant doping ratio, reaction time, and stirring speed. The results indicated that the concentration of SO₄²⁻ in brine could be reduced to less than 5 g L⁻¹ at a raw material ratio of nCa²⁺ to nSO₄²⁻ of 1.1 : 1, a stirring speed of 300 rpm, and a reaction time of 120 min. Ca²⁺ in the solution could be removed by introducing carbon dioxide, and the removal rate of Ca²⁺could reach 99.89% by adjusting the pH of the solution to an appropriate value. This work paves a new way for efficient brine refining to boost sustainable development in the chlor-alkali industry.