PROCESS FOR REMOVING CALCIUM AND MAGNESIUM IONS FROM AN AQUEOUS ALKALI CHLORIDE SOLUTION FOR USE IN MEMBRANE ELECTROLYSIS

摘要

The aqueous alkali chloride solution is coarsely purified first. In the succeeding fine purifier the solution, which contains calcium ions, magnesium ions and undissolved magnesium compounds, is passed through a plurality of purification stages (ion exchange stages), which contain cation exchange granulate. In the fine purifier the solution having a pH value of about 10 to 11 is passed through a first ion exchange stage and the solution coming from the first ion exchange is acidified to decrease its pH value by at least 0.5. The solution is subsequently passed through at least one second ion exchange stage and a solution which is virtually free of undissolved magnesium compounds is withdrawn from the fine purification means. The acidified solution fed to the second ion exchange stage has preferably a pH value of 5 to 10.