PROCESS FOR THE FINE PURIFICATION OF AN AQUEOUS ALKALI CHLORIDE SOLUTION FOR USE IN MEMBRANE ELECTROLYSIS

摘要

The aqueous alkali chloride solution is coarse- ly purified first. In the succeeding fine purification means the solution, which contains calcium ions, magnesium ions and undissolved magnesium compounds, is passed through a plu- rality of purification stages (ion exchange stages), which contain cation exchange granulate. In the fine purification means 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 stage is acidified to de- crease its pH value by at least 0.5. The solution is subse- quently passed through at least one second ion exchange stage and a solution which is virtually free of undissolved mag- nesium compounds is withdrawn from the fine purification means.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.