make-up water for sodium hydroxide and chlorine production electrolytic systemsReading time:
Membrane cells develop current densities of up to 7 000 A·m–2 and, therefore, require very advanced qualities from the NaCℓ brine they receive, resulting in the following treatments :
- sulphate removal by precipitating BaSO4 in Densadeg (injecting BaCO3 or Ba Cℓ2);
- removing traces of Ca2+ from specific softening resins (down to below 50 mg · L–1 Ca2+);
- vacuum dechlorination, often in sidestream mode and, if necessary, supplemented with bisulphite (figure 25).