production of chlorine and sodium hydroxide solution by electrolysis of aqueous solutions of sodium chloride

摘要

The crude brine, after removal of alkaline-earth and heavy metals by treatment with alkaline Na carbonate solns., is led to the cells in a quantiy to replace the NaCl consumed, and a part, 0.60% of the liq. leaving the cells, according to the electrical energy consumed, is recycled as working brine at the entry to the cells, while the raminder, 40-100% of the liq., after removal of dissolved chlorine, in evaporation-concentrated till saturated with NaCl, 40-95% of this conc. soln. then being recycled directly into the cells where, before entry, it is mixed with the purified crude brine and the working solbn., the residue, 5-60% of the conc. soln. being freed, by treatment with CaCl2 soln., of sulphate ions in excess of those corresponding to the solububility of CaSO4, and then mixed with the crude brine befor ethe alkaline-earth and heavy metal removal stage.