Removal of chlorate and hypochlorite from electrolyte cell brine

A process for purifying a metal halide brine liquor for use in the electrolytic production of sodium hydroxide and chlorine which comprises electrolytically decomposing sodium chloride brine in an electrolytic cell comprising an anode chamber, a cathode chamber and a permselective cationic membrane separating said anode chamber from said cathode chamber;

• recovering said brine at the conclusion of said electrolysis as a chlorine containing anolyte liquor, further containing between about 1 and about 15% combined sodium hypochlorite and sodium chlorate dechlorinating and resaturating said liquor and returning said liquor to said membrane cell anode chamber;
• said process further comprising collecting from about 10 to about 30 percent of said liquor and contacting said collected portion with at least a stoichiometric amount of an aldehyde containing from about 1 to about 6 carbon atoms sufficient to react with the sodium hypochlorite present and sufficient hydrochloric acid to adjust the pH of said liquor to a range from about 0 to about 2.0 and to substantially decompose the sodium hypochlorite and sodium chlorate therein, recombining said collected portion with said liquor coming from said anode chamber to reduce the total chlorate content to an acceptable level prior to said liquor being recirculated back into said anode chamber.