Evaluation of the efficiency of oxidized chlorine compounds synthesis by electrodialysis from membrane desalination concentrates

This study investigates the processing of reverse osmosis desalination concentrates containing sodium chloride, calcium bicarbonate, and magnesium bicarbonate. Water desalination was carried out using a Filmtec TW 30-1812-50 reverse osmosis membrane cassette in two stages. When desalinating water with a permeate recovery rate of 66% at the first stage, the membrane's selectivity for chlorides ranged from 74% to 95%. In the second stage, the obtained concentrate ([Cl–]=110 mg-eq/dm3) was further desalinated using the same membrane. At a permeate recovery rate of 74%, the membrane's selectivity reached 70%. The two-stage filtration process reduced the concentrate volume from 34% to 8.2% of the initial water volume. During the electrolysis of model solutions of reverse osmosis desalination concentrates, a two-chamber electrolyzer with an MA-41 anion-exchange membrane was used. A sodium chloride solution was placed in the anode chamber, while the cathode chamber was filled with an alkaline solution with a concentration of 200 mg-eq/dm3. Electrolysis processes were conducted at a current density ranging from 0.83 to 16.7 A/dm2, using solutions with chloride concentrations between 59 and 480 mg-eq/dm3. It was found that the intensity of chloride oxidation increased with higher anode current density and higher chloride concentration in the solution. A decrease in the current efficiency of oxidized chlorine compounds was observed as chloride concentration in the solution decreased. The concentration of oxidized compounds in the anolyte of an open electrolyzer did not exceed 180 mg-eq/dm3 due to significant losses of Cl2 and ClO2 caused by degassing.