Concentration of sodium chloride solutions in the processing of concentrates for reverse osmotic water desalification

Abstract

The paper examines the processes of concentrating sodium chloride solutions by the electrodialysis method. Given the shortage of reagents and their high prices, this electrodialysis method can be implemented to obtain acid and alkali from solutions of sodium sulfate, alkali, aluminum and iron coagulants. Today, the technologies that, as a result of the process, allow us to obtain valuable materials, substances, products, coagulants as a secondary product, are very justified, economically feasible and, most importantly, allow us to successfully implement the principles of low-waste production. The essence of the process is the use of sodium chloride solutions, which are formed during the desalination of water by reverse osmosis in the form of concentrates. The concentration process was implemented in a three-chamber electrolyzer, in the cathode, anode and working areas, a sodium chloride solution with a concentration of 360 mmol/dm3 was placed. An alkali solution with a concentration of 480 mg-eq/dm3 was used in the anode area. During electrolysis, alkali was formed in the cathode area, due to the diffusion of sodium in the working area and the cathodic reduction of water. Chlorides from the working area moved to the anode area. Hydroxide anions on the anode were oxidized to oxygen, chlorides with sodium formed sodium chloride, the concentration of which increased to 660 mg-eq/dm3. Alkalinity decreased to 68-70 mg-eq/dm3. When changing cathodes and anodes, the process was repeated in some places until the alkalinity in the cathode zone and the concentration of chlorides in the anode zone increased. . A solution of sodium chloride with a concentration of 360 mmol/dm3 was added to the working area where water desalination took place. After nine cycles of electrolysis, a sodium chloride solution with a concentration of 100-150 g/dm3 was obtained. The residual content of sodium chloride in desalinated water reached 50-100 mg/dm3. Sodium chloride solutions with a concentration of 4 to 30 g/dm3 can be used for concentration. It should be noted that after conducting nine cycles of the experiment, we can state that the process of concentration by this electrodialysis method does not lead to an increase in system resistance and energy consumption.