Evaluation of the efficiency of the processing of sodium chloride solutions by electrodialysis in a three-chamber electrolyzer using a high-basic anionite

The desalination process of highly mineralized waters is a rather multifactorial process that depends on a number of technical, economic and environmental aspects. This is an important stage for obtaining fresh water for its further use in various areas: from drinking water supply to industry. Processing of reverse osmosis water desalination concentrates is a relevant area of research not only in terms of waste disposal, but also in the development of low-waste resource-efficient production, which requires the implementation of innovative solutions and obtaining secondary useful products. One of the promising approaches to the implementation of processes for processing sodium chloride solutions is the use of electrochemical methods of chloride oxidation to obtain sodium hypochlorite and other products of oxidized chlorine - effective reagents for water disinfection, bleaching of fibrous materials, disinfection of various environments. The aim of the article is to study the processes of electrochemical processing of sodium chloride solutions - waste from the processes of desalination of water containing chlorides in three-chamber electrolyzers with the production of oxidized chlorine compounds and alkali solutions, determining the efficiency of capturing active chlorine in the anode chamber using a highly basic anion exchanger. To achieve the set goal, the following tasks were solved: - The parameters of the process of effective purification of solutions from sodium chloride in the working chamber of a three-chamber electrolyzer were determined depending on the concentration of sodium chloride and the anode density of the steam. - The efficiency of capturing active chlorine in the anode region by a highly basic anion exchanger was studied depending on the parameters of the electrolysis process. The processes of processing sodium chloride solutions, close in composition to the concentrates of reverse osmosis water desalination by electrodialysis in a three-chamber electrolyzer using a cationic membrane MA-40 and anionic membrane MA-41, were studied. The cathode chamber is filled with an alkali solution with a concentration of 50 mg-eq/dm3, the anode chamber is filled with a sodium chloride solution and highly basic anion exchanger AB-17-8, the working chamber is filled with a sodium chloride solution. During electrolysis, alkalinity was determined at equal intervals in the cathode region; in the working chamber, the concentration of chlorides and alkalinity or acidity; in the anode chamber, the concentration of chlorides, active chlorine, and acidity were determined. Also, during the electrolysis process, the exchange capacity of the anion exchanger for active chlorine was determined. For this, a certain volume of the anion exchanger was placed in a flask and filled with a sodium sulfite solution of a certain concentration. The flask was hermetically sealed and left for a day. The next day, the residual amount of active in the solution was determined by the iodometric method. It has been shown that the efficiency of chloride oxidation increases with increasing their concentration and increasing the electrolysis time. The electrolysis process proceeds with the formation of active chlorine and hypochlorite. In addition to these substances, the formation of chlorite, chlorate and chlorine dioxide is possible. Degassing of active chlorine and chlorine dioxide leads to significant losses of oxidized chlorine compounds and to a decrease in the current yield of these products. The process is accompanied by significant acidification of the anolyte, which contributes to the acceleration of degassing of active chlorine, a decrease in its current yield, and a decrease in the intensity of chloride diffusion from the working chamber to the anode zone. The use of a highly basic anion exchanger that adsorbs hypochlorite anions, as well as, in the case of formation, chlorite and chlorate anions, contributes to the reduction of losses of oxidized chlorine compounds.