Evaluating of efficiency of concentrated sodium chloride solutions conversion processes for obtaining aluminum coagulant

Abstract

In this work, the processes of sodium chloride solutions electrochemical processing in order to obtain aluminum chloride and alkali in a three-chamber electrolyzer with anion exchange membrane MA-41 and a cation exchange membrane MС-40 and in a two-chamber electrolyzer with a cation exchange membrane МС-40 were investigated. The presented method of processing salt concentrates using a soluble aluminum anode is economically feasible, as the electrolysis simultaneously demineralizes liquid waste to the level of regulatory requirements and production from source concentrates of marketable products. The disadvantage of this method of obtaining a coagulant is the interaction of aluminum with water. However, it is proved that with increasing anodic current density during electrolysis, the yield of aluminum chloride is almost entirely due to the electrochemical dissolution of the anode, and the chemical dissolution of aluminum is almost absent. The stability of the obtained solutions of coagulants for a long time is maintained by low values of the reaction medium (pH ≤ 3). Thus, at a current of 1A (current density 8.34 A/dm2) and an initial concentration of sodium chloride of 1900 mg-eq/dm3, the total concentration of aluminum ions in the resulting solution reaches 3884 mg-eq/dm3. Chemically dissolved aluminum is not more than 12 %. According to the initial parameters, the yield of aluminum ions, taking into account the chemical dissolution of the anode is 100–108 %. At the same time in the cathode chamber is the concentration of alkali to a level of approximately 1500 mg-eq/dm3. Its current output reaches 92 %. The degree of diffusion of chloride ions through the anion exchange membrane from the working chamber into the anode region is 99 %. It is shown that the process of sodium chloride solution electrolysis in a two-chamber electrolyzer with a cation exchange membrane is not as efficient as when using a three-chamber electrolyzer. At the initial stage of the process, the current yield is 61 % for aluminum chloride and 64 % for alkali. Subsequently, due to the poisoning of the cation exchange membrane by aluminum cations, which block all the anionic functional groups of this membrane, the process stops.