Study On The Selective Separation Mechanism Of Typical Anion Electrodialysis

The zero discharge and resource utilization of high-salt wastewater is a hot topic of current research,especially the problem of the separation of miscellaneous salts in wastewater.The water contains a large amount of ions that can be recycled and reused.Nowadays,the commonly used treatment technologies mainly include reverse osmosis,nanofiltration,membrane distillation,and thermal evaporation,but they all have problems such as difficulty in separation,high cost,and unsuitability for treating large amounts of wastewater.Selective electrodialysis not only has the advantages of green,high efficiency,and pollution-free,but also can selectively separate ions.This paper selects the typical anions in high-salt wastewater:Cl^-and SO4^2-for selective separation.According to the different migration rates and resistances of the two ions when they pass through the ion exchange membrane,the two ions can be separated.Use electrochemical impedance spectroscopy to explore the influence conditions of electrochemical characteristics and ion selectivity,and use electrodialysis technology to treat high-salt wastewater,and explore its optimal operating conditions to achieve maximum separation of Cl^-and SO4^2-;The scale was expanded to pilot test,and the actual high-salt wastewater was treated and optimized.The main conclusions are as follows:（1）For monovalent anions,the resistance when passing through the membrane is F^->I^->NO₃^->Br^->Cl^-;when the valence of the anion is different,PO₄^3->SO4^2->Cl^-.This is related to the Gibbs free energy of the anion,the radius of the hydrated ion,the molecular sieve effect and the charge effect in the channel.（2）Using electrochemical impedance technology to study the selective separation mechanism of Cl^-and SO4^2-,it was found that the higher the concentration,the smaller the membrane resistance;when pH=7,the membrane resistance is the smallest and the separation efficiency of the two ions is the highest;Increasing temperature will reduce the resistance of the membrane and its interface layer and increase the migration speed;changing the voltage has little effect on the membrane resistance of the two ions,but the separation efficiency of the two ions will increase with the increase of the voltage;increase the flow rate It will reduce the resistance and capacitance of the diffusion boundary layer,which has a great impact on the separation efficiency of the two ions,but has little effect on the membrane resistance;when the two ions are mixed to different degrees,the higher the Cl^-concentration,the greater the membrane resistance.（3）When the flow rate of the desalted chamber is 500 m L/min,the voltage is 8 V,the concentration ratio of Cl^-and SO4^2-is 1:1,and the pH is 7,the electrodialysis experiment is carried out.This condition is the selective separation of Cl^-by electrodialysis.And SO4^2-the best conditions.Under this condition,after the electrodialysis device was operated for 2 hours under this condition,the permeability of Cl^-reached 66.45%,and the leakage rate of SO4^2-was 38.09%.the separation effect is good.（4）Using selective electrodialysis to treat a certain actual high-salt wastewater,the Cl^--removal rate can reach 60%after 120 minutes,the SO4^2-removal rate can reach 30%,and the two ions can be separated to a certain extent.This study shows that the use of electrodialysis technology to selectively separate Cl-and SO4^2-is feasible,can realize the resource utilization of high-salt wastewater,and has certain environmental protection and economic significance.