The electrodialysis process is a combination of electrochemical process and diffusion process. Driven by an external DC electric field, the anion and cation move to the anode and cathode respectively by the selective permeability of the ion exchange membrane (i.e. the cation can pass through the cation exchange membrane and the anion can pass through the anion exchange membrane). In the process of ion migration, if the fixed charge of the membrane is opposite to the charge of the ion, the ion can pass through; if their charges are the same, the ion is rejected, so as to achieve the purpose of solution desalination, concentration, refining or purification
Electrodialysis is a mature technology in membrane separation process, which has been widely used in desalination of brackish water and is the main method of producing fresh water in some areas of the world. Because the newly developed charged membrane has higher selectivity, lower membrane resistance, better thermal stability, phase chemical stability and higher mechanical strength, the electrodialysis process is not only limited to desalination, but also has many other industrial applications in food, medicine and chemical industry, such as industrial wastewater treatment, mainly including acid cleaning Acid and metal are recovered from waste liquid formed on metal surface; heavy metal ions are recovered from electroplating waste water; sulfate is recovered from synthetic fiber waste water; sulfite is recovered from pulp waste water, etc. It can be used in food industry, such as milk desalination infant milk powder; separation of ionic and non-ionic substances in chemical industry; electrodialysis can be used as artificial kidney in clinical treatment .
Automatic control frequent reverse electrodialysis (EDR) makes operation management more convenient. The utilization rate of raw water can reach 80%, and the recovery rate of raw water is generally between 45-70%. Electrodialysis is mainly used for the primary desalination of water, the desalination rate is between 45-90%. It is widely used in desalination of seawater and brackish water, primary desalination in preparation of pure water and desalination and softening of boiler and power equipment feed water.
In fact, electrodialysis is a kind of desalting technology, because there is a certain amount of salt in different kinds of water (including natural water, tap water, industrial wastewater), and the anion and cation that make up these salts will move towards the opposite electrode under the action of DC electric field. If one anion exchange membrane and one cation exchange membrane are inserted into an electrodialysis device, because the ion exchange membrane has selective permeability, that is, the cation exchange membrane only allows the free passage of cations, and the anion exchange membrane only allows the passage of anions, so that in the middle compartment of the two membranes, the salt concentration will be reduced due to the directional migration of ions, while the two compartments close to the electrode will It is the concentration chamber of anion and cation respectively, and desalination is achieved in the middle desalination chamber at last.
In practical application, an electrodialyzer is not composed of a pair of anion and cation exchange membranes (because of the low efficiency), but uses a hundred pairs, or even hundreds of exchange membranes, thus greatly improving the efficiency.
At present, electrodialysis is widely used in desalination and desalination of water, salt production and refining of dairy products by sea water concentration, deacidification and purification of fruit juice, production of chemical products, etc. it can also be used in the pre-treatment of high-purity water production in industries such as food, light industry, etc. The primary softening desalination of boiler feed water desalinates brackish water into drinking water. 报错
The electrodialyzer is suitable for water treatment in the industries of electronics, medicine, chemical industry, thermal power generation, food, beer, beverage, printing and dyeing, coating, etc. It can also be used in the concentration, purification, separation and other physical and chemical processes of materials.
Electrodialysis can also be used for the treatment of waste water and waste liquid and the recovery of precious metals, such as the recovery of nickel from electroplating waste liquid.