The EDI (Electrodeionization) electric desalination system, as a prerequisite for continuous electric desalination technology, has gradually demonstrated its unique advantages in the field of pure water preparation. This technology abandons the acid-base regeneration step in traditional ion exchange (DI) devices and instead uses a combination of mixed ion exchange resin and ion exchange membrane to achieve efficient ion removal.
The core of EDI technology lies in the use of mixed ion exchange resins to adsorb anions and cations in water supply. These adsorbed ions are separated and removed through a cation exchange membrane under the action of a direct current voltage. This process realizes the electro continuous regeneration of ion exchange resin, thus avoiding the tedious steps of frequent use of acid and alkali for regeneration in traditional methods.
The working principle of ion exchange membranes is similar to that of ion exchange resins, both of which can selectively pass through ions. Anion exchange membranes only allow anions to pass through, while cation exchange membranes only allow cations to pass through. When mixed ion exchange resin is filled between the anion and cation exchange membranes, an EDI unit is formed. The resin filled space in this unit is called a fresh water chamber, and the combination of multiple EDI units forms a complete EDI system.
Driven by direct current voltage, the ion exchange resin in the freshwater chamber begins to exert its function. The cations and anions in the resin migrate towards the positive and negative electrodes respectively, and enter the concentrated water chamber through the corresponding ion exchange membrane. At the same time, ions in the water are adsorbed by ion exchange resin, occupying the vacancies left by ion migration. The migration and adsorption processes of these ions occur simultaneously and continuously, thereby achieving efficient removal of ions from the feedwater.
The ions in the concentrated water chamber maintain electrical neutrality after passing through the cation exchange membrane. The current of EDI components is proportional to the migration of ions, with a portion of the current coming from the migration of removed ions and another portion from the migration of H+and OH - ions generated by the ionization of water itself. In EDI components, due to the high voltage gradient, water undergoes electrolysis to produce a large amount of H+and OH -. These on-site generated ions have a continuous regeneration effect on the ion exchange resin, further improving the performance and stability of the EDI system.
It is worth noting that the ion exchange resin in EDI components can be divided into two parts: working resin and polishing resin. Working resin is mainly responsible for removing most ions, while polishing resin is responsible for removing ions that are difficult to clean, such as weak electrolytes. This division of labor enables the EDI system to more efficiently remove various ions from the feedwater, thereby producing ultrapure water with a resistivity higher than 15M Ω· cm.
In summary, the EDI electric desalination system has brought changes to the field of pure water preparation with its unique ion exchange technology and electric continuous regeneration mechanism. It can not only replace traditional ion exchange devices, reduce operating costs and maintenance difficulties, but also produce higher quality ultrapure water to meet various industrial and scientific research needs. With the continuous advancement of technology and the expansion of application fields, the EDI electric desalination system is expected to play a greater role in the future.