Electrode ionization (EDI)
Electrode ionization (EDI)
Electrode ionization (EDI)
EDI is a membrane separation process that utilizes the potential difference as the driving force for ion transport. It is commonly used for the production of drinking water or industrial water from sources with Total Dissolved Solids (TDS) less than 5000 ppm. The basic principle of the electro-deionization process is illustrated in the diagram. The system employs polymer membranes containing ion exchange resins. These resins are coated onto polymer sheets such as polyethylene. The cationic membranes are permeable to cations, while anionic membranes only allow anions to pass through.
If a container of saline water is prepared and two electrodes are placed in it, a continuous electric current is established. The positively charged ions (e.g., Na+) are attracted to the cathode (cations), while the negatively charged ions (e.g., Cl-) are drawn toward the anode (anions). However, if selective membranes are introduced in the container, which blocks certain types of ions, water in cells 2 and 4 undergoes desalination, while the concentration increases in cell 3. Chlorine is liberated from the anode, and hydrogen is released from the cathode close to the electrodes.