Mixed-bed ion exchange unit

Mixed-bed ion exchange unit

Working Principle
Anion and cation exchange (mixed bed) is used for the further purification of primary pure water, typically installed after the anion and cation exchange units. It can also be used in series after electrodialysis or reverse osmosis. When the incoming water quality has a normal salt content, the output water can be reduced to below 0.1 mg/L, with silicon content ≤ 0.05 mg/L, and conductivity ≤ 1 microsiemens/cm. The treated high-purity water is suitable for industrial applications such as high-pressure boilers, electronics, pharmaceuticals, papermaking, and chemical industries.
Operation Principle: The Mixed Bed Ion Exchange method involves placing both cation and anion exchange resins in the same exchange unit, and mixing them evenly before operation. This results in a multi-stage mixed bed where countless cation and anion exchange resins are interlaced. The salt ions in the water pass through this exchange unit and are exchanged by the resins, yielding highly purified water. In the mixed bed, since the cation and anion resins are mixed together, their exchange reactions occur almost simultaneously, or said differently, the cation and anion exchange of water is repeatedly interlaced. The H+ produced by H-type exchange and the OH- produced by OH-type exchange cannot accumulate, effectively eliminating the influence of counter-ions and ensuring a thorough exchange process. Due to the high quality of the primary pure water entering the mixed bed, the load on the exchange unit is light, and the exchange capacity of the resins is exhausted over a long period. This mixed bed employs an in situ regeneration method, where the resins are first separated using their different specific gravities by backwashing, with the cationic resin settling at the bottom and the anionic resin floating to the top. Then, the cationic resin is regenerated with hydrochloric acid (or sulfuric acid), and the anionic resin is regenerated with caustic soda.