The anion exchange resin has the same organic skeleton as the cation exchange resin, but introduces dissociatable basic groups, such as - NH, - NH, - NHR, etc. If this kind of resin is treated with NaOH solution, it will undergo exchange reaction and change into - OH anion exchange resin. The reaction is as follows:

R—N(CH)Cl + OH ====== R—N(CH)OH + C1

The hydroxyl ions on these groups can be exchanged by anions in the sample solution.

Cation resin is divided into weak resin and strong resin. Molecular formula H-R (of course, it can also be Na-R type), H is hydrogen ion. The resin height is about 0.8m to 1.6m. When the water passes through the resin layer from top to bottom, the cations in the water exchange with the H ions of the resin, and the top layer of the resin is iron, calcium and magnesium ions, followed by potassium, sodium and ammonia ions.

The effluent quality is acidic, and the PH value is generally less than 3. After about one day of operation, sodium ions begin to appear in the effluent, indicating that the reaction has reached the end point, and acid (HCl) backwashing is required to replace sodium and calcium ions.