The general principle of selecting ion exchange resin is to select resin with large exchange capacity, easy regeneration and durable use. Specifically:
(1) The exchange capacity is an important index of the performance of ion exchange resin. The larger the exchange rate is, the more ions can be adsorbed by the resin of the same volume, and the larger the water yield in an exchange cycle. Generally speaking, the exchange capacity of weak acid or weak base resin is larger than that of strong acid or strong base resin. In addition, in the same kind of resin, due to the different degree of crosslinking, the exchange capacity is also different. Generally, the resin with small cross-linking degree has large exchange capacity, and the resin with large cross-linking degree has small exchange capacity. Therefore, pay attention to the selection of resin.
(2) The resin should be selected according to the nature of the ions to be removed from the raw water. Strong acid or strong basic resin must be selected if only weak ion exchange adsorption in water needs to be removed.
(3) The resin should be selected according to the effluent quality requirements. If only partial demineralization system is needed, strong acid cation resin and weak alkali anion resin can be used together. For the pure water or high-purity water system that must be completely desalted, the strong acid cation exchange resin with the strongest adsorption should be used in combination with the basic anion exchange resin to remove the ions that are difficult to be adsorbed.
(4) The resin shall be selected according to the composition of impurities in the raw water. If there are many organics in the raw water or the radius of removing ions is large, the resin with larger cross-linking pore diameter should be selected. Try to choose high-strength porous resin.
(5) Most of the resins used in the mixed bed are the combination of strong acid and strong basic resin. However, it is necessary to consider that it is easy to separate the resin in the mixed bed during regeneration. Therefore, the difference between the wet and true densities of the two resins should be larger, generally not less than 15% - 20%. In addition, it should be considered that the exchange velocity of the mixed bed is relatively large and the resin wear is relatively serious, so the wear-resistant resin should be selected.
(6) The resin shall be selected according to the process requirements of desalted water. For example, double chamber bed is used with strong and weak resin, because weak resin is easy to regenerate, and the quality requirements for regenerating agent are relatively low. The regenerated liquid of strong resin can be used to regenerate weak resin, so the consumption of regenerating agent is low and the cost of water production is low.