NAV

1、 Reasons for resin oxidation
Resin oxidation mainly occurs on strong resins. That is, strong acid resin and strong alkali resin. The residual active chlorine in tap water is the main reason for the oxidation of strong acid cation resins. In recent years, with the deterioration of water quality, the requirements for water quality have become increasingly high. Water supply units often add excessive liquid chlorine to the water to strengthen the killing of bacteria in the water. However, the excessive residual free chlorine content was ignored, resulting in the oxidation of the cation resin. After the cation resin is oxidized, its skeleton breaks, producing low molecular weight sulfonic acid compounds and carboxylic acid groups, and causing pollution to the subsequent strong base anion resin. After oxidation, the appearance of the cation resin shows a decrease in color, increased transparency, increased water content, increased volume, and fragmentation, resulting in an increase in operating pressure difference. In recent years, strong cation resins have been oxidized throughout the country. According to the standard requirements, the content of free chlorine in water must be less than 0.1mg/l.
2、 The main methods to prevent the oxidation of cation resin are as follows:
1. Control the amount of chlorine added during pre-treatment to ensure that the final free chlorine content entering the cation bed is less than 0.1mg/l, with special attention paid to the free chlorine content using tap water as the water source.
2. Add reducing agents such as Na2SO3. For Cl2 with a content of 1mg/l, adding 2mg/l Na2SO3 can protect the resin from oxidation. The comparison of the effects of adding Na2SO3 is shown in the table below:

Test number	Running time (months)	Addition of Na2SO3	Somatic comparison（mmol/l）
1	6	Not added	0.9
2	12	added	1，86
3	12	added	1.90

3. Activated carbon adsorption of free chlorine
Activated carbon chlorine removal is not just a simple physical adsorption. When the chlorine content on the surface of activated carbon reaches a certain concentration, the following reactions occur:
Cl2+H2O→HOCl+HCl
C′+HOCl→CO′+HCl
In the formula: C 'is activated carbon;
CO 'is the oxide generated on the surface of activated carbon;
The amount of water containing active chlorine in the treatment of activated carbon is about 100000 times its volume. If activated carbon is only used as a function for removing free chlorine, Cl2>0.1mg/l can be used as the failure endpoint of activated carbon.
In addition to the presence of artificially added free chlorine in water, some regenerants such as hydrochloric acid also contain strong oxidizing agents such as hypochlorite (or sodium hypochlorite). Therefore, the use of by-product hydrochloric acid is strictly prohibited.
4. Choose strong acid resin with large pore size
In addition to the known oxidation of strong cation resins by oxides, there has also been damage to cation resins by oxides of unknown composition. If existing water treatment detection methods are used to detect the composition of oxides in these water qualities, it is difficult to detect them. However, the abnormal phenomenon reflected by the resin conforms to all the characteristics of oxidation. Therefore, the current trend of changes in raw water quality also reflects the complexity of environmental degradation. For such water quality, it is recommended to use macroporous cation resin (D001) because of its high cross-linking degree and strong antioxidant properties.
5. After the oxidation of strong alkali resins, the main manifestation is the gradual degradation of quaternary amine groups into weak alkali groups such as tertiary amine (secondary, primary amine), which reduces (or even loses) the resin's ability to exchange weak acid anions and fails to achieve the effect of silicon removal. The dissolved oxygen in water is the main reason for the oxidation of strong anion resins. The increase in temperature and the presence of heavy metals can accelerate the oxidation process. In addition, ClO3- and (FeO4) 2- (ferrates, strong oxidants) in the alkaline solution are also sources of oxidants for strong anion resins, and attention should be paid to the quality of the alkaline solution.