What Is Water Softener Resin?

Soft water resin is a special resin used to soften hard water. Through ion exchange technology, the hardness of water is less than 50 mg / L (CaCO3)

Soft water resin

Principle of resin softening water

Soft water resin uses the built-in resin tank of the water softener to replace the hardness ions in the water when the water passes. It is generally called "ion exchange softening method" and its principle is as follows:

Ion-exchanged water treatment refers to the use of ion exchangers to exchange the ions in the exchanger and the aqueous solution to produce a reversible exchange that conforms to the quantity rules of such substances, resulting in improved water quality without substantial (chemical) structure of the exchanger. Changing water treatment. In this water treatment method, only those cations that participate in the exchange reaction are called cation exchange water treatment; those that have only anions in the exchange reaction are called anion exchange water treatment; those that have both cations and anions in the exchange reaction are called cation and anion exchange Water treatment. Because the quality of raw water varies widely, and the quality of effluent water is diverse, there are many types of ion exchange and a combination of water treatment methods. Using these water treatment methods, the raw water is softened, alkali and salt removed. When the ion involved in the exchange reaction is sodium ion Na +, this method is called sodium (Na) type ion exchange method, and this exchanger is called sodium (Na) type cation exchanger. Similarly, there is hydrogen (H ) Type ion exchange method and hydrogen (H) type cation exchanger.

Resin regeneration principle

After a certain amount of hardness ions such as calcium and magnesium in the water is replaced by the soft water resin, the water cannot be softened any more. At this time, a water softener is needed to regenerate the resin, that is, the reduction and regeneration method after the resin is polluted with calcium.

(1) When regenerating strong cation exchange resin with Na solution, a stepwise regeneration method should be adopted. Regeneration was started with a low-concentration Na solution, because the Ca2 + concentration desorbed from the resin was high at this time, but the Na concentration was low, and even a small amount of Ca2 + Na precipitates would be washed away by the solution. Then gradually increase the Na concentration. At this time, the concentration of Ca2 + desorbed from the resin is low, and no Na precipitate is formed.

(2) Because the weak cation exchange resin is regenerated with the regeneration waste liquid of the strong cation exchange resin. Therefore, at the same time as the acid is fed, the weak cation exchanger must be fed with diluted water (filtered water from JF9201), and the amount of water input should not exceed the acid inlet of the exchanger. In addition, pay attention to observe the color of the regeneration waste liquid discharged from the weak cation exchanger, such as white turbidity, even if the acid concentration is adjusted.

(3) After acid feeding, the weak cation exchanger must be immediately replaced with water after JF9201 filtration, and the strong cation exchanger must be immediately replaced with purified water.

(4) Calcium pollution is more likely to occur in winter due to the low temperature of the regeneration solution. Therefore, before regeneration, the weak cation exchanger must be scrubbed and backwashed, and the pipeline for the regeneration waste liquid between the weak cation exchanger and the strong cation exchanger must be backflushed to prevent it from happening.

This process takes 2-3 hours in a domestic water softener and is commonly referred to as water softener backwash regeneration. A certain amount of resin regenerant (Na) is required depending on the model of the water softener.

Regeneration conditions

Resin regeneration is an important part of ion exchange water treatment. There are many factors that affect the regeneration effect, such as the regeneration method, the type, purity, and amount of the regenerant, the concentration, flow rate, and temperature of the regeneration solution. To obtain a good regeneration effect, adjustment experiments must be performed to determine the optimal regeneration conditions.

1. Regeneration method

The softening resin regeneration method is divided into three types: forward flow, convection flow and shunt flow according to the regeneration liquid flow direction and the water flow direction during operation.

Downstream regeneration refers to the regeneration mode in which the regeneration liquid flows in the same direction as the water flow during operation, and usually flows from top to bottom.

Convection regeneration means that the direction of regeneration fluid is opposite to the direction of water flow during operation. Conventionally, the water treatment process in which the water flow flows downward during the operation and the regeneration liquid flows upward is called a countercurrent regeneration process. The water treatment process in which the water flows upward during operation and the bed floats; the water treatment process in which the regeneration liquid flows downward during regeneration is called a floating bed process. Convection regeneration can maximize the regeneration of the resin layer at the water outlet, and the water quality is good.

Shunt regeneration means that the regeneration liquid enters from the upper and lower ends of the exchanger at the same time, and is discharged by the drainage device in the middle of the resin layer. During operation, water flows from the top to the bottom through the bed. The upper bed of this exchanger adopts the co-current regeneration process, and the lower bed adopts the convection regeneration process.

2. Variety and purity of regenerant

Generally speaking, the regeneration effect of hydrochloric acid is better than sulfuric acid, and the regeneration cost of sulfuric acid is lower than that of hydrochloric acid. The purity of the regenerant is high, the content of impurities is small, and the degree of regeneration of the resin is high, especially the effect on the anion resin is greater.

3.Regenerant dosage

The amount of regenerant is an important factor affecting regeneration. The concept is the amount of regenerant used per unit volume of resin, the unit is kg / m3 (resin) or g / L (resin). Another commonly used indicator is the specific consumption of regenerant, which refers to the ratio of the amount of regenerant input to the working exchange capacity of the obtained resin. There is also a notation of regenerant consumption, which is the expected pure regenerant dose required to obtain a unit of work exchange capacity, in units of g / mol.

Softening resin theoretically, 1 mol of regenerant should restore the exchange capacity of 1 mol of exchange resin, but in practice the regeneration reaction can only proceed to the equilibrium state of ion exchange chemical reaction at most, and only the theoretical amount of regenerant is used to regenerate the resin. Fully restored its capacity, so the amount must exceed the theoretical amount.

Increasing the amount of regenerant can increase the degree of regeneration of the resin, but after the specific consumption of the regenerant increases to a certain extent, the increase in the degree of regeneration is not obvious. The amount of regenerant is related to the properties of ion exchange resin. Generally, the amount of regenerant required for strong resin is higher than that for weak resin. Different regeneration methods have different amounts of regenerants. Generally, the amount of regenerants used in downstream regeneration is higher than that in countercurrent regeneration.

When the softening resin regeneration method adopts a downstream flow, since the regeneration liquid first contacts the resin that completely fails at the upper part, this part of the resin is well regenerated. When the regeneration solution flows down again and comes into contact with the resin at the bottom of the exchanger, a large amount of replaced ions have accumulated in the regeneration solution, which seriously affects the regeneration degree of the exchange resin, so that this part of the resin is not fully regenerated, and the effluent quality . If you want to increase the degree of regeneration of this part of the resin, you need to increase the amount of regenerant.

When the softening resin regeneration method adopts counter current, the resin at the bottom of the exchanger is always in contact with fresh regenerant, so it can reach a high degree of regeneration. During operation, water finally contacts the resin with a high degree of regeneration to ensure the quality of the effluent water. . When countercurrent regeneration is used, the resin on the upper part of the exchanger is poor in regeneration. Although it is in contact with the water first, the ion content can still be exchanged because the ion content exchanged from the resin in the water is still small. The exchange capacity of this part of the resin can still be sufficient. Play. Therefore, this regeneration method is superior and widely used.

4.Concentration of softening resin regeneration solution

The concentration of the regeneration solution is related to the regeneration method. Generally, the regeneration solution concentration in the downstream regeneration should be higher than that in the counter current regeneration. Generally, HCl is preferably 3% to 5%, and NaOH is preferably 2% to 4%.

5.Temperature and flow rate of softening resin regeneration solution

Increasing the temperature of the regeneration solution can increase the degree of resin regeneration, but the regeneration temperature cannot exceed the maximum allowable temperature of the resin. Generally, strong acidic cation resin does not need to be heated when it is regenerated with hydrochloric acid. The temperature of the regeneration solution of the strongly basic type I anion resin is 35-50 ° C. The suitable regeneration temperature of strong alkaline type II anion resin is 35 ± 3 .

The flow rate of the regeneration liquid affects the contact time between the regeneration liquid and the resin, and generally 4 to 8 m / h is appropriate. The flow rate of the regeneration liquid in the countercurrent regeneration should ensure that the resin does not mess up. When the temperature of the regeneration solution is very low, it is not appropriate to increase the flow rate.