Ion exchange resin has the advantages of good chemical stability, high mechanical strength and large exchange capacity, so it has been widely used in boiler water treatment and the production of desalinized water and purified water. However, in the process of use, the cleaning water often increases, the effluent water quality is poor, the periodic water production continues to decline, the color becomes darker, and the resin exchange capacity continues to decline. According to the above phenomenon, the resin can be identified as contaminated. If reasonable measures are not taken in time to regenerate it, it will cause resin failure or even scrap, affecting normal production. Combined with the production practice, today we will discuss the causes of resin pollution, preventive measures and treatment methods. The surface of the ion exchange resin is covered by impurities such as organic matter or the exchange hole inside the resin is blocked, so that the working capacity of the resin is significantly reduced, but the phenomenon of no change in the structure of the resin is called resin pollution.
1. Analysis of pollution causes
1.1 Pollution caused by organic matter
Organic matter mainly exists in natural water humic acid, relative molecular weight from 500 ~ 5000 polymer compounds and multiple organic carboxylic acids, etc. These substances are often negatively charged in water, becoming the main material of anion exchange resin pollution. This kind of pollution can be detected from COD monitoring.
1.2 Pollution caused by grease
The water often contains oils that form membranes that block or encase the micropores of the resin, preventing the active groups in the micropores from exchanging ions.
1.3 Pollution caused by colloidal substances
Colloidal particles in water often carry negative ions, which contaminates the anionic resin. Among colloidal substances, colloidal silicon is the most harmful to resin, which adsorbs and polymerizes on the surface of the resin to prevent exchange.
1.4 Pollution caused by high-priced metal ions
The high-priced metal ions in water (such as the backward movement of high-priced metal ions in coagulants, etc.), such as A1+, Fe3+, etc., diffuse into the interior of the cation exchange resin. Due to the high exchange potential energy of these high-priced metal ions, they firmly combine with the fixed ion SO3 in the resin to form A1 (SO3) , Fe (SO3) , etc. Thus, these fixed ions lose their function and lose their ion exchange ability.
1.5 Pollution caused by impurity of regenerant
Regenerants are often mixed with many impurities, such as Fe3+, NaCI, Na2CO3, etc., which have the most serious impact on anion exchange resins.
2. Pollution identification methods
2.1 Viewing Resin Appearance
From the appearance of the contaminated resin, the color of the transparent yellow (cationic resin) or milky white (anionic resin) becomes significantly darker or even black.
2.2 Laboratory Indicators
The effluent conductivity of the shade bed gradually increases, and the pH value gradually decreases (can be as low as 5.4-5.7). Because the organic matter that is not removed during regeneration will free out and enter the water when resuming operation.
2.3 Analysis of iron content in resin
Because iron pollution is the most common, the iron content in the resin can be analyzed, if Fe < 0.01%, there is no iron pollution; If Fe > 0.1%, it indicates serious pollution.
2.4 Immersion test
Soak the resin in clean water and observe the "color" of the water surface. If there is "color", it indicates that it is polluted by oil substances. Because the factors of resin contamination do not exist alone, they are often cross-pollinated, and a variety of reasons accumulate and superposition, so when there is a problem, a full range of inspection and identification should be carried out to prevent one from losing the other; At the same time, when taking regeneration measures, it should also be considered comprehensively and carefully check all aspects to ensure that there are no loopholes.
3. Measures to prevent pollution
To prevent the resin from being polluted, it is necessary to control the water treatment process indicators, and strictly pay attention to the following issues:
3.1 Selection of coagulant
In order to do a good job in coagulation and clarification treatment, it is necessary to correctly select coagulant, and determine the best dosage of the agent by experiment, prevent the backward movement of aluminum salt and iron salt, and strictly control the turbidity in the effluent of sand filter and activated carbon filter. Al3+ and Fe3+ are less than 0.3 mol/L; Chemical oxygen demand COD is less than 1 mol/L. And filter through activated carbon to adsorb organic matter.
3.2 Control the chlorine content
Do a good job of sterilization and algal elimination of pretreatment, control the amount of residual chlorine before entering the cation exchanger.
3.3 Prevent the regenerant from being polluted
In order to prevent the impurities in the regenerant from causing pollution to the resin, in addition to the selection of high-quality regenerant, anti-corrosion measures should be taken in the container during the transportation and storage of the regenerant to prevent rust and organic coating from falling off.
3.4 Prevent oil pollution
For compressed air that may come into contact with resin, it is necessary to purify and remove oil to prevent oil mist; Prevent oil pollution near the water source suction.
3.5 Blow and suck resin
Periodically blow the resin with compressed air to remove suspended matter, organic matter and iron.
4. Regeneration treatment method
Although various measures can be taken to prevent the resin from being contaminated, after a period of operation, the resin will sometimes be contaminated, which is common in desalted water treatment, and the following methods can be used to regenerate it.
4.1 Regeneration of anionic resins
In actual production, anionic resin is the most susceptible to pollution, and the pollution degree is also the most serious. When the anion resin is contaminated, it can be treated with alkaline salt water, and its operating parameters are shown in Table 1. Table 1 anion regeneration operation parameters No. Item Value 1 Salt solution concentration 10%2pH 103 Soaking method 35-45. 48h4 circulation flow rate 2.6m/h; The addition of caustic soda in the 24h alkaline salt water treatment process can increase the solubility of substances such as humic acid, and adjust the pH value to 10 with the ratio of NaCl to NaOH is 5. This method can remove more than 95% of organic substances, if it can be properly heated, the effect is better. When it is seriously polluted, an appropriate amount of sodium hypochlorite (generally less than 0.5%) is added to the solution of alkaline salt water to oxidize humic acid organic matter and decompose it.
4.2 Cationic resin regeneration
If the cationic resin is polluted, it can be removed by acid or salt water, and its operating parameters are shown in Table 2: Table 2 Cationic regeneration operating parameters Index No. Item Parameter Value Regenerated liquid concentration 10%HCI15% NaCI2 Soaking method 8 h32 h3 circulating flow rate 2m/h; 4h flow rate 2m/h; 16h
4.3 Regeneration of resin contaminated with iron
When contaminated by iron impurities, hydrochloric acid - salt - sodium sulfite regeneration method can be used: the mixture of 4% hydrochloric acid, 4% salt and 0.08% sodium sulfite is added to the iron poisoning resin to soak fully. Hydrochloric acid has the same effect as salt as shown above. SO32- in Na2SO3 reduces Fe3+ to Fe2+, thus reducing the binding of the resin to Fe3+, and the H+ generated by the reaction can promote the dissolution of Fe2O3·xH2O, the equation is: SO32- + 2Fe3+ + H2O = SO42- + 2Fe3+ + 2H+ Finally, the sodium hydrogen mixed resin can be converted into sodium resin and put into use. It should be noted that the concentration of Na2SO3 should be determined by the experiment, and its mass fraction should not be greater than 0.1%, because the concentration of Na2SO3 is too high, easy to produce SO2 gas, in addition, the concentration of SO42 produced will produce CaSO4 precipitation. Practice has proved that this method is an ideal treatment method with less regenerant consumption, short time, low concentration of hydrochloric acid in the regenerant, less corrosive to the exchanger and good regeneration effect.
