How should organic contamination of resin be dealt with?

Contamination of cation resins by organic substances occurs very rarely; merely deposits on the surface of the cation resin particles may be observed, and these deposits can be removed through air scouring and backwashing with water. However, organic substances can easily contaminate anionic resins. In desalination systems, strongly basic anion resins are prone to contamination by organic substances. 　　I. Characteristics of resin contamination by organic substances 　　1. After being contaminated, anion exchange resins change color, shifting from light yellow to dark brown and even black; 　　2. The effective exchange capacity of the resins decreases, and the amount of water that can be processed per cycle in the anion bed drops significantly; 　　3. The pH value of the effluent decreases while its conductivity increases. This is due to organic acids leaking into the effluent as a result of resin contamination, which can reduce the pH value of the effluent to between 5.4 and 5.7; 　　4. The cleaning time required for the anion bed increases, along with the amount of water used for cleaning. Since the organic substances adsorbed on the resin contain a large number of –COOH groups, these groups turn into –COONa during resin regeneration. During the cleaning process, the Na+ ions in –COONa are continuously replaced by mineral acids present in the water used for cleaning, which increases both the cleaning time and the amount of water required for cleaning. 5. Diethylenebisphenol, which is a product of the oxidation and degradation of strongly acidic cationic resins, as well as gel-like substances formed due to the mechanical breakdown of cationic resins and containing negative charge groups, can also cause contamination of anionic resins. 　　II. Identification of resin contamination Place the anionic resin in a small glass bottle with a stopper and pores, add distilled water and shake it; wash it 3–4 times in succession to remove any substances attached to its surface, and finally drain all the washing water. Replace it with 10% saline solution, shake for 5–10 minutes, then observe the color of the saline to determine the degree of contamination based on its hue. 　　III. Recovery of resin 　An effective method to remove organic contamination from resin is to treat it with an alkaline saline solution (a 10% NaCl solution supplemented with 2% NaOH); the effect is even better if the solution is heated to 40–50°C. The amount of alkaline saline solution used is 1 to 3 times the volume of the resin, and the treatment flow rate is 3 to 6 m/h. During processing, the treatment fluid discharged at the beginning is dark brown in color. When the effluent is light yellow, it can be considered that the purification process is complete. The resin is then rinsed, followed by regeneration using twice the dose of regenerating agent. 　　Under normal circumstances, strongly basic anion resins are regenerated every 6 to 12 months. 　　IV. Measures to prevent organic substances from contaminating anionic resins 1. Use chlorination or ozone oxidation, which are common methods for removing organic substances from natural water; 2. Employ coagulation or clarification filtration, as this method is very effective when there are suspended and colloidal organic substances in the water; 3. Activated carbon filtration can be used for adsorption, thereby removing various substances from water, including inorganic and organic colloids as well as dissolved polymeric organic compounds; 4. Organic substance removers commonly include Cl-type and OH-type organic substance removers. The former is an ion exchanger filled with Type Cl gel or macroporous ion exchange resin, while the latter is an ion exchanger filled with new styrene-based strong-base resin or used strong-base resin. The former increases the Cl+ content in the effluent, which is not favorable for the corrosion protection requirements of the equipment, while the latter is clearly safer and more economical.

Revival treatment for resin contamination by organic substances: The most commonly used method is alkaline saline solution, but for organic contamination, using only alkaline saline solution cannot completely remove the organic substances accumulated in the anion resin. An oxidant also needs to be added for oxidative decomposition and removal. However, oxidants can easily damage the resin. Therefore, the impact of oxidants on the safety of the resin must be considered during the recovery process.