If you want to produce ultra-high purity water, you must use ion exchange resin to prepare it, and improve the water purity through the form of ion replacement. However, many people are not very familiar with the exchange principle. Today, I will take you to understand the exchange principle of ion exchange resin.
The basic principle of ion exchange resin to prepare pure water
The cation and anion resins are dissociated in water. When the raw water passes through the cation resin, the cations in the water are absorbed by the resin, and the cation H+ on the resin is replaced into the water, and forms the corresponding inorganic acid with the anion in the water; When the water passes through the anion resin, the anions in the water are adsorbed by the resin, and the anion OH- on the resin is replaced into the water and combined with the H+ in the water to form water. In this way, the raw water is continuously exchanged through the cation and anion resins to obtain deionized water.
The treatment and transformation of new ultrapure water resin
New resins are often mixed with soluble oligomers and other impurities, which affect the exchange reaction of the resin and the quality of effluent. For this reason, the new resin must be processed and transformed before use. Most of the commercially available cation resins are sodium type, and most of the anion resins are chlorine type, so it must be converted into active hydrogen type and hydroxide type.
The new cation resin is soaked in normal water for 1-2 days to fully absorb water and expand. Repeatedly rinse with normal water to remove soluble matter in the water until the washing water is clear, and remove the remaining water as much as possible. Add the same amount of 7% hydrochloric acid solution to soak for about 1 hour and stir at any time to remove the acid solution, then wash with normal water until the pH of the washed water is 3.0-4.0, and then pour out the remaining water. Then add the same amount of 8% sodium hydroxide solution to soak for 1 hour, and stir at any time to remove the lye, wash with water or deionized water exchanged by cation resin to pH 9.0 of the eluate, and pour out the remaining water. Finally, add 3 times the volume of 7% hydrochloric acid solution to soak for 2 hours and stir to turn the cation resin into hydrogen form, pour out the acid solution, wash with deionized water to pH 3.0-4.0, and then pack the column.
The new anion resin is soaked in normal water, and then washed repeatedly with water to remove the strong odor. If the odor cannot be removed, it can be soaked in 95% ethanol to remove the odor, pour the ethanol, and then wash with normal water until it is clear and odorless. Add the same amount of 8% sodium hydroxide solution to soak for 1 hour and stir to remove the lye, and then wash with water or deionized water that has passed through the cation resin until the pH of the eluate is 9.0 (not suitable for washing with normal water, because of the Ca2+, Mg2+ in normal water In case of lye, insoluble hydroxide precipitates), and the remaining water is decanted. Add the same amount of 7% hydrochloric acid solution and soak for 1 hour to remove the acid solution, then wash with normal water until the pH of the wash solution is 3.0, and pour out the remaining water. Finally, add 3 times the amount of 8% sodium hydroxide solution to soak for 2 hours and stir to convert the anion resin to the hydroxide type, pour out the lye, and wash with deionized water to pH 8.0-9.0.
The combination of ultrapure water resin column
generally has four forms: (1) single bed; (2) composite bed; (3) combined bed; (4) mixed bed. In various combinations (except for mixed beds), the cation resin bed must be ranked first and cannot be reversed. Because the water contains alkaline earth metal ions (Ca2+, Mg2+) and enters the anion resin without first passing through the cation resin bed, the anion resin exchanges with the anions in the water, and the exchanged OH and alkaline earth metal ions form a precipitate and coat the anion resin. Affect exchange capacity.
Ion exchange resin to prepare pure water is actually mainly through the exchange of ions in the resin particles with ions in the water to remove other ions except hydroxide ions in the water. Moreover, the resin will be saturated during the replacement process, and the ultrapure water ion exchange resin needs to be regenerated at this time.