The purpose of deionization is to remove inorganic ions dissolved in water. Like hard water softeners, it also uses the principle of ion exchange resin. Two resins are used here-cation exchange resin and anion exchange resin. Cation exchange resins use hydrogen ions (H+) to exchange cations; while anion exchange resins use hydroxide ions (OH-) to exchange anions. Hydrogen ions and hydroxide ions combine to form neutral water. The reaction equation is as follows:
M +x +xH-Re → M-M-Re x +xH +1
A -z +zOH-Re → A-Re z +zOH -1
In the above formula, M +x represents cation, x represents valence number, M +x cation exchanges with H-Re hydrogen ion on cationic resin, A -z represents anion, z represents valence number, A -z exchanges with anion After the resin is combined, OH-ions are released. The combination of H + ion and OH-ion becomes neutral water.
hese resins also need to be reduced after the adsorption capacity is exhausted. The cation exchange resin needs a strong acid to reduce; on the contrary, the anion needs a strong base to reduce. The adsorption capacity of cation exchange resin for various cations is different, and their strength and relative relationship are as follows:
Ba 2+ >Pb 2+ >Sr 2+ >Ca 2+ >Ni 2+ >Cd 2+ >CU 2+ >Co 2+ >Zn 2+ >Mg 2+ >Ag 1+ >Cs 1+ >K 1 + >NH4 1+ >Na 1+ >H 1+
The affinity strength of the anion exchange resin and each anion is as follows:
S0 2- 4+ >I->NO 3- >NO 2- >Cl->HCO 3- >OH->F-
If the anion exchange resin is exhausted without reduction, the weakest adsorbed fluorine will gradually appear in the dialysis water, causing cartilage disease, osteoporosis and other bone lesions; if the cation exchange resin is exhausted, hydrogen ions It will also appear in the dialysis water, resulting in an increase in the acidity of the water quality, so whether the deionization function is effective requires frequent monitoring. It is generally judged by the resistivity or conductivity of water quality. It is worth noting that the ion exchange resin used in the deionization method can also cause the reproduction of bacteria and bacteremia.