Introduction To Ion Exchange Resin Affinity And Adsorption Capacity

Ion exchange resins have different affinities for different ions in the solution and are selective in their adsorption. There are general rules for how strongly various ions are exchanged and adsorbed by resins, but different resins may have slight differences. The main rules are as follows:

1. Adsorption of cations
High-valent ions are usually preferentially adsorbed, while low-valent ions are weakly adsorbed. Among ions of the same valence, ions with larger diameters are more strongly adsorbed. The order in which some cations are adsorbed is as follows:
Fe3+>Al3+>Pb2+>Ca2+>Mg2+>K+>Na+>H+

2. Adsorption of anions
The general order of adsorption of inorganic acid radicals by strong basic anionic resin is:
SO42－>NO3－>Cl－>HCO3－>OH－
The general sequence of adsorption of anions by weakly basic anionic resin is as follows:
OH->Citrate 3->SO42->Tartrate 2->Oxalate 2->PO43->NO2->Cl->Acetate->HCO3-

3. Adsorption of colored substances
Strongly alkaline anionic resin is often used for decolorizing sugar liquid. It has strong adsorption of pseudomelanin (reaction product of reducing sugar and amino acid) and alkaline decomposition products of reducing sugar, but weak adsorption of caramel pigment. This is thought to be due to the fact that the first two are generally negatively charged, while caramel has a weak charge.

Generally, resins with a high degree of cross-linking have stronger ion selectivity, and macroporous structure resins have less selectivity than gel-type resins. This selectivity is greater in dilute solutions and smaller in concentrated solutions.