ion exchange resins have different affinities for different ions in the solution and are selective in their adsorption. There are general rules for the strength of various ions subjected to resin exchange adsorption, but different resins may be slightly different. The main rules are as follows:
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 strongly adsorbed. Some cations are adsorbed in the following order:
Fe3+> Al3+> Pb2+> Ca2+> Mg2+> K+> Na+> H+
The general order of the adsorption of inorganic acid radicals by strong basic anion resin is:
SO42－> NO3－> Cl－> HCO3－> OH－
The general order of the adsorption of anions by weakly basic anion resin is as follows:
OH－> Citrate 3－> SO42－> Tartrate 2－> Oxalate 2－> PO43－ >NO2－> Cl－ >Acetate－> HCO3－
sugar solution decolorization often uses strong alkaline anion resin, which has strong adsorption of pseudomelanin (reducing sugar and amino acid reaction product) and alkaline decomposition products of reducing sugar, while the adsorption of carabohydrate pigment is weak. This is believed to be because the first two are usually negatively charged, while caramel has a weak charge.
Generally, resins with a high degree of cross-linking have higher ion selectivity, and macroporous resins have lower selectivity than gel-type resins. This selectivity is greater in dilute solutions and less in concentrated solutions.