Adsorption Principle Of Ion Exchange Resin

Ion-exchange resins have different affinities to different ions in solution and are selective for their adsorption. The degree of adsorption of various ions by resin exchange has a general rule, but different resins may be slightly different. The main rules are as follows:

Adsorption of cations

Valence ions are usually preferentially adsorbed, while valence ions are weakly adsorbed. Among the similar ions of the same valence, the ions with larger diameter are adsorbed more strongly. Some cations are adsorbed in the following order:

Fe3+ > Al3+ > Pb2+ > Ca2+ > Mg2+ > K+ > Na+ > H+

Adsorption of anions

The general order of adsorption of inorganic acid by strong basic anionic resin is as follows:

SO42-> NO3- > Cl- > HCO3- > OH-

The general order of adsorption of anions by weak basic anion resins is as follows:

OH-> Citrate 3- > SO42- > tartrate 2- >; Oxalate 2- > PO43- >NO2- > Cl- >; Acetate - > HCO3-

Adsorption of colored matter

Strong basic anionic resin is often used for decolorization of sugar solution. It has strong adsorption of melanin (reaction product of reducing sugar and amino acid) and basic decomposition product of reducing sugar, but weak adsorption of caramel pigment. This is thought to be due to the fact that the first two are usually negatively charged, whereas caramel has a weak charge.

In general, the selectivity of cross-linked resins to ions is stronger, and the selectivity of macroporous resins is less than that of gel resins. This selectivity is larger in dilute solution and smaller in concentrated solution.