Some semi-quantitative characterizations of polystyrene-based sulfonic, phosphinic, and carboxylic ion-exchangers

The aim of this research was to investigate and compare the metal-ion exchange properties of three types of cation exchange resins. The three resins were all prepared by substitution of functional groups onto a polystyrene-divinylbenzene base. One type of resin was a carboxylic resin, another a phosphinic resin, and the third a sulfonic resin. All resins were completely substituted with the functional group, but various degrees of divinylbenzene crosslinking were investigated for each type, and resins in both the gel and macroporous forms were employed. Detailed metal ion affinity series have not previously been determined for carboxylic and phosphinic resins of this type, although data have been accumulated for carboxylic resins with an acrylic base and for phosphonic resins with a polystyrene-divinyl benzene base. Detailed metal ion affinity series are well known for sulfonic resins with a polystyrene-divinylbenzene base.

Extractions of metal cations ( Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺, Mg⁺², Ca⁺², Sr⁺², Ba⁺², Cr⁺³, Mn⁺², Fe⁺³, Co⁺², Ni⁺², Cu⁺², Zn⁺², Al⁺³, Y⁺³, Ag⁺, Cd⁺², La⁺³, Pb⁺², and Th⁺⁴ ) from aqueous solutions were made using both the gel and macroporous forms of cation exchange resins. The effects of acid concentration, amount of the metal cation introduced, degrees of resin crosslinking, and resin capacities were examined.

Samples were equilibrated for 24 hours, and the aqueous metal cation concentrations were determined either by EDTA titrations, pH measurements, radioactivity determinations, atomic absorption, or atomic emission techniques.

By constructing appropriate plots of the logarithm of the organic/aqueous distribution coefficients of the metal ions against the logarithm of the organic/aqueous hydrogen-ion, sodium-ion, or potassium-ion concentrations, the affinities of the resins for metal ions were quantitatively compared.

Most data could be explained by a simple stoichiometric displacement reaction involving the metal cation with the resin, except when redox reactions and/or hydrolyses were involved.

The first detailed affinity series of the polystyrene-divinyl benzene based phosphinic resins and carboxylic resins were obtained. The affinity series for the phosphinic resins are very similar to those for the phosphonic resins, while the affinity series for the polystyrene-divinylbenzene based carboxylic resins are very similar to the acrylic based carboxylic resins.