Sorption equilibrium of Cr(VI) ions by strong base anion exchangers with pyridine structures

Chromate sorption on pyridine strong base anion exchangers with different functional groups (methyl, ethyl, and butyl groups), at the quaternary nitrogen atoms, was studied as a function of various initial concentrations (100–1500 mg Cr/L) and counterion type. The studied resins in the Cl−[ form have higher Cr(VI)‐retention capacities than those in the SO form. The pyridine strong base anion exchangers showed a selectivity reversal for the sulfate and chromate anions compared to that of the commercial resins. The alkyl substituent length of the quaternary nitrogen atoms exerted a substantial influence on the Cr(VI)‐retention capacity values for the resins in the Cl− form; the chromate anions preferred resins with methyl functional groups, that is, resins with a greater hydrophilic structure. For the resins in the SO form the length of the substituent at the quaternary nitrogen atom had only a negligible influence on their Cr(VI)‐retention values.