ABSTRACT
The predominant carboxylic acid and sulfonic acid poly- and perfluorinated alkyl substances (PFAS) are strong acids and therefore almost completely dissociate at common water pH values. The molecular structure of most PFAS compounds can be broken into two functional units: the hydrophobic, nonionic "tail," consisting of the fluorinated carbon chain, and the anionic "head," having a negative charge. Anion exchange resins are highly effective at removing PFAS from water because of the multiple removal methods involved. Ion exchange (IEX) capacity is based on the total number of fixed sites available for exchange, whereas operating capacity is a measure of the useful capacity observed during site-specific operating conditions. Kinetics is the speed or rate at which IEX or adsorption takes place. Several resin manufacturers have developed selectivity coefficients of various ions for both cation and anion IEX resins. Swelling of IEX resins results from hydration of the fixed IEX group.
