Selectivity of bicarbonate-form anion exchange for drinking water contaminants: Influence of resin properties

Bicarbonate was investigated as a new counterion for six strong-base anion exchange resins considering the selective removal of six drinking water contaminants: Nitrate, bromide, perchlorate, sulfate, chromate, and Suwannee River natural organic matter (SRNOM). The most selective bicarbonate-form resin for each contaminant was evaluated based on qualitative binary ion exchange plots and quantitative separation factor calculation. The influence of resin properties and ion characteristics was evaluated on resin selectivity for each contaminant. The type of functional group and polymer composition of the resin were shown to influence selectivity for inorganic contaminants, and the pore structure and polymer composition of resin were shown to influence selectivity for SRNOM. Bicarbonate-form resin with wide spacing of functional groups (i.e., triethylamine) and polystyrene composition was favorable for monovalent, hydrophobic contaminants, including nitrate, bromide, and perchlorate, whereas resin with close spacing of functional groups (i.e., trimethylamine) and polystyrene composition was favorable for relatively hydrophobic chromate and resin with same functional group and polyacrylic composition was favorable for relatively hydrophilic sulfate ion. For organic contaminant, bicarbonate-form resin with macroporous structure and polyacrylic composition was most selective for SRNOM. In addition, the resin selectivity sequence for each contaminant based on separation factor calculations was compared with adsorption isotherm parameters, and the similarities and differences are discussed. The separation factor method is based on ion exchange stoichiometry, whereas adsorption method is robust in terms of simplifying calculation.