Development of bifunctional anion-exchange resins with improved selectivity and sorptive kinetics for pertechnetate: Batch-equilibrium experiments

A novel class of strong-base anion-exchange resins, bearing two different types of exchange sites, is described. These bifunctional resins have anion-exchange sites composed of two separate and differently sized trialkylammonium groups. In pertechnetate (TcO₄^-) uptake experiments from a solution matrix containing anions commonly encountered in groundwater, bifunctional resins containing exchange sites derived from tri-n-hexylamine in combination with either triethylamine, tri-n-propylamine, or tri-n-butylamine were shown to possess superior 24-h distribution ratios (K(d)) for pertechnetate over all monofunctional anion-exchange resins (derived from a single trialkylamine) examined. For example, although monofunctional resins containing a tri-n-hexylammonium exchange site possessed excellent selectivity for pertechnetate over other anions, the exchange kinetics were poor. The superior performance of these resins can be attributed to the combination of a large trialkylammonium site for enhanced selectivity for large anions and a smaller trialkylammonium site for the retention of good exchange kinetics.