Sorption and binary exchange of nitrate, sulfate, and uranium on an anion-exchange resin

Competitive ion-exchange reactions were studied on a strong-base anion-exchange resin to remove NO3- and uranium from a contaminated groundwater containing high levels of NO3- (similar to140 mM), SO42- (similar to10 mM), and U(VI) (similar to0.2 mM). Results indicate that although SO42- carries divalent negative charges, it showed the least selectivity for sorption by the Purolite A-520E resin, which is functionalized with triethylamine exchange sites. Nitrate was the most strongly sorbed. Sorption selectivity followed the order of NO3- > Cl- > SO42- under the experimental conditions. Nitrate competitively sorbed and displaced previously sorbed SO42- in a column flow-through experiment and resulted in a high elution front of SO42- in the effluent. Although the concentration of uranium in groundwater is orders of magnitude lower than that of NO3- or SO42-, it was found to be strongly sorbed by the anion-exchange resin. Because the most stable uranium species in oxic and suboxic environments is the UO22+ cation, its strong sorption by anion-exchange resins is hypothesized to be the result of the co-ion effect of NO3- by forming anionic UO2(NO3)(3)(-) complexes in the resin matrix. These observations point out a potential alternative remediation strategy that uses strong-base anion-exchange resins to remove uranium from this site-specific groundwater, which has a low pH and a relatively high NO3- concentration.