Part I: Predicting performance of Purolite A532E resins for remediation of comingled contaminants in groundwater

Abstract

Ion exchange (IX) resins are used in pump-and-treat (P&T) facilities to remove soluble groundwater contaminants. However, natural anions present at concentrations orders of magnitude higher than contaminants can compete for IX sites and impact resin lifecycles. Here, the Hanford Site’s 200 West Area P&T facility (Washington State, USA) was selected as a case study because it currently uses two IX resins: Purolite® A532E (A532E) to remove pertechnetate (TcO4-) and DOWEX 21K (DOWEX) to remove uranium from groundwater. Nitrate (NO3-), sulfate (SO42-), chloride (Cl-), and carbonate (CO32-) anions have been identified to potentially compete for A532E and DOWEX IX sites. Hanford-relevant anion groundwater concentrations were used to design a series of laboratory-scale batch experiments to evaluate the impact of competing anions on resin performance and potential kinetic effects. These data are then modeled to obtain Cl--normalized equilibrium exchange coefficients (K) needed to predict IX resin performance. The work is presented in two parts, with IX performance evaluated for A532E in Part I and DOWEX in Part II. Part I results demonstrate that TcO4- uptake is not impacted by NO3-, SO42-, Cl-, CO32- (as HCO3-) and U(VI) carbonate anions, with KTcO4-/Cl- > 4,000, likely due to the high selectivity of A532E trihexylammonium sites for the large, weakly hydrated TcO4- anion. Other anion K values were KNO3-/Cl- = 20, KSO4--/Cl- = 0.2, KHCO3-/Cl- = 0.09, KU/Cl- = 370–1000. These K values provide conservative parameters for predicting A532E performance, and demonstrate that, under these test conditions, A532E will remove TcO4- from current and future influent streams to meet groundwater treatment objectives.