Performance of three resin-based materials for treating uranium-contaminated groundwater within a PRB

Three materials that are designed to treat uranium-contaminated water were investigated. These are a cation exchange resin, IRN 77: an anion exchange resin, Varion AP; and a recently developed material called PANSIL (quartz sand coated with 2%, amidoxime resin by weight). The reaction rate, capacity, and effective pH range of the three materials are reported. The capacity and conditional distribution coefficient in neutral, uranyl-contaminated synthetic groundwater containing carbonate are also reported. The suitability of each material tor treating uranium-contaminated groundwater using a permeable reactive barrier (PRB) approach is then discussed. All three materials react rapidly in the pH range 5-7, reaching equilibrium in less than 4 h at similar to23degreesC. The unconditioned cation exchange resin removed 8 g UO22+ per kg of resin from neutral synthetic groundwater containing 30 mg/l of UO22+, but a lower capacity is anticipated in groundwater with either higher ionic strength or lower UO22+ concentrations. It operates by first acidifying the solution. then sorbing UO22+, and can release UO22+ when its buffering capacity has been exhausted. The anion exchange resin is very effective at removing anionic uranyl carbonate species from solutions with a pH above 5, with good specificity. Up to 50 g/kg of uranium is removed from contaminated groundwater at neutral pH. PANSIL is effective at sequestering cationic and neutral uranyl species from solutions in the pH range 4.5-7.5. with very good specificity. The capacity of PANSIL is pH-dependent, increasing from about 0.4 g/kg at pH 4.5, to about 1 g/kg at pH 6. and 1.5 g/kg around pH 7.5. In neutral groundwater containing carbonate. both the anion exchange resin and PANSIL exhibit conditional distribution coefficients exceeding 1470 ml/g, which is about an order of magnitude higher than comparable reactive barrier materials reported in the literature. (C) 2004 Elsevier B.V. All rights reserved.