A new active material for the treatment of uranium-contaminated groundwater using permeable reactive barriers has been developed. This material, called PANSIL, is an example of a tailored ligand system that selectively removes a contaminant from solution. The active medium in PANSIL is a polyacryloamidoxime resin derived from polyacrylonitrile, which is deposited from solution onto the surface of quartz sand to form a thin film coating. PANSIL is highly effective at sequestering UO2(2+) from solution when the pH is between about 5 and 8 and can preferentially sequester UO2(2+) from solutions that are typical of the groundwater from a mine tailings site, due to the stability of the polyacryloamidoxime uranyl complex formed. Uranium sequestration capacity will depend on the surface area of the sand that is resin coated, but in the batch of PANSIL tested (<2% resin by weight), it exceeds 4000 mg of UO2 per kg of PANSIL at pH 4.5 when the dissolved UO2(2+) concentration is greaterthan 300 mg/L. PANSIL largely retains the permeability and strength of the sand employed and therefore has suitable engineering properties for permeable reactive barrier applications.

Three materials that are designed to treat uranium-contaminated water were investigated.These are a cation exchange resin, IRN77, an anion exchange resin, Varion AP, and a recently developed material called PANSIL (quartz sand coated with 2% amidoxime resin by wt.). 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 for treating uraniumcontaminated groundwaters using a permeable reactive barrier approach is then discussed.All three materials react rapidly in the pH range 5-7, reaching equilibrium in less than 4 hours at ~23°C. The unconditioned cation exchange resin removed 8 g UO 2 2+ per kg of resin from neutral synthetic groundwater containing 30 mg/l of UO 2 2+ , but a lower capacity is anticipated in groundwater with either higher ionic strength or lower UO 2 2+ concentrations. It operates by first acidifying the solution, then sorbing UO 2 2+ , and can release UO 2 2+ 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 to 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.

The performance of an active material for treating uranium contaminated groundwater within a permeable reactive barrier (PRB) is reported. This material, called PANSIL, has a tailored ligand system that selectively removes the uranyl (UO 2 2+) cation from solution. The active uranyl ligand in PANSIL is a polyacryloamidoxime resin derived from polyacrylonitrile, which is deposited from solution onto the surface of quartz sand to form a thin film coating.PANSIL is effective at sequestering cationic and neutral uranyl species when the solution pH is above 4, due to the stability of the polyacryloamidoxime-uranyl complex formed. However the rate of sequestration decreases rapidly when the pH exceeds about 8 where neutral uranyl species are present only at very low concentrations. It can preferentially sequester UO 2 2+ in the presence of typical divalent groundwater cations. In mildly alkaline conditions the sequestration performance in groundwater is sensitive to the concentration of uranyl complexing ligands, such as bicarbonate. Such behaviour has important consequences for PRB design as it will determine the barrier thickness required to treat a particular groundwater flow rate.1

The performance of an active material for treating uranium contaminated groundwater within a permeable reactive barrier (PRB) is reported. This material, called PANSIL, has a tailored ligand system that selectively removes the uranyl (UO 2 2+) cation from solution. The active uranyl ligand in PANSIL is a polyacryloamidoxime resin derived from polyacrylonitrile, which is deposited from solution onto the surface of quartz sand to form a thin film coating.PANSIL is effective at sequestering cationic and neutral uranyl species when the solution pH is above 4, due to the stability of the polyacryloamidoxime-uranyl complex formed. However the rate of sequestration decreases rapidly when the pH exceeds about 8 where neutral uranyl species are present only at very low concentrations. It can preferentially sequester UO 2 2+ in the presence of typical divalent groundwater cations. In mildly alkaline conditions the sequestration performance in groundwater is sensitive to the concentration of uranyl complexing ligands, such as bicarbonate. Such behaviour has important consequences for PRB design as it will determine the barrier thickness required to treat a particular groundwater flow rate.1

No abstract