Environ. Sci. Technol. 2005, 39, 901-907
Sorption and Desorption of Perchlorate and U(VI) by Strong-Base Anion-Exchange Resins BAOHUA GU,* YEE-KYOUNG KU, AND GILBERT M. BROWN Environmental Sciences Division and Chemical Sciences Division, Oak Ridge National Laboratory, P.O. Box 2008, MS-6036, Oak Ridge, Tennessee 37831
This study investigated the sorption affinity and capacity of six strong-base anion-exchange (SBA) resins for both uranium [U(VI)] and perchlorate (ClO4-) in simulated groundwater containing varying concentrations of sulfate (SO42-). Additionally, desorption of U(VI) from spent resins was studied to separate U(VI) from resins with sorbed ClO4- for waste segregation and minimization. Results indicate that all SBA resins investigated in this study strongly sorb U(VI). The gel-type polyacrylic resin (Purolite A850) showed the highest sorption affinity and capacity for U(VI) but was the least effective in sorbing ClO4-. The presence of SO42- had little impact on the sorption of U(VI) but significantly affected the sorption of ClO4-, particularly on monofunctional SBA resins. A dilute acid wash was found to be effective in desorbing U(VI) but ineffective in desorbing ClO4- from bifunctional resins (Purolite A530E and WBR109). A single wash removed ∼75% of sorbed U(VI) but only ∼0.1% of sorbed ClO4- from the bifunctional resins. On the other hand, only 21.4% of sorbed U(VI) but ∼34% of sorbed ClO4- was desorbed from the Purolite A850 resin. This study concludes that bifunctional resins could be used effectively to treat water contaminated with ClO4- and traces of U(VI), and dilute acid washes could minimize hazardous wastes by separating sorbed U(VI) from ClO4- prior to the regeneration of the spent resin loaded with ClO4-.
Introduction Perchlorate (ClO4-) contamination has become a major concern in more than 24 states since the Environmental Protection Agency disclosed in 2002 that its presence in drinking water poses dangers to human health because of its effects on thyroid hormone production (1). Perchlorate has been widely used as a rocket propellant and in munitions, and its improper disposal has resulted in widespread contamination of groundwater and drinking water supplies in the United States (1, 2). Of the treatment technologies under development, ion exchange has been identified as one of the most promising for removing low levels of ClO4- at a high flow rate (3-6). For example, in a small-scale field experiment, Gu et al. (3) demonstrated that a selective bifunctional anion-exchange resin was able to treat >100 000 bed volumes of groundwater before a significant breakthrough of ClO4- occurred (at an initial influent concentration * Corresponding author phone: (865)574-7286; fax: (865)576-8543; e-mail:
[email protected]. 10.1021/es049121f CCC: $30.25 Published on Web 12/21/2004
2005 American Chemical Society
of ∼50 µg ClO4-/L). At a higher influent concentration of ∼450 µg/L ClO4-, the bifunctional resin treated ∼40 000 bed volumes of groundwater before the breakthrough of ClO4in a pilot-scale field demonstration at the Edwards Air Force Base (AFB) site in California (4). Field experiments at Edwards AFB also revealed that these strong-base anion-exchange (SBA) resins sorbed and concentrated naturally occurring uranium [U(VI)] in the resin bed even though the uranium concentration in groundwater was generally low (99%). On the other hand, when the degree of sorption is relatively low, the measured U(VI) concentration and the calculated Kd are usually within an error of
