A Novel Bifunctional Anion Exchange Resin Shows Promise for Tough Groundwater Cleanup Problems

For tough environmental problems where the contaminant is present at extremely low concentrations, it's only a small exaggeration to say that you need all the selectivity that you can get. At the USDOE uranium-enrichment plants at Paducah, Kentucky, and Portsmouth, Ohio, radioactive technetium pollutes the groundwater, forming plumes that can have an excess of 400 nanograms per liter. That's just a speck of matter dissolved in a quart of water, but considering the long half-life and mobility of technetium together with the health risk of its ingestion, this pollution represents a significant regulatory concern at these sites. In terms of a separation, though, it's like pulling a needle out of a haystack, because the technetium is on the order of a millionth of the concentration of ordinary constituents of groundwater. Although off-the-shelf anion-exchange resins have a well-known applicability to problems such as this, the most common materials are an order of magnitude less selective than theory says they could be. The key to gaining this selectivity boost was available in ongoing fundamental research at Oak Ridge National Laboratory and the University of Tennessee. Application of theory in fact suggested increasing the size of the fixed positively charged sites on the resin. When this was done, selectivity increased as expected, but the rate of uptake of the negatively charged pertechnetate ion TcO₄^-, the mobile form of technetium in groundwater, slowed dramatically. To solve this problem, the researchers created the bifunctional resin they call "BiQuat," shown in the figure below. The secret to BiQuat is the presence of both small and large positively charged groups within the resin. The small groups promote fast exchange, while the large groups provide highly selective sites. In field tests at Paducah, BiQuat performed five-fold better than the resin used at the site. Field tests for a similar ion, perchlorate, have shown equally impressive results. A patent application is pending, and a commercial material is in development by the Purolite Company, a major producer of ion-exchange resins. A 1999 Lockheed Martin Technical Accomplishment Award recognized this work. Both applied and fundamental research continues.

Chemical Separations Group R & D Projects

Provided by Oak Ridge National Laboratory's Chemical Sciences Division
Rev:   October 20, 2005