TECHNOLOGY UPDATE Phytic acid immobilizes radionuclides Chemists at Argonne National Laboratory are testing a new technology for protecting groundwater by chemically immobilizing underground radionuclides. The new method uses phytic acid, a natural chelating agent, to capture the heavy-metal ions through cation exchange. Ultimately, it may provide a more cost-effective means of treating nuclear contaminants that have migrated deep into the soil. With support from the lab's Efficient Separations and Processes Program, Kenneth Nash came across phytic acid during a search for thermally unstable complexants capable of decomposing spontaneously, thereby releasing phosphate. It was only after investigating phytic acid as a relatively inexpensive compound meeting those requirements that he realized it would also be a good cation exchanger. Phosphate is a good medium for isolating and immobilizing actinides, according to Nash. When it decomposes, phytic acid releases phosphate, which then joins with heavy metals to form insoluble minerals and harmless sugars. Nash foresees that the compound could be particularly valuable for situations such as those found at the Idaho National Engineering Laboratory, where actinide metals have migrated to considerable depths. In such C3.SGS he it's not CCO" nomical or practical to excavate, then wash or clean the soil When contaminated soil samples were tested, the phytic acid decomposed six milli-equivalents of uranium per equivalent. "It will load uranium very nearly up to the stoichiometric limit of uranium," Nash noted. The phytic acid was "very successful and effective in removing uranium from our synthetic groundwater. It increased the sorptive capacity of the test soil by nearly 2 orders of magnitude," he reported. In the field, of course, the amount of phytic acid needed to sequester an actinide element would
the probe has been used to detect dissolved hydrogen peroxide and iodide, as well as soluble forms of iron sulfide and colloidal material with Fe3 oxy-hydroxide. Luther says preliminary testing in contaminated waters has shown that the probe can detect copper, cadmium, lead, and zinc. "If we want to understand how pollution resulting from George Luther III examines the microelectrode probe he devel- human activities oped to continuously monitor contaminants in aquatic environ- might have an imments. (Photo by Robert Cohen, University of Delaware) pact on fresh water and marine water," said Luther, "we first need to know be site specific. Soil microbes conexacdy what's happening in the syssider phytic acid to be food, so "you tems on a day-to-day basis. The midon't necessarily want to activate the croelectrode is an extremely useful microbial activity in the subsurface tool for gathering this information." by putting down the compound in Luther is currently using the probe excess," said Nash. to study the dynamics of the ChesaNash is currently working with peake Bay, which—like many bays, soil samples from the Idaho laboraestuaries and lakes around the tory and plans to conduct a field test within a year. —KELLYN S. BETTS world becomes seasonally anoxic because of the eutrophication resulting from agricultural runoff and Microprobe remotely wastewater Once the oxygen is used monitors marine waters UD the sulfate in the water is oxidized thereby producing hydrogen sulfide After proving itself in a wide variety "We determined that when oxvof harsh field environments, a migen was present hydrogen sulfide croelectrode probe developed at the was not and when hydrogen sulfide University of Delaware has been outwas present oxvepn was not That's fitted with a cable that allows it to x . '• I • ' * I remotely sense the chemical compoofe geochemical andA environmental sition of fresh water and marine warelevance, he said. ter. The probe can now be conThe University of Delaware scienstructed with a tip width of either tists have operated the probe re300 or 40 micrometers. motely with batteries that allow it to remain in situ for several days. The The probe, developed by George W advantage of this remote capability Luther III, professor of oceanography, is that it rules out the possibility of builds on a previous model [Environ. sampling artifacts, says Luther. The Sci. Technoll.195,29, ,71-61) )nd scientists are discussing the use of uses the voltammetric method and their probe in Turkey's Black Sea and mercury-plated gold microelectrodes. the fjords of Norway, and Luther is In addition to detecting the hallmark investigating the possibility of patchemicals of the marine environenting elements of the technology. ment—dissolved species of iron, —KELLYN S. BETTS oxygen, sulfide, and manganese—
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VOL. 31, NO. 6, 1997 / ENVIRONMENTAL SCIENCE & TECHNOLOGY / NEWS • 2 6 3 A
