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A sieve for selecting cesium.

A sieve for selecting cesium

One of the more deadly products of a nuclear reactor accident is the radioactive isotope cesium-137. Because this metal vaporizes easily, winds can carry it over long distances, contaminating large areas. Two researchers have now discovered a form of the mineral mica that acts as a highly selective sieve for capturing cesium ions. Such an ion trap could be useful for decontaminating the environment after accident releases of nuclear material. Sridhar Komarneni and Rustum Roy of Pennsylvania State University in University Park report their discovery in the March 11 SCIENCE.

The researchers start with samples of a naturally occurring mineral known as phlogopite mica. The mineral is ground into a fine powder and then chemically treated to replace its potassium ions with sodium ions and water molecules. This process increases the spacing between the layers that make up the mica's structure. The modified material, when immersed in a cesium-containing solution, readily sodium ions while taking in cesium ions.

Presently, clay minerals and zeolites, both naturally occuring and synthetic, are used extensively in the decontamination and disposal of radioactive wastes. For example, after the Chernobyl nuclear accident, the mineral mordenite was added to animal feed in Sweden to remove cesium-137 from the gastrointestinal tracts of contaminated animals. The use of modified, powdered mica offers greater selectivity for cesium and much better resistance to acidic conditions like those found in an animal's stomach. Komarneni and Roy suggest that the mica powder can be used for decontamination by dispersing it in water or soil and then filtering out the cesium-laden product or by letting cesium-contaminated humans or animals ingest the material, which would later be excreted.

The newly discovered cesium ion sieve, the researchers say, "not only selectively exchanges cesium ions but also immobilizes them at room temperature through chemical bonding that. . . leads to the formation of a crystalline waste form at room temperature."
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Title Annotation:phlogopite mica used to decontaminate radioactive cesium
Publication:Science News
Date:Mar 26, 1988
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