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Printer FriendlyReprinted with permission from Popular
Science, March 1999.
© Copyright, Times Mirror Magazines, Inc.
Metal Eaters
AMONG THE most serious contaminants of the nation's waterways are toxic metals such as lead, mercury, and chromium. A new chemical technique could prove extremely effective not only in cleaning up these waterways but also in recovering such precious metals as gold.
Developed by researchers at the Department of Energy's Pacific Northwest National Laboratory in Richland, Washington, the new method relies on two key components. The first is a silicate ceramic that can take the form of a bead or powder. Each grain of the ceramic material, only 5 to 15 micrometers in diameter, is honeycombed with a dense array of cylindrical pores.
The second component is called a monolayer: It's a single layer of densely packed molecules that are chemically tailored to bond with metallic contaminants. The Richland researchers have found a way to attach monolayers within the pores of the ceramic grains, with one end of the monolayer binding to the ceramic and the other end left free to "eat" a targeted metal that is passing through the pore.
The multitude of pores provides a large surface area for trapping metals. "In fact," says Jun Liu, a staff scientist who directed the research, "a mere teaspoon of this material in powder form has the surface area of a football field." Field tests have shown that the ceramic can reduce the concentration of a targeted metal to far below what is required by drinking-water standards.
The Department of Energy is considering the new technique for water and soil cleanup at sites where mercury is prevalent, and for extracting mercury from hazardous wastes. If it proves successful, the technique may later be used to clean up other toxic metals. Eventually, the molecule-lined ceramic grains could even be used for mining, to recover valuable materials such as gold from water.-Arthur Fisher
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