Catalyst cleans up

From San Francisco, at a meeting of the American Chemical Society

A new chemical catalyst can remove the pollutant perchlorate from water, chemists report. The catalyst could be used with current methods of ridding drinking water of this contaminant.

Found in, among other places, the brew that fuels a rocket’s takeoff, perchlorate has been reported in water and soil in 35 states, according to the Environmental Protection Agency. The pollutant can disrupt thyroid-hormone synthesis thereby disrupting the growth and development of fetuses and young children.

The most common method for removal of perchlorate from drinking water is to use ion-exchange resins, which pull out the pollutant but don’t destroy it. The resins are either burned after one use or treated with a concentrated salt solution to regenerate them. The latter technique leaves behind a perchlorate-contaminated brine that’s typically incinerated, explains John R. Shapley of the University of Illinois at Urbana-Champaign.

In their search for another approach, Shapley and his graduate student Keith D. Hurley used a powdered catalyst made of carbon and the metal palladium. To it, they added ammonium perrhenate, a salt that contains the metal rhenium surrounded by four oxygen atoms. They put the powder in water, pumped in hydrogen gas, and then added perchlorate, which consists of a chlorine atom that is bound to four oxygen atoms.

The resulting reaction sequentially stripped the perchlorate of its oxygen, explains Shapley. First, the palladium broke the bonds between two hydrogen atoms. Water formed when these two hydrogens removed an oxygen atom attached to the rhenium. Meanwhile, the rhenium filled its oxygen void by grabbing one of the oxygen atoms attached to the perchlorate. The reaction continued until the perchlorate lost all its oxygen and became chloride.

The catalyst works most effectively in acidic conditions, so it can’t directly treat drinking water. But Shapley says the catalyst could be used to remove the perchlorate from the brine left over after the regeneration of used ion-exchange resins. Along with testing the catalyst on the brine, “we are certainly going to be looking at how to deal with the [acid] problem” to move toward direct water purification with the catalyst, says Shapley.

Aimee Cunningham is the biomedical writer. She has a master’s degree in science journalism from New York University.

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