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NMSU researcher using pecan shells in pollution removal process

A New Mexico State University researcher is exploring the possibilities of using one industry's waste to solve waste issues for other industries.

San Saba Pecans has been providing David Rockstraw with shells for his research in activated carbon production. (NMSU photo by Michael Kiernan)

David Rockstraw, associate professor of chemical engineering, has been conducting research using pecan shells as the basis for removing pollutants, such as metals and TNT, from wastewater. Rockstraw's research, which began in 1996, has been funded by NMSU-based WERC: A Consortium for Environmental Education and Technology Development.

Rockstraw's process involves grinding pecan shells into a fine powder. The powder is treated with phosphoric acid, resulting in an activated carbon. The activated carbon can be used to adsorb substances such as nuclear waste, heavy metals and high explosives that are a result of governmental and industrial processes.

The use of activated carbon is not new. "It has been used since Biblical times," said Rockstraw, "when people used it to remove the odor from wounds and to purify metals in the production of alloys."

Nor is it uncommon. Many of our homes are equipped with activated carbon filters to purify water. It is used on a large scale by the food industry to remove color from processed sugar. The mining industry uses it to recover valuable metals that would otherwise be lost and to meet compliance with wastewater discharge standards.

What is novel is Rockstraw's process for creating the activated carbon, which uses temperatures less than 350 C. Traditional methods involve temperatures as high as 900 C. And while greater than 90 percent of commercial activated carbon produced is made from coal and coconut shells, this new process utilizes a substance that is abundant and inexpensive. Analysis has shown that pecan-based activated carbon is more efficient than high-priced ion-exchange resins as found in residential water softener for the removal of copper, zinc and iron.

Rockstraw believes this process could revolutionize the manufacture of activated carbon and has widespread commercial potential. His process is currently being patented and plans call for the patenting of new techniques that Rockstraw and several graduate students are working on.

Seyed Dastgheib, a Ph.D. student from Iran, is responsible for making improvements to the original process developed in 1996-97, and has developed mathematical models for predicting the performance of the activated carbon under various operating conditions.

Yan Ping Guo, a Ph.D. student from China, is investigating the viability of producing activated carbon by the new process using other agricultural wastes, such as wheat straw, corncobs, soybean hulls, and cottonseed hulls.

A Ph.D. student from Mexico, Alma Cota, is collaborating with Los Alamos National Laboratory to remove high explosives, such as TNT, from groundwater. The method involves treating the activated carbon surface with organic materials that will enable it to capture the toxic wastes and render them benign.

This four-year research project began when Rockstraw and former Ph.D. student Reyad Shawabkeh were considering ways for Shawabkeh to continue research that he had begun in his native Jordan. There he used olive pits for production of activated carbon. Rockstraw arrived at pecan shells, the agricultural waste product that is plentiful here, as a substance to be investigated. Shawabkeh completed his degree and has since returned to Jordan where he is an assistant professor at Mutah University.

Pecan shells at present have no commercial value and are discarded in landfills. "At this point, disposing of the shells is a cost to producers," said Rockstraw. "We're taking a substance that has little to no value and producing a high-value product from it."

New Mexico is the third largest producer of pecans, following Georgia and Texas, respectively. In 1997, the New Mexico growers produced 40 million pounds of pecans, with an estimated half of that weight being waste.

"This unique process could prove beneficial on a worldwide scale," said WERC Executive Director Abbas Ghassemi.

Rockstraw's research has been funded through WERC's Technology Development Program. The WERC consortium consists of New Mexico State University, New Mexico Institute of Mining and Technology, University of New Mexico, Dine College, Los Alamos and Sandia National Laboratories, and industrial affiliates.

Photo is available at http://kiernan.nmsu.edu/newsphoto/Rockstraw.jpg.
For a print, call (505) 646-3221.
CUTLINE: San Saba Pecans has been providing David Rockstraw with shells for his research in activated carbon production. (NMSU photo by Michael Kiernan)

Linda Fresques
Oct. 16, 2000