Nut Shells on Tap for Industrial Clean Up

Macadamia, pecan and almond shells are of little commercial value other than the nuts’ natural packaging--or livestock bedding. But U.S. Department of Agriculture scientists are converting the shells into powerful industrial clean-up tools in the form of granular activated carbons (GACs).

GAC uses run the gamut, from fish tank filters and water purifiers, to waste-water treatment, soil remediation and gas chromatographic analysis. In the U.S., such applications consume over 300 million pounds of carbons annually--over half the 600 million pounds used worldwide.

What makes them so useful is a highly porous surface that draws heavy metals like lead and organic compounds like toluene and benzene. Both are common ingredients in fuels, dyes and paints. Once they escape into the environment, however, they can become contaminants.

Many GAC products are made from coconut shells and coal, though both are costly. Coal also is a nonrenewable resource. Chemists Wayne Marshall and Linda Wartelle are testing discarded nutshells as a more plentiful and inexpensive alternative. Both work at the Agricultural Research Service’s Southern Regional Research Center in New Orleans, La. ARS is USDA’s chief scientific agency. Colleague Chris Toles, formerly ARS, is now at Northeastern University in Boston.

Under a microscope, nutshell carbons resemble tiny, pockmarked asteroids. But one gram can have 900 square meters of surface area, a plus in adsorbing metals or chemicals with low molecular weights, like benzene.

In comparative studies with six commercial carbons, use of macadamia GACs produced a three to four-fold increase in the ability of a standard EPA air sampling procedure to detect benzene at concentrations of 100 parts per billion.

A longer story appears in the September issue of Agricultural Research magazine, and on the Web at:

http://www.ars.usda.gov/is/AR/archive/sep99/carb0999.htm

Scientific contact: Wayne Marshall, ARS Commodity Utilization Research Unit, Southern Regional Research Center, New Orleans, phone (504) 286-4356, fax (504) 286-4367, marshall@commserver.srrc.usda.gov.