Nut Shells on Tap for Industrial Clean Up
By Jan Suszkiw
September 13, 1999
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 Services
Research Center in New Orleans, La. ARS is USDAs 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:
Scientific contact: Wayne Marshall, ARS
Research Unit, Southern Regional Research Center, New Orleans, phone (504)
286-4356, fax (504) 286-4367,