Granular activated carbons from nutshells for the uptake of metals and organic compounds

Almond and pecan shells were chosen as hard, lignocellulosic precursors for the production of granular activated carbons (GACs) in order to create carbons for the adsorption of both organic compounds and metals. They were activated either chemically, with H3PO4, or physically, with CO2, under a variety of conditions. Following activation, a portion of the GACs were oxidized with air. The acid-activated samples had higher BET surface areas and greater product yields than the CO2-activated carbons. Unoxidized, CO2-activated carbons generally sequestered more Cu2+ from solution than the unoxidized acid-activated GACs, when evaluated in batch assays at pH 4.8. Oxidative treatment, however, improved Cu2+ adsorption in both types of carbon to levels significantly greater than comparable commercial carbons. Nutshell-based carbons were also examined for their ability to adsorb a variety of low molecular weight organic compounds with differing polarities. For CO2-activated pecan shell carbons there was a distinct increase in organic uptake that was usually not altered by oxidation. Both acid- and CO2-activated pecan shell carbons took up similar amounts of the non-polar benzene and toluene, but the CO2-activated carbons took up more polar compounds. There were several GACs that outperformed commercial carbons in their ability to adsorb significant quantities of Cu2+ or organics on the same carbon. Our data show that nutshells provide a plentiful and inexpensive precursor for the production of GACs which may be competitive with commercial carbons in wastewater or potable water treatment. (C) 1997 Elsevier Science Ltd.