Nutshells as granular activated carbons: physical, chemical and adsorptive properties

Nutshells from seven different sources (pistachio, hazelnut, almond, black walnut, English walnut, macadamia nut, pecan) were converted to granular activated carbons (GACs) by carbon dioxide activation. A portion of the GACs were oxidized with compressed air and the physical (yield, surface area, attrition), chemical (pH, surface charge) and adsorptive (organics uptake, metal ion uptake) properties of both oxidized and non-oxidized carbons were determined. Differences in uptake of organics, especially of polar compounds, were found between GACs made from almond shells, the group consisting of black walnut shells, English. walnut shells and pecan shells, and macadamia nutshells. Oxidation had its greatest effects on pH, surface charge and uptake of metal ions. The changes due to oxidation were found to be independent of carbon source material. GACs with specific properties can be produced with judicious selection of carbon precursor and oxidative treatment. (C) 2001 Society of Chemical Industry.