Submitted to: Journal of Chemical Technology & Biotechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/19/1998
Publication Date: N/A
Interpretive Summary: Activated carbons are used in industry and environmental remediation to adsorb organic and some inorganic materials from waste streams and for recovery operations. Agricultural wastes can be used as a feedstock for the production of activated carbons. This provides a low cost, environmentally friendly precursor and it develops a market for what is otherwise low-value waste materials. To this end almond, pecan, English walnut, black walnut and macadamia nut shells were used to create high surface area, high porosity activated carbon adsorbents for the removal of metal ions (such as copper) as well as organic contaminants from water. These activated carbons were created using a variety of methods. Variations on the activation and oxidation steps were investigated to optimize the carbons adsorptive capacity as well as streamline the process. The carbons that were synthesized adsorbed several organic priority pollutants nearly as effectively as the commercially available carbons and all of them out-performed the commercial carbons in metals uptake capability by as much as 200%. It was determined that oxidized, acid-activated carbons from nutshells produce a very good carbon for the adsorption of copper and several organic compounds from water and that certain parameters could be optimized to create an effective carbon in minimum number of steps. The nutshell commodity groups will benefit from this research because it will add value to surplus by-products. Carbon users will also benefit because it offers a viable alternative to coal based activated carbons; potential lower cost; and potential to be used for different pollutants.
Technical Abstract: Almond, pecan, English walnut, black walnut and macadamia nut shells were chosen as hard, lignocellulosic precursors for the production of granular activated carbons (GACs). They were activated with H3PO4 under a variety of conditions. Following activation, a portion of the GACs were oxidized in air at 300 C for 4h in order to create a carbon surface presumably with more oxygen functional groups for the adsorption of metal cations. Also investigated was a streamlining of the production techniques used. Several of the samples were subjected to a "Continuous" process in which the carbon was activated and upon cooling to 300 C was oxidized with air. Beyond this activation, methods were developed wherein the activation process took place under air and without a discrete, separate oxidation step. These processes were designed to determine if any of the carbon's capabilities would be lost or enhanced in comparison to the more standard activate- cool- wash-oxidize method. The carbons produced from these various activation/oxidation methods consistently, and without regard to precursor composition, sequestered over 90% of available copper from a 3mM copper chloride test solution and often adsorbed organic contaminants as effectively as some commercial carbons.