Submitted to: Carbon
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/31/1997
Publication Date: N/A
Interpretive Summary: Almond and pecan 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 employing either carbon dioxide or phosphoric acid in contact with the raw nutshells at temperatures of either 700-800 deg C (for the carbon dioxide carbons), or 450 deg C (for the acid-activated carbons). Portions of these carbons were then oxidized under air at 300 deg C. A Number of analyses were performed on these carbons to determine their efficiency at adsorption of organic contaminants and metal ions in solution in water and compared against several commercially available carbons. Both the oxidized and unoxidized acid- and carbon dioxide-activated nutshell carbons adsorbed several organic priority pollutants as well as the commercially available carbons and several of the nutshell carbons out-performed the commercial carbons in metals uptake capability. 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.
Technical Abstract: Almond and pecan shells were chosen as hard, lignocellulosic precursors for the product of granular activated carbons (GACs). They were activated either chemically, with phosphoric acid, or physically, with carbon dioxide under a variety of conditions. Following activation, a portion of the GACs were oxidized in air at 300 C for 4h. The acid-activat tmples had higher BET surface areas and greater product yields that the carbon dioxide-activated carbons. Chemical activation resulted in surface area (BET) values generally between 900-1200 meters squared/g, which physical activation developed typical surface areas of 300-500 meters squared/g. Unoxidized acid-activated GACs when evaluated in batch assays at pH 4.8. Oxidative treatment, however, improved copper ion adsorption in both types of carbons compared to their unoxidized counterparts. The effect of oxidation was greater in the acid-activated carbons, which produced the highest levels of copper ion adsorption of 9.4-0.6 meq/g carbon. All of the oxidized GACs evaluated removed more copper acid than any of the commercial carbons examined. Nutshell-based carbons were also examined for their ability to adsorb a variety of low effectiveness of the samples toward a mixture of methanol, acetone, acetonitrile, benzene, 1,4-dioxane, and toluene varied considerably, but some general trends were observed. For carbon dioxide activated pecan shell carbons there was a distinct increase in organic uptake that was usually not altered by oxidation. Both acid- and carbon dioxide-activated shell carbons took up similar amounts of the non-polar benzene and toluene, but the carbon dioside activated carbons took up more polar compounds.