title: Interaction of planar and nonplanar organic contaminants with coal fly ash: effects of polar and nonpolar solvent solutions.
abstract: Coal fly ash has a very high sorption capacity for a variety of anthropogenic contaminants and has been used to cleanse wastewater of pollutants for approximately 40 years. Like other black carbons, the planar structure of the residual carbon in fly ash results in elevated affinities for planar organic contaminants, such as polycyclic aromatic hydrocarbons (PAHs) and some polychlorinated biphenyls (PCBs). The present study was performed to understand better the mechanisms affecting the strong interaction between planar contaminants and coal fly ash. The removal of 10 PCBs and 10 PAHs by several fly ashes and other sorbents was evaluated under different experimental conditions to highlight the intermolecular forces influencing adsorption. Varying fly ash concentration and solvent system composition indicated that dispersive interactions were most prevalent. For the PCBs, empirical results also were compared to molecular modeling estimates of the energy necessary for the PCB molecule to assume a planar conformation (PCe). The PCe levels ranged from 8 to 25 kcal/mol, depending on the degree of ortho-substituted chlorination of the PCB. A significant correlation between PCe and PCB removal from solution was observed for the fly ashes and activated carbon, whereas the nonplanar sorbent octadecyl (C18) indicated no relationship. These findings demonstrate the strong interaction between black carbon fly ash and planar organic contaminants. Furthermore, as exemplified by the PCBs, these results show how this interaction is a function of a contaminant's ability to assume a planar conformation.
authors.affiliation: US Environmental Protection Agency, Office of Research and Development/National Health and Environmental Effects Research Laboratory-Atlantic Ecology Division, 27 Tarzwell Drive, Narragansett, Rhode Island 02882, USA. burgess.robert@epa.gov
authors.forename: Robert M
authors.initials: RM
authors.lastname: Burgess
authors.forename: Stephan A
authors.initials: SA
authors.lastname: Ryba
authors.forename: Mark G
authors.initials: MG
authors.lastname: Cantwell
authors.forename: Jennifer L
authors.initials: JL
authors.lastname: Gundersen
authors.forename: Rex
authors.initials: R
authors.lastname: Tien
authors.forename: Monique M
authors.initials: MM
authors.lastname: Perron
mesh_terms: D002244:Carbon; D003031:Coal; D060729:Coal Ash; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D052638:Particulate Matter
chemical_list: D003031:Coal; D060729:Coal Ash; D052638:Particulate Matter; D002244:Carbon