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INTERACTION OF PLANAR AND NONPLANAR ORGANIC CONTAMINANTS WITH COAL FLY ASH: EFFECTS OF POLAR AND NONPOLAR SOLVENT SOLUTIONS
Citation:
BURGESS, R. M., S. A. RYBA, M. G. CANTWELL, J. GUNDERSEN, R. TIEN, AND M. PERRON. INTERACTION OF PLANAR AND NONPLANAR ORGANIC CONTAMINANTS WITH COAL FLY ASH: EFFECTS OF POLAR AND NONPOLAR SOLVENT SOLUTIONS. ENVIRONMENTAL TOXICOLOGY AND CHEMISTRY. Society of Environmental Toxicology and Chemistry, Pensacola, FL, 25(8):2028-2037, (2006).
Impact/Purpose:
to better understand the mechanisms affecting the strong interaction between planar contaminants and coal fly ash
Description:
Coal fly ash has several uses but much of the material is treated as waste and disposed of in various ways including land filling. Coal fly ash also has a very high sorption capacity for a variety of anthropogenic contaminants and has been used to cleanse wastewater of such 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 like polycyclic aromatic hydrocarbons (PAHs) and some polychlorinated biphenyls (PCBs). The current study was performed to better understand the mechanisms affecting the strong interaction between planar contaminants and coal fly ash. The removal of ten PCBs and ten PAHs by several fly ashes and other absorbents was evaluated under different experimental conditions to highlight the intermolecular forces influencing adsorption. Varying fly ash concentrations and solvent system composition indicated dispersive interactions were most prevalent in most instances. For the PCBs, empirical results were compared to molecular modeling estimates of the energy necessary for the PCB molecule to assume a planar conformation (PCe). PCe levels ranged from 8 to 25 kcal/mol, depending on the degree of ortho-substituted chlorines of the PCB. A significant correlation between PCe and PCB removal from solution was observed for the fly ashes and activated carbon while the non-planar sorbent octadecyl (C18) demonstrated no relationship. These findings demonstrate the strong interaction between black carbon and planar organic contaminants. Further, as exemplified by the PCBs, these results show how this interaction is a function of a contaminants ability to assume a planar conformation.