Sorption and manganese-induced oxidative coupling of hydroxylated aromatic compounds by natural geosorbents

The sorption/desorption equilibria and solvent extractabilities of phenol, o-cresol, and p-chlorophenol with respect to natural sorbents having different types of soil organic matter were investigated. Parallel tests in systems amended with birnessite (delta-MnO2), a solid-phase oxidative coupling catalyst, were also conducted. Sorption/desorption isotherms and solvent extraction data reveal that the relative isotherm linearities, desorption hysteresis, and extractabilities of these compounds are related to the geochemical nature of the sorbent organic matter and to the existence of system conditions that promote oxidative coupling reactions. When suitable coupling catalysts are present, soils containing primarily diagenetically "young" and highly amorphous organic matter (e.g., humic materials) are more likely to retain those solutes than are those containing primarily diagenetically "old" and more condensed organic matter (e.g., kerogens). The sorption/desorption properties of the solutes were significantly altered in the presence of birnessite as a result of both cross-coupling reactions with reactive soil organic matter components and self-coupling reactions with each other to form polymeric species. Under appropriate conditions, mineral-catalyzed oxidative coupling may exert a dominant influence on the sorption and transport of hydroxylated aromatic compounds in soil and sediment systems.