Influence of Mineral-Bound Humic Substances on the Sorption of Hydrophobic Organic Compounds

Authors

Ellyn M. Murphy, Pacific Northwest National Laboratory
John M. Zachara, Pacific Northwest National LaboratoryFollow
Steven C. Smith, Pacific Northwest National LaboratoryFollow

Date of this Version

1990

Citation

Environ. Sci. Technol. 1990, 24, 1507-1516

Abstract

The sorption of three hydrophobic organic compounds (HOC) was investigated on hematite and kaolinite that had been coated with natural humic substances over a mass percent carbon range of 0.01-0.5%. Increasing quantities of sorbed humic substances increased the sorption of HOC. Anthracene, the most hydrophobic HOC, showed the greatest sorption enhancement, while the most aromatic coating, peat humic acid, was the strongest sorbent. Depending on the type of humic acid coating and the mineral substrate, the experimental K_oc values were either higher or lower than those predicted by the K_ow The sorptivity of a given humic acid for HOC was not the same on kaolinite and hematite, suggesting that the orientation and structure of the humic substance on the mineral may affect the surface area of the organic phase and the accessibility of hydrophobic domains that control HOC sorptivity. Sorption isotherms for HOC on the humic-coated mineral substrates were nonlinear, implying that the sorption phenomenon was adsorption onto rather than partitioning into the surface organic phase.