The Sorption of Pyrene and Anthracene to Humic Acid-Mineral Complexes: Effect of Fractional Organic Carbon Content
1997
Onken, B. M. | Traina, S. J.
Carbon-normalized distribution coefficients (Kₒc) of organic solutes appear to increase as the amount of organic C in a system decreases. This study was conducted to determine the effect of fractional organic C content (fₒc) on the sorption of anthracene and pyrene. Batch-sorption experiments were conducted on reagent CaCO₃, a geologic calcite, and a montmorillonite to measure anthracene and pyrene sorption. An organic C-free mineral surface and two surface loadings of humic acid (HA) were evaluated. The Kₒc of anthracene and pyrene varied with fₒc as well as with the underlying mineral surface. The sorption of anthracene and pyrene to all HA-mineral complexes increased with increases in fₒc, while Kₒc for the compounds decreased. In higher fₒc systems (>3 × 10⁻⁵), isotherms were C-type curves indicative of partitioning. In lower fₒc systems (<3 × 10⁻⁵), isotherms were commonly L and S-type curves indicative of adsorption and condensation. Sources of potential experimental artifact examined were loss of HA from the mineral surface to solution, dissolution of CaCO₃ during the experiment, and loss of NOS to experimental glassware or volatilization. None were found to contribute to the observations made. Our results suggest that adsorption-condensation of pyrene and anthracene created more surface excess than predicted by partitioning alone as evidenced by the large experimental Kₒc values obtained. B.M. Onken, present address: Dep. of Plant and Soil Sciences, Univ. of Delaware, 149 Townsend Hail, Newark, DE 19717-1303.
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