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Sorption of polycyclic aromatic hydrocarbons to minerals and low-organic-carbon aquifer sediments
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The molecular mechanisms and major geochemical factors ics. controlling the sorption of nontoxic organic chemicals (NOC) to mineral surfaces in low-organic-carbon soils and sediments remain unclear. The objectives of this research were to study the influence of exchangeable cations and mineral surface chemistry on the sorption of polycyclic aromatic hydrocarbons (PAH) to minerals, including kaolinite, quartz, hematite, vermiculite, and a low-organic-carbon aquifer sediment. Pyrene was selected as representative PAH. Equilibrium sorption isotherms for a11 minerals and sediment were linear. Results show a strong influence of the mineral type on pyrene sorption, confirming previous studies where surface area could not account for differences in Kd values. Pyrene sorption varied over one order of magnitude for the different minerals. Results show a significant effect of the saturating cation on pyrene's K4 value. Na-saturated minerals sorbed more than the Mg-saturated versions. Quartz and vermiculite showed the highest Kd values for all the cations tested. Cs-and Be-vermiculite sorbed between 3 and 22 times more than other minerals saturated with the same cations. This difference may be caused by specific a-cation bonds formed between the aromatic  electrons in pyrene molecules and exchangeable cations On the mineral surface. Although no quantitative correlation was found between Kd values and cation properties that describe their hardness or softness, some qualitative relationships were evident. Softer cations (e.g., Ba and Cs) promoted pyrene sorption to vermiculite, where the effect could be observed due to the higher cation exchange capacity of this mineral. Pyrene sorption to all minerals, except kaolinite, was highest when Cs saturated the surface. Equilibrium sorption of pyrene to the aquifer sand was the same for peroxide-treated and untreated samples, suggesting that mineral surfaces control pyrene sorption. A composite Kd value was calculated by addition of the distribution coefficients of individual minerals weighted by their contribution to the total surface area. The calculated Kd was the same order of magnitude as the measured value, which is reasonable given the semi-quantitative estimates of mineral composition in the sediment and the possible influence of coatings and particle aggregation on the type and amounts of surfaces available for pyrene sorption.
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Includes bibliographical references (leaves 63-68).
Grimaldi, Gabriel Orlando (1999). Sorption of polycyclic aromatic hydrocarbons to minerals and low-organic-carbon aquifer sediments. Master's thesis, Texas A&M University. Available electronically from
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