Sorption studies for evaluating the effects of thermally altered carbonaceous matter on fate and transport of chlorinated volatile organic compounds
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The sorption effects of thermally altered carbonaceous matter (TACM) in subsurface sediments were investigated for chlorofluorocarbons (CFC: CFC-11, CFC-12, and CFC-113) using laboratory batch techniques. The purpose of this research was to determine the CFC sorption properties and mechanisms to TACM (e.g., black carbon and kerogen) and to link these to sorption behavior in surficial sedimentary environments. For the surficial sediments, aquifer and aquitard sediments deposited in late Quaternary were obtained from two different sedimentary basins containing kerogen-rich shale formation as potential TACM source rock. The TACM in these young sediments were little affected by weathering processes compared to the TACM in old sediments. Wood char, kerogen-rich shales, and kerogen-containing surficial sediments exhibited nonlinear sorption behavior for the CFCs with ∼10–1000 times greater C -normalized partition coefficients ( K oc ) than the reference K oc at low concentrations relative to compound solubilities ( C w /S ). Adsorption based on pore-filling mechanism characterized the observed CFC sorption to the wood char, while heterogeneous kerogen in the shales and surficial sediments showed both of partitioning and adsorption behavior. Predominant composition of the kerogen was unstructured carbonaceous matter (CM) with minor fraction of condensed CM. It is believed that the observed dual-mode sorption behavior reflects the kerogen composition. Adsorption component of the dual-mode sorption dominantly contributed to overall CFC sorption at low relative concentrations, C w /S <∼10 −2 . The estimated retardation factors for the kerogen-containing aquifer sediment increased 2–7 times more than the retardation determined by partitioning only. Solubility-normalized sorption isotherms are coincident for each of the kerogen-containing subsurface sediment with three CFCs. The CFC isotherms were quite consistent with sorption isotherms for other similar hydrophobic chlorinated contaminants at C w /S ∼10 −5 –10 −1 .