Sorption of trichloroethylene in hydrophobic micropores of dealuminated Y zeolites and natural minerals

Sorption of volatile organic compounds (VOCs) in low organic carbon (< 0.1%) geosorbents is difficult to predict because the sorption capacity of the mineral matrix is poorly understood. This research demonstrates hydrophobic micropores can be important sorption sites for VOCs. We studied the sorption of water and TCE on three dealuminated Y zeolites ranging from hydrophilic (CBV-300) to hydrophobic (CBV-720 and CBV-780), with the surface cation density decreasing from 2.07 to 0.42 and 0.16 sites/nm(2), respectively. Water sorption and dehydration data indicate water affinity of the zeolite micropores decreases with micropore hydrophobicity. TCE sorption on the wet zeolites decreased with increasing surface cation density. At a relative pressure (P/P-0) of 0.136, TCE filled only 0.034% of the micropore volume in wet CBV-300, but 16.9% and 18.6% in wet CBV-720 and CBV-780, respectively. TCE desorption data from dry and wet silica sand (Min-U-Sil 30), kaolinite (KGa-1), and smectite (SWy-1) confirmed VOC sorption in wet microporous minerals is controlled by both the micropore volume and hydrophobicity. Results suggest TCE adsorbs in hydrophobic micropores by displacing loosely bound water, consistent with the theoretical considerations indicating the process of transferring loosely bound water from hydrophobic micropores to the bulk phase is energetically favorable.