Contaminant transformation rates in the subsurface can be slowed by sorption onto geosorbents. We evaluated the effect of micropore sorption on contaminant transformation in a model system consisting of dealuminated Y zeolites and 2,2-dichloropropane (2,2-DCP). 2,2-DCP dehydrochlorinates in water to 2-chloropropene (2-CP) at a rate of 2.93 × 10{sup}(-4) min{sup}(-1) at 24℃. The Y zeolites used range from hydrophilic (CBV-300) to hydrophobic (CBV-720 and CBV-780). Wet zeolite samples were loaded with 2,2-DCP at 24℃ and reacted at 50℃ for 10 h. Results show that the hydrophobic zeolites (CBV-720 and CBV-780) sorbed nearly 900 times more 2,2-DCP than the hydrophilic CBV-300 under wet conditions. 2,2-DCP transformed less when sorbed in micropores of CBV-720 (6.3) and CBV-780 (5.0) than in micropores of CBV-300 (81.5), and significantly less than in water (>99.85). Inhibition in hydrophobic micropores is interpreted as lack of water solvating the transition state of 2,2-DCP dehydrohalogenation and the H{sup}+ and Cl{sup}- formed. Near the micropore openings, the transformation was relatively fast, consistent with greater abundance of water associated with the hydrophilic edge sites. These results indicate that in the subsurface the half-lives of reactive organic contaminants may be longer than predicted from bulk water data.
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