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Diffusion of Sorbing Organic Chemicals in the Liquid and Gaseous Phases of Repacked Soil

^a Dept. of Environmental Engineering, Aalborg Univ., Sohngaardsholmsvej 57, DK-9000 Aalborg, Denmark
^b Dep. of Social and Environmental Engineering, Graduate School of Engineering, Hiroshima Univ., 1-4-1 Kagamiyama, Higashi-Hiroshima, 739, Japan
^c Soils and Biogeochemistry, Dep. of Land, Air and Water Resources, Univ. of California, Davis, CA 95616

View larger version (24K): [in a new window]   Fig. 1. Measured freon-12, TCE, and toluene effective diffusion coefficients in Yolo loam, compared with predictions by the WLR model, Eq. [1], in combination with retardation factors calculated from Eq. [7]. For freon-12 Rg = Rl = 1. Data from Petersen et al. (1994).

View larger version (28K): [in a new window]   Fig. 2. Comparison of measured lindane effective diffusion in Gila silt loam and predictions by the two-phase diffusion and two-component equilibrium sorption (DATES) model. The influence of the separate diffusion and sorption processes on Deff is illustrated. Data from Ehlers et al. (1969). (a) 20°C; (b) 30°C.

View larger version (23K): [in a new window]   Fig. 3. Measured and predicted diffusivities for nonsorbing tracers (O2 and Cl) in Lerbjerg sandy clay (L5).

View larger version (26K): [in a new window]   Fig. 4. Examples of measured concentration versus distance profiles for naphthalene diffusion at different soil-water contents () and incubation times (t). The solid lines are model fit to measured data to obtain the Deff value, while the dotted lines represent model predictions using measured gas and solute diffusivities (Fig. 3) and adsorption KD (equal to 9.5 cm3 g-1).

View larger version (24K): [in a new window]   Fig. 5. Twenty-one day naphthalene adsorption isotherm for Lerbjerg sandy clay (L5) and subsequent 2 d desorption steps. The adsorption is approximated by a linear isotherm . A linear isotherm is plotted for the first and the last desorption step corresponding to an apparent KD value between 13 cm3 g-1 and 93 cm3 g-1 for contact times (adsorption plus desorption time) between 552 and 1080 h.

View larger version (24K): [in a new window]   Fig. 6. Apparent KD value as a function of contact time (equilibration plus incubation time) for the column diffusion experiments. Only experiments in the Henry range are included ( > 0.17 cm3 cm-3). For comparison, apparent KD values from the desorption batch experiments (contact time equals adsorption plus desorption time) are shown.

View larger version (34K): [in a new window]   Fig. 7. Effects of apparent KD on DATES predicted effective diffusion coefficients for naphthalene in Lerbjerg sandy clay(L5). The influence of each diffusion and sorption process on Deff is illustrated.