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Comparison of Naphthalene Diffusion and Nonequilibrium Adsorption-Desorption Experiments

^a Environment and Resources, Technical University of Denmark DK-2800 Kgs. Lyngby, Denmark
^b Dep. of Environmental Engineering, Aalborg University, DK-9000 Aalborg, Denmark
^c Soils and Biogeochemistry, Dep. of Land, Air and Water Resources, Univ. of California, Davis, CA 95616
^d Graduate School of Science and Engineering, Saitama University, 255 Shimo-okubo, Saitama, 338-8570 Japan

View larger version (26K): [in a new window]   Fig. 1. Relative gas diffusivity data for repacked Hiroshima, Yolo, Lerbjerg 5, Lundgaard, and Forbes soils. data from present study (Freon 12), data from Moldrup et al. (2000) (O2).

View larger version (27K): [in a new window]   Fig. 2. Measured adsorption-desorption isotherms on either a short-term (closed symbols, 48-h adsorption and 48-h desorption step) or a longer-term (open symbols, 504-h adsorption and 48-h desorption step) basis. Best-fit Freundlich isotherms (Eq. [6]) for adsorption-desorption isotherms are shown as solid lines. data from present study, data from Gamst et al. (2001) measured under similar conditions and time scales.

View larger version (23K): [in a new window]   Fig. 3. Degree of nonsingularity, (Eq. [8]), of the measured naphthalene adsorption-desorption isotherms as a function of the adsorption isotherm nonlinearity, n'A. Open symbols represent short-term (48-h adsorption and 48-h desorption step) and closed symbols longer-term (504-h adsorption and 48-h desorption step) experiments. The broken line at = 100% defines whether the soil is a Type I or II soils (Gamst et al., 2001). data from present study, data from Gamst et al. (2001), data from Yuan and Xing (2001).

View larger version (29K): [in a new window]   Fig. 4. Examples of measured concentration versus distance profiles for naphthalene diffusion at either high initial concentration (Ch, open symbols) or low initial concentration (Cl, closed symbols) at selected contact times (equilibrium time + incubation time) in (a) Hiroshima ( 0.13 m3 m-3, t = 722 h), (b) Yolo ( 0.18 m3 m-3, t = 504 h) (c) Lerbjerg 5 ( 0.24 m3 m-3, t = 386 h), (d) Lundgaard ( 0.07 m3 m-3, t = 143 h) and (e) Forbes ( 0.21 m3 m-3, t = 2448 h). The lines are model fit (Eq. [5]) to measured data to obtain the Deff value.

View larger version (22K): [in a new window]   Fig. 5. Concentration versus distance profile for naphthalene diffusion in Hiroshima soil ( 0.13 m3 m-3, contact time = 722 h). The solid line represents best fit to data in the desorption half-cell and the broken line represents best fit to data in the adsorption half-cell.

View larger version (20K): [in a new window]   Fig. 6. Apparent KD–values obtained in either the whole cell (closed symbols), the desorption half-cell (open symbols) or in the adsorption half-cell (dotted open symbols) for Hiroshima, Yolo, and Lerbjerg 5 as a function of contact time in the diffusion experiments. Part of the data for Lerbjerg 5 are from Olesen et al. (2001).

View larger version (31K): [in a new window]   Fig. 7. Obtained Deff–values in either the whole cell, the source (desorption) half-cell or in the recipient (adsorption) half-cell for (a) Hiroshima (t = 1200 h, except for tshort equilibrium = 840 h, (b) Yolo (t = 816 h), (c) Lerbjerg 5 (t = 672 h) and (d) Lundgaard (t = 456 h, except for tshort incubation = 384 h), shown as a function of water content. Also shown is the Deff values estimated from the batch adsorption (broken line) or desorption (solid line) using Freundlich isotherm parameters (Table 4) and the best-fit longer-term linear isotherm (KD) (dotted line).

View larger version (20K): [in a new window]   Fig. 8. (a) Half-cells nonsingularity, H (Eq. [9]), as a function of batch nonsingularity, (Eq. [8]), the broken line is the linear correlation and the dotted line is the linear correlation forced through (1.0, 1.0) and (b) Half-cells nonsingularity, H, as a function of adsorption isotherm nonlinearity, n'A, the broken line is the linear correlation and the dotted line is the linear correlation forced through (1.0, 1.0). Error bars represent standard deviation.