The influence of mass transfer on solute transport in column experiments with an aggregated soil |
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Authors: | Paul V. Roberts Mark N. Goltz R. Scott Summers John C. Crittenden Peter Nkedi-Kizza |
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Affiliation: | 1. School of Sciences, Zhejiang Agriculture and Forestry University, Lin’an, Zhejiang 311300, PR China;2. Zhejiang Provincial Key Laboratory of Chemical Utilization of Forestry Biomass, Zhejiang A & F University, Lin’an, Zhejiang 311300, PR China;1. Department of Mathematics, Xi’an Polytechnic University, Xi’an, Shaanxi 710048, China;2. Departamento de Análise Matemática, Estatística e Optimización, Facultad de Matemáticas, Universidad de Santiago de Compostela, Santiago de Compostela 15782, Spain;1. Departamento de Matemáticas, Universidad de Cádiz, Campus de Puerto Real, 11510 Cádiz, Spain;2. Dipartimento di Matematica e Informatica, Università di Catania, Viale A. Doria 6, Catania 95125, Italy;1. Institute for Problems in Mechanics, Russian Academy of Sciences, 101 Vernadsky Avenue, Bldg 1, Moscow 119526, Russia;2. Bauman Moscow State Technical University, 5 Second Baumanskaya Street, Moscow 105005, Russia;3. National Research Nuclear University MEPhI, 31 Kashirskoe Shosse, Moscow 115409, Russia;4. Cardiff University, Heath Park, Cardiff CF14 4XY, UK |
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Abstract: | The spreading of concentration fronts in dynamic column experiments conducted with a porous, aggregated soil is analyzed by means of a previously documented transport model (DFPSDM) that accounts for longitudinal dispersion, external mass transfer in the boundary layer surrounding the aggregate particles, and diffusion in the intra-aggregate pores. The data are drawn from a previous report on the transport of tritiated water, chloride, and calcium ion in a column filled with Ione soil having an average aggregate particle diameter of 0.34 cm, at pore water velocities from 3 to 143 cm/h. The parameters for dispersion, external mass transfer, and internal diffusion were predicted for the experimental conditions by means of generalized correlations, independent of the column data. The predicted degree of solute front-spreading agreed well with the experimental observations. Consistent with the aggregate porosity of 45%, the tortuosity factor for internal pore diffusion was approximately equal to 2. Quantitative criteria for the spreading influence of the three mechanisms are evaluated with respect to the column data. Hydrodynamic dispersion is thought to have governed the front shape in the experiments at low velocity, and internal pore diffusion is believed to have dominated at high velocity; the external mass transfer resistance played a minor role under all conditions. A transport model such as DFPSDM is useful for interpreting column data with regard to the mechanisms controlling concentration front dynamics, but care must be exercised to avoid confounding the effects of the relevant processes. |
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