Tracer diffusion coefficients in sedimentary rocks: correlation to porosity and hydraulic conductivity.
Matrix diffusion is an important transport process in geologic materials of low hydraulic conductivity. For predicting the fate and transport of contaminants, a detailed understanding of the diffusion processes in natural porous media is essential. In this study, diffusive tracer transport (iodide) was investigated in a variety of geologically different limestone and sandstone rocks. Porosity, structural and mineralogical composition, hydraulic conductivity, and other rock properties were determined. The effective diffusion coefficients were measured using the time-lag method. The results of the diffusion experiments indicate that there is a close relationship between total porosity and the effective diffusion coefficient of a rock (analogous to Archie's Law). Consequently, the tortousity factor can be expressed as a function of total porosity. The relationship fits best for thicker samples (> 1.0 cm) with high porosities (> 20%), because of the reduced influence of heterogeneity in larger samples. In general, these correlations appear to be a simple way to determine tortuosity and the effective diffusion coefficient from easy to determine rock porosity values.
Boving
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Department of Geosciences, University of Rhode Island, Kingston 02881, USA. boving@uri.edu
Grathwohl
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D004058:Diffusion; D055593:Geological Phenomena; D005844:Geology; D008962:Models, Theoretical; D016062:Porosity; D012989:Soil Pollutants; D014873:Water Pollutants
D012989:Soil Pollutants; D014873:Water Pollutants