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Diffusion of Strontium and Chloride in Compacted Clay‐based Materials
Author(s) -
Robin M. J. L.,
Gillham R. W.,
Oscarson D. W.
Publication year - 1987
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj1987.03615995005100050002x
Subject(s) - diffusion , ionic strength , strontium , chemistry , tortuosity , analytical chemistry (journal) , water content , bentonite , ionic bonding , bulk density , mineralogy , ion , nuclear chemistry , soil water , porosity , thermodynamics , soil science , environmental chemistry , geology , aqueous solution , geotechnical engineering , organic chemistry , physics
This study examines the effect of pore solution composition and temperature on the measured and calculated diffusion coefficients ( D m and D c , respectively) for Sr 2+ in a compacted mixture of bentonite (50 wt%) and sand. D m for Sr 2+ and Cl ‐ in the soil was determined at a dry bulk density of ∼1.7 Mg m −3 using deionized water (DW) and two synthetic groundwater solutions (SGW) with ionic strengths of 0.27 and 1.4 mol L −1 to saturate the soil, and at 25, 60, and 90°C. The D c for Sr 2+ was calculated from D c = D o τ/(1 + ρ b K d /θ v ), where D o is the diffusion coefficient of Sr 2+ in free solution; τ is a tortuosity factor, obtained for the compacted soil from Cl ‐ diffusion experiments; ρ b is the dry bulk density; θ v is the volumetric moisture content; and K d is a distribution coefficient that accounts for the interaction of Sr 2+ with the soil. Both D m and D c for Sr 2+ increased with an increase in the ionic strength of the saturating solutions and with an increase in temperature. The D m values were, however, always greater than D c values by a factor of 6.2 to 8.0 for DW and 1.3 to 1.8 for the SGW with an ionic strength of 1.4 mol L −1 . This difference is believed to be the result of obtaining K d values in solutions that differed significantly from the pore solution of the compacted soil. Nevertheless, the results indicate that D c values, which are often more convenient and less time‐consuming to obtain than D m values, can at least be used to establish relationships and trends between the diffusion rates of some contaminants in clay‐based materials and the properties of these materials.