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Aging Effects on Cadmium Transport in Undisturbed Contaminated Sandy Soil Columns
Author(s) -
Seuntjens P.,
Tirez K.,
Šimůnek J.,
Genuchten M.Th.,
Cornelis C.,
Geuzens P.
Publication year - 2001
Publication title -
journal of environmental quality
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.888
H-Index - 171
eISSN - 1537-2537
pISSN - 0047-2425
DOI - 10.2134/jeq2001.3031040x
Subject(s) - sorption , soil water , chemistry , retardation factor , cadmium , leaching (pedology) , tracer , environmental chemistry , mass transfer , diffusion , freundlich equation , soil science , geology , thermodynamics , aqueous solution , adsorption , chromatography , physics , organic chemistry , column chromatography , nuclear physics
Limited information is available on the effects of contaminant aging (i.e., the contact time of Cd with the soil) on Cd transport in soils. We conducted displacement experiments in which indigenous Cd and freshly applied Cd were leached simultaneously from undisturbed samples of three Spodosol horizons. Sorption of Cd was described using Freundlich isotherms, whereas transport was described as a convection–dispersion process. Parameter optimization analysis using a mobile–immobile transport model applied to nonsorbing tracer displacement data showed that 16 to 22% of the water in the columns was immobile. The low dimensionless mass transfer coefficients in the mobile–immobile model were indicative of diffusion‐limited transfer between mobile and immobile water, and hence physical nonequilibrium. A two‐site kinetic sorption model could be fitted closely to breakthrough curves of the non‐aged Cd for three soil horizons. No conclusive evidence was found that contaminant aging in soil affects cadmium transport. On the one hand, predictions of aged Cd leaching, using parameters estimated from displacement experiments with non‐aged Cd, differed from those for the aged Cd in the E horizon. On the other hand, no meaningful differences in transport behavior between aged and non‐aged Cd were found for the humus Bh and Bh/C horizons. The two‐site kinetic rate coefficient α c was found to depend on water flux, further indicating that mass transfer between sorption sites and the liquid is limited by diffusion rather than by kinetic sorption.