Journal ArticleDOI
Validity of the local equilibrium assumption for modeling sorbing solute transport through homogeneous soils
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TLDR
In this article, a method is described whereby formulas for solute breakthrough curve time moments can be determined without knowledge of the nalytical solution to the mass transport model, and criteria for local equilibrium to be valid are derived by comparing the time moment formulas for the nonequilibrium and equilibrium models.Abstract:
Sorption processes that occur during reactive solute movement through porous media can be modeled using either an equilibrium or kinetic approach. Because of the resulting conceptual and mathematical simplification, many transport models assume local chemical equilibrium is valid for describing sorption reactions. This paper presents quantitative criteria to assess the validity of the local equilibrium assumption for one-dimensional, steady flow through homogeneous soils. A method is described whereby formulas for solute breakthrough curve time moments can be determined without knowledge of the nalytical solution to the mass transport model. This method is applied to several commonly used nonequilibrium formulations as well as the standard linear equilibrium model. The formulations considered include both the physical nonequilibrium models where the sorption rate is controlled by diffusive solute transfer between mobile and stagnant fluid zones and the chemical nonequilibrium models where the overall sorption rate is governed by the rate of reaction at the soil-solution interfaces. Criteria for local equilibrium to be valid are derived by comparing the time moment formulas for the nonequilibrium and equilibrium models. These criteria explicitly show that basic system parameters (e.g., seepage velocity, dispersion coefficient, distribution coefficient, sorption rate, boundary conditions) have a significant influence on the attainment of local equilibrium.read more
Citations
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Sorption isotherms: A review on physical bases, modeling and measurement
G. Limousin,Jean-Paul Gaudet,Laurent Charlet,Stéphanie Szenknect,Véronique Barthès,Mohamed Krimissa +5 more
TL;DR: In this article, the authors present the physical bases underlying the definition of a sorption isotherm, different empirical or mechanistic models, and details several experimental methods to acquire a sink.
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Multiple‐Rate Mass Transfer for Modeling Diffusion and Surface Reactions in Media with Pore‐Scale Heterogeneity
Roy Haggerty,Steven M. Gorelick +1 more
TL;DR: In this paper, a multirate model is proposed to model small-scale variation in rates and types of mass transfer by using a series of first-order equations to represent each of the mass transfer processes.
Journal ArticleDOI
A review of immiscible fluids in the subsurface: properties, models, characterization and remediation
James W. Mercer,Robert M. Cohen +1 more
TL;DR: In the past few years, as hazardous waste sites have been studied more often and in more detail, immiscible fluids have been encountered in the subsurface with greater frequency as discussed by the authors.
Journal ArticleDOI
Sorption nonideality during organic contaminant transport in porous media
TL;DR: In this paper, the relative importance of these factors is scale-dependent and their relative impact on contaminant transport is evaluated for hydrophobic organic compounds, physical nonequilibrium (i.e., rate-limited mass transfer in aggregated or layered systems) and intraorganic matter diffusion (rate-limited diffusion within the sorbent organic matter matrix) are probably the predominant factors causing nonideality.
Journal ArticleDOI
Water flow and solute transport processes in the unsaturated zone
TL;DR: A review of the current conceptual understanding of the basic processes of water flow and chemical transport in the untsaturated (vadose) zone and of various deterministic mathematical models that are being used to describe these processes can be found in this article.
References
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Journal ArticleDOI
Mass transfer studies in sorbing porous media. I. Analytical solutions
TL;DR: An analytical solution for the movement of chemicals through a sorbing porous medium with lateral or intra-aggregate diffusion is presented in this paper, where the liquid phase in the porous medium is divided into mobile and immobile regions.
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Dead-End Pore Volume and Dispersion in Porous Media
Keith H. Coats,B.D. Smith +1 more
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Numerical Inversion of Laplace Transforms: An Efficient Improvement to Dubner and Abate's Method
TL;DR: An accurate method is presented for the numerical inversion of Laplace transform, which is a natural continuation to Dubner and Abate's method, and the error bound on the inverse f{t) becomes independent of t, instead of being exponential in t.
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On the physical meaning of the dispersion equation and its solutions for different initial and boundary conditions
TL;DR: In this article, it is shown that similarly to the movement in capillaries, also in other dispersive systems, the distinction between the concentration of solute in res is also made by known and new transformations.