Literature Review and Model (COMET) for Colloid/Metals Transport in Porous Media

Abstract

This paper summarizes topics related to colloid transport in subsurface media. The ultimate objective of the paper is to present a model that can be used to evaluate the significance of colloid facilitated transport on the mobility of metals. Field and laboratory studies are first reviewed to evaluate evidence that colloids are transported in subsurface media. Second, researchers active in the field are contacted to identify areas of ongoing research, and to solicit opinions concerning the level of understanding of mechanisms that control colloid migration. Third, the literature on colloid transport mechanisms is reviewed, with particular emphasis on colloid (and particle) filtration and on colloid stability as influenced by electrical repulsion and Van der Waals attraction. Fourth, a conceptual colloids‐metal transport model (COMET) is developed and incorporated into EPA's CML model, a model that simulates solute migration from a landfill in the unsaturated zone to a receptor (i.e., drinking‐water well) in the saturated zone. Among the major features of the COMET model are the capability to simulate multiple metal species either dissolved or adsorbed to mobile colloids (in conjunction with results from a geochemical equilibrium model), the capability to simulate the influence of multiple colloid types, and to adjust source concentration and duration in the presence of colloids that migrate from a source. These capabilities are embodied in equations (2) and (3) in the main text of this paper. As expected, results from the COMET simulations indicate that mobile phase metal concentrations (dissolved concentration plus concentration adsorbed to mobile colloids) increase as colloid concentrations increase, and arrival times of soluble metal species (solutes) to stationary receptors decrease. When the partition coefficients for solute‐colloid adsorption and solute‐soil matrix adsorption are the same, neither the increase in mobile phase concentration nor decrease in travel time is always significant. However, when partition coefficients for solute‐colloid adsorption are greater than partition coefficients for solute‐soil matrix adsorption, travel times to stationary receptors can dramatically decrease and total mobile phase concentrations dramatically increase.

Review on subsurface colloids and colloid-associated contaminant transport in saturated porous media

“…Majority of the studies concerning the development of mathematical models to describe the colloid-facilitated transport of contaminants have been carried out by various researchers during the past ten years [1,2,17,42,137,153,169,176,177,189,202,203]. Most of these studies have assumed equilibrium interactions between the colloidal particles and the contaminant in the dissolved phase [176,189,202,203] and analogous to model developed by Corapcioglu and Jiang [177].…”

“…Most of these studies have assumed equilibrium interactions between the colloidal particles and the contaminant in the dissolved phase [176,189,202,203] and analogous to model developed by Corapcioglu and Jiang [177]. These models predict a reduction of the effective retardation arising out of sorption on to the solid matrix depending on the concentration of the colloidal fines and the partition coefficient for contaminant sorption on the colloidal fines.…”

Geochemical factors affecting radionuclide transport through near and far fields at a Low-Level Waste Disposal Site

“…The third step in this experimentation involves sorbing radionuclides to colloids (precipitating or adsorbiig radionuclides to the QOO-nm fraction of site-specific sediment or radionuclide homogeneous precipitates), introducing them to unsaturated Hanford sediment packed in columns, and then determining the activity of the radionuclides in ultrafiltered effluent. The results of these experiments can be modelled by a number of already existing codes (Bengtsson et al 1987, Mills et al 1991 Smith and Degueldre 1993). As is the case in many fields of science, empirical modeling of three-phase solute transport is more advanced than the understanding of the phenomena.…”

Simulation des transferts réactifs multi-constituants au sein des lits d’infiltration percolation – évaluation des capacités d’oxygénation

“…Du fait de la complexité de la représentation du biofilm (modèles de Monod, des Micro-colonies et du Biofilm) et des interactions physico-chimiques, la majorité des problèmes traités sont unidimentionnels. Quelques modèles numériques bidimensionnels (RIFAI et al, 1988;ODENCRANTZ, 1992;MILLS et al, 1991) et tridimensionnels (SLEEP et SYKES, 1993;ZHENG, 1993) ont toutefois été développés. Optant pour une simplicité dans l'approche modélisatrice qui n'enlève rien à une exploitation efficiente des résultats, le problème étudié ici est unidimensionnel.…”