Model of contaminant transport in porous media in the presence of colloids applied to actinide migration in column experiments

Abstract

Our model considers the contaminants as dissolved in the aqueous phase and sorbed to the sediment or sorbed to mobile and immobile colloids. All sorption processes are assumed to be reversible and are modeled as a kinetic-Langmuir reaction. The Europium Migration ExperimentThe column experiments with •52Eu(II!) in a humic-rich groundwater were performed by Klotz and Lazik [1996]. Batch experiments with the same groundwater sediment system were conducted to determine the s0rption .distribution coefficient Rs More than 98% of europium in the injected solution is bound to colloidal humic particles, and the predominant humic colloid size is in the range from 1 to 100 nm.

Geochemical far-field processes in performance assessments for underground radioactive waste repositories

“…It has been shown that this unretarded fraction is an actinide-humate fraction. Simulations of the nuclide transport show that kinetically controlled processes play an important role in these column experiments [7].…”

“…Breakthrough curves from experiments performed with calcium in humic-rich water exhibit two distinct peaks, one from colloid bound and the other from dissolved calcium [9]. We have carried out some principle studies with the computer code TRAPIC [7] in order to investigate the influence of the interaction processes between dissolved pollutants, colloids and sediment matrix and to understand the experimental results. An example is shown in Fig.…”

Colloid-Facilitated Transport of Radionuclides through the Vadose Zone

“…In a column experiment using sediment from the Hanford Formation, we showed that both ion exchange and colloid-facilitated transport of Cs is important: the main mass of Cs was transported via an ion exchange process in molar NaNO 3 , but a fraction of remaining Cs was eluted with colloidal material at millimolar Na concentration Many contaminants, such as Cs, exhibit xation" behavior, in which at least some fraction of the ion is chemisorbed to sorption sites and not easily subject to ion exchange Other metals may form colloidal polymers, e.g., PuO 2 H 2 O x amorphous or crystalline, such that suspended particles may be mobile where precipitation of immobile solids is predicted or assumed Kim et al, 1985;Kersting et al, 1999 . Complexes with organic matter can result in humic colloids that are transported under favorable conditions of solution composition and water content Klotz et al, 1997;Randall et al, 1994;Warwick et al, 2000;Luhrmann et al, 1998. Contardi et al 2001 show that inclusion of colloids into a conceptual model of contaminant transport can result in a several order of magnitude reduction in the retardation factor for strongly retained ions like Am and Th.…”

Parameter and model sensitivities for colloid‐facilitated radionuclide transport on the field scale

“…Both have been used previously in interpreting laboratory experiments Lührmann and Noseck, 1998;van de Weerd and Leijnse, 1997;Noell et al, 1998. In both cases we simplify the transport problem by neglecting colloid retardation and filtration.…”

“…Van de Weerd and Leijnse [1997] used a nonlinear (Langmuir) kinetic model for all the exchanges between the solution, colloids (mobile as well as immobile), and the porous matrix; their model was used for interpreting americium breakthrough curves in columns with aquifer material and groundwater which contained humic colloids. A Langmuir kinetic sorption model was also used by Lührmann and Noseck [1998] for interpreting breakthrough of europium from porous media columns with humic-rich groundwater. Noell et al [1998] interpreted transport of cesium through glass bead columns with silica colloids using both linear and nonlinear kinetic sorption models for the solution-colloid-porous matrix exchange; a bilinear kinetic sorption model was used as the nonlinear model, similar to the model of Corapcioglu and Jiang [1993].…”