Physical factors affecting the transport and fate of colloids in saturated porous media

Abstract

Saturated soil column experiments were conducted to explore the influence of colloid size and soil grain size distribution characteristics on the transport and fate of colloid particles in saturated porous media. Stable monodispersed colloids and porous media that are negatively charged were employed in these studies. Effluent colloid concentration curves and the final spatial distribution of retained colloids by the porous media were found to be highly dependent on the colloid size and soil grain size distribution. Relative peak effluent concentrations decreased and surface mass removal by the soil increased when the colloid size increased and the soil median grain size decreased. These observations were attributed to increased straining of the colloids; i.e., blocked pores act as dead ends for the colloids. When the colloid size is small relative to the soil pore sizes, straining becomes a less significant mechanism of colloid removal and attachment becomes more important. Mathematical modeling of the colloid transport experiments using traditional colloid attachment theory was conducted to highlight differences in colloid attachment and straining behavior and to identify parameter ranges that are applicable for attachment models. Simulated colloid effluent curves using fitted first‐order attachment and detachment parameters were able to describe much of the effluent concentration data. The model was, however, less adequate at describing systems which exhibited a gradual approach to the peak effluent concentration and the spatial distribution of colloids when significant mass was retained in the soil. Current colloid filtration theory did not adequately predict the fitted first‐order attachment coefficients, presumably due to straining in these systems.

Fracture Characterization in Enhanced Geothermal Systems by Wellbore and Reservoir Analysis

“…These processes affecting particle transport are the same as those that influence solute transport, i.e., advection, diffusion, dispersion, and adsorption (Bradford et al, 2002). Particle motion along fluid streamlines is advection.…”

“…Diffusion of particles into porous media can result in more contact with the grains (Tufenkji and Elimelech, 2004). Bradford et al (2002) suggested that smaller particles are primarily removed by diffusive transport, while larger ones are removed by interception and sedimentation.…”

“…Adsorption processes, which are commonly referred to as attachment through interactions (chemisorbed or physisorbed) leading to a filtration effect, are assumed to be the main processes that limit particle transport. Particle attachment is the removal of particles from solution by collision with and deposition onto a pore or fracture surface (Bradford et al, 2002). Particle removal by physical mechanisms includes Brownian diffusion, interception, and gravitational sedimentation.…”

Mobilization and Leaching of Natural and Water Dispersible Colloids in Aggregated Volcanic Ash Soil Columns

“…Colloid attachment occurs due to the net interaction (i.e., summation of van der Waals forces and electrostatic double-layer forces) between colloidal and grain surfaces (DeNovio et al, 2004). Colloid straining, on the other hand, is the entrapment of colloids in pore throats and at grain-grain junctions which are too small to allow particle passage (Bradford et al, 2002).…”

Local position of colloid clusters in a packed bed of spheres

“…Their results indicate a distinction between irreversible deposited contact retardation and a reversible surface retardation with subsequent reentrainment after attachment. Straining due to trapping in the pore throats is another effect of particle retention; however this is not included in colloid attachment theory [22]. Although straining is obviously an important effect in quantitative filtration theory, it is not necessary to regard this effect for the investigation concerning the local deposition rate on a model sphere, where the particle position due to straining occurs everywhere on the model sphere with the same probability.…”