Release and transport of colloidal particles in natural porous media: 1. Modeling (original) (raw)
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Water Resources Research, 2001
We present an extensive experimental data set of particle release from natural porous media saturated with monovalent cations. The generation process of mobile colloidal particles is studied by means of leaching of saturated laboratory columns packed with a noncalcareous soil material with various monovalent electrolytes and by analyzing the colloids in the effluent over typically 1000 pore volumes. The concentration of released particles cannot be modeled with simple first-order kinetics but can be rationalized in terms of a distribution of release rate coefficients k. The experimentally observed effluent concentration often decays with time as a power law c cr t-(s+ 1) for long times, suggesting a distribution of release rate coefficients p(k) cr k •-1 for small k. The observed values of exponent a range between 0.01 and 0.8. The composition of the pore water is found to have a profound influence on the particle release characteristics. With decreasing salt concentration the rate for particle release increases. Anionic organic and inorganic ligands have a major effect on the release process. For the ligands studied, the amount of released particles decreases in the sequence malonate, chloride, phtalate, and azide.
Long-Term Release Kinetics of Colloidal Particles from Natural Porous Media
Environmental Science & Technology, 1999
Release of colloidal particles from natural porous media saturated with monovalent cations is studied with saturated laboratory column experiments packed with a noncalcareous soil material. The column outflow was monitored over 1000 pore volumes. The composition of released particles remains constant over the course of the experiment. The major finding of the present study is that the release process cannot be modeled with simple first-order kinetics, but the effluent concentration decays in a nonexponential fashion. The experimentally observed effluent concentration decays as t-(1+R) where the exponent R typically has values between of 0.01 and 0.3. Such a powerlaw decay can be rationalized in terms of an exponential distribution of the activation energies of release rate coefficients, and the exponent R turns out to be inversely proportional to the average activation energy. We observe a strong dependence of the release on the ionic strength, which can be interpreted as a systematic increase of the average activation energy for particle release with increasing ionic strength. In the present system pH was accurately controlled, and the release pattern was surprisingly insensitive to pH variations.
Release of colloidal particles in natural porous media by monovalent and divalent cations
Journal of Contaminant Hydrology, 2006
We study mobilization of colloidal particles from natural porous media, such as soils and groundwater aquifers. Extensive laboratory scale column experiments of particle release from four different subsurface materials are presented. The important characteristics of the release process are (i) its non-exponential kinetics, (ii) the finite supply of colloidal particles and (iii) the strong dependence of the release kinetic on the nature of the adsorbed cations. Particle release depends most sensitively on the relative saturation of the medium with divalent cations. We propose a mathematic model, which captures all these aspects quantitatively, and can be used to describe the coupling between transport of major cations and the release of colloidal particles. The present experimental investigations as well as the developed modeling framework represent an important step towards the understanding of colloid-facilitated transport phenomena in natural porous media.
Colloid release and transport processes in natural and model porous media
Colloids and Surfaces A-physicochemical and Engineering Aspects, 1996
Colloid release was observed from packed columns for two natural porous media (sands) and one model system (glass beads with deposited latex colloids). Colloid release was found to occur in all cases when the ionic strength was reduced in columns that were in equilibrium with Na+ ions. Most of the released colloids from the natural porous media were smaller than
Aggregation and deposition kinetics of mobile colloidal particles in natural porous media
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2001
A novel method for assessing the deposition kinetics of colloidal particles in natural porous media is presented. The method is applied for studying the deposition kinetics of in situ mobilized colloidal particles in a non-calcareous soil in mixed electrolytes containing sodium and calcium as counter ions. Particle deposition rate constants were measured by combining deposition experiments in packed columns and aggregation measurements by dynamic light scattering. The relative deposition and aggregation rate constants follow very similar trends, featuring fast (favorable) and slow (unfavorable) regimes at high and low salt concentrations, respectively. These regimes are separated by the critical coagulation or deposition concentrations (CCC or CDC, respectively), which sensitively depend on the type of counterion. In systems containing a single electrolyte, the CCC and CDC follow the classical Schulze-Hardy rule. In mixed sodium-calcium electrolytes, a gradual transition of the CCC and CDC between the values obtained for the corresponding pure (single) electrolyte systems is observed. The present approach provides a facile route for assessing deposition rates of mobile colloidal particles in natural porous media.
Environmental Science & Technology, 2013
The prediction of colloid transport in unsaturated porous media in the presence of large energy barrier is hampered by scant information of the proportional retention by straining and attractive interactions at surface energy minima. This study aims to fill this gap by performing saturated and unsaturated column experiments in which colloid pulses were added at various ionic strengths (ISs) from 0.1 to 50 mM. Subsequent flushing with deionized water released colloids held at the secondary minimum. Next, destruction of the column freed colloids held by straining. Colloids not recovered at the end of the experiment were quantified as retained at the primary minimum. Results showed that net colloid retention increased with IS and was independent of saturation degree under identical IS and Darcian velocity. Attachment rates were greater in unsaturated columns, despite an over 3-fold increase in pore water velocity relative to saturated columns, because additional retention at the readily available air-associated interfaces (e.g., the air−water− solid [AWS] interfaces) is highly efficient. Complementary visual data showed heavy retention at the AWS interfaces. Retention by secondary minima ranged between 8% and 46% as IS increased, and was greater for saturated conditions. Straining accounted for an average of 57% of the retained colloids with insignificant differences among the treatments. Finally, retention by primary minima ranged between 14% and 35% with increasing IS, and was greater for unsaturated conditions due to capillary pinning. ■ INTRODUCTION Colloidal transport in porous media has gained notable attention over the past few decades as facilitated contaminant transport in groundwater aquifers, reduced permeability of oil and gas reservoirs, and in situ remediation strategies have become topics of concern in various fields. 1,2 A large body of experimental and theoretical work has been carried out to understand key physicochemical factors affecting colloid transport and deposition in natural porous media. Solution composition has been extensively investigated with particular emphasis on ionic strength (IS) 3−5 and pH 5−8 for affecting electrostatic interactions, natural organic matter, 5,8 and surfactants as electrosteric stabilizers, and cation valence 8 in terms of neutralizing surface charge. Each of these factors affects surface interactions between colloids and between colloids and the porous medium's surface. In addition, unsaturated conditions significantly increase colloid retention by the presence of a gas phase, which restricts the geometry of the fluid phase and partitions deposited colloids toward interfaces that are absent in fully saturated media (e.g., air− water and air−water−solid interfaces). 9−15 Flow rate affects low-flow or flow-stagnation zones where colloids can become trapped. 3,15 Moreover, high flow velocities have been related to increased applied torque from strong hydrodynamic drag forces
Transport of in Situ Mobilized Colloidal Particles in Packed Soil Columns
Environmental Science & Technology, 1998
A systematic investigation of the transport behavior of in situ mobilized soil colloidal particles in their parent soil matrix medium is presented. Particle advection, dispersion, and deposition kinetics were studied by analysis of particle breakthrough curves as a response to short-pulse particle injections to the inlet of packed soil columns. The transport of the heterogeneous soil particles was compared to the transport of monodisperse carboxyl latex particles to further understand the various particle transport mechanisms. Results show that colloidal particles travel much faster than a conservative tracer (nitrate) due to size exclusion effects, whereby mobile colloidal particles are excluded from small pores within the soil medium. Dispersivity of the natural and latex particles was compared to that of the conservative tracer, and the results indicate that particle dispersivity is greater than the tracer dispersivity. Dispersivity of colloidal particles was shown to be essentially independent of pore water velocity, whereas tracer dispersivity increased with increasing pore water velocity due to a combination of convective and diffusive transport of tracer molecules in small pores within the soil aggregates. The effect of divalent counterions on particle deposition kinetics was also investigated by comparing the results to deposition kinetics with monovalent counterions. Particle deposition rate with Ca 2+ was shown to be higher than with Na + , and the critical deposition concentrations with Na + were greater than those with Ca 2+ . In contrast to the marked effect of ionic strength and divalent cations, changes in proton activity over more than 1 order of magnitude (from pH 4.0 to 5.5) did not have a significant effect on particle deposition kinetics. Quantitative analysis of the observed particle transport results demonstrates that the transport of the natural colloidal particles in the packed soil columns can be adequately described by the advection-dispersion equation with a first-order, irreversible deposition kinetics term.
A Model System to Study the Precipitation and Migration of Colloidal Particles in Porous Media
Journal of Colloid and Interface Science, 1996
these fines lead to severe changes in the permeability of Studies on the formation and migration of colloidal iron sulfide the porous rock that result in a decline of the overall oil in porous media were carried out using consolidated artificial aluproduction. In the petroleum industry this phenomena is mina-kaolin cores sintered at 1500ЊC. The artificial aluminacalled ''formation damage'' (2). kaolin cores were imbibed with a solution containing thioacetam-Despite its importance, there are few studies on the formaide and ferrous ions and heated at 80ЊC to obtain the formation tion and migration of colloidal particles in porous media. of FeS particles. Scanning electron micrographs showed particles Matijevic and co-workers have studied the adhesion of partiless than 1 mm in diameter and aggregates of different sizes covcles to macroscopic flat surfaces and the mechanisms inering the surface of the porous media. Core flooding experiments volved in their removal or mobilization (3, 4). Their results, showed that the migration of the fine FeS particles reduced the permeability of core and the injection of surfactant solutions at however, do not apply to porous rocks. The migration of constant salinity restored the original permeability after the profines in porous media has received attention due, mainly, to duction of the redispersed iron sulfide particles, in some cases. its importance in oil production (5). In most of the studies, ᭧ 1996 Academic Press, Inc. porous rocks, like Berea sandstone (6, 7), already containing particles have been used and the results are usually interpreted in terms of colloidal forces, assuming a particular composition for both the porous media and the particles. Another 1
The trapping of colloid particles in porous media: Mechanisms and applications, review
This review paper will serve to explain how a particle is trapped on a porous media, and describe the mobility of those particles when passing through a media. It also presents the different parameters that play an important role on the trapping mechanism and the role of biofilm formation. The deposition and trapping mechanism of particles in porous media is governed by the action of different mechanisms such as interception, sieving, diffusion, gravitational and Van Der Waals forces, Brownian diffusion, and inertia. The particle retention through the porous media leads to the formation of a biofilm and the clogging of the media. The understanding of particle retention, clogging, and biofilm formation is interesting because it plays a major role in soil recovery process such as bioremediation, biosorption and filtration (on sand and activated carbon) used for degradation of particles (colloids and microorganisms) and harmful contaminants (heavy metals, drugs) by microorganisms.