Colloids In Porous Media Research Articles

Cotransport of fullerene nanoparticles and clay colloids in porous media: the relation between aggregation and transport

Cotransport of fullerene nanoparticles and clay colloids in porous media: the relation between aggregation and transport

A Novel Image Processing Approach for Colloid Detection in Saturated Porous Media.

Over recent decades, natural and artificial colloids, as well as nanoparticles, have been increasingly used in various applications. Consequently, with this rising consumption, surface and subsurface environments are more exposed to these particles. The presence of these particles and the colloid-facilitated transport of microorganisms, the interactions between dissolved contaminants and mobile colloids in porous media, and the fate and transport of colloids through groundwater-one of the primary sources of water supply for human societies-have attracted extensive research. This study investigates the performance of several image processing methods in the field of colloid detection, which is a prerequisite for the subsequent steps in porous media research. We employed four different categories of image processing approaches on microscopy images-segmentation-based methods, background-detection-based methods, filter-based methods, and morphology-based methods-to conduct the detection process of colloids. Eight methods were applied and subsequently analyzed in terms of their drawbacks and advantages to determine the best ones in this domain. Finally, we proposed an ensemble approach that leverages the strengths of the three best methods using a majority vote to detect colloids more accurately. In experiments, Precision, Recall, F-measure, and TCR criteria were considered as evaluation tools. Experimental results demonstrate the high accuracy of image processing methods in recognizing colloids. Among all these methods, morphology-based methods were the most successful, achieving the best detection performance and improving the limited distinguishing features of small colloids. Moreover, our ensemble approach, achieving perfect scores across all evaluation criteria, highlights its superiority compared with other detection methods.

Different co-transport forms of ciprofloxacin with montmorillonite colloids in porous media as affected by pH and cations

Different co-transport forms of ciprofloxacin with montmorillonite colloids in porous media as affected by pH and cations

Unveiling colloidal transport and deposition: Exploring pore network and random forest models for insights

The transport and deposition of colloids in porous media are common phenomena in nature and industry. In this study, a pore network model (PNM) was used to model the geometry, flow field, and colloidal mass transfer of porous media. The finite element method (FEM) was utilized to establish a database of the contact efficiency ηt of the pore-scale collectors, and a random forest model (RFM) was trained. Reasonable prediction of ηt shows that the developed RFM greatly improves the computational efficiency and frees users from repeated numerical simulations. The effects of the colloidal size and seepage velocity on colloidal transport and the surface deposition behavior were studied, the ηt distribution in the PNM was determined, and breakthrough and retention curves were calculated. The results show that the ηt distribution width and mean value increase with the increase in the colloidal particle size and decrease with the increase in the seepage velocity in the range of colloidal particle sizes and seepage velocities considered in this paper. The peak concentration of the breakthrough curve decreases with increasing colloidal particle size and increases with increasing seepage velocity. Surface deposition produces exponential or uniformly shaped retention curves, with retention concentrations increasing with increasing colloidal particle size and decreasing with increasing seepage velocity. The evolution analysis of the retention curve revealed notable detachment and reattachment effects of the colloids in porous media. The results of this study have potential applications in various fields such as environmental remediation, groundwater management, and filtration technology optimization.

Cotransport of fullerene nanoparticles and montmorillonite colloids in porous media: Critical role of divalent cations of montmorillonite

While the cotransport of carbon nanoparticles (CNPs) and clay colloids in porous media has been widely studied, the influence of the cation exchange capacity (CEC) of clay colloids on the transport process remains unclear. In this study, batch adsorption and column transport experiments were conducted to investigate the fate and transport of CNPs and clay colloids in quartz sand, with respect to the effect of monovalent-cation exchange capacity (mono-CEC), divalent-cation exchange capacity (di-CEC) and total CEC of clays. Fullerene nanoparticles (nC60) and six types of montmorillonite (ML) with different CEC were selected as modeled CNPs and clay colloids, respectively. Transport behavior of nC60 and ML was characterized using breakthrough curves (BTCs) and fitted with two-kinetic-sites colloid transport model. Results of the adsorption experiments showed a good linear correlation between the deposition of nC60 on the sand surface and the di-CEC of ML. Transport of ML and nC60 was inhibited by each other. The calculated mass recovery of nC60, as well as the fitted maximum deposition capacity and attachment rate coefficients of nC60 exhibited a strong linear relationship with the di-CEC of ML. These results indicate that divalent cations in ML interlayers play a significant role in aggregation between nC60 and ML and their cotransport. Through measurements of the particle size and zeta potentials of sole nC60 and mixtures of ML and nC60, FTIR and XPS analysis of nC60 under different conditions, and a release experiment of nC60 in a sand column, it demonstrated cation bridging (Ca2+-π) between nC60 and ML mediated by the divalent cations in ML interlayers. The study highlighted the potential of using di-CEC of clays as an indicator to predict the mobility of nC60 in clay-containing porous media and added insights to the transport behavior of CNPs in porous media.

CFD-DEM study on transport and retention behaviors of nZVI-clay colloids in porous media

Transportation process of nano scale zero valent iron (nZVI) in clay-rich soils is complicated and crucial for in-situ remediation of contaminated sites. A coupled computational fluid dynamic and discrete element method (CFD-DEM) was used to investigate the interplays of repulsive and attractive forces and the injection velocity of this process. The screened Coulomb’s law was used to represent the electrostatic interaction, and surface energy density was introduced to represent the effects of the van der Waals interaction. A phase diagram was constructed to describe the interplay between injection velocity and repulsive force (in terms of charge of colloids). Under the boundary and initial conditions in this study, clogging formed at low repulsive force (colloidal charge = −1 ×10-15 C), where increment of injection velocity (from 0.002 m/s to 0.02 m/s) cannot prevent clogging, as in the case of bare nZVI transportation with limited mobility; On the other hand, excessive repulsive force (charge = −4 ×10-14 C) is detrimental to nZVI-clay transportation due to repulsion from the concentrated colloids in pore throats, a phenomenon as in the overuse of stabilizers and was defined as the “membrane repulsion effect” in this study. At moderate charge (−1 ×10-14 C), injection velocity increment induced clogging due to aggregates formed at the windward of cylinder and accumulated at the pore throats.

Review of Colloid (Nano‐ and Micro‐Particle) Transport and Surface Interaction in Groundwater. William P. Johnson and Eddy F. Pazmino. The Groundwater Project. 111 pp. ISBN: 978‐1‐77470‐070‐9. DOI: https://doi.org/10.21083/978‐1‐77470‐070‐9

Review of <i>Colloid (Nano‐ and Micro‐Particle) Transport and Surface Interaction in Groundwater</i>. William P. Johnson and Eddy F. Pazmino. The Groundwater Project. 111 pp. ISBN: 978‐1‐77470‐070‐9. DOI: https://doi.org/10.21083/978‐1‐77470‐070‐9

Prediction of colloid sticking efficiency at pore-scale and macroscale using a pore network model

The sticking efficiency (α) is a vital parameter to predict the transport and deposition of colloids in porous media. The value of α depends on various factors such as the interaction energy between colloids and the solid-water interface (SWI), kinetic energy fluctuations of diffusing colloids, and the hydrodynamics of the flow field in the pore structure. However, α is usually assumed to be spatially constant and fitted from experimental data. In this study, a theoretical method is proposed to predict the distribution of the sticking efficiency at pore scale (αt) using a pore network model (PNM) and the macroscale sticking efficiency of the whole porous media (αM) by means of upscaling. A PNM is established to simulate the pore structure of porous media and to obtain the flow field, and energy and torque balances are calculated throughout the spatial pore structure to determine the distribution of αt under different physiochemical conditions. The value of αM is determined through breakthrough curves provided by the PNM under favorable and unfavorable conditions. Results show the distribution of αt is sensitive to various factors including colloid characteristics, pore surface features, geochemical environment and hydrodynamic conditions. Colloid characteristics like colloid surface zeta potential, geochemical environment such as solution ionic strength, and pore surface characteristics including nanoscale roughness and especially charge heterogeneity have a controlling influence on αt for nanoparticles (<100 nm) due to their impact on interaction energies. Hydrodynamic conditions played an increasingly important and eventually dominant role in determining αt for larger colloids by changing the sticking of weakly associated colloids (e.g., at secondary minima). When hydrodynamic torques are weak, the influence of colloid size on αt can be non-monotonic due to the combined influence of interaction energy and hydrodynamic torques. As a result, higher values of αM occurred for smaller colloid sizes, lower flow velocities, larger pore sizes, and in the presence of microscopic roughness. The method proposed by this study can be used to predict the sticking efficiency under different solution and solid phase chemistries, nanoscale heterogeneities, microscopic roughness, flow velocities, and pore structure conditions.

Fluid flow and colloid transport experiment in single-porosity sample; tracking of colloid transport behavior in a saturated micromodel

Release of colloids and their subsequent transport into the subsurface environments takes place during a wide range of applications such as industrial, energy storage, and agricultural activities. Therefore, processes contributing to transport, attachment, and re-mobilization of colloids in porous media are attracting attention. A fraction of the released colloids may cross the soil vadose zone to reach the saturated groundwater. In this study, we explored colloid transport in a micromodel with high repulsion energy barrier where colloid retention is assumed to be low. Three major shortcomings were improved: pore space domain size, imaging resolution, and speed of imaging. The flow path of 1357 colloids with a size of 4 µm were tracked and these enabled precise determination of individual colloid transport mechanism as well as the integrated behavior of the system.Our direct observations have shown that even under unfavorable attachment conditions (defined based on the DLVO theory) colloids deposition occurred which was mainly due to the local flow velocity fluctuations and grain surface heterogeneity. Using the information from collective trajectories, we have quantified the contribution of differently behaved colloids in the observed breakthrough curve which show an integrated, macroscopic, behavior of the system and is often the only available information when performing column or field scale experiments to explore colloid transport in porous media. Furthermore, we have shown that attachment and remobilization of colloids increased the dispersion coefficient, and consequently the dispersivity value of the media.

A two-way coupled model for the co-transport of two different colloids in porous media

Models for the co-transport of two different colloids commonly assume a one-way coupling. This is because often a large colloid and small colloid are involved. Therefore, they assume that the spread of smaller colloid is affected by the transport of larger colloids, but not the other way around. However, a number of studies have shown that this assumption is not valid, even for large and small colloids. Therefore, in this study, a two-way coupled model is developed to simulate the co-transport of two different colloids in porous media and their effect on each other. We have considered the interactions of the two colloids with the grain surface, kinetics of heteroaggregation (of the two colloids), and heteroaggregate deposition onto the grain surface. We assumed a first-order kinetic model to represent heteroaggregate formation and its deposition on the grain surface. The model is evaluated by fitting the experimental data reported in four different papers from the literature on the co-transport of clay colloids and viruses, bacteria and graphene oxide nanoparticles, and clay colloids and graphene oxide nanoparticles. The model performance is compared with the commonly-used one-way coupled model. The two-way coupled model is found to satisfactorily simulate most of the experimental conditions reported in the above papers, except for the co-transport of montmorillonite–adenovirus, and Staphylococcus aureus- graphene oxide nanoparticles.

Interpolation for the lattice-Boltzmann method to simulate colloid transport in porous media.

The lattice-Boltzmann method is convenient for simulating flow fields in porous media. However, due to its lattice characteristics, the velocity near a solid surface is not accurate, which results in significant errors when simulating colloid transport in porous media. Based on the general properties of a flow field close to a solid surface, we propose an alternative velocity interpolation method in which the velocity at a solid surface is strictly zero. Numerical simulation results show that the proposed method can give more accurate results than the usual bilinear interpolation. In addition, we use this method to simulate the contact efficiency of colloids in porous media and obtain a new power-law form of the contact efficiency.

Ultrasound-enhanced diffusion and streaming of colloids in porous media

Diffusion of colloidal particles in porous media is critical for the development of specially engineered colloids used to aid the recovery of oil from a petroleum reservoir. However, shielded structures, such as dead-end pores, prevent these colloids from reaching the available oil. This article examines the use of ultrasound fields as a mechanism for increasing the mobility of colloidal particles in porous media. Particle tracking of optical video microscopy experiments performed in micromodels of varying porosity are used to construct mean square displacement, from which effective diffusion coefficients and average particle velocities can be measured. We introduce an acoustic field by sweeping a phase space that consists of multiple voltages, frequencies and porosities. Our experiments show that diffusion scales linearly with voltage, while average particle velocity scales quadratically. We found that the diffusion and average velocity peaked near a frequency of ~40 kHz for porosities of 0.62, 0.76 and 0.9, suggesting the presence of a natural frequency. A second natural frequency with a value close to ~90 kHz was also observed in experiments conducted at 0.62 and 0.76. The effective diffusion at 40 kHz has a maximum value ~0.4 μm2/s, which is a factor of 5.5 times greater than in the absence of an acoustic field. Outside of the 40 kHz resonance peak, diffusion remains enhanced, with a measured coefficient of ~0.15 μm2/s. This is still a factor of 2 greater than when no acoustic field is present. Overall, our results demonstrate that ultrasound enhances the transport of colloidal particles through porous media. Future work aims to use these results as the foundation for improved modelling of acoustically stimulated transport through porous media as well as applying these results to problems related to particulate separation.

Colloid retention and mobilization mechanisms under different physicochemical conditions in porous media: A micromodel study

Clear understanding of pore-scale mechanisms that control transport and retention of colloids in porous media at different physicochemical conditions is critical to improve design and efficient cleanup methodologies of filter beds. The objective of this work was to investigate the impact of hydrophobicity, solution ionic strength, and pH on colloid retention mechanisms in single-phase and two-phase flow in porous media systems. A series of experiments were conducted using a geometrically representative micromodel. Hydrophilic and hydrophobic colloids were dispersed in water at different solution ionic strength and pH conditions. Findings indicate that hydrophilic colloids exhibit high filtration efficiency as the colloids interact attractively with other colloids and solid-water-interface irrespective of the solution chemistry. However, for hydrophobic colloids, changes in solution chemistry significantly increase colloid retention where the colloid interaction become attractive with the increase in ionic strength and decrease in pH values. Colloids attached to the collector surfaces mobilized by the strong capillary forces induced by the moving gas-water interface and transported along with the interface. However, hydrophilic colloids redeposited on gas-water-solid interfaces or thin water films because of their greater capillary potential. Therefore, greater filtration efficiency is achieved with the hydrophilic colloids compared to the hydrophobic colloids for which the efficiency can be improved by changing the solution chemistry. Moreover, the removal efficiency by the moving gas-water interface was observed to be more for hydrophobic colloids compared to hydrophilic colloids for which the efficiency can be improved by lowering the ionic strength or increasing the pH value. This study indicates that the coupled effects of solution chemistry and colloid hydrophobicity should be taken into account while investigating efficient filtration and cleaning practices for the filter beds.

Water level and mobilisation of colloids in porous media

Unforeseen clogging and low well productivity during exploitation of oil and gas reservoirs result from a mobilisation of densely deposited particles. The proposed model predicts the mobilisation in unsaturated porous media based on the changes in water level, and hydrophilicity and size of mobilisable particles. Domains of particle attachment, sliding, rolling, and lifting were found from a phase diagram based on a mechanical equilibrium. The degree of mobilisation was correlated with experimental data through a maximum retention function. The validity of the proposed model was confirmed by a close match of theoretical predictions with results of 46 laboratory tests on particle detachment.Our analysis shows that it is practically impossible to remove 2 μm charged colloids from a dry porous media. Nearly desalinated water with ionic strength of 0.001 M or less are needed to mobilise particles in saturated media at typical groundwater conditions. A gradual increase in water level is key for mobilisation in unsaturated media. The proposed model can be used to forecast a potential well clogging.

Surface and colloid properties of biochar and implications for transport in porous media

Biochar contains a large amount of colloidal particles. Biochar colloids are generated (1) during pyrolysis of the feedstock, where some of the biochar formed is in the colloidal size fraction, and (2) by the breakdown of larger biochar particles. Here, we review the surface and colloid properties of biochar and the implications for transport of biochar colloids in porous media. We discuss the origin of biochar colloids and their physical and chemical properties relation to feedstock and pyrolysis temperature. We then review the transport of colloidal biochar in sand columns and soils and relate the transport behavior to surface characteristics. We finally examine the effects of aging, i.e., natural and simulated environmental weathering, on the surface properties of biochar colloids. Biochar colloids tend to have lower zeta potential and lower aromaticity than the bulk biochar. Due to their smaller size, biochar colloids are more stable in aquatic environments and more mobile in the subsurface than the parent biochar particles. Like the parent biochar material, pristine biochar colloids contain a variety of hydrophobic functional groups (e.g., alkyl, aromatic), and become more hydrophilic as the biochar ages. At environmentally relevant pH, biochar colloids are negatively charged.

Kinetic determination of sedimentation for GMZ bentonite colloids in aqueous solution: Effect of pH, temperature and electrolyte concentration

Bentonite colloids are readily generated by eroding the compacted bentonite blocks with flowing groundwater and facilitate the transport of radionuclides due to their high mobility. The geological fate of colloids is highly relevant to the aggregation and sedimentation of colloids in porous media. In the present work, the week-scale stability of bentonite colloids concerning sedimentation was determined by photon correlation spectroscopy (PCS) as a function of pH, temperature, and electrolyte concentration. The related mechanisms governing colloidal stability were elucidated by employing the DLVO model. The results showed that the alkaline condition was favorable for bentonite colloidal stability, while high temperature and high salinity destabilized colloids due to the decrease in repulsive potential energy. Ca2+ contributed more significantly to colloid sedimentation than Na+ because of the favorable replacement in the Stern layer. The critical coagulation concentration (CCC) values calculated theoretically from DLVO theory were applicable to predict the stability of bentonite colloids. Knowledge from the present work provides deep insight into the stability of bentonite colloids and has potential implication for understanding the detailed physico-chemical processes governing colloid migration under various subsurface environments.

Self-Limited Accumulation of Colloids in Porous Media.

We present local direct imaging of the progressive adsorption of colloidal particles inside a 3D model porous medium. By varying the interparticle electrostatic interactions, we observe a large range of particle deposition regimes, from a single layer of particles at the surface of the medium to multiple layers and eventually clogging of the system. We derive the complete deposition dynamics and show that colloid accumulation is a self-limited mechanism towards a deposited fraction associated with a balance between the particle interactions and the imposed flow rate. These trends are explained and predicted using a simple probability model considering the particle adsorption energy and the variation of the drag energy with evolving porosity. This constitutes a direct validation of speculated particle transport mechanisms, and a further understanding of accumulation mechanisms.

Special features of the functional dependences of magnetic susceptibility of magnetic colloids in porous media

The frequency and temperature dependences of the magnetic susceptibility of magnetic colloids with large particle sizes placed in porous media have been found to be different from the similar dependences for bulk samples. The observed peculiarities can be explained by the influence of surface phenomena on the processes of relaxation of the magnetic moment of colloidal particles.

Mobilization of Attached Clustered Colloids in Porous Media

AbstractThe models for colloidal mobilization in porous media are often based on Derjaguin‐Landau‐Verwey‐Overbeek interaction energy profiles. Despite abundant evidence on mobilization of particle clusters, the models to date have been limited to single colloid‐surface Derjaguin‐Landau‐Verwey‐Overbeek calculations. We show through visualization tests, qualitative and quantitative modeling, and data evaluation, that the widely accepted single colloid‐single surface isolation does not always adequately describe colloid behavior. The experiments were performed with kaolinite and latex particles mobilized from sand grains and glass beads in a transparent visualization cell. The particles were mobilized under increasing velocity and pH and decreasing salinity. The detachment conditions were determined by a torque balance of electrostatic, drag, lifting, and gravity forces, combined with a theory of a contact area between a single soft particle and a plane surface. The tests show that the calculations based on the mechanical equilibrium of a single particle on a plane surface significantly underestimate the critical detachment velocity. A better prediction is obtained using a cluster approximation. High‐resolution images taken during mobilization tests show 2‐12 particle clusters on media surface and in its proximity. The mechanical‐equilibrium calculations show that the attaching torque for clusters with assumed size and cylindrical shape is significantly higher than that for single particles. The critical detachment velocity of clusters, derived from the mechanical‐equilibrium force and torque balances, is higher than for single particles and provides a better fit to the experimental data. Our study suggests that a cluster approximation can accurately predict the mobilization of colloids in porous media.

Opportunities for Particles and Particle Suspensions to Experience Enhanced Transport in Porous Media: A Review

Understanding the fate of colloids in porous media plays a vital role in applications such as enhanced oil recovery (EOR), colloid-facilitated transport or groundwater remediation. Although considerable research has been dedicated toward the retention characteristics of colloids over the last couple of years, less attention has been paid to their transport characteristics in porous media, and hence little knowledge is available on how colloids flow through a medium of complex channel alignment. This lack of understanding becomes apparent for nanoparticle applications in EOR, where relatively concentrated nanofluids are injected into low-permeable sedimentary rocks. Here, two flow phenomena arise: an earlier breakthrough of nanoparticles compared to a conservative tracer and an apparent slip effect, by which the measured pressure drop is less than that calculated via Darcy’s law. The underlying mechanism that couples both phenomena is typically attributed to the depleted layer effect—a theory that presumes that the nanoparticles are excluded from the low-velocity region near a wall at a distance typically larger than the nanoparticles. This depletion causes the particles to move on average faster than the bulk fluid containing them and causes that fluid to exhibit a viscosity lower than when measured in a viscometer. However, the depleted layer theory is not predicated on any direct observation during flow in porous media. In a broader sense, this review paper not only aims at finding answers as to why particles drive away from a wall so that a depleted layer occurs. It also questions the aforementioned hypothesis that early breakthrough and reduced apparent viscosity can be interrelated, and assesses whether each phenomenon should be treated independently. In a strict sense, this review presents both potential mechanisms of particles flow enhancement and how its manifestation can be hindered, as well as opportunities for particle suspensions to experience enhanced flow as a whole. It is meant to be an overview for readers who are not familiar with the characteristic transport features of particles. Accordingly, this review highlights also outstanding challenges in allocating the underlying mechanisms behind the flow enhancement phenomena and shows thereby future research opportunities.