Colloid Transport Research Articles

Relating mechanistic fate with spatial positioning for colloid transport in surface heterogeneous porous media

Hypotheses: The transport behavior of colloids in subsurface porous media is altered by surface chemical and physical heterogeneities. Understanding the mechanisms involved and distribution outcomes is crucial to assess and control groundwater contamination. The multi-scale processes that broaden residence time distribution for particles in the medium are here succinctly described with an upscaling model. Experiments/model: The spatial distribution of silver particles along glass bead-packed columns obtained from X-ray micro-computed tomography and a mechanistic upscaling model were used to study colloid retention across interface-, collector-, pore-, and Darcy-scales. Simulated energy profiles considering variable colloid-grain interactions were used to determine collector efficiencies from particle trajectories via full force-torque balance. Rate coefficients were determined from collector efficiencies to parameterize the advective–dispersive-reactive model that reports breakthrough curves and depth profiles. Findings: Our results indicate that: (i) with surface heterogeneity, individual colloid-grain interactions are non-unique and span from repulsive to attractive extremes; (ii) experimentally observed spatial positioning of retention at grain-water interfaces and grain-to-grain contacts is governed respectively by mechanistic attachment to the grain surface and retention without contact at rear-flow stagnation zones, and (iii) experimentally observed non-monotonic retention profiles and heavy-tailed breakthrough curves can be modeled with explicit implementation of heterogeneity at smaller scales.

Surface charge property governing co-transport of illite colloids and Eu(III) in saturated porous media

The transport of colloids and radionuclides is sophisticated because of the variety of charge properties between colloidal particles and host subsurface media, which causes great difficulty in establishing a reliable model of radionuclides migration by taking the colloid phase into consideration. In this work, the co-transport of illite colloids (IC) and Eu(III) in the quartz sand and iron-coated sand porous media was investigated by column experiments to address the predominant mechanism of charge properties on co-transport. Results showed that Eu(III) transport was driven by the illite colloids and electrostatic interaction was critical in governing the co-transport patterns. The promotion of Eu(III) transport by IC was attenuated in the iron-coated sand systems; more IC-Eu(III) complexes were retained uniformly in the column. The pore throat shrinkage caused by electrostatic attachment between aggregated IC and iron oxides exacerbated the physical straining and size exclusion effect of IC-Eu(III) complexes. An aggravated irreversible retention of IC-Eu(III) was detected in iron-coated sand column due to the electrostatic attraction of IC-Eu(III) to host media. The findings are essential for improving the understanding on the potential transport, retention and release risk of colloids associated radionuclides, and imply that the positively charged permeable reactive barrier is an effective strategy to reduce the transport risk of colloid associated radionuclides.

Bridging transport and deposition of colloidal nanoparticles on cylindrical microfibers

Colloidal deposition on fibers is central to industrial applications including fibrous filters and textiles. We propose a self-consistent Eulerian model to bridge the gap between long-range convective-diffusive transport and short-range Derjaguin-Landau-Verwey-Overbeek (DLVO) deposition of colloidal nanoparticles on microfibers. Starting from a single fiber flow cell, our model extends freely to fiber pairs and multi-fiber arrays. For fiber pairs, we found that the deposition efficiency deviates from Péclet number dependence of Pe-2/3, and that the pressure loss is reduced for cross-stream bundles. For multi-fiber arrays, we show how colloidal deposition can be spatially controlled through fiber zeta potentials and how colloids with poly-disperse zeta potentials can be sorted. Interesting deposition hotspots are accessible on surfaces of fibers, such as in compact or composite filters. Together, our work highlights a simple, flexible and scalable approach for modelling colloidal transport phenomena on fibers separated by hydrodynamic length scales.

Effect of different aging treatments on the transport of nano-biochar in saturated porous media

Widely used for soil amendment, carbon sequestration, and remediation of contaminated soils, biochars (BCs) inevitably produce a large number of nanoparticles with relatively high mobility. Geochemical aging alters chemical structure of these nanoparticles and thus affect their colloidal aggregation and transport behavior. In this study, the transport of ramie derived nano-BCs (after ball-milling) was investigated by different aging treatments (i.e., photo (PBC) and chemical aging (NBC)) as well as the managing BC under different physicochemical factors (i.e., flow rates, ionic strengths (IS), pH, and coexisting cations). Consequences of the column experiments indicated aging promoted the mobility of the nano-BCs. Compared to the nonaging BC, consequences of spectroscopic analysis demonstrated the aging BCs exhibited a number of tiny corrosion pores. Both of these aging treatments contribute to a more negative zeta potential and a higher dispersion stability of the nano-BCs, which is caused by the abundance of O-functional groups. Also the specific surface area and mesoporous volume of both aging BCs increased significantly, with the increase being more pronounced for NBC. The breakthrough curves (BTCs) obtained for the three nano-BCs were modelled by the advection-dispersion equation (ADE), which included first-order deposition and release terms. The ADE revealed high mobility of aging BCs, which meant their retention in saturated porous media was reduced. This work contributes to a comprehensive understanding of the transport of aging nano-BCs in the environment.

Phosphorus-Enhanced and Calcium-Retarded Transport of Ferrihydrite Colloid: Mechanism of Electrostatic Potential Changes Regulated via Adsorption Speciation.

The transport of ferrihydrite colloid (FHC) through porous media is influenced by anions (e.g., PO43-) and cations (e.g., Ca2+) in the aqueous environment. This study investigated the cotransport of FHC with P and P/Ca in saturated sand columns. The results showed that P adsorption enhanced FHC transport, whereas Ca loaded onto P-FHC retarded FHC transport. Phosphate adsorption provided a negative potential on the FHC, while Ca added to P-FHC led to electrostatic screening, compression of the electric double layer, and formation of Ca5(PO4)3OH followed by heteroaggregation at pH ≥ 6.0. The monodentate and bidentate P surface complexes coexisted, and Ca mainly formed a ternary complex with bidentate P (≡(FeO)2PO2Ca). The unprotonation bidentate P at the Stern 1-plane had a considerable negative potential at the Van der Waals molecular surface. Extending the potential effect to the outer layer of FHC, the potential at the Stern 2-plane and zeta potential exhibited a corresponding change, resulting in a change in FHC mobility, which was validated by comparison of experimental results, DFT calculations, and CD-MUSIC models. Our results highlighted the influence of P and Ca on FHC transport and elucidated their interaction mechanisms based on quantum chemistry and colloidal chemical interface reactions.

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

Visualization of biochar colloids transport and retention in two-dimensional porous media

Biochar colloids (BCs) have received considerable attention in recent years due to the unique environmental behavior and potential risks. In this work, a real-time visualization system to reveal the transport and retention mechanisms of biochar colliods in two-dimensional (2-D) porous media under the ionic strength (IS), pH and media grain size was developed. The system consists of charge coupled device (CCD) microscope camera and flow cell (connected to a pump and sample collector). The breakthrough curve of flow cell effluent concentration was used to quantitatively analyze the migration behavior of BCs. BCs transport in 2-D porous media was simulated with a simplified Double Monod model. The results show that BCs had a strong migration capacity in 2-D porous media. Electronegativity of BCs and quartz sand increases with the decrease of IS and the increase of pH, and the electrostatic repulsion between them then increases, resulting in the reduction of the adhesion of BCs on the sand surface, which promotes the migration and reduces the retention of BCs in the 2-D porous media. In addition, the reduction of media grain size had an inhibitory effluence on the transport of BCs, and the finer sand could provide more deposition sites for BCs. Meanwhile, the Double Monod model also fitted the transport behavior nicely (R2 > 0.94). The visualization method in this study properly explains the migration behavior of BCs in 2-D porous media, which provides reasonable support for more comprehensive evaluation environmental risk.

Three-dimensional dynamic optical trapping using non-iterative computer-generated holography

Holographic optical trapping enables three-dimensional (3D) particle manipulation based on a traditional iterative algorithm. However, this type of particle manipulation is typically unstable. It is challenging to realize continuous dynamic 3D optical trapping because a unique solution of uniformity cannot be obtained over several time-consuming iterations. In this study, 3D multifocal spots with high uniformity were generated via non-iterative algorithms (using a complex amplitude coding method and fan-shaped subzone phase method) to realize stable dynamic optical trapping for 3D particle manipulation. The corresponding experimental results pave the way for potential applications of colloid transport and the micro-assembly of objects in the micro-operation field.

Colloidal iron species driven enhanced H2O2 decomposition into hydroxyl radicals for efficient removal of methylene blue from water

Colloids are wide-spread in natural waters and colloid-facilitated transport via adsorption was established as the most important mechanism for the mobilization of aqueous contaminants. This study reports another possible, but reasonable, role of colloids for the contaminants driven by redox reactions. Under the same conditions (pH 6.0, 0.3 ml 30% H2O2, and 25 °C), the degradation efficiencies of methylene blue (MB) at 240 min over Fe colloid, Fe ion, Fe oxide and Fe(OH)3 were 95.38%, 42.66%, 4.42% and 9.40%. We suggested that, Fe colloid can promote the H2O2 based in-situ chemical oxidation process (ISCO) compared with other iron species such as Fe(Ⅲ) ion, Fe oxide and Fe(OH)3 in natural water. Furthermore, the MB removal via adsorption by Fe colloid was only 1.74% at 240 min. Hence, the occurrence, behavior and fate of MB in Fe colloid containing natural water system mainly depends on the reduction-oxidation rather than adsorption-desorption process. Based on the mass balance of colloidal iron species and characterization of iron configurations distribution, Fe oligomers were the active and dominant components for Fe colloid-driven enhanced H2O2 activation among three types of Fe species. The quick and steady conversion of Fe(III) to Fe(II) was proven to be reason why Fe colloid can efficiently react with H2O2 to produce hydroxyl radicals.

Diffusiophoresis and Diffusio-osmosis into a Dead-End Channel: Role of the Concentration-Dependence of Zeta Potential.

Chemically induced transport methods open up new opportunities for colloidal transport in dead-end channel geometries. Diffusiophoresis, which describes particle movement under an electrolyte concentration gradient, has previously been demonstrated in dead-end channels. The presence of solute concentration gradients in such channels induces particle motion (phoresis) and fluid flow along solid walls (osmosis). The particle velocity inside a dead-end channel is thus influenced by particle diffusiophoresis and wall diffusio-osmosis. The magnitude of phoresis and osmosis depends on the solute's relative concentration gradient, the electrokinetic parameters of the particle and the wall, and the diffusivity contrast of cations and anions. Although it is known that some of those parameters are affected by electrolyte concentration, e.g., zeta potential, research to date often interprets results using averaged and constant zeta potential values. In this work, we demonstrate that concentration-dependent zeta potentials are essential when the zeta potential strongly depends on electrolyte concentration for correctly describing the particle transport inside dead-end channels. Simulations including concentration-dependent zeta potentials for the particle and wall matched with experimental observations, whereas simulations using constant, averaged zeta potentials failed to capture particle dynamics. These results contribute to the fundamental understanding of diffusiophoresis and the diffusio-osmosis process.

Colloidal stability and aggregation behavior of CdS colloids in aquatic systems: Effects of macromolecules, cations, and pH

Redox-dynamic environments such as river floodplains and paddy fields have been demonstrated to be important sources of CdS colloids. To date, the aggregation kinetics of CdS colloids had not yet been studied, and the structure and properties of macromolecules on the interaction between different macromolecules and CdS colloids, as well as the aggregation behavior of CdS colloids are unclear. This study investigated the colloidal stability of CdS colloids in model aqueous systems with various solution chemistry and representative of macromolecules. The results showed that increased electrolyte concentration destabilized CdS colloids by charge screening, with the cationic effect following Ca2+ > Mg2+ > K+ > Na+; Higher solution pH stabilized CdS colloids by raising the critical coagulation concentration from 33 to 56 mM NaCl. Electron microscopy and spectroscopy verified the strong interaction between macromolecules and CdS colloids, and macromolecule adsorbed on the surface of CdS to form a protective layer called “NOM corona”. The interaction between macromolecules and CdS induced distinct aggregation behaviors in NaCl and CaCl2 solutions. The steric repulsion generated by “NOM corona” significantly stabilized CdS colloids in NaCl solution, and the stabilizing order was consistent with the adsorbing capacity of macromolecules on CdS colloids, namely Bovine serum albumin (BSA) > sodium alginate (SA) > calf thymus DNA (DNA) > Suwannee River humic acid (HA). BSA and DNA also inhibited CdS colloids aggregation in the CaCl2 solution due to the balance of steric hindrance, cation bridging, and electrostatic repulsion. For HA and SA, Ca2+ bridging and EDL compression contributed to their destabilization of CdS colloids in CaCl2 solution. Macromolecules concentration affect corona formation that alter stability of CdS colloids. There results showed that the complex influences of solution chemistry and macromolecules on fate and transport of CdS colloids in environment. The findings will help to understand the potential risks of CdS colloids in environment.

Initial soil moisture conditions affect the responses of colloid mobilisation and associated cadmium transport in opposite directions

The effects of initial soil moisture on colloid-associated transport are still poorly understood given the well-recognized significance of colloid-facilitated transport of strongly-sorbing contaminants. In this study, Cd leaching was sequentially conducted in an intact soil column under three initial moisture conditions (near saturation, field capacity and dryness). Soil colloids were always the dominant carriers for Cd. However, upon the lowering of initial soil moisture, increased transport of colloids (96.2→101.0→168.2 mg) was observed, surprisingly, along with decreased transport of colloid-associated Cd (C-Cd) (23.9→10.7→8.2 µg) and enrichment factor (248.4→105.9→48.8 mg/kg) of Cd on colloids, resulting from pH reduction which increased Cd desorption and colloid size increase and/or ζ-potential decrease that showed lower affinity for Cd. Correlation, redundancy analysis and structural equation modelling revealed the dominantly positive role of colloids, EC plus cations (Ca2+ and Mg2+) in the release of C-Cd and dissolved Cd (D-Cd), respectively, under initial moistures of near saturation and field capacity. Under initially dry conditions, soil water potential showed dominantly negative effects on the transport of both C-Cd and D-Cd. These findings highlighted the critical role of initial moisture conditions in modulating colloid-facilitated Cd mobilisation, providing insights into the environmental risk assessment of heavy metals in other leaching scenarios.

Co transport of bentonite colloids and Eu(III) transport in saturated heterogeneous porous media

Co transport of bentonite colloids and Eu(III) transport in saturated heterogeneous porous media

Three-Dimensional Visualization Reveals Pore-Scale Mechanisms of Colloid Transport and Retention in Two-Phase Flow.

Colloids are ubiquitous in the natural environment, playing an important role in facilitating the transport of absorbed contaminants. However, due to the complexities arising from two-phase flow and difficulties in three-dimensional observations, the detailed mechanisms of colloid transport and retention under two-phase flow are still not well understood. In this work, we visualize the colloid transport and retention during immiscible two-phase flow based on confocal microscopy. We find that the colloid transport and retention behaviors depend strongly on the flow rate and pore/grain size. At low levels of saturation (high flow rate) with the wetting liquid mainly present as pendular rings, the colloids can aggregate at the liquid filaments in small-grain packings and are uniformly distributed in large-grain packings. Through theoretical analysis of the pendular ring geometry, we elucidate the mechanism responsible for the strong dependence of colloid clogging behavior on solid grain size. Our results further demonstrate that even at dilute concentrations, colloids can alter the flow paths and the wetting fluid topology, suggesting a strong two-way coupling dynamics between immiscible two-phase flow and colloid transport and calling for improved predictive models to incorporate the overlooked clogging behavior.

Coupled effects of pH and kaolinite colloids on antibiotic transport in porous media

Antibiotics can interact with natural colloids and the surrounding media upon entry into soil and groundwater systems, which significantly alters their dynamic behavior and complicates our understanding of antibiotic fate and transport in porous media. In this study, co-transport of antibiotics and kaolinite colloids was systematically investigated using combined column experiments and numerical simulation under different pH conditions. Sulfadiazine (SDZ) transport was enhanced by kaolinite colloids under neutral and alkaline conditions, which was attributed to the higher mobility of colloids as SDZ carriers, as well as competitive sorption. However, most injected SDZ was transported in a dissolved form owing to the low sorption capacity of SDZ to kaolinite colloids and quartz sand. The colloid-facilitated transport model provided a good description of total SDZ transport, but underestimated colloidal SDZ transport using parameters from kinetic sorption experiments. Kaolinite colloids significantly promoted ciprofloxacin (CIP) transport at pH 4.0, but inhibited it at pH 7.0 and 9.0. Interestingly, enhanced CIP transport was due to the decreased number of effective sorption sites on quartz sand and the increased desorption of CIP from kaolinite colloids. Under neutral and alkaline conditions, deposited colloids provided additional sorption sites for CIP, which contributed to CIP retention. Moreover, CIP significantly inhibited the transport of kaolinite colloids owing to the increases in colloidal aggregate size and zeta potential. Overall, our results highlighted the different effects of mobile and immobile colloids on antibiotic transport, in addition to the implications of antibiotic speciation and clay colloids when predicting the transport behavior of these compounds.

Exploring the Role of Nanobubbles in the Fate and Transport of Spilled Oil on Shorelines

Nanobubbles (NBs) generated by wave breaking and shearing are abundant and stable in the ocean. However, few studies have focused on the effects of NBs in the fate and transport of pollutants in the shoreline environment. In this study, the properties of NBs were determined, as well as the influencing factors. The role of NBs in the fate and transport of spilled oil were further investigated. The results showed that NBs significantly increased the concentration of dissolved oxygen as well as changed the pH, zeta potential, and surface tension of the water. Low salinity favored the generation of NBs, while high salinity inhibited this process. The surface active materials played a positive role in the generation and stabilization of NBs. With the assistance of external energy, the bulk NBs enhanced the efficiency in oil detachment from the surface of the substrate. At the same time, the surface NBs on the substrate obstructed the downward transport of oil colloids. Considering the behavior between the NBs in two different phases and the oil droplets, the oil droplets tended to bind to the NBs. This study demonstrates that NBs can play a significant role in the environmental behaviors of pollutants in the coastal areas.

Transport of Colloids and Colloid-facilitated Cadmium in a Sri Lankan Agricultural Soil

Transport of Colloids and Colloid-facilitated Cadmium in a Sri Lankan Agricultural Soil

The Investigation of the Mechanical Properties of EICP-Treated Sand Specimens Prepared by a Double-Reservoir Injection System for Uniform Precipitation of Carbonate via Triaxial Tests

Abstract The injection condition of enzymatic-induced carbonate precipitation (EICP) grouting for uniform precipitation and the mechanical properties of EICP-treated soil specimens were investigated in this study. Urease derived from yellow soybeans was used as the catalyst for the precipitation of the carbonate instead of the expensive purified urease commonly used. The uniformity of the calcium carbonate distribution was investigated by measuring the calcium carbonate content at various locations within the EICP-treated soil specimens through the soil column injection tests. The results showed that the uniformity of the calcium carbonate distribution depends on the reservoir system for the storage of the injection solutions and the injection volume that is associated with the colloidal transport of urease. Based on the proposed injection method, the EICP-treated soil specimens were prepared for two soil types and a series of consolidated undrained triaxial compression tests were conducted to investigate the mechanical properties. It was confirmed that the undrained shear behavior of the EICP-treated sand specimens shows more softening behavior. In addition, the use of a high molarity urea-CaCl2 solution resulted in pronounced reinforcing effects on the strength, which included both the peak and residual strength and the stiffness. The effects of the confining pressure and the soil types on the strength and stiffness were also investigated.

Polycyclic aromatic hydrocarbons in groundwater of oil-rich regions of upper Brahmaputra Valley, India: linkages of colloidal transport

Polycyclic aromatic hydrocarbons in groundwater of oil-rich regions of upper Brahmaputra Valley, India: linkages of colloidal transport

Soil Aggregate Breakdown with Colloidal Particles Release and Transport in Soil: A Perspective from Column Experiments

The strongest fortresses often disintegrate from the inside. Likewise, soil internal forces play a critical role in the initial breakdown process of soil aggregate, thus accelerating soil erosion and the release of soil colloid particles. To date, research on the effect of soil internal forces, especially separating the electrostatic force, and on the process of soil aggregate breakdown with particle release and transport in soil is largely inadequate. Therefore, column experiments were used to investigate the properties of transport and soil particles released from the disintegration of model soil aggregates caused by different levels of electrostatic forces. We found that the increase of electrostatic repulsive pressure was the immediate cause of soil aggregate breakdown, that the highest concentration of released soil particles could reach 808.36 mg L−1, and that the mean particle sizes of the released soil ranged from 100 nm to 300 nm. The particle size distributions and clay mineral composition of the released soil particles were not dominated by the electrostatic force. In practice, the change of external conditions of agricultural soil would lead to the change of soil internal forces, then affect soil aggregate stability. This study aims to provide a micro perspective to understand the release of fine particles from soil matrix and its implication for agricultural soil.