Transport Of Nanoscale Zero-valent Iron Research Articles

Transport of nanoscale zero-valent iron in the presence of rhamnolipid

Nanoscale zero-valent iron (nZVI) particles have gained widespread use for in-situ treatment of various chlorinated hydrocarbons. Their non-toxic nature, affordability, and minimal maintenance requirements have made them a favored material for nanoremediation. The treatment typically involves the injection of nZVI particles into contaminated sites using direct-push well injection systems. However, their small size leads to high surface energy, causing aggregation that alters their physiochemical properties, reactivity, and transport behavior. To counteract aggregation, nZVI suspension can be stabilized with different surfactants, reducing the surface energy during subsurface soil transport. This study investigates the impact of rhamnolipid, a biosurfactant produced by Pseudomonas aeruginosa during the late growth phase, on the aggregation and mobility of nZVI particles. The retardation factor of nZVI in the model media of zeolite, ZK406H, decreased from 1.66 in the absence of rhamnolipid to 1.03, 0.98, 0.93, and 0.87, corresponding to the presence of rhamnolipid at concentrations of 20, 50, 80, and 100 mg/L. The deposition coefficient also decreased from 2.39 in the absence of rhamnolipid to 0.459, 0.279, 0.217, and 0.0966, corresponding to the presence of rhamnolipid at concentrations of 20, 50, 80, and 100 mg/L. The transport parameters of nZVI in ZK406H were linked to the interactions of nZVI particles with ZK406H by the DLVO theory.

Carboxymethyl cellulose stabilization induced changes in particle characteristics and dechlorination efficiency of sulfidated nanoscale zero-valent iron

Polymer stabilization, exemplified by carboxymethyl cellulose (CMC), has demonstrated effectiveness in enhancing the transport of nanoscale zero-valent iron (nZVI). And, sulfidation is recognized for enhancing the reactivity and selectivity of nZVI in dechlorination processes. The influence of polymer stabilization on sulfidated nZVI (S-nZVI) with various sulfur precursors remains unclear. In this study, CMC-stabilized S-nZVI (CMC-S-nZVI) was synthesized using three distinct sulfur precursors (S2−, S2O42−, and S2O32−) through one-step approach. The antioxidant properties of CMC significantly elevated the concentration of reduced sulfur species (S2−) on CMC-S-nZVIs, marking a 3.1–7.0-fold increase compared to S-nZVIs. The rate of trichloroethylene degradation (km) by CMC-S-nZVIs was observed to be 2.2–9.0 times higher than that achieved by their non-stabilized counterparts. Among the three CMC-S-nZVIs, CMC-S-nZVINa2S exhibited the highest km. Interesting, while the electron efficiency of CMC-S-nZVIs surged by 7.9–12 times relative to nZVI, it experienced a reduction of 7.0–34% when compared with S-nZVIs. This phenomenon is attributed to the increased hydrophilicity of S-nZVI particles due to CMC stabilization, which inadvertently promotes the hydrogen evolution reaction (HER). In conclusion, the findings of this study underscores the impact of CMC stabilization on the properties and dechlorination performance of S-nZVI sulfidated using different sulfur precursors, offering guidance for engineering CMC-S-nZVIs with desirable properties for contaminated groundwater remediation.

Transport of nanoscale zero-valent iron in saturated porous media: Effects of grain size, surface metal oxides, and sulfidation

Knowledge of the fate and transport of nanoscale zero-valent iron (nZVI) in saturated porous media is crucial to the development of in situ remediation technologies. This work systematically compared the retention and transport of carboxymethyl cellulose (CMC) modified nZVI (CMC-nZVI) and sulfidated nZVI (CMC-S-nZVI) particles in saturated columns packed with quartz sand of various grain sizes and different surface metal oxide coatings. Grain size reduction had an inhibitory effect on the transport of CMC-S-nZVI and CMC-nZVI due to increasing immobile zone deposition and straining in the columns. Metal oxide coatings had minor effect on the transport of CMC-S-nZVI and CMC-nZVI because the sand surface was coated by the free CMC in the suspensions, reducing the electrostatic attraction between the nZVI and surface metal oxides. CMC-S-nZVI displayed greater breakthrough (C/C0 = 0.82–0.90) and higher mass recovery (84.9%–89.3%) than CMC-nZVI (C/C0 = 0.70–0.80 and mass recovery = 70.9%–79.6%, respectively) under the same experimental conditions. A mathematical model based on the advection-dispersion equation simulated the experimental data of nZVI breakthrough curves very well. Findings of this study suggest sulfidation could enhance the transport of CMC-nZVI in saturated porous media with grain and surface heterogeneities, promoting its application in situ remediation.

Escherichia coli and phosphate interplay mediates transport of nanoscale zero-valent iron synthesized by green tea in water-saturated porous media

Green synthesized nano-zero-valent iron (GT-nZVI) has been considered an excellent material for in-situ soil remediation due to its high stability and environmental benignity. However, sufficient transportability of GT-nZVI downstream towards the contaminated sites, likely affected by the physicochemical properties of soil-groundwater, is required for improved in-situ remediation. Thus, the effect of soil components (i.e., bacteria and phosphate) on GT-nZVI transportability is significant. Hence, we studied the transport of GT-nZVI (Fe0 core wrapped by green tea polyphenols) with the existence of E. coli and phosphate in water-saturated porous sand media in NaCl and CaCl2 solutions at pHs 6.0 and 8.0. Also studied were the stability, surface characteristics, and two-site kinetics attachment modeling (TKAM) with Escherichia coli or/and phosphate. The results showed that phosphate could further enhance GT-nZVI co-transport with E. coli by increasing the negative charge on GT-nZVI at pH 6.0. However, E. coli reduced GT-nZVI mobility at pH 8.0 because the cell-cell interactions could mask the negative charges of pre-deposited GT-nZVI on E. coli, forming the large clusters between GT-nZVI and E. coli. Then, phosphate occurrence diminished E. coli inhibition by detaching GT-nZVI from nZVI-E. coli-phosphate polymers due to the stronger phosphate adsorption on E. coli than GT-nZVI at pH 8.0. Overall, TKAM describes the transport and retention of GT-nZVI adequately under various conditions, indicating the deposition order with k2str value as follows: GT-nZVI alone > with (w.) E. coli > w. phosphate > w. combined E. coli & phosphate at pH 6.0. By contrast, w. phosphate > w. E. coli > w. combined E. coli & phosphate > GT-nZVI alone ensued at pH 8.0. This investigation highlights the transport behavior of GT-nZVI associated with surface property changes in complex environments for effective in-situ remediation.

Transport of Nanoscale Zero-Valent Iron in Saturated Porous Media: Effects of Grain Size, Surface Metal Oxides, and Sulfidation

Transport of Nanoscale Zero-Valent Iron in Saturated Porous Media: Effects of Grain Size, Surface Metal Oxides, and Sulfidation

Field-scale investigation of nanoscale zero-valent iron (NZVI) injection parameters for enhanced delivery of NZVI particles to groundwater

The effects of the injection parameters on delivery of nanoscale zero-valent iron (NZVI) to contaminated groundwater were investigated. The first two NZVI injections (gravity injection at low flow rates) resulted in NZVI being poorly mobile and gave total cumulative mass recoveries at the monitoring wells of 1.07%–2.43%. NZVI reached some wells (KDMW-3, MW-2, MW-4, and MW-7) earlier than the bromide tracer. The dominant travel directions for NZVI and the bromide tracer were very different. The NZVI transport characteristics suggested that targeted NZVI delivery requires preferential groundwater flow paths and local heterogeneity to be considered. In the gravity injection tests, the maximum NZVI concentrations and cumulative NZVI mass recoveries in the wells decreased markedly as the injected NZVI concentration and dose increased. In the third and fourth tests, in which NZVI was injected under pressure at high flow rates, NZVI was effectively delivered to the wells despite the injected NZVI concentration and dose being high. Relatively high cumulative mass recoveries of 26.0% and 74.5% were found for the third and fourth injections, respectively. Controlling the flow rate (pressure) and NZVI concentration and dose simply and effectively controlled NZVI mobility in the groundwater. The colloidal and electrostatic characteristics of the NZVI particles were monitored and modeled, and the results indicated that NZVI particles without Derjaguin–Landau–Verwey–Overbeek energy barriers were successfully delivered to the target zone and that decreased magnetic attractive forces between NZVI particles caused by iron corrosion probably decreased the degree of NZVI particle aggregation and therefore contributed to NZVI being delivered to the target zone.

Modification of zero valent iron nanoparticles by sodium alginate and bentonite: Enhanced transport, effective hexavalent chromium removal and reduced bacterial toxicity

The rapid aggregation/sedimentation and decreased transport of nanoscale zero-valent iron (nZVI) particles limit their application in groundwater remediation. To decrease the aggregation/sedimentation and increase the transport of nZVI, sodium alginate (a natural polysaccharide) and bentonite (one type of ubiquitous clay) were employed to modify nZVI. Different techniques were utilized to characterize the modified nZVI. We found that modification with either sodium alginate or bentonite could disperse nZVI and shifted their zeta potentials from positive to negative. Comparing with the bare nZVI, the sedimentation rates of modified nZVI either by sodium alginate or bentonite are greatly decreased and their transport are significantly increased. The transport of modified nZVI can be greatly increased by increasing flow rate. Furthermore, Cr(VI) can be efficiently removed by the modified nZVI (both sodium alginate and bentonite modified nZVI). Comparing with bare nZVI, the two types of modified nZVI contain lower toxicities to Escherichia coli. The results of this study indicate that both sodium alginate and bentonite can be employed as potential stabilizers to disperse nZVI and improve their application feasibility for in situ groundwater remediation.

Carboxymethyl cellulose stabilized and sulfidated nanoscale zero-valent iron: Characterization and trichloroethene dechlorination

Polymer stabilization can enhance subsurface transport of nanoscale zero-valent iron (nZVI) while sulfidation can reduce its hydrogen evolution reaction (HER) and enhance electron utilization efficiency (εe). However, the combined impacts of stabilization and sulfidation on particle characteristics, reactivity and efficiency, and therefore longevity for contaminant remediation/capacity, has not been adequately investigated. Carboxymethyl cellulose stabilized and sulfidated nZVI (CMC-S-nZVI) was synthesized by both one-pot and two-step approaches and characterized with SEM, TEM-SAED, XRD, XPS and FTIR techniques. Dithionite was used as the sulfur source for the one-pot particles and sulfide was used for the two-step particles. We found that CMC stabilization did not affect the degree of sulfidation. Both stabilization of S-nZVI and sulfidation of CMC-nZVI enhanced particle reactivity by one order of magnitude. The two-step CMC-S-nZVI generally exhibited much higher reactivity than the one-pot counterparts, mainly because dithionite consumes Fe0. CMC stabilization significantly decreased εe, an effect not quantified before, while sulfidation compensated for the decrease. Almost full εe compensation against stabilization was obtained at S/Fe 0.5, where the εe was ∼14% and 13%, for the non-stabilized and the two-step CMC-S-nZVI, respectively. Sulfidation at S/Fe > 0.2 completely eliminated the HER in the two-step CMC-S-nZVI after 2d with > 73% of Fe0 preserved, and had a perfect εe of 100% after 8d of ageing (i.e., the longevity of CMC-nZVI). Our results suggest that through stabilization and sulfidation, a balance between particle stability and longevity/capacity of nZVI could be achieved.

Adsorption, transformation, and colloid-facilitated transport of nano-zero-valent iron in soils

ABSTRACTBecause of its unique reductive properties, nanoscale zero-valent iron (NZVI) has been widely used in soil and groundwater remediation. It is crucial to understand the fate of NZVI in soils. In this work, a range of laboratory experiments was conducted to examine the adsorption, transformation, and transport of NZVI. The NZVI particles showed relatively strong sorption onto vertic shajiang-aquic cambosols, typic-hapli-udic argosols and typic ochri-aquic cambosols and isotherms can be well described by the Langmuir model. When cultivated in the soils, the NZVI was oxidized within seven days and the particle size also increased with average size reaching around 100 nm at 28 days. Columns were packed with quartz sand, sandy soil and diatomite as saturated porous media to evaluate the role of soil colloids in affecting the transport of NZVI. The results showed that NZVI transport in the columns was strongly affected by medium types, dispersion agent types, and soil colloids. Comparisons of breakthrough curves of different types of dispersed NZVI and corresponding colloid-NZVI revealed that natural soil colloids facilitated NZVI transport in porous media. Findings from this work can provide useful information to better evaluate the applications and impacts of NZVI as an environmental remediation agent.

Characteristics of Aggregate Size Distribution of Nanoscale Zero-Valent Iron in Aqueous Suspensions and Its Effect on Transport Process in Porous Media

Bare nanoscale zero-valent iron (NZVI) particles in aqueous suspensions aggregate into micron to submicron sizes. The transport process of enlarged aggregates or multi-sized aggregates is different from that of nanoparticles. In this work, we performed aggregate size distribution analysis of NZVI suspension using a laser grain size analyzer and conducted a series of continuous injection column experiments with different injected NZVI concentrations. The results show that aggregates in NZVI suspensions range from submicron to submillimeter size and are mainly distributed around 5–9 μm and 50–100 μm. Quantitative calculation of iron transport and retention showed that the retained iron linearly correlates with injected concentration. The cross-section images revealed that clogging weakened from inlet to outlet. Furthermore, larger aggregates (>40 μm) appeared more often in the rising-declining stages of breakthrough curves, whereas small aggregates (<30 μm) dominated the steady stage. Indeed, relatively preferential flow facilitated the transport and discharge of both large and small iron aggregates. Straining of glass beads especially for the large iron aggregates resulted in a decline in breakthrough. Moreover, the blocking of attached and plugged iron prevented later retention of iron, resulting in a certain concentration of iron in the effluents. Our study provides greater insight into the transport of NZVI.

Transport of CMC-Stabilized nZVI in Saturated Sand Column: the Effect of Particle Concentration and Soil Grain Size

A considerable number of studies have been conducted to investigate the effect of physical and chemical variables on the transport of nanoscale zerovalent iron (nZVI) in granular media. However, the role of soil grain size as a crucial factor in nanoparticle mobility is less understood. The present research work sought to examine the simultaneous effects of soil grain size and particle concentration on the transport of nZVI coated with carboxymethyl cellulose (CMC-nZVI), using saturated sand packed column experiments. To this end, a total of 12 tests were conducted by combining four different particle concentrations (C = 10, 200, 3000, 10,000 mg/l) and three grain sizes (dc = 0.297–0.5 mm, 0.5–1 mm, 1–2 mm). The effluent nZVI concentration and water pressure drop along the column were measured. The results showed that during the injection time, decreasing the grain size and increasing the particle concentration reduces the mobility of CMC-nZVI due to ripening phenomena, while during the flushing time (introducing deionized water), such changes in grain size and particle concentration increase the mobility of CMC-nZVI due to a release from the secondary energy minimum well (in the DLVO theory).

Effect of injection velocity and particle concentration on transport of nanoscale zero-valent iron and hydraulic conductivity in saturated porous media

Successful groundwater remediation by injecting nanoscale zero-valent iron (NZVI) particles requires efficient particle transportation and distribution in the subsurface. This study focused on the influence of injection velocity and particle concentration on the spatial NZVI particle distribution, the deposition processes and on quantifying the induced decrease in hydraulic conductivity (K) as a result of particle retention by lab tests and numerical simulations. Horizontal column tests of 2m length were performed with initial Darcy injection velocities (q0) of 0.5, 1.5, and 4.1m/h and elemental iron input concentrations (Fe0in) of 0.6, 10, and 17g/L. Concentrations of Fe0 in the sand were determined by magnetic susceptibility scans, which provide detailed Fe0 distribution profiles along the column. NZVI particles were transported farther at higher injection velocity and higher input concentrations. K decreased by one order of magnitude during injection in all experiments, with a stronger decrease after reaching Fe0 concentrations of about 14–18g/kg(sand). To simulate the observed nanoparticle transport behavior the existing finite-element code OGS has been successfully extended and parameterized for the investigated experiments using blocking, ripening, and straining as governing deposition processes. Considering parameter relationships deduced from single simulations for each experiment (e.g. deposition rate constants as a function of flow velocity) one mean parameter set has been generated reproducing the observations in an adequate way for most cases of the investigated realistic injection conditions. An assessment of the deposition processes related to clogging effects showed that the percentage of retention due to straining and ripening increased during experimental run time resulting in an ongoing reduction of K. Clogging is mainly evoked by straining which dominates particle deposition at higher flow velocities, while blocking and ripening play a significant role for attachment, mainly at lower injection velocities. Since the injection of fluids at real sites leads to descending flow velocities with increasing radial distance from the injection point, the simulation of particle transport requires accounting for all deposition processes mentioned above. Thus, the derived mean parameter set can be used as a basis for quantitative and predictive simulations of particle distributions and clogging effects at both lab and field scale. Since decreases in K can change the flow system, which may have positive as well as negative implications for the in situ remediation technology at a contaminated site, a reliable simulation is thus of great importance for NZVI injection and prediction.

Transport of carboxymethyl cellulose-coated zerovalent iron nanoparticles in a sand tank: Effects of sand grain size, nanoparticle concentration and injection velocity

The transport of nanoscale zerovalent iron (NZVI) particles colloidally stabilized with 70,000 Da carboxymethyl cellulose (CMC), through sands with mean grain diameters of 180, 340 and 1140 μm (referred to as fine, intermediate and coarse-sized sand, respectively) was investigated in a 70-cm long, two-dimensional tank. The effect of NZVI concentrations (1 and 3 g-Fe L−1) and CMC concentrations (1 and 2 g L−1) and injection velocities (0.96 and 0.40 cm min−1) on particle transport were also evaluated with the intermediate sand. The overall NZVI mass fractions eluted from the tank were 36%, 25% and 16% in the coarse, intermediate and fine sands, respectively, when injected with 1 g L−1 NZVI stabilized in 1 g L−1 CMC. However, the mass fraction eluted reduced to 2.33% when the injection velocity was reduced from 0.96 to 0.40 cm min−1 in the intermediate-sized sand. Maximum transport efficiency (38% NZVI mass eluted) in the intermediate-sized sand was achieved with 3 g L−1 NZVI suspended in 2 g L−1 CMC at an injection velocity of 0.96 cm min−1. The transport efficiency was substantially decreased (11% NZVI mass eluted) when 3 g L−1 NZVI was stabilized with only 1 g L−1 CMC. The NZVI mean particle diameters in the porewaters remained unchanged at different locations in the tank suggesting that straining or gravity settling did not influence NZVI deposition. After NZVI injection, the hydraulic conductivity in the tank reduced by 80%–96%, depending on the CMC concentration and injection velocity.

Enhanced transport of Si-coated nanoscale zero-valent iron particles in porous media

ABSTRACTLaboratory column experiments were conducted to evaluate the effect of previously described silica coating method on the transport of nanoscale zero-valent iron (nZVI) in porous media. The silica coating method showed the potential to prevent the agglomeration of nZVI. Transport experiments were conducted using laboratory-scale sand-packed columns at conditions that were very similar of natural groundwater. Transport properties of non-coated and silica-coated nZVI are investigated in columns of 40 cm length, which were filled with porous media. A suspension was injected in three different Fe particle concentrations (100, 500, and 1000 mg/L) at flow 5 mL/min. Experimental results were compared using nanoparticle attachment efficiency and travel distances which were calculated by classical particle filtration theory. It was found that non-coated particles were essentially immobile in porous media. In contrast, silica-coated particles showed significant transport distances at the tested conditions. Results of this study suggest that silica can increase nZVI mobility in the subsurface.

Modified MODFLOW-based model for simulating the agglomeration and transport of polymer-modified Fe0 nanoparticles in saturated porous media.

The solute transport model MODFLOW has become a standard tool in risk assessment and remediation design. However, particle transport models that take into account both particle agglomeration and deposition phenomena are far less developed. The main objective of the present study was to evaluate the feasibility of adapting the standard code MODFLOW/MT3D to simulate the agglomeration and transport of three different types of polymer-modified nanoscale zerovalent iron (NZVI) in one-dimensional (1-D) and two-dimensional (2-D) saturated porous media. A first-order decay of the particle population was used to account for the agglomeration of particles. An iterative technique was used to optimize the model parameters. The model provided good matches to 1-D NZVI-breakthrough data sets, with R 2 values ranging from 0.96 to 0.99, and mass recovery differences between the experimental results and simulations ranged from 0.1 to 1.8%. Similarly, simulations of NZVI transport in the heterogeneous 2-D model demonstrated that the model can be applied to more complicated heterogeneous domains. However, the fits were less good, with the R 2 values in the 2-D modeling cases ranging from 0.75 to 0.95, while the mass recovery differences ranged from 0.7 to 6.5%. Nevertheless, the predicted NZVI concentration contours during transport were in good agreement with the 2-D experimental observations. The model provides insights into NZVI transport in porous media by mathematically decoupling agglomeration, attachment, and detachment, and it illustrates the importance of each phenomenon in various situations. Graphical Abstract ᅟ.

The effects of viscosity of carboxymethyl cellulose on aggregation and transport of nanoscale zerovalent iron

Abstract This study demonstrates that both polyelectrolyte viscosity and electrosteric stabilization forces contribute to colloidal stability and mobility of nanoscale zerovalent iron (NZVI) particles at high concentrations (g/L levels) required for groundwater remediation. Carboxymethyl cellulose (CMC) of different molecular weights of 90,000, 250,000 and 700,000 g/mol was used for colloidal stabilization of NZVI. The diameters of the CMC-NZVI aggregates were characterized by light scattering techniques and microscopy. The molecular weight of CMC significantly influenced the mean aggregate size of NZVI particles. NZVI stabilized in 700 K CMC (1 g/L) resulted in aggregates of 540 nm mean diameter, whereas in 90 K CMC (1 g/L) resulted in 1115 nm aggregates, as measured by dynamic light scattering. This study demonstrates that the increased colloidal stability with 700 K CMC compared to 90 K or 250 K CMC is due to effects of viscosity of CMC in solution which reduces the Brownian movement of nanoparticles, and due to higher electrosteric stabilization of NZVI. The transport (steady-state effluent concentration) of CMC-NZVI particles was significantly enhanced with the increase in molecular weight of CMC, as a result of formation of smaller aggregates and due to the dependence of viscosity on the single collector contact efficiency and deposition rate coefficients.

Surface coating with Ca(OH)2 for improvement of the transport of nanoscale zero-valent iron (nZVI) in porous media

A novel thermal deposition method was developed to coat Ca(OH)2 on the surface of nanoscale zero-valent iron (nZVI). The nZVI particles with the Ca(OH)2 coating layer, nZVI/Ca(OH)2, had a clear core-shell structure based on the transmission electron microscopy observations, and the Ca(OH)2 shell was identified as an amorphous phase. The Ca(OH)2 coating shell would not only function as an effective protection layer for nZVI but also improve the mobility of nZVI in porous media for its use in environmental decontamination. A 10% Ca/Fe mass ratio was found to result in a proper thickness of the Ca(OH)2 shell on the nZVI surface. Based on the filtration tests in sand columns, the Ca(OH)2-based surface coating could greatly improve the mobility and transport of nZVI particles in porous media. In addition, batch experiments were conducted to evaluate the reactivity of Ca(OH)2-coated nZVI particles for the reduction of Cr(VI) and its removal from water.

Carbonate minerals in porous media decrease mobility of polyacrylic acid modified zero-valent iron nanoparticles used for groundwater remediation

The limited transport of nanoscale zero-valent iron (nZVI) in porous media is a major obstacle to its widespread application for in situ groundwater remediation. Previous studies on nZVI transport have mainly been carried out in quartz porous media. The effect of carbonate minerals, which often predominate in aquifers, has not been evaluated to date. This study assessed the influence of the carbonate minerals in porous media on the transport of polyacrylic acid modified nZVI (PAA-nZVI). Increasing the proportion of carbonate sand in the porous media resulted in less transport of PAA-nZVI. Predicted travel distances were reduced to a few centimeters in pure carbonate sand compared to approximately 1.6 m in quartz sand. Transport modeling showed that the attachment efficiency and deposition rate coefficient increased linearly with increasing proportion of carbonate sand.

Electrophoresis enhanced transport of nano-scale zero valent iron

Electrokinetics (EK) has been used extensively to remove heavy metals from low permeability porous media. Electrokinetics (EK) or more specifically electrophoresis (EP) has also been proposed to enhance transport of nanoscale zero valent iron (NZVI) in fine grained porous media in the subsurface. However, increased dissolved oxygen and lower pH, due to electrolysis of water at the anode oxidizes NZVI particles and thus affects the remediation potential of EP with NZVI. This study focuses on minimization of NZVI oxidation and quantification of NZVI migration enhancement through the application of EP. Application of 50 and 100mA currents under constant current conditions with an oxygen scavenger enhanced NZVI transport from the cathode to the anode. The enhancement in transport compared to diffusion was proportional to the applied current. Predictions of a numerical model, based on traditional colloidal filtration theory (CFT), were consistent with experimental results. In developing the model, the traditional CFT based mass balance equation was modified for the case of no advection. This study suggests that EP has the potential to deliver NZVI in low permeability porous media and that the numerical simulator can be used to predict NZVI mobility with EP.

Enhanced transport of polyelectrolyte stabilized nanoscale zero-valent iron (nZVI) in porous media

Laboratory experiments including column and batch sedimentation studies were conducted to investigate the transport of nanoscale zero-valent iron (nZVI) particles stabilized by three polyelectrolytes: polyvinyl alcohol-co-vinyl acetate-co-itaconic acid (PV3A), poly(acrylic acid) (PAA) and soy proteins. Results of the continuous packed column study suggest that the both PV3A and PAA can increase nZVI mobility by reducing particle size and generating negatively charged surfaces of nZVI. PV3A stabilized nZVI has the best transport performance among the three materials. It was found that approximately 100% of nZVI flowed through the column. Retardation of nZVI is observed in all tests. Due to the large surface area of nZVI, large amounts of polyelectrolytes are often needed. For example, soy proteins exhibited an excellent stabilization capability only at the dose over 30% of nZVI mass. Approximately 57% of nZVI remained in the column when nZVI was stabilized with PAA at the dosage of 50%. Results suggest that nZVI may be prepared with tunable travel distance to form an iron reactive zone for the in situ remediation.