nZVI Mobility Research Articles

Two-Dimensional Modeling of Nano Zero-Valent Iron Transport and Retention before and after Phosphate Adsorption.

The mobility of nano zero-valent iron (nZVI) will greatly affect its practical application as a remediation material for contaminated groundwater. One-dimensional (1D) column tests are commonly used in previous work to study its migration behavior, but the two-dimensional (2D) test is still very limited. This study reports a novel research system to study the 2D transport and retention behavior of colloids and solutes, which includes a 2D model test setup and the corresponding image analysis method. The transport behaviors of methyl orange (MO), nZVI, and phosphate-loaded nZVI (PnZVI) are studied using this system. The results show that the research system can reasonably describe the tempo-spatial concentration distribution of colloids and solutes. After phosphate adsorption, the mobility of nZVI is enhanced due to the increase in negative surface charge, which implies a potential environmental risk of nZVI to facilitate contaminant transport. The migration of PnZVI is not significantly influenced by its density, which is faster than MO in the longitudinal direction. The range of the plume of PnZVI in the longitudinal direction is larger than that of MO, which implies that PnZVI has a stronger longitudinal dispersion than MO.

NZVI Mobility and Transport: Laboratory Test and Numerical Model

Zerovalent iron nanoparticles (nZVI) are becoming one of the most widely recommended nanomaterials for soil and groundwater remediation. However, when nZVI are injected in the groundwater flow, the behavior (mobility, dispersion, distribution) is practically unknown. This fact generally results in the use of enormous quantities of them at the field scale. The uncertainties are on the effective volumes reached from the plume of nZVI because their tendency to aggregate and their weight can cause their settling and deposition. So, the mobility of nanoparticles is a real issue, which can often lead to inefficient or expensive soil remediation. Furthermore, there is another aspect that must be considered: the fate of these nZVI in the groundwater and their possible impact on the subsoil environment. All these considerations have led us to propose an application of nZVI simulating the permeation technique through a laboratory experience, finalized to have a better, or even simpler description of their real behavior when injected in a flow in the subsoil. A two-dimensional laboratory-scale tank was used to study the dispersion and transport of nZVI. A nZVI solution, with a concentration equal to 4.54 g/L, was injected into glass beads, utilized as porous medium. The laboratory experiment included a digital camera to acquire the images. The images were then used for calibrating a numerical model. The results of the mass balance confirm the validity of the proposed numerical model, obtaining values of velocity (5.41 × 10−3 m/s) and mass (1.9 g) of the nZVI of the same order of those from the experimental tests. Several information were inferred from both experimental and numerical tests. Both demonstrate that nZVI plume does not behave as a solute dissolved in water, but as a mass showing its own mobility ruled mainly from the buoyancy force. A simple simulation of a tracer input and a nZVI plume are compared to evidence the large differences between their evolution in time and space. This means that commercial numerical models, if not corrected, cannot furnish a real forecast of the volume of influence of the injected nZVI. Further deductions can be found from the images and confirmed by means the numerical model where the detachment effect is much smaller than the attachment one (ratio kd/ka = 0.001). From what is reported, it is worthwhile to pay attention on the localization of the contaminants source/plume to reach an effective treatment and it is important to go further in the improvement of solution for the limiting the nanoparticles aggregation phenomenon.

Mobility of nZVI in a Reconstructed Porous Media Monitored by an Image Analysis Procedure

Zero-valent iron nanoparticle (nZVI) technology has been found to be promising and effective for the remediation of soils or groundwater. However, while nanoparticles are traveling through porous media, they can rapidly aggregate, causing their settling and deposition. When nZVI are injected in the groundwater flow, the behavior (mobility, dispersion, distribution) is unknown in groundwater, causing the use of enormous quantities of them if used at the field scale. In this paper, a laboratory experiment was carried out with groundwater flow in a two-dimensional, laboratory-scale tank to assess the nanoparticle behavior by means of an image analysis procedure. A solution of zero-valent iron nanoparticles, Nanofer 25S particles, were used and glass beads were utilized as porous medium. The laboratory experiment included the use of a digital camera for the acquisition of the images. The image analysis procedure was used to assess the behavior of nZVI plume. A calibration procedure and a mass balance were applied to validate the proposed image analysis procedure, with the hypothesis that nanoparticles would be uniformly distributed in the third dimension of the tank (thickness). The results show that the nanoparticles presented small dispersive effects and the motion was strongly influenced from the higher weight of them with respect to the water. Therefore, the results indicate that nanoparticles have an own motion not strongly influenced by the fluid flow but more determined from the injection phase and gravity. The statistical elaborations show that the nZVI plume did not respond to the classical mechanisms of the dispersion.

Effect of the modification sequence on the reactivity, electron selectivity, and mobility of sulfidated and CMC-stabilized nanoscale zerovalent iron

Dual modification in which carboxymethyl cellulose (CMC) stabilization and sulfidation are coupled is an effective strategy to solve the insufficient electron selectivity, reactivity, and mobility of nanoscale zerovalent iron (nZVI). We compared the sulfur content, suspension composition, viscosity, zeta potential, and sedimentation of dual-modified nZVI suspensions synthesized in different modification sequences to analyze the interaction among CMC, the sulfidation reagent, and nZVI. The results show that the dissolved CMC does not take up S2−, and the CMC coating on the surface does not block S2− during sulfidation. However, CMC can peel off the FeS shell, resulting in a low sulfur content in nZVI. The Na+ of the sulfidation reagent and the Fe2+ dissolved from the FeS precipitates reduce the CMC viscosity, causing accelerated sedimentation and reduced mobility of nZVI. The peeled off FeS shell increases the free Fe2+ concentration, thereby enhancing nitrobenzene reduction. Additionally, CMC promotes nitrobenzene reduction and hydrogen evolution reactions due to the increased nZVI dispersibility. These findings explain why postsulfidated and one-pot nZVI has higher reactivity and electron selectivity, while presulfidated nZVI has higher mobility. This study highlights the importance of the modification sequence for the dual-modified nZVI properties and provides support for the synthesis method.

Effects of multiple injections on the transport of CMC-nZVI in saturated sand columns

The multiple injections of nanoscale zero valent iron (nZVI) slurry, an efficient method to remediate contaminated groundwater, requires an accurate assessment of the transport and risks of these particles in saturated porous medium. However, the influencing mechanism of nZVI transport under multiple injection conditions is not fully understood. In this experimental study, one-dimensional sand columns were used to evaluate the effects of injection concentrations, particle sizes and surface chemical corrosion on the transport of carboxymethyl cellulose modified nZVI (CMC-nZVI) under triple injection conditions, where the different volumes of NaCl solution were flushed through the columns between the injections. Based on the breakthrough curves and retention profiles under flushing 4 pore volumes of NaCl solution between the injections, the transport of CMC-nZVI particles was gradually enhanced attributable to the exclusion among these particles at injection concentration of 200 mg/L, but the opposite was observed due to large aggregation caused by strong magnetic force among particles at 500 mg/L. However, the magnitudes of enhancement or reduction on maximum C/C0 under the above injection concentrations were related to the smallest particle size of Dh = 3.926 μm because of high particle number concentrations leading to intense competition on depositional sites at 200 mg/L and significant aggregation at 500 mg/L. Conversely, the transport of CMC-nZVI was reduced under flushing 76 pore volumes of NaCl solution between the injections because of pronounced corrosion of CMC-nZVI in water as evidenced by the XPS and XRD analyses of particles. This corrosion could cause the decrease in repulsion among particles due to the increase in surface negative zeta potential and the CMC desorption from nZVI. Accordingly, this study revealed that relative high injection concentrations and chemical corrosion in groundwater could restrain the mobility of nZVI under multiple injection conditions and the potential risks posed by CMC-nZVI are controllable.

Impact of phosphate adsorption on the mobility of PANI‐supported nano zero‐valent iron

AbstractNano zero‐valent iron (nZVI) has been used for in situ groundwater remediation due to its strong adsorption and reaction characteristics. However, oxyanion contaminants in groundwater can ready adsorbed onto the surface of nZVI. This can potentially alter the mobility of nZVI and create a secondary pollution source, but these issues have not yet been systematically investigated. In this study, polyaniline‐supported nZVI (PnZVI) and phosphate‐sorbed PnZVI (PS‐PnZVI) were synthesized in the laboratory. The sedimentation and transport behavior of these two nZVI particles were investigated, compared, and mathematically modeled to better understand the impact of phosphate adsorption on these processes. Results showed that phosphate adsorption can enhance the stability and mobility of PnZVI. Interaction energy calculations that considered van der Waals and magnetic attraction, electrostatic double layer and Born repulsion, and the influence of nanoscale roughness and binary charge heterogeneity were conducted to better infer mechanisms causing nZVI particle sedimentation and retention. Nanoscale roughness and binary charge heterogeneity were found to significantly decrease the energy barrier, but not to low enough levels to explain the observed behavior. The rapid settling of PnZVI was attributed to strong magnetic attraction between particles, which produced rapid aggregation and retention due to straining and/or hydrodynamic bridging. Phosphate adsorption enhanced the mobility of PS‐PnZVI in comparison with PnZVI due to a decrease in particle size and aggregation, and an increase in the energy barrier with the porous media. A potential risk of nZVI particles to facilitate oxyanion contaminant transport was demonstrated for phosphate.

A Review on Montmorillonite-Supported Nanoscale Zerovalent Iron for Contaminant Removal from Water and Soil

Nanoscale zerovalent iron (nZVI) has shown great promise for water treatment and soil remediation. However, the rapid aggregation of nZVIs significantly affects their mobility and reactivity, which considerably limits the practical applications. Montmorillonite- (Mt-) supported nZVI (Mt-nZVI) has received increasing attention for the past decade because it can prevent the aggregation of nZVI and incorporate the advantages of both nZVI and Mt in soil and water treatment. This work thus had a comprehensive review on the use of Mt-nZVI for soil and water treatment. We first summarized existing methods used to prepare Mt-nZVI, indicating the advantages of using Mt to support nZVI (e.g., increase of the dispersion and mobility of nZVI, reduction of the size and oxidation tendency of nZVI). We then presented the reaction mechanisms of Mt-nZVI for contaminant removal and evaluated the critical factors that influence the removal (e.g., pH, temperature, and dosage of the adsorbent). We further presented examples of applications of Mt-nZVI for the removal of typical contaminants such as heavy metals and organic compounds in soil and water. We finally discussed the limitations of the use of Mt-nZVI for water treatment and soil remediation and presented future directions for the application of nZVI technology for soil and water treatment.

Removal of uranium(VI) from aqueous solution by Mg(OH)2-coated nanoscale zero-valent iron: Reactivity and mechanism

Nanoscale zero-valent iron (nZVI) is considered to be an effective material for removing U(VI), but its application in in-situ remediation is limited due to its easy oxidation and agglomeration. In order to solve this problem, nZVI@Mg(OH)2 was synthesized by modified liquid phase reduction method and used to remove U(VI) from aqueous solution. The effects of pH, contact time, dosage and initial concentration on the removal of U(VI) by nZVI@Mg(OH)2 were studied by batch experiments. The results showed that nZVI@Mg(OH)2 presented better removal efficiency than nZVI, the removal ratio and amount reached 97.8 % and 122.3 mg/g respectively at 0.4 g/L dosage with 50 mg/L U(VI) solution. Various techniques were implemented to characterize nZVI@Mg(OH)2. The results indicated that Mg(OH)2 was successfully coated on the nZVI surface, thus turned rough, aggregation and oxidation of Fe° particles was minimized, then the removal performance of U(VI) increased. Mechanisms were also explored by a comparative study of the phase, morphology, and surface valence state of composite before and after reaction, indicating that nZVI@Mg(OH)2 remove U(VI) mainly through reduction and adsorption. The results of column experiments and sedimentation experiments showed that the suspension stability and mobility of nZVI have been improved after coating. It can be seen that nZVI@Mg(OH)2 has certain potential for in-situ remediation of U(VI).

Improved Affinity of Nanoscale Zero Valent Iron toward Hydrophobic Organic Solvent using Poly(1-vinylpyrrolidone-co-vinyl acetate)

Objectives : Levels of organic contaminants in excess of the standard minimum have been detected in many commercial and residential sites, and the severity of soil and groundwater pollution is increasing. In particular, non-aqueous phase liquids (NAPLs) are hydrophobic organic pollutants that do not mix with water and are difficult to remove with existing soil remediation technology. These pollutants slowly dissolve into the groundwater over long periods of time, thus contaminating the groundwater. With the increasing need to remove NAPLs for soil and groundwater remediation, widespread interest has focused on the use of nanoscale zero valent iron (nZVI). However, nZVI has the disadvantage of reduced subsurface mobility. Hence, in the present study, the nZVI surface is modified with poly(1-vinylpyrrolidone-co-vinyl acetate) (PVP/VA), which has both hydrophilic and hydrophobic groups, to improve the mobility and selectivity of nZVI for the removal of NAPL.Methods : The PVP/VA modified nZVI is synthesized through the reaction of FeSO4･7H2O and NaBH4 in the presence of PVP/VA. To confirm the dispersibility of the prepared material, a precipitation experiment is performed using a visible light spectrometer, and the mobility through a sand-filled column is evaluated. In addition, the variation in particle size and characteristics according to the presence of PVP/VA is examined via transmission electron microscopy. The nitrate reduction ability of nZVI with PVP/VA is also evaluated to reveal changes in reactivity depending upon the degree of dispersion. To confirm the selective mobility towards NAPL, trichloroethylene and dodecane are used to evaluate the mobility with and without PVP/VA. Finally, the ratio of nZVI passing through the sponge layer absorbing dodecane is evaluated to determine the selective mobility towards NAPL in the porous medium.Results and Discussion : Although the dispersibility of the PVP/VA-nZVI is not significantly changed, the particle size is significantly decreased. Both the mobility in porous media and the nitrate reduction rate are improved via PVP/VA modification. The affinity for hydrophobic contaminants and the selective migration of PVP/VA-nZVI towards the NAPL layer are also improved. The high affinity for the NAPL was also shown by the column with NAPL layer.Conclusions : Surface-modification with PVP/VA, which has both hydrophilic and hydrophobic ends, enabled the synthesis of nZVI with a smaller and more uniform particle size, thus providing high mobility in porous media and high reactivity towards contaminants. The combined hydrophilicity and hydrophobicity of PVP/VA is shown to increase the affinity of nZVI towards NAPL and, thus, promote its migration to the NAPL layer. Thus, it is anticipated that the efficiency of soil remediation can be improved by promoting the movement of nZVI towards the target NAPL layer.

Use of Nanoscale Zero-Valent Iron for Remediation of Clayey Soil Contaminated with Hexavalent Chromium: Batch and Column Tests.

This study investigated the reduction of hexavalent chromium (Cr(VI)) in a clayey residual soil using nanoscale zero-valent iron (nZVI). Five different ratios between nZVI and Cr(VI) were tested in batch tests (1000/11; 1000/23; 1000/35; 1000/70, and 1000/140 mg/mg) with the soil. With the selected proportion resulting best efficiency, the column tests were conducted, with molded specimens of 5 cm in diameter and 5 cm in height, with different nZVI injection pressures (10, 30, and 100 kPa). The soil was contaminated with 800 mg/kg of Cr(VI). The Cr(VI) and Cr(III) analyses were performed following the USEPA 3060A and USEPA 7196A standards. The results show that the reduction of Cr(VI) is dependent on the ratio between nZVI and Cr(VI), reaching 98% of efficiency. In column tests, the pressure of 30 kPa was the most efficient. As pressure increased, contaminant leaching increased. The permeability decreased over time due to the gradual increase in filtration and formation of oxyhydroxides, limiting nZVI mobility. Overall, nZVI is efficient for soil remediation with Cr(VI), but the injection process can spread the contaminated if not properly controlled during in situ application.

The Role of Stabilizer Concentration in the Mobility of Carbon‐Supported Nanozerovalent Iron (nZVI) in Fractured Media

AbstractThe mobility of nanozerovalent iron (nZVI) particles is of major importance when assessing their effectiveness for use in contaminated sites. Here, the influence of the stabilizer loading on nZVI mobility was investigated in fractured media. nZVI in the form of Carbo‐Iron Colloids (CIC), a composite material of activated carbon as a carrier for nZVI, was used for the tests. CIC was supplemented with carboxymethyl cellulose stabilizer, at three different loadings: 5% wt., 20% wt., and 80% wt., in a moderately saline solution of 250 mM. Transport experiments were conducted in a fractured chalk core, and the characteristics of the solutions and particles were analyzed. The effect of ionic strength was investigated by application of the 80% loading, also in a lower salinity solution of ~3 mM. Transport experiments were modeled, and all results were compared with especially high 1,600% wt. stabilizer loading, from a previous study. Among the different carboxymethyl cellulose loadings, significant differences in mobility and a correlation between mobility and stability were observed. Though, differences in stability were found insignificant. Higher stabilizer concentration and, to a greater extent, a higher number of free stabilizer molecules in solution enhance particle stability and, hence, mobility. A good fit was obtained between the transport experiment results and a model of solute and colloid transport in a single fracture. The model attachment parameters showed a good correlation with the decay rate constants of the stability tests, indicating yet again the significant role played by stability in CIC mobility and the possibility for mobility prediction.

Removal of hexavalent chromium from groundwater using sodium alginate dispersed nano zero-valent iron

Hexavalent chromium (Cr), one of the most common heavy metals, is widely found in contaminated soil and groundwater. Nano zero-valent iron (nZVI) is used to treat Cr(VI) in polluted groundwater. However, due to agglomeration, rapid sedimentation, and limited mobility of nanoparticles in the aquatic environment, nZVI is not widely used in groundwater treatment. In this study, we used sodium alginate (SA) to modify nZVI to generate dispersed SA-nZVI. SA-nZVI particles were found to embed in the polymer material and exist as an amorphous state with a diameter less than 100 nm. Compared with traditional nZVI and carboxymethyl cellulose (CMC)-nZVI, SA-nZVI had better stability and higher absolute zeta potential. The presence of SA enhanced mobility of nZVI and effectively prevented sedimentation and aggregation. Furthermore, SA-nZVI had a higher Cr(VI) removal rate than (CMC)-nZVI under both acidic and alkaline conditions. XPS analysis showed that Cr(VI) was reduced to Cr(III) and formed Cr(OH)3 as precipitates after treatment with SA-nZVI. In addition, NO3− had no effect on the final removal rate of Cr(VI) by SA-nZVI. These results suggest that SA-nZVI has high penetration and a high removal rate in Cr(VI) removal and can be used to stabilize nZVI to remediate Cr(VI)-contaminated groundwater in the future.

Synthesis and characterizations of nZVI-AC composites from coconut shells and its application for the adsorption of Pb(II) and Cr(VI) ions

The nanotechnology development has spread not only in developed country but also in developing country such as Indonesia. This technology can be used in the management of sustainable and environment friendly of soil water resources. The nanoparticle which has particle size in the magnitude of nanometer exhibit a great potent in the treatment of water, wastes and pollution. Nano zero valent iron (nZVI) although is a promising material for such application, suffer from drawback of easily forms aggregate which decrease its mobility and reactivity towards degrading contaminant. To overcome this disadvantage property, synthesis of composite containing nZVI and activated carbon from coconut shell was conducted. Among supporting materials which added to improve stability, reactivity and mobility of nZVI, activated carbon is the most feasible choice due to its high adsorption capacity, large surface area, porous structure and abundantly available. Composite of nZVI and activated carbon is expected to possess combined property i.e. high adsorption capacity and the ability of nZVI to degrade contaminant. Preparation was conducted via sulphate method using NaBH4 reductor and FeSO4 as Fe2+ source. The ratio of nZVI and activated carbon was made by 1:1, 1:2 and 1:3. Particle size of the composite was reduced to 200 mesh and shows surface area of 398.721 m2/g. Characterization methods was carried out by using gas sorption analyser, XRD, SEM/EDS and FTIR. The composite made with 1:3 ratio was used to adsorb Pb(II) and Cr(VI). Characterization result shows that nZVI-activated carbon was formed as confirm by XRD and SEM/EDS. The reduction percentage against Pb(II) and Cr(VI) are 99.7% and 99.6% and the adsorption capacity according to these metal ions are 124.6 mg/g and 124.55 mg/g respectively.

Stabilization of nanoscale zero-valent iron in water with mesoporous carbon (nZVI@MC)

Two challenges persist in the applications of nanoscale zero-valent iron (nZVI) for environmental remediation and waste treatment: limited mobility due to rapid aggregation and short lifespan in water due to quick oxidation. Herein, we report the nZVI incorporated into mesoporous carbon (MC) to enhance stability in aqueous solution and mobility in porous media. Meanwhile, the reactivity of nZVI is preserved thanks to high temperature treatment and confinement of carbon framework. Small-sized (~16 nm) nZVI nanoparticles are uniformly dispersed in the whole carbon frameworks. Importantly, the nanoparticles are partially trapped across the carbon walls with a portion exposed to the mesopore channels. This unique structure not only is conductive to hold the nZVI tightly to avoid aggregation during mobility but also provides accessible active sites for reactivity. This new type of nanomaterial contains ~10 wt% of iron. The nZVI@MC possesses a high surface area (~500 m2/g) and uniform mesopores (~4.2 nm) for efficient pollutant diffusion and reactions. Also, high porosity of nZVI@MC contributes to the stability and mobility of nZVI. Laboratory column experiments further demonstrate that nZVI@MC suspension (~4 g Fe/L) can pass through sand columns much more efficiently than bare nZVI while the high reactivity of nZVI@MC is confirmed from reactions with Ni(II). It exhibits remarkably better performance in nickel (20 mg/L) extraction than mesoporous carbon, with 88.0% and 33.0% uptake in 5 min, respectively.

Field Scale Mobility and Transport Manipulation of Carbon-Supported Nanoscale Zerovalent Iron in Fractured Media.

In field applications, mostly in porous media, transport of stabilized nano zerovalent iron particles (nZVI) has never exceeded a few meters in range. In the present study, the transport of Carbo-Iron Colloids (CIC), a composite material of activated carbon as a carrier for nZVI stabilized by carboxymethyl cellulose (CMC), was tested under field conditions. The field site lies within a fractured chalk aquitard characterized by moderately saline (∼13 mS) groundwater. A forced gradient tracer test was conducted where one borehole was pumped at a rate of 8 L/min and CMC-stabilized CIC was introduced at an injection borehole 47 m up-gradient. Two CIC-CMC field applications were conducted: one used high 100% wt CMC (40 g/L) and a second used lower 9% wt loading (∼2.7 g/L). Iodide was injected as a conservative tracer with the CIC-CMC in both cases. The ratio between the CIC-CMC and iodide recovery was 76% and 45% in the high and low CMC loading experiments, respectively. During the low CMC loading experiment, the pumping rate was increased, leading to an additional CIC recovery of 2.5%. The results demonstrate the potentially high mobility of nZVI in fractured environments and the possibility for transport manipulation through the adjustment of stabilizer concentration and transport velocity.

Do natural biofilm impact nZVI mobility and interactions with porous media? A column study

Nanoparticles (NP) used as remediation agents for groundwater treatment may interact with biofilms naturally present, altering NP mobility and/or reactivity and thereby NP effectiveness. The influence of the presence of a multi species biofilm on the mobility of two types of zero-valent iron NP (nZVI; NANOFER 25S and optimized NANOFER STAR, NanoIron s.r.o. (Czech Republic)) was tested in laboratory experiments with columns mimicking aquifer conditions. Biofilms were grown in columns filled with sand in nitrate reducing conditions using groundwater from an industrial site as inoculum. After two months growth, they were composed of several bacterial species, dominated by Pseudomonas stutzeri. Biofilm strongly affected the physical characteristics of the sand, decreasing total porosity from ~30% to ~15%, and creating preferential pathways with high flow velocities. nZVI suspensions were injected into the columns at a seepage velocity of 10mday−1. Presence of biofilm did not impact the concentrations of Fe at the column outlet nor the amount of total Fe retained in the sand, as attested by the measurement of magnetic susceptibility. However, it had a significant impact on NP size sorting as well as on total Fe distribution along the column. This suggests nZVI-biofilm interactions that were confirmed by microscopic observations using SEM/STEM coupled with energy-dispersive X-ray spectroscopy. Our study shows that biofilm modifies the water flow velocity in the porous media, favoring the transport of large aggregates and decreased NP mobility due to physical and chemical interactions.

Evaluating the mobility of polymer-stabilised zero-valent iron nanoparticles and their potential to co-transport contaminants in intact soil cores

The use of zero-valent iron nanoparticles (nZVI) has been advocated for the remediation of both soils and groundwater. A key parameter affecting nZVI remediation efficacy is the mobility of the particles as this influences the reaction zone where remediation can occur. However, by engineering nZVI particles with increased stability and mobility we may also inadvertently facilitate nZVI-mediated contaminant transport away from the zone of treatment. Previous nZVI mobility studies have often been limited to model systems as the presence of background Fe makes detection and tracking of nZVI in real systems difficult. We overcame this problem by synthesising Fe-59 radiolabelled nZVI. This enabled us to detect and quantify the leaching of nZVI-derived Fe-59 in intact soil cores, including a soil contaminated by Chromated-Copper-Arsenate. Mobility of a commercially available nZVI was also tested. The results showed limited mobility of both nanomaterials; <1% of the injected mass was eluted from the columns and most of the radiolabelled nZVI remained in the surface soil layers (the primary treatment zone in this contaminated soil). Nevertheless, the observed breakthrough of contaminants and nZVI occurred simultaneously, indicating that although the quantity transported was low in this case, nZVI does have the potential to co-transport contaminants. These results show that direct injection of nZVI into the surface layers of contaminated soils may be a viable remediation option for soils such as this one, in which the mobility of nZVI below the injection/remediation zone was very limited. This Fe-59 experimental approach can be further extended to test nZVI transport in a wider range of contaminated soil types and textures and using different application methods and rates. The resulting database could then be used to develop and validate modelling of nZVI-facilitated contaminant transport on an individual soil basis suitable for site specific risk assessment prior to nZVI remediation.

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.

Mechanism, synthesis and modification of nano zerovalent iron in water treatment.

Owing to its strong reducing ability, high reaction activity, excellent adsorption properties, good mobility and relatively low cost, nano zerovalent iron (nZVI) is an extremely promising nanomaterial for use in water treatment. In this paper, the working mechanisms of nZVI in the degradation of various contaminants in water are outlined and discussed. Synthesis methods and their respective advantages and disadvantages are discussed in detail. Furthermore, a variety of modification methods which have been developed to improve the mobility and stability of nZVI as well as to facilitate the separation of nZVI from degraded systems are also summarized and discussed. Numerous studies indicate that nZVI has considerable potential to become an efficient, versatile and practical approach for large-scale water treatment.

Transport characteristics of nanoscale zero-valent iron carried by three different “vehicles” in porous media

This study investigated the transport properties of nanoscale zero-valent iron (Fe0) (nZVI) carried by three vehicles: water, sodium dodecyl sulfate (SDS) solution, and SDS foam. Batch experiments were conducted to assess the sedimentation capability of nZVI particles in these three vehicles. Column experiments were conducted to investigate the transport properties of nZVI in porous media formed with different sizes of sand (0.25 mm to 0.5 mm, 0.5 mm to 0.9 mm, and 0.9 mm to 1.4 mm). Three main results were obtained. First, the batch experiments revealed that the stabilities of nZVI particles in SDS solution and SDS foam were improved, compared with that of nZVI particles in water. Moreover, the sedimentation of nZVI in foam was closely associated with the foam drainage volume. The nZVI content in foam was similar to that in the original foaming suspension, and the nZVI particle distribution in foam became significantly more uniform at a stirring speed of 3000 r/min. Second, the transport of nZVI was enhanced by foam compared with water and SDS solution for 0.25 mm to 0.5 mm diameter sand. For sand with diameters of 0.5 mm to 0.9 mm and 0.9 mm to 1.4 mm, the mobility of nZVI carried by SDS solution was optimal, followed by that of nZVI carried by foam and water. Thus, the mobility of nZVI in finer sand was significantly enhanced by foam, compared with that in coarse sand. In contrast, compared with the bare nZVI suspension and nZVI-laden foam, the spatial distribution of nZVI particles carried by SDS solution was significantly uniform along the column length. Third, the SDS concentration significantly influenced the migration of nZVI in porous media. The enhancement in the migration of nZVI carried by SDS solution was greater at an SDS dose of 0.25% compared with that at the other three doses (0.2%, 0.5%, and 1%) for sand with a 0.25 mm to 0.5 mm diameter. Increased SDS concentrations positively affected the transport of nZVI by foam for sand with a 0.25 mm to 0.5 mm diameter, and the SDS concentrations for enhancing the mobility of nZVI carried by SDS foam satisfied the following order: 1% > 0.5% > 0.25% > 0.2%. Thus, SDS solution and SDS foam were better vehicles than water for delivering nZVI particles to porous media for contamination remediation.