Reactivity Of Nanoscale Zero-valent Iron Research Articles

Integrated influence of sulfide modification on the reactivity of nanoscale zero-valent iron towards decabromodiphenyl ether under an electromagnetic field

Individual application of sulfide modification and electromagnetic field (EMF) can enhance the reactivity of nanoscale zero-valent iron (nZVI), yet the potential of both in combination is not clear. This work found that the reactivity of nZVI towards decabromodiphenyl ether was significantly enhanced by the combined effect of sulfidation and EMF. The specific reaction rate constant of nZVI increased by 7 to 10 times. A series of characterization results revealed that the sulfidation level not only affects the inherent reactivity but also the magnetic-induced heating (MIH) and corrosion (MIC) of nZVI. These collectively influence the degradation efficiency of nZVI under EMF. Sulfidation generally diminished the MIH effect. The low degree of sulfidation (S/Fe = 0.1) slightly reduced the MIC effect by 21.4%. However, the high degree of sulfidation (S/Fe = 0.4) led to significantly enhanced MIC effect by 107.1%. For S/Fe = 0.1 and 0.4, the overall enhancement in the reactivity resulting from EMF was alternately dominated by the contributions of MIH and MIC. This work provides valuable insights into the MIH and MIC effects about the sulfidation level of nZVI, which is needed for further exploration and optimization of this combined technology.

Core to concept: synthesis, structure, and reactivity of nanoscale zero-valent iron (NZVI) for wastewater remediation

Core to concept: synthesis, structure, and reactivity of nanoscale zero-valent iron (NZVI) for wastewater remediation

Can polymeric surface modification and sulfidation of nanoscale zerovalent iron (NZVI) improve arsenic-contaminated agricultural soil restoration via ex situ magnet-assisted soil washing?

Environmental context Arsenic (As) contamination in agricultural soil threatens safe agricultural production. Therefore, an ex situ magnet-assisted soil washing, using different types of nanoscale zerovalent iron was tested as a remediation option in soil restoration. Uncoated nanoparticles was the best tested option, with As removal at 45.5% and the nanoparticles were reusable up to four times. Rationale Arsenic (As) contamination in agricultural soil threatens safe food and medicinal herb production for millions of people. Methodology Therefore, ex situ magnet-assisted soil washing of metal-contaminated soil using bare nanoscale zerovalent iron (NZVI) is proposed as a novel remediation alternative. Conceptually, metal-contaminated soil is mixed with water and bare NZVI, and metals in the soil are transferred to the bare NZVI. The metal-sorbed NZVI is then retrieved from the soil slurry through magnetic separation, leaving behind treated soil. This study evaluated if advanced surface modification can improve ex situ soil restoration efficacy including polymeric coating and sulfidation of NZVI, proven beneficial in situ NZVI application. Sulfur and carboxymethylcellulose (CMC) at various S/Fe and CMC/NZVI ratios were used to modify NZVI via sulfidation and physisorption. Result Results revealed that sulfidised NZVI (S-NZVI) performed poorer (41.0%) than bare NZVI (45.5%) in As removal, even at the optimised S/Fe ratio of 0.31. This could be due to acid release via oxidative dissolution of FeS2 on the S-NZVI surface driven by O2. The incidental acid-dissolved NZVI sorption sites decreased As removal efficacy. Similarly, CMC-modified NZVI failed to improve As removal efficacy (11.0%) because it reduced NZVI reactivity and blocked As accessibility to NZVI sorptive sites. Discussion Nevertheless, S-NZVI and CMC-modified NZVI promoted non-phytoavailable As fractions in the treated soil. Overall, bare NZVI performed the best for As removal but moderately transformed As into more non-phytoavailable fractions. Bare NZVI can be reused for four cycles of soil washing. In every case, mobile As in treated soil was lower than the maximum contamination level.

Aging and reactivity assessment of nanoscale zerovalent iron in groundwater systems

In this study, changes in the reactivity of nanoscale zerovalent iron (NZVI) in five different groundwater (GW) systems under anoxic and oxic conditions were examined over a wide range of aging time (0 − 60 d). p-nitrophenol (p-NP) was used as a redox-sensitive probe, whereas nalidixic acid (NA), a typical antibiotic found in the natural environment, was used as a sorbing compound. Investigation of the p-NP reduction in pure water systems showed that NZVI lost 41% and 98% of its reductive activity under anoxic and oxic conditions after 60 d, while enhancement of its reactivity was observed after short-term aging in GW (1 − 5 d), followed by a further decline. This behavior has been ascribed to the formation of secondary Fe(II)-bearing phases, including magnetite and green rust, resulting from NZVI aging in GW. Adsorption experiments revealed that GW-anoxic-aged NZVI samples exhibited a good affinity toward NA, and a greater NA adsorption (∼27 µmol g − 1) than that of pristine NZVI (∼2 µmol g − 1) at alkaline pH values. Surface complexation modeling showed that the enhanced adsorption of NA onto secondary minerals can be attributed to the Fe(II)-NA surface complexation. This considerable change in the reductive ability and the adsorption capacity of NZVI arising from groundwater corrosion calls for greater attention to be paid in assessment studies, where NZVI is injected for long-term remediation in groundwater.

Interactions between nanoscale zerovalent iron (NZVI) and silver nanoparticles alter the NZVI reactivity in aqueous environments

The increasing production and broad application of engineered nanoparticles (ENPs) have led to a substantial release of ENPs into natural systems. Despite their different utilization prospects, ENPs such as nanoscale zero-valent iron (NZVI) and silver nanoparticles (AgNPs) have been co-found in aquatic environments. This study comprehensively examined the effect of AgNPs on the reductive ability of NZVI, which was probed through the conversion of p-nitrophenol (p-NP) to p-aminophenol (p-AP).Electron microscopic and spectroscopic investigations and Derjaguin–Landau–Verwey–Overbeek (DLVO) calculations showed that the aggregation of NZVI with a low dose of AgNPs dramatically decreased the NZVI reactivity. In contrast, enhanced NZVI reactivity was observed when a high dose of AgNPs was used. The collision between self-assembled aggregates of AgNPs and NZVI can lead to the exposure of inner Fe(0), thereby improving the reductive ability of NZVI. The same behavior was observed for other nanosized (e.g., TiO2) and microsized (e.g., quartz sand) particles, which suggests the predominance of physical processes in NZVI peeling. Further investigations showed that the presence of sulfate and humic acid enhanced the p-NP removal in the NZVI-AgNP suspension, in contrast to other groundwater constituents. Our findings provide a better understanding of potential ENP interactions, particularly in the context of groundwater remediation.

Confining polyacrylic acid on the surface of nanoscale zero-valent iron by aluminum hydroxide for in-situ anti-passivation

Aggregation and surface passivation of nanoscale zero-valent iron (NZVI) particles have limited their reactivity and application for environmental remediation. In this study, an aluminum hydroxide/polyacrylic acid (Al(OH)3/PAA) hybrid shell was homogeneously coated on the NZVI surface to overcome the limitations. PAA molecules were confined onto the NZVI surface by hydration of Al(III) cations. The Al(OH)3/PAA coating shell provided more electrostatic repulsion forces between NZVI particles to hinder the particle aggregation and preserve the NZVI reactivity. On the other hand, the surface-anchored PAA provided a thickened reactive layer for Cr(VI) reduction. Besides, XPS and TEM results showed that the surface carboxylic groups bound produced Cr(III) and Fe(III) cations and inhibited the precipitation of hydroxides on the NZVI surface. The reduced passivation layer increased the longevity of NZVI for surface reactions. As a result, the 24-h Cr(VI) reduction capacity of NZVI particles was improved from 49.4 to 92.6 mg/g with a 2 wt% (Al/Fe) Al(OH)3/PAA coating shell. Overall, this study presented a promising strategy to effectively tune the surface properties of nanoparticles and improve the feasibility of NZVI for environmental remediation.

Carbothermal Synthesis of Ni/Fe Bimetallic Nanoparticles Embedded into Graphitized Carbon for Efficient Removal of Chlorophenol.

The reactivity of nanoscale zero-valent iron is limited by surface passivation and particle agglomeration. Here, Ni/Fe bimetallic nanoparticles embedded into graphitized carbon (NiFe@GC) were prepared from Ni/Fe bimetallic complex through a carbothermal reduction treatment. The Ni/Fe nanoparticles were uniformly distributed in the GC matrix with controllable particle sizes, and NiFe@GC exhibited a larger specific surface area than unsupported nanoscale zero-valent iron/nickel (FeNi NPs). The XRD results revealed that Ni/Fe bimetallic nanoparticles embedded into graphitized carbon were protected from oxidization. The NiFe@GC performed excellently in 2,4,6-trichlorophenol (TCP) removal from an aqueous solution. The removal efficiency of TCP for NiFe@GC-50 was more than twice that of FeNi nanoparticles, and the removal efficiency of TCP increased from 78.5% to 94.1% when the Ni/Fe molar ratio increased from 0 to 50%. The removal efficiency of TCP by NiFe@GC-50 can maintain 76.8% after 10 days of aging, much higher than that of FeNi NPs (29.6%). The higher performance of NiFe@GC should be ascribed to the significant synergistic effect of the combination of NiFe bimetallic nanoparticles and GC. In the presence of Ni, atomic H* generated by zero-valent iron corrosion can accelerate TCP removal. The GC coated on the surface of Ni/Fe bimetallic nanoparticles can protect them from oxidation and deactivation.

Modified nanoscale zero-valent iron in persulfate activation for organic pollution remediation: a review

Under the action of different activators, persulfate can produce sulfate radicals (SO4·-) with strong oxidizing ability, which can destruct many organic compounds. Meanwhile, persulfate is widely used in groundwater and soil remediation because of its fast reaction and wide application. With the high specific surface area and reactivity of nanoscale zero-valent iron (nZVI), it can enhance the degradation efficiency of the persulfate system on organic pollutants in soil and water as a persulfate activator. However, nZVI is easy to get oxidized and has a tendency to aggregation. To solve these problems, a variety of nZVI modification methods have been put forward and put into to applications in the activation of persulfate. This article will give a systematic introduction of the background and problems of nZVI-activated persulfate in the remediation of organic pollution. In addition, the modification methods and mechanisms of nZVI are summarized, and the applications and progress of modified nZVI-activated persulfate are reviewed. The factors that affect the removal of organic compounds by the activation system are discussed as well. Worldwide, the field studies and full-scale remediation using modified nZVI in persulfate activation are yet limited. However, the already known cases reveal the good prospect of applying modified nZVI in persulfate activation to organic pollution remediation.

Exploration of the reactivity of nanoscale zero-valent iron (NZVI) associated nanoparticles in diverse experimental conditions

The bimetallic nanoparticles have been used to improve the reactivity of Nanoscale Zero-Valent Iron (NZVI) during environmental contamination remediation. The main objective of this research was to determine the reactivity of the metal-doped NZVI (bimetallic) nanoparticles in aqueous solutions. In this study, FeCu, FeNi and FeAg bimetals were synthesized through the chemical reduction of ferric chloride with sodium borohydride then deposition of 1% (wt/wt) of the corresponding metal. The reactivity of these bimetallic nanoparticles in specific reaction conditions being; temperature, oxygen supply, pH, dosage and interferences (nitrate and phosphate) was studied. The results revealed that more iron dissolution was in acidic pH, high dosage (3 g/L) and continuous oxygen supply. Furthermore, nitrate was removed more in alkaline pH due to co-precipitation whereas phosphate was adsorbed more in acidic pH due to the positively charged surface that attracts negatively charged species. FeCu, FeNi and FeAg showed the best dissolution of iron in 90 °C, 5 °C and 25 °C respectively. Loaded metals (Cu, Ni, Ag) catalyzed NZVI reaction, promoted electrons’ transfer and minimized oxidation.

Graphene oxide-induced formation of a boron-doped iron oxide shell on the surface of NZVI for enhancing nitrate removal

The surface products have a significant influence on the reactivity of zero-valent iron-based materials. Although the enhancing effect of graphene on the reactivity of nanoscale zero-valent iron (NZVI)/graphene composites have been confirmed, the effect of graphene on the formation of surface products of NZVI is not well understood. In order to assess the effect of graphene on the structural of the outer iron oxide layers of NZVI, the NZVI was pre-oxidized by graphene oxide (ONZVI-GO). Compared with the NZVI oxidized by O2 (ONZVI-O2), ONZVI-GO was shown to be effective at NO3− removal with a high efficiency over a wide range of initial pH values. The results from characterization showed that GO could induce the formation of a tight iron oxide shell with dense spinel structures. The boron introduced during the preparation of NZVI was doped into iron oxides on the surface of ONZVI-GO. The B–O in adsorbed borate was transformed to B–B/B–Fe in the lattice structure of iron oxides, causing the formation of highly electron-deficient Lewis acid sites on the surface of ONZVI-GO, which could effectively gather NO3− and OH−, leading to the higher efficiency removal of NO3− than ONZVI-O2 over a wide range of initial pH values. This study provides new insight into the interaction between graphene and the surface species of NZVI.

Mutual effect of U(VI) and phosphate on the reactivity of nanoscale zero-valent iron (nZVI) for their co-removal

Nanoscale zero-valent iron (nZVI) has been widely considered as a promising permeable barrier material for remediating U(VI)-contaminated waters. Little information is available regarding co-removal of U(VI) and oxyanion contaminants by nZVI, yet in the majority of areas polluted by U(VI), co-existence of phosphate is found to be common especially in eutrophic water. Herein, the mutual influence of U(VI) and phosphate on the effectiveness of nZVI in co-removing U(VI) and phosphate is investigated by macroscopic and microscopic approach. The results indicate that nZVI can effectively co-remove U(VI) and phosphate and the processes intensively depend on the solution pH and the additional order due to the formation of nZVI-U(VI)-phosphate complexes and will change the morphology of nZVI through the formation of a new phase. Furthermore, the maximum removal capacity of nZVI increases by 21.63% at pH 6.0 for U(VI) ions and by 34.28% at pH 7.0 for phosphate when both U(VI) and phosphate are present simultaneously. In short, the co-presence of U(VI) and phosphate has a great impact on the reactivity and morphology of nZVI. The findings will be beneficial to broaden the potential feasibility of nZVI in simultaneous radionuclide and phosphate pollution cleanup.

Fast degradation, large capacity, and high electron efficiency of chloramphenicol removal by different carbon-supported nanoscale zerovalent iron

It remains unclear that which kind of carbon support is better for improving the reactivity of nanoscale zerovalent iron (nZVI) without the adsorption effects of carbon. Finding appropriate contaminants that could be degraded by nZVI with high capacity and electron utilization is crucial for exploring the applications of nZVI. High degradation rate (up to 3.70 min−1) and high capacity (up to 3000 mg g−1) of antibiotic chloramphenicol (C11H12Cl2N2O5, CAP) removal with high electron utilization (>97%) was achieved by different carbon supported nZVI in this study. Carbon powder (CP) was found to be the best support, possessing good distribution and reactivity of nZVI. 99% of CAP was removed by CP-nZVI after 3 min, without the electron consumption via the side reaction between nZVI and water, suggesting that CAP could outcompete with water for the electrons from nZVI. The entire pathway of CAP removal was elucidated based on UPLC-MS/MS analysis. Partial degradation of CAP (denitration and dechlorination) was enough to take away the antimicrobial properties. These results suggest a promising application scenario of carbon supported nZVI for the remediation of CAP-contaminated water to reduce the antibiotic selection pressure of the environment.

Estimating dehalogenation reactivity of nanoscale zero-valent iron by simple colorimetric assay by way of 4-chlorophenol reduction

Estimating dehalogenation reactivity of nanoscale zero-valent iron by simple colorimetric assay by way of 4-chlorophenol reduction

Hexavalent chromium removal by a new composite system of dissimilatory iron reduction bacteria Aeromonas hydrophila and nanoscale zero-valent iron

Core-shell Fe@Fe2O3 nanowire is one special nanoscale zero-valent iron (NZVI) with an iron core and an outside shell of iron oxide containing the surface bound ferrous ions, which has been used to remove various pollutants including Cr(VI). However, it can be easily oxidized to accumulate iron oxides on the shell, resulting in the loss of reactive activity during its long-term application. Therefore, the dissolution of iron oxides by reduction is required to maintain NZVI reactivity. In this study, we combine NZVI and a dissimilatory iron reduction bacteria (DIRB), Aeromonas hydrophila HS01, to establish a composite system for a sustainable anoxic reduction of Cr(VI). HS01 can stably coexist with NZVI, reduce the oxidized Fe on NZVI and generate more dissolved Fe(II) under anoxic conditions. This presence of HS01 can maintain the core-shell structured morphology and relatively more Fe0 and Fe(II) on NZVI surface, and enhance the reactivity in Cr(VI) removal. Our results indicated that a suitable DIRB can be used to prolong the reactivity of NZVI, and their combination is an efficient method for anoxic Cr(VI) removal.

Advances in Surface Passivation of Nanoscale Zerovalent Iron: A Critical Review

Nanoscale zerovalent iron (NZVI) is one of the most extensively studied nanomaterials in the fields of wastewater treatment and remediation of soil and groundwater. However, rapid oxidative transformations of NZVI can result in reduced NZVI reactivity. Indeed, the surface passivation of NZVI is considered one of the most challenging aspects in successfully applying NZVI to contaminant degradation. The oxidation of NZVI can lead to the formation of FeII-bearing phases (e.g., FeIIO, FeII(OH)2, FeIIFeIII2O4) on the NZVI surface or complete oxidation to ferric (oxyhydr)oxides (e.g., FeIIIOOH). This corrosion phenomenon is dependent upon various factors including the composition of NZVI itself, the type and concentration of aqueous species, reaction time and oxic/anoxic environments. As such, the coexistence of different Fe oxidation states on NZVI surfaces may also, in some instances, provide a unique reactive microenvironment to promote the adsorption of contaminants and their subsequent transformation via redox reactions. Thus, an understanding of passivation chemistry, and its related mechanisms, is essential not only for effective NZVI application but also for accurately assessing the positive and negative effects of NZVI surface passivation. The aim of this review is to discuss the nature of the passivation processes that occur and the passivation byproducts that form in various environments. In particular, the review presents: (i) the strengths and limitations of state-of-the-art techniques (e.g., electron microscopies and X-ray-based spectroscopies) to identify passivation byproducts; (ii) the passivation mechanisms proposed to occur in anoxic and oxic environments; and (iii) the effects arising from synthesis procedures and the presence of inorganics/organics on the nature of the passivation byproducts that form. In addition, several depassivation strategies that may assist in increasing and/or maintaining the reactivity of NZVI are considered, thereby enhancing the effectiveness of NZVI in contaminant degradation.

Effect of bicarbonate on aging and reactivity of nanoscale zerovalent iron (nZVI) toward uranium removal

Bicarbonate, ubiquitous in natural and waste waters is an important factor regulating the rate and efficiency of pollutant separation and transformation. For example, it can form complexes with U(VI) in the aqueous phase and at the solid-water interface. In this work, we investigated the effect of bicarbonate on the aging of nanoscale zero-valent (nZVI) in the context of U(VI) reduction and removal from wastewater. For fresh nZVI, over 99% aqueous uranium was separated in less than 10 min, of which 83% was reduced from U(VI) to U(IV). When nZVI was aged in water, its activity for U(VI) sequestration and reduction was significantly reduced. Batch experiments showed that for nZVI aged in the presence of 10 mM bicarbonate, only 20.3% uranium was reduced to U(IV) after 6 h reactions. Characterizations of the iron nanoparticles with spherical aberration corrected scanning transmission electron microscopy (Cs-STEM) suggest that in fresh nZVI, uranium was concentrated at the nanoparticle center; whereas in nZVI aged in bicarbonate, uranium was largely deposited on the outer surface of the nanoparticles. Furthermore, aged nZVI without bicarbonate contained more lepidocrocite (γ-FeOOH) while aged nZVI in the presence of bicarbonate had more magnetite/maghemite (Fe3O4/γ-Fe2O3). This could be attributed to the formation of carbonate green rust and pH buffer effect of ▪. Primary mechanisms for U(VI) removal with nZVI include reduction, sorption and/or precipitation. Results demonstrate that bicarbonate alter the aging products of nZVI, and reduces the separation efficiency and reduction capability for uranium removal.

Influence of a thin aluminum hydroxide coating layer on the suspension stability and reductive reactivity of nanoscale zero-valent iron

A novel structured material, aluminum hydroxide–coated nanoscale zero-valent iron (NZVI@Al(OH)3), was synthesized to improve the applicability of NZVI in environmental remediation. Using a rate-control precipitation method, the surface of NZVI was covered with a thin shell of amorphous Al(OH)3. ζ-potential of NZVI under a weak alkaline condition became positive after coating with the Al(OH)3 shell. NZVI@Al(OH)3 performed remarkably higher suspension stability in aqueous phase than bare NZVI, owing to the increased electrostatic repulsion and the reduction of magnetic attraction between the NZVI@Al(OH)3 particles. Results of H2 generation test indicated that the pH buffering capacity of the Al(OH)3 shell and the enlarged surface area benefitted the reductive reactivity of NZVI@Al(OH)3. Additionally, the adsorption capability of the positive Al(OH)3 shell facilitated the reduction and detoxification of contaminants on the NZVI surface. Consequently, the core-shell structure dependent modification with a thin inorganic shell with multiple functions is a promising design for environmental nanomaterials, and the NZVI@Al(OH)3 synthesized in this study is a feasible and environmentally benign material for environmental remediation.

Well-Dispersed Nanoscale Zero-Valent Iron Supported in Macroporous Silica Foams: Synthesis, Characterization, and Performance in Cr(VI) Removal

Well-dispersed nanoscale zero-valent iron (NZVI) supported inside the pores of macroporous silica foams (MOSF) composites (Mx-NZVI) has been prepared as the Cr(VI) adsorbent by simply impregnating the MOSF matrix with ferric chloride, followed by the chemical reduction with NaHB4 in aqueous solution at ambient atmosphere. Through the support of MOSF, the reactivity and stability of NZVI are greatly improved. Transmission electron microscopy (TEM) results show that NZVI particles are spatially well-dispersed with a typical core-shell structure and supported inside MOSF matrix. The N2 adsorption-desorption isotherms demonstrate that the Mx-NZVI composites can maintain the macroporous structure of MOSF and exhibit a considerable high surface area (503 m2·g−1). X-ray photoelectron spectroscopy (XPS) and powder X-ray diffraction (XRD) measurements confirm the core-shell structure of iron nanoparticles composed of a metallic Fe0 core and an Fe(II)/Fe(III) species shell. Batch experiments reveal that the removal efficiency of Cr(VI) can reach 100% when the solution contains 15.0 mg·L−1 of Cr(VI) at room temperature. In addition, the solution pH and the composites dosage can affect the removal efficiency of Cr(VI). The Langmuir isotherm is applicable to describe the removal process. The kinetic studies demonstrate that the removal of Cr(VI) is consistent with pseudo-second-order kinetic model.

Oxalate-enhanced reactivity of nanoscale zero-valent iron under different conditions of O2, N2 or without aeration

Being that the influence of organic ligands on contaminant removal by nanoscale zero valent iron (nZVI) has been explored in quite a few studies, there is little information on reaction mechanisms of the ZVI-ligand system under different aeration conditions. The degradation of nitrobenzene (NB) by nZVI-oxalic acids (OA) was investigated under N2, O2 and without aeration conditions. From the findings, it was evident that OA dramatically improved NB degradation by nZVI with all of the aeration conditions. Approximately 100% of NB was degraded by nZVI-OA+N2 system after 60 min of reaction, followed in effectiveness by nZVI-OA+ without aeration (95%) as well as nZVI-OA+O2 (85%). Operation parameters including OA concentration and pH had significant effect on the removal of NB in the nZVI-OA system. 3mM OA concentration and pH 3.0 were found to be favourable. The Fe2+, total dissolved iron concentrations, pH and ORP values in the nZVI-OA systems had also been monitored. Intermediates and trapping experiments showed that reduction played a fundamental role in the NB degradation by nZVI-OA under N2 or without aeration conditions. The formation of Fe(OA)0 and Fe(OA)22− complexes had lower standard ORP, which could improve the strength of reductant in the systems, and thus resulting in an increased degradation efficiency of NB by nZVI-OA+N2. Under O2 aeration condition, the NB degradation process could be regarded as an oxidation. In the meantime, OA promoted the production of reactive oxidants species by speeding up the oxidation rates of Fe2+ by O2 and H2O2. Summarily, the improved reactivity of nZVI was largely as a result of the strong complexation ability of OA.

Effects of oxidants on in situ treatment of a DNAPL source by nanoscale zero-valent iron: A field study

This study aimed to evaluate the efficiency of a nanoscale zero-valent iron (NZVI)-based treatment process for an aquifer contaminated with trichloroethylene (TCE) in which TCE in dense non-aqueous phase liquid (DNAPL) form was also present. The study further investigated the effects of site oxidants on the reactivity and lifetime of NZVI. The injection of 30 kg of NZVI into the site successfully removed 95.7% of TCE in the groundwater within the first 60 days without producing chlorinated intermediates. The chloride balance analysis estimated that 2214 g of TCE was removed and confirmed the presence of DNAPL TCE. The oxidation of NZVI particles by nitrate, dissolved oxygen (DO), and TCE consumed 29.5%, 13.5%, and 14.3% of the Fe(0) initially present, respectively, over 60 days. Thus, nitrate was identified as the priority among groundwater oxidants. The reactive lifetime of NZVI at the site was found to be at least 103 days, based on the monitoring of TCE, DO, and nitrate concentrations, oxidation-reduction potential (ORP), and the residual Fe(0) content of the NZVI particles. Solid samples that were retrieved from the site on the 165th day still contained substantial amounts of Fe(0), occupying up to 21.9% of the total mass, and retained considerable reactivities towards TCE. This indicates that the NZVI particles aged more than 5 months at the site can potentially be reused for TCE reduction even after extensive corrosion of Fe(0) has occurred.