Performance Of Zero-valent Iron Research Articles

A comparative study of different modification methods on zero-valent iron performance toward nitrate selective reduction to nitrogen

A comparative study of different modification methods on zero-valent iron performance toward nitrate selective reduction to nitrogen

Resolve the species-specific effects of iron (hydr)oxides on the performance of underlying zerovalent iron for metalloid removal: Identification of their key properties

Despite the importance of surface iron (hydr)oxides (Fe-(hydr)oxides) for the decontamination performance of zerovalent iron (ZVI) -based technologies has been well recognized, controversial understandings of their exact roles still exist due to the complex species distribution of Fe-(hydr)oxides. Herein, we re-structured the surface of ZVI using eight distinct Fe-(hydr)oxides and analyzed their species-specific effects on the performance of ZVI for Se(IV) under well-controlled conditions. The kinetics-relevant performance indicators (Se(IV) removal rates, Fe2+ release rates, and the utilization ratio of ZVI) under the effect of each Fe-(hydr)oxide roughly followed the order: δ-FeOOH >Fe5HO8·4H2O >α-FeOOH >β-FeOOH >γ-FeOOH >γ-Fe2O3 >Fe3O4 >α-Fe2O3. Multiple linear regression analysis shows that the large pore volume and size (instead of specific surface area), low open-circuit potential, and low electrochemical impedance are key positive properties for kinetics-relevant performance. Besides, for electron efficiency of ZVI, only Fe3O4 increased the value to 50.0%, due to the contribution of its ferrous components, while others did not change it (∼20%). Additional experiments with commercial ZVI covered by individual Fe-(hydr)oxides confirmed the observed species-specific trends. All these results not only provide new basis for mechanism explanation but also have practical implications for the production or modification of ZVI.

Insights into the contrasting effects of sulfidation on dechlorination of chlorinated aliphatic hydrocarbons by zero-valent iron

Contrasting effects of sulfidation on contaminants reduction by zero-valent iron (ZVI) has been reported in literature but the underlying mechanisms remain unclear. Here, under well-controlled conditions, we compared the performance of ZVI and sulfidated ZVI (S-ZVI) toward a series of chlorinated compounds. Results revealed that, although S-ZVI was more reactive than ZVI toward hexachloroethane, pentachloroethane, tetrachloroethylene, and trichloroethene, sulfidation hindered the dechlorination of the other ten tested chlorinated aliphatics by a factor of 1.5-125. Moreover, S-ZVI may lead to an accumulation of toxic partially-dechlorinated products. Analogous to its effects on ZVI reactivity, sulfidation also exerted positive, negligible, or negative effects on the electron efficiency of ZVI. Solvent kinetic isotope effect analysis suggested that direct electron transfer rather than reaction with atomic hydrogen was the dominant reduction mechanism in S-ZVI system. Hence, the sulfidation enhancing effects could be expected only when direct electron transfer is the preferred reduction route for target contaminants. Furthermore, linear free energy relationships analysis indicated one-electron reduction potential could be used to predict the transformation of chlorinated ethanes by S-ZVI, whereas for chlorinated ethenes, their adsorption properties on S-ZVI determined the dechlorination process. All these findings may offer guidance for the decision-making regarding the application of S-ZVI.

Zero-valent iron to advance anaerobic membrane bioreactors for wastewater treatment and reuse: A critical review

Zero-valent iron to advance anaerobic membrane bioreactors for wastewater treatment and reuse: A critical review

Cheap, fast and durable degradation of azo dye wastewater by zero-valent iron structural composites

Insufficient chemical activity of zero-valent iron (ZVI) is the main problem that limits its performance in degrading dyeing wastewater. Currently, the methods of creating acidic reaction condition and reducing the particle size of ZVI are widely used to improve the degradation activity of ZVI. However, they have disadvantages such as high reactor requirements and oxides accumulation. Herein, peculiar porous structural composites constructed with porous ferroalloy supported iron powders were prepared depending on magnetic force, the effects of pH, material structure, and powder size on the degradation performance of iron in Orange II solutions were detailedly investigated. The porous structure endowed the composite materials with greatly enhanced degradation performance, especially in near-neutral and alkaline environments, enable a cheap, fast, and durable degradation. The results show that the compositing porous ferroalloy with iron powder can largely increase the kinetic rate constant by more than 15 times, which is much more advantageous than increasing the specific surface area of the powder or increasing the acidity. This work reveals the determinants that affect the degradation performance of ZVI, and presents an effective method for tuning the properties of magnetic materials using porous structural composites.

Selenium-rich mine effluents treatment using zero-valent iron: Mechanism and removal efficiency in the cold climate of Québec, Canada

Selenium contamination in mine effluents is a notorious environmental concern due to its toxicity and potential to bioaccumulate. This element is not yet regulated in Canada, and requires the development of sophisticated water treatment technologies at large scale. Increasing evidences suggest that zero-valent iron (ZVI) is an effective reagent for the treatment and removal of selenium from mine water. Accordingly, the results of this study showed that ZVI decreases the selenium concentration below the detection limit (0.0005 mg/L) in a mine effluent containing about 50% selenite and 50% selenate when employed at 1.25% solid: liquid ratio for 8h of contact time. However, for mine effluents having a predominance of selenate (almost 90%), the iron ratio was increased to 2% to reach a final selenium concentration inferior to 0.0005 mg/L. Low temperature (4 °C) decreased ZVI performance to 68% selenium removal for an increased contact time (12 h). These findings allowed us to determine the key operational parameters: ZVI: liquid ratio and the contact time in order to design laboratory columns to further explore this low-cost and effective treatment technology for selenium removal from mining effluents at industrial scale.

Simply closing the reactor improves the electron efficiency of zerovalent iron toward various metal(loid)s removal.

The controlled corrosion of zerovalent iron (ZVI) is crucial for the favorable performance of ZVI toward metal(loid)s removal, and dissolved oxygen (DO) plays an important role in the process of ZVI corrosion. However, few efforts have been made to control the concentration of DO in real practice. In this study, we found that the electron efficiency and the specific removal capacity of ZVI toward the removal of four metal(loid)s were increased by 1.2-9.1 times and 1.2-3.6 times, respectively, by simply closing the reactor, while the removal kinetics of metal(loid)s was slightly influenced. The rate constants obtained under open condition were always greater than those obtained under closed condition, and the removal amounts of metal(loid)s by ZVI at the reaction equilibrium under closed condition were nearly equivalent to those under open condition. Compared with the case under open condition, the consumption-redissolution process of DO was decelerated under closed condition, and the rapid corrosion of ZVI was alleviated subsequently. Although closing the reactor is simple, it does contribute much to the favorable electron efficiency of ZVI toward metal(loid)s sequestration and can be easily adopted in real practice. © 2021 Water Environment Federation PRACTITIONER POINTS: Closing the reactor promoted the selectivity of ZVI towards four metal(loid)s removal. The consumption-redissolution process of DO and corrosion of ZVI were decelerated by closing the reactor. Metal(loid)s were reduced to lower valence by ZVI under closed condition. Effect of DO was different when ZVI was applied to remove different metal(loid)s.

Evaluation of commercial zerovalent iron sources in combination with solar energy to remove microcontaminants from natural water at circumneutral pH

Solar zerovalent iron (ZVI) was studied at circumneutral pH in combination with hydrogen peroxide and persulfate for removal of imidacloprid as a model contaminant in natural water. Three commercial ZVI sources, steel wool (ZVI-SW) and two iron micro-powders (ZVI-MS and ZVI-S) were independently evaluated. First, different ZVI corrosion conditions were tested in contact with air, exposed to natural solar radiation and with addition of oxidants, such as H2O2 and S2O82-, demonstrating the importance of released iron. Then, the technical feasibilities of solar/H2O2/ZVI and solar/S2O82-/ZVI were assessed for the elimination of 1mg/L of imidacloprid. In general, H2O2 concentrations and treatment times were high. Only ZVI-MS (1mM) reached 80% imidacloprid degradation after 157min and 3mM (102mg/L) of H2O2. Solar/S2O82-/ZVI performance was better, reaching >80% imidacloprid degradation in <60min with 1mM (192mg/L) S2O82- for all ZVI sources. Efficiency was highest with ZVI-MS, which was therefore selected for feasibility testing of a microcontaminant (MC) mixture containing 100μg/L each of atrazine, carbendazim, imidacloprid and thiamethoxam with both solar/oxidizing agents/ZVI. H2O2 took 180min to achieve 76% degradation of the sum of MCs, while 80% total degradation was reached after 69min by adding S2O82-, confirming its higher efficiency. Finally, this study showed that ZVI in combination with solar radiation does not enhance significantly the photocatalytic cycle.

Ethylenediaminetetraacetic acid induces surface erosion of zero-valent iron for enhanced hexavalent chromium removal

Abstract The wide application of zero-valent iron (ZVI) technology was limited by its slow electron transfer rate because of the dense iron oxide on ZVI surface. In this study, we reported a method to improve the performance of ZVI by ball-milling ZVI with ethylenediaminetetraacetic acid (ZVI-EDTA). The pretreatment of ZVI with EDTA provided acidic sites for ZVI surface corrosion, and thus increased the amount of surface Fe0 from 7.23% to 30.12%. Because of the promoted surface Fe0 amount, the corrosion potential of ZVI-EDTA shifted from −0.66 V to −0.75 V, and the concentration of dissolved ferrous ions and total ions increased, resulting in high efficiency in Cr(VI) removal. This study provides an effective method for enhancing the reactivity of commercial ZVI powder, which could contribute to the wide application of ZVI technology, especially in heavy metal remediation.

Enhanced trichloroethylene dechlorination by carbon-modified zero-valent iron: Revisiting the role of carbon additives

Given that there are still some debates on the influence of carbon modification on zerovalent iron (ZVI) decontamination process, the roles of carbon on trichloroethylene (TCE) reduction by ZVI were re-investigated in this work. Compared to activated carbons (AC) with high adsorption ability, carbon fibers (CF) with good electronic conductivity performed much better in enhancing ZVI performance in terms of both reactivity and selectivity. Moreover, it was interesting to observe that a low carbon loading is sufficient to effectively improve TCE reduction and this promoting effect would decline with further increasing the carbon amounts from 1.0 wt.% to 50 wt.%. Regarding to the ZVI selectivity, a relatively high carbon loading (especially for CF, it may be as high as 50 wt.%) was needed to protect ZVI from non-productive reactions with H2O/H+ effectively. However, a mixture of 10 wt.% AC and 1.0 wt.% CF could combine their respective merits of inhibiting side reactions and enhancing TCE reduction, and thus simultaneously enhanced the reactivity and selectivity of ZVI. Mechanistic investigations revealed that carbon modification could enhance the ZVI performance through improving TCE adsorption and/or accelerating electron transfer, while the latter one may play a more important role especially at high carbon loadings.

Common Anions Affected Removal of Carbon Tetrachloride in Groundwater Using Granular Sponge Zerovalent Iron

Significant attention has been devoted over the past two decades to research and field applications of zerovalent iron (ZVI) technologies for groundwater remediation. The uncertainty of ZVI effectiveness under complex subsurface environment will affect the application of ZVI remedial techniques. The effects of groundwater common anions Cl−, SO42−, and HCO3− on CCl4 degradation by sponge ZVI were investigated through batch experiments. The surface structure and composition of ZVI before and after reaction were determined by SEM-EDS, X-ray diffraction, and X-ray photoelectron spectroscopy. Cl−, SO42−, and HCO3− promoted the degradation of CCl4 with the order of HCO3− > SO42− > Cl−. HCO3− enhanced the effect of ZVI on CCl4 degradation as a buffer and an oxidant providing cathodic reaction; SO42− dissolved the hydroxide on the ZVI surface to promote the degradation; and Cl− accelerated the degradation rate by pitting corrosion on the ZVI surface. After reaction, the iron oxides on ZVI surface were FeOOH and Fe2O3 in Cl−, SO42− system and the FeOOH was the only iron oxide in HCO3− system. The results suggest that the performance of ZVI will be affected by the composition of field groundwater.

Coupled Effect of Sulfidation and Ferrous Dosing on Selenate Removal by Zerovalent Iron Under Aerobic Conditions.

Both the reactivity and the removal capacity of zerovalent iron (ZVI) for the target contaminant are important for applying ZVI in wastewater treatment. In this study, the feasibility of combining sulfidation treatment and Fe2+ dosing (S-ZVI/Fe2+) to enhance the performance of ZVI for Se(VI) removal was comprehensively investigated under aerobic conditions. Se(VI) was first adsorbed on the surface of ZVI particles and then reduced to Se(IV) and Se(0) with Se(0) being the final product in S-ZVI/Fe2+ system. This system bore the advantages of both sulfidation treatment (S-ZVI) and Fe2+ dosing (ZVI/Fe2+) for Se(VI) removal. The amounts and rate constants of Se(VI) removal in S-ZVI/Fe2+ system were increased by 1.8-32.8 times and 11.7-194.0 times, respectively, compared to those in pristine ZVI system. Sulfidation significantly accelerated the corrosion of Fe0 thus improved the removal rate of Se(VI). The promoting effect of Fe2+ on Se(VI) sequestration by S-ZVI should be mainly associated with the following facts: Fe2+ could maintain a relatively low pH level during Se(VI) removal by S-ZVI; Compared to S-ZVI alone, the consumption of Fe0 in S-ZVI/Fe2+ by O2/H+ was slower, and thus the electron efficiency of S-ZVI was elevated; Fe2+ dosing facilitated electron transfer by forming semiconductive Fe3O4.

Selenate removal by Fe0 coupled with ferrous iron, hydrogen peroxide, sulfidation, and weak magnetic field: A comparative study

Dosing ferrous ions (ZVI/Fe2+), combining with oxidants (e.g., H2O2) (ZVI/H2O2), sulfidation treatment (S-ZVI), and introducing a weak magnetic field (ZVI/WMF) have been widely used to enhance the performance of zerovalent iron (ZVI) for reductive removal of contaminants. Taking Se(VI) as a probe contaminant, this study systematically compared the performances of different ZVI systems (i.e., ZVI/Fe2+, ZVI/H2O2, S-ZVI, and ZVI/WMF) for contaminant removal. All the four tested methods could greatly improve the performance of ZVI for Se(VI) removal. Se(VI) was removed by S-ZVI at S/Fe molar ratio of 0.05 with a much greater rate constant than other enhanced-ZVI technologies while the maximum amount of Se(VI) removal was obtained in ZVI/Fe2+ system with Fe2+ applied at 0.5 mM among the four tested enhanced-ZVI technologies at initial pH 6.0. In addition, Se(VI) removal by ZVI/Fe2+ was least influenced by initial pH compared to the other tested enhanced-ZVI systems, implying its good adaptability of pH. The application of these tested methods could significantly increase the electron efficiency from ∼0.5% to 4.06-8.72% and Fe2+ application was much more efficient in enhancing the electron efficiency than the other three methods. Finally, the perspective of these enhanced-ZVI technologies was compared in terms of their reactivity, selectivity, chemical cost, and pH adaptability and some suggestions for their possible application were provided.

Effect of pH on Zero Valent Iron Performance in Heterogeneous Fenton and Fenton-Like Processes: A Review.

Heterogeneous Fenton processes with solid catalysts have gained much attention for water and wastewater treatment in recent years. In the field of solid catalysts, zero valent iron (ZVI) is among the most applicable due to its stability, activity, pollutant degradation properties and environmental friendliness. The main limitation in the use of ZVI in heterogeneous Fenton systems is due to its deactivation in neutral and alkaline conditions, and Fenton-like processes have been developed to overcome this difficulty. In this review, the effect of solution pH on the ZVI-Fenton performance is discussed. In addition, the pH trend of ZVI efficiency towards contaminants removal is also considered in oxic solutions (i.e., in the presence of dissolved O2 but without H2O2), as well as in magnetic-field assisted Fenton, sono-Fenton, photo-Fenton and microwave-Fenton processes at different pH values. The comparison of the effect of pH on ZVI performance, taking into account both heterogeneous Fenton and different Fenton-like processes, can guide future studies for developing ZVI applications in water and wastewater treatment.

Zero-valent iron nanofibers (ZVINFs) immobilized on the surface of reduced ultra-large graphene oxide (rULGO) as a persulfate activator for treatment of landfill leachate

Abstract In this research, the performance of zero-valent iron nanofibers/reduced ultra-large graphene oxide (ZVINFs/rULGO) as a persulfate (PS) activator was investigated for the treatment of synthetic and real leachate. Ultra-large graphene oxide (ULGO) was prepared by chemical expansion of natural flake graphite using chromium trioxide and hydrogen peroxide and then oxidation using potassium permanganate. ZVINFs/rULGO was prepared by adding sodium borohydride as a reducing agent to a solution containing Fe(II) ions and ULGO. The material characterization was performed by XRD, SEM, EDS, and BET analysis. The effects of the pH, ZVINFs/rULGO dosage, PS/COD ratio, reaction time, and temperature on the removal of COD and NH3 were evaluated to find the optimum operational conditions (i.e., pH 3, ZVINFs/rULGO dosage: 1.6 g L−1, PS/COD: 3, and reaction time: 45 min). Under the optimum conditions, the removal efficiencies of COD and NH3 were 93.64 and 84.8%, respectively. The presence of ZVINFs/rULGO led to 3.8 and 4.2 times decrease in the activation energies of COD and NH3, respectively. Finally, the ZVINFs/rULGO-PS system was applied for removal of COD and NH3 in real leachate obtained from the Aradkouh’s landfill located in Tehran, Iran. The COD and NH3 removal efficiencies for the fresh leachate were 80.87 and 72.38%, respectively, and the biodegradability (BOD5/COD) of the real leachate enhanced from 0.25 to 0.52, respectively.

Effect of solution chemistry on the reactivity and electron selectivity of zerovalent iron toward Se(VI) removal

Abstract Both the reactivity and electron selectivity (ES) of zerovalent iron (ZVI) are critical for successful application of ZVI. In this study, taking Se(VI) as a probe contaminant, the influences of pH (3.0–10.0) and coexisting ions (e.g., Ca2+, Mg2+, Cl−, SiO32−, SO42−, and PO43−) on the reactivity and ES of ZVI were comprehensively investigated. It was demonstrated that, the ES of ZVI was low in general and merely 0.9–12.1% of electrons donated by ZVI were effectively used for Se(VI) reduction under different conditions. Both Se(VI) removal rate and ES were significantly influenced by pH and both of them achieved maximum at pH 5.0, while further increasing or decreasing pH values would deteriorate the ZVI performance. Depending on the types and concentrations, coexisting ions could exert different effects on ZVI reactivity and ES, negatively, negligibly or positively. For example, relative to Cl−, Ca2+, Mg2+, and SiO32− did not show any significant influence on Se(VI) removal rate but could enhance ES by 3.0–50.3%. The presence of SO42− and PO43− hindered Se(VI) removal rate during their tested concentration range, while they could enhance ES at a low concentration level and depress ES at high concentration levels. X-ray absorption fine structure analysis revealed that, pH and coexisting ions could influence the transformation of ZVI corrosion products and thereby impact the electron transfer from ZVI to Se species at the water-particle interface.

Enhanced dyes removal by sulfidated zerovalent iron: Kinetics and influencing factors

Abstract Sulfidation has been considered to be a promising method to improve the performance of zerovalent iron (ZVI). In this study, taking different kinds of dyes (including azo, anthraquinone and triphenylmethane dyes) as model contaminants, the feasibility of applying sulfidation (herein sulfidated ZVI was synthesized by ball-milling with ZVI and elemental sulfur (S-ZVI bm )) to enhance the reactivity of ZVI was systematically investigated. The results showed that, S-ZVI bm could enhance dyes removal efficiency from 52.8–79.4% to 69.5%–100% within 150 min and the ratio of rate constants for dyes decolorization by S-ZVI bm to that of unsulfidated ZVI generally fell in the range of 1.3–4. Although the decolorization process of Acid Red 27 (AR27) by S-ZVI bm could be inhibited when solution pH values increased from 4.0 to 10.0, S-ZVI bm still achieved higher removal rate and efficiency than unsulfidated ZVI. For Pri-ZVI and ZVI bm , the decolorization rate of AR27 increased linearly with iron dosage. However, it was interesting to observe that the kinetic constants of AR27 removal by S-ZVI bm increased more sharply than unsulfidated ZVI, implying more available reactive sites could be provided after sulfidation treatment. In sum, from a wide-spectrum perspective, this study provided some insights into the effects of sulfidation on ZVI performance toward various dyes removal.

Pentachlorophenol dechlorination with zerovalent iron: a Raman and GCMS study of the complex role of surficial iron oxides.

The dechlorination of chlorinated organic pollutants by zero valent iron (ZVI) is an important water treatment process with a complex dependence on many variables. This complexity means that there are reported inconsistencies in terms of dechlorination with ZVI and the effect of ZVI acid treatment, which are significant and are as yet unexplained. This study aims to decipher some of this complexity by combining Raman spectroscopy with gas chromatography-mass spectrometry (GC-MS) to investigate the influence of the mineralogy of the iron oxide phases on the surface of ZVI on the reductive dechlorination of pentachlorophenol (PCP). Two electrolytic iron samples (ZVI-T and ZVI-H) were found to have quite different PCP dechlorination reactivity in batch reactors under anoxic conditions. Raman analysis of the "as-received" ZVI-T indicated the iron was mainly covered with the ferrous oxide (FeO) wustite, which is non-conducting and led to a low rate of PCP dechlorination. In contrast, the dominant oxide on the "as-received" ZVI-H was magnetite which is conducting and, compared to ZVI-T, the ZVI-H rate of PCP dechlorination was four times faster. Treating the ZVI-H sample with 1N H2SO4 made small change to the composition of the oxide layers and also minute change to the rate of PCP dechlorination. However, treating the ZVI-T sample with H2SO4 led to the loss of wustite so that magnetite became the dominant oxide and the rate of PCP dechlorination increased to that of the ZVI-H material. In conclusion, this study clearly shows that iron oxide mineralogy can be a contributing factor to apparent inconsistencies in the literature related to ZVI performance towards dechlorination and the effect of acid treatment on ZVI reactivity.

Enhanced Reactivity and Electron Selectivity of Sulfidated Zerovalent Iron toward Chromate under Aerobic Conditions.

When zerovalent iron (ZVI) is used in reductive removal of contaminants from industrial wastewater, where dissolved oxygen (DO) competes with target contaminant for the electrons donated by ZVI, both the reactivity and the electron selectivity (ES) of ZVI toward target contaminant are critical. Thus, the reactivity and ES of two sulfidated ZVI (S-ZVI) samples, synthesized by ball-milling with elemental sulfur (S-ZVIbm) and reacting with Na2S (S-ZVINa2S), toward Cr(VI) under aerobic conditions were investigated. Sulfidation appreciably increased the reactivity of ZVI and the ratio of the rate constants for Cr(VI) removal by S-ZVIbm or S-ZVINa2S to their counterparts without sulfur fell in the range of 1.4-29.9. ES of S-ZVIbm and S-ZVINa2S toward Cr(VI) were determined to be 14.6% and 13.3%, which were 10.7- and 7.5-fold greater than that without sulfidation, respectively. This was mainly ascribed to the greater improving effect of sulfidation on the reduction rate of Cr(VI) than that of DO by ZVI. The improving effects of sulfidation on the performance of ZVI were mainly due to the following mechanisms: sulfidation increased the specific surface area of ZVI, the FeS x layer facilitated the enrichment of Cr(VI) anions on S-ZVI surface because of its anions selective property and favored the electron transfer from Fe0 core to Cr(VI) at the surface because of its role as efficient electron conductor.

Enhanced Nitrobenzene reduction by zero valent iron pretreated with H2O2/HCl

In this study a novel iron-based reducing agent of highly effective reduction toward nitrobenzene (NB) was obtained by pretreating zero valent iron (ZVI) with H2O2/HCl. During the H2O2/HCl pretreatment, ZVI undergoes an intensive corrosion process with formation of various reducing corrosion products (e.g., Fe2+, ferrous oxides/hydroxides, Fe3O4), yielding a synergetic system (prtZVI) including liquid, suspensions and solid phase. The pretreatment process remarkably enhances the reductive performance of ZVI, where a rapid reduction of NB (200 mg L-1) in the prtZVI suspension was accomplished in a broad pH range (3-9) and at low dosage. Nitrosobenzene and phenylhydroxylamine are identified as the intermediates for NB reduction with the end-product of aniline. Compared with the virgin ZVI as well as another nanosized ZVI, the prtZVI system exhibits much higher electron efficiency for NB reduction as well as higher utilization ratio of Fe0. A rapid reduction of various nitroaromatics in an actual pharmaceutical wastewater further demonstrated the feasibility of the prtZVI system in real wastewater treatment.