Reactivity Of Fe0 Research Articles

Biochar-supported Fe/Ni bimetallic nanoparticles for the efficient removal of Cr(VI) from aqueous solution

Nano-zero-valent iron (nZVI) can efficiently control Cr(VI) pollution in groundwater, but its application is hindered by the tendency of Fe0 to agglomerate and form a passivation layer. In this study, to increase the reactivity of Fe0, biochar (BC) -supported Fe/Ni bimetal nanoparticles ([email protected]/Ni) were developed to promptly remove Cr(VI) from water. The results demonstrated that the mesoporous structure of BC can provide a supportive environment for Fe0 and reduce the aggregation of Fe0. The removal efficiency of [email protected]/Ni was found to be better than that of BC and Fe/Ni. Good performance was achieved when the Ni content was approximately 5%. At pH 2.0, the removal rate of Cr(VI) reached 99.62%. A higher temperature was found to be favorable for the reaction, indicating that [email protected]/Ni is endothermic in removing Cr(VI). The mechanism of [email protected]/Ni and Cr(VI) is as follows. First, a part of Cr(VI) is adsorbed on [email protected]/Ni via electrostatic attraction; then, the driving force for Cr(VI) reduction is mainly the continuous electron transfer of Fe0 and Fe(II); moreover, Ni promotes the formation of Fe(II) and H atoms. In conclusion, this work demonstrates that [email protected]/Ni is a promising material for controlling Cr(VI) pollution. This work will serve as a reference for the improvement of bimetallic nanomaterials and the treatment of Cr(VI) contamination.

Even Incorporation of Nitrogen into Fe0 Nanoparticles as Crystalline Fe4N for Efficient and Selective Trichloroethylene Degradation.

Surface modification of microscale Fe powder with nitrogen has emerged recently to improve the reactivity of Fe0 for dechlorination. However, it is unclear how an even incorporation of a crystalline iron nitride phase into Fe0 nanoparticles affects their physicochemical properties and performance, or if Fe0 nanoparticles with a varied nitridation degree will act differently. Here, we synthesized nitridated Fe0 nanoparticles with an even distribution of N via a sol-gel and pyrolysis method. Nitridation expanded the Fe0 lattice and provided the Fe4N species, making the materials more hydrophobic and accelerating the electron transfer, compared to un-nitridated Fe0. These properties well explain their reactivity and selectivity toward trichloroethylene (TCE). The TCE degradation rate by nitridated Fe0 (up to 4.8 × 10-2 L m-2 h-1) was much higher (up to 27-fold) than that by un-nitridated Fe0, depending on the nitridation degree. The materials maintained a high electron efficiency (87-95%) due to the greatly suppressed water reactivity (109-127 times lower than un-nitridated Fe0). Acetylene was accumulated as the major product of TCE dechlorination via β-elimination. These findings suggest that the nitridation of Fe0 nanoparticles can change the materials' physicochemical properties, providing high reactivity and selectivity toward chlorinated contaminants for in situ groundwater remediation.

Multi-functional magnesium hydroxide coating for iron nanoparticles towards prolonged reactivity in Cr(VI) removal from aqueous solutions

In this study, the reactive performance of magnesium hydroxide-coated iron nanoparticles (Fe0 @Mg(OH)2) was investigated for the removal of hexavalent chromium (Cr(VI)) from aqueous solutions. Short- and long-term progressive-release of Fe0 @Mg(OH)2 reactivity was evaluated through several batch tests. The Multi-functional effect of the environmentally-friendly Mg(OH)2 coating shell was represented by the progressive shell-dissolution in water and preventing the rapid corrosion of Fe0-core, which resulted in a controlled release of Fe0 reactivity towards Cr(VI). Fe0 @Mg(OH)2 showed good performance in preserving Fe0 long-term reactivity within a wide range of pH (3.0 – 9.0) and temperature (15–55 oC). The long-term investigation of Fe0 @Mg(OH)2 performance towards Cr(VI) removal confirmed the progressive and maintained reactivity, represented by the continuous release of Fe0 electrons, to achieve 100% removal efficiency of 40 mg/L initial Cr(VI) concentration over 50 days reaction time, to be reported for the first time in the literature. Fe0 @Mg(OH)2 showed high regeneration abilities up to 5 cycles with 1.36 times average enhancement in Cr(VI) removal efficiency compared to that of Fe0. Moreover, Fe0 @Mg(OH)2 achieved an increase in the shelf-live longevity performance up to 30 days without any storing solution with 90% final Cr(VI) removal efficiency after 180 min reaction time.

Effect of pyrite on enhancement of zero-valent iron corrosion for arsenic removal in water: A mechanistic study

In this study, the enhanced effect of pyrite (FeS2) on zero-valent iron (Fe0) corrosion for arsenic (As) removal was investigated in a combined-Fe0/FeS2 system. The effects of different Fe0/FeS2 composition, dosage and initial pH were evaluated by batch experiments. Results showed that the best combination ratio of Fe0:FeS2 (w/w) was 1:1 and the optimal dosage of mixture was 2.0 g/L. The combination of Fe0 and FeS2 in a system significantly enhanced the reactivity of Fe0 for effective As removal within a broad pH range (3.0–9.0). The effective As removal in the combined-Fe0/FeS2 system was primarily ascribed to being enhanced corrosion of Fe0 by addition of FeS2. SEM and XRD characterizations strongly verified this point. Specifically, the mechanism study (the releases of Fe2+ and total Fe ion, variations of pH values as well as XPS characterization) suggested that FeS2 in the combined-Fe0/FeS2 system could alleviate the passivation of Fe0 (pHini 3.0–5.0) and accelerate the dissolution of pristine oxide film that coated on Fe0 surface (pHini 6.8–9.0). Besides, FeS2 in combined-Fe0/FeS2 system could also accelerate the reactions between Fe0 to O2 at pHini 3.0–9.0. These phenomena were well explained by a galvanic couple between Fe0 and FeS2, where FeS2 was a cathode and Fe0 was an anode. Consequently, electrons released from Fe0 that mediated by FeS2 to oxide film, passivation layer and O2 were accelerated in combined-Fe0/FeS2 system and thereby enhanced the corrosion of Fe0 for efficient As removal. Our findings suggest that utilizing FeS2 to enhance the corrosion of Fe0 would be a promising technology for remediation of As-contaminated water.

Premagnetization enhancing the reactivity of Fe0/(passivated Fe0) system for high concentration p-nitrophenol removal in aqueous solution

In order to strengthen the treatment efficiency of Fe0 based system for high concentration wastewater treatment, Fe0 particles were passivated by concentrated nitric acid, and a premagnetization Fe0/(passivated Fe0) system was setup for high concentration p-nitrophenol (PNP) removal in this study. The significant parameters of this system were optimized. Under the optimal conditions, the premagnetization Fe0/(passivated Fe0) system could obtain high kobs value for PNP removal (0.100 min−1) and COD removal (15.0% after 60 min) for high concentration PNP (500 mg/L) treatment. In addition, five control experiments were set up to confirm the advantage of the premagnetization Fe0/(passivated Fe0) system. The results suggest that passivated Fe0 particles could be stimulated better than Fe0 particles by premagnetization process, and the premagnetization Fe0/(passivated Fe0) systems is much superior to the other five control systems. Furthermore, the pathway for PNP destruction treated by 6 different systems was also proposed according to intermediates determination by High Performance Liquid Chromatography (HPLC) and UV–vis spectrum, and the carbon mass balance was demonstrated according to the COD and HPLC analyses. Finally, the characteristics of (premagnetization) Fe0 and passivated Fe0 was detected by scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS) and vibrating sample magnetometer (VSM), and the mechanism of premagnetization effectively enhancing the reactivity of Fe0/(passivated Fe0) system (better than that of Fe0 system) was proposed. Consequently, the premagnetization for reactivity improvement of Fe0/(passivated Fe0) system is a promising technology to enhance the efficiency of this system for high concentration wastewater treatment.

Strengthening the reactivity of Fe0/(Fe/Cu) by premagnetization: Implications for nitrate reduction rate and selectivity

In order to develop a better Fe0 based system, premagnetization was used to enhance the reactivity of Fe0 particles and Fe/Cu bimetallic particles micro-electrolysis (Fe0/(Fe/Cu)) system for nitrate wastewater treatment. In this study, the significant parameters (i.e., initial pH, premagnetization time and intensity of magnetic field) were optimized firstly. Under the optimal conditions, the premagnetization Fe0/(Fe/Cu) system could obtain a high rate (kobs=0.732min−1) and better selectivity ([TN removal]/[NO3−-N removal] ratio=54.3%) for nitrate reduction, which were much superior to the 7 control experiments (i.e., Fe0/(Fe/Cu) system, premagnetization Fe0 particles and Cu0 particles micro-electrolysis (premagnetization Fe0/Cu0) system, Fe0/Cu0 system, premagnetization Fe0 system, Fe0 system, premagnetization Fe/Cu system and Fe/Cu system). Meanwhile, it was confirmed that the prepared Fe0/(Fe/Cu) could keep the high reactivity even after vacuum drying and longtime storage. Furthermore, the operational life of premagnetization Fe0/(Fe/Cu) system is better than that of Fe0/(Fe/Cu) system (for more than 12.6L wastewater treatment). The used Fe0/(Fe/Cu) could recover high reactivity after acid washing as well. Moreover, the characteristics of the medium materials before and after employment were analyzed by scanning electron microscopy, energy dispersive X-ray spectroscopy, and X-ray diffraction. Besides, the reasonable mechanism of premagnetization improving the rate and selectivity for nitrate reduction of Fe0/(Fe/Cu) system was also proposed. The possible reasons why premagnetization process could strengthen both rate and selectivity for nitrate reduction and why premagnetization could strengthen the Fe0/(Fe/Cu) system better were also given. Finally, it was proved that the new developed system not only could effectively treat different pollutants but also is suitable for different quality wastewater treatment. As a conclusion, the premagnetization Fe0/(Fe/Cu) system is a promising Fe0 based technology for wastewater treatment.

Application of electrochemical depassivation in PRB systems to recovery Fe0 reactivity

Permeable reactive barriers (PRBs) show remarkable Cr(VI) removal performance. However, the diminished removal rate because of mineral fouling over time is the bottleneck for application of PRBs. The present study demonstrated that electrochemical depassivation was effective for recovering the Fe0 reactivity, and minerals can be cleaned layer by layer with no secondary ion contamination and no transformation from Cr(III) to Cr(VI). The removal recovery rate increased with increasing electrolysis voltage before reaching the optimal electrolysis voltage, and then decreased as the electrolysis voltage further increased. The recovery effect at electrolysis voltages of 5, 10, and 15 V show the same trend as a function of electrolysis time, where recovery rate first increased and then decreased after reaching the optimal electrolysis time. The Cr(VI) removal rate significantly decreased with increasing electrolysis distance. Furthermore, Fe0 brush meshes electrode, Fe0 fillings, and polyvinyl chloride (PVC) meshes separators were combined to create an Electro-PRB configuration for the caisson excavation construction technique, which lays the foundation for establishment of promising Electro-PRB systems to treat Cr(VI)-contaminated groundwater.

Biphasic reduction model for predicting the impacts of dye-bath constituents on the reduction of tris-azo dye Direct Green-1 by zero valent iron (Fe0)

Influence of common dye-bath additives, namely sodium chloride, ammonium sulphate, urea, acetic acid and citric acid, on the reductive decolouration of Direct Green 1 dye in the presence of Fe0 was investigated. Organic acids improved dye reduction by augmenting Fe0 corrosion, with acetic acid performing better than citric acid. NaCl enhanced the reduction rate by its ‘salting out’ effect on the bulk solution and by Cl− anion-mediated pitting corrosion of iron surface. (NH4)2SO4 induced ‘salting out’ effect accompanied by enhanced iron corrosion by SO42− anion and buffering effect of NH4+ improved the reduction rates. However, at 2g/L (NH4)2SO4 concentration, complexating of SO42− with iron oxides decreased Fe0 reactivity. Urea severely compromised the reduction reaction, onus to its chaotropic and ‘salting in’ effect in solution, and due to it masking the Fe0 surface. Decolouration obeyed biphasic reduction kinetics (R2>0.993 in all the cases) exhibiting an initial rapid phase, when more than 95% dye reduction was observed, preceding a tedious phase. Maximum rapid phase reduction rate of 0.955/min was observed at pH2 in the co-presence of all dye-bath constituents. The developed biphasic model reckoned the influence of each dye-bath additive on decolouration and simulated well with the experimental data obtained at pH2.

Dual Effects of Humic Acid in Trichloroethylene Removal from Groundwater by Zero-Valent Iron: Hydrophobic Partition and Surface Adsorption

Natural organic matter (NOM) in groundwater is a factor of concern in long-term operation of Fe0 permeable reactive barrier (PRB). In this study, humic acid, a major component of NOM, showed dual effects in trichloroethylene (TCE) removal from simulated groundwater by Fe0 in batch and column experiments. In the initial stage of contacting with Fe0, humic acid promoted TCE removal due to its hydrophobic partitioning towards TCE and the subsequent fast adsorption onto Fe0 surfaces. In a long run, humic acid inhibited TCE removal because the buildup of adsorbed humic acid on Fe0 surfaces passivated Fe0 reactivity and limited TCE mass transfer. Ca2+ enhanced the co-aggregation of humic acid with Fe0 corrosion products and led to a faster depletion of TCE removal capacity by diminishing Fe0 matrix porosity. Revealed by FTIR analysis, part of TCE removed through hydrophobic partitioning was retained in humic acid accumulated on Fe0 surfaces rather than reductively degraded by Fe0. It raises a concern of using Fe0 PRB to treat organic contaminants in NOM-rich groundwater. Releasing back of NOM retained organic contaminants might take place once the accumulated NOM is desorbed or detached from Fe0 surfaces, resulting in a rebound of organic contaminants in the groundwater beyond the confine of PRB.

Sustaining reactivity of Fe0 for nitrate reduction via electron transfer between dissolved Fe2+ and surface iron oxides

The mechanism of the effects of Fe2+aq on the reduction of NO3− by Fe0 was investigated. The effects of initial pH on the rate of NO3− reduction and the Fe0 surface characteristics revealed Fe2+aq and the characteristics of minerals on the surface of Fe0 played an important role in NO3− reduction. Both NO3− reduction and the decrease of Fe2+aq exhibited similar kinetics and were promoted by each other. This promotion was associated with the types of the surface iron oxides of Fe0. Additionally, further reduction of NO3− produced more surface iron oxides, supplying more active sites for Fe2+aq, resulting in more electron transfer between Fe2+ and surface iron oxides and a higher reaction rate. Using the isotope specificity of 57Fe Mossbauer spectroscopy, it was verified that the Fe2+aq was continuously converted into Fe3+ oxides on the surface of Fe0 and then converted into Fe3O4 via electron transfer between Fe2+ and the pre-existing surface Fe3+ oxides. Electrochemistry measurements confirmed that the spontaneous electron transfer between the Fe2+ and structural Fe3+ species accelerated the interfacial electron transfer between the Fe species and NO3−. This study provides a new insight into the interaction between Fe species and contaminants and interface electron transfer.

Designing Metallic Iron Packed‐Beds for Water Treatment: A Critical Review

Filtration systems based on metallic iron (Fe0 filters) have been successfully used for water treatment over the past two decades. Relevant Fe0 filters expand from subsurface permeable reactive barriers (PRBs) to household filters. Fe0 filters systems are shown efficient for the remediation of biological and chemical contamination. Properly designing a Fe0 filter is finding a long‐term balance between two major interdependent design parameters: (i) Fe0 reactivity, and (ii) filter permeability. Other relevant design parameters include (i) aqueous flow velocity, (ii) bed thickness, and (iii) water chemistry. Water chemistry includes nature and extent of contamination. To date, attempts to design more sustainable Fe0 filters have been mostly pragmatic as: (i) reactive Fe0 has failed to be considered as in situ generator of contaminant collectors (and “secondary” reducing agents), and (ii) the volumetric expansive nature of iron corrosion has been overlooked. On the other hand, valuable design criteria were available in the hydrometallurgical literature (cementation using elemental metals) prior to the advent of Fe0 filters. As a consequence the literature is full of seemingly controversial results which are easily conciliated by the physico–chemistry of the system. The present review is limited at identifying some misconceptions and demonstrating their proliferation. Tools for better analyses are recalled. Recent X‐ray tomography data are used as illustration of how valuable data are insufficiently discussed. It is hoped that the present contribution will boost systematic research for the design of more sustainable Fe0 filters.

Comparative study on the reactivity of Fe/Cu bimetallic particles and zero valent iron (ZVI) under different conditions of N2, air or without aeration

In order to further compare the degradation capacity of Fe0 and Fe/Cu bimetallic system under different aeration conditions, the mineralization of PNP under different aeration conditions has been investigated thoroughly. The results show that the removal of PNP by Fe0 or Fe/Cu system followed the pseudo-first-order reaction kinetics. Under the optimal conditions, the COD removal efficiencies obtained through Fe0 or Fe/Cu system under different aeration conditions followed the trend that Fe/Cu (air)>Fe/Cu (N2: 0–30min, air: 30–120min)>control-Fe (air)>Fe/Cu (without aeration)>Fe/Cu (N2)>control-Fe (N2). It revealed that dissolved oxygen (DO) could improve the mineralization of PNP, and Cu could enhance the reactivity of Fe0. In addition, the degradation of PNP was further analyzed by using UV–vis, FTIR and GC/MS, and the results suggest that Fe/Cu bimetallic system with air aeration could completely break the benzene ring and NO2 structure of PNP and could generate the nontoxic and biodegradable intermediate products. Meanwhile, most of these intermediate products were further mineralized into CO2 and H2O, which brought about a high COD removal efficiency (83.8%). Therefore, Fe/Cu bimetallic system with air aeration would be a promising process for toxic refractory industry wastewater.

Simultaneous removal of co-contaminants: acid brilliant violet and Cu2+ by functional bimetallic Fe/Pd nanoparticles

Effluents from the textile industry often contain dyes and metals that are a serious environmental concern. It is a challenge to develop a method for simultaneous removal of mixed contaminants. In this study, kaolinite supported bimetallic Fe/Pd (K–Fe/Pd) is firstly reported to be used for simultaneous catalytic removal of acid brilliant violet (ABV) and Cu2+ in aqueous solution, where the presence of kaolinite as a stable supporter and disperser maintains the reactivity of Fe0 as a reductant, while Pd0 as a catalyst accelerates the reaction. This was confirmed by scanning electron microscopy (SEM), X-ray diffraction (XRD), and batch experiments. 96.23 % of ABV and 100 % of Cu2+ was removed using K–Fe/Pd within 60 min, while only 77.50 % of ABV and 99.45 % of Cu2+ using K–Fe, and 19.75 % of ABV and 4.00 % of Cu2+ using kaolinite was removed, respectively. However, both efficiency and rate of removal in the mixed solution were higher than that of the single one regarding both ABV and Cu2+, which is attributable to the formation of in situ trimetallic Cu/Fe/Pd in the mixed solution. Different factors impacting on the removal of ABV–Cu2+ using K–Fe/Pd showed that the catalytic reduction decreased when pH, initial concentration, and temperature increased. Finally, the reuse and application of K–Fe/Pd in dyeing wastewater led to a removal efficiency of 96.35 % for ABV and 100 % for Cu2+, respectively.

Competitive Reduction of Nitrate, Nitrite, and Nitrobenzene in Fe0-Water Systems

AbstractTreating mixed contaminants with zerovalent iron (Fe0) for environmental remediation requires a thorough understanding of the competition among electron acceptors. The authors conducted aqueous batch tests to determine competitive reduction of nitrate, nitrite, and nitrobenzene by Fe0 under varying conditions. Results indicate that nitrate reduction by Fe0 was accompanied by substantial Fe0 oxidation by water. Nitrite and nitrobenzene were concomitantly reduced by Fe0, forming a lepidocrocite (γ-FeOOH) coating on the Fe0 grains. When present together, nitrite and nitrobenzene reduction proceeded without apparent interference from nitrate. Nitrate reduction, however, did not occur in the presence of nitrite or nitrobenzene. Adding aqueous Fe(II) facilitated nitrate reduction by Fe0, but not until the lepidocrocite coating on the Fe0 grains was transformed to magnetite (Fe3O4), a process that is significantly accelerated by surface-bound Fe(II). This study illustrates the relative reactivity of Fe0 ...

Passivation process and the mechanism of packing particles in the Fe0/GAC system during the treatment of ABS resin wastewater

This study provides mechanistic insights into the passivation of the packing particles during the treatment of acrylonitrile–butadiene–styrene (ABS) resin wastewater by the Fe0/GAC system. The granular-activated carbon (GAC) and iron chippings (Fe0) were mixed together with a volumetric ratio of 1:1. GAC has a mean particle size of approximately 3–5 mm, a specific surface of 748 m2 g−1, a total pore volume of 0.48 mL g−1 and a bulk density of 0.49 g cm−3. The iron chippings have a compact and non-porous surface morphology. The results show that the packing particles in the Fe0/GAC system would lose their activity because the removal of TOC and for ABS resin wastewater could not carried out by the Fe0/GAC system after 40 days continuous running. Meanwhile, the availability of O2 and intrinsic reactivity of Fe0 play a key role on the form of passive film with different iron oxidation states. The passive film on the surface of iron chippings was formed by two phases: (a) local corrosion phase (0–20 d) and (b) co-precipitation phase (20–40 d), while that of GAC was mainly formed by the co-precipitation of corrosion products with and because and would not easily reach the Fe0 surface. Therefore, in order to avoid the occurrence of filler passivation, high concentrations of and in wastewater should be removed before the treatment process of the Fe/GAC system.

Characterising the reactivity of metallic iron in Fe<sup>0</sup>/As-rock/H<sub>2</sub>O systems by long-term column experiments

The intrinsic reactivity of 4 metallic iron materials (Fe0) was investigated in batch and column experiments. The Fe0 reactivity was characterised by the extent of aqueous fixation of in-situ leached arsenic (As).  Air-homogenised batch experiments were conducted for 1 month with 10.0 g/. of an As-bearing rock (ore material) and 0.0 or 5.0 g/. of Fe0. Column experiments were performed for 2 and 3 months. Each dynamic  experiment was made up of 2 glass columns in series. The first column contained 2.5 or 5.0 g of the ore material and the second column 0.0 or 5.0 g of a Fe0 material. Results showed no significant reactivity difference in batch studies for all 4 materials; ZVI2 was by far the most reactive material in column experiments. This observation was attributed to the relative kinetics of production of aqueous As and Fe species under the experimental conditions and their impact on the formation of a protective film on Fe0. Accordingly, no protective film could be built at the surface of the least reactive materials. The results corroborated the urgent need for unified experimental procedures to characterise Fe0 materials.

Investigating the processes of contaminant removal in Fe0/H2O systems

The instability of the premise of direct quantitative contaminant reduction by elemental iron (Fe0) materials in Fe0/H2O systems is pointed out. Basic knowledge of aqueous iron corrosion shows that the Fe0 surface is not available for decontamination in nature. A comparison of the reactivity of Fe0 and Zn0 shows that the effectiveness of Fe0 materials for environmental remediation is due to the formation of a non-adhesive, porous oxide scale on Fe0. Contaminants are enmeshed within the scale and possibly reduced by FeII and H/H2. An evaluation of current experimental conditions shows that well-mixed batch systems have disturbed the process of scale formation. Therefore, the majority of published works have operatively created conditions for contaminant reduction that are not likely to occur in nature. Since working under such unrealistic conditions has mediated the above-mentioned premise, interactions in Fe0/H2O systems yielding contaminant removal should be revisited.

Electrochemical depassivation for recovering Fe0 reactivity by Cr(VI) removal with a permeable reactive barrier system

A new electrochemical permeable reactive barrier (Electro-PRB) system for removal of hexavalent chromium [Cr(VI)] using Fe0 meshes was developed. Electro-PRB was found to be effective for electrochemical depassivation of Fe0 to remove Cr(VI) during treatment. During initial treatment, Cr(VI) removal rates decreased with time, due to loss of Fe0 reactivity by mineral fouling. After Fe0 was passivated, electrochemical depassivation was introduced for different electrolysis times to recover Fe0 reactivity. It was found that there was approximately 100.4–131.3% initial removal rate recovery, due to the electrochemical break down of precipitates on the Fe0 surfaces. During the treatment, the decreasing pH and increasing oxidation–reduction Potential (ORP) of the effluent implied the passivation of Fe0 surfaces. Scanning electron microscope analysis of acid-washed, electrochemically depassivated, and passivated Fe0 confirmed the efficiency of Elecro-PRB in the recovery Fe0 reactivity. The results indicate that the Electro-PRB system proposed here is capable of recovering the reactivity of Fe0, which may prolong the operation of Cr(VI) removal processes.

Removal of Chromium(VI) by Zero Valent Iron: Effects of Environmental Factors

The influences of various geochemical factors, such as pH, phosphate, bicarbonate, humic acid, permanganate, and dissolved oxygen, on hexavalent chromium(Cr(VI)) removal by zero-valent iron(Fe0) were investigated in a batch setting. Results showed that low pH environments were favorable to removal of Cr(VI) compared with high pH environments. Phosphate significantly inhibited removal of Cr(VI) possibly due to competition of adsorption sites on corrosion products. Humic acid introduced a marginal influence on Fe0 reactivity toward Cr(VI) reduction, whereas bicarbonate enhanced Cr(VI) removal by maintaining the solution pH near neutral. Permanganate cumbered the removal of Cr(VI) due to its competition for electron from oxidation of Fe0. The removal efficiency of Cr(VI) was higher in oxic conditions than that in anoxic conditions.

Effects of electrolytes on the reduction of 2,4‐dinitrotoluene by zero‐valent iron

AbstractBACKGROUND: Dinitrotoluenes (DNTs) are environmentally persistent, making the remediation of contaminated streams and groundwater difficult. Zero‐valent iron (Fe0) can be used as an electron source for the reduction of recalcitrant DNTs in waste‐water and thus enhance their biodegradability. However, little is known about the qualitative effects of major anions and cations present in waste‐water on the reduction of DNTs by Fe0.RESULTS: The presence of Na2SO4 and NaCl at levels between 0.25 and 2 mmol L−1 was observed to enhance the reactivity of Fe0 towards 2,4‐DNT. The positive effect of K2SO4 is stronger than that of Na2SO4 at the same level (1 mmol L−1). Varying (NH4)2SO4 from 0.1 to 1.0 mmol L−1 improved the efficiency of 2,4‐DNT degradation by Fe0. The effects of varying NaNO3 and NaNO2 from 0 mmol L−1 to 4.7 mmol L−1 and 0 mmol L−1 to 5.8 mmol L−1, respectively, were also investigated. Both NaNO3 and NaNO2 at low concentration improved the efficiency of 2,4‐DNT degradation by Fe0, however, at high concentration, inhibiting effects appeared.CONCLUSION: SO42−, Cl−, Na+, K+ and NH4+ notably enhanced 2,4‐DNT reduction by Fe0 at the tested concentrations. The positive effect of K+, Cl− was relatively stronger than that of Na+ and sulfate (SO42−). However, the effect of NH4+ was relatively weaker at concentrations greater than 1.0 mmol L−1. The presence of low concentrations of NO3− and NO2− promoted 2,4‐DNT reduction by Fe0 and inhibited the reaction. The results suggest that 2,4‐DNT reduction by Fe0 can be controlled by the ions composition of the waste‐water. Copyright © 2010 Society of Chemical Industry