Effects of brining on the corrosion of ZVI and its subsequent As(III/V) and Se(IV/VI) removal from water

Enhanced Chromium (VI) Removal by Micron-Scale Zero-Valent Iron Pretreated with Aluminum Chloride under Aerobic Conditions

Micron-scale zero-valent iron (ZVI)-based material has been applied for hexavalent chromium (Cr(VI)) decontamination in wastewater treatment and groundwater remediation, but the passivation problem has limited its field application. In this study, we combined aluminum chloride solution with ZVI (pcZVI-AlCl3) to enhance Cr(VI) removal behavior under aerobic conditions. The optimal pre-corrosion conditions were found to be 2.5 g/L ZVI, 0.5 mM AlCl3, and a 4 h preconditioning period. Different kinds of techniques were applied to detect the properties of preconditioned ZVI and corrosion products. The 57Fe Mössbauer spectra showed that proportions of ZVI, Fe3O4, and FeOOH in pcZVI-AlCl3 were 49.22%, 34.03%, and 16.76%, respectively. The formation of Al(OH)3 in the corrosion products improved its pHpzc (point of zero charge) for Cr(VI) adsorption. Continuous-flow experiments showed its great potential for Cr(VI) removal in field applications. The ZVI and corrosion products showed a synergistic effect in enhancing electron transfer for Cr(VI) removal. The mechanisms underlying Cr(VI) removal by pcZVI-AlCl3 included adsorption, reduction, and precipitation, and the contribution of adsorption was less. This work provides a new strategy for ZVI pre-corrosion to improve its longevity and enhance Cr(VI) removal.

Enhanced hydrodechlorination of 4-chlorophenol through carboxymethylcellulose-modified Pd/Fe nanosuspension synthesized by one-step methods

Palladized iron (Pd/Fe) represents one of the most common modification strategies for nanoscale zero-valent iron (nZVI). Most studies prepared Pd/Fe by reducing iron salts and depositing Pd species on the surface of pre-synthesized nZVI, which can be called the two-step method. In this study, we proposed a one-step method to obtain Pd/Fe by the concurrent formation of Fe0 and Pd0 and investigated the effects of these two methods on 4-chlorophenol (4-CP) removal, with carboxymethylcellulose (CMC) coated as a surface modifier. Results indicated that the one-step method, not only streamlined the synthesis process, but also Pd/Fe-CMCone-step, synthesized by it, exhibited a higher 4-CP removal rate (97.9%) compared to the two-step method material Pd/Fe-CMCtwo-step (82.4%). Electrochemical analyses revealed that the enhanced activity of Pd/Fe-CMCone-step was attributed to its higher electron transfer efficiency and more available reactive species, active adsorbed hydrogen species (Hads*). Detection of intermediate products demonstrated that, under the influence of Pd/Fe-CMCone-step, the main route of 4-CP was through hydrodechlorination (HDC) to form phenol and H* was the main active specie, supported by EPR tests, quenching experiments and product analysis. Additionally, the effects of initial 4-CP concentration, initial pH, O2 concentration, anions such as Cl-, SO42-, HCO3-, and humic acid (HA) were also investigated. In conclusion, the results of this study suggest that Pd/Fe-CMCone-step, synthesized through the one-step method, is a convenient and efficient nZVI-modifying material suitable for the HDC of chlorinated organic compounds.

Enhanced activation of persulfate by modified red mud biochar for degradation of dye pollutant: Resource utilization and non-radical activation

The substantial development of the dyeing and printing industry has resulted in an increased discharge of dye wastewater containing a large amount of recalcitrant organic pollutants. Furthermore, the landfill disposal of red mud has led to significant environmental pollution such as soil erosion and groundwater contamination. Therefore, this study aimed to promote the resource utilization of red mud by preparing advanced oxidation catalyst, resulting in effective treatment of dye wastewater, and the primary reaction mechanism was revealed. In this study, biochar-loading red mud (RBC) was applied to activate persulfate (PDS) for the degradation of acid orange 7 (AO7) with the initial concentration of 50 mg L-1. The maximum removal rate of 2.45 mg L·min-1 was achieved in 20 min and corresponding with the removal ratio of 98.0% under the PDS concentration of 20 mM (4.76 g L-1). Eventually, the removal ratio of 99.2% was attained within 60 min. The high catalytic efficiency was probably ascribed to the singlet oxygen (1O2) dominant non-radical pathway and RBC-mediated electron transfer mechanism. It was found that Fe(II), specific surface areas and functional groups on the catalyst were highly related to its catalytic efficiency and passivation. RBC had better reusability due to the loading of biochar and the reduction of zero-valent iron. The non-radical pathway mechanism and electron transfer mechanism were proposed for the activation of PDS, and non-radical pathway played a dominant role. Besides, the degradation pathways and toxicity assessment were analyzed. This research proposed a new electron transfer mechanism for activation process of PDS, which can provide a theoretical support for further studies. Overall, this study demonstrated that catalysts synthesized from red mud and biomass exhibit highly efficient activation in degrading the model pollutant AO7 through PDS activation. The catalyst displayed promising reusability and practical applicability, offering potential advancements in both the resource utilization and reduction of red mud.

Reductive sequestration of Cr (VI) by phosphorylated nanoscale zerovalent iron

The cracked phosphorylated nanoscale zerovalent iron (p-nZVI) has a strong electron selectivity towards the reductive removal of many heavy metal ions in waters. However, the unintended environmental risk after interactions with impurities or wastewater are not involved. Therefore, in this study, the phosphate group was successfully adsorbed into p-nZVI, and the cracked p-nZVI was successfully prepared with an optimal P/Fe ratio of 0.5%. The dosages of p-nZVI and temperatures were positively correlated with the removal rates. The removal process of Cr(VI) was more suitable by the Langmuir isothermal model（R2 > 0.99). The process of Cr (VI) (10, 20 and 40 mg/L) removal more fitted the pseudo first-order reaction model, while the process of Cr (VI) (60, 80 mg/L) removal more fitted the pseudo second-order reaction model. The Cr (VI) removal rates gradually decreased when the pH was increased. Dissolved oxygen slowed nanoiron reaction rates. The order of inhibition on the reactivity towards Cr(VI) was SiO32- > SO42- > PO43- > NO3- > HCO3-.The facilitation followed the order of Cd2+>Cu2+>Mg2+>Mn2+>Ca2+. Ca2+ showed an inhibitory effect, but all other cations showed different degrees of facilitation. The promotion effect is relatively similar in presence of Mn2+ or Mg2+. HA had a significant inhibitory effect. Environmental friendly p-nZVI had a good effect in simulated groundwater, seawater, river water and secondary effluent of the urban sewage treatment plant. The main pathway to remove Cr (VI) was in situ reduction by p-nZVI. The improved adsorption and reduction effect of p-nZVI on heavy metal ions in water was due to the structural change and the phosphate group.

Efficient rhodamine B dye degradation by red mud-grapefruit peel biochar catalysts activated persulfate in water

The continuous and rapid development of textile industry intensifies rhodamine B dye (RhB) wastewater pollution. Meanwhile, massive red mud (RM) solid waste generated by the industrial alumina production process poses detrimental effects to the environment after leaching. For resource utilization and to reduce the expansion of RhB pollution, RM and peel red mud-biochar composite (RMBC) catalyst were synthesized in activating peroxydisulfate (PDS) for RhB degradation. Firstly, characterization results showed that compared to RM, RMBC had a higher content of catalytically active metals (Fe, Al, Ti) (higher than 0.92-4.18%), smaller pore size, and larger specific surface area (10 times), which verified RMBC had more potential catalytic oxidation activity. Secondly, under optimal dosage (catalyst, PDS), pH 4.6, and 20 mg L-1 RhB, it was found that the RhB degradation ratio of RM was 76.70%, which was reduced to 41% after three cycles, while that of RMBC was 89.98% and 67%, respectively. The results indicated that the performance of RMBC was significantly superior to that of RM. Furthermore, the quenching experiments, electron paramagnetic resonance spectroscopy tests, FTIR, and XPS analysis showed the function of O-H, C=O, C-O, Fe-O, and Fe-OH functional groups, which converted the PDS to the active state and hydrolyzed it to produce free radicals ([Formula: see text], 1O2, [Formula: see text]) for RhB degradation. And, Q Exactive Plus MS test obtained that RhB was degraded to CO2, H2O, and intermediate products. This study aimed to raise a new insight to the resource utilization of RM and the control of dye pollution.

Acid-modified red mud biochar for the degradation of tetracycline: Synergistic effect of adsorption and nonradical activation

In this study, a novel acid-modified red mud biochar catalyst (MMBC) was synthesized by industrial waste red mud (RM) and peanut shell (PSL) to activate peroxodisulfate (PDS) for the degradation of TC. Meanwhile, MMBC exhibited remarkable adsorption capacity, reaching a 60% removal ratio of TC within 60 min (equilibrium adsorption capacity = 12 mg/g). After adding PDS, MMBC/PDS system achieved a 93.8% removal ratio of TC within 60 min. Quenching experiments and electron paramagnetic resonance (EPR) results showed that 1O2 played a dominant role in the degradation of TC and O2•- was the mainly precursor for the production of 1O2 in the MMBC/PDS system. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) analysis showed that the surface Fe(II), -OH and -COOH provided the active sites for the activation of PDS by MMBC. In addition, acid modification optimised the surface structure of the catalyst and enhanced the conversion of Fe (mainly Fe(III) to Fe(II)), thereby improving the adsorption and catalytic efficiency of MMBC. This study confirmed that modified red mud biochar is an efficient composite with both adsorption and catalysis, providing new ideas for the practical treatment of antibiotic wastewater and the resource utilization of red mud.

Supporting nanoscale zero-valent iron onto shrimp shell-derived N-doped biochar to boost its reactivity and electron utilization for selenite sequestration

Nanoscale zero-valent iron (nZVI) has been widely used in the reductive removal of contaminants from water, yet it still fights against the inherent passive cover and the raise of medium pH. In this study, nZVI was supported onto a nitrogen-doped biochar (NBC) that was prepared by pyrolyzing shrimp shell for efficiently sequestrating aqueous selenite (Se(IV)). The resultant composite (NBC-nZVI) revealed a higher reactivity and electron utilization efficiency (EUE) than the bare nZVI in Se(IV) sequestration because of the positive charge, the buffering effect and the good conductivity of NBC. The kinetic rate and EUE of NBC-nZVI were increased by 143.4% and 15.3% compared to the bare nZVI, respectively, at initial pH of 3.0. The high removal capacity of 605.4 mg g^-1 for NBC-nZVI was obtained at Se(IV) concentration of 1000 mg L^-1, initial pH of 3.0, NBC-nZVI dosage of 1.0 g L^-1 and contact time of 12 h. Moreover, NBC-nZVI exhibited a strong tolerance to solution pHs and coexisting compounds (e.g., humic acid) and could reduce the Se(IV) concentration from 5.0 mg L^-1 to below the limit of drinking water (50 μg L^-1) in real-world samples. This work exemplified a utilization of shrimp shell-derived NBC to simultaneously enhance the reactivity and EUE of nZVI for reductively removing contaminants.

Selenium Oxoanions Removal from Wastewater by MoS42− Intercalated FeMgAl LDH: Catalytic Roles of Fe and Mechanism Insights

FeMgAl−MoS4 LDH was successfully synthesized by a one-pot hydrothermal process followed by ion-exchange methods, and this novel adsorbent was first conducted for aqueous selenite and selenate elimination. The Fe as a component for metal cation layers of LDHs could modulate the layer charge density, leading to more functional groups inserted into layers, and more importantly, this heterogeneous Fe can catalyze the surface reactions between Se(IV) or Se(VI) with S(-II) for oxoanions sequestration. The mechanisms are ion exchange between functional groups with HSeO3− and SeO32− for Se(IV) or SeO42− for Se(VI), followed by reduction by S(-II) from MoS42− groups. The existence of Fe in LDH cation layers, obviously enhanced the reactions (almost two times more for Se(IV) and three times more for Se(VI), respectively), resulting in satisfying adsorption capacities of 483.9 mg/g and 167.2 mg/g for Se(IV) and Se(VI), respectively. Mechanisms were further revealed by elementary analysis, XRD, FT−IR, SEM−EDX, and XPS, as well as the quantitative study. For sorption kinetics, the calculated values of capacities from the pseudo-second-order model are much closer to the experimental values. For sorption isotherms, Langmuir is better than the Freundlich isotherms model for closer capacities (505 mg/g for selenite and 172 mg/g for selenate). All these results demonstrated that the presence of heterogeneous Fe could catalyze the reduction of Se (IV/VI) for the aqueous system, and maybe other high oxidative states hazardous ions. So FeMgAl−MoS4 is a kind of novel adsorbent that offers a promising multi-functional and highly efficient solution for water selenium purification.

A Bibliometric Analysis of Research on Selenium in Drinking Water during the 1990-2021 Period: Treatment Options for Selenium Removal

A bibliometric analysis based on the Scopus database was carried out to summarize the global research related to selenium in drinking water from 1990 to 2021 and identify the quantitative characteristics of the research in this period. The results from the analysis revealed that the number of accumulated publications followed a quadratic growth, which confirmed the relevance this research topic is gaining during the last years. High research efforts have been invested to define safe selenium content in drinking water, since the insufficient or excessive intake of selenium and the corresponding effects on human health are only separated by a narrow margin. Some important research features of the four main technologies most frequently used to remove selenium from drinking water (coagulation, flocculation and precipitation followed by filtration; adsorption and ion exchange; membrane-based processes and biological treatments) were compiled in this work. Although the search of technological options to remove selenium from drinking water is less intensive than the search of solutions to reduce and eliminate the presence of other pollutants, adsorption was the alternative that has received the most attention according to the research trends during the studied period, followed by membrane technologies, while biological methods require further research efforts to promote their implementation.

Effect of Spatial Distribution of nZVI on the Corrosion of nZVI Composites and Its Subsequent Cr(VI) Removal from Water

There have been many studies on contaminant removal by fresh and aged nanoscale zero-valent iron (nZVI), but the effect of spatial distribution of nZVI on the corrosion behavior of the composite materials and its subsequent Cr(VI) removal remains unclear. In this study, four types of D201-nZVI composites with different nZVI distributions (named D1, D2, D3, and D4) were fabricated and pre-corroded in varying coexisting solutions. Their effectiveness in the removal of Cr(VI) were systematically investigated. The results showed acidic or alkaline conditions, and all coexisting ions studied except for H₂PO₄⁻ and SiO₃²⁻ enhanced the corrosion of nZVI. Additionally, the Cr(VI) removal efficiency was observed to decrease with increasing nZVI distribution uniformity. The corrosion products derived from nZVI, including magnetite, hematite, lepidocrcite, and goethite, were identified by XRD. The XPS results suggested that the Cr(VI) and Cr(III) species coexisted and the Cr(III) species gradually increased on the surface of the pre-corroded D201-nZVI with increasing iron distribution uniformity, proving Cr(VI) removal via a comprehensive process including adsorption/coprecipitation and reduction. The results will help to guide the selection for nZVI nanocomposites aged under different conditions for environmental decontamination.

Mini art review for zero valent iron application in anaerobic digestion and technical bottlenecks

Zero valent iron (ZVI) has been used extensively to control environmental pollution owing to its strong reducibility and low cost. Herein, we evaluate the impact of ZVI (iron scrap and ZVI powder with different scales) on anaerobic digestion (AD) reactor performance improvement and syntrophic relationship stimulation among various microbial groups in the methanogenesis process. In recent studies, ZVI addition significantly enhanced methane and volatile fatty acid (VFA) yields and alleviated excessive acidification, ammonia accumulation, and odorous gas production. Further, we reviewed the changes in enzyme activity and microbial metabolism after the addition of ZVI throughout the reaction process. Certain innovative technologies, such as bioelectrochemical system assistance and combined usage of conductive materials, may improve AD performance compared to the use of ZVI alone, the mechanism of which has been discussed from various viewpoints. Furthermore, the primary technical bottlenecks, such as poor mass transfer efficiency in dry AD and high ZVI dosage, have been illustrated, and syntrophic methanogenesis regulated by ZVI addition can be further studied by conducting theoretical research.

Preparation and application of a novel biochar-supported red mud catalyst：Active sites and catalytic mechanism

A novel catalyst RM-BC_(HP) was synthesized by hydrothermal treatment and pyrolysis (800 ℃) using red mud and coconut shells. Influence of different preparation conditions on catalyst performance was explored. SEM showed that RM-BC_(HP) was porous and RM was successfully loaded on the outside surface and inside the pores of BC. XRD revealed that Fe₂O₃ in RM was reduced to Fe⁰ and Fe₃O₄ in the pyrolysis process, in which pyrolysis temperature and addition ratio of coconut shells were critical. TGA-MS, FT-IR and XPS were also applied to character the catalyst. 100% of AO7 was removed within 30 min with conditions of 2 mM PS, 50 mg/L AO7 and 0.5 g/L RM-BC_(HP), and the Fe leaching was negligible. High removal rate was obtained in tap, river, and lake water. RM-BC_(HP)/PS system also exhibited excellent degradation performance for other dyes (MB, MG and RhB) and antibiotics (TC, OTC and CTC). The mechanism studies demonstrated that PS was mainly activated by Fe⁰ and Fe²⁺ in RM-BC_(HP) to produce different radicals, then ¹O₂ was generated by the reactions among these radicals to degrade AO7. Finally, nine intermediate products of AO7 were identified by FT-ICR-MS and a probable degradation pathway was proposed.

Enhanced kinetic performance of peroxymonosulfate/ZVI system with the addition of copper ions: Reactivity, mechanism, and degradation pathways

Advanced oxidation processes (AOPs) based on the bimetallic system has been demonstrated as a promising way to enhance the degradation of pollutants in the water. In this study, the degradation of Rhodamine B (RhB) in a zero-valent iron (ZVI)/ peroxymonosulfate system with Cu²⁺ was thoroughly investigated. RhB could be efficiently removed (99.3 %) in the optimal ZVI/PMS/Cu²⁺ system, while only 58.2 % of RhB could be degraded in the ZVI/PMS system. The influence of reaction parameters on the degradation of RhB was further investigated. Quenching experiments and electron paramagnetic resonance (EPR) tests revealed that various reactive oxygen species could be generated in the ternary system, of which, ¹O₂ and O₂^- were identified for the first time. The effect of various anions, NOM and different water matrix were also considered at different concentrations. A variety of byproducts and degradation pathways were identified using HPLC/MS/MS. Finally, the Quantitative Structure Activity Relationship (QSAR) method of Toxicity Estimation Software Tool (TEST) was applied to estimate the toxicity of the byproducts and the results indicated that the overall toxicity of the target was relatively reduced. This study demonstrated the potential for the removal of environmental reluctant pollutants in water via the combined radical and non-radical pathways.

One-step preparation of ZVI-sludge derived biochar without external source of iron and its application on persulfate activation

Zero Valent Iron (ZVI) is an important and widely employed environmental remediation material in brownfield. However, the instability of fine size ZVI and the strong aggregation of nanoscale-ZVI limited its further application. To overcome these drawbacks, ZVI-Sludge Derived Biochar (SDBC) was prepared without external iron source through the one-step process of pyrolysis. The characterization results including SEM-EDX, XRD and XPS confirmed the successful loading of Fe⁰ on the surface of SDBC. The activation efficiency of persulfate (PS) in in-situ chemical oxidation system was studied. The environmental remediation properties of ZVI-SDBC/PS system were evaluated employing acid orange (AO7) and landfill leachate as target pollutants. ZVI-SDBC/PS system was highly efficient as that 99.0% of AO7 (0.06 mM) was removed by 0.925 mM of PS and 0.5 g L^-1 of ZVI-SDBC. In addition, total organic carbon (TOC) and ammonia in leachate were removed by 62.8% and 99.8%, respectively. The removal efficiency of AO7 was nearly independent on initial pH as that 89.1% and 99.1% of AO7 were removed at pH of 9.08 and 2.13 respectively. Hydroxyl radicals dominated in the reaction under neutral and alkaline conditions with contribution rates of 71.9% and 86.1% respectively. Noticeably, not only free radicals but also non-radical species such as singlet oxygen contributed to the degradation, which favored the pH-independent performance. The reuse performance of ZVI-SDBC was higher than these of previously reported ZVI-based catalysts as that the first-order rate constant of AO7 removal decreased not much from 0.0718 to 0.0502 min^-1 after the three-cycle reuse assays. In summary, ZVI-SDBC showed advantages such as the facile and chemical-saving preparation method, reliable disposal of municipal sewage sludge, remarkable efficiency and stability. These advantages proved ZVI-SDBC/PS system as an effective strategy of controlling waste by waste, and implicated its potential application in full-scale for environmental remediation in brownfield.

Versatility of iron-rich steel waste for the removal of high arsenic and sulfate concentrations in water

The aim of this work is to evaluate the application of a steel waste, basic oxygen furnace sludge (BOFS), rich in iron, to treat water contaminated with elevated arsenic and sulfate concentrations. In the first step, three doses (10, 60, and 80 g L^-1) of BOFS were tested to investigate the removal of As(III) and As(V) (67 mg L^-1) and sulfate (3700 mg L^-1) separately from an aqueous solution. In the second step, the efficacies of BOFS (10 g L^-1) and commercial ZVI (5 g L^-1) were compared to simultaneously remove arsenic and sulfate. The pH of the feed solution was adjusted to 2.5 and monitored during the experiment. The use of BOFS achieved arsenic removal up to 92% and sulfate removal of nearly 40% after 72 h of contact time. Use of BOFS also increased the solution pH to 12. Similar removal levels were achieved with both BOFS and ZVI. These results confirm the potential application of BOFS to remove high arsenic and sulfate concentrations from acidic solutions. The data obtained here should be used as a basis for further studies on the remediation of acid mine drainage with high concentrations of arsenic and sulfate using an abundant and low-cost steel waste.

Characteristics of trichloroethene (TCE) dechlorination in seawater over a granulated zero-valent iron

The accumulation of halogenated organic contaminants in estuaries near harbor areas has been receiving increasing attention. This work demonstrates the reductive treatment of trichloroethene (TCE) within seawater and freshwater using a polymeric surfactant (polyvinyl alcohol-co-vinyl acetate-coitaconic acid) modified nanoscale zero-valent iron (GnZVI). Experimental parameters included the ratio of seawater to freshwater, reaction pH, dosage of GnZVI and initial TCE concentration. It was found that the rate of TCE reduction decreased with increasing weight ratio of seawater to freshwater (k_a = 0.075 min^-1 in freshwater and 0.01 min^-1 in seawater); however, the rate substantially improved by increasing the dosage of GnZVI. A consecutive reaction model of adsorption/desorption and reductive dechlorination was established to assess the chemical kinetics of TCE and the intermediates over the GnZVI. The experimental results suggested that both the amount of free sites on the reductant and reactivity of iron to TCE dominated the degradation efficiency. Desorption was a rate-limiting step for the intermediates that evolved (DCE, VC and ethene) in the bulk solution. Under conditions: GnZVI = 5 g/L, reaction pH around 8 and initial TCE = 10 mg/L, the removal efficiency attained 95%, while the decline in the removal rate of TCE from the seawater could be simply improved by increasing GnZVI dosage (10 g/L). As a role of electron donor for water and TCE, ZVI might passivate with contact time, leading to formation of the main crystalline phase magnetite (Fe₃O₄) by the coprecipitation of oxidized iron (Fe(II)/Fe(III)) over the surfaces of ZVI particles.

Enhanced removal of Se(VI) from water via pre-corrosion of zero-valent iron using H2O2/HCl: Effect of solution chemistry and mechanism investigation

Although the removal of Se(VI) from water by using zero-valent iron (ZVI) is a promising method, passivation of ZVI severely inhibits its performance. To overcome such issue, we proposed an efficient technique to enhance Se(VI) removal via pre-corrosion of ZVI with H₂O₂/HCl in a short time (15 min). The resultant pcZVI suspension was weakly acidic (pH 4.56) and contained abundant aqueous Fe²⁺. ⁵⁷Fe Mössbauer spectroscopy showed that pcZVI mainly consisted of Fe⁰ (66.2%), hydrated ferric oxide (26.3%), and Fe₃O₄ (7.5%). Efficient removal of Se(VI) from sulfate-rich solution was achieved by pcZVI compared with ZVI (in the absence and presence of H₂O₂) and acid-pretreated ZVI. Moreover, the efficient removal of Se(VI) by pcZVI sustained over a broad pH range (3-9) due to its strong buffering power. The presence of chloride, carbonate, nitrate, and common cations (Na⁺, K⁺, Ca²⁺, and Mg²⁺) posed negligible influence on the removal of Se(VI) by pcZVI, while the inhibitory effect induced by sulfate, silicate, and phosphate indicated the significance of Se(VI) adsorption as a prerequisite step for its removal. The consumption of aqueous Fe²⁺ was associated with Se(VI) removal, and X-ray absorption near edge structure revealed that the main pathway for Se(VI) removal by pcZVI was a stepwise reduction of Se(VI) to Se(IV) and then Se⁰ as the dominant final state (78.2%). Moreover, higher electron selectivity of pcZVI was attributed to the enhanced enrichment of Se oxyanions prior to their reduction.

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.

Deiodination of iopamidol by zero valent iron (ZVI) enhances formation of iodinated disinfection by-products during chloramination

Iodinated X-ray contrast media (ICM) is considered as one of iodine sources for formation of toxic iodinated disinfection byproducts (I-DBPs) during disinfection. This study investigated transformation of a typical ICM, iopamidol (IPM) by zero valent iron (ZVI) and the effect of transformation on the formation of I-DBPs during chloramination. It was found that the presence of ZVI could deiodinate IPM into I^- and the transformation of IPM exhibited a pseudo-first-order kinetics. Acidic circumstance, SO₄^2-, Cl^- and monochloramine could promote the transformation of IPM by ZVI, while SiO₃^2- inhibited the transformation of IPM. Moreover, the transformation of IPM by ZVI changed both the formed species and amounts of I-DBPs during chloramination. During the chloramination of IPM-containing water, CHCl₂I and iodoacetic acid were the predominant iodinated trihalomethanes (I-THMs) and iodinated haloacetic acids (I-HAAs), respectively in the absence of ZVI, while CHI₃ and triiodoacetic acid became the predominant ones with 1.0 g L^-1 ZVI. The addition of 5.0 g L^-1 ZVI increased I-DBPs formation amounts by 6.0 folds after 72 h and maximum formation of I-DBPs occurred at pH 5.0. Enhanced I-DBPs formation was also observed with various real water sources. Given that ZVI ubiquitously exists in the unlined cast iron distribution pipes, the deiodination of IPM by ZVI during distribution may increase the formation of I-DBPs, which needs receive enough attention.