Zero-valent Iron Surface Research Articles

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

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.

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.

The sequestration of Cr(VI) by zero valent iron under a non-uniform magnetic field: An interfacial dynamic reaction

A non-uniform magnetic field was applied to sequester Cr(VI) with microscale zero-valent iron (ZVI). When the non-uniform magnetic field was applied, the average removal rate of Cr(VI) was increased and the lag phase was shortened with the increasing of magnetic field intensity. The instantaneous rate was fast at the beginning and about 40% of the Cr(VI) was sequestered rapidly when ZVI was added into the magnetic field system. Later, the sequestration rate of Cr(VI) was reduced and remained stable with time until Cr(VI) was removed completely. The instantaneous removal rate was positively correlated with ZVI dosage and the rate per unit mass of ZVI was 0.455 mg/(L·min·gZVI). The constant rate stage was not affected by the initial and the residual concentration of Cr(VI). In the case where no magnetic field was applied, the removal of Cr(VI) is a process in which ZVI is depassivated and its reactivity is restored continuously. The promotion of a magnetic field on the removal of Cr(VI) is mainly due to increasing the role of adsorbed reducing species of Fe2+ or Fe0 on the ZVI surface. Aging of ZVI under a magnetic field could enhance the release rate of Fe2+ in the initial 5 min though the remanence of this kind of ZVI had little effect on the enhancement of the sequestration of Cr(VI).

Effects of Persulfate Activation with Pyrite and Zero-Valent Iron for Phthalate Acid Ester Degradation

Phthalic acid esters (PAEs) are often detected in remediated groundwater using appropriate oxidant materials by in situ groundwater treatment. The study compares zero-valent iron–persulfate with a pyrite–persulfate system to degrade three PAEs—di(2-ethylhexyl) phthalate (DEHP), dibutyl phthalate (DBP), and dimethyl phthalate (DMP). Column experiments were conducted, and rapid oxidation occurred in a pyrite–persulfate system due to sulfate radical generation. DMP concentration was found at about 60.0% and 53.0% with zero-valent iron (ZVI) and pyrite activation of persulfate, respectively. DBP concentration was measured as 25.0–17.2% and 23.2–16.0% using ZVI–persulfate and pyrite–persulfate systems, respectively. However, DEHP was not detected. The total organic carbon concentration lagged behind the Ʃ3 PAEs. Persulfate consumption with ZVI activation was half of the consumption with pyrite activation. Both systems showed a steady release of iron ions. Overall, the oxidation–reduction potential was higher with pyrite activation. The surface morphologies of ZVI and pyrite were investigated using scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and XPS. Intensive corrosion occurs on the pyrite surface, whereas the ZVI surface is covered by a netting of iron oxides. The pyrite surface showed more oxidation and less passivation in comparison with ZVI, which results in more availability of Fe 2 + for persulfate activation. The pyrite–persulfate system is relatively preferred for rapid PAE degradation for contamination.

Ferrous ion mitigates the negative effects of humic acid on removal of 4-nitrophenol by zerovalent iron

In this study, Fe2+ addition was employed to overcome the negative effects of humic acid (HA) on contaminant removal by zerovalent iron (ZVI), and its feasibility to improve electron efficiency of ZVI was also tested. HA at high concentrations suppressed the removal of 4-nitrophenol (4-NP) by ZVI, while the addition of 0.25–1.0 mM Fe2+ could greatly mitigate this inhibitory effect and enhance 4-NP reduction. Specifically, with a mixed-order model, global fitting results showed that the addition of Fe2+ increased the rate constant from 0.124 × 10−2–0.219 × 10−2 mM/min to 0.227 × 10−2–0.417 × 10−2 mM/min and shortened lag period from 19.7–47.9 min to 8.0–15.2 min for 4-NP removal. The mechanistic investigation revealed this trend could be explained by the following aspects: i) Fe2+ can facilitate the generation of Fe(II)-containing oxides, which can act as an electron mediator or direct electron donor for 4-NP reduction; ii) the presence of Fe2+ could lead to aggregation of HA particles and accordingly reduced its coverage on ZVI surface. But the results of respike experiments indicate that Fe2+ addition did not show remarkable effect on the electron efficiency of 4-NP by ZVI, which should be associated with that Fe2+ was not able to favor the enrichment of 4-NP on ZVI surface.

Cr(VI) removal by micron-scale iron-carbon composite induced by ball milling: The role of activated carbon

The oxide film coated on the surface of zero-valent iron (ZVI) greatly limits the reducibility of ZVI. Application of iron-based materials especially microscale or nanoscale for water treatment can be more effective when modified with activated carbon (AC). In the study, the removal efficiency of Cr(VI) was significantly enhanced by mZVI/AC composite synthesized by ball milling (BM) under acidic and anaerobic conditions, and reached 94.01% within 120 min. And BM promoted effective contact or collision between mZVI and AC, which was a necessary condition for strengthening Cr(VI) removal by mZVI/AC. By detecting pH changes and the dissolution of total iron during batch experiments, it was shown that AC enhanced the corrosion of mZVI, accompanied by consumption of H+. Tafel scans further confirmed that the corrosion of mZVI was promoted when coupled with AC. Compared with mZVI, AC enhanced the adsorption-reduction ability, and also enhanced the homogeneous reduction reaction (the role of the secondary reducing agent Fe2+) in the process of Cr(VI) removal by mZVI/AC. Based on X-ray photoelectron spectroscopy (XPS), valence analysis of chromium and 1,10-phenanthroline shielding experiments, the Cr(VI) removal mechanism by mZVI/AC was also unraveled. Furthermore, the reusability of mZVI/AC was limited by the accumulation of (hydr)oxide on its surface and the loss of surface AC, but can be easily rejuvenated by BM again with a small amount of AC. In conclusion, mZVI/AC composite synthesized by BM are a promising green material to remove Cr(VI) from wastewater.

Improving sewage sludge dewaterability with rapid and cost-effective in-situ generation of Fe2+ combined with oxidants

Zero-valent iron (ZVI) combined with oxidants is a promising conditioning strategy for improving sewage sludge dewaterability. However, challenges, such as a low dewatering rate and utilization efficiencies of ZVI, restrict further application of ZVI/oxidant treatments. This study employs, for the first time, rapid and cost-effective in-situ generation of Fe2+ combined with common oxidants, namely H2O2, Na2S2O8, and KMnO4, to effectively improve sludge dewaterability. A comparative investigation of a standalone ZVI/oxidants treatment and when combined with a thermal and acid-wash (TA) pretreatment (TA/ZVI/oxidants) was systematically conducted to determine the sludge dewatering efficiency. Under the optimal operational conditions, the average water content of dewatered cake (Wc) was 18.47% less with the TA/ZVI/oxidants treatment when compared with the ZVI/oxidants treatment. The Wc values decreased to 54.81, 58.06, and 59.32 wt%, after the TA/ZVI/H2O2, TA/ZVI/Na2S2O8, and TA/ZVI/KMnO4 treatments, respectively. The potential mechanism by which the TA/ZVI/oxidants treatment enhanced dewatering was investigated by determining the characteristics of both the sludge and the ZVI surface structure. Results indicate that the TA/ZVI/oxidants process caused more Fe2+ dissolution, more strong oxidizing radicals and more strong flocculating Fe3+. The large amount of strong oxidizing radicals and strong flocculating Fe3+ caused cell lysis and disrupted the protein-like and polysaccharide-like materials in the EPS, thereby decreasing the particle size, negative zeta potential, viscosity and colloidal forces, which then released the bound water trapped within the net-like floc and led to improved sludge dewaterability. In the ZVI reuse experiment, the TA/ZVI/oxidants treatment remained highly effective for sludge dewatering even after four cycles. Furthermore, economic analysis indicates that the TA/ZVI/H2O2 treatment can save approximately 52.32% per year compared with using the traditional polyacrylamide (PAM) treatment.

Selenate removal by zero-valent iron under anoxic conditions: effects of nitrate and sulfate

Batch experiments were conducted to examine aqueous Se(VI) removal by zero-valent iron (ZVI) under anoxic conditions in the presence and absence of NO3− and SO42−. Initial concentrations for Se(VI), SO4, and NO3–N of 5 mg L−1, 1800 mg L−1, and 13 mg L−1, respectively, were employed to mimic mine waters. In the control experiment, 90% Se(VI) removal occurred within 1.5 h without SO42− and NO3− (B1). This removal threshold was reached after 3 h with NO3− added (B3) and after 33 h with SO42− added (B2). Removal reached 90% after 42 h with both SO42− and NO3− added (B4). Modeled Se(VI) removal rates consistently followed first-order kinetics and revealed that the presence of SO42− and, to a lesser extent, NO3− inhibited Se(VI) removal. Increases in pH and Fe coupled with decreasing Eh are consistent with ZVI corrosion under anoxic conditions. Transmission electron microscopy, Raman spectroscopy, and X-ray diffraction revealed magnetite [Fe3O4] and lepidocrocite [γ-FeOOH] formed at ZVI surfaces during the experiments. X-ray absorption near edge structure spectroscopy indicated that Se(VI) was predominantly reduced to Se(0) (70–80%), but Se(IV) (10–13%) and Se(-II) (2–13%) were also detected at reacted ZVI surfaces. Overall, the results show that although SO42− and NO3− present in mine wastes can reduce reaction rates, Se(VI) removal by ZVI under anoxic conditions is associated with extensive reduction to insoluble Se(0).

Effect of O2, Ni0 coatings, and iron oxide phases on pentachlorophenol dechlorination by zero-valent iron.

This study explores the zero-valent iron (ZVI) dechlorination of pentachlorophenol (PCP) and its dependence on the dissolved oxygen (O2), presence/formation of iron oxides, and presence of nickel metal on the ZVI surface. Compared to the anoxic system, PCP dechlorination was slower in the presence of O2, which is a potential competitive electron acceptor. Despite O2 presence, Ni0 deposited on the ZVI surfaces catalyzed the hydrogenation reactions and enhanced the PCP dechlorination by Ni-coated ZVI bimetal (Nic/Fe). The presence of O2 led to the formation of passivating oxides (maghemite, hematite, lepidocrocite, ferrihydrite) on the ZVI and Nic/Fe bimetallic surfaces. These passive oxides resulted in greater PCP incorporation (sorption, co-precipitation, and/or physical entrapment with the oxides) and decreased PCP dechlorination in the oxic systems compared to the anoxic systems. As received ZVI comprised of a wustite film, and in the presence of O2, only ≈ 17% PCP dechlorination observed after 25days of exposure with tetrachlorophenol being detected as the end product. Wustite remained as the predominant oxide on as received ZVI during the 25days of reaction with PCP under oxic and anoxic conditions. ZVI acid-pretreatment resulted in the replacement of wustite with magnetite and enhanced PCP degradation (e.g. ≈ 52% of the initial PCP dechlorinated after 25days under oxic condition) with accumulation of mixtures of tetra-, tri-, and dichlorophenols. When the acid-washed ZVI was rinsed in NiSO4/H2SO4 solution, Ni0 deposited on the ZVI surface and all the wustite were replaced with magnetite. After 25days of exposure to the Nic/Fe, ≈ 78% and 97% PCP dechlorination occurred under oxic and anoxic conditions, respectively, producing predominantly phenol. Wustite and magnetite are respectively electrically insulating and conducting oxides and influenced the dechlorination and H2 production. In conclusion, this study clearly demonstrates that the dissolved oxygen present in the aqueous solution decreases the PCP dechlorination and increases the PCP incorporation when using ZVI and Nic/Fe bimetallic systems. The findings provide novel insights towards deciphering and optimizing the performance of complex ZVI and bimetallic systems for PCP dechlorination in the presence of O2.

Liquid Nitrogen Activation of Zero-Valent Iron and Its Enhanced Cr(VI) Removal Performance.

In this study, we report that liquid nitrogen treatment is a promising zero-valent iron activation method that does not remove the iron oxide shell; this can improve the apparent Cr(VI) removal rate constant of zero-valent iron by about 4-120 times, depending on the particle sizes and the suppliers of zero-valent iron. It was found that liquid nitrogen, with its low temperature of 77 K, could crack the iron oxide shell of zero-valent iron to produce abundant fractures because of the different thermal expansion coefficients of iron oxide and iron. These fractures provided suitable mass transfer channels for the inward transfer of water/oxygen molecules to the iron core and the subsequent in situ generation of Fe(II) for the reduction of Cr(VI) to Cr(III). More importantly, systematic characterizations confirmed the generation of an Fe(III)/Cr(III)/Cr(VI) composite on the surface of zero-valent iron during the removal, suggesting its environmental benignancy. This study provides a novel physical zero-valent iron activation method, sheds light on the importance of the iron oxide shell of zero-valent iron on Cr(VI) removal, and clarifies the intrinsic Cr(VI) removal mechanism of zero-valent iron.

Formation of active zero-valent iron by simple co-grinding with CaCO3 to protect fresh active surface for efficient removal of hexavalent chromium

A novel composite material consisting of zero-valent iron (ZVI) and CaCO3 was successfully prepared through a simple grinding operation. The as-synthesized ZVI/CaCO3 composites were applied to the reduction precipitation of hexavalent chromium (Cr(VI)) and a tremendous improvement in reaction capacity was obtained compared with raw ZVI and ground ZVI sample without CaCO3 addition. Many factors of the grinding operation and ZVI/CaCO3 mass ratios were investigated to evaluate material properties and to study reaction mechanism. A high removal efficiency of 99.68% within just 30 min on Cr (VI) (10 mg/L) was obtained by the ZVI/CaCO3 composite with ZVI mass ratio at 30 wt%. X-ray diffraction (XRD), Fourier transformed infrared (FTIR), scanning electron microscope (SEM), energy dispersive spectrometer (EDS) and X-ray photoelectron spectroscopy (XPS) were used to investigate the chemical constitution and physicochemical properties of composites before and after the reaction. Addition of CaCO3 played very important role in both grinding iron particles into fine powders and protecting the fresh surface of active ZVI to enable the superior performance as zero-valent iron. Besides the environment-friendliness of the process itself without any pollutant emission, waste solid materials containing iron particles may serve as the starting sample to decrease the product cost.

Performance and mechanism of arsenic removal in waste acid by combination of CuSO4 and zero-valent iron

Zero-valent iron (ZVI) has been extensively used to remove different contaminants in wastewater including heavy metals and arsenic compounds. This study demonstrates that a continuously accelerated ZVI corrosion driven by depositing copper on the ZVI surface to form a Fe–Cu galvanic cell system, thereby increasing the ZVI corrosion rate and arsenic removal rate. Experimental studies showed that ZVI simply coupled with CuSO4 resulted in almost complete arsenic remove in waste acid within 30 min under the experimental conditions of an iron-to-arsenic molar ratio of 6, a CuSO4 concentration of 0.5 g/L, and a reaction temperature of 35 °C. Under the optimal conditions, the concentration of arsenic in waste acid decreased from 525 mg/L to 1.04 mg/L, and the arsenic removal rate reached 99.8%. Products such as magnetite and As2O3 were characterized by X-ray diffraction analyses, while As(III), Fe(III), Fe(II), and Cu0 were detected on the surface of these corrosion products through X-ray photoelectron spectroscopy. During ZVI surface corrosion accelerated by the Fe–Cu galvanic cell system, copper plays a continuous and stable activation (overcoming iron passivation) on the ZVI surface. A large amount of fresh and reactive magnetite and hydroxyl radicals was continuously generated, and arsenic was effectively removed through various mechanisms such as adsorption and precipitation. Thus, a simple combination of ZVI and CuSO4 could remove arsenic from waste acid quickly and efficiency.

Mechanisms of phosphate removal from aqueous solution by zero-valent iron: A novel kinetic model for electrostatic adsorption, surface complexation and precipitation of phosphate under oxic conditions

Mechanisms of phosphate removal from aqueous solution by zero-valent iron (ZVI) were examined. Solution pH largely affected phosphate removal efficiency. The phosphate removal decreased from 96.4 to 48.4% with increasing pH from 3 to 4.5 and subsequently increased with further increase in pH. The maximum removal efficiency of 97.3% was obtained at pH 7. When pH was higher than 7, the removal efficiency decreased with increasing pH. At pH 11 the phosphate removal was drastically reduced to 8.6%. To quantify effect of pH on mechanisms of phosphate removal by ZVI, i.e., contributions of adsorption on ZVI surface and precipitation in solution to phosphate removal, the fractions of removals by adsorption and precipitation were experimentally defined and a novel phenomenological kinetic model was developed. In the modelling, electrostatic adsorption, surface complexation and precipitation of phosphate were taken into account as predominant mechanisms of phosphate removal by ZVI. Their contributions linked with each other varied with solution pH. Since the increase in pH resulted in the decrease of ZVI dissolution causing the deceleration of elution of Fe ions from ZVI, the precipitation in solution was inhibited at higher pH. For pH < ∼9 (the isoelectric point of ZVI), with increasing pH the renewal of ZVI surface was suppressed and the active-sites for phosphate adsorption onto ZVI surface increased. As a result, the overall adsorption onto ZVI surface or the sum of electrostatic adsorption and surface complexation of phosphate on ZVI surface dominated phosphate removal. The proposed kinetic model could successfully predict the contributions of overall adsorption and precipitation to phosphate removal by ZVI in the range of pH from 3 to 11 with the average relative deviations of 7.3 and 15.1%, respectively.

Kinetics and mechanism of selenite reduction by zero valent iron under anaerobic condition activated and enhanced by dissolved Fe(II)

Batch test was conducted to investigate Se(IV) removal kinetics and mechanism by zero valent iron (ZVI) in presence of Fe(II) under anaerobic condition. Dissolved Fe(II) activated and enhanced Se(IV) reduction by ZVI, which also determined the removal efficiency, reduction rate, final corrosion products and their structures. Se(IV) was completely removed at initial Fe(II)/Se(IV) ≥ 1.0, and the specific rate constant significantly increased from 0.6 to 3.44 L h−1 m−2 with the augment of ratio from 1.0 to 1.4. At Fe(II)/Se(IV) < 1.0 (take 0.6 as an example), Raman, XPS, SEM-EDS and XRD results suggested that Se(IV) was reduced to amorphous Se(0) in forms of red suspended solids, amorphous FeSe and crystal maghemite (γ-Fe2O3) coated on ZVI surface. At Fe(II)/Se(IV) ≥ 1.0 (take 1.0 and 1.4 as examples), crystal FeSe and magnetite (Fe3O4) deposits formed on ZVI surface with a core-shell structure. Additionally, final pH increased due to Se(IV) reduction. This study suggested that traditional ZVI passivation problem could be overcome through the addition of excess dissolved Fe(II) under anaerobic condition, which also provided an alternative method to produce a reactive ammonia-free Fe3O4/ZVI/Fe(II) system.

Removal behavior of Cu(II) during Cr(VI) reduction by cast iron powder in absence and presence of ultrasound

ABSTRACTCu(II) is an important and typical heavy metal ion in the wastewater containing Cr(VI), and its removal during Cr(VI) reduction by zero valent iron (ZVI) may make it separately be recovered as a kind of copper resource. In this study, the removal behavior of Cu(II) during Cr(VI) reduction by cast iron powder in absence and presence of ultrasound was investigated by atomic absorption spectrometry (AAS), X-ray powder diffractometer (XRD), scanning electron microscope-energy dispersion spectrum (SEM-EDS) and X-ray photoelectron spectroscopy (XPS). The AAS tests indicated that the ultrasound could not only obviously enhance the removal of Cu(II) but also improve the reduction rate of Cr(VI). The XRD and SEM-EDS analyses showed that Cu(II) in the solution was reduced to metallic copper and then was deposited at the surface of ZVI. The ultrasound could remove the Fe-Cr oxides and hydroxides at the ZVI surfaces, resulting in the active surfaces of iron increased. The XPS analyses demonstrated that the surface of metallic copper would be transformed into the film of copper oxide (CuO) in the ultrasound system. The obtained metallic copper and copper oxide could be recovered alone by traditional method of the acid pickling.

Removal efficiency and mechanism of phycocyanin in water by zero-valent iron

The efficiencies and mechanism of phycocyanin removal from water by zero-valent iron (ZVI) were studied. The trend for dissolved organic nitrogen removal was similar to phycocyanin and the removal efficiency was high at ∼81% and 95%, respectively, in 90 min. The experimental results showed that the phycocyanin removal efficiency was higher at pH < 6, with an almost complete removal. However, only 68% was removed at pH 9. Within 30 min, the removal efficiency of phycocyanin for 1–4 tested cycles was reduced from 55.8% to 15.2%. Scanning electron microscopy and energy dispersive spectroscopy, Fourier transform infrared spectroscopy analysis and X-ray photoelectron spectroscopy were used to analyze the mechanisms of phycocyanin removal, which indicated that a small amount of phycocyanin was immobilized on the ZVI surface by adsorption. In addition, the main removal pathway was coagulation by dissolved iron ions. The Fe oxide formed in situ from ZVI had a higher removal efficiency than that in FeCl3, which can play improved roles in charge neutralization. The production of disinfection byproducts also decreased because of the decrease of precursors.

The roles of pyrite for enhancing reductive removal of nitrobenzene by zero-valent iron

Zero-valent iron (ZVI) is a popular reductant that has been successfully applied for remediation of groundwater contaminated with various pollutants, but it still suffers from surface passivation and pH increase in the reaction media. In this study, pyrite, a ubiquitous sulfide mineral in anaerobic environment, was adopted to enhance the reactivity of ZVI for removal of nitrobenzene. The synergetic effect between pyrite and ZVI was observed for nitrobenzene reduction, and the rate constant kobs at the initial pH (pH0) 6.0 was enhanced by 8.55–23.1 folds due to the presence of pyrite with pyrite/ZVI mass ratio ranging from 1.0 to 6.0. Moreover, nitrobenzene could be removed effectively at pH0 ranging from 5.0 to 10.0 in the presence of pyrite, while negligible removal of nitrobenzene by ZVI (0.5 g/L) alone was observed at pH0 ≥7.0. ZVI sample recovered from the reacted ZVI/pyrite mixture was also more effective for nitrobenzene degradation than pristine ZVI. The mechanism study revealed that pyrite could suppress the pH increase in reaction media, boost the production of reactive Fe2+, and activate the ZVI surface through replacing partially the passive oxide film with iron sulfide (FeS). In particular, the formation of highly reactive FeS@Fe in the reaction system of ZVI/pyrite mixture was proved by XRD, Mössbauer, XANES, XPS and SEM-EDS analyses, which provides a facile way for in-situ sulfidation of ZVI and for enhancing the removal of contaminants with ZVI technology.

Weak magnetic field accelerates chloroacetamide removal by zero-valent iron in drinking water

Chloroacetamides (CAMs) as a class of highly toxic nitrogenous disinfection by-products (N-DBPs) have been widely detected in drinking water. It has been reported that weak magnetic field (WMF) could improve the removal ability of zero-valent iron (ZVI) to some pollutants, but CAMs removal by ZVI coupled with WMF has never been studied. This study through oxic batch experiments was executed to investigate the effect of WMF on trichloroacetamide (TCAM) removal by different doses of ZVI under different pH levels and to explore how WMF works on TCAM removal for the first time. The results showed that the WMF improved TCAM removal by ZVI and the strengthening effect of WMF was more significant at lower ZVI dose or higher pH conditions. The formation of trichloroacetic acid indicated the occurrence of TCAM hydrolysis. Chlorine mass balance was observed in TCAM and its potential products, dichloroacetamide, monochloroacetamide, and chloride, indicating these were all the products and a dechlorination process occurred when TCAM contacted with ZVI. By calculating the yields of hydrolytic products and dechlorinated products, it was determined that dechlorination of TCAM was the dominant reaction for TCAM removal by ZVI with and without WMF, while hydrolysis reaction played a minor role. Mechanism analysis showed that the WMF promoted TCAM hydrolysis through impacting the electromigration within the oxide scale and improving the migration of paramagnetic oxygen to the surface of magnetized ZVI. Taken together, ZVI coupled with WMF is a potential effective technology for TCAM removal in effluent of chlorination.

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.

Effect of a weak magnetic field on triclosan removal using zero-valent iron under aerobic and anaerobic conditions

The aim of this study was to quantify the removal of halogenated pollutants (using triclosan as a model pollutant) from aqueous solution by zero-valent iron coupled with a weak magnetic field. We determined the removal efficiency of triclosan from a sodium sulfate solution at different pH values under both aerobic and anaerobic conditions. The removal of triclosan followed pseudo-first-order kinetics in both the presence and absence of a weak magnetic field. The calculated rate constants indicated higher removal efficiencies of triclosan under the aerobic condition compared to the anaerobic condition. In addition, increase of triclosan removal from acidic solutions was achieved with the assistance of weak magnetic field. X-ray diffraction and X-ray photoelectron spectroscopy analysis indicated that FeO(OH) and Fe3O4 were the main aerobic transformation products, suggesting that the zero-valent iron surfaces were completely oxidized. The aerobic and anaerobic transformation products of triclosan were analyzed by liquid chromatography tandem mass spectrometry. The results indicated that the application of a weak magnetic field could be an efficient and cheap treatment process to improve the removal of halogenated pollutants by zero-valent iron, which may be developed for future use.