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Effects of pH on dechlorination of trichloroethylene by zero-valent iron
Abstract
The surface normalized reaction rate constants (ksa) of trichloroethylene (TCE) and zero-valent iron (ZVI) were quantified in batch reactors at pH values between 1.7 and 10. The ksa of TCE linearly decreased from 0.044 to 0.009 l/h m2 between pH 3.8 and 8.0, whereas the ksa at pH 1.7 was more than an order higher than that at pH 3.8. The degradation of TCE was not observed at pH values of 9 and 10. The ksa of iron corrosion linearly decreased from 0.092 to 0.018 l/h m2 between pH 4.9 and 9.8, whereas it is significantly higher at pH 1.7 and 3.8. The ksa of TCE was 30–300 times higher than those reported in literature. The difference can be attributed to the pH effects and precipitation of iron hydroxide. The ksa of TCE degradation and iron corrosion at a head space of 6 and 10 ml were about twice of those at zero head space. The effect was attributed to the formation of hydrogen bubbles on ZVI, which hindered the transport the TCE between the solution and reaction sites on ZVI. The optimal TCE degradation rate was achieved at a pH of 4.9. This suggests that lowering solution pH might not expedite the degradation rate of TCE by ZVI as it also caused faster disappearance of ZVI, and hence decreased the ZVI surface concentration.
... From the view of chemical reactions, carboxylation of nZVI with carboxylic acids such as oxalic acid (OA), citric acid (CA) and formic acid (FA) can promote nZVI corrosion by providing H + and transform the nZVI surface properties by providing carboxyl functional groups. In the presence of pH buffering carboxylic acids (i.e., 30 mM FA), the TCE removal rate by nZVI increased 1.48-fold because the optimal TCE degradation pH of~4.9 was maintained; when the pH was lower than 4.9, the faster disappearance of nZVI decreased the TCE removal rate (Chen et al., 2001). OA and CA have a strong tendency to form complexes with ferrous ions or ferric ions and can degrade a limited set of organic pollutants, such as pentachlorophenol (Hou et al., 2009). ...
... It was interesting to note that S-nZVI displayed distinct properties from pure nZVI. The weak acid solution was beneficial for the remediation of TCE-or PCB-contaminated soil using nZVI, and TCE removal using nZVI was not observed at pH values of 9 and 10 (Chen et al., 2001). Nevertheless, the TCE removal rate constant using S-nZVI increased from 0.104 h −1 to 0.240 h −1 as the pH increased from 7 to 11 due to the deprotonation of FeS increasing the electron availability (Rajajayavel and Ghoshal, 2015). ...
... With increased pH, large amounts of H + were consumed, which hindered organic pollutants removal by nZVI. Chen et al. (2001) compared the removal of TCE by nZVI at pH values from 1.7 to 10. The optimal removal of TCE was achieved at pH 4.9, and TCE removal was not observed at pH values of 9 and 10. ...
In recent years, nanoscale zero-valent iron (nZVI) has been gradually applied in soil remediation due to its strong reducing ability and large specific surface area. Compared to conventional remediation solutions, in situ remediation using nZVI offers some unique advantages. In this review, respective merits and demerits of each approach to nZVI synthesis are summarized in detail, particularly the most commonly used aqueous-phase reduction method featuring surface modification. In order to overcome undesired oxidation and agglomeration of fresh nZVI due to its high reactivity, modifications of nZVI have been developed such as doping with transition metals, stabilization using macromolecules or surfactants, and sulfidation. Mechanisms underlying efficient removal of organic pollutants enabled by the modified nZVI lie in alleviative oxidation and agglomeration of nZVI and enhanced electron utilization efficiency. In addition to chemical modification, other assisting methods for further improving nZVI mobility and reactivity, such as electrokinetics and microbial technologies, are evaluated. The effects of different remediation technologies and soil physicochemical properties on remediation performance of nZVI are also summarized. Overall, this review offers an up-to-date comprehensive understanding of nZVI-driven soil remediation from scientific and practical perspectives.
... For the dehalogenation step, zero-valent iron (ZVI) sounds to be a promising environmental reactant with broad range of unique characteristics such as high reductive capacity, excellent catalytic functions, environmental friendliness, ubiquity, low cost and production of non-toxic by-products after the treatment process [16][17][18][19]. There are many studies carried out on reductive dehalogenation of a single CAHs using ZVI [5,11,20,21]. ZVI is supposed to reduce PCE and its chlorinated degradation products through two main interconnected degradation pathways: hydrogenolysis (replacement of a halogen by a hydrogen) and reductive elimination (in which two halide ions are released) [22,23]. Indeed, complete degradation of the CAHs and their degradation products are of supreme importance regarding much higher toxicity and health hazards of some transformation products like VC in comparison with the mother compound [7,24]. ...
... In this condition, 0.08 mg/L PCE was detected in the effluent. It is hypothesized that the main redox reactions happen on ZVI surface consuming H + based on Eq. (8) leading to increase of solution pH [21,40]. Hence, solution pH increased from 5 to 7.29 as flow passed through the permeable ZVI column up to 26 cm height. ...
... H + in excessive concentrations leads to quick loss of ZVI particles as RRM through Fe dissolution and generation of hydrogen bubbles attaching on the surface of the media affecting the hydraulic behavior of the influent entering the column [16]. Clearly, this phenomenon inhibits the redox reactions resulting in lower dechlorination efficiency [21,41]. Chen et al. [21] reported excessive amounts of H + as one of the major suppressive reasons in reductive dechlorination as it decreases the available reactive surface area. ...
Chlorinated aliphatic hydrocarbons (CAHs) are amongst concerning contaminants with high detection in aquifers and soils. This work is focused on removal of tetrachloroethylene and its degradation products through a two-step process including a permeable ZVI column followed by UV/Fe/PDS process. The permeable ZVI column experiments were designed using response surface method with central composite design. Optimum condition of the permeable ZVI column was initial solution pH = 5, 2 mL/min flow and 26 cm column height which brought about 96% dechlorination efficiency. Total iron leach in the column effluent was 0.34 mg/L. The concentrations of CAHs in permeable ZVI column’s effluent were as follows: PCE ≤ 0.08 mg/L, TCE = 0.23 mg/L, cis-1,2-DCE = 0.36 mg/L, VC = 0.34 mg/L. Thus, further treatment step was required to comply with the corresponded standards. Regarding iron leach, a PDS-based advanced oxidation process was applied on the ZVI column’s effluent with focus on cumulative removal of CAHs. Complete removal of CAHs and 79.2% TOC removal were obtained at pH = 6 using 0.75 mM PDS, 6 W UV at 15 min reaction time. In UV/Fe/PDS process, synergy effect of 67% was observed.
... Iron nanoparticles with the surface of 500-2000 m 2 /g represent reducing agents for heavy metal ions and easily participate in redox reactions. For example, reduction of Cr 2 O 7-2 or CrO 4-2 is implemented by the following scheme [1][2][3][4][5][6][7][8]: ...
... pentacarbonyl: Impregnation of supports with iron was carried out at low temperature (150-200°C) by passing a vapor of Fe(CO) 5 . 5ml of Fe(CO) 5 was placed in the gas bubbler and heated to 50-55°C in the area of argon. ...
... pentacarbonyl: Impregnation of supports with iron was carried out at low temperature (150-200°C) by passing a vapor of Fe(CO) 5 . 5ml of Fe(CO) 5 was placed in the gas bubbler and heated to 50-55°C in the area of argon. Carbonyl vapor flows through a quartz pipe where samples of supports are placed. ...
... Iron nanoparticles with the surface of 500-2000 m 2 /g represent reducing agents for heavy metal ions and easily participate in redox reactions. For example, reduction of Cr 2 O 7-2 or CrO 4-2 is implemented by the following scheme [1][2][3][4][5][6][7][8]: ...
... pentacarbonyl: Impregnation of supports with iron was carried out at low temperature (150-200°C) by passing a vapor of Fe(CO) 5 . 5ml of Fe(CO) 5 was placed in the gas bubbler and heated to 50-55°C in the area of argon. ...
... pentacarbonyl: Impregnation of supports with iron was carried out at low temperature (150-200°C) by passing a vapor of Fe(CO) 5 . 5ml of Fe(CO) 5 was placed in the gas bubbler and heated to 50-55°C in the area of argon. Carbonyl vapor flows through a quartz pipe where samples of supports are placed. ...
oiron-containing adsorbents have been widely used for cleaning of waters contaminated with organic and inorganic pollutants. Nanoiron can be spread over an organic and inorganic liner. Using renewable bioresources (timber, agricultural wastes, waste of biotechnological processes, etc.) to obtain sorbents containing nanoiron and iron oxide is quite promising. Iron-containing sorbents were obtained using Alnus incana wood. To avoid the emission of organic components from the wood into water, their partial pyrolysis was carried out with the formation of 1-3 mm coal layer. 13-17% of iron was impregnated in pyrolyzed and non-pyrolyzed samples. Impregnation was performed by 0.2 M FeCL36H2O and 0.2 M Fe(NO)39H2O solutions. Reduction of impregnated in the wood Fe+3 ions to nanoiron was carried out by NaBH4 in an inert atmosphere. By this method, polyfunctional sorbents like Fe/wood and Fe0/C/wood were obtained. Fe3O4/C/Wood type sorbents were obtained by pyrolysis of Fe(NO3)3-wood complexes. The nanoiron was spread on wood linen by passing steam of iron (0) pentacarbonyl at 150–200°. Wood-Fe(CO)5 system fibers composed from spatial grains are formed in an autoclave during heating. Magnetite partially impregnated into 74the wood. The obtained sorbents easily cause degradation of halogenated organic pollutants (1,4-dichlorbenzol and 4-bromanaline) and completely remove Cu+2 ion from model solutions.
... Iron nanoparticles with the surface of 500-2000 m 2 /g represent reducing agents for heavy metal ions and easily participate in redox reactions. For example, reduction of Cr 2 O 7-2 or CrO 4-2 is implemented by the following scheme [1][2][3][4][5][6][7][8]: ...
... pentacarbonyl: Impregnation of supports with iron was carried out at low temperature (150-200°C) by passing a vapor of Fe(CO) 5 . 5ml of Fe(CO) 5 was placed in the gas bubbler and heated to 50-55°C in the area of argon. ...
... pentacarbonyl: Impregnation of supports with iron was carried out at low temperature (150-200°C) by passing a vapor of Fe(CO) 5 . 5ml of Fe(CO) 5 was placed in the gas bubbler and heated to 50-55°C in the area of argon. Carbonyl vapor flows through a quartz pipe where samples of supports are placed. ...
... Iron nanoparticles with the surface of 500-2000 m 2 /g represent reducing agents for heavy metal ions and easily participate in redox reactions. For example, reduction of Cr 2 O 7-2 or CrO 4-2 is implemented by the following scheme [1][2][3][4][5][6][7][8]: ...
... pentacarbonyl: Impregnation of supports with iron was carried out at low temperature (150-200°C) by passing a vapor of Fe(CO) 5 . 5ml of Fe(CO) 5 was placed in the gas bubbler and heated to 50-55°C in the area of argon. ...
... pentacarbonyl: Impregnation of supports with iron was carried out at low temperature (150-200°C) by passing a vapor of Fe(CO) 5 . 5ml of Fe(CO) 5 was placed in the gas bubbler and heated to 50-55°C in the area of argon. Carbonyl vapor flows through a quartz pipe where samples of supports are placed. ...
Nanoiron-containing adsorbents have been widely used for cleaning of waters contaminated with organic and inorganic pollutants. Nanoiron can be spread over an organic and inorganic liner. Using renewable bioresources (timber, agricultural wastes, waste of biotechnological processes, etc.) to obtain sorbents containing nanoiron and iron oxide is quite promising. Iron-containing sorbents were obtained using Alnus incana wood. To avoid the emission of organic components from the wood into water, their partial pyrolysis was carried out with the formation of 1-3 mm coal layer. 13-17% of iron was impregnated in pyrolyzed and non-pyrolyzed samples. Impregnation was performed by 0.2 M FeCL 3 •6H 2 O and 0.2 M Fe(NO) 3 •9H 2 O solutions. Reduction of impregnated in the wood Fe +3 ions to nanoiron was carried out by NaBH 4 in an inert atmosphere. By this method, polyfunctional sorbents like Fe/wood and Fe 0 /C/wood were obtained. Fe 3 O 4 /C/Wood type sorbents were obtained by pyrolysis of Fe(NO 3) 3-wood complexes. The nanoiron was spread on wood linen by passing steam of iron (0) pentacarbonyl at 150-200°. Wood-Fe(CO) 5 system fibers composed from spatial grains are formed in an autoclave during heating. Magnetite partially impregnated into
... The successfulness of in situ particle-based remediation often depends on the longevity of the reactant, which generally is first assessed in controlled laboratory environments that mimic subsurface conditions. For nZVI, multiple studies have determined changes in TCE reactivity as a function of aging time (e.g., Lowry, 2006, Farrell et al., 2000) and/or varying groundwater chemistries (e.g., Liu et al., 2007, Parbs et al., 2007, Chen et al., 2001, Reinsch et al., 2010, Liu et al., 2013. Similar investigations with S-nZVI are, however limited, in particular for S-nZVI produced via two-step synthesis. ...
... As such, attractive electrostatic interactions may have led to a close association between white rust and S-nZVI particles, also indicated by SEM images (Fig. S5). In turn, this could have lowered accessibility for TCE to FeS m surface sites (argued to be the active sites for TCE reduction) Hayes, 1998, 2001), and hence lowered TCE reduction rates (Kim et al., 2011;Rajajayavel and Ghoshal, 2015;Chen et al., 2001;Butler and Hayes, 2001). ...
Sulfidized nanoscale zerovalent iron (S-nZVI) is an Fe-based reactant widely studied for its potential use for groundwater remediation. S-nZVI reactivity has been widely investigated testing various contaminants in various water matrices, but studies on S-nZVI corrosion behaviour and reactivity upon exposure to complex groundwater chemistries are limited. Here, we show that anoxic aging of S-nZVI for 7 days in the absence and presence of key groundwater solutes (i.e., Cl-, SO42-, Mg2+, Ca2+, HCO3-, CO32-, NO3-, or HPO42-) impacts Fe0 corrosion extent, corrosion product and reduction rates with trichloroethene (TCE). White rust was the dominant corrosion product in ultrapure water and in SO42-, Cl-, Mg2+ or Ca2+ solutions; green rust and/or chukanovite formed in HCO3- and CO32- solutions; magnetite, formed in NO3- solutions and vivianite in HPO42- solutions. The aged S-nZVI materials expectedly showed lower reactivities with TCE compared to unaged S-nZVI, with reaction rates mainly controlled by ion concentration, Fe0 corrosion extent, type(s) of corrosion product, and solution pH. Comparison of these results to observations in two types of groundwaters, one from a carbonate-rich aquifer and one from a marine intruded aquifer, showed that S-nZVI corrosion products are likely controlled by the dominant GW solutes, while reactivity with TCE is generally lower than expected, due to the multitude of ion effects. Overall, these results highlight that S-nZVI corrosion behaviour in GW can be manifold, with varied impact on its reactivity. Thus, testing of S-nZVI stability and reactivity under expected field conditions is key to understand its longevity in remediation applications.
... In this study, it was also observed that with the extension of the reaction time from 2 to 4 hours, the rate constant at pH 10 becomes higher than at pH 4. This result is surprising because it is well known that ferrous and hydroxylic ions readily form ferrous hydroxide and precipitate at an alkaline pH. Consequently, the precipitation of ferrous hydroxide on the surface of zero valence iron could theoretically hinder the transport of chlorinated molecules and decrease the rate of reaction ( Chen et al., 2001). However, in this study by Tian et al. (2009), a faster degradation rate of DDT at pH 10 than at pH 4 was obtained with a reaction time of 4 hours. ...
... Chen et al. (2001)studied the effects of pH on the dechlorination of trichloroethylene by zerovalent iron and showed that dechlorination reactions are typically initiated by the ionization of zerovalent metals as shown in the reactions depicted in Eqs. (12.9)À(12.12). ...
... pH'ın alkali pH değerlerine arttırılması ile sıfır değerlikli demir ile renk giderim veriminde azalmanın meydana geldiği Chen vd. tarafından yapılan çalışmada belirtilmiştir [60]. Demirin yüzey üzerinde bir oksihidroksit tabakası oluşturmak üzere sulu ortamda su ile reaksiyona girdiği bilinmektedir [6]. ...
Bu çalışma, sulardan C.I. Vat Green 1 boyar maddesinin adsorpsiyonu için mikro ölçekli sıfır değerlikli demirin (mZVI) uygulanabilirliğini göstermektedir. mZVI partikülleri SEM, EDX, BET yüzey alanı analizi ve pHzpc ile karakterize edilmiştir. Analizlerden kullanılan mZVI partiküllerinin yüzey özelliklerinde meydana gelen değişimler ise SEM ve EDX ile belirlenmiştir. 5.2 m2/g BET yüzey alanı ile yaklaşık 5 m’den küçük olan küresel partiküller, yüksek giderim verimini desteklemiştir. Analiz sonrasında partikül boyut ve şekilleri ile elementel bileşimde meydana gelen değişiklikler yüksek adsorpsiyon verimini doğruladığı gibi 5.73 olan pHzpc değeri de düşük pH’larda yüksek giderim veriminin gözlenmesini sağlamıştır. C.I. Vat Green 1’in giderim verimi ile adsorpsiyon kinetik ve izotermlerini değerlendirebilmek için çözelti pH’sı, demir dozajı, reaksiyon sıcaklığı, kirletici konsantrasyonu gibi parametreler kesikli deney serileri ile incelenmiştir. 3’ten büyük pH değerlerinde, 1 g/L’den büyük mZVI dozajlarında ve kirletici derişiminin arttığı durumlarda giderim verimi azalırken 1 g/L’ye kadar olan dozajlarda ve sıcaklık artışı ile verim artmıştır. Optimum pH, 3 ve optimum mZVI dozajı 1 g/L olarak belirlenmiştir. TOK sonuçları da giderim mekanizmasının adsorpsiyon olduğunu doğrulamıştır. Kinetik verilerin en iyi olarak pseudo ikinci dereceden modele uyduğu bulunmuştur. Adsorpsiyon denge verileri Langmuir modeli ile temsil edilmiş ve maksimum adsorpsiyon kapasitesi 36.50 mg/g olarak bulunmuştur.
... The reduction of contaminants by ZVI is also highly pH dependent and decreases as pH increases, indicating that alkaline conditions are less favorable for contaminant reduction (Bae and Hanna, 2015;Yin et al., 2012). This is explained by the precipitation of Fe(III) corrosion products on ZVI surfaces inhibiting electron transfer from the Fe 0 core (Bae and Hanna, 2015;Chen et al., 2001;Dong et al., 2010). Under ambient conditions, iron oxidation proceeds as follows: ...
Radioactive technetium-99 (Tc) present in waste streams and subsurface plumes at legacy nuclear reprocessing sites worldwide poses potential risks to human health and environment. This research comparatively evaluated efficiency of zero-valent iron (ZVI) toward reductive removal of Tc(VII) in presence of Cr(VI) from NaCl and Na2SO4 electrolyte solutions under ambient atmospheric conditions. In both electrolytes, anticorrosive Cr(VI) suppressed oxidation of ZVI at elevated concentrations resulting in the delay of initiation of Tc(VII) reduction to Tc(IV). In the absence of Cr(VI), no delay was observed in the analogous systems. At low ionic strength (IS), retarded ZVI oxidation inhibited Tc(VII) reduction. Higher IS favored reduction of both Tc(VII) and Cr(VI), which followed second-order reaction rates in both electrolytes attributed to the more efficient iron oxidation as evident from solids characterization studies. Magnetite was the primary iron oxide phase, and its higher fraction in the SO4²⁻ solutions facilitated reductive removal of Tc(VII) and Cr(VI). In the Cl⁻ matrix, Cr(VI) promoted further oxidation of magnetite as well as formation of chromite diminishing overall reductive capacity of this system and resulting in less effective removal of Tc(VII) compared to the SO4²⁻ solutions.
... Similarly, the results of a study on the effects of pH in the range of 1.7 to 10 on dechlorination of trichloroethylene (TCE) by ZVI declared that pH 4.9 had the most efficiency. No removal was observed at pH 9 and 10 and with increasing pH, the removal efficiency had dramatic reduction (37). This result is consistent with those reported by other studies (3,19,38). ...
Background: Recalcitrant organics remediation from water resources continues to be a significant
environmental problem and there is a continued effort to demonstrate practicable and economical
treatment options for pollution removal.
Methods: In this study, the efficiency of the permeable reactive barrier (PRB) in a column reactor using
zero-valent iron (ZVI) particles and sand mixture in the removal of methyl tert-butyl ether (MTBE)
from aquatic phases was investigated. The system performance was MTBE removal while initial pH,
reaction time, pollutant content, catalyst load, hydraulic loading rate (HLR), and the reaction rate
constant were independent variables.
Results: The results showed that the process efficiency decreased by increasing pH, HLR, and pollutant
concentration. In this case, the optimal conditions were obtained at pH = 7, HLR = 0.23 m3/m2·d,
and C0 = 1 mg/L, which achieved a remarkable removal efficiency up to 90.32%. The high nitrate
concentrations and hardness as intervening factors reduced process efficiency to less than 44.61 and
51.4%, respectively. The lack of interfering factors had a considerable effect on the reaction rate of
MTBE reduction, which is approximately 2.65 and 4.11 times higher than that in the presence of
calcium hardness and nitrate, respectively.
Conclusion: The PRB technology can be suggested as a reliable and robust system to remediate
groundwater containing hydrocarbons based on filling media and hydraulic conditions.
... The reduction of contaminants by ZVI is also highly pH dependent and decreases as pH increases, indicating that alkaline conditions are less favorable for contaminant reduction (Bae and Hanna, 2015;Yin et al., 2012). This is explained by the precipitation of Fe(III) corrosion products on ZVI surfaces inhibiting electron transfer from the Fe 0 core (Bae and Hanna, 2015;Chen et al., 2001;Dong et al., 2010). Under ambient conditions, iron oxidation proceeds as follows: ...
... Similarly, the results of a study on the effects of pH in the range of 1.7 to 10 on dechlorination of TCE by ZVI declared that pH 4.9 had the most e ciency. No observed any removal at pH 9 and 10 and with increasing pH, the removal e ciency had dramatic reduction (Chen et al. 2001). This result is in agreement with those reported by other works (Noubactep 2008, Levchuk et al. 2014). ...
In this study, the efficiency of the permeable reactive barrier (PRB) in a column reactor using zero-valent iron (ZVI) particles and sand mixture in the removal of methyl tert-butyl ether (MTBE) from aquatic phases was investigated. The main operating parameters influence reactor performance such as pH, reaction time, pollutant content, catalyst load, hydraulic loading rate, and the reaction rate constant was evaluated. The results showed that the efficiency of process decreased with increasing pH, inflow, and pollutant concentration. In this case, the optimal conditions were obtained at pH=7, flow rate=0.23 m ³ /m ² .d and C 0 =1 mg/L, which achieved a remarkable removal efficiency up to 90.32%. The being of high nitrate and hardness concentrations as intervening factors were led to reduce process efficiency to less than 44.61% and 51.4%, respectively. Lack of interfering factors had a considerable effect on the reaction rate of MTBE reduction that is approximately 2.65 and 4.11 times higher than in the presence of calcium hardness and nitrate, respectively. The PRB can be operated to remediate groundwater containing hydrocarbons based on filling media and hydraulic conditions.
... It was noted that the pH of the medium in the P reactor increased markedly to a final pH around 9.6 ( Table 1). The data suggested that the factor limiting the contribution of ZVI to the methane yield might be the excessively produced hydroxide ions via the oxidation reaction of ZVI [29]: ...
The aim of this study was to evaluate the addition of zero valent iron (ZVI) in scrap form to an anaerobic digestion reactor in order to enhance methane production from high-strength, sulfate-rich wastewater. The wastewater contained 6,000 mg/L COD and 3,000 mg/L sulfate. From an initial set of batch tests, the addition of either ZVI powder or ZVI scrap to the medium resulted in comparable methane yields of around 0.13 L CH4/g COD added. In a fed-batch operation treating the sulfate-rich wastewater for 60 days, the reactor with added ZVI scrap was found to have higher media pH (6.3-8.1), increased sulfate reduction efficiency (65-85%) and higher concentrations of dissociated sulfide (106-1,020 mg S/L) than a fed-batch operation without added ZVI scrap. The reactor with added ZVI had a maximum methane yield of 0.25 L CH4/g COD added⋅day and a maximum methane composition in the biogas of 53%. In contrast, the control reactor without added ZVI gave a methane yield of 0.07 L CH4/g COD added⋅day and a methane composition in the biogas of 27%. The control reactor also had higher concentrations of undissociated sulfide (153-612 mg S/L) and relatively high volatile fatty acids (VFA) to alkalinity ratios (0.4-0.7 g CH3COOH/g CaCO3). The experimental results suggested that ZVI provided favorable pH values for methanogenesis, reduced the toxicity of sulfides and thus enhanced the competitiveness of methanogens with sulfate-reducing bacteria (SRB). Moreover, the larger negative oxygen reduction potential (ORP) values in the reactor with added ZVI scrap indicated that the ZVI might enhance electron transfer activities of microbes in the reactor.
... [18] These newly formed Fe oxyhydroxides showed no obvious inhibitory effect nor barriers for the electron flow from the inner Fe 0 and even many of these can take part in the dechlorination directly by utilizing active adsorbed Fe 2+ . [25][26][27][28] In addition, because of the attraction for magnetic substances in the system, Fe 3 O 4 could make the oxide shell thinner and therefore provided a better contact between active sites on the surface of nZVI and the target contaminants. [29] In comparison with the single nZVI system, when CT was treated with Fe 0 @Fe 3 O 4 , magnetite also formed under anaerobic conditions, as generated by equation (5). ...
Nano‐scale zero‐valent iron (nZVI) attached to Fe3O4 nanoparticles (Fe0@Fe3O4), which has better dispersibility and a larger specific surface area than the nanoparticles alone, were prepared and applied to the reductive dechlorination of carbon tetrachloride (CT). CT removal efficiencies by Fe0@Fe3O4 composites with different ratios of the two components were compared. Under optimum conditions, when the Fe0/Fe3O4 ratio was 1:2, almost no CT was detected after 50 min and it took only about 30 min to reach a removal efficiency of 90%, compared with 120 min for an Fe0/Fe3O4 ratio of 1:4. An increase in the amount of nZVI in the catalyst effectively improved the removal of CT and accelerated the reaction rate. Chloroform was the main product. Compared with Fe3O4 alone, a significant increase in the solution concentrations of ferrous and ferric ions occurred in the Fe0@Fe3O4 system: both Fe2+ and Fe3+ reached their maximum concentrations at 60 min and then tended to decline over the next 60 min. The increase in Fe2+ concentration was attributed to the reaction between nZVI and CT, which produces ferrous ions when electrons transfer from Fe0 to organic chlorides. Synergistic effects between the composite constituents promoted the relative rates of mass transfer to reactive sites and Fe2+ generated in solution facilitated the reduction of chlorinated organic pollutants by magnetite. Thus, Fe0@Fe3O4 nanoparticles effectively achieved reductive dechlorination of CT and provide an improved nZVI catalyst for the remediation of chlorinated organic compounds. Products during the dechlorination of CT by Fe0@Fe3O4 particles were analyzed. Removal ability for CT between catalysts with different Fe0/Fe3O4 ration was compared. Samples before and after reaction were characterized, change of Fe2+/Fe3+ was studied. Degradtion Pathway of Fe0@Fe3O4 composite was proposed.
... pH is a very important variable which affects the %DC and % DCOD in the SZVI/H 2 O 2 oxidation process. Chen et al. (2001) reported that the zero valent iron decolorization rate decreases when the pH is alkaline. At such pH, Fe 2þ ions and hydroxyl ions may precipitate as ferrous hydroxide on the surface of SZVI occupying the reactive sites and interfering with the reaction. ...
A Fenton like advanced oxidation process (AOP) employing scrap zerovalent iron (SZVI) and hydrogen peroxide (H2O2) was studied for industrial textile wastewater treatment from a textile manufacturing plant located at Medellín, Colombia (South America). The wastewater effluent studied contains a mixture of organic compounds resistant to conventional treatments. The effect of initial pH and SZVI concentration and H2O2 concentration were studied by a response surface methodology (RSM) Box-Behnken design of experiment (BBD). The combined SZVI/H2O2 process led to reductions of 95% color, 76% of chemical oxygen demand (COD) and 71% of total organic carbon (TOC) at optimal operating conditions of pH = 3, SZVI = 2000 mg/L and [H2O2] = 24.5 mM. Molecular weight distribution measurement (MWD), ultraviolet-visible (UV-Vis) spectroscopy, HPLC, biodegradability and toxicity were used to characterize the pollutants after the treatment process finding that the resulting effluent was polluted mostly by low molecular weight carboxylic acids. A remarkable biodegradability enhancement of the effluent was evidenced by a BOD5/COD ratio increase from 0.22 to 0.4; also, the SZVI/H2O2 process successfully reduced the toxicity from 60% to 20% of dead A. Salina crustaceans.
... But in the case of the column without PHB was lower at 199 days and after this, the column completely lost its removal efficiency. The Fe-PHB column operated under acidic condition compared to Fe-column and it observed from earlier findings that reactivity of ZVI is strongly affected by pH and the degradation rate increases with increase in acidic condition (Chen et al., 2001). A microbial and mineral progress in a zero-valent iron based permeable reactive barrier operated for a long time was carried out by (Kumar et al., 2016). ...
It is an indisputable fact that any environmental clean-up technology generating certain kind of effective result would be easily supported. One of them includes Permeable reactive bio-barrier which is an innovative technology started from 90’s to treat a variety of contaminants along the natural gradient flow of groundwater through immobilization or transformation of pollutants into less toxic and harmful form. Despite of any broad acknowledgement, there are lesser known knowledge about use of microorganisms in permeable reactive barriers, mingling of microorganisms with other reactive media and their effect on each other’s reactivity. The current review deals with an overview of the types of reactive media used in Permeable Reactive Barriers (PRBs) as well as different bio-barriers (PRBBs) utilized for the treatment of various contaminants, long–term performance of permeable reactive barrier and combination of microorganism and reactive media to look forward for their symbiotic relationship in permeable reactive barrier for environmental remediation.
... However, lowering solution pH to high acidic condition (> 4) might diminish the performance of iron nanoparticles, as it could cause a fast loss of iron nanoparticles through iron dissolution, and/or lead to an excessive accumulation of hydrogen bubbles on the nanoparticle sur- face which may decrease the available reactive surface area for con- taminants removal. While at a high pH, the performance of n-ZVI re- duce due to additional mineral precipitation which inhibits mass transfer [58,59]. The FT-IR analysis of the spent nanoparticles at dif- ferent pH values (Fig. 4) reveals that the peak intensity of ?-Fe 2 O 3 at 570 cm ?1 increases with an increase in the pH value indicating in- creased oxide formation at higher pH. ...
Ferrous ions (Fe²⁺) can effectively promote the removal of pollutants by sulfidated zero-valent iron (S-ZVI), but the role of anions coexisting with Fe²⁺ was often ignored. This study systematically compared the performances of S-ZVI/FeCl2 and S-ZVI/FeSO4 systems for chloramphenicol (CAP) and nitrobenzene (NB) removal. The results showed that FeCl2 and sulfidation had a synergistic promoting effect on the reaction, but FeSO4 could not promote the removal of nitro compounds by S-ZVI. Liquid chromatography/mass spectrometry (LC/MS) and UV-vis analysis showed that only the nitro group was reduced during the removal of CAP and NB. The results of batch experiments showed that both NaCl and Na2SO4 could effectively promote the reaction, but the promotion effect of Na2SO4 weakened with the decrease of pH. X-ray photoelectron spectroscopy (XPS) analysis showed that Fe²⁺ could promote the adsorption of SO4²⁻ on the surface of S-ZVI. A possible mechanism was proposed: Fe²⁺ could maintain a low pH level because of hydrolysis, which promoted the adsorption of Cl⁻ and SO4²⁻ on the surface of S-ZVI. Cl⁻ promoted the reaction because of its pitting corrosion, while SO4²⁻ competed with nitro groups for the adsorption sites. Our findings suggest that the coexisting anions are quite essential in the removal of nitro compounds by S-ZVI/Fe²⁺ systems.
Surfactants and nanoparticles have been effectively used for environmental remediation for many years. Over the years, various methods have been developed to synthesize nanoparticles using different surfactants to obtain a s higher treatment efficiency for organic contaminated soil. Compared to conventional remediation methods, the in-situ remediation technique provides advantages, such as being more eco-friendly and cost-effective. This review provides an overview of the remediation of organic contaminated soil using surfactant-stabilized Fe-based nanoparticles, mostly surfactant-stabilized nanoscale zero-valent iron (nZVI). In addition, the use of other stabilizers and the mechanisms of stabilization are discussed. The combination of surfactants and Fe-based nanoparticles can be effectively used to remediate organic contaminants from soil, such as trichloroethylene (up to 99%), polychlorinated biphenyls (up to 80%), perchloroethylene (up to 93%). The treatment efficiency organic contaminants in soil by surfactant-stabilized nanoparticles is higher than only surfactant (less than 90%) or nanoparticles (less than 80%) due to the synergistic effects between surfactants and nanoparticles. This technique is generally more effective to use as a strong reductant, such as reductive dehalogenation or reductive immobilization of metals, while less cost-effective as an adsorbent. In addition, the remediation rate depends on various factors, such as pH, temperature, natural organic matter, ionic strength, type and concentration of stabilizers, site characteristics, contaminant features, nanoparticle and surfactant properties. However, short lifetimes or potential toxicity of nanoparticles are some limitations of this technique.
Reactive Zero Valent Iron (ZVI) nanoparticles have been widely explored for in situ ground water remediation to degrade both non-aqueous phase liquid (NAPL) and water-soluble contaminants. However, they usually suffer from rapid oxidation and severe agglomerations restricting their delivery at NAPL/water interface. Aim of this study was to encapsulate the ZVI nanoparticles (50 nm) in amphiphilic bicompartmental Janus particles (711±11 nm) fabricated by EHDC (electrohydrodynamic co-jetting). The dual compartments were composed of PLA (polylactic acid) and a blend of PLA, PE (poly (hexamethylene 2,3-O-isopropylidenetartarate) and PAG (photo acid generator). Upon UV irradiation, PAG releases acid to unmask hydroxyl groups present in PE to make only PE compartment hydrophilic. The entrapped ZVI nanoparticles (20 w/w%; ~99% encapsulation efficiency) were observed to degrade both hydrophilic (methyl orange dye) and hydrophobic (trichloro ethylene) contaminants. UV treated Janus particles provided stable dispersion (dispersed up to 3 weeks in water), prolonged reactivity (~24 days in contaminated water), and recyclability (recyclable up to 9 times) as compared to non-treated ones. In addition, the amphiphilic Janus particles demonstrated high transportability (>95%) through porous media (sand column) with very low attachment efficiency (0.07), making them a promising candidate to target contaminants at NAPL/water interface prevailed in groundwater.
To enhance the decontamination capacity of zero-valent iron and mitigate its susceptibility to oxidation and passivation, manganese (Mn) was introduced in the current study to prepare the iron‑manganese bimetallic material by one-step chemical reduction method to remove tetracycline (TC). A series of methods including Scanning Electron Microscope-Energy Dispersive Spectrometer (SEM-EDS), Transmission Electron Microscope (TEM), Vibrating Sample Magnetometer (VSM) and X-ray Photoelectron Spectroscopy (XPS) were applied to investigate the characteristics of the nanocomposite. Furthermore, batch experiments were conducted to explore the effects of key parameters such as dosage, pH, initial concentration and coexisting ions on the removing TC with Fe-Mn bimetal nanocomposite. At the same time, reaction mechanism and degradation pathways were examined. The results showed that the bimetallic particles were highly paramagnetic for recover and evenly distributed, consisting of zero-valent Fe and Mn as well as their respective oxides. The removal kinetics of TC showed a fast process and reached a removal capacity of 330.17 mg/g within a reaction time of 60 min under TC concentration of 100 mg/L, pH = 3 and dosage of 0.3 g/L. The coexistence of both cations and anions had significant effect on the TC removal in the experimental conditions. Finally, OH and O2⁻ played a major role in the redox reaction and the possible reaction mechanism and degradation pathways were demonstrated. To sum up, the Fe-Mn bimetal nanocomposite was proved to be promising and effective for treating TC-containing wastewater.
Sulfidated nanoscale zero-valent iron (S-nZVI) was applied in the treatment of pentachlorophenol (PCP)-polluted water to explore the reaction pathways and the effects of water chemistry on PCP adsorption and transformation.
The development of new effective Fenton-like catalysts is of interest for solving a wide range of problems related to toxic organic pollutants’ destruction in aqueous media. In this chapter, an attempt was made to obtain g-C3N4-MgFe2O4 composites of various structures and morphologies, as well as to justify their effectiveness as Fenton-like catalysts. The prepared composites were characterized by XRD, FTIR, and SEM-EDX methods. It was shown that all composites were characterized by the formation of g-C3N4 with the s-heptazine structure and a different ratio of g-C3N4 and MgFe2O4 on the surface. The catalytic properties of g-C3N4-MgFe2O4 composites in the degradation reaction of the thiazine dye Methylene Blue under various conditions (dark-, visible-, and UV-driven processes), as well as under multiply catalytic cycles, were studied. The most effective sample of composite I under UV irradiation provided 99% Methylene Blue degradation efficiency for 20 min at four cycles. The mechanism of catalytic destruction of Methylene Blue mainly due to the formation of hydroxyl radicals in the reaction mixture was proposed.KeywordsCarbon nitrideMagnesium ferriteNanostructured compositesHeterogeneous fenton catalystsAdvanced oxidation processesMethylene blue degradation
Textile industries are considered as one of the major contributors for water pollution. Textile wastewater primarily contains organic dye molecules along with heavy metal ions and some polymeric waste material which causes adverse effects on aquatic system and human health. Insufficient and incomplete treatment of textile wastewater is a major concern especially when it is discharged directly into the water bodies. Removal of dye molecules from wastewater has been addressed by several researchers using various physical, chemical, and biological processes. This chapter highlights applications and challenges with conventional and advanced treatment processes. Advanced oxidation process using various combinations of oxidants and energy sources has emerged as a significant technique. Applications of nanomaterials and polymers have also been explored significantly for the degradation of pollutants present in textile wastewater. Integration of suitable technologies is proposed to achieve complete degradation of pollutants discharged in textile wastewater.
Tetrabromobisphenol A (TBBPA), a widely used brominated flame retardants, has been detected in various environmental matrices and is known to cause various adverse effects on human bodies. This study examined the feasibility and effectiveness of remediating TBBPA using Cu/Fe bimetallic nanoparticles (Cu/Fe BNPs) at various environmental and operational conditions. In general, TBBPA removal rate and debromination efficiency increased with higher Cu doping, higher Cu/Fe BNPs loading, higher temperature, and lower pH. At optimal conditions, TBBPA was completed removed at a rate constant >0.2 min⁻¹ where over 90% TBBPA was transformed to BPA within 30 min. The activation energy was found to be 35.6 kJ/mol, indicating that TBBPA was predominantly removed via surface-controlled reactions. Under pH 3-7 and ≥ 25 oC, debromination was the dominant removal mechanism compared to adsorption. The complete debromination pathway and the time-evolution of intermediates byproducts at different pHs were also presented. Cu/Fe BNPs can be used more than 6 times. Genotoxic tests showed that the treated solution did not find a significant hazardous potential. The byproducts can be further degraded by additional H2O2 through Fenton reaction. These results demonstrated the efficacy of Cu/Fe BNPs for treating TBBPA and its potential for degrading other halogenated organic compounds.
This paper provides an experimental study on development of heat transfer and pressure drop of hybrid nanofluids flow in coil
heat exchanger of the solar collector in Iraq. The two methods were utilized in this article to enhance heat transfer and pressure drop.
Firstly, spirally coiled tube heat exchange was tested in evacuated tube solar collector then the pure water was replaced with
different concentration of hybrid nanoparticles fluids ranging from (1 – 5 vol %). The hybrid nanoparticles used in this study
(copper Cu (40nm) + silver Ag (40nm)) and (Aluminum Oxide Al2O3 (80nm)+ Zirconium oxide ZrO2 (80nm)) as well as the pure
water. The effects of various factors together with hybridnanofluid temperature, concentration, hybridnanoparticle type and flow
Reynolds number, on pressure drop and heat transfer coefficient of the flow, has been studied. The results show 50.76 % increment
in heat transfer coefficient Cu + Ag – Pw and 38.56 % for Al2O3+ ZrO2 – Pw at the concentration of 5 vol% compared with the pure
water. The pressure drop and coefficient of heat transfer are increased by using hybrid nanofluids (Cu+ Ag– Pw, Al2O3+ ZrO2 –
Pw) instead of the pure water. In addition to the results indicated that using the heat exchanger with helically coiled tube and shell,
the heat transfer performance is improved moreover the pressure drop enhancement because of the curvature of the coil tube. The
most increase of 38.42% (Cu + Ag – Pw) and 25.41% (Al2O3 + ZrO2 – Pw) in Nusselt number ratio for several of Reynolds
numbers of 200 – 800. This article decided that the hybrid nanofluid behaviors are near to common Newtonian fluids through the
relationship between shear rate and viscosity. Moreover to overall performance index are used to give the corresponding heat
transfer method and flow. The type and size hybridnanoparticles, as well as synergistic impact, play an important function within
the enhancement of heat transfer rate.
As a technology for in situ treatment and remediation of groundwater contamination, permeable reaction barriers (PRBs) have the advantages of operational efficiency and low infrastructure footprint. In order to clarify previous research results and provide references for future research on remediation of contamination by dissolved oil contaminants in groundwater, the focus of this article is to review and compare the application of PRBs for the removal of dissolved oil contaminants and highlights the research gaps. We concentrate on the relationship between structure design, media types and service life of PRBs, along with groundwater flow velocity, temperature, pH and other hydrochemical conditions. These influencing factors are used to make a detailed explanation and analysis of remediation of oil contamination in groundwater. The current application of PRBs is mainly limited to heavy metals and inorganics, rather than persistent organics such as components in oil. The application of new PRB materials and combination of multiple remediation technologies in oil-contaminated sites will be the focus of future research.
The Fe41Co7Cr15Mo14C15B6Y2 amorphous alloy powder was prepared by gas atomization. It was interesting that rhodamine B can be completely degraded within only 6 min by 1 g/L Fe41Co7Cr15Mo14C15B6Y2 and 3 mM H2O2 at pH 5.0 at 313 K. This result can be repeated at least 30 times. It is worth mentioning that the catalyst surface spontaneously formed a double passivation film during the degradation process. The passivation film composed of Cr2O3 and Cr(OH)3 is located in the outer layer, while the passivation film composed of MoO2 and MoO3 is located in the inner layer. This double passivation film regulates the contact of ions on the catalyst surface with the solution, which makes the catalyst have a stable catalytic efficiency in the reaction. The findings have important implications in developing Fe-based amorphous alloys for functional application materials in the field of wastewater treatment.
The existence of sulfonamides (SAs) in water bodies leads to a series of human health problems and environmental risks. Ultrasound (US) enhanced zero-valent iron catalyzed persulfate (ZVI/PS) process is a potential approach to eliminate SAs. However, high energy consumption and large ZVI usage limited its application. In this study, a novel two-stage US-ZVI/PS process was first proposed, which reduced 35% of ZVI usage and saved 74.2% energy consumption compared with traditional US-ZVI/PS process. The effect of introduction time and operation mode of US on sulfadiazine (SD, 20 mg L⁻¹) degradation was first investigated. The intermittent operation method of US (60s on/60s off) could help controlling the releasing of Fe²⁺ in a reasonable range (0.37-0.56 mg L⁻¹), which was the key reason for the high SD degradation efficiency. SO4• –, ·OH were confirmed as the key radicals for SD removal, and four degradation pathways were proposed. The initial pH of 5.0-7.0, the initial ZVI and PS doses of 0.6 mM and 1.4 mM were determined as the optimal conditions for high SD removal efficiency. Compared to other SD removal processes (traditional US/ZVI/PS, ozonation and UV-based process), two-stage US-ZVI/PS saved 68.3–98.5% energy consumption and enhanced 0.7–14.0 times degradation rate. Therefore, two-stage US-ZVI/PS system is promising and cost-effective for the removal of SD.
Chlorinated aliphatic hydrocarbons (CAHs) have been frequently detected in aquifers in recent years. Owing to the bioaccumulation and toxicity of CAHs, it is essential to explore high-efficiency technologies for their complete dechlorination in groundwater. At present, the most widely used abiotic and biotic remediation technologies are based on zero-valent iron (ZVI) and functional anaerobic bacteria (FAB), respectively. However, the main obstacles to the full potential of both technologies in the field include their lowered efficiencies and increased economic costs due to the co-existence of a variety of natural electron acceptors in the environment, such as dissolved oxygen (DO), nitrate (NO3⁻), sulfate (SO4²⁻), ferric iron (Fe (III)), bicarbonate (HCO3⁻), and even water, which compete for electrons with the target contaminants. Therefore, a clear understanding of the mechanisms governing electron competition and electron selectivity is significant for the accurate evaluation of the effectiveness of both technologies under natural hydrochemical conditions. We collected data from both abiotic and biotic CAH-remediation systems, summarized the dechlorination and undesired reactions in groundwater, discussed the characterization methods and general principles of electron competition, and described strategies to improve electron selectivity in both systems. Furthermore, we reviewed the emerging ZVI-FAB coupled system, which integrates abiotic and biotic processes to enhance dechlorination performance and electron utilization efficiency. Lastly, we propose future research needs to quantitatively understand the electron competition in abiotic, biotic, and coupled systems in more detail and to promote improved electron selectivity in groundwater remediation.
In this study, nano zero-valent iron (nZVI) was utilized to activate persulfate (PS) for the degradation of metoprolol (MTP), a commonly used drug for curing cardiovascular diseases, in water. Quenching tests indicated that both the sulfate radical (SO4˙⁻) and hydroxyl radical (˙OH) contributed to the degradation of MTP, while SO4˙⁻ seemed to play a large role under natural pH conditions. Batch tests were conducted to investigate the effects of several influencing factors, such as PS concentration, initial MTP concentration, pH, temperature and common anions, on the degradation performance of MTP. Generally, lower MTP concentration and pH values, and higher PS concentration and temperature favoured MTP degradation. HCO3⁻, NO3⁻ and SO4²⁻ were found to inhibit MTP degradation, while Cl⁻ enhanced MTP degradation. Several corrosion products of nZVI, including Fe3O4, Fe2O3 and FeSO4, were formed during the reaction, which was reflected by the combined XRD and XPS analysis. Degradation pathways of MTP were proposed according to the identified transformation products, and the peak areas of the major products along with the time were also monitored. Finally, the toxicity of the reaction solution was assessed by experiments using Aliivibrio fischeri. Overall, it could be concluded that nZVI/PS might be a promising method for the rapid treatment of MTP-caused water pollution.
Chlorinated organic compounds (COCs) are common anthropogenic
contaminants encountered in soil and groundwater. COCs were
industrially produced for different applications, such as dry cleaning,
degreasing, or as pesticides. The presence of COCs in the environment is a major concern because of their toxicity and persistence. The most widely used method for their removal is the conventional pump-and-treat approach. However, this technology can hardly achieve a complete remediation because of geological characteristics and the presence of pore space pollution/adsorbed pollution, leading to a residual saturation.
Hence, in addition to the improvement of pump-and-treat systems, In situ chemical processes have been largely developed. These chemical processes involve the injection of chemical reagents for the removal of residual pollution source and/or the treatment of contamination plume. Chemical degradation of COCs can be achieved by oxidative or reductive processes. If chemical oxidation has been first developed for in situ application, chemical reduction is one of the most important emerging remediation techniques for COCs treatment. Due to the electronegative character of chlorine substituents, COCs can effectively be transformed via reductive pathways. Moreover, reductive dechlorination has shown higher efficiency on highly chlorinated compounds.
This chapter focuses on the presentation of the chemical reduction of the most common COCs pollutants, followed by kinetic and mechanistic approaches related to the use of iron-based particles. Developments of in situ chemical reduction technologies aiming to enhance remediation rates are also exposed. Influence of environmental conditions for in situ applications is then developed. Finally, a case study is presented.
This chapter addresses a case study of long-term assessment of a field application of environmental nanotechnology. Dense Non-Aqueous Phase Liquid (DNAPL) contaminants such as Tetrachloroethene (PCE) and Trichloroethene (TCE) are a type of recalcitrant compounds commonly found at contaminated sites. Recent research has focused on their remediation using environmental nanotechnology in which nanomaterials such as nanoscale Emulsified Zerovalent Iron (EZVI) are added to the subsurface environment to enhance contaminant degradation. Such nanoremediation approach may be mostly applicable to the source zone where the contaminant mass is the greatest and source removal is a critical step in controlling the further spreading of the groundwater plume. Compared to micro-scale and granular counterparts, NZVI exhibits greater degradation rates due to its greater surface area and reactivity from its faster corrosion. While NZVI shows promise in both laboratory and field tests, limited information is available about the long-term effectiveness of nanoremediation because previous field tests are mostly less than two years. Here an update is provided for a six-year performance evaluation of EZVI for treating PCE and its daughter products at a Superfund site at Parris Island, South Carolina, USA. The field test consisted of two side-by-side treatment plots to remedy a shallow PCE source zone (less than 6 m below ground surface) using pneumatic injection and direct injection, separately in October 2006. For the pneumatic injections, a two-step injection procedure was used. First, the formation was fluidized by the injection of nitrogen gas alone, followed by injection of the EZVI with nitrogen gas as the carrier. In the pneumatic injection plot, 2,180 liters of EZVI containing 225 kg of iron (Toda RNIP-10DS), 856 kg of corn oil, and 22.5 kg of surfactant were injected to remedy an estimated 38 kg of chlorinated volatile compounds (CVOC)s. Direct injections were performed using a direct push rig. In the direct injection plot, 572 liters of EZVI were injected to treat an estimated 0.155 kg of CVOCs. Visual inspection of collected soil cores before and after EZVI injections shows that the travel distance of EZVI was dependent on the method of delivery with pneumatic injection achieving a greater distance of 2.1 m than did direct injection reaching a distance of 0.89 m. Significant decreases in PCE and TCE concentrations were observed in downgradient wells with corresponding increases in degradation products including significant increases in ethene. In the pneumatic injection plot, there were significant reductions in the downgradient groundwater mass flux values for chlorinated ethenes (>58%) and a significant increase in the mass flux of ethene (628%). There were significant reductions in total CVOCs mass (78%), which was less than an estimated 86% decrease in total CVOCs made at 2.5 years due to variations in soil cores collected for CVOCs extraction and determination; an estimated reduction of 23% (vs.63% at 2.5 years) in the sorbed and dissolved phases and 95% (vs. 93% at 2.5 years) reduction in the PCE DNAPL mass. Significant increases in dissolved sulfide, volatile fatty acids (VFA), and total organic carbon (TOC) were observed and dissolved sulfate and pH decreased in many monitoring wells. The apparent effective destruction of CVOC was accomplished by a combination of abiotic dechlorination by nanoiron and biological reductive dechlorination stimulated by the oil in the emulsion. No adverse effects of EZVI were observed for the microbes. In contrast, populations of dehalococcoides showed an increase up to 10,000 fold after EZVI injection. The dechlorination reactions were sustained for the six-year period from a single EZVI delivery. Repeated EZVI injections four to six years apart may be cost-effective to more completely remove the source zone contaminant mass. Overall, the advantages of the EZVI technology include an effective “one-two punch” of rapid abiotic dechlorination followed by a sustained biodegradation; contaminants are destroyed rather than transferred to another medium; ability to treat both DNAPL source zones and dissolved-phase contaminants to contain plume migration; ability to deliver reactants to targeted zones not readily accessible by conventional permeable reactive barriers; and potential for lower overall costs relative to alternative technologies such as groundwater pump-and-treat with high operation and maintenance costs or thermal technologies with high capital costs. The main limitations of the EZVI technology are difficulty in effectively distributing the viscous EZVI to all areas impacted with DNAPL; potential decrease in hydraulic conductivity due to iron corrosion products buildup or biofouling; potential to adversely impact secondary groundwater quality through mobilization of metals and production of sulfides or methane; injection of EZVI may displace DNAPL away from the injection point; and repeated injections may be required to completely destroy the contaminants.
This study involves the mixing method of nano-materials addition and interaction with cement mortar behavior for many mortar samples under variable curing time with constant water to cement ratio (W/C=0.45).Some mechanical properties such as (compressive, flexural strength and wear tests). In this study the main parameters depend include the small amount replacement ratio of nano-particle (Fe2O3) with respect to the mass of the (Al-Mass cement) Ordinary Portland Cement (OPC) type (I). The percentage of nano-material replacement on the mixture of cement mortar includes (0.25, 0.5, 1.0 and 1.5%) for nano-materials with constant W/C ratio and also the amount of the fine aggregate use 2.75 from the amount of cement .The results shows that, the strength of the mortar consist of with colloidal nano materials give better properties than reference specimens in all test. But the nano- ferric oxide materials give good properties up to 1%.
The poly(methacrylic acid) (PMAA) was synthesized in the pores of commercial microfiltration PVDF membranes to allow incorporation of catalytic palladium/iron (Pd/Fe) nanoparticles for groundwater remediation. Particles of 17.1 ± 4.9 nm size were observed throughout the pores of membranes using a focused ion beam. To understand the role of Pd fractions and particle compositions, 2-chlorobiphenyl was used as a model compound in solution phase studies. Results show H2 production (Fe0 corrosion in water) is a function of Pd coverage on the Fe. Insufficient H2 production caused by higher coverage (> 10.4% for 5.5 wt%) hindered dechlorination rate. With 0.5 wt% Pd, palladized-Fe reaction rate (surface area normalized reaction rate, ksa = 0.12 L/(m2-h) was considerably higher than isolated Pd and Fe particles. For groundwater, in a single pass of Pd/Fe-PMAA-PVDF membranes (0.5 wt% Pd), chlorinated organics, such as trichloroethylene (177 ppb) and carbon tetrachloride (35 ppb), were degraded to 16 and 0.3 ppb, respectively, at 2.2 seconds of residence time. The degradation rate (observed ksa) followed the order of carbon tetrachloride > trichloroethylene > tetrachloroethylene > chloroform. A 36 h continuous flow study with organic mixture and the regeneration process show the potential for on-site remediation.
محمود فاضلیسنگانیو همکاران101نشریه پژوهشهاي حفاظت آب و خاكجلد بیست و سوم، شماره ششم، 1395http://jwsc.gau.ac.irبررسی عوامل مؤثر بر انتقال نانوذره آهن صفر ظرفیتی با پوشش کربوکسی متیل سلولز در خاك محمود فاضلیسنگانی1 ،*علیرضا آستارایی2، امیر فتوت2و حجت امامی21دانشجوي دکتري گروه علوم خاك، دانشگاه فردوسی مشهد ،2دانشیار گروه علوم خاك، دانشگاه فردوسی مشهدتاریخ دریافت: 1/3/94؛ تاریخ پذیرش: 24/6/95چکیده1سابقه و هدف:نانوذرهآهن صفر ظرفیتی )NZVI( بهعنوان موادي مستعد براي حذف درجاي طیف گستردهاي از آلایندههاي آب و خاك از جمله ترکیبات آلی کلردار، آفتکشها، آنیونهاي غیرآلی و فلزات سنگین مورد استفاده قرار گرفتهاست. از آنجا که براي اجراي موفقیتآمیز یک برنامه پاکسازي، لازم است تا عامل رفع آلودگی به مجاورت آلاینده انتقال یابد، پژوهشهايزیادي عوامل مؤثر بر انتقالذرههايNZVIرا درمحیطهاي متخلخل مورد بررسی قرار دادهاند. با توجه به تحرك کمNZVI، عوامل پوششدهنده مختلفی مانند کربوکسی متیل سلولز )CMC( براي اصلاح سطح این ذرههايو بهمنظور افزایش تحركپذیري این مواد در محیطهاي متخلخل طبیعی مورد استفاده قرار گرفتهاند.در این پژوهش، عوامل کنترلکننده انتقال نانوذرهآهن صفر ظرفیتی با پوشش کربوکسی متیل سلولز )CMC-NZVI( در ستونهاي خاك اشباع،مورد بررسی قرار گرفت .مواد و روشها:ویژگیهايفیزیکی، شیمیایی و هیدرولیکی 20نوع خاك متفاوت و سوسپانسیون CMC-NZVIدر عصاره خاك )شامل 29پارامتر( اندازهگیري شد و پارامترهاي انتقال CMC-NZVIدر خاك نیز با استفاده از منحنیهاي رخنه و با بهکارگیري مدل سینتیکی دو مکانی معادله انتشار-همرفت تخمین زده شد. سپس بررسی عوامل مؤثر بر انتقال CMC-NZVI، از طریق آنالیز چندمتغیره به روش تجزیه به مؤلفههاي اصلی )PCA( انجام شد. رابطه رگرسیون خطیچندگانهبین درصد عبور ذرههايCMC-NZVIازستونخاكاشباعو ویژگیهايخاك و نانوذرهمورد بررسی قرار گرفت.یافتهها:نتایج نشان داد که بسته به نوع خاك بین 2/10تا 9/61درصد جرمی از ذرههايCMC-NZVIوارد شده به ستون خاك، از آن عبور کردند که نشاندهنده تحركپذیري این ذرههايدر محیط خاكاست. هر چند ذرههايCMC-NZVIدر خاكهایی که میزان رس و شوري بالاییداشتند بهمیزان قابلتوجهی جذب شدند. نتایج PCAنشان داد که تغییرپذیري ویژگیهايمورد مطالعه بهوسیله 7مؤلفه اصلی و با پوشش 2/88درصدي تغییرات کل، قابل توصیف است. در بین ویژگیهايمورد بررسی، ویژگیهايمربوط به شیمی محلول، بیشترین مقادیر بردارهاي ویژه را در مؤلفهاصلی اول دارا میباشند. بررسی رابطه رگرسیونی خطی چندگانه با دو نوع متغیر ورودي شامل متغیرهاي اولیه و نمرههاي عاملی بهعنوان متغیرهاي ثانویه،با درصد CMC-NZVIانتقال یافته از ستونخاك ،نشان داد کهمدل *مسئول مکاتبه: astaraei@um.ac.ir
نشریه پژوهشهاي حفاظت آب و خاك جلد )23(، شماره )6 (1395102رگرسیونی با متغیر ورودي نمرههاي عاملی،با دارا بودن R2بیشتر و RMSEکمتر،تخمین بهتري از انتقالپذیري ذرههايCMC-NZVIدر محیط خاك ارائه میدهد. نتیجهگیري:نتایج PCAاهمیت شیمی محلول، مقدار رس و ویژگیهايهیدرودینامیکی خاك را در میزان انتقالپذیري ذرههايCMC-NZVI،نشان میدهد. نتایج این مطالعه پیشنهاد میکند که ذرههايCMC-NZVIتحرك کافی براي استفاده بهعنوان عامل اصلاحکننده آلودگی را در خاك دارند مگر در شرایطی که مقدار رس و شوري خاك بالا باشد. هرچند پژوهشهايبیشتري براي بررسی کارآیی این ذرههابراي حذف آلایندهها از خاك و محیطهاي زیرزمینی نیاز است. واژههاي کلیدي:پارامترهاي انتقال، ویژگیهايخاك، تجزیه به مؤلفههاي اصلی، محیط متخلخلمقدمهخاصیت کاهندگی بالا و غیرسمی بودن آهن صفر ظرفیتی )آهن به فرم فلزي( باعث شده است تا این ماده از دیرباز در پالایش خاك و منابع آب سطحی و زیرزمینی مورد استفاده قرار گیرد )16،34(. با توسعه تکنولوژي نانو و بهکارگیري ذرههايآهن صفر ظرفیتی در مقیاس نانو با واکنشپذیري و سطح قابل دسترس بیشتر براي واکنش با آلایندهها نسبت به این ذرههادر مقیاس میکرو و ماکرو، امکان پاكسازي درجاي منابع آبو خاك از آلایندههاي مختلف، با کارآیی بیشتر و هزینه کمتر فراهم شده است )29 .(پژوهشهايمتعددي کاربرد موفقیتآمیز نانوذرهآهن صفرظرفیتی1)NZVI( در رفع آلایندههاي مختلف مانند ترکیبات آلی کلردار، آفتکشها، آنیونهاي غیرآلی و فلزات سنگین در محیطهاي آبی، رسوبات و خاكرا تأیید کردهاند )4 ،16،32.(براي استفاده از ذرهNZVIبهعنوان عملگر درجا در رفع آلودگی، آگاهی از فرآیند انتقال آنبه مجاورت آلاینده مورد نظر و توزیع آنها در محیطهايمتخلخل آلوده مانند خاك، رسوبات و آبهاي زیرزمینی ضرورت دارد )10،20(. از اینرو پژوهشهايزیادي براي فهم مکانیسمها و عوامل کنترلکننده انتقال 1-Nano zero valent ironNZVIدر محیطهاي متخلخل طبیعی که نقش کلیدي در افزایش کارایی استفاده از این ذرههادر پالایش محیطی دارد، انجام شده است )8 ،12 ،15 ،22 ،25 .(در بسیاري از پژوهشهايانجام شده، دانههاي کروي یکنواخت و خالص شیشهاي یا کوارتزي بهعنوان محیط متخلخل مدل و سوپانسیونهاي آزمایشگاهی با ترکیب معین در قالب آزمایشهاي ستونی براي بررسی انتقال NZVIدر محیط متخلخل مورد استفاده قرار گرفتهاند )15،24(. نتایج حاصل از این پژوهشهانشان داده است که تحرك نانوذرهدر محیط متخلخل تحتتأثیر ویژگیهاي محیط متخلخل )اندازه قطر ذرهها، ترکیب شیمیایی، فیزیکی و مینرالوژیکی(، ویژگیهايذاتی نانوذره)اندازه، سطح ویژه، پتانسیل سطحی، مورفولوژي، پوشش سطحی(، شیمی سوسپانسیونحامل نانوذره)غلظت، قدرت یونی، اسیدیته، ترکیب یونی( و ویژگیهايهیدرودینامیکی سیستم )شدت جریان، ضریب انتشار هیدرودینامیکی، سرعت منفذي(میباشد )6 ،19،23(. هر چند نتایج حاصل از بررسی انتقال نانوذرهدر چنین سیستمهاي ایدهآلو یکنواختی براي تعیین مکانیسمها، عوامل کنترلکننده و اثرات متقابل آنها ضروري است، اما انتقال نانوذرهدر محیطهاي متخلخل غیریکنواخت طبیعی مانند رسوباتو خاك، از پیچیدگی بیشتري برخوردار است که
نشریه پژوهشهاي حفاظت آب و خاك جلد )23(، شماره )6 (139512029.Tratnyek, P.G., and Johnson, R.L. 2006. Nanotechnologies forEnvironmental Cleanup. Nanotoday.1: 2. 44-48.30.Tufenkji, N. 2007. Colloid and Microbe Migration in Granular Environments: A Discussion of Modelling Methods, P 119-142, In: F. Frimmel, et al. (Eds.), Colloidal Transport in Porous Media, Springer Berlin Heidelberg. 31.Tufenkji, N., Quevedo, I.R., Petosa, A.R., Fatisson, J., and Wilkinson, K.J. 2009. Experimental investigations of nanoparticle transport and deposition in aquatic environments. Geochimica Et Cosmochimica Acta. 73:1351-1351.32.Wang, C., Luo, H., Zhang, Z., Wu, Y., Zhang, J., and Chen, S. 2014. Removal of As(III (and As(V) from aqueous solutions using nanoscale zero valent iron-reduced graphite oxide modified composites. J. Hazard. Mater. 268:124-131.33.Wilding, L.P. 1985. Spatial variability, Its documentation, accommodation, and implication to soil surveys. P 166-194, In: D.R. Nielsen and J. Bouma (Eds.), Soil Variability, Pudo, Wagenigen, The Netherlands.34.Zhang, W.X. 2003. Nanoscale Iron Particles for Environmental Remediation: An Overview. J. Nanoparticle Res. 5:323-332.
محمود فاضلیسنگانیو همکاران121J. of Water and Soil Conservation, Vol. 23(6), 2017http://jwsc.gau.ac.irFactors affecting the Transport of Carboxymethyl Cellulose coated Zero Valent Iron Nano-particles in SoilM. Fazeli Sangani1, *A.R. Astaraei2, A. Fotovat2and H. Emami21Ph.D. Student, Dept. of Soil Science, Ferdowsi University of Mashhad, 2Associate Prof., Dept. of Soil Science, Ferdowsi University of Mashhad Received: 05/22/2015; Accepted: 09/14/2016Abstract1Background and Objectives:As versatile materials, zero valent iron nanoparticles (NZVI) have been employed for in-situ decontamination of a wide range of water and soil contaminants, including organic chlorinated compounds, pesticides, inorganic anions and heavy metals. To carry out a successful clean-up plan, it is necessary to deliver the decontaminant agent to the vicinity of pollutant. Therefore a considerable number of studies have investigated thefactors which affecttransport behavior of NZVI particles in natural subsurface environments. As bare (unmodified) NZVI particles has been found to be immobile even in homogeneous porous media, different coating agent such as Carboxymethyl cellulose (CMC)has been used for surface modification of NZVI in order to improve their mobility in subsurface environments. So far, no investigation has been conducted on undisturbed soil columns, considering the real properties of the media in which the NZVI particlesare transported. So in this study, different soil types covering a wide range of soil properties in terrestrial systems are examined and the main characteristics associated with NZVI mobility in saturated soil media.Materials and Methods:Several parameters (n=29) including physiochemical and hydraulic properties of 20 different soil types and nanoparticle characteristics in soil extract suspension were measured and the transport parameters estimated from breakthrough curves employing a two-site kinetic model of advection-dispersion equation. Principal component analysis (PCA) was then used to explore the significant factors which control CMC-NZVI transport.Multi-linear regression modelwas investigated between the percentage of transported CMC-NZVI through the soil and the properties of soil and nanoparticles.Results:Results showed that depending on the soil type, 10.2 to 61.9 percent of introduced CMC-NZVI mass passed through the soil columns which indicates CMC-NZVI particles are mobile in soil medium; However CMC-NZVI particles were significantly retained by soils with higher clay contents and salinity. PCA results showed that 7 selected principal components (PC) described 88.2% of the total variance of the input variables where, Solution chemistry had high loading valuesin PC1among the examined parameters. A multi-linear regression model developed between two kinds of input variables including primary variables and factor scores(FSs)as secondary variables,and percentageoftransported CMC-NZVI through the soil column,showed thatregression model employing FSs assecondaryinput variables presents a better estimation of CMC-NZVI particles transportability in soil with higher R2and lower RMSE values.Conclusion:PCA results indicate the significance of solution chemistry, clay content and hydrodynamic properties of soil in CMC-NZVI transport. Results of this study suggest CMC-NZVI particles are mobile enough to be employed for subsurface remediation when clay content and salinity of soil are not so high. However more investigations are need to explore the efficiency of these materials for removing different pollutants from natural soils and subsurface media.
Groundwater pH is one of the most important geochemical parameters in controlling the interfacial reactions of zero-valent iron (ZVI)with water and contaminants. Ball milled, microscale ZVI (mZVI bm )efficiently dechlorinated TCE at initial stage (<24 h)at pH 6–7 but got passivated at later stage due to pH rise caused by iron corrosion. At pH > 9, mZVI bm almost completely lost its reactivity. In contrast, ball milled, sulfidated microscale ZVI (S-mZVI bm )didn't experience any reactivity loss during the whole reaction stage across pH 6–10 and could efficiently dechlorinate TCE at pH 10 with a reaction rate of 0.03 h ⁻¹ . Increasing pH from 6 to 9 also enhanced electron utilization efficiency from 0.95% to 5.3%, and from 3.2% to 22%, for mZVI bm and S-mZVI bm , respectively. SEM images of the reacted particles showed that the corrosion product layer on S-mZVI bm had a puffy/porous structure while that on mZVI bm was dense, which may account for the mitigated passivation of S-mZVI bm under alkaline pHs. Density functional theory calculations show that covered S atoms on the Fe(100)surface weaken the interactions of H 2 O molecules with Fe surfaces, which renders the sulfidated Fe surface inefficient for H 2 O dissociation and resistant to surface passivation. The observation from this study provides important implication that natural sulfidation of ZVI may largely contribute to the long-term (>10 years)efficiency of TCE decontamination by permeable reactive barriers with pore water pH above 9.
In this study, a chambered dual‐anode design, which consisted of an inert anode (platinum anode or boron‐doped diamond anode) and a secondary iron anode (SIA), was proposed for the treatment of 2,4‐dichlorophenols in aqueous solution. The introduction of SIA greatly improved the performance of the electro‐oxidation system. In the dynamic experiments using the flow reactor with chambered dual‐anode design, the 2,4‐dichlorophenol in effluent was lower than 0.3 mg/L, while a near‐neutral pH value was maintained for the effluent. image
Experimental investigations using materials ranging from high purity single crystals of iron to polycrystalline Armco iron establish the effects of grain boundaries, nitrogen in solution, and overall purity on the plastic deformation and fracture of iron. The behavior under tensile stress in the presence of hydrogen is divided into three steps, which are discussed under the headings: displacement of dislocations in a slip plane in the presence of obstacles to this displacement and of hydrogen, nucleation and development of microdefects, and crack propagation. It is concluded that the ferrite lattice itself cannot be embrittled by hydrogen.
Batch experiments examining the kinetics and mechanism of vinyl chloride (VC) reduction by metallic iron in aqueous systems were performed. The effects of various iron loadings, VC concentrations, pH conditions, temperatures, and Fe(II)/Fe(III) chelating agents (1,10-phenanthroline, 2,2‘-dipyridyl, and nitrilotriacetic acid) on reduction kinetics were examined. Ethylene was the major carbon-containing product of VC reduction under all conditions examined, indicating hydrogenolysis. The reaction was pseudo-first-order with respect to aqueous VC concentration. The amount of VC adsorption on iron surfaces was estimated from the rapid initial loss of VC from solution, and the resultant sorption isotherm was linear over the concentration range examined. The first-order kinetics and the linear sorption for VC suggest that the portion of VC sorption to surface reactive sites relative to nonreactive sorption sites is constant, unlike the behavior observed for the higher chlorinated ethenes. The activation energy of the reaction was measured to be 41.6 ± 2.0 kJ/mol, sufficiently large to indicate that the chemical reaction at the surface, rather than aqueous phase diffusion to the surface, controls the overall rate of the reaction. Experiments with the chelating agents suggest that the effect of available Fe(II) on VC reduction is not significant.
There is a limited amount of information about the effects of mineral precipitates and corrosion on the lifespan and long-term performance of in situ Fe° reactive barriers. The objectives of this paper are (1) to investigate mineral precipitates through an in situ permeable Fe° reactive barrier and (2) to examine the cementation and corrosion of Fe° filings in order to estimate the lifespan of this barrier. This field scale barrier (225-ft long x 2-ft wide x 31-ft deep) has been installed in order to remove uranium from contaminated groundwater at the Y-12 plant site, Oak Ridge, TN. According to XRD and SEM-EDX analysis of core samples recovered from the Fe° portion of the barrier, iron oxyhydroxides were found throughout, while aragonite, siderite, and FeS occurred predominantly in the shallow portion. Additionally, aragonite and FeS were present in up-gradient deeper zone where groundwater first enters the Fe° section of the barrier. After 15 months in the barrier, most of the Fe° filings in the core samples were loose, and a little corrosion of Fe° filings was observed in most of the barrier. However, larger amounts of corrosion (10-150 m thick corrosion rinds) occurred on cemented iron particles where groundwater first enters the barrier. Bicarbonate/carbonate concentrations were high in this section of the barrier. Byproducts of this corrosion, iron oxyhydroxides, were the primary binding material in the cementation. Also, aragonite acted as a binding material to a lesser extent, while amorphous FeS occurred as coatings and infilings. Thin corrosion rinds (2-50 m thick) were also found on the uncemented individual Fe° filings in the same area of the cementation. If corrosion continues, the estimated lifespan of Fe° filings in the more corroded sections is 5 to 10 years, while the Fe° filings in the rest of the barrier perhaps would last longer than 15 years. The mineral precipitates on the Fe° filing surfaces may hinder this corrosion but they may also decrease reactive surfaces. This research shows that precipitation will vary across a single reactive barrier and that greater corrosion and subsequent cementation of the filings may occur where groundwater first enters the Fe° section of the barrier.
We have hypothesized that hydrogen gas intercalated in a palladium lattice is the powerful reducing agent that reductively dechlorinates chlorinated organic compounds that are adsorbed on the surface of palladized electrodes. We have shown that dechlorination of 4-chlorophenol to phenol occurs rapidly on palladized carbon cloth or pal ladized graphite electrodes. The reactions on the palladized carbon cloth and graphite depend on the adsorption of the chlorinated organic compound on the carbon surface and the reaction with hydrogen at the palladium/carbon interface. Palladium was much more effective in promoting the dechlorination reaction than platinum, probably because of its ability to intercalate hydrogen in its lattice.
Flow-through column tests were conducted to investigate the products of degradation of aqueous trichloroethene (TCE) in contact with granular iron metal. The results indicated the degradation process to be pseudo-first-order and the rate constant to be relatively insensitive to the initial concentration of TCE over the range from about 1.3 to 61 mg/L. The principal degradation product was ethene, followed by ethane with substantially smaller amounts of other C1−C4 hydrocarbons. About 3.0−3.5% of the initial TCE appeared as chlorinated degradation products, including the three dichloroethene isomers and vinyl chloride. Although the chloride mass balance was generally between 98 and 102%, a maximum of 73% of the carbon could be accounted for in the identified products. Based on the low concentrations of chlorinated degradation products in the solution phase, it is proposed that most of the TCE remains sorbed to the iron surface until complete dechlorination is achieved.
Batch experiments examining the kinetics and mechanism of vinyl chloride (VC) reduction by metallic iron in aqueous systems were performed. The effects of various iron loadings, VC concentrations, pH conditions, temperatures, and Fe(II)/Fe(III) chelating agents (1,10-phenanthroline, 2,2‘-dipyridyl, and nitrilotriacetic acid) on reduction kinetics were examined. Ethylene was the major carbon-containing product of VC reduction under all conditions examined, indicating hydrogenolysis. The reaction was pseudo-first-order with respect to aqueous VC concentration. The amount of VC adsorption on iron surfaces was estimated from the rapid initial loss of VC from solution, and the resultant sorption isotherm was linear over the concentration range examined. The first-order kinetics and the linear sorption for VC suggest that the portion of VC sorption to surface reactive sites relative to nonreactive sorption sites is constant, unlike the behavior observed for the higher chlorinated ethenes. The activation energy of the reaction was measured to be 41.6 ± 2.0 kJ/mol, sufficiently large to indicate that the chemical reaction at the surface, rather than aqueous phase diffusion to the surface, controls the overall rate of the reaction. Experiments with the chelating agents suggest that the effect of available Fe(II) on VC reduction is not significant.
The degradation of trichloroethene (TCE) at 2 mg L-1 in headspace free aqueous solution by zerovalent iron (Fe0) and tin (Sn0) was studied in batch tests at 10, 25, 40, and 55 °C and HCl-treated Fe0 and Sn0 at 25 and 55 °C. Surface area normalized pseudo-first-order rate constants (kSA) ranged from 0.44 × 10-3 to 4.3 × 10-3 h-1 m-2 L for Fisher Fe0, 0.029 × 10-3 to 0.27 × 10-3 h-1 m-2 L for Peerless and Master Builders Fe0, and 0.011 × 10-3 to 1.31 × 10-3 h-1 m-2 L for Fisher and Aldrich Sn0. The Aldrich Fe0 was the least reactive with kSA values ranging from 0.0016 × 10-3 to 0.011 × 10-3 h-1 m-2 L. The HCl-washing increased metal surface area and observed rate constant (k) values but generally decreased kSAvalues. The calculated apparent activation energy (Ea) using the Arrhenius law for the four temperature levels ranged from 32.2 to 39.4 kJ mol-1 for the untreated Fe0 metals and 40.5−76.8 kJ mol-1 for the untreated Sn0 metals. Greater temperature effect was observed for Sn0 than for Fe0. Our results indicate that TCE reduction by Fe0 and Sn0 is likely controlled primarily by chemical reaction-limited kinetics rather than by mass transport of the TCE to the metal surface. Both reductive β-elimination reaction and hydrogenolysis reaction are likely involved in the reduction of TCE by both Fe0 and Sn0.
Dehalogenation is among the most important processes involved in contaminant fate, but despite all the work that has been done on the kinetics of dehalogenation, there are few linear free energy relationships (LFERs) that can be used to explain or predict rates of dehalogenation by environmental reductants. Previously, we summarized kinetic data for dehalogenation of chlorinated alkanes and alkenes by zero-valent iron (Fe0) and showed that correlation analysis of these data with published two-electron reduction potentials did not give a simple relationship. In this study, we report successful LFERs based on estimated lowest unoccupied molecular orbital (LUMO) energies calculated from semiempirical (AM1 and PM3) and ab initio methods (6-31G*) and one-electron reduction potentials. Solvation effects can be modeled with COSMO and incorporated into semiempirical estimates of ELUMO, but this did not improve the correlation with k. The best LFER (log k = −5.7−1.5 ELUMO) explains 83% of the variability in surface area-normalized rate constants (k) with ab initio LUMO energies. The LFER is improved by correcting for statistical bias introduced by back transformation from log-linear regression models. New kinetic data for six compounds are compared with rate constants predicted using the unbiased LFER.
A combination of new and previously reported data on the kinetics of dehalogenation by zero-valent iron (Fe0) has been subjected to an analysis of factors effecting contaminant degradation rates. First-order rate constants (kobs) from both batch and column studies vary widely and without meaningful correlation. However, normalization of these data to iron surface area concentration yields a specific rate constant (kSA) that varies by only 1 order of magnitude for individual halocarbons. Correlation analysis using kSA reveals that dechlorination is generally more rapid at saturated carbon centers than unsaturated carbons and that high degrees of halogenation favor rapid reduction. However, new data and additional analysis will be necessary to obtain reliable quantitative structure−activity relationships. Further generalization of our kinetic model has been obtained by accounting for the concentration and saturation of reactive surface sites, but kSA is still the most appropriate starting point for design calculations. Representative values of kSA have been provided for the common chlorinated solvents.
Laboratory tests were conducted to examine zero-valent iron as an enhancing agent in the dehalogenation of 14 chlorinated methanes, ethanes, and ethenes. All compounds were tested by batch procedures in which 10 g of 100-mesh electrolytic iron was added to 40 ml hypovials. Aqueous solutions of the respective compounds were added to the hypovials, and the decline in concentration was monitored over time. Substantial rates of degradation were observed for all compounds tested with the exception of dichloromethane. The degradation process appeared to be pseudo first-order with respect to the organic compound, with the rate constant appearing to be directly proportional to the surface area to volume ratio and increasing with increasing degree of chlorination. Column tests showed the process to proceed under flow conditions with degradation rates indpendent of velocity and consistent with those measured in the batch tests. When normalized to 1 m2/ml, the t50 values ranged from 0.013 to 20 hr, and were about 5 to 15 orders of magnitude lower than values reported for natural rates of abiotic degradation. The results indicate abiotic reductive dechlorination, with iron serving as the source of electrons; the mechanism is, however, uncertain. Based on the rapid rates of degradation, both in situ and aboveground applications for remediation of contaminated ground water are proposed.
The use of granular iron for in situ degradation of dissolved chlorinated organic compounds is rapidly gaining acceptance as a cost-effective technology for ground water remediation. This paper describes the first field demonstration of the technology, and is of particular importance since it provides the longest available record of performance (five years). A mixture of 22% granular iron and 78% sand was installed as a permeable “wall” across the path of a contaminant plume at Canadian Forces Base, Borden, Ontario. The major contaminants were trichloroethene (TCE, 268 mg/L) and tetrachloroethene (PCE, 58 mg/L). Approximately 90% of the TCE and 86% of the PCE were removed by reductive dechlorination within the wall, with no measurable decrease in performance over the five year duration of the test. Though about 1% of the influent TCE and PCE appeared as dichloroethene isomers as a consequence of the dechlorination of TCE and PCE, these also degraded within the iron-sand mixture. Performance of the field installation was reasonably consistent with the results of laboratory column studies conducted to simulate the field behavior. However, if a more reactive iron material, or a higher percentage of iron had been used, complete removal of the chlorinated compounds might have been achieved. Changes in water chemistry indicated that calcium carbonate was precipitating within the reactive material; however, the trace amount of precipitate detected in core samples collected four years after installation of the wall suggest that the observed performance should persist for at least another five years. The study provides strong evidence that in situ use of granular iron could provide a long-term, low-maintenance cost solution for many ground water contamination problems.
1,1,2-Trichloroethylene (TCE), 1,1-dichloroethylene, cis and trans-1,2-dichloroethylene and tetrachloroethylene (PCE), at concentrations of 20 ppm in aqueous solutions were rapidly hydrodechlorinated to ethane (in a few minutes), on the surface of palladized iron in batch experiments that were performed in closed vials. No intermediate reaction products such as 1,1-dichloroethylene, 1,2-dichloroethylenes and vinyl chloride were detected at concentrations > 1 ppm either in the headspace or in solution. The chloromethanes, CCl4, CHCl3 and CH2Cl2 were also dechlorinated to methane on palladized iron; the CCl4 was dechlorinated in a few minutes, the CHCl3, in less than an hour and the CH2Cl2, in 4–5 h. These results indicate that an above-ground treatment method can be designed for the treatment of groundwater contaminated with low molecular weight chlorinated hydrocarbons.
Sorption and reduction kinetics of trichloroethylene (ICE) and tetrachloroethylene (PCE) with metallic (zero-valent) iron were determined in a closed, well-mixed, anaerobic batch system by measuring aqueous and total system concentrations of the respective chlorinated solvent as a function of time. The reaction orders with respect to TCE and PCE total system concentrations were 2.7 and 1.3, respectively, indicating that the reaction mechanisms are complex. Both compounds exhibited nonlinear sorption behavior and could be fitted by the generalized Langmuir isotherm expression. After accounting for the mass sorbed to the iron, the reduction rates of PCE and TCE are first-order. This indicates that the bulk of sorption is to nonreactive sites. Competitive sorption was observed when both PCE and TCE were present; however, no competition for reaction was detected. The design and study of treatment systems for chlorinated solvents using metallic iron requires consideration of sorption processes.
Reduction of chlorinated solvents by fine-grained iron metal was studied in well-mixed anaerobic batch systems in order to help assess the utility of this reaction in remediation of contaminated groundwater. Iron sequentially dehalogenates carbon tetrachloride via chloroform to methylene chloride. The initial rate of each reaction step was pseudo-first-order in substrate and became substantially slower with each dehalogenation step. Thus, carbon tetrachloride degradation typically occurred in several hours, but no significant reduction of methylene chloride was observed over 1 month. Trichloroethene (TCE) was also dechlorinated by iron, although more slowly than carbon tetrachloride. Increasing the clean surface area of iron greatly increased the rate of carbon tetrachloride dehalogenation, whereas increasing pH decreased the reduction rate slightly. The reduction of chlorinated methanes in batch model systems appears to be coupled with oxidative dissolution (corrosion) of the iron through a largely diffusion-limited surface reaction.
Anaerobic corrosion of iron metal produces Fe2+, OH-, and H-2(g). Growing interest in the use of granular iron in groundwater remediation demands accurate corrosion rates to assess impacts on groundwater chemical composition. In this study, corrosion rates are measured by monitoring the hydrogen pressure increase in sealed cells containing iron granules and water. The principal interference is hydrogen entry and entrapment by the iron. The entry rate is described by Sievert's law (R = kP(H2)(0.5)), and the rate constant, k, is evaluated by reducing the cell pressure once during a test. For the 10-32 mesh iron used in this study, k initially was 0.015 but decreased to 0.009 mmol kg(-1) d(-1) kPa(-0.5) in 150 d. The corrosion rate in a saline groundwater was 0.7 +/- 0.05 mmol of Fe kg(-1) d(-1) at 25 degrees C-identical under water-saturated or fully-drained conditions. The rate decreased by 50% in 150 d due to alteration product buildup. The first 40-200 h of a corrosion test are characterized by progressively increasing rates of pressure increase. The time before steady-state rates develop depends on the solution composition. Data from this period should be discarded in calculating corrosion rates. Tests on pure sodium salt solutions at identical equivalent concentrations (0.02 equiv/L) show the following anion effect on corrosion rate: HCO3 > SO42- > Cl-. For NaCl solutions, corrosion rates decrease from 0.02 to 3.0 m.
- C Grittini
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Grittini, C., Malcomson, M., and Korte, N. 1995. Environ. Sci. Technol. 29,
2898-2900.
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Cheng, I.F., Fernando, Q., and Korte, N. 1997. Environ. Sci. Technol. 31,
1074-1078.
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Gillham, R.W. and O'Hannesin, S.F. 1994. Ground Water, 6, 958-967.
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Su, C. and Puls, R.W. 1999. Environ. Sci. Technol. 33, 163-168.
- R Muftikian
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Muftikian, R., Fernando, Q., and Korte, N. 1995. Wat. Res. 29, 2434-2439.
Mineql+ Chemical Equilibrium Modeling System
- W D Schecher
- D C Mcavoy