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SCOPUS chronological bibliometry of Khudenko [67] showing citation by eight (8) sources comprising four (4) review and four (4) research articles. (Access: 2018/10/19)
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Elemental iron (Fe0) has been widely used in groundwater/soil remediation, safe drinking water provision and wastewater treatment. It is still mostly reported that a surface-mediated reductive transformation (direct reduction) is a relevant decontamination mechanism. Thus, the expressions "contaminant removal" and "contaminant reduction" are interc...
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Context 1
... other words, the oxidation-reduction of organics is induced as a parallel reaction to this cementation reaction. A SCOPUS search on October 19 th 2018 indicated that Khudenko [67] has been only referenced eight (8) times (Table 3) [162-166] and has not been considered in some literature discussing the removal mechanisms of organics in Fe 0 /H 2 O systems [10,24,25,167]. The concept of Khudenko [67] was based on a profound understanding of the Fe 0 /H 2 O system [168][169][170] and corresponds to Noubactep's concept [39,40] that has been difficult to accept [48,49]. ...
Citations
... Although there are examples of a good longevity of this reactive medium in full scale (Wilkin et al., 2014), there are numerous cases when a significant reduction of the barrier permeability occurred (Henderson and Demond, 2007). This phenomenon is mainly caused by the formation of iron oxides and hydroxides which, due to their expansive nature, reduce the porosity and permeability of the barrier (Cao et al., 2021;Hu et al., 2018). Mixing ZVI with another granular medium is a well-established strategy to prevent permeability reduction (Bilardi et al., 2020;Hu et al., 2020;Moraci et al., 2017Moraci et al., , 2015Ruhl et al., 2014). ...
... Therefore, it is clear that a proper design of Fe 0 -based filters implies the careful consideration of a balance between acceptable removal efficiency and acceptable long-term hydraulic performance [8,16]. It must be noted here, however, that the Fe 0 -H 2 O system is an ion-selective system with the highest affinity towards negatively charged pollutants [4,19]. The aforementioned studies have dealt with neutral [17] or cationic contaminants [8,18] with low affinity for the positively-charged (at circumneutral pH) iron (hydr)oxides covering the surface of Fe 0 . ...
... Due to increasing industrial activities during the 20th century, water pollution has become a global issue of concern. Fe 0 has been extensively applied, especially as reactive material in permeable reactive barriers (PRB), as a viable and cost-effective alternative for the conventional pump-and-treat technology, due to its low cost, widely availability and environmental friendliness; in addition, Fe 0 is also very versatile and can be applied for the removal of various contaminants because it can act as adsorbent, reductant, as well as a generator of adsorbing, reducing and coagulation agents [2][3][4][5]. Both laboratory experiments and full-scale applications have warned that practical application (i.e., long-term operation) of Fe 0 -based filter treatment systems is impacted by the loss of filter hydraulic conductivity (caused by the expansive nature of iron corrosion products, mineral precipitation and gas formation that progressively fill the pore space within an Fe 0 -based filter) and loss of Fe 0 efficiency caused by metal surface passivation, leading eventually to an incomplete utilization of Fe 0 [6][7][8][9][10]. ...
The aim of the present study was to provide new knowledge regarding the effect of non-expansive inert material addition on anionic pollutant removal efficiency in Fe0-H2O system. Non-disturbed batch experiments and continuous-flow-through column tests were conducted using CrVI as a redox–active contaminant in three different systems: “Fe0 + sand”, “Fe0 only” and ”sand only”. Both experimental procedures have the advantage that formation of (hydr)oxide layers on Fe0 is not altered, which makes them appropriate proxies for real Fe0-based filter technologies. Batch experiments carried out at pH 6.5 showed a slight improvement of CrVI removal in a 20% Fe0 system, compared to 50, 80 and 100% Fe0 systems. Column tests conducted at pH 6.5 supported results of batch experiments, revealing highest CrVI removal efficiencies for “Fe0 + sand” systems with lowest Fe0 ratio. However, the positive effect of sand co-presence decreases with increasing pH from 6.5 to 7.1. Scanning electron microscopy—energy dispersive angle X-ray spectrometry and X-ray diffraction spectroscopy employed for the characterization of Fe0 before and after experiments indicated that the higher the volumetric ratio of sand in “Fe0 + sand” system, the more intense the corrosion processes affecting the Fe0 grains. Results presented herein indicate the capacity of sand at sustaining the efficiency of CrVI removal in Fe0-H2O system. The outcomes of the present study suggest that a volumetric ratio Fe0:sand = 1:3 could assure not only the long-term permeability of Fe0-based filters, but also enhanced removal efficiency of CrVI from contaminated water.
... The first is the reduction in the reactivity of the filling material, which does not allow for the achievement of remediation goals downstream of the barrier. The second is the reduction in hydraulic conductivity, which obstructs the aquifer flow through the barrier, causing the possible circumvention of the contaminated plume or significant increases in internal pore pressure [22,48,49]. ...
Permeable reactive barriers (PRBs) based on the use of zero valent iron (ZVI) represent an efficient technology for the remediation of contaminated groundwater, but the literature evidences “failures”, often linked to the difficulty of fully understanding the long-term performance of ZVI-based PRBs in terms of their hydraulic behavior. The aim of this paper is to provide an overview of the long-term hydraulic behavior of PRBs composed of ZVI mixed with other reactive or inert materials. The literature on the hydraulic performance of ZVI-based PRBs in full-scale applications, on long-term laboratory testing and on related mathematical modeling was thoroughly analyzed. The outcomes of this review include an in-depth analysis of factors influencing the long-term behavior of ZVI-based PRBs (i.e., reactive medium, contamination and the geotechnical, geochemical and hydrogeological characteristics of the aquifer) and a critical revision of the laboratory procedures aimed at investigating their hydraulic performance. The analysis clearly shows that admixing ZVI with nonexpansive granular materials is the most suitable choice for obtaining a long-term hydraulically efficient PRB. Finally, the paper summarizes a procedure for the correct hydraulic design of ZVI-based PRBs and outlines that research should aim at developing numerical models able to couple PRBs’ hydraulic and reactive behaviors.
... Due to the corrosion process, iron oxides and hydroxides and hydrogen gas are produced [16][17][18]. In particular, solid iron corrosion Water 2022, 14, 3613 2 of 14 products (iron oxides and hydroxides) are involved in the removal of contaminants but reduce the initial porosity of the barrier [19][20][21][22]. It was found that these products occupy a volume larger than that occupied by corroded iron [21,23]. ...
... In particular, solid iron corrosion Water 2022, 14, 3613 2 of 14 products (iron oxides and hydroxides) are involved in the removal of contaminants but reduce the initial porosity of the barrier [19][20][21][22]. It was found that these products occupy a volume larger than that occupied by corroded iron [21,23]. Depending on the level of oxidation and on environmental conditions, iron can expand up to six times its original volume, and this can be considered as the very first cause of hydraulic conductivity loss in PRB [22]. ...
... Due to the corrosion process, iron oxides and hydroxides and hydrogen gas are produced [16][17][18]. In particular, solid iron corrosion products (iron oxides and hydroxides) are involved in the removal of contaminants but reduce the initial porosity of the barrier [19][20][21][22]. It was found that these products occupy a volume larger than that occupied by corroded iron [21,23]. ...
Zero valent iron (ZVI) is widely used in permeable reactive barriers (PRBs) for the remediation of contaminated groundwater. The hydraulic conductivity of ZVI can be reduced due to iron corrosion processes activated by water and its constituents including pollutants. To overcome this issue, ZVI particles can be mixed with granular materials that avoid a drastic reduction in the hydraulic conductivity over time. In light of the most recent studies concerning iron corrosion processes and recalling the basic principles of century-old chemistry of iron corrosion, we have revised the results of 24 long-term column tests investigating the hydraulic and reactive behavior of granular mixtures composed of ZVI and pumice or lapillus. From this analysis, we found a clear correlation between the reactive behavior, described by the retardation factor (i.e., the ratio between flow velocity and propagation velocity of the contamination front), and the hydraulic behavior, described by means of the permeability ratio of the reactive medium (i.e., the ratio between the final and initial value of hydraulic conductivity). In particular, the permeability ratio decreased with the increase in the retardation factor. Moreover, it was found that the retardation factor is a useful parameter to evaluate the influence of flow rate, contaminant concentration, and ZVI content on the reactive behavior of the granular medium.
... In other words, using reactions similar to Eq. 1 to predict the service life of Fe 0 filters [44,46] is faulty [29,30]. When it is additionally considered that Fe 0 is corroded only by H + [29,45,[47][48][49], it becomes evident that the proper discussion of the permeability loss of Fe 0 is yet to be started [29][30][31]. Admixing Fe 0 and various aggregates is part of these efforts [25,27,34,50,51]. ...
Metallic iron (Fe0) corrosion under immersed conditions (Fe0/H2O system) has been used for water treatment for the past 170 years. Fe0 generates solid iron corrosion products (FeCPs) which are known to in-situ coat the surface of aggregates, including granular activated carbon (GAC), gravel, lapillus, manganese oxide (MnO2), pyrite (FeS2), and sand. While admixing Fe0 and reactive aggregates to build hybrid systems (e.g. Fe0/FeS2, Fe0/MnO2, Fe0/sand) for water treatment, it has been largely overlooked that those materials would experience reactivity loss upon coating. This communication clarifies the relationships between aggregate addition and the sustainability of Fe0/H2O filtration systems. It is shown that any enhanced contaminant removal efficiency in a Fe0/aggregate/H2O system relative to the Fe0/H2O system is related to the avoidance/delay of particle cementation by virtue of the non-expansive nature of the aggregates. The argument that aggregate addition sustains any reductive transformation of contaminants mediated by electrons from Fe0 is disproved by the evidence that Fe0/sand systems are equally more efficient than pure Fe0 systems. This demonstration corroborates the concept that aqueous contaminant removal in iron/water systems is not a process mediated by electrons from Fe0. This communication reiterates that only hybrid Fe0/H2O filtration systems are sustainable.
... The success in the use of the ZVI is mostly linked to the multiple removal mechanisms that it is able to activate [10]. Figure 2 shows a schematic diagram of the removal of heavy metals or metalloids [38,39]. ...
... The operating limits of a reactive medium composed of ZVI are the reduction of its reactivity (mainly linked to the uncertainty in assessing long-term corrosion rate [40]) and/or permeability over time [10,11,38,41]. The permeability reduction of ZVI filters is mainly due to the expansive volumetric nature of iron corrosion, which occurs even in deionized water [42]; other causes, to be analyzed on a case by case basis, are particle clogging (e.g., the retention into PRB pores of fine particles coming from upstream soil [43], particles are cemented by voluminous corrosion products that are gelatinous at their formation under oxic conditions [44,45]); the precipitations of mineral species, especially those present in the aquifer that also precipitate because of the pH increase [46] (e.g. ...
Granular materials can be used in the context of different technologies for the treatment of contaminated solutions, such as groundwater, stormwater, wastewater, water intended for potable use, or leachate. For all such technologies, it is essential that the filtering media guarantee reactivity and permeability over a reasonably long time, avoiding the rapid replacement of the materials or the failure of the treatment goals. This mini-review provides an update on materials recently tested at the laboratory scale for heavy metal removal during batch or column tests. A recent trend in this field of research is the use of reactive materials derived from agricultural and industrial waste, alone or in combination with other conventional materials, such as zerovalent iron. Lack of knowledge of their long-term behavior is the main challenge related to the use of these new active materials, and therefore, long-term column tests are strongly recommended to correctly simulate the filtration process.
... Water (H 2 O or H + ) is a relevant oxidizing agent for Fe 0 under environmental conditions. The electrode potential for the redox couple H + /H 2 is 0.00 V. Fe 0 immersed in (contaminated or polluted) water is corroded to form H/H 2 and Fe II (and mixed Fe II /Fe III ) species which are stand-alone reducing agents [19][20][21][22][23][24][25][26]. Clearly, it is not surprising that selected species undergo reductive transformations in a Fe 0 /H 2 O system [19,[26][27][28][29]. ...
... There is a transfer of electrons from the Fe 0 body (solid state) to the Fe 0 /H 2 O interface whenever a piece of a reactive Fe 0 specimen is immersed in an aqueous solution (Fe 0 /H 2 O system) [1,5,6,76]. This occurs because Fe 0 is not stable under environmental conditions or because the redox couple H + /H 2 (E 0 = 0.00) is higher than that of Fe II /Fe 0 (E 0 = -0.44) in the electrochemical series [1,[22][23][24][25][26]. Equation 1 reveals that the oxidative dissolution of Fe 0 by protons (H + ) and Equation 1a considers that protons are from water (H 2 O H + + HO -). ...
... Another key feature in investigating the remediation Fe 0 /H 2 O system is that, at pH > 4.5, the Fe 0 surface is permanently covered by an oxide scale. The oxide scale acts both as: (i) conduction barrier for electrons from the metal body, and (ii) physical barrier for dissolved species, including O 2 and pollutants of concern [22][23][24][25][26]53,54]. The net result is that Fe 0 is oxidized by water (electrochemical reaction -Equation 1), and O 2 and dissolved contaminants are reduced by reducing species present in the oxide scale (Fe II and Fe II /Fe III species, H 2 ) (chemical reaction). ...
A critical survey of the abundant literature on environmental remediation and water treatment using metallic iron (Fe 0) as reactive agent raises two major concerns: (i) the peculiar properties of the used materials are not properly considered and characterized, and, (ii) the literature review in individual publications is very selective, thereby excluding some fundamental principles. Fe 0 specimens for water treatment are typically small in size. Before the advent of this technology and it application for environmental remediation, such small Fe 0 particles have never been allowed to freely corrode for the long-term spanning several years. As concerning the selective literature review, the root cause is that Fe 0 was considered as a (strong) reducing agent under environmental conditions. Subsequent interpretation of research results was mainly directed at supporting this mistaken view. The net result is that, within three decades, the Fe 0 research community has developed itself to a sort of modern knowledge system. This communication is a further attempt to bring Fe 0 research back to the highway of mainstream corrosion science, where the fundamentals of Fe 0 technology are rooted. The inherent errors of selected approaches, currently considered as countermeasures to address the inherent limitations of the Fe 0 technology are demonstrated. The misuse of the terms "reactivity", and "efficiency", and adsorption kinetics and isotherm models for Fe 0 systems is also elucidated. The immense importance of Fe 0 /H 2 O systems in
... Le Fe 0 est un matériau réactif non toxique et peu coûteux qui est facilement accessible (Wu et al. 2015, Gwenzi et al. 2016, Gatcha-Bandjun et al. 2017. La recherche au cours des trois dernières décennies a démontré l'efficacité du Fe 0 pour le traitement des eaux physiquement (couleur, turbidité), chimiquement (As, colorants, les métaux, les composés azotés, radionucléides) et microbiologiquement (exemple: bacteries, virus) contaminées (You et al. 2015, Ghauch 2015, Guan et al. 2015Naidu and Birke 2015, Noubactep 2015a, Tomizawa et al. 2016, Heimann et al. 2018a, Hu et al. 2018, Ndé-Tchoupé et al. 2019a). ...
... Les recherches visant à comprendre ou expliquer le mode de fonctionnement des filtres à lit de Fe 0 (Noubactep 2009a, 2009b, 2009d, Miyajima 2012, Miyajima et Noubactep 2012, 2013, Tepong-Tsindé et al. 2015c, Gheju et al. 2016, Gatcha-bandjun et al. 2017, Hu et al. 2018, 2019a et de bien les dimensionner , Caré et al. 2013, Bilardi et al. 2013a, Btatkeu-K et al. 2014, Noubactep 2015b, Domga et al. 2015, Tepong-Tsindé et al. 2015a, 2015b, Btatkeu-K et al. 2016) n'ont pas encore abouti à des résultats faisant l'unanimité au sein de la communauté scientifique (Noubactep 2015a, 2015b, Noubactep 2018a De plus, il est conseillé de procéder à un prétraitement (lavage au vinaigre ou à l'acide) du matériau utilisable (acier oxydable) afin d'éliminer les éventuelles impuretés (exemple: huile, graisses ou hydr(oxydes) de fer) qui pourraient se trouver à sa surface avant son utilisation (Tseng et al. 1984, Chen et al. 2012, Deng et al. 2013). ...
This thesis deals with metallic iron (Fe(0))for water treatment.
Steel wool was tested as Fe(0) source, and characterized for both its intrinsic reactivity (material screening) and efficiency (for water treatment) for the first time. Other achievements encompassed (I) testing the suitability of pozzolan as an alternative material to sand for the construction of metallic iron filters, and (II) testing the suitability of steel Fe(0)-based filters for water defluoridation. The work concludes that steel wool holds good promise as Fe(0)-bearing material for the construction of efficient, low-cost and reliable decentralized water treatment systems.
... Afterwards, the city of Antwerp was supplied for some 30 years by water treated in a "revolving purifier", a Fe 0 -based fluidized bed [13]. Thus, engineered Fe 0 -based systems for safe drinking water provision have a scientific history dating back to more than 160 years ago [14,15]. ...
... The long history of engineered Fe 0 -based systems for water treatment is not a continuous one [15]. Related systems have been abandoned and (partly) independently rediscovered several times [11,[16][17][18][19][20][21][22][23]. ...
... Lauderdale and Emmons [18] introduced the Emmons Process independently from past knowledge on using Fe 0 (steel wool (SW) or Fe 0 SW) for safe drinking water provision [15]. The Emmons Process is a compact unit designed at Oak Ridge National Laboratory (USA) to treat small volumes of radioactive polluted waters. ...
Researchers and engineers using metallic iron (Fe0) for water treatment need a tutorial review on the operating mode of the Fe0/H2O system. There are few review articles attempting to present systematic information to guide proper material selection and application conditions. However, they are full of conflicting reports. This review seeks to: (i) summarize the state-of-the-art knowledge on the remediation Fe0/H2O system, (ii) discuss relevant contaminant removal mechanisms, and (iii) provide solutions for practical engineering application of Fe0-based systems for water treatment. Specifically, the following aspects are summarized and discussed in detail: (i) Fe0 intrinsic reactivity and material selection, (ii) main abiotic contaminant removal mechanisms, and (iii) relevance of biological and bio-chemical processes in the Fe0/H2O system. In addition, challenges for the design of the next generation Fe0/H2O systems are discussed. This paper serves as a handout to enable better practical engineering applications for environmental remediation using Fe0.
... Micrometer size ZVI has been widely used in PRBs as the reactive medium to reductively dechlorinate a range of chlorinated organics (Cheng et al. 2007;Choi et al. 2008;Chun et al. 2010;Feng and Lim 2005;Kim and Carraway 2000;Matheson and Tratnyek 1994). The process of reductive transformation of contaminants present in a ZVI/water system is driven by a combination of reducing agents that are concurrently present in the system, i.e., (1) direct reduction through electrons from elemental iron (Fe 0 ) and (2) indirect reduction by secondary reductants (electrons from adsorbed/structural Fe II , H/H 2 ) and tertiary/quaternary reductants (such as Fe 3 O 4 and green rust) (Hu et al. 2018). ...
... Wustite (Fe II O) acts as a passivating iron oxide due to a large band gap (2.3 eV) (Cornell and Schwertmann 2003) between its valence and conduction bands. Thus, the low electrical conductivity of wustite can be linked to the poor PCP dechlorination reactivity which requires electron transfer from the Fe 0 , Fe 2+ ions, or other tertiary/quaternary reducing agents (Hu et al. 2018). Conversely, the large amounts of magnetite present on the acid washed samples, and even larger amounts in the Nic/Fe bimetal can be linked to their superior dechlorination characteristics. ...
... The pH of the reaction (Fig. 4b) was not controlled and there was a general increase in pH over the reaction time from pH 6 to 7 initially to pH 6.7 to 7.8 after 25 days of reaction. There was a slight decrease in pH between 15 and 25 days for Nic/Fe systems, and this may reflect the greater role of dechlorination of PCP by H/H 2 in the Nic/Fe bimetallic systems; i.e., H/H 2 + RCl → H + + RH + Cl − (Hu et al. 2018). ...
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 25 days of exposure with tetrachlorophenol being detected as the end product. Wustite remained as the predominant oxide on as received ZVI during the 25 days 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 25 days 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 25 days 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.
