Assessment of Long-Term Performance and Chromate Reduction Mechanisms in a Field Scale Permeable Reactive Barrier

Flury, Bettina; Frommer, Jakob; Eggenberger, Urs; Mäder, Urs; Nachtegaal, Maarten; Kretzschmar, Ruben

doi:10.1021/es803526g

Cited by 91 publications

(46 citation statements)

References 30 publications

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“…In addition, hematite, maghemite and lepidocrocite were also detected. While Cr VI was not detected, Cr III occurred in the form of two different (in terms of Cr/Fe ratio) mixed Cr III -Fe III hydroxides [60]. Based on these observations, the authors suggested following possible reaction pathways that may contribute to Cr VI removal: (1) heterogeneous reduction of Cr VI with Fe 0 ; (2) heterogeneous reduction of Cr VI with Fe II bearing solids; (3) homogeneous reduction of Cr VI with dissolved Fe II ; and (4) precipitation of the resulted Cr III as mixed Cr III -Fe III -hydroxides.…”

Section: Willisau (Switzerland)mentioning

confidence: 89%

“…The occurrence of two different Cr III species at the surface of exhausted Fe 0 shavings strongly supports this conclusion: (1) Cr III -Fe III hydroxides with Cr/Fe ratio > 1/3, produced via heterogeneous reduction of Cr VI with Fe II bearing solids; and (2) Cr III -Fe III hydroxides with Cr/Fe ratio of about 1/3, resulted from the homogeneous reduction of Cr VI with dissolved Fe II . In addition, the existence of Cr III -Fe III hydroxides not only on Fe 0 shavings, but also on the surface of gravel particles, further suggested that the homogeneous reduction process with dissolved Fe II , occurring within the pores space, was a very important pathway [60]. Accordingly, one of the main limiting factors for the longevity of the PRB was found to be the availability and accessibility of Fe II [59].…”

Section: Willisau (Switzerland)mentioning

confidence: 99%

“…The PRB had an innovative design, consisting of two different components: (1) a single row of cylinders for lower expected Cr VI concentrations; and (2) an offset double row of cylinders for higher expected Cr VI -concentrations. The reactive filling inside the cylinders (d = 1.3 m) was installed from 12 to 23 m below ground surface, and consisted in a mixture of Fe 0 shavings (5-20 mm) and gravel (2-5 mm) in the ratio of 1:3 (by weight); this ratio was selected to ensure an initial permeability of the reactive material approximately three times larger than the surrounding subsoil, and to prevent the rapid clogging of the barrier due to precipitation of secondary phases in pore spaces [59,60]. The double row of cylinders successfully treated the Cr VI contamination at normal groundwater flow velocities (residual Cr VI concentrations < 0.01 mg/L); however, during events of exceptionally high groundwater levels (which result in a substantial mobilization of Cr VI ) the remediation effectiveness was only 96%.…”

Section: Willisau (Switzerland)mentioning

confidence: 99%

“…However, it was considered that, due to the rapid corrosion of Fe 0 , the direct reduction with Fe 0 was not significant; therefore, only a reduction of Cr VI with Fe II -containing minerals and with dissolved Fe II were taken into consideration as main paths for the first step of Cr VI removal, reduction to Cr III [59,60]. The occurrence of two different Cr III species at the surface of exhausted Fe 0 shavings strongly supports this conclusion: (1) Cr III -Fe III hydroxides with Cr/Fe ratio > 1/3, produced via heterogeneous reduction of Cr VI with Fe II bearing solids; and (2) Cr III -Fe III hydroxides with Cr/Fe ratio of about 1/3, resulted from the homogeneous reduction of Cr VI with dissolved Fe II .…”

Section: Willisau (Switzerland)mentioning

confidence: 99%

“…After four years of operation, Fe 0 shavings were found to be covered by a layer of Fe-hidroxides, which lead to a volume increase; nevertheless, the reduction of pore space in the reactive media appeared to be minor [60]. The innovative design of the Willisau PRB possesses several advantages, including: (1) it represents a good geotechnical solution for installation at large depths, in heterogeneous soils; (2) low risk of disturbing the hydrological regime in case the filling material becomes partially clogged by ferric hydroxides; (3) minimizes the amount of reactive material needed, since it partly relies on a dispersive Fe II -plume; and (4) good remediation effectiveness even under exceptionally high groundwater level events [59,60].…”

Section: Willisau (Switzerland)mentioning

confidence: 99%

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Progress in Understanding the Mechanism of CrVI Removal in Fe0-Based Filtration Systems

Gheju¹

2018

Water

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Hexavalent chromium (Cr VI ) compounds are used in a variety of industrial applications and, as a result, large quantities of Cr VI have been released into the environment due to inadequate precautionary measures or accidental releases. Cr VI is highly toxic to most living organisms and a known human carcinogen by inhalation route of exposure. Another major issue of concern about Cr VI compounds is their high mobility, which easily leads to contamination of surface waters, soil, and ground waters. In recent years, attention has been focused on the use of metallic iron (Fe 0 ) for the abatement of Cr VI polluted waters. Despite a great deal of research, the mechanisms behind the efficient aqueous Cr VI removal in the presence of Fe 0 (Fe 0 /H 2 O systems) remain deeply controversial. The introduction of the Fe 0 -based filtration technology, at the beginning of 1990s, was coupled with the broad consensus that direct reduction of Cr VI by Fe 0 was followed by co-precipitation of resulted cations (Cr III , Fe III ). This view is still the dominant removal mechanism (reductive-precipitation mechanism) within the Fe 0 remediation industry. An overview on the literature on the Cr geochemistry suggests that the reductive-precipitation theory should never have been adopted. Moreover, recent investigations recalling that a Fe 0 /H 2 O system is an ion-selective one in which electrostatic interactions are of primordial importance is generally overlooked. The present work critically reviews existing knowledge on the Fe 0 /Cr VI /H 2 O and Cr VI /H 2 O systems, and clearly demonstrates that direct reduction with Fe 0 followed by precipitation is not acceptable, under environmental relevant conditions, as the sole/main mechanism of Cr VI removal in the presence of Fe 0 .

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Section: Willisau (Switzerland)mentioning

confidence: 89%

Section: Willisau (Switzerland)mentioning

confidence: 99%

Section: Willisau (Switzerland)mentioning

confidence: 99%

Section: Willisau (Switzerland)mentioning

confidence: 99%

Section: Willisau (Switzerland)mentioning

confidence: 99%

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Progress in Understanding the Mechanism of CrVI Removal in Fe0-Based Filtration Systems

Gheju¹

2018

Water

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

Noubactep¹

2016

CLEAN Soil Air Water

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

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Synthesis, Mechanism, and Performance Assessment of Zero‐Valent Iron for Metal‐Contaminated Water Remediation: A Review

Ullah

Faiz

Leng

2020

CLEAN Soil Air Water

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Recently, increased industrial and agriculture activities have resulted in toxic metal ions, which has increased public concern about the quality of surface and groundwater. Various types of physical, biological, and chemical approaches have been developed to remove surface and groundwater metal ions contaminants. Among these practices, zero‐valent iron (ZVI) is the most studied reactive material for environmental clean‐up over the last two decade and so. Although ZVI can remove the contaminants even more efficiently than any other reactive materials. However, low reactivity due to its intrinsic passive layer, narrow working pH, and the loss of hydraulic conductivity due to the precipitation of metal hydroxides and metal carbonates limits its wide‐scale application. The aim of this work is to document properties, synthesis, and reaction mechanism of ZVI for the treatment of metal ions from the surface and groundwater in recent 10 years (2008–2018). So far, different modified techniques such as conjugation with support, bimetal alloying, weak magnetic field, and ZVI/oxidant coupling system have been developed to facilitate the use of ZVI in various environmental remediation scenarios. However, some challenges still remain to be addressed. Therefore, development and research in this field are needed to overcome or mitigate these limitations.

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Assessment of Long-Term Performance and Chromate Reduction Mechanisms in a Field Scale Permeable Reactive Barrier

Cited by 91 publications

References 30 publications

Progress in Understanding the Mechanism of CrVI Removal in Fe0-Based Filtration Systems

Progress in Understanding the Mechanism of CrVI Removal in Fe0-Based Filtration Systems

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

Synthesis, Mechanism, and Performance Assessment of Zero‐Valent Iron for Metal‐Contaminated Water Remediation: A Review

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