Permeable Reactive Barriers with Zero-Valent Iron and Pumice for Remediation of Groundwater Contaminated with Multiple Heavy Metals

Njaramba, Lewis Kamande; Park, Jung-Bo; Lee, Chang‐Soo; Nzioka, Antony Mutua; Kim, Young‐Ju

doi:10.1089/ees.2020.0109

Cited by 8 publications

(8 citation statements)

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“…Assumptions for reductive transformation Counter-arguments against the reductive transformation concept RCl reduction is an electrochemical process (Matheson and Tratnyek 1994;Weber 1996) Oxide scale is a non-conductive barrier; thus, electron transfer is blocked RCl must diffuse across the oxide scale to the Fe 0 surface. This migration cannot be quantitative A fraction of electrons from Fe 0 is transferred to RCl (electron efficiency concept) (Liu et al 2013) No RCl can receive electrons from Fe 0 (Hu et al 2021b) RCl is reduced by an indirect mechanism (Jiao et al 2009) Shaking or stirring experimental vessels in batch studies accelerates mass transfer (Lee et al 2004) In field Fe 0 PRBs, diffusion controls all transport processes in the vicinity of Fe 0 (Hu et al 2021b) The Fe 0 amount for a PRB can be determined from the stoichiometry of the electrochemical reaction between Fe 0 and RCl (Sarr 2001) Non-reducible contaminants such as Zn 2+ (Njaramba et al 2021) and methylene blue (Konadu-Amoah et al 2022) have been quantitatively removed in Fe 0 /H 2 O systems Contaminants and O 2 are exclusively reduced by an indirect mechanism (Whitney 1903;Hu et al 2021b) The volumetric expansive nature of the corrosion process must be considered (Caré et al 2013;Domga et al 2015;Yang et al 2021;Tao et al 2022) 4. Because of the very low solubility of Fe II and Fe III species, iron oxides and hydroxides must precipitate close to the Fe 0 surface and cannot migrate far.…”

Section: Discussionmentioning

confidence: 99%

Realizing the potential of metallic iron for the mitigation of toxics: flee or adapt?

Konadu-Amoah

Cao

et al. 2022

Appl Water Sci

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Metallic iron (Fe0) has been increasingly used to remove toxics from water over the past three decades. However, the idea that metallic iron (Fe0) is not an environmental reducing agent has been vigorously refuted. Researchers presenting their findings in a scientific journal have to accept the burden of proving that their argument has any validity. This 30-year-lasting discussion within the Fe0 remediation community is alien to electro-chemists, as it is a century-old knowledge. Nevertheless, the peer-reviewed literature on “remediation using Fe0” seems to be dominated by evaluators thinking that Fe0 is a reducing agent. This communication challenges the view that Fe0 donates any electron to any dissolved species. The sole goal is to reconcile a proven efficient technology with its scientific roots and enable the design of better Fe0 remediation systems.

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Section: Discussionmentioning

confidence: 99%

Realizing the potential of metallic iron for the mitigation of toxics: flee or adapt?

Konadu-Amoah

Cao

et al. 2022

Appl Water Sci

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“…These applications have been discussed in earlier papers (Naseri et al, 2017;Antia, 2020, Huang et al, 2021a, thus, a detailed review is beyond the scope of the present paper. In summary, typical applications of Fe0-based remediation systems documented in literature include: i) decentralized safe drinking water provision in low-income settings (Huang et al, 2021b;Mueller et al, 2021), ii) industrial wastewater treatment systems (Li et al, 2019;Kulkarni et al, 2020), iii) recovery of heavy metals from industrial effluents (Vollprecht et al, 2018;Calabrò et al, 2021;Noubactep, 2021), iv) urban stormwater treatment (Rahman et al, 2013;Tian et al, 2019), v) treatment of drainage water from agroecosystems (Das et al, 2017;Lanet et al, 2021), vi) subsurface permeable reactive barriers (PRBs) for remediation of contaminated groundwater (Thakur et al, 2020;Njaramba et al, 2021, Wang et al, 2022, and vii) treatment of domestic wastewater (Wakatsuki et al, 1993;Latrach et al, 2018).…”

Section: The Chemistry Of the Fe0/h2o Systemmentioning

confidence: 99%

“…Permeability loss describes the time-dependent decrease of the hydraulic conductivity of Fe 0 -based filter (Caré et al, 2013, Domga et al, 2015, Cao et al, 2020, Antia, 2020, Njaramba et al, 2021. While considering Fe 0 as the reducing agent and corrosion by water as a side reaction, permeability loss has been mainly attributed to the precipitation of foreign species evolving for instance CO 3 2− or HCO 3− (Henderson and Demond 2007;Henderson and Demond, 2011;Santisukkasaem and Das, 2019).…”

Section: Permeability Lossmentioning

confidence: 99%

Metallic Iron for Environmental Remediation: The Fallacy of the Electron Efficiency Concept

Ndé-Tchoupé

Cao

et al. 2021

Front. Environ. Chem.

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The suitability of remediation systems using metallic iron (Fe0) has been extensively discussed during the past 3 decades. It has been established that aqueous Fe0 oxidative dissolution is not caused by the presence of any contaminant. Instead, the reductive transformation of contaminants is a consequence of Fe0 oxidation. Yet researchers are still maintaining that electrons from the metal body are involved in the process of contaminant reduction. According to the electron efficiency concept, electrons from Fe0 should be redistributed to: i) contaminants of concern (COCs), ii) natural reducing agents (e.g., H2O, O2), and/or iii) reducible co-contaminants (e.g. NO3-). The electron efficiency is defined as the fraction of electrons from Fe0 oxidation which is utilized for the reductive transformations of COCs. This concept is in frontal contradiction with the view that Fe0 is not directly involved in the process of contaminant reduction. This communication recalls the universality of the concept that reductive processes observed in remediation Fe0/H2O systems are mediated by primary (e.g., FeII, H/H2) and secondary (e.g., Fe3O4, green rusts) products of aqueous iron corrosion. The critical evaluation of the electron efficiency concept suggests that it should be abandoned. Instead, research efforts should be directed towards tackling the real challenges for the design of sustainable Fe0-based water treatment systems based on fundamental mechanisms of iron corrosion.

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“…However, over the years, Fe 0 filters have been designed on a pragmatic basis, often without critical evaluation of the published works to enable the advancement of the technology [23][24][25][26][27][28][29][30][31]. Accordingly, although it was known before 1883 that Fe 0 filters clog because of cementation between gravel/sand and Fe 0 particles [3,19,32], the post-1990 research on Fe 0 filtration continued using pure Fe 0 beds (100% Fe 0 ) [33,34]. Moreover, pretreatment zones with up to 50% Fe 0 (w/w) were tested as oxygen scavengers [34][35][36].…”

Section: Introductionmentioning

confidence: 99%

“…Accordingly, although it was known before 1883 that Fe 0 filters clog because of cementation between gravel/sand and Fe 0 particles [3,19,32], the post-1990 research on Fe 0 filtration continued using pure Fe 0 beds (100% Fe 0 ) [33,34]. Moreover, pretreatment zones with up to 50% Fe 0 (w/w) were tested as oxygen scavengers [34][35][36]. This occurred despite the fact that, under field conditions, quantitative contaminant removal in a field Fe 0 reactive permeable reactive barrier containing only 22% Fe 0 (w/w) was reported [23,37,38].…”

Section: Introductionmentioning

confidence: 99%

The Suitability of Hybrid Fe0/Aggregate Filtration Systems for Water Treatment

Tao

Yang

Cui

et al. 2022

Water

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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 these 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 Fe0/aggregate/H2O systems 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.

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Permeable Reactive Barriers with Zero-Valent Iron and Pumice for Remediation of Groundwater Contaminated with Multiple Heavy Metals

Cited by 8 publications

References 50 publications

Realizing the potential of metallic iron for the mitigation of toxics: flee or adapt?

Realizing the potential of metallic iron for the mitigation of toxics: flee or adapt?

Metallic Iron for Environmental Remediation: The Fallacy of the Electron Efficiency Concept

The Suitability of Hybrid Fe0/Aggregate Filtration Systems for Water Treatment

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