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Guo J, Wang D, Shi Y, Lyu H, Tang J. Minor chromium passivation of S-ZVI enhanced the long-term dechlorination performance of trichlorethylene: Effects of corrosion and passivation on the reactivity and selectivity. WATER RESEARCH 2024; 249:120973. [PMID: 38071903 DOI: 10.1016/j.watres.2023.120973] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/31/2023] [Revised: 11/14/2023] [Accepted: 12/03/2023] [Indexed: 01/03/2024]
Abstract
The corrosion and surface passivation of sulfidized zero-valent iron (S-ZVI) by common groundwater ions and contaminants are considered to be the most challenging aspects in the application of S-ZVI for remediation of chlorinated contaminants. This study investigated the impacts of corrosive chloride (Cl-) and passivation of hexavalent chromium (Cr(VI)) on the long-term reactivity, selectivity, corrosion behavior, and physicochemical properties during the 60-day aging process of S-ZVI. Although the co-existing of Cl- promoted the initial reactivity of S-ZVI, the rapid consumption of Fe° content shortened the reactive lifetime owing to the insufficient electron capacity. Severe passivation by Cr(VI) (30 mg L-1) preserved the Fe° content but significantly interfered with the reductive sulfur species, resulting in an increase in electron transfer resistance. In comparison, minor passivated S-ZVI (5.0 mg L-1 Cr(VI)) inhibited the hydrogen evolution while concurrently mitigating the further oxidation of the reductive iron and sulfur species, which significantly enhanced the long-term reactivity and selectivity of S-ZVI. Furthermore, the enhancement effect of minor passivation could be detected in the aging processes of one-step, two-step, and mechanochemically synthesized S-ZVI particles with different S/Fe ratios and precursors, which further verified the advantages of minor passivation. This observation is inspirable for the development of innovative strategies for environmental remediation by S-ZVI-based materials.
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Affiliation(s)
- Jiaming Guo
- MOE Key Laboratory of Pollution Processes and Environmental Criteria/Tianjin Engineering Center of Environmental Diagnosis and Contamination Remediation, College of Environmental Science and Engineering, Nankai University, Tianjin 300350, China
| | - Dong Wang
- Environmental Protection Institute, SINOPEC Beijing Research Institute of Chemical Industry, Beijing 100013, China
| | - Yinghao Shi
- MOE Key Laboratory of Pollution Processes and Environmental Criteria/Tianjin Engineering Center of Environmental Diagnosis and Contamination Remediation, College of Environmental Science and Engineering, Nankai University, Tianjin 300350, China
| | - Honghong Lyu
- Tianjin Key Laboratory of Clean Energy and Pollution Control, School of Energy and Environmental Engineering, Hebei University of Technology, Tianjin 300401, China.
| | - Jingchun Tang
- MOE Key Laboratory of Pollution Processes and Environmental Criteria/Tianjin Engineering Center of Environmental Diagnosis and Contamination Remediation, College of Environmental Science and Engineering, Nankai University, Tianjin 300350, China.
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2
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Wang A, Hou J, Xu Q, Wu J, Xing B. Green synthesis of zero valent iron using tannins to activate persulfate for sulfamethoxazole degradation. ENVIRONMENTAL POLLUTION (BARKING, ESSEX : 1987) 2023; 336:122418. [PMID: 37625770 DOI: 10.1016/j.envpol.2023.122418] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/18/2023] [Revised: 08/17/2023] [Accepted: 08/18/2023] [Indexed: 08/27/2023]
Abstract
Majority zero-valent iron (ZVI) materials are prepared by reducing agents in liquid phase, resulting in the high environmental pollution and poor particle size distribution uniformity. Therefore, this study employed a green synthesis method to prepare ZVI. Tannins (TA) with phenolic hydroxyl groups that are characterized by strong reducing capacity were employed to synthesize ZVI (TA@ZVI). The dispersity and stability of ZVI was improved by TA, which inhibited the agglomeration of ZVI. Meanwhile, the specific surface area of TA@ZVI was higher than chemical prepared ZVI, increasing the reactive sites. The organic matter components enriched on TA could promote the adsorption of pollutants and complex with Fe(II/III) to enhance the reactivity of TA@ZVI. Also, the polyphenol structure in TA was oxidized to quinone, which facilitated electron transport. In order further test the performance of TA@ZVI, SMX was chosen as a target pollutant to study the oxidative degradation performance of TA@ZVI. SO4•- degraded about 16.4%-25.5% SMX and •OH degraded about 49.8%-63.9% SMX in the pH range of 4-6 while •OH played a dominant role in the neutral and alkaline conditions. Moreover, the presence of TA reduced Fe(III) to Fe(II) and promoted the release of Fe(II), providing a continuous source of •OH for the oxidative degradation of SMX. Besides, the conversion of Fe(II/III) was accelerated due to TA, which delayed the formation of passivation layer. Thus, TA enhanced the antioxidant capacity of ZVI. Generally, this study provided an environmental-friendly technology to synthesize and improve the reactivity of ZVI.
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Affiliation(s)
- Anqi Wang
- Key Laboratory of Integrated Regulation and Resources Development on Shallow Lakes of Ministry of Education, College of Environment, Hohai University, Nanjing, 210098, China
| | - Jun Hou
- Key Laboratory of Integrated Regulation and Resources Development on Shallow Lakes of Ministry of Education, College of Environment, Hohai University, Nanjing, 210098, China
| | - Qichen Xu
- Key Laboratory of Integrated Regulation and Resources Development on Shallow Lakes of Ministry of Education, College of Environment, Hohai University, Nanjing, 210098, China
| | - Jun Wu
- Key Laboratory of Integrated Regulation and Resources Development on Shallow Lakes of Ministry of Education, College of Environment, Hohai University, Nanjing, 210098, China.
| | - Baoshan Xing
- Stockbridge School of Agriculture, University of Massachusetts, Amherst, MA, 01003, USA
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3
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Metzgen AD, Dahmke A, Ebert M. Significance of temperature as a key driver in ZVI PRB applications for PCE degradation. JOURNAL OF CONTAMINANT HYDROLOGY 2023; 258:104236. [PMID: 37660464 DOI: 10.1016/j.jconhyd.2023.104236] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/12/2023] [Revised: 07/14/2023] [Accepted: 08/25/2023] [Indexed: 09/05/2023]
Abstract
We report on the potential of elevated groundwater temperatures and zero-valent iron permeable reactive barriers (ZVI PRBs), for example, through a combination with underground thermal energy storage (UTES), to achieve enhanced remediation of chlorinated hydrocarbon (CHC) contaminated groundwater. Building on earlier findings concerning deionized solutions, we created a database for mineralized groundwater based on temperature dependence of tetrachloroethylene (PCE) degradation using two popular ZVIs (i.e., Gotthart-Maier cast iron [GM] and ISPAT sponge iron [IS]) in column experiments at 25 °C-70 °C to establish a temperature-dependent ZVI PRB dimensioning approach. Scenario analysis revealed that a heated ZVI PRB system in a moderate temperature range up to 40 °C showed the greatest efficiency, with potential material savings of ~55% to 75%, compared to 10 °C, considering manageability and longevity. With a 25 °C-70 °C temperature increase, rate coefficients of PCE degradation increased from 0.4 ± 0.0 h-1 to 2.9 ± 2.2 h-1 (GM) and 0.1 ± 0.1 h-1 to 1.8 ± 0.0 h-1 (IS), while TCE rate coefficients increased from 0.6 ± 0.1 h-1 to 5.1 ± 3.9 h-1 at GM. Activation energies for PCE degradation yielded 32 kJ mol-1 (GM) and 56 kJ mol-1 (IS). Temperature-dependent anaerobic iron corrosion was key in regulating mineral precipitation and passivation of the iron surface as well as porosity reduction due to gas production.
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Affiliation(s)
- Adrian D Metzgen
- Department of Applied Geology, Aquatic Geochemistry and Hydrogeology, Institute of Geoscience, Kiel University, Ludewig-Meyn-Straße 10, 24118 Kiel, Germany.
| | - Andreas Dahmke
- Department of Applied Geology, Aquatic Geochemistry and Hydrogeology, Institute of Geoscience, Kiel University, Ludewig-Meyn-Straße 10, 24118 Kiel, Germany
| | - Markus Ebert
- Department of Applied Geology, Aquatic Geochemistry and Hydrogeology, Institute of Geoscience, Kiel University, Ludewig-Meyn-Straße 10, 24118 Kiel, Germany
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4
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Gong L, Chen J, Hu Y, He K, Bylaska EJ, Tratnyek PG, He F. Degradation of Chloroform by Zerovalent Iron: Effects of Mechanochemical Sulfidation and Nitridation on the Kinetics and Mechanism. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2023. [PMID: 37339398 DOI: 10.1021/acs.est.3c02039] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/22/2023]
Abstract
Chloroform (CF) is a widely used chemical reagent and disinfectant and a probable human carcinogen. The extensive literature on halocarbon reduction with zerovalent iron (ZVI) shows that transformation of CF is slow, even with nano, bimetallic, sulfidated, and other modified forms of ZVI. In this study, an alternative method of ZVI modification─involving simultaneous sulfidation and nitridation through mechanochemical ball milling─was developed and shown to give improved degradation of CF (i.e., higher degradation rate and inhibited H2 evolution reaction). The composite material (denoted as S-N(C)-ZVI) gave synergistic effects of nitridation and sulfidation on CF degradation. A complete chemical reaction network (CRN) analysis of CF degradation suggests that O-nucleophile-mediated transformation pathways may be the main route for the formation of the terminal nonchlorinated products (formate, CO, and glycolic polymers) that have been used to explain the undetected products needed for mass balance. Material characterizations of the ZVI recovered after batch experiments showed that sulfidation and nitridation promoted the formation of Fe3O4 on the S-N(C)-ZVI particles, and the effect of aging on CF degradation rates was minor for S-N(C)-ZVI. The synergistic benefits of sulfidation and nitridation on CF degradation were also observed in experiments performed with groundwater.
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Affiliation(s)
- Li Gong
- College of Environment, Zhejiang University of Technology, Hangzhou 310014, China
- School of Environmental Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, China
| | - Jingting Chen
- College of Environment, Zhejiang University of Technology, Hangzhou 310014, China
| | - Yao Hu
- College of Environment, Zhejiang University of Technology, Hangzhou 310014, China
| | - Kai He
- College of Environment, Zhejiang University of Technology, Hangzhou 310014, China
| | - Eric J Bylaska
- Physical Sciences Division, Pacific Northwest National Laboratory, Richland, Washington, 99354, United States
| | - Paul G Tratnyek
- OHSU-PSU School of Public Health, Oregon Health & Science University, Portland, Oregon 97239, United States
| | - Feng He
- College of Environment, Zhejiang University of Technology, Hangzhou 310014, China
- Institute of Environmental Processes and Pollution Control, and School of Environment and Civil Engineering, Jiangnan University, Wuxi 214122, China
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5
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Hu L, Zhang P, Xu X, Ren J, Zhao L, Qiu H, Cao X. Immobilization of arsenic in different contaminated soils by zero-valent iron-embedded biochar: Effect of soil characteristics and treatment conditions. THE SCIENCE OF THE TOTAL ENVIRONMENT 2023; 868:161597. [PMID: 36646221 DOI: 10.1016/j.scitotenv.2023.161597] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/10/2022] [Revised: 01/09/2023] [Accepted: 01/10/2023] [Indexed: 06/17/2023]
Abstract
Although zero-valent iron-embedded biochar (ZVI-BC) has been proposed as an effective amendment for arsenic (As)-contaminated soils, the impacts of soil characteristics and treatment conditions on the remediation process remained poorly understood. Herein, the immobilization of As in four As-contaminated soils (i.e., smelting soil, storage soil, agricultural soil, and mining soil) by ZVI-BC under different amendment dosages, cultivation temperatures, and soil moisture contents were investigated. ZVI-BC showed high As immobilization capacity in all four soils via forming the AsFe co-precipitation, and the liable As was reduced by 82.4-97.0 % with a 2 % (w/w) amendment. The higher temperature could raise the concentration of liable As in all four soils, especially for the storage soil, in which liable As at 35 °C was almost 3 times of that at 25 °C after 50-days treatment, because the elevated temperature enhanced the destruction of the generated AsFe coprecipitation as well as the desorption of As in soils. Too much soil moisture was unfavorable for the As immobilization after 50-days treatment. Flooding tended to inhibit the community diversity of As-detoxicated bacteria, e.g., Halomonas, Bryobacter, and Anaerolinea, thus resulting in the release of liable As. According to the correlation analysis, the crucial influencing factor for As immobilization was different in four soils, which was determined by the soil properties and proportion of liable As. Our study indicates that ZVI-BC is an effective amendment for As immobilization under various conditions, and the biogeochemical processes of As-associated Fe minerals determine the As immobilization during amendment.
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Affiliation(s)
- Liyang Hu
- School of Environmental Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, China
| | - Pengyu Zhang
- School of Environmental Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, China
| | - Xiaoyun Xu
- School of Environmental Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, China.
| | - Jia Ren
- School of Environmental Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, China
| | - Ling Zhao
- School of Environmental Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, China
| | - Hao Qiu
- School of Environmental Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, China
| | - Xinde Cao
- School of Environmental Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, China; Shanghai Engineering Research Center for Solid Waste Treatment and Resource Recovery, Shanghai 200240, China
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Wang A, Hou J, Tao C, Miao L, Wu J, Xing B. Performance Enhancement of Biogenetic Sulfidated Zero-Valent Iron for Trichloroethylene Degradation: Role of Extracellular Polymeric Substances. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2023; 57:3323-3333. [PMID: 36729963 DOI: 10.1021/acs.est.2c07289] [Citation(s) in RCA: 10] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/18/2023]
Abstract
Chemical sulfidation has been considered as an effective strategy to improve the reactivity of zero-valent iron (S-ZVI). However, sulfidation is a widespread biogeochemical process in nature, which inspired us to explore the biogenetic sulfidation of ZVI (BS-ZVI) with sulfate-reducing bacteria (SRB). BS-ZVI could degrade 96.3% of trichloroethylene (TCE) to acetylene, ethene, ethane, and dichloroethene, comparable to S-ZVI (97.0%) with the same S/Fe ratio (i.e., 0.1). However, S-ZVI (0.21 d-1) exhibited a faster degradation rate than BS-ZVI (0.17 d-1) based on pseudo-first-order kinetic fitting due to extracellular polymeric substances (EPSs) excreted from SRB. Organic components of EPSs, including polysaccharides, humic acid-like substances, and proteins in BS-ZVI, were detected with 3D-EEM spectroscopy and FT-IR analysis. The hemiacetal groups and redox-activated protein in EPS did not affect TCE degradation, while the acetylation degree of EPS increased with the concentration of ZVI and S/Fe, thus inhibiting the TCE degradation. A low concentration of HA-like substances attached to BS-ZVI materials promoted electron transport. However, EPS formed a protective layer on the surface of BS-ZVI materials, reducing its TCE reaction rate. Overall, this study showed a comparable performance enhancement of ZVI toward TCE degradation through biogenetic sulfidation and provided a new alternative method for the sulfidation of ZVI.
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Affiliation(s)
- Anqi Wang
- Key Laboratory of Integrated Regulation and Resources Development on Shallow Lakes of Ministry of Education, College of Environment, Hohai University, Nanjing210098, China
| | - Jun Hou
- Key Laboratory of Integrated Regulation and Resources Development on Shallow Lakes of Ministry of Education, College of Environment, Hohai University, Nanjing210098, China
| | - ChunMei Tao
- Lianyungang Water Conservancy Bureau (Director of Engineering Technology Center), 9 Lingzhou East Road, Haizhou District, Lianyungang22206, China
| | - Lingzhan Miao
- Key Laboratory of Integrated Regulation and Resources Development on Shallow Lakes of Ministry of Education, College of Environment, Hohai University, Nanjing210098, China
| | - Jun Wu
- Key Laboratory of Integrated Regulation and Resources Development on Shallow Lakes of Ministry of Education, College of Environment, Hohai University, Nanjing210098, China
| | - Baoshan Xing
- Stockbridge School of Agriculture, University of Massachusetts, Amherst, Massachusetts01003, United States
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Konadu-Amoah B, Hu R, Ndé-Tchoupé AI, Gwenzi W, Noubactep C. Metallic iron (Fe 0)-based materials for aqueous phosphate removal: A critical review. JOURNAL OF ENVIRONMENTAL MANAGEMENT 2022; 315:115157. [PMID: 35526394 DOI: 10.1016/j.jenvman.2022.115157] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/24/2022] [Revised: 04/06/2022] [Accepted: 04/22/2022] [Indexed: 06/14/2023]
Abstract
The discharge of excessive phosphate from wastewater sources into the aquatic environment has been identified as a major environmental threat responsible for eutrophication. It has become essential to develop efficient but affordable techniques to remove excess phosphate from wastewater before discharging into freshwater bodies. The use of metallic iron (Fe0) as a reactive agent for aqueous phosphate removal has received a wide attention. Fe0 in-situ generates positively charged iron corrosion products (FeCPs) at pH > 4.5, with high binding affinity for anionic phosphate. This study critically reviews the literature that focuses on the utilization of Fe0-based materials for aqueous phosphate removal. The fundamental science of aqueous iron corrosion and historical background of the application of Fe0 for phosphate removal are elucidated. The main mechanisms for phosphate removal are identified and extensively discussed based on the chemistry of the Fe0/H2O system. This critical evaluation confirms that the removal process is highly influenced by several operational factors including contact time, Fe0 type, influent geochemistry, initial phosphate concentration, mixing conditions, and pH value. The difficulty in comparing independent results owing to diverse experimental conditions is highlighted. Moreover, contemporary research in progress including Fe0/oxidant systems, nano-Fe0 application, Fe0 material selection, desorption studies, and proper design of Fe0-based systems for improved phosphate removal have been discussed. Finally, potential strategies to close the loop in Fe0-based phosphate remediation systems are discussed. This review presents a science-based guide to optimize the efficient design of Fe0-based systems for phosphate removal.
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Affiliation(s)
- Bernard Konadu-Amoah
- School of Earth Science and Engineering, Hohai University, Fo Cheng Xi Road 8, Nanjing, 211100, China.
| | - Rui Hu
- School of Earth Science and Engineering, Hohai University, Fo Cheng Xi Road 8, Nanjing, 211100, China.
| | - Arnaud Igor Ndé-Tchoupé
- School of Earth Science and Engineering, Hohai University, Fo Cheng Xi Road 8, Nanjing, 211100, China.
| | - Willis Gwenzi
- Biosystems and Environmental Engineering Research Group, Department of Agricultural and Biosystems Engineering, University of Zimbabwe, P.O. Box MP167, Mount Pleasant, Harare, Zimbabwe.
| | - Chicgoua Noubactep
- School of Earth Science and Engineering, Hohai University, Fo Cheng Xi Road 8, Nanjing, 211100, China; Centre for Modern Indian Studies (CeMIS), University of Göttingen, Waldweg 26, 37073, Göttingen, Germany; Department of Water and Environmental Science and Engineering, Nelson Mandela African Institution of Science and Technology, Arusha P.O. Box 447, Tanzania; Faculty of Science and Technology, Campus of Banekane, Université des Montagnes, P.O. Box 208, Bangangté, Cameroon.
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Metzgen AD, Dahmke A, Ebert M. Temperature Effects on PCE Degradation on ZVI in Column Experiments with Deionized Water. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2022; 56:10084-10094. [PMID: 35786861 DOI: 10.1021/acs.est.2c01235] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
The effects of rising groundwater temperatures on zerovalent iron (ZVI)-based remediation techniques will be critical in accelerating chlorinated hydrocarbon (CHC) degradation and side reactions. Therefore, tetrachloroethylene (PCE) degradation with three ZVIs widely used in permeable reactive barriers (Gotthart-Maier cast iron [GM], Peerless cast iron [PL], and ISPAT sponge iron [IS]) was evaluated at 10-70 °C in deionized water. From 10 to 70 °C, PCE degradation half-lives decreased from 25 ± 2 to 0.9 ± 0.1 h (PL), 24 ± 3 to 0.7 ± 0.1 h (GM), and 2.5 ± 0.01 to 0.3 ± 0.005 h (IS). Trichloroethylene (TCE) degradation half-lives at PL and GM decreased from 14.3 ± 3 to 0.2 ± 0.1 h (PL) and 7.6 ± 2 to 0.4 ± 0.1 h (GM). This acceleration of CHC degradation and the stronger shift toward reductive β-elimination reduced the concentration of potentially harmful metabolites with increasing temperatures. PCE and TCE degradation yields an activation energy of 28 (IS), 58 and 40 kJ mol-1 (GM), and 62 and 53 kJ mol-1 (PL). Hydrogen gas production by ZVI corrosion increased by 3 orders of magnitude from 10 to 70 °C, and an increased chance of gas clogging was observed at high temperatures.
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Affiliation(s)
- Adrian D Metzgen
- Department of Applied Geology, Aquatic Geochemistry and Hydrogeology, Institute of Geoscience, Kiel University, Ludewig-Meyn-Straße 10, 24118 Kiel, Germany
| | - Andreas Dahmke
- Department of Applied Geology, Aquatic Geochemistry and Hydrogeology, Institute of Geoscience, Kiel University, Ludewig-Meyn-Straße 10, 24118 Kiel, Germany
| | - Markus Ebert
- Department of Applied Geology, Aquatic Geochemistry and Hydrogeology, Institute of Geoscience, Kiel University, Ludewig-Meyn-Straße 10, 24118 Kiel, Germany
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9
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Metallic Iron for Water Remediation: Plenty of Room for Collaboration and Convergence to Advance the Science. WATER 2022. [DOI: 10.3390/w14091492] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
Scientific collaboration among various geographically scattered research groups on the broad topic of “metallic iron (Fe0) for water remediation” has evolved greatly over the past three decades. This collaboration has involved different kinds of research partners, including researchers from the same organization and domestic researchers from non-academic organizations as well as international partners. The present analysis of recent publications by some leading scientists shows that after a decade of frank collaboration in search of ways to improve the efficiency of Fe0/H2O systems, the research community has divided itself into two schools of thought since about 2007. Since then, progress in knowledge has stagnated. The first school maintains that Fe0 is a reducing agent for some relevant contaminants. The second school argues that Fe0 in-situ generates flocculants (iron hydroxides) for contaminant scavenging and reducing species (e.g., FeII, H2, and Fe3O4), but reductive transformation is not a relevant contaminant removal mechanism. The problem encountered in assessing the validity of the views of both schools arises from the quantitative dominance of the supporters of the first school, who mostly ignore the second school in their presentations. The net result is that the various derivations of the original Fe0 remediation technology may be collectively flawed by the same mistake. While recognizing that the whole research community strives for the success of a very promising but unestablished technology, annual review articles are suggested as an ingredient for successful collaboration.
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