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Reductive transformation of hexavalent chromium by ferrous ions in a frozen environment: mechanism, kinetics, and environmental implications

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Title
Reductive transformation of hexavalent chromium by ferrous ions in a frozen environment: mechanism, kinetics, and environmental implications
Other Titles
극한지역 철이온에 의한 독성 6가 크롬 제거기작 연구
Authors
Nguyen, Quoc Anh
Kim, Bomi
Chung, Hyun Young
Nguyen, Anh Quoc Khuong
Kim, Jungwon
Kim, Kitae
Subject
Environmental Sciences & Ecology; Toxicology
Keywords
Ice chemistry; Hexavalent chromium; Ferrous ion; Natural detoxification; Cr6+-contaminated wastewater
Issue Date
2021-01
Citation
Nguyen, Quoc Anh, et al. 2021. "Reductive transformation of hexavalent chromium by ferrous ions in a frozen environment: mechanism, kinetics, and environmental implications". ECOTOXICOLOGY AND ENVIRONMENTAL SAFETY, 208(1): 1-8.
Abstract
The transformation between hexavalent chromium (Cr6+) and trivalent chromium (Cr3+) has a significant impact on ecosystems, as Cr6+ has higher levels of toxicity than Cr3+. In this regard, a variety of Cr6+ reduction processes occurring in natural environments have been studied extensively. In this work, we investigate the reductive transformation of Cr6+ by ferrous ions (Fe2+) in ice at-20 degrees C, and compare the same process in water at 25 degrees C. The Fe(2+-m)ediated reduction of Cr6+ occurred much faster in ice than it did in water. The accelerated reduction of Cr6+ in ice is primarily ascribed to the accumulation of Cr6+, Fe2+, and protons in the grain boundaries formed during freezing, which constitutes favorable conditions for redox reactions between Cr6+ and Fe2+. This freeze concentration phenomenon was verified using UV-visible spectroscopy with o-cresolsulfonephthalein (as a pH indicator) and confocal Raman spectroscopy. The reductive transformation of Cr6+ (20 mu M) by Fe2+ in ice proceeded rapidly under various Fe2+ concentrations (20-140 mu M), pH values (2.0-5.0), and freezing temperatures (-10 to-30 degrees C) with a constant molar ratio of oxidized Fe2+ to reduced Cr6+ (3:1). This result implies that the proposed mechanism (i.e., the redox reaction between Cr6+ and Fe2+ in ice) can significantly contribute to the natural conversion of Cr6+ in cold regions. The Fe2+-mediated Cr6+ reduction kinetics in frozen Cr(6+)contaminated wastewater was similar to that in frozen Cr6+ solution. This indicates that the variety of substrates typically present in electroplating wastewater have a negligible effect on the redox reaction between Cr6+ and Fe2+ in ice; it also proposes that the Fe2+/freezing process can be used for the treatment of Cr6+-contaminated wastewater.
URI
https://repository.kopri.re.kr/handle/201206/11974
DOI
http://dx.doi.org/10.1016/j.ecoenv.2020.111735
Appears in Collections  
2020-2020, Investigation of ice microstructure properties for developing low-temperature purification and environment/energy materials (20-20) / Kim, Kitae (PE20030)
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