Korea Polar Research Institute (KOPRI), Incheon 21990, Republic of Korea; Department of Polar Sciences, University of Science and Technology (UST), Incheon 21990, Republic of Korea.
Department of Chemistry, Hallym University, Chuncheon, Gangwon-do 24252, Republic of Korea.
Ecotoxicol Environ Saf. 2021 Jan 15;208:111735. doi: 10.1016/j.ecoenv.2020.111735. Epub 2020 Dec 4.
The transformation between hexavalent chromium (Cr) and trivalent chromium (Cr) has a significant impact on ecosystems, as Cr has higher levels of toxicity than Cr. In this regard, a variety of Cr reduction processes occurring in natural environments have been studied extensively. In this work, we investigate the reductive transformation of Cr by ferrous ions (Fe) in ice at -20 °C, and compare the same process in water at 25 °C. The Fe-mediated reduction of Cr occurred much faster in ice than it did in water. The accelerated reduction of Cr in ice is primarily ascribed to the accumulation of Cr, Fe, and protons in the grain boundaries formed during freezing, which constitutes favorable conditions for redox reactions between Cr and Fe. 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 Cr (20 µM) by Fe in ice proceeded rapidly under various Fe concentrations (20-140 µM), pH values (2.0-5.0), and freezing temperatures (-10 to -30 °C) with a constant molar ratio of oxidized Fe to reduced Cr (3:1). This result implies that the proposed mechanism (i.e., the redox reaction between Cr and Fe in ice) can significantly contribute to the natural conversion of Cr in cold regions. The Fe-mediated Cr reduction kinetics in frozen Cr-contaminated wastewater was similar to that in frozen Cr solution. This indicates that the variety of substrates typically present in electroplating wastewater have a negligible effect on the redox reaction between Cr and Fe in ice; it also proposes that the Fe/freezing process can be used for the treatment of Cr-contaminated wastewater.
六价铬（Cr）和三价铬（Cr）之间的转化对生态系统有重大影响，因为 Cr 的毒性比 Cr 更高。在这方面，已经广泛研究了在自然环境中发生的各种 Cr 还原过程。在这项工作中，我们研究了-20°C 冰中的亚铁离子（Fe）对 Cr 的还原转化，并将相同的过程与 25°C 下的水进行了比较。Fe 介导的 Cr 在冰中的还原速度比在水中快得多。Cr 在冰中的加速还原主要归因于 Cr、Fe 和质子在冻结过程中形成的晶界中的积累，这为 Cr 和 Fe 之间的氧化还原反应创造了有利条件。这种冷冻浓缩现象通过使用邻甲酚磺酞（作为 pH 指示剂）的紫外可见光谱和共聚焦拉曼光谱得到了验证。在各种 Fe 浓度（20-140 μM）、pH 值（2.0-5.0）和冻结温度（-10 至-30°C）下，Fe 对 Cr（20 μM）的还原转化在冰中快速进行，氧化 Fe 与还原 Cr 的摩尔比保持恒定（3:1）。这一结果表明，所提出的机制（即在冰中 Cr 和 Fe 之间的氧化还原反应）可以显著促进寒冷地区 Cr 的自然转化。冷冻含 Cr 废水和冷冻 Cr 溶液中 Fe 介导的 Cr 还原动力学相似。这表明电镀废水中通常存在的各种基质对冰中 Cr 和 Fe 之间的氧化还原反应几乎没有影响；这也提出了可以使用 Fe/冻结工艺来处理含 Cr 废水。
