Aerobic Fe transformation induced decrease in the adsorption and enhancement in the reduction of Cr(VI) by humic acid-ferric iron coprecipitates.

Journal of hazardous materials Pub Date : 2024-10-05 Epub Date: 2024-08-22 DOI:10.1016/j.jhazmat.2024.135595
Hui Wang, Fengping Liu, Yankun Zhang, Xueying Gong, Jinqi Zhu, Wenbing Tan, Ying Yuan, Jia Zhang, Honghan Chen, Beidou Xi
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Abstract

Humic substance (HS)-ferric iron (Fe(III)) coprecipitates are widespread organo-mineral associations in soils and aquifers and have the capacity to immobilize and detoxify Cr(VI). These coprecipitates undergo transformation owing to their thermodynamic instability; however, the effects of this transformation on their environmental behaviors remain unclear, particularly in aerobic environments. In this study, the aerobic transformation of humic acid (HA)-Fe(III) coprecipitates, a representative of HS-Fe(III) coprecipitates, was simulated. The environmental effect was then evaluated after conducting an adsorption-reduction batch experiment toward Cr(VI). The aerobic transformation characteristics, as well as the adsorption/reduction capacity of HA-Fe(III) coprecipitates, were found to depend strongly on their structures. In ferrihydrite (Fh)-like coprecipitates, amorphous Fh is readily transformed into crystalline hematite and goethite at aerobic environments, leading to a much lower specific surface area and adsorption capacity. However, this increasing degree of crystallization enhanced the inductive reduction ability towards Cr(VI) owing to the more significant shift of electron pairs in the FeOC bond toward the HA direction. In HS-like coprecipitates, Fe(III) always serves as a cation bridge connecting HA molecules, but can be reduced to Fe(II) by the associated HA after aerobic transformation. The produced Fe(II), therefore, drove the reduction of the adsorbed Cr(VI). These findings emphasize the pivotal role of aerobic transformation in enhancing the reduction capacity for Cr(VI), which opens a new avenue for the development of in-situ remediation agents for Cr(VI)-contaminated sites.

有氧铁转化导致腐殖酸-铁共沉淀物对六价铬的吸附减少和还原增强。
腐殖质(HS)-铁(Fe(III))共沉淀物是土壤和含水层中广泛存在的有机矿物结合体,具有固定和解毒六价铬的能力。由于其热力学不稳定性,这些共沉淀会发生转化;然而,这种转化对其环境行为的影响仍不清楚,尤其是在有氧环境中。本研究模拟了腐植酸(HA)-铁(III)共沉淀物(HS-铁(III)共沉淀物的代表)的有氧转化过程。然后在对六价铬进行吸附还原批量实验后,对其环境效应进行了评估。研究发现,HA-Fe(III) 共沉淀的好氧转化特性以及吸附/还原能力在很大程度上取决于其结构。在类似于水铁矿(Fh)的共沉淀物中,无定形的 Fh 很容易在有氧环境中转化为结晶赤铁矿和高铁铁矿,从而导致比表面积和吸附容量大大降低。然而,结晶程度的提高会增强对 Cr(VI) 的感应还原能力,这是因为 FeOC 键中的电子对向 HA 方向发生了更显著的移动。在类似 HS 的共沉淀物中,Fe(III) 始终是连接 HA 分子的阳离子桥,但在有氧转化后会被相关的 HA 还原成 Fe(II)。因此,生成的 Fe(II) 推动了吸附的 Cr(VI) 的还原。这些发现强调了有氧转化在增强六价铬还原能力方面的关键作用,为开发六价铬污染场地的原位修复剂开辟了一条新途径。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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