Enhanced oxidation of Cr(III) with the mineral transformation of CrxFe1-x(OH)3 in the presence of Mn(II): overlooked process during the reoccurrence of Cr(VI) in reduced chromite ore processing residue

IF 7.6 2区环境科学与生态学 Q1 ENVIRONMENTAL SCIENCES

Environmental Pollution Pub Date : 2025-04-28 DOI:10.1016/j.envpol.2025.126327

Shenhao Xie , Kunpeng Yang , Shuai Zhang , Jie Chen , Jiating Zhao , Lizhong Zhu

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Abstract

The reoccurrence of Cr(VI) in reduced chromium ore processing residue (rCOPR) causes secondary pollution after remediation, with Mn(II)-induced catalytic oxidation identified as one of its key contributors. The mineral transformation of Cr-Fe coprecipitate (Cr_xFe_1-x(OH)_3, dominant phase in rCOPR) tends to form goethite along with Cr(III) in alkaline environments. However, the effect of this critical process on Cr(VI) reoccurrence remains unknown and requires further investigation. Our results showed that after the mineral transformation, approximately 10 times higher concentration of Cr(VI) (2261.67 ± 108.13 μg L⁻¹) produced within 24 h than pre-transformation levels (212.92 ± 22.71 μg L⁻¹). Mn (oxyhydr)oxides (MnO_xs) produced from Mn(II) oxidation served as the direct oxidant of Cr(III). The alteration in Cr(VI) generation kinetics after the mineral transformation indicated distinct speciation patterns and interactions of Cr(III) and MnO_xs in this process. Three predominant crystalline phases in MnO_xs, hausmannite (Mn₃O₄), feitknechtite (β-MnOOH), and manganite (γ-MnOOH) were identified through XPS, XRD, SEM and TEM-EDS. Theoretical calculations revealed the hierarchical adsorption ability for Cr(III): ferrihydrite (−9.69 eV) > MnO_xs (−9.50, −9.30 eV) > goethite (−9.27 eV). The synergistic interplay between MnO_xs’ oxidation capacity and Cr(III) accessibility governed the release of Cr(VI). Our findings elucidated the kinetic process and underlying mechanisms of Cr(VI) generation induced by Mn(II) oxidation with the mineral transformation of Cr-Fe coprecipitate in Cr contaminated environments. These new insights support pollution control of Cr(VI) reoccurrence in rCOPR and may guide future research on promoting the long-term stability and safety of rCOPR.

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Mn（II）存在下CrxFe1-x(OH)3矿物转化对Cr（III）的强化氧化：Cr（VI）在还原性铬铁矿选矿渣中重现时被忽视的过程

还原铬矿处理渣（rCOPR）中Cr（VI）在修复后再次出现，造成二次污染，其中Mn（II）诱导的催化氧化是造成二次污染的主要原因之一。Cr- fe共沉淀物（CrxFe1-x(OH)3， rCOPR中的优势相）在碱性环境下随Cr（III）形成针铁矿。然而，这一关键过程对Cr（VI）再发的影响尚不清楚，需要进一步研究。结果表明，矿物转化后24 h内产生的Cr（VI）浓度（2261.67±108.13 μg·L-1）比转化前（212.92±22.71 μg·L-1）高约10倍。Mn（II）氧化产生的Mn（氧）氧化物（MnOxs）作为Cr（III）的直接氧化剂。矿物转化后Cr（VI）生成动力学的变化表明在这一过程中Cr（III）和MnOxs有不同的形态模式和相互作用。通过XPS、XRD、SEM和TEM-EDS等手段鉴定了锰氧化物中主要的三种晶相：豪氏锰矿（Mn3O4）、铁锰矿（β-MnOOH）和锰矿（γ-MnOOH）。理论计算表明，对Cr(III)：铁水合物（-9.69 eV） >的分级吸附能力；MnOxs (-9.50, -9.30 eV) >；针铁矿（-9.27 eV）；MnOxs的氧化能力与Cr（III）可及性之间的协同相互作用支配着Cr（VI）的释放。研究结果阐明了Cr污染环境中Mn（II）氧化诱导Cr（VI）生成的动力学过程及其机制。这些新发现为rCOPR中Cr（VI）的再发污染控制提供了支持，并对未来促进rCOPR长期稳定和安全的研究具有指导意义。

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来源期刊

Environmental Pollution 环境科学-环境科学

CiteScore

16.00

自引率

6.70%

发文量

2082

审稿时长

2.9 months

期刊介绍： Environmental Pollution is an international peer-reviewed journal that publishes high-quality research papers and review articles covering all aspects of environmental pollution and its impacts on ecosystems and human health. Subject areas include, but are not limited to: • Sources and occurrences of pollutants that are clearly defined and measured in environmental compartments, food and food-related items, and human bodies; • Interlinks between contaminant exposure and biological, ecological, and human health effects, including those of climate change; • Contaminants of emerging concerns (including but not limited to antibiotic resistant microorganisms or genes, microplastics/nanoplastics, electronic wastes, light, and noise) and/or their biological, ecological, or human health effects; • Laboratory and field studies on the remediation/mitigation of environmental pollution via new techniques and with clear links to biological, ecological, or human health effects; • Modeling of pollution processes, patterns, or trends that is of clear environmental and/or human health interest; • New techniques that measure and examine environmental occurrences, transport, behavior, and effects of pollutants within the environment or the laboratory, provided that they can be clearly used to address problems within regional or global environmental compartments.