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Tan X, Qi F, Liu Q, Qie H, Duan G, Lin A, Liu M, Xiao Y. Is Cr(III) re-oxidation occurring in Cr-contaminated soils after remediation: Meta-analysis and machine learning prediction. JOURNAL OF HAZARDOUS MATERIALS 2024; 465:133342. [PMID: 38150755 DOI: 10.1016/j.jhazmat.2023.133342] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/20/2023] [Revised: 11/18/2023] [Accepted: 12/20/2023] [Indexed: 12/29/2023]
Abstract
Whether Cr(III) in Cr(III)-containing sites formed after Cr(VI) reduction and stabilization remediation are re-oxidized and pose toxicity risks again has been a growing concern. In this study, 1030 data were collected to perform a meta-analysis to clarify the effects of various factors (oxidant type, soil and Cr(III) solid compound properties, aging conditions, and testing methods) on Cr(III) oxidation. We observed that the soil properties of clay, pH ≥ 8, the lower CEC capacity, easily reducible Mn content, and Cr(III) content, and the higher Eh value and Fe content can promote the re-oxidation of Cr(III). Publication bias and sensitivity analyses confirmed the stability and reliability of the meta-analysis. Subsequently, we used five machine learning algorithms to construct and optimize the models. The prediction results of the RF model (RMSE <1.36, R2 >0.71) with good algorithm performance showed that after ten years of remediation, the extractable Cr(VI) concentration in the soil was 0.0087 mg/L, indicating a negligible secondary pollution risk of Cr(III) re-oxidation. This study provides theoretical support for subsequent risk management and control after Cr(VI) soil remediation and provides a solution for the quantitative prediction of Cr(III) re-oxidation.
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Affiliation(s)
- Xiao Tan
- College of Chemical Engineering, Beijing University of Chemical Technology, Beijing 100029, People's Republic of China
| | - Fang Qi
- College of Chemical Engineering, Beijing University of Chemical Technology, Beijing 100029, People's Republic of China
| | - Qi Liu
- College of Chemical Engineering, Beijing University of Chemical Technology, Beijing 100029, People's Republic of China
| | - Hantong Qie
- College of Chemical Engineering, Beijing University of Chemical Technology, Beijing 100029, People's Republic of China
| | - Guilan Duan
- State Key Laboratory of Urban and Regional Ecology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, People's Republic of China
| | - Aijun Lin
- College of Chemical Engineering, Beijing University of Chemical Technology, Beijing 100029, People's Republic of China
| | - Meng Liu
- College of Chemical Engineering, Beijing University of Chemical Technology, Beijing 100029, People's Republic of China.
| | - Yong Xiao
- College of Chemical Engineering, Beijing University of Chemical Technology, Beijing 100029, People's Republic of China.
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Ao M, Sun S, Deng T, Zhang F, Liu T, Tang Y, Li J, Wang S, Qiu R. Natural source of Cr(VI) in soil: The anoxic oxidation of Cr(III) by Mn oxides. JOURNAL OF HAZARDOUS MATERIALS 2022; 433:128805. [PMID: 35381512 DOI: 10.1016/j.jhazmat.2022.128805] [Citation(s) in RCA: 33] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/18/2022] [Revised: 03/16/2022] [Accepted: 03/25/2022] [Indexed: 06/14/2023]
Abstract
Cr(VI) from oxidation of geogenic Cr(III) minerals is gradually becoming the primary source of Cr(VI) in soils and groundwater instead of direct emissions. Thermodynamically, natural oxidants of Cr(III) are limited to O2 and Mn oxides. The oxidation of Cr(III) occurs commonly in oxic soils but the difference in the oxidative dissolution of Cr(III) by Mn oxides in different redox soils (especially under anoxic conditions) is not fully understood and field evidence is lacking. Here, the relationship between Cr(VI) and Mn oxides in basalt-origin soil profiles under three different redox conditions (anoxic, suboxic and oxic) was studied. The oxidative dissolution of chromite was validated by synthesising δ-MnO2 that was close to biogenic Mn oxides under anoxic and oxic conditions. In anoxic soils, high levels of Cr(VI) were detected in the same horizons as those where Cr(III)-minerals co-existed with Mn(III/IV) oxides, suggesting an exclusive pathway for Cr(VI) generation through oxidation by Mn oxides where there was a deficiency of other oxidants, such as O2. In oxic soils, the highly abundant Fe oxides combined with Cr(III) to form Cr(III)-Fe(III) oxyhydroxides and Cr(VI) was generated mainly via slow oxidation by O2. The chromite oxidation experiment results also indicated that a high abundance of Mn oxides could promote chromite oxidative dissolution to generate Cr(VI), even under anoxic conditions. Additionally, the form of Cr and the reactivity and abundance of Mn oxides and reducing agents controlled the net content of Cr(VI) in the soil. This study showed that, even under reducing conditions, Cr(III) is readily oxidised by Mn oxides to generate Cr(VI) in reductant-deficient and Mn-rich soils, which may lead to the continuous introduction of Cr(VI) into groundwater and agricultural soils.
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Affiliation(s)
- Ming Ao
- School of Environmental Science and Engineering, Sun Yat-sen University, Guangzhou 510006, China
| | - Shengsheng Sun
- School of Environmental Science and Engineering, Sun Yat-sen University, Guangzhou 510006, China
| | - Tenghaobo Deng
- Institute of Quality Standard and Monitoring Technology for Agro-products of Guangdong Academy of Agricultural Sciences, Guangzhou 510640, China
| | - Feng Zhang
- School of Environmental Science and Engineering, Sun Yat-sen University, Guangzhou 510006, China
| | - Ting Liu
- Guangdong Provincial Key Laboratory of Agricultural & Rural Pollution Abatement and Environmental Safety, College of Natural Resources and Environment, South China Agricultural University, Guangzhou 510642, China
| | - Yetao Tang
- School of Environmental Science and Engineering, Sun Yat-sen University, Guangzhou 510006, China; Guangdong Provincial Key Laboratory of Environmental Pollution Control and Remediation Technology, Sun Yat-sen University, Guangzhou 510006, China
| | - Jingjing Li
- Guangdong Provincial Key Laboratory of Agricultural & Rural Pollution Abatement and Environmental Safety, College of Natural Resources and Environment, South China Agricultural University, Guangzhou 510642, China
| | - Shizhong Wang
- School of Environmental Science and Engineering, Sun Yat-sen University, Guangzhou 510006, China; Guangdong Provincial Key Laboratory of Environmental Pollution Control and Remediation Technology, Sun Yat-sen University, Guangzhou 510006, China.
| | - Rongliang Qiu
- School of Environmental Science and Engineering, Sun Yat-sen University, Guangzhou 510006, China; Guangdong Provincial Key Laboratory of Agricultural & Rural Pollution Abatement and Environmental Safety, College of Natural Resources and Environment, South China Agricultural University, Guangzhou 510642, China; Guangdong Laboratory for Lingnan Modern Agriculture, South China Agricultural University, Guangzhou 510642, China
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