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      Green remediation of Cd and Hg contaminated soil using humic acid modified montmorillonite: Immobilization performance under accelerated ageing conditions.

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          Abstract

          Solidification/Stabilization (S/S) is an effective way to immobilize toxic metals in contaminated soil. However, utilization of ordinary Portland cement (PC) in this process has raised environmental concerns owing to the high carbon footprint from PC manufacturing and the risk of toxic element leaching in the long term. Hence there is an urgent need to seek for "green" immobilization approaches with long-term stability. In this study, a clay-based material, humic acid modified montmorillonite (HA-Mont) was applied to a Cd and Hg contaminated soil. Field emission scanning electron microscopy combined with energy-dispersive X-ray spectroscopy (FESEM/EDS), N2 adsorption-desorption, Fourier transform infrared (FTIR) spectroscopy and X-ray diffraction (XRD) analyses were performed to investigate the characteristics of this material. Compared to the soil without any treatment, dosage of 5 % HA-Mont could effectively reduce Cd and Hg concentrations by 94.1 % and 93.0 %, respectively and to below the regulatory limits in the TCLP (Toxicity Characteristic Leaching Procedure) leachates. Compared to the soil treated with virgin montmorillonite, HA modification resulted in the reduction of leachate concentrations of Cd and Hg by 69.5 % and 65.9 %, respectively. Long-term immobilization performance of the HA-Mont treatment was examined using a quantitative accelerated ageing method. In order to examine the ageing features, a novel method based on conditional probability was developed, and the reliability of HA-Mont immobilization was found to fit the Weibull model well, as the ageing rate of immobilization effect increased with time. After 120 years of ageing, reliability of both metals could still remain above 0.95. Cd concentration in TCLP leachates at 120th year could still remain below the regulatory limit (294 μg/L vs 1000 μg/L), while Hg concentration reached the regulatory limit of 200 μg/L in 96th year. This is the first attempt developing a green S/S method of Cd and Hg contaminated soil using HA-Mont and examining the long-term ageing characteristics of the stabilized soil using a probability-based approach.

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          Author and article information

          Journal
          J Hazard Mater
          Journal of hazardous materials
          Elsevier BV
          1873-3336
          0304-3894
          April 05 2020
          : 387
          Affiliations
          [1 ] School of Environment, Tsinghua University, Beijing 100084, China.
          [2 ] Department of Civil and Environmental Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong, China.
          [3 ] School of Engineering, University of Glasgow, Glasgow G12 8QQ, United Kingdom.
          [4 ] School of Environment, Tsinghua University, Beijing 100084, China. Electronic address: houdeyi@tsinghua.edu.cn.
          Article
          S0304-3894(19)31959-4
          10.1016/j.jhazmat.2019.122005
          31918052
          750da7d3-75f3-4d2f-9ae2-3d9b83df6b5b
          Copyright © 2020 Elsevier B.V. All rights reserved.
          History

          Accelerated ageing,Clay minerals,Long-term leachability,Metal immobilization,Probability-based approach

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