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<p>Cadmium (Cd) contamination in soil poses a serious threat to food safety and human health, necessitating effective remediation strategies. While biochar and clay minerals are recognized as cost-effective immobilization materials for remediating Cd–contaminated soils, their individual adsorption capacities are limited, and the potential of their composites remains largely unexplored. This study aims to fill these critical research gaps by systematically evaluating wood chip biochar (WBC), sepiolite (Sep), and their composite (WBC + Sep) for Cd immobilization through comprehensive batch experiments and field trials. The composite WBC + Sep exhibits an exceptional Cd<sup>2</sup>⁺ adsorption capacity of 32.40 mg·g⁻<sup>1</sup>, significantly outperforming individual WBC (13.64 mg·g⁻<sup>1</sup>) and Sep (9.28 mg·g⁻<sup>1</sup>). The adsorption kinetics followed pseudo-second-order dynamics (R<sup>2</sup> &gt; 0.98), and the fitting to the Langmuir isotherm (R<sup>2</sup> &gt; 0.95) confirms the predominance of monolayer chemisorption. Field trials demonstrated that the application of WBC + Sep reduced DTPA–extractable Cd by 28.95% to 36.84%, effectively converting exchangeable and carbonate-bound Cd into more stable residual forms. Furthermore, Cd concentrations in maize grains were reduced by 6.99%–45.25%. The application of WBC + Sep also led to improvements in soil properties, including increased pH (0.36% − 2.40%) and dissolved organic carbon (4.23% − 13.43%), which were negatively correlated with bioavailable Cd fractions (<i>P</i> &lt; 0.01). Moreover, the activities of soil enzymes such as urease, phosphatase, and catalase were enhanced. Mechanistic investigations using SEM–EDS, XRD, and FTIR revealed that Cd immobilization occurred through a combination of pore filling, precipitation, ion exchange, and complexation. These findings demonstrate the potential of WBC + Sep as an effective and sustainable passivation material for the remediation of Cd − contaminated soils, offering a promising approach to simultaneously improve soil quality and ensure safer maize production.</p>

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Evaluation of Biochar, Sepiolite, and Their Composites for Immobilization Remediation of Cadmium Contamination Soil: Insights From Batch Experiments and Field Trials

  • 期刊论文

  • 发表日期：

    2025年6月25日

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  • Chao Wang,
  • Shan Gao,
  • Tao Sun,
  • Shihang Wu,
  • Yuebing Sun,
  • Hongtao Jia

摘要

Cadmium (Cd) contamination in soil poses a serious threat to food safety and human health, necessitating effective remediation strategies. While biochar and clay minerals are recognized as cost-effective immobilization materials for remediating Cd–contaminated soils, their individual adsorption capacities are limited, and the potential of their composites remains largely unexplored. This study aims to fill these critical research gaps by systematically evaluating wood chip biochar (WBC), sepiolite (Sep), and their composite (WBC + Sep) for Cd immobilization through comprehensive batch experiments and field trials. The composite WBC + Sep exhibits an exceptional Cd2⁺ adsorption capacity of 32.40 mg·g⁻1, significantly outperforming individual WBC (13.64 mg·g⁻1) and Sep (9.28 mg·g⁻1). The adsorption kinetics followed pseudo-second-order dynamics (R2 > 0.98), and the fitting to the Langmuir isotherm (R2 > 0.95) confirms the predominance of monolayer chemisorption. Field trials demonstrated that the application of WBC + Sep reduced DTPA–extractable Cd by 28.95% to 36.84%, effectively converting exchangeable and carbonate-bound Cd into more stable residual forms. Furthermore, Cd concentrations in maize grains were reduced by 6.99%–45.25%. The application of WBC + Sep also led to improvements in soil properties, including increased pH (0.36% − 2.40%) and dissolved organic carbon (4.23% − 13.43%), which were negatively correlated with bioavailable Cd fractions (P < 0.01). Moreover, the activities of soil enzymes such as urease, phosphatase, and catalase were enhanced. Mechanistic investigations using SEM–EDS, XRD, and FTIR revealed that Cd immobilization occurred through a combination of pore filling, precipitation, ion exchange, and complexation. These findings demonstrate the potential of WBC + Sep as an effective and sustainable passivation material for the remediation of Cd − contaminated soils, offering a promising approach to simultaneously improve soil quality and ensure safer maize production.