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<p>Phytoremediation of heavy metal-contaminated soils generates large quantities of metal-enriched plant residues that require safe disposal. Herein, we report an integrated valorization strategy for <i>Sedum alfredii</i> Hance residues: pyrolysis for heavy metal stabilization, followed by magnetic modification on the resulting biochar for Congo red (CR) adsorption. Pyrolysis was conducted at 400–900&#xa0;°C, and the transformation behavior of Pb, Zn, and Cd was evaluated. The results demonstrated that pyrolysis effectively converted the acid-soluble/exchangeable fractions of Pb, Zn, and Cd into more stable residual forms, and their leaching concentrations decreased significantly with increasing pyrolysis temperature. Biochar produced at ≥ 700&#xa0;°C exhibited no phytotoxicity in wheat seed germination tests. To enhance its adsorptive performance, the biochar pyrolyzed at 700&#xa0;°C was magnetically modified with MnFe<sub>2</sub>O<sub>4</sub>. The modification improved the pore structure and surface function groups, facilitating CR adsorption. The resulting MnFe<sub>2</sub>O<sub>4</sub>-SBC biochar possessed a specific surface area of 91.68&#xa0;m<sup>2</sup>/g and a maximum CR adsorption capacity of 199.89&#xa0;mg/g, following the Langmuir isotherm and pseudo-second-order kinetic models. After five adsorption–desorption cycles, MnFe<sub>2</sub>O<sub>4</sub>-SBC retained high CR adsorption capacity, with minimal metal leaching. Mechanistic analysis revealed that adsorption was governed by electrostatic attraction, ion exchange, hydrogen bonding, π-π interactions, and surface complexation. Collectively, this study demonstrates that pyrolysis is a viable route for the safe disposal and value-added utilization of hyperaccumulator residues, turning a disposal burden into a functional biochar material.</p>

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Pyrolysis of heavy metal-enriched plant residues: stabilization of Pb/Zn/Cd and MnFe2O4-modified biochar for Congo red adsorption

  • 期刊论文

  • 发表日期：

    2026年7月14日

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  • Liying Jiang,
  • Baolin Fang,
  • Kejia He,
  • Yuhao Cao,
  • Mengjie Yang

摘要

Phytoremediation of heavy metal-contaminated soils generates large quantities of metal-enriched plant residues that require safe disposal. Herein, we report an integrated valorization strategy for Sedum alfredii Hance residues: pyrolysis for heavy metal stabilization, followed by magnetic modification on the resulting biochar for Congo red (CR) adsorption. Pyrolysis was conducted at 400–900 °C, and the transformation behavior of Pb, Zn, and Cd was evaluated. The results demonstrated that pyrolysis effectively converted the acid-soluble/exchangeable fractions of Pb, Zn, and Cd into more stable residual forms, and their leaching concentrations decreased significantly with increasing pyrolysis temperature. Biochar produced at ≥ 700 °C exhibited no phytotoxicity in wheat seed germination tests. To enhance its adsorptive performance, the biochar pyrolyzed at 700 °C was magnetically modified with MnFe2O4. The modification improved the pore structure and surface function groups, facilitating CR adsorption. The resulting MnFe2O4-SBC biochar possessed a specific surface area of 91.68 m2/g and a maximum CR adsorption capacity of 199.89 mg/g, following the Langmuir isotherm and pseudo-second-order kinetic models. After five adsorption–desorption cycles, MnFe2O4-SBC retained high CR adsorption capacity, with minimal metal leaching. Mechanistic analysis revealed that adsorption was governed by electrostatic attraction, ion exchange, hydrogen bonding, π-π interactions, and surface complexation. Collectively, this study demonstrates that pyrolysis is a viable route for the safe disposal and value-added utilization of hyperaccumulator residues, turning a disposal burden into a functional biochar material.