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<p>Hexavalent chromium (Cr(VI)) is a highly toxic and mobile heavy metal that poses serious risks to human health and the environment. In this research, for the Cr(VI) adsorptive removal, magnetic biochar is developed by a novel one-step pyrolysis process using iron-pretreated agricultural waste: pigeon pea leaves and chickpea stems named as BC@P and BC@C. The developed biochar is utilized to investigate the removal of Cr(VI) in an aqueous solution by batch and column mode. The results indicate that both biochar BC@P and BC@C exhibited higher efficiency, with maximum Cr(VI) removal of 99.98% and 96.81%, respectively. Each biochar was characterized using SEM, FTIR, XRD, XPS, and pH<sub>ZPC</sub> to evaluate the Cr(VI) adsorption-mechanisms. SEM analysis demonstrated that the both biochar surface is rough and irregular, while EDS confirmed the presence of iron and a high carbon content on both composite biochar surfaces. Characterization results of FTIR, XRD, and XPS, confirmed the formation of various iron oxides (FeOOH, Fe₂O₃, and Fe₃O₄) and oxygenated functional groups on BC@P and BC@C surfaces. The Cr(VI) removal by both biochar followed the Freundlich isotherm (R<sup>2</sup> = 0.9981 for BC@P and 0.9897 for BC@C) and pseudo-second-order kinetics (R<sup>2</sup> = 0.99943–0.9998), indicating heterogeneous-multilayer-adsorption and chemisorption. Thermodynamic analyses reveal that Cr(VI) adsorption is endothermic for BC@P and exothermic and spontaneous for BC@C. The proposed mechanism for Cr(VI) adsorption on each biochar involves surface complexation, reduction, and electrostatic attraction. Additionally, the biochar exhibited recyclability for up to six cycles and effective for Cr(VI) removal.</p> Graphical Abstract <p></p>

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Removal of Hexavalent Chromium from Aqueous Solution by Iron-Oxide-Based Biochar Composite Derived from Agricultural-Waste: Kinetics, Mechanisms, and Cost Analysis

  • 期刊论文

  • 发表日期：

    2025年8月8日

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  • Naincy Sahu,
  • Siddharth Shukla,
  • Vinod Kumar Chaudhary,
  • Saurabh Kumar

摘要

Hexavalent chromium (Cr(VI)) is a highly toxic and mobile heavy metal that poses serious risks to human health and the environment. In this research, for the Cr(VI) adsorptive removal, magnetic biochar is developed by a novel one-step pyrolysis process using iron-pretreated agricultural waste: pigeon pea leaves and chickpea stems named as BC@P and BC@C. The developed biochar is utilized to investigate the removal of Cr(VI) in an aqueous solution by batch and column mode. The results indicate that both biochar BC@P and BC@C exhibited higher efficiency, with maximum Cr(VI) removal of 99.98% and 96.81%, respectively. Each biochar was characterized using SEM, FTIR, XRD, XPS, and pHZPC to evaluate the Cr(VI) adsorption-mechanisms. SEM analysis demonstrated that the both biochar surface is rough and irregular, while EDS confirmed the presence of iron and a high carbon content on both composite biochar surfaces. Characterization results of FTIR, XRD, and XPS, confirmed the formation of various iron oxides (FeOOH, Fe₂O₃, and Fe₃O₄) and oxygenated functional groups on BC@P and BC@C surfaces. The Cr(VI) removal by both biochar followed the Freundlich isotherm (R2 = 0.9981 for BC@P and 0.9897 for BC@C) and pseudo-second-order kinetics (R2 = 0.99943–0.9998), indicating heterogeneous-multilayer-adsorption and chemisorption. Thermodynamic analyses reveal that Cr(VI) adsorption is endothermic for BC@P and exothermic and spontaneous for BC@C. The proposed mechanism for Cr(VI) adsorption on each biochar involves surface complexation, reduction, and electrostatic attraction. Additionally, the biochar exhibited recyclability for up to six cycles and effective for Cr(VI) removal.

Graphical Abstract