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<p>In this study, sludge biochars (SBCs) were prepared from aluminum electrolytic sludges in electrolytic aluminum plants and used for the treatment of carbon dross flotation wastewater (CDFW). Under the optimum condition, the KOH-modified SBC showed a high adsorption capacity of 58.3&#xa0;mg·g<sup>−1</sup> for fluoride removal, which is higher than that of most biochars from natural wastes. Brunauer–Emmett–Teller (BET) analysis revealed abundant meso/microporous structures, enabling efficient adsorption of fluoride ions. Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) confirm that the SBC-KOH surface contains M–OH<sub>2</sub>/M–OH (M=Al/Fe) groups. Fluoride ions form Al–F/Fe–F bonds via ion exchange and complexation with these groups. Adsorption kinetics and isotherms were well described by the pseudo-first-order (PFO), pseudo-second-order (PSO), and Langmuir models, suggesting chemisorption as the dominant mechanism with ion diffusion involvement. Thermodynamic analysis indicated a spontaneous, endothermic process driven by entropy. Thus, its adsorption mechanism involves synergistic pore diffusion filling, ion exchange, and surface complexation. Density functional theory (DFT) calculations on plate models of Fe<sub>3</sub>O<sub>4</sub>(100) and KAlO<sub>2</sub>(002) show negative adsorption energy, indicating a spontaneous exothermic process: Fe<sub>3</sub>O<sub>4</sub> adsorbs F<sup>−</sup> through Fe–F complexation, while KAlO<sub>2</sub> relies on Al–F complexation. Interestingly, the F<sup>−</sup> adsorbed by SBC-KOH achieved the highest capacity in alkaline conditions, unlike previously activated carbon in acidic solutions. SBC-KOH with good fluoride ion adsorption performance provides a new way for the resource utilization of sludge.</p> Graphical abstract <p></p>

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Preparation of biochar from carbon dross flotation sludge and its adsorption behaviors in flotation wastewater treatment

  • 期刊论文

  • 发表日期：

    2026年7月3日

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  • Qiang Huo,
  • Wen Song,
  • Chenhong Zu,
  • Qianying Zhang,
  • Shengjuan Zhou,
  • Yunkang Sun,
  • Xi Liu,
  • Qijing Jia,
  • Chunqiang Chen

摘要

In this study, sludge biochars (SBCs) were prepared from aluminum electrolytic sludges in electrolytic aluminum plants and used for the treatment of carbon dross flotation wastewater (CDFW). Under the optimum condition, the KOH-modified SBC showed a high adsorption capacity of 58.3 mg·g−1 for fluoride removal, which is higher than that of most biochars from natural wastes. Brunauer–Emmett–Teller (BET) analysis revealed abundant meso/microporous structures, enabling efficient adsorption of fluoride ions. Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) confirm that the SBC-KOH surface contains M–OH2/M–OH (M=Al/Fe) groups. Fluoride ions form Al–F/Fe–F bonds via ion exchange and complexation with these groups. Adsorption kinetics and isotherms were well described by the pseudo-first-order (PFO), pseudo-second-order (PSO), and Langmuir models, suggesting chemisorption as the dominant mechanism with ion diffusion involvement. Thermodynamic analysis indicated a spontaneous, endothermic process driven by entropy. Thus, its adsorption mechanism involves synergistic pore diffusion filling, ion exchange, and surface complexation. Density functional theory (DFT) calculations on plate models of Fe3O4(100) and KAlO2(002) show negative adsorption energy, indicating a spontaneous exothermic process: Fe3O4 adsorbs F− through Fe–F complexation, while KAlO2 relies on Al–F complexation. Interestingly, the F− adsorbed by SBC-KOH achieved the highest capacity in alkaline conditions, unlike previously activated carbon in acidic solutions. SBC-KOH with good fluoride ion adsorption performance provides a new way for the resource utilization of sludge.

Graphical abstract