Kinetic and Characterization Analysis on Mercury Adsorption by Magnetic Biochar in Flue Gas

Mercury pollution from coal-fired flue gas presents many risks to human health and the environment, necessitating the development of cost-effective and efficient adsorbents for mercury removal. This study investigates magnetic biochar adsorbents for mercury removal, with a focus on the impact of biomass types and CuCl2 modification on adsorption performance. Magnetic biochars were prepared from bamboo, wood, walnut shell, and corn stover. Among these, walnut shell biochar showed the highest mercury removal efficiency and adsorption capacity. The addition of CuCl2 improves the performance, with 0.08 mol/L CuCl2-modified MWSC (magnetic walnut shell carbon) achieving an 83% removal rate and a cumulative adsorption capacity of 195.10 μg/g. Characterization through BET, XRD, and XPS analyses revealed that CuCl2 modification improved pore structure and active sites, promoting both physical and chemical adsorption of Hg0. The adsorbent exhibited superparamagnetic properties, ensuring its recyclability. The adsorption process of Hg0 was analyzed using kinetic models, including the pseudo-first-order, pseudo-second-order, and intraparticle diffusion models. The results indicate that although the adsorption rate of Hg0 depends on both external mass transfer and intraparticle diffusion, external mass transfer is the primary rate-limiting step. These findings contribute to the commercial application of magnetic adsorbents in activated carbon injection technology and provide a theoretical foundation for effective mercury removal strategies.