Abstract:

In response to the pressing challenge of environmental cadmium (Cd) pollution, magnetic adsorbent materials have attracted significant attention as highly efficient and environmentally sustainable solutions for Cd remediation. These materials offer enhanced performance and eco-friendliness, making them promising tools to mitigate Cd contamination. Their ability to effectively absorb Cd, combined with their facile recovery through magnetic separation, underscores their potential for practical applications and environmental protection. Our research group previously developed millimeter-scale magnetic composite clay-based remediation materials by utilizing iron (Ⅱ, Ⅲ) oxide (Fe₃O₄) as the magnetic matrix and combining it with thiol-modified palygorskite-clay minerals. These materials have demonstrated significant advancements in Cd adsorption and removal from contaminated soils, resulting in notable improvements in the soil quality and environmental restoration. Despite these successes, the comprehensive characterization of the structural properties of such materials remains limited, and the mechanisms governing their Cd adsorption behavior are not fully understood. To address these gaps, this study systematically characterized the microstructure and structural properties of millimeter-scale magnetic composite clay-based remediation materials using advanced analytical techniques. These include scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET) surface area analysis, Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), zeta potential measurements, thermogravimetric/differential thermal analysis (TG/DSC), and magnetic property testing. By integrating the adsorption kinetics and isotherm models, this study thoroughly investigated the Cd adsorption characteristics of the materials and explored the relationship between their structure and functionality to elucidate the mechanisms underlying Cd adsorption. The results reveal that millimeter-scale magnetic composite clay-based remediation materials possess a spherical morphology with an average diameter of 1.27 mm and exhibit a highly wrinkled, porous surface. These materials offer several unique advantages, including an optimal particle size, abundance of functional groups, robust structural stability, and facile magnetic recoverability. The adsorption kinetics followed the pseudo-second-order kinetic model, whereas the adsorption isotherms were aligned with the Langmuir model, indicating monolayer adsorption on the homogeneous sites. The theoretical maximum adsorption capacity for Cd was determined to be 46.14 mg·g⁻¹. Cd adsorption by millimeter-scale magnetic composite clay-based remediation materials likely involves multiple mechanisms including intraporous diffusion, coordination complexation, ion exchange, and electrostatic adsorption. This study provides a scientific basis for understanding the properties and contaminant removal efficacy of millimeter-scale magnetic composite clay-based remediation materials, thereby advancing their potential applications in environmental remediation.

Key words: millimeter-scale magnetic adsorbent materials, clay minerals, structural properties, adsorption characteristics, cadmium

摘要： 面对严峻的环境镉（Cd）污染问题，磁性吸附材料作为一种高效吸附Cd且环境友好的修复材料，受到广泛关注。前期以四氧化三铁（Fe₃O₄）为磁性基体，通过与巯基改性黏土矿物凹凸棒复合，制备了毫米级磁性复合黏土矿物修复材料，并成功用于土壤中Cd的吸附去除，实现了土壤减污修复。然而，目前对毫米级磁性复合黏土矿物修复材料的结构性质缺乏系统表征，其对Cd的吸附特征尚不明确，吸附机理亦缺少探讨。基于此，通过多种材料分析手段系统表征了毫米级磁性复合黏土矿物修复材料的微观特征、结构性质，结合吸附动力学与等温吸附模型探讨了其对Cd的吸附特征，探究了材料结构与功能的相互关系，分析了其对Cd的吸附机理。结果表明，毫米级磁性复合黏土矿物修复材料呈球形（直径为1.27 mm），表面褶皱多孔，具有尺寸适宜、富含官能团、结构稳定性强、可磁性回收的独特优势，对Cd的吸附过程符合准二级动力学模型和Langmuir等温模型，最大理论吸附量为46.14 mg·g⁻¹。此外，毫米级磁性复合黏土矿物修复材料对Cd的吸附可能涉及多种作用机制，包括孔隙内扩、配位络合、离子交换、静电吸附作用等。该研究可为认识毫米级磁性复合黏土矿物修复材料的特征与减污净土作用提供科学依据。

关键词: 毫米级磁性吸附材料, 黏土矿物, 结构性质, 吸附特征, 镉