Abstract:

Cadmium (Cd) pollution is a significant soil environmental issue in China and has been a focus of research in the field of polluted soil remediation. Biochar has been widely used in soil remediation due to its large surface area, rich porosity, and availability of raw materials. However, the lack of selective adsorption sites and functionalization of biochar limit its effectiveness in remediating Cd-contaminated soil. Modification of biochar has been found to enhance soil remediation efficiency. In this study, S-BC and Si-BC were prepared by modifying biochar using Na₂S and Na₂O∙3SiO₂, respectively. The physicochemical properties of biochar before and after modification were analyzed. The remediation of Cd-contaminated soil by biochar was investigated in terms of remediation time, physicochemical properties of soil after remediation, and transformation of Cd speciation. Non-metallic modification of biochar increased its specific surface, functional groups, dispersibility, and stability. The remediation efficiency of Cd-contaminated soil increased with longer remediation time and higher material dosage, and the maximum remediation efficiency by BC, S-BC, and Si-BC could reach 14.3%, 27.9%, and 59.2%, respectively. The application of biochar increased soil pH, CEC, and organic matter content, promoting the fixation of Cd in the soil. BC, S-BC, and Si-BC reduced exchangeable Cd in the soil, whereas the proportions of iron manganese oxide bound Cd, organic matter bound Cd, and residual Cd in original soils, SBC remediated soils, and Si-BC remediated soils were 50.3%, 54.5%, and 64.8%, respectively. The results showed that biochar could be used in Cd-contaminated soil remediations. Compared with S-BC, Si-BC was more efficient in promoting the transition of exchangeable and carbonate-bound Cd to iron-manganese oxide-bound Cd and organic matter-bound Cd, further reducing the mobility and bioavailability of soil Cd. This study provides insights into the use of low-cost, high-efficient, and environment-friendly biochar for soil remediation. The results in this study can inform the investigations on biochar, and help expand the application of biochar in the remediation of Cd-contaminated soil.

Key words: cadmium pollution, modified biochar, polluted soil remediation, sequential extraction procedures, interaction mechanism

摘要：

镉（Cd）污染已成为中国主要的土壤环境污染问题之一，是土壤污染治理领域的研究热点。生物炭因具有原材料丰富，提高土壤肥力等优势已被广泛用于土壤修复中，然而原始生物炭在Cd污染土壤修复中仍然存在局限性。通过对其修饰改性，进而提高生物炭的修复效果是拓展其在土壤修复领域应用的良方。分别利用Na₂S和Na₂O∙3SiO₂对生物炭进行改性，制备了S-BC（硫掺杂）和Si-BC（硅掺杂）改性生物炭修复材料，分析了改性前后生物炭的理化性质，并从修复时间、修复后土壤理化性质及镉不同形态变化等维度开展了土壤Cd污染修复研究。结果表明：非金属改性增加了生物炭的比表面积和官能团，且有利于减少其颗粒间的团聚，提高分散性及稳定性；Cd污染土壤的修复效率随修复时间和生物炭材料投加量的增加而增加，且BC、S-BC和Si-BC对镉的最大修复效率可达14.3%、27.9%和59.2%；Cd污染土壤经生物炭修复后，其土壤pH、CEC和有机质含量均提高，证实生物炭材料可改善土壤质量，提高土壤肥力，正向促进其对土壤中Cd的固定；3种生物炭材料均可降低土壤中可交换态Cd，且未修复、SBC修复和Si-BC修复的土壤中铁锰氧化物结合态、有机物结合态和残渣态占比和分别为50.3%、54.5%和64.8%，证明3种生物炭都可修复镉污染土壤，且相比S-BC，Si-BC更有利于促进可交换态和碳酸盐结合态镉向铁锰氧化物结合态和有机物结合态转变，进而降低Cd的可移动性及生物有效性，实现了Cd污染土壤高效修复目的。该研究提供了低成本、高效且安全的土壤修复材料，同时丰富了生物炭的改性及其对Cd污染土壤修复的应用研究。

关键词: 镉污染土壤, 改性生物炭, 土壤污染修复, 连续提取法, 作用机制