基于绿色合成的nZVI@BC复合材料对Cd、As污染土壤修复机制的研究

In view of the increasingly serious situation of heavy metal contaminated soil, it is crucial to develop green and efficient solidified/stabilized materials, and biochar-based nanocomposites have become a focus recently. In this project, nZVI@BC (biochar-supported nanoscale zero-valent iron) composite with green synthesis is applied for in-situ remediation of Cd and As contaminated soil. The main research contents are as follows: (1) Using agricultural and forestry wastes as raw materials, biologic reductants are efficiently extracted with microwave. By the regulation of the structure and morphology, green, efficient and economical nZVI@BC composites are synthesized. (2) With different influencing factors, single factor experiments and response surface method are conducted to clarify the effects of nZVI@BC composite on the single and combined pollution with Cd and As, and the mathematical model is established to obtain the optimal reaction conditions. (3) Based on the batch equilibrium oscillation method, BCR step by step extraction method and so on, the adsorption properties of nZVI@BC composite, the variation of physical and chemical properties of soil as well as the distribution of existing forms of Cd and As are systematically explored. It is expected that the research results will provide a new green, environmental friendly, efficient and economical remediation material for soil contaminated by Cd and As, reveal the remediation mechanism of nZVI@BC composite, and elucidate the migration and transformation behavior of Cd and As, which will provide an important theoretical basis and wide application value for the popularization and application of nZVI@BC composite, efficient remediation of heavy metal contaminated soils and improvement of the soil quality.

针对日益严峻的土壤重金属污染形势，开发绿色高效的固化/稳定化材料成为关键，其中以生物炭为基质的纳米复合材料成为当前研究热点。本项目以Cd、As污染土壤为对象，采用绿色合成的生物炭负载纳米零价铁复合材料（nZVI@BC）修复，重点研究：（1）以农林废弃物为原料，微波高效提取生物还原剂，调控材料表观形貌与结构形态，绿色合成高效、经济的nZVI@BC；（2）通过单因素及响应面实验明确不同因素下nZVI@BC对Cd、As单一和复合污染修复效果的影响规律，构建数学模型，获取最优化条件；（3）采用批量平衡振荡法、BCR逐级提取法等明确nZVI@BC吸附性能、土壤理化性质及Cd、As形态分布。预期结果将为Cd、As污染土壤提供高效、环保、经济的新型修复材料，揭示nZVI@BC的修复机制，阐明Cd、As的迁移转化行为，为nZVI@BC的推广应用、重金属污染土壤高效修复提供重要的理论基础和广泛的应用价值。

我国土壤重金属污染日益严重，以生物炭为基质的纳米复合材料作为重金属固化稳定化材料受到广泛关注，而当前研究多集中于液相体系，对重金属污染土壤修复的研究较少且修复机制不明确。本项目以Cd、As等重金属污染土壤为对象，采用绿色合成的nZVI@BC进行修复，研究了复合材料表观形貌、结构与性能；明确了不同nZVI负载比、反应时间、pH、投加量等因素对Cd、As等重金属污染土壤修复效果与土壤理化性质的影响规律并获取优化条件；阐明了nZVI@BC对单一及复合重金属污染土壤的修复机制。结果表明，nZVI与BC官能团键合增加了Fe-O、Fe-O-H等特征峰，丰富了官能团种类，增加了吸附位点，随着nZVI:BC比例降低，复合材料的稳定性和流动性增强。nZVI@BC的加入显著提高了土壤有效态铁含量、pH与CEC。相同投加量下，Cd固化稳定化效果1:1＞3:1＞1:3，随着投加量、反应时间增加，Cd在土壤中弱酸提取态、可还原态、可氧化态占比逐渐减少，残渣态含量逐渐增加。初始pH越高，Cd的钝化效果越好，其修复机制涉及静电吸引、表面络合、物理吸附、共沉淀和离子交换。随着反应时间延长，nZVI@BC会促进土壤中砷由无定形铁铝氧化物结合态向晶质铁铝氧化物结合态和残渣态的转化，投加量、nZVI:BC比与土壤砷固化稳定化成正相关，增加了土壤中铁氧化物、芳香碳等的含量，通过共沉淀、表面络合、离子交换等作用增强了土壤中砷的固化稳定化效果。在Cu、Zn、As、Cd、Pb复合重金属污染土壤修复过程中发现，As的存在会协同促进对Pb和Cd的固化稳定化，Zn的存在可以促进残渣态Cd的转化，Pb/Cu对吸附位点具有更强的竞争力，其固定效率优于Zn/Cd。通过本项目研究，为重金属污染土壤提供高效固化稳定化修复材料，为nZVI@BC的应用以及土壤环境质量改善提供重要的理论基础和科学价值。

内容获取失败，请点击重试