多元素调控水热碳对Cd、As重金属污染土壤修复及机理研究

The remediation of heavy metal-contaminated soil is an urgent task in the world. Chemistry passivation is one of the most efficient methods to stabilize the heavy metals in contaminated soil. However, there are several disadvantages for this method, such as the lack of efficient passivation materials, incomprehension of passivation mechanism. For solving these disadvantages and achieving the remediation of heavy metal-contaminated soil, in this project, a kind of high-efficient passivation material, hydrochar, will be prepared using biomass as raw material based on hydrothermal method. On the basis of understanding that the surface functional groups and microstructure of carbon materials are the critical factors for immobilizing heavy metal, the prepared hydrochar will be modified with different compounds (containing O, N, S and P, etc) or nanomaterials (such as zeolite or ferric oxide), which can make the surface of hydrochar with different functional groups, and change the mesh distribution and pore structure of hydrochar. The adsorption performances of modified hydrochar towards different heavy metals (such as Cd, As, etc) will be investigated, the chemical mechanism between modified hydrochar and Cd, As heavy metals will be revealed. The rhizospheric effect of modified hydrochar will be investigated, the effect of modified hydrochar to plant uptake Cd, As heavy metals and environmental effects of modified hydrochar will be investigated, the passivation and remediation effect of modified hydrochar for Cd, As heavy metal contamination will be discussed, the transport and transformation mechanism of heavy metal in plant-soil system and the effect of reducing bioavailability of Cd, As heavy metals of modified hydrochar will be illuminated. This project can not only provide novel nanomaterials to develop new and efficient remedy technology for heavy metals contaminated soil with advantages of practicability, economy, and safety, but also offer useful theoretical foundation for chemical passivation remediation of heavy metals contaminated soil.

土壤重金属污染治理是当今社会面临的迫切任务。化学钝化修复是解决土壤重金属污染的有效方式之一，但存在高效钝化材料缺乏、修复机理不明等影响修复的关键问题。课题组前期利用水热法将生物质转化为水热碳，明确了水热碳表面官能团及微观结构是影响其对重金属固定的关键因素。在此基础上，本项目拟利用含氧、氮、硫、磷等元素的化合物或纳米材料（沸石或铁氧化物）等对水热碳进行改性，调控水热碳的表面官能团、孔径分布及孔结构，提高其对土壤中重金属固定的有效性，进而探讨改性水热碳对土壤中Cd、As重金属离子的吸附固定性能，揭示改性水热碳对Cd、As的化学作用机理。研究改性水热碳的根际效应，考察改性水热碳对植物吸收Cd、As的影响及环境效应，阐明改性水热碳对土壤-植物系统中Cd、As迁移转化机制及降低Cd、As生物有效性的效果。本项目的实施将为发展实用、经济、安全的土壤重金属污染修复技术提供新材料及理论依据。

土壤重金属污染治理是当今社会面临的迫切任务，化学钝化修复是解决土壤重金属污染的有效方式之一。本项目针对当前对土壤中Cd、As高效钝化材料缺乏、修复机理不明等影响修复的关键问题。制备了铁改性多孔碳、纳米铁生物碳（nZVI@BC）、EDTA改性三维磁性氮掺杂多孔碳（N-MPC-EDTA）、几丁质改性地聚物、三维花状的氮掺杂的铁铜双金属纳米粒子复合物（FeCu-N-PC）、有序石墨化氮化碳(g-C3N4)管束材料等多种改性碳材料。利用X射线粉末衍射、透射电子显微镜、扫描电子显微镜、傅里叶变换红外光谱、荧光光谱对材料的表面性能、结构形态进行了表征，证实了这些材料表面具有丰富的官能团，孔结构及荷电差异，适合对环境中重金属Cd、As等离子的吸附钝化。通过静态吸附实验，探讨了改性碳材料对重金属Cd(II)和As(V)的吸附性能，探讨了最佳吸附条件，筛选了对重金属Cd、As最佳吸附的铁基改性碳材料，通过拟一阶模型和拟二阶模型拟合，Langmuir和Freundlich等温线模型描述和分析，验证了材料对Cd、As重金属离子吸附动力学模型。进一步考察了nZVI@BC对土壤中Cd(II)和As(V)的钝化效果，经nZVI@BC处理后土壤pH和CEC均有所增加，对施用于土壤中的nZVI@BC XPS分析，证实了Cd(II)被nZVI@BC稳定化，其机理涉及静电吸引、表面络合、物理吸附、共沉淀和离子交换。nZVI@BC表面存在的铁氧化物，与土壤中非专性吸附态、专性吸附态等不稳定形态的砷结合，形成无定型或晶型铁砷氧化物结合态和不溶性矿物FeAsO4是nZVI@BC对土壤砷固定化的主要原因。通过nZVI@BC在Cd、As污染土壤中土壤微生物数量和功能的研究，初步明确了添加nZVI@BC改变了土壤细菌群落结构，显著降低了受Cd、As影响的菌群。