微波诱导铁载凹土修复硝基苯类-砷复合污染土壤的作用机理

Contaminated soil from organoarsenic feed additives industry is one type of typical contaminated sites in China. Microwave-assisted iron modified attapulgite (Fe/ATP) was used in the remediation of nitrobenzenes and arsenic (As)-contaminated soils from organoarsenic feed additives industry. The catalytic oxidation of nitrobenzenes and stabilization/solidification of As in soil could be obtained at the same time induced by Fe/ATP under microwave irradiation. The main contents to be investigated include:(1) the pathway of interfacial electron transfer, active species generation, active species types and their formation on Fe/ATP in the microwave catalytic system; (2) the pathway, kinetic, and mechanism of catalytic oxidation of nitrobenzenes and As(III), the correlation of catalytic performance to structural characteristics of Fe/ATP, the influence of pH value, dissolved oxygen content, soil temperature, and the coexistence of metal; (3) the removal mechanism of As by Fe/ATP via adsorption, surface precipitation, surface complexation, mineralization, and redox process; (4) the stabilization/ solidification mechanism and influence factors of As by Fe/ATP under microwave irradiation, and the relationship between the stability of arsenate and its chemical speciation distribution. On the base of the laboratory studies, pilot scale experiments will be carried out to evaluate the long-term stability of As in soil. Both land disposal in areas where rainwater is stimulated and underground landfill disposal in areas where hydrogeochemistry environment is stimulated will be likely to test As release performance from Fe/ATP stabilized soils and microwave-assisted Fe/ATP stabilized/solidified soils. This project would provide theoretical and technical support for the development of microwave remediation for organic pollutants and heavy metals-contaminated soil.

源于饲料添加剂洛克沙砷生产过程中引起的场地污染是具有代表性的一类，且数量众多，该类场地多呈现高浓度硝基苯类有机物和无机砷复合污染特征。本研究针对该类场地特征污染物提出一种微波辅助铁载凹土(Fe/ATP)的绿色土壤修复技术，同时实现土壤中硝基苯类的矿化和砷的稳定/固化。分析微波催化体系中Fe/ATP界面电子转移行为、活性物种的产生、消亡规律和影响因素，研究活化分子氧/溶剂水的分子机制，探讨土壤中硝基苯类的微波催化历程、去除路径和影响因素。分析砷在Fe/ATP上的吸附、表面沉淀、表面络合、矿化等分子机制和氧化还原的过程，研究微波对铁砷矿化固定的作用机制，揭示砷的稳定性与分布形态特征之间的关系和规律以及影响因素。构建中试放大试验，研究稳定/固化处理后土壤中砷的释放行为，探讨砷的长期稳定性及影响因素等地球环境化学基础问题。本研究可为发展有机-重金属复合污染土壤修复提供理论和技术支持。

本研究提出一种微波辅助铁基修复剂的绿色土壤修复技术，快速同步实现土壤中硝基苯（PNP）的去除和砷的稳定/固定化。研究表明，微波激发铁基修复剂活化分子氧产生活性物种（ROS），快速氧化PNP和As(III)，微波辐照5-10 min，PNP通过热解吸和降解被去除；10-20 min，吸附的砷固定在修复剂晶格中，或形成铁砷晶体矿物，从而实现砷的长效稳定。密度泛函理论（DFT）计算表明，与Fe2O3相比，铁载凹土（Fe/ATP）中的Fe-3d轨道与As中的O-2p发生更强的杂化，导致了Fe/ATP对As更强吸附亲和力。ATP中的Al−O八面体是Fe的主要结合位点，八面体中的Al和O将电子传递给Fe，增强了Fe的离域性，提高了其化学活性，从而增强了对As的结合力。偏态密度分析表明，微波辐照后，固化结晶成矿后的物质结构更稳定，微波辐照引起修复剂与As更强的杂化，导致其结合较微波辐照前更为紧密。基于本研究，提出一种微波强化铁基修复剂稳定雄黄尾矿渣的方法，利用微波驱动铁盐水解氧化，促进不稳定钙(硫)砷矿物向稳定的晶型铁砷矿物转化。微波场下，砷酸钙的得以快速溶解、硫化砷被充分氧化、而形成的铁砷矿物能快速结晶成矿，达到了危废填埋场的最新标准，跟踪一年填埋场数据发现，该技术并实现了雄黄尾矿渣的长效稳定。另外，利用微波激发铁基材料活化分子氧快速产ROS的特性处理了含砷废水，将铁基修复剂电镀负载到碳化硅表面，形成从内到外的Fe0-FeII-FeIII铁壳，微波辐照下，表层FeIII脱落，持续暴露出新鲜的Fe0-FeII活化分子氧产生ROS，从而氧化As(III)为As(V)，而生成的氧化铁膜脱落进入水体，吸附和包裹As(V)，从而去除水体中As，该技术能在较宽pH范围（pH2.5-9.5）实现对含砷废水的处理，突破了传统Fenton技术受pH影响的局限。