关键词: 重金属, 纳米零价铁, 核-壳结构, 反应机理, 扫描透射电镜, 环境应用

Heavy metals are nonbiodegradable and bioaccumulative contaminants with high toxicity, thus heavy metal contamination and treatment have been hot research topics in recent years. Nanoscale zero-valent iron (nZVI) has received considerable attentions for its potential as a remedial agent for heavy metal sequestration and immobilization. In this paper, an overview is provided highlighting recent research progress on heavy metal-nZVI reactions, both laboratory studies and engineering applications are discussed. The core-shell structure with the core being metallic and the shell being iron oxides and the surface chemistry properties endow nZVI with unique and multifaceted functions for heavy metal removal including sorption, reduction and precipitation. Particle size of nZVI is in the range of nanoscale that imparts it with large specific surface area, high surface activity, and high density of reactive surface sites. A hybrid of effects, including instant separation, isolation, immobilization, and toxicity reduction can be achieved at the same time, making nZVI an effective remedial reagent for various heavy metals. Recent progress in instrumental analysis, especially the development of high-resolution electron microscopy, offers much-enhanced capability and new insights into the core-shell nature of nZVI and mechanisms of the heavy metal-nZVI reactions on a single nanoparticle. Research results obtained from a spherical aberration corrected scanning transmission electron microscopy (Cs-STEM) integrated with high sensitive X-ray energy dispersive spectroscopy (EDS) provide detailed information on the fine structural features of nZVI and the intraparticle reactions with individual nanoparticles. Technical feasibility and operational advantages of using nZVI for the treatment of industrial wastewater are assessed through systematic laboratory and pilot scale studies. Based on the encouraging results of bench-scale experiments, we have successfully applied nZVI for large scale applications of nZVI for treatment of industrial wastewater containing heavy metals such as Cu, As, Pb and Zn. The long-term operation results show tremendous potentials of nZVI-based process as an efficient method for heavy metal treatment.

Key words: heavy metal, nanoscale zero-valent iron (nZVI), core-shell structure, reaction mechanisms, STEM, environmental applications