绿色合成纳米零价铁复合材料及修复重金属铬复合污染土壤的研究

Land pollution by many heavy metals produced mainly by chromium (Cr) slag yard becomes increasingly urgent. Nano zero valent iron (nZVI) is increasingly being considered as an effective material for remediation of water and soils by many countries in the word. However, the consideration takes into account the high cost and the potential threats of nZVI to environments during the apllication. Especially, many unknown are relative to the mobility in soils and the physichemical characteristcs of nZVI due to the vairous environmental media. The clay-supported nZVI will be synthesized through the green method using the agricultural plants and fruits waste. In order to the increase the physichemical functions of composite, the particle size, the purity of Fe0 and furface characteristcs will be controlled during the process of synthesis. Importance here would be studies involving the stability and transportability of nanoparticles; the effect of various matrices in soils on the physicochemical properties of mobile nZVI composites. Also important thing is going to clarify the interactions between nZVI composites and metal ions (i.e. Cr (VI) and Ni (II)) at solid-water infterface using the modern advanced analysis, and the stability of those complexes in relation to variable environmental conditions and in relation to the degree of transformation of nZVI composites. Results of this project will provide the sientific surpport for the better appllication of clay-supported nZVI composites introduced into various soils, to ensure effectively reaching the Cr contaminated location for in-situ heavy metal-contaminated soil remediation in order to develop a healthy and long-term engineering of nZVI in the future.

国内铬渣污染场地造成土壤以铬Cr(VI)为主的重金属复合污染迫在眉睫。纳米零价铁（nZVI）是一种净化不同水体或土壤污染的有效工具，受到各国广泛重视。针对实际应用中大多改性nZVI高成本和潜在的环境危害，以及nZVI在土壤中迁移与滞留、物理化学性质不明确，本项目利用农林植物或水果废弃物，建立绿色合成方法，通过黏土矿物为载体负载nZVI，有效调控粒子大小、提高Fe0产率、增加表面特性。系统研究该材料的流动性及运移参数，揭示影响其土壤迁移过程及物理化学特征的主控因子。运用现代先进仪器手段，从分子水平上阐明多重金属污染物（如：铬Cr(VI)和镍Ni(II)）在nZVI固-液界面的相互作用，及这些复合物相对于可变微环境与nZVI转化程度相关稳定性的构-效关系。使该nZVI复合材料在特定土壤环境中能够有效迁移到污染地区，选择性地原位修复重金属铬复合污染土壤，以期发展持续健康的纳米零价铁修复工程。

近年来，纳米零价铁（nZVI）在废水处理和土壤修复中受到广泛的关注。以绿茶提取物（茶多酚, TPs）为还原剂，采用环保、低成本的绿色方法，通过羧甲基纤维素钠（CMC）、维生素C（VC）、蒙脱土（Mont）和高岭土（Kaolin）等稳定剂成功制备了TPs包裹的纳米零价铁（GT-nZVI）。 同时研究环境影响因子（如大肠杆菌（E. coli）、磷酸盐、硫酸盐和腐殖酸（HA）等）对GT-nZVI修复重金属的能力及其迁移性的影响，另外采用先进的仪器手段表征及迁移模型解释主要作用机理。.研究发现：1）pH 6.0时E. coli和磷酸盐会促进GT-nZVI迁移：GT-nZVI+ E. coli +磷酸盐> GT-nZVI+磷酸盐> GT-nZVI+ E. coli > GT-nZVI。在pH 8.0时抑制GT-nZVI迁移：GT-nZVI> GT-nZVI+ E. coli +磷酸盐> GT-nZVI+ E. coli > GT-nZVI+磷酸盐。2）在酸性条件下，硫酸盐主要促进GT-nZVI溶解将Cr(VI)转化为Cr(OH)3，有利于Cr(VI)还原。而磷酸盐抑制GT-nZVI溶解生成Cr2O3。当两者共存时，磷酸盐的抑制占主导作用，并且随着P/S的摩尔比增加0.1-10，GT-nZVI去除Cr(VI)能力从88.9降至72.4 mg g-1。3）当pH≤6.0，磷酸盐和HA都抑制GT-nZVI溶解和TPs释放从而降低Cr(VI)还原率分别为39.86%和70.58%。pH 3.0时，HA优先促进形成Cr2O3，以及Cr(III)-HA-nZVI 络合物的生成发生协同共迁移。而磷酸盐抑制了材料对Cr(VI)吸附和Cr2O3的生成，从而促进了Cr(VI)迁移。4）经过CMC、VC、Mont和Kaolin改性和TPs包裹的协同作用促进材料的迁移性和对Cr(VI)去除率，分别提高了46%、85%、220%、132%。Mont-nZVI对Pb(II) 固定能力提高了69.9%。5）磷酸盐和HA都会促进Mont-nZVI和Kaolin-nZVI与Cr(VI)迁移，但磷酸盐的促进作用强于HA，主要是由于相对于HA有机大分子PO43-内层吸附使颗粒表面电荷更负，从而增加颗粒间斥力。.本课题通过研究环保、低成本的绿色纳米零价铁材料，为重金属污染土壤和地下水原位修复提供新的理论支持。