有氧条件下地下水中纳米FeS物相性能演变及Cr(VI)非生物去除机制

Groundwater pollution caused by chromate (Cr(VI)) is very serious in China, however, the research findings on the mechanism of the removal of Cr(VI) in groundwater are not enough to support the remediation alternatives. In this research, we will focus on the processes of anthropic removal or natural attenuation of Cr(VI) in groundwater by nano FeS, construct a groundwater-simulating system containing O2, FeS nanoparticles and Cr(VI), and study the mechanisms of the removal of Cr(VI) in groundwater under oxic conditions. Combining dynamic batch tests and characterization analysis such as XRD, XPS and EXAFS，the evolution of mineral phase and properties of nano FeS and the production of reactive oxygen species (ROS) under the fundamental environmental conditions of oxic groundwater will be observed; abiotic Cr(VI) removal capacity of minerals transformed from nano FeS will be calculated and verified through a quantum chemistry theory method; based on the simulation of chemical quasi-equilibrium for the established chemical system, non-biological Cr(VI) removal pathway by nano FeS will be explored. It is expected that the end-member minerals transformed from nano FeS will be recognized, the ROS products of the oxygenation processes of nano FeS will be identified, and the reoxidation of the species reduced from Cr(VI) will be confirmed; the dynamic models for the evolution of mineral phase of nano FeS and oxygenation kinetics of nano FeS will be estabilished, and finally the abiotic removal mechanisms of Cr(VI) under oxic conditions by nano FeS and its evolutive minerals will be elucidated to support the control of Cr(VI) pollution in groundwater theoretically.

当前我国地下水环境Cr(VI)污染严重，但是对地下水中Cr(VI)的去除机制研究还不够深入。本项目针对纳米FeS对地下水中Cr(VI)人工或天然去除过程，构建O2、FeS NPs和Cr(VI)共存地下水体系，研究有氧条件下地下水中Cr(VI)的去除机理。采用动态批试验测试结合XRD、XPS和EXAFS等手段，研究在有氧地下水环境中纳米FeS物相、性能演变和ROS产生过程；运用量子化学理论计算验证纳米FeS演化端元矿物对Cr(VI)去除性能；对构建的研究体系进行准化学平衡模拟，探究纳米FeS对Cr(VI)非生物去除路径。预期将识别出纳米FeS演化端元矿物种类，明确溶解氧氧化纳米FeS的ROS产物及其对Cr(VI)还原产物的再氧化作用，建立纳米FeS物相动态转化和溶解氧氧化动力学模型，阐明有氧条件下纳米FeS及其演化矿物对Cr(VI)非生物去除机制，为地下水中Cr(VI)污染控制提供理论依据。

地下水环境通常处于还原性状态，但在自然和人为活动扰动中地下水环境常由无氧转变为有氧状态。采用纳米FeS对Cr(VI)污染地下水修复过程中常伴随无氧-有氧条件的转变。还原性纳米FeS与O2反应会发生物相转化，影响Cr(VI)去除路径。本项目完善了FeS NPs溶解氧氧化产生H2O2和•OH等典型ROS的反应路径；明确了有氧条件下FeS NPs对典型Cr(VI)还原产物氧化的动力学控制过程；揭示了FeS NPs的多组分矿物演替机制，构建了FeS NPs转变的动力学模型，通过测试和理论计算研究了FeS NPs转变矿物对Cr(VI)的还原与吸附（收）性能；厘清了O2对FeS NPs去除Cr(VI)的关键作用，阐明了有氧条件下FeS NPs对Cr(VI)的非生物去除机制。本项目的主要研究发现如下：（1）H2O2产生过程除涉及≡Fe(II)与O2反应外，还包括≡S(-II)与O2反应；•OH产生过程主要包括Fe(II)活化H2O2，结构态Fe(III)与吸附态H2O反应以及SO32-/S2O32-/S0等S(-II)氧化产物与Fe(II)、O2反应。（2） FeS NPs溶解氧氧化过程对Cr(III)氧化活化包括Cr(III)被氧化生成Cr(VI)和新生Cr(VI)还原为Cr(III)等两个过程；•OH通过FeS NPs或Cr(OH)3固体的表面氧化过程，将Cr(III)氧化为Cr(VI)，随后新生Cr(VI)被还原为Cr(III)。（3）有氧条件下地下水中FeS NPs转化包括Fe(II)与S(-II)协同氧化、质子溶解-氧化和FeS NPs固体表面介导氧化等复杂物理化学过程；FeS NPs转变动力学模型可主要表述为FeS NPs经Fe7S8、Fe3S4、FeS2向S0、α-FeOOH和γ-FeOOH等逐步转化；FeS NPs及其转变矿物对Cr(VI)具有还原、吸附（收）性能，但受pH和FeS NPs溶解氧氧化时间影响显著。（4）溶解氧对地下水中Cr(VI)去除既有促进作用又可起到抑制作用；中碱性条件下溶解氧通过FeS NPs转化的新生黄铁矿和独特核壳结构促进Cr(VI)去除，酸性条件下溶解氧消耗还原剂抑制Cr(VI)还原。本项目的研究发现丰富了纳米FeS动态转变过程和纳米FeS对地下水中Cr(VI)去除的基本理论，为地下水中Cr(VI)污染控制提供了一定的理论基础。