【作者】 冯婧微；

【导师】 梁成华；

【作者基本信息】 沈阳农业大学 ， 土壤学， 2012， 博士

【摘要】 工业活动加剧了环境问题的产生，如由于重金属的积累导致生态系统恶化问题。重金属在工业生产上的重要性使其应用非常广泛，但未经处理或处理不完全的重金属污染物排入环境后，就会对土壤和水体等造成相当严重的后果，而且，重金属的量超过某一数值后，就会对有机体造成危害。如Cr（Ⅵ）、Cd²⁺、Cu²⁺及Ni²⁺等离子已经证实能够引起人的肝、肾损伤及威尔士（Wilson）综合症。因此重金属污染治理正日益引起人们的重视。铁基材料，包括铁（氢）氧化物和零价铁均可对多种环境污染物起到修复作用。铁（氢）氧化物，尤其是赤铁矿和针铁矿在土壤和沉积物中广泛存在，对环境中重金属具有良好的吸附性能，多年来一直作为治理重金属污染物的重要材料之一。而零价铁尤其是纳米零价铁由于具有高的反应活性，能够有效治理水体及土壤中多种重金属，成为目前重金属污染修复技术中一个非常活跃的研究领域。纳米零价铁是指粒子的三维尺度中至少有一维处于1-100nm之间的零价铁。由于其颗粒粒径小，比表面积大，表面原子占原子总数比例高，展现出量子化效应，由此表现出独特的优越性能，远非宏观体相材料所媲美。但由于粒径极小，粒子具备较高的化学反应活性，为保持稳定状态通常表现出相互聚集的倾向，为此需要对新合成的纳米铁材料进行表面改性以钝化或稳定化纳米铁颗粒，满足他们在实际应用中的需要。本文以纳米零价铁、赤铁矿（α-Fe₂O₃）、针铁矿（α-FeOOH）为供实材料，对比研究了溶液中Cr（Ⅵ）的去除效果，考察不同铁基材料对重金属Cr（Ⅵ）的去除能力；在此基础上，以效果显著的纳米零价铁为基础，对其进行表面改性以解决其在空气中容易发生团聚和氧化问题，并将改性前后纳米铁材料应用于Cr（Ⅵ）和Cu²⁺污染物的治理上，考察稳定前后零价纳米铁对重金属污染物去除效果的影响。实验对水体中Cr（Ⅵ）和Cu²⁺的去除考察了多种影响因素，探讨了反应动力学，揭示了反应机理；以期为纳米零价铁或铁（氢）氧化物治理重金属污染物提供理论依据。主要研究结果如下：以均匀沉淀法和碱性条件水解高氯化铁方法制备赤铁矿（α-Fe₂O₃）和针铁矿（α-FeOOH）；以NaBH4液相还原FeCl₃·6H₂O制备普通纳米零价铁（N-Fe⁰），并通过三系列、多种分散剂的筛选，制备出以2-膦酸丁烷-1,2,4-三羧酸（PBTCA）改性的纳米零价铁P-Fe⁰、工业用水处理剂TH-904改性的纳米零价铁T-Fe⁰。运用XRD、SEM、TEM及FTIR等多手段对制备产品的表征表明，合成的α-Fe₂O₃、α-FeOOH结晶度好，性能优良；改性后纳米铁表面检测到PBTCA分子中-PO₃H₂基团，TH-904分子中的-COOH基团，证明改性实验成功，合成的P-Fe⁰及T-Fe⁰的平均粒径分别为73和64nm。以纳米零价铁系列产品N-Fe⁰、P-Fe⁰及T-Fe⁰为一组，以铁（氢）氧化物产品α-Fe₂O₃和α-FeOOH为一组，分别对水溶液中Cr（Ⅵ）的去除效果进行对比考察，通过pH、初始浓度、温度等因素考察、吸附动力学分析，XPS手段机理揭示，得出纳米零价铁系列所有产品对溶液中Cr（Ⅵ）的去除效果均优于铁（氢）氧化物产品。其中，N-Fe⁰、P-Fe⁰及T-Fe⁰产品中，改性后的P-Fe⁰及T-Fe⁰对溶液中Cr（Ⅵ）的去除率和反应动力学表观速率常数均高于改性前的N-Fe⁰；α-Fe₂O₃和α-FeOOH相比较，α-FeOOH对溶液中Cr（Ⅵ）的去除率和吸附速率常数均较α-Fe₂O₃高。反应机理分析表明纳米零价铁对水溶液中Cr（Ⅵ）的去除机制主要为零价铁的氧化-还原反应，其次还有吸附及共沉淀等作用。而铁（氢）氧化物产品对Cr（Ⅵ）的去除则主要借助吸附作用。反应后铁以Fe（Ⅲ）形式存在，纳米零价铁表面的Cr（Ⅵ）被还原为Cr（Ⅲ）。以纳米零价铁系列产品N-Fe⁰、P-Fe⁰及T-Fe⁰为水处理材料，对水溶液中Cu²⁺的去除效果进行考察，通过pH、初始浓度等因素考察、吸附动力学分析，XPS手段机理揭示，得出N-Fe⁰、P-Fe⁰及T-Fe⁰对Cu²⁺的去除能力顺序为P-Fe⁰>T-Fe⁰>N-Fe⁰，吸附动力学符合准二级速率方程，反应机理包括Fe（0）对Cu²⁺的还原作用和吸附作用，反应后铁以Fe₂O₃和FeOOH形式存在，纳米零价铁表面的铜被还原为Cu0和Cu2O。以工业常用水处理剂PBTCA及TH-904作为稳定剂对纳米零价铁进行表面改性处理。PBTCA分子中含有1个-PO₃H₂及3个-COOH基团，TH-904分子含有多个-COOH基团，改性后纳米零价铁颗粒表面吸附-PO₃H₂及-COOH基团，空间位阻效应减弱了颗粒间相互聚集的倾向，增大了纳米颗粒间的距离；此外，PBTCA及TH-904分子在溶液中水解后改变了粒子的表面电荷分布，颗粒间增大的静电斥力也阻碍纳米颗粒间的相互团聚。空间位阻和静电稳定双重作用使纳米铁颗粒得到有效分散，对增加Cr（Ⅵ）和Cu²⁺去除起到了重要作用。更多还原

【Abstract】 The surge of industrial activities has intensified more environmental problems as seen forexample in the deterioration of several ecosystems due to the accumulation of dangerouspollutants，such as heavy metals. Heavy metals are still being used in various industries due totheir technological importance. Yet, untreated or imperfect treatment of waste products fromthese industries will carry other serious issues to human health and environment. Aside fromthe environmental damage, human health is likely to be affected as the presence of heavymetals beyond a certain limit brings serious hazards to living organisms. For instance, Cr （VI）,Cd²⁺, Cu²⁺and Ni²⁺ions have been proven to cause kidney damage, liver damage or Wilsondisease and dermatitis or chronic asthma. Therefore, heavy metal pollution treatment isurgent.Iron based materials, including iron hydroxides and zero-valent iron are usedsuccessfully for remediation of a variety of environmental pollutants. Goethite and hematiteare always considered to be important environmental materials which can be functioned asadsorbents for heavy metals. They widely exist in soil particles and rock, aquatic sediment.Due to large specific surface area and more active sites, the use of zero-valent iron （Fe⁰），especially nanoscale zero-valent iron （N-Fe⁰）, as reactive media for treatment of heavymetals and for remediation of contaminated soil and groundwater has been extensivelyinvestigated. Nanoparticles are defined as particles with size in the range of1to100nm atleast in one of the three dimensions. Because of this very small size scale, they possess animmense surface area per unit volume, a high proportion of atoms in the surface and nearsurface layers, and the ability to exhibit quantum effects. The resulting unique properties ofnanoparticles can not be anticipated from a simple extrapolation of the properties of bulkmaterials. The synthesized nanoparticles have to be surface modified in most cases, in orderto passivate and stabilize them since their nanoscale renders them chemically very reactiveand/or physically aggregative. The nanoparticles are also surface functionalized in order tomeet the needs of specific applications.In this research work, the wastewater containing Cr （VI） was treated through contrastresearch by N-Fe⁰, α-Fe₂O₃and α-FeOOH synthesized in the lab. On the bases of theexperimental results, the intensive efforts have been made to coat and protect Fe⁰nanoparticles from agglomeration and air oxidation. The influences of pH, initialconcentrations of heavy metal ions, temperature and the dosages of iron bases materials onthe Cr （VI） and Cu²⁺ions removal were investigated. The kinetics and mechanisms of Cr （VI）and Cu²⁺ions removal were also discussed in this research work. The main details and results were presented:Microcrystalline precipitates of hematiteα-Fe₂O₃and goethite α-FeOOH were preparedfrom ferric ions. The N-Fe⁰nanoparticles were prepared with FeCl₃·6H₂O and NaBH4byliquid reduction, and the P-Fe⁰and T-Fe⁰nanoparticles were modified by2-phosphonobutane-1,2,4-tricarboxylic acid （PBTCA） and TH-904respectively with thesame method. The X-ray diffraction （XRD）, scanning electron microscope （SEM）,transmission electron microscope （TEM） and Fourier transform infrared spectroscopy （FTIR）were conducted to characterize the structure of these products. The results show that hematiteα-Fe₂O₃and goethite α-FeOOH had good crystallinity and excellent performance. The-PO₃H₂group on the P-Fe⁰nanoparticle surface and the-COOH group on the T-Fe⁰nanoparticle surface were detected by FTIR spectroscopy, which demonstrated themodification for N-Fe⁰nanoparticles were successful. TEM images illustrated that theaverage diameters of produced P-Fe⁰and T-Fe⁰nanoparticles were about73and64nmrespectively.The experiment results on Cr （VI） removal by N-Fe⁰, P-Fe⁰and T-Fe⁰nanoparticlesshowed that the removal efficiencies by P-Fe⁰and T-Fe⁰nanoparticles were higher than thoseby N-Fe⁰nanoparticles, as well as the reaction kinetics apparent rate constants. The findingsby hematite α-Fe₂O₃and goethite α-FeOOH demonstrated that the goethite α-FeOOH wasbetter than hematite α-Fe₂O₃on Cr （VI） removal. Furthermore, all the iron nanoparticles（N-Fe⁰, P-Fe⁰and T-Fe⁰） were greatly superior to α-Fe₂O₃and α-FeOOH on Cr （VI） removal.Mechanism analysis indicated that the Cr （VI） uptake by the iron nanoparticles （N-Fe⁰, P-Fe⁰and T-Fe⁰） was mainly via a redox by Fe （0） particles, but the one by hematite α-Fe₂O₃andgoethite α-FeOOH was primarily of adsorption.The experiment results on Cu²⁺ions removal by N-Fe⁰, P-Fe⁰and T-Fe⁰nanoparticlesshowed that the Cu²⁺ions removal efficiencies by P-Fe⁰and T-Fe⁰nanoparticles were higherthan those by N-Fe⁰nanoparticles, as well as the adsorption rate constants. The efficiencies ofCu²⁺ions removal for different iron nanoparticles were P-Fe⁰>T-Fe⁰>N-Fe⁰, which obtainedthrough investigating the influencing factors, such as pH, Cu²⁺ions initial concentration,temperature, as well as analyzing the kinetics and mechanisms. The rate of Cu²⁺ionsadsorption kinetics on the iron nanoparticles followed the pseudo-second order equation. Themechanism was mainly of redox by Fe（0） nanoparticles. XPS results showed that Fe（0）particles was oxided to Fe₂O₃和FeOOH and the Cu²⁺ions was reduced to Cu0和Cu2O afterreaction.The nanoscale zero-valent iron was modified by PBTCA and TH-904. There is a-PO₃H₂group and three–COOH groups in a PBTCA molecule, and many–COOH groups in aTH-904molecule. On one hand, the-PO₃H₂and–COOH groups on the P-Fe⁰and T-Fe⁰ nanoparticle surfaces increased the distances and, therefore, weaken the aggregation forcesbetween the iron nanoparticles, on the other hand, the hydrolysis of PBTCA and TH-904molecules in the solution changed the charge distribution on the iron nanoparticle surfaces,which increased the electrostatic repulsion hence hindering the interaction between ironnanoparticles. The modified iron nanoparticles can achieve good dispersibility when theelectrostatic stabilize effect and space steric hindrance stabilize effect act simultaneously. Thegood dispersibility of iron nanoparticles played an important role in increasing theefficiencies of Cr （VI） and Cu²⁺ions removal.更多还原