【作者】 熊慧欣；

【导师】 周立祥；

【作者基本信息】 南京农业大学 ， 生态学， 2008， 博士

【摘要】 重金属铬污染主要来源于采矿、电镀、颜料、皮革等工业废水和垃圾渗滤液等,含Cr（Ⅲ）和Cr（Ⅵ）的排泄废水易引起地表水和地下水的铬污染。其中,Cr（Ⅵ）毒性极强,对人体有致畸致癌作用。目前,利用生物和矿物材料（铝硅酸盐矿物、碳酸盐矿物和铁的氢氧化物等）去除重金属是研究者们关注的热点。羟基氧化铁（FeOOH）广泛存在于土壤、水体沉积物和矿山废水等自然环境中,通常以针铁矿（α-FeOOH）、纤铁矿（γ-FeOOH）和四方纤铁矿（β-FeOOH）等多种同质多像体形式存在,它们可通过沉淀、离子交换和吸附等作用,有效去除环境介质中的污染金属。羟基氧化铁因具有较稳定的化学性质,较高的比表面积和细微的颗粒结构,作为重金属等污染物的吸附材料倍受关注。但不同因素作用下形成的FeOOH产物矿相、结构性质的差异,及其对环境功能的影响,却少有报道。为此,本论文系统研究了不同合成途径（水解中和、化学氧化、生物氧化和凝胶网格作用）和不同影响因素（反应铁盐、pH、温度、离子、生物氧化和有机大分子固定等）作用下羟基氧化铁的制备,并对其结构性质进行了表征,在此基础上比较了它们对水中重金属Cr（Ⅵ）的吸附去除效果,重点探讨了四方纤铁矿的生物合成及其对Cr（Ⅵ）的去除效能与作用机理,为环境材料的研发提供科学依据。主要研究结果如下:化学水解中和合成FeOOH时,pH8条件下,所有Fe（Ⅲ）溶液水解产物均为二线水铁矿（Fe₅HO_B·4H₂O）;随着pH升高,Fe₅HO₈·4H₂O会向α-FeOOH相转化;Cl^-、NO₃^-离子的存在分别有利于β-FeOOH、α-FeOOH的形成;SO₄^2-会阻碍Fe₅·HO₈·4H₂O向a-FeOOH相转化。在Fe²⁺作用下,会促进Fe₅HO₈·4H₂O向α-FeOOH相转化。加热陈化可促进Fe₅HO₈·4H₂O转化为α-FeOOH,且有利于良好结晶α-FeOOH的形成;但pH<5,富含Cl^-的铁盐溶液加热水解有利于β-FeOOH的生成。四方纤铁矿A1、A2和针铁矿Gl、G4的合成条件和产物颗粒形貌结构,使其表现出更为优越的吸附Cr（Ⅵ）的界面特性,对Cr（Ⅵ）的最大吸附量可达到24-27mg g^-1,是一种较好的环境吸附材料。亚铁空气氧化合成FeOOH时,不同反应pH下,形成的铁矿物产物分别为γ-FeOOH（^pH6.7）、γ-FeOOH和α-FeOOH的混合相（pH为6.7和7.0）、α-FeOOH（pH为8.5、11和12）,它们均由“短棒”状细小颗粒组成。（NH₄）₂Fe（SO₄）₂反应溶液（pH6.7-4.0）中形成的沉淀物以纤铁矿为主要矿相,H₂PO_<sup>-的加入会抑制纤铁矿的形成,而获得水铁矿产物,不同矿相铁矿物的颗粒形貌极相似,皆由直径约为20nm球形颗粒组成,且颗粒间易团聚。FeSO₄反应溶液（^pH4.0）中形成的沉淀物以针铁矿为主要矿相,A.ferrooxidans细胞的加入可促进Fe²⁺氧化,但对产物矿相和形貌不会产生影响,皆由易团聚的球形颗粒（直径约为20nm）组成。于室温下静置70天,γ-FeOOH样品Lep（～pH6.7）未发生矿相转化,只是其结晶度在静置70天后较30天明显要好。同样条件下,负载Cr（Ⅵ）的铁矿物样品Lep（^pH6.7）和Gth（pH8.5）溶液中Cr（Ⅵ）的释放量间的关系为γ-FeOOH（pH7.0）<γ-FeOOH（pH5.5）<α-FeOOH（pH7.O）<α-FeOOH（pH5.5）,对应值分别为7.2、8.2、8.7和9.6 mg g^-1;70天后,溶液中Cr（）的释放率依次为17.9、15.7、31.1和15.3%,α-FeOOH（pH7.0）溶中的Cr（Ⅵ）释放率约是另三者的2倍。显然,针铁矿样品Gth（pH8.5）在溶液pH7.0条件下,与Cr（Ⅵ）的结合能力较其在pH5.5时和纤铁矿样品Lep（^pH6.7）要差得多。室温下,FeCl₂溶液在Cl^-驯化A.ferrooxidans氧化作用下可形成表面粗糙的“纺锤形"四方纤铁矿颗粒,长约200nm、长宽比5;化学结构式为Fe₈O₈（OH）_7.1（Cl）_0.9,其中Fe/Cl的摩尔比为8.93;比表面积为100 m² g^-1。不同Cl^-/SO₄^2-摩尔比对形成铁矿物的影响为:很少量SO₄^2-就会抑制四方纤铁矿形成,即使溶液中含约10%的SO₄^2-时,铁矿物仍以施氏矿物为主要矿相;但较高Cl^-浓度对所生成施氏矿物颗粒形貌及大小会产生明显影响。所有含SO₄^2-反应中形成的沉淀物中施氏矿物相的理论化学计量表达式均可表示为Fe₈O₈（OH）_8-2x（SO₄）_x,其中1.09≤x≤1.79,其对应Fe/S摩尔比范围为4.3-8。FeCl₂溶液经Cl^-驯化A.ferrooxidans氧化形成铁沉淀物过程中,在反应1-10d内,产物均为四方纤铁矿,反应产物3d后的结晶度明显比1d时要好。生物β-FeOOH样品BiO-Aka用于去除污染水体中的Cr（Ⅵ）,比化学方法所制备FeOOH的去除效果有明显优势。该生物四方纤铁矿在pH3-12条件下均不会发生溶解现象,且在较宽的pH范围（pH3-8）内对Cr（Ⅵ）的去除效果较好。生物四方纤铁矿对Cr（Ⅵ）的吸附容量在pH5.5和pH7.0条件下分别约为58.5 mg g^-1和42.2 mg g^-1,约是化学法合成FeOOH中吸附效果(吸附容量约为26 mg g^-1)较好的四方纤铁矿A1和针铁矿G4的2倍或1.5倍。该矿物与Cr（Ⅵ）的作用机理主要为配位络合作用,随时间变化,反应符合Lagergren二级速度方程。用凝胶网格沉淀法,即明胶含量为12%,且铁盐浓度为0.6M时,可制备颗粒分散、大小均一的纳米结晶针铁矿微粒,其为短棒状形,轴长约110nm,直径平均约35nm。更多还原

【Abstract】 Chromium, existing in two major oxidation states such as Cr（Ⅲ） and Cr（Ⅵ）, mainly arising from the discharge wastewater of various industries including mining operation, metal plating, leather tanning, and pigment manufacturing, is among the common and persistent surface and ground water contamination. And Cr（Ⅵ） is most toxic and carcinogenic to organism.Presently, it is hot topic noticed by researchers that the biology and mineral materials such as alumino-silicates minerals, carbonate minerals and iron oxyhydroxides, are utilized to remove the heavy metals. Iron oxyhydroxides （FeOOH）, as a group ofα,β,γ-FeOOH polymorphs, are commonly found in some soils, sedmiments of water bodies, and acid mine drainage natural environments. They can availably remove the heavy metals from the contaminated environments by the approachs of coprecipitation, ions exchange and adsorption. Due to holding the stable chemistry properties, more large specific surface areas and fine particle structures, iron oxyhydroxides, as the adsorbent materials of heavy metals and other contaminants in environment media, are doubly noticed. However, little information is available on the FeOOH prepared under various conditions, existed differences in their phases and structural properties, inducing some differences in their environmental functions.Therefore, the objective of the paper firstly is to systematically investigate the synthesis of iron oxyhydroxides by the various methods, for example, ferric hydrolysis and neutralization , ferrous oxidation by air, ferrous biooxidation and gel-network precipitation methods, under the different conditions such as the kind of iron salt, pH, temperature, exterior ion, biological oxidation, and fixation by organic biological molecule. The resulting products are characterized by spectral methods to examine the phases and structural properties of iron oxyhydroxides. The other objective is that some of the characterized FeOOH are applied to remove Cr（Ⅵ）. In the present works, it is especially important work to formation of the bio-akaganeite and its application in removal of Cr（Ⅵ）, which provides a scientific proof for searching the potential adsorbent materials. The results of all works are presented as following.The iron oxyhydroxides were prepared by hydrolysis and neutralization of ferric ion from FeCl₃, Fe（NO₃）₃ and Fe₂（SO₄）₃ salts, under the conditions of the various pH values and aging for about 6 days at 60℃.Results showed that ferrihydrite formed in the ferric solutions containing Cl^-, NO₃^- and SO₄^2- at pH values of 8 and 10, except that the poor crystalline akaganeite phase generated in the FeCl₃ solution at pH10.It testified that the presence of Cl^- was favorable for the formation of akaganéite. Meanwhile, the poor crystalline goethite phase was observed to be formed in FeCl₃ or Fe（NO₃）₃ solution, but not be formed in Fe₂（SO₄）₃ solution at pH12.It indicated that the presence of SO₄^2- obviously inhibited the formation of goethite. However, the goethite phase formed in Fe₂（SO₄）₃ solution when addition of ferrous ion, indicating ferrous ion could promote the formation of goethite in SO₄^2--rich solution. In addition, it was usually easy to the crystalline goethite be transformed from the above generated ferrihydrite precipitates by aging at 60℃. Furthermore, the phase of akaganeite also was obtained in the Cl^--rich acid （pH<5） solution by aging at 60℃.Tthe resulting akaganeite （A1 and A2） and goethite （G1 and G4） comprised of fine particle, with large specific surface area, and interface property, were valid and potential adsorbents for removal of Cr（Ⅵ）, with a maximal sorption capacity of 24-27mg g^-1.Iron oxyhydroxides were also prepared from ferrous chemical oxidation by air at room temperature, with various reaction pH values, the H₂PO₄^- ion or Acidithiobacillus ferrooxidans. Results showed that lepidocrocite for sample Lep（⁶.7）, the mixture of lepidocrocite and goethite for samples of Gth+Lep（6.7） and Gth+Lep（7.0）, and goethite for samples of Gth（8.5）, Gth（11） and Gth（12）, were obtained from FeSO₄ solution with a constant pH of 6.7, a final pH of 6.7 or 7.0, and a final pH of 8.5,11 or 12, respectively. And all the above FeOOH were composed of small particles with the short-rod shaped morphologis. At one time, in the （NH₄）₂Fe（SO₄）₂ solution with a reaction pH range of 6.7-4.0, lepidocrocite phase generated, while ferrihydrite formed in the solution when the exterior H₂PO₄^- ion was added. It indicated that H₂PO₄^- ion inhibited the formation of lepidocrocite phase. In addition, in the FeSO₄ solution with a constant pH of 4.0, goethite phase could form in the solution with/without Acidithiobacillus ferrooxidans cells, but the microbe obviously accelerated the oxidation of ferrous ion. Furthermore, it was noticed that the similar morphologies of sphere shaped for the resulting particles with the diameter of 20nm, were obtained from the solutions, though the pH of the reaction solutions are 6.7-4.0 and 4.0, respectively.Furthermore, during testing the stability of sample Lep（-6.7） withγ-FeOOH phase, it was observed not to be transformed to goethite in aqueous solution with a solid/liquid weight ratio of 1/1000 and a pH of 5.5 or 7.0,when the resulting suspensions were placed undisturbedly at 24℃for 70 days, but better crystallineγ-FeOOH be indentified for solid sample at the 70th day than at the 30th day. Moreover, in the above similar experimental conditions, the capacities of keeping Cr（Ⅵ） for sample Lep（-6.7） withγ-FeOOH phase and sample of Gth（8.5） withα-FeOOH were determined by the released percentages of Cr（Ⅵ） from the saturated Cr（Ⅵ）-loading samples. Results showed that the quantities of Cr（Ⅵ） released fromγ-FeOOH（pH7.0）,γ-FeOOH（pH5.5）,α-FeOOH（pH7.0） andα-FeOOH（pH5.5） orderly were 0.72, 0.82, 0.87 and 0.96 mg g^-1, resulting a increasing order. In addition, at the 70th day, the corresponding released percentages of Cr（Ⅵ） for the above samples were 17.9, 15.7, 31.1 and 15.3%, respectively. Obviously, the released percentage of Cr（Ⅵ） forα-FeOOH（pH7.0） is about two times of those of other samples. It proved that Gth（8.5） withα-FeOOH had a lower ability of keeping Cr（Ⅵ） in aqueous solution with a pH of 7.0, following higher risk to the ambient.Akaganeite biosynthesis from FeCl₂ solution oxidized by chrolide-acclimated Acidithiobacillus ferrooxidans LX5 cells at 28℃,with spindle-shape approximately 200 nm in length with an axial ratio of about 5 and the spindles having a rough surface, its chemical formula of the crystalloid akaganeite could be expressed as Fe₈O₈（OH）_7.1（Cl）_0.9 with Fe/Cl molar ratio of 8.93. The biogenic akaganeite had a specific surface area of about 100 m² g^-1by BET method. In addition, the results of effect of Cl^-/SO₄^2- mole ratio showed that sulfate inhibited drastically the formation of akaganeite, resulting in only schwertmannite occurrence in the ferrous solution containing both sulfate and chloride. The presence of chloride in ferrous solution containing sulfate would enable the obtained schwertmannite possess different morphologies and characteristics depending on Cl^-/SO₄^2- mole ratio in initial reaction system. It implied that iron（Ⅲ） oxyhydroxysulfate might be the only iron mineral phase in acidic ferrous and Acidithiobacillus ferrooxidans -rich solutions as long as the presences of trace sulfate. Finally, in the reaction time of 0-10 days, the resulting precipitates were always the phase ofβ-FeOOH,except that it had a better crystallinity after reaction for 3 days than ahead. The above obtained bio-akaganeite had a notable advantage in removal of Cr（Ⅵ）, comparing the chemo-akaganeite. Firstly, the bio-akaganeite didn’t dissolve in the aqueous solutions with the pH ranges of 3-12. Furthermore, it was testified that the bio-akaganeite had a similar removal efficiency of Cr（Ⅵ） in a wide pH rangs of 3-8. In addition, under the pH of 5.5 and 7.0, the bio-akaganeite had a maximal load capacity of 58.5 and 42.2 mg g^-1, respectively, correspondly being about 2 and 1.5 times of the load capacities of chemo-akaganeite （A1） and chemo-goethite （G4）. It concluded that the adsorption of Cr（Ⅵ） on bio-akaganeite by the major adsorption mechanism of surface complexiation models and the kinetic model of Lagergren secord order rate equation for Cr（Ⅵ） in aqueous solution with a pH of 7.0.In the last work, a novel gel-network precipitation method was developed to synthesize goethite in the presence of the optimum concentrations of glutin （12%） and FeCl₃ solution （0.6 M）. Resulting particle had better monodispersity, and had a short rod-type shape approximately 110 run in length with an average diameter of about 35 run.更多还原