【作者】 刘云；

【导师】 党志；

【作者基本信息】 华南理工大学 ， 环境工程， 2011， 博士

【摘要】 黄铁矿作为一种最为常见的硫化物矿物,普遍存在于各种矿石及尾矿堆中,同时也常见于各种贵金属伴生矿中。黄铁矿的氧化能引起矿山酸性废水AMD （acid mine drainage）的产生,而AMD将会造成生态环境的重金属及酸污染。为了从源头上控制酸性废水的产生,有必要先了解黄铁矿的氧化机理,从而找出有效的钝化处理方法以减少黄铁矿的氧化程度。本文利用开路电位（OCP）、循环伏安（CV）、Tafel极化曲线、交流阻抗（EIS）等电化学分析技术研究黄铁矿在无菌体系和有菌体系中的电化学行为,从电化学角度揭示黄铁矿的化学和生物氧化机理。在此基础上,探讨了三乙烯四胺（TETA）抑制黄铁矿化学氧化和生物氧化的可能性。得到如下主要结果与结论:黄铁矿在酸性溶液中的氧化过程是通过两个步骤完成:第一步是铁溶出而被氧化为亚铁或Fe（Ⅲ）,此时将会在黄铁矿表面形成中间产物如单质硫、多硫化物（FeSn）和缺铁硫化物(Fe_1-xS₂)。第二步为黄铁矿表面中间产物的进一步氧化成SO₄^2-。当溶液中不含氧化亚铁硫杆菌（A.f菌）时,Fe³⁺离子对黄铁的氧化将起非常重要的作用。Fe³⁺离子的加入不会改变黄铁矿的氧化机理,但却能大大加速黄铁矿的第一步氧化速率。同时Fe³⁺离子对黄铁矿表面形成的硫膜的氧化并不明显。Tafel极化曲线和EIS的测量表明随着Fe³⁺离子浓度的增加,黄铁矿的表面越容易产生钝化层。微生物浸矿实验表明氧化亚铁硫杆菌的存在能极大的促进了黄铁矿的氧化溶解。浸矿实验结束时,有菌体系中的铁离子的浓度可达到无菌体系中铁离子浓度的8倍。而且经黄铁矿驯化培养后的A.f菌对黄铁矿的氧化能力要高于未经驯化的细菌。黄铁矿细菌浸出过程中体系的氧化还原电位上升较快,这是因为细菌可以迅速的促进溶液中的亚铁离子氧化为Fe（Ⅲ）离子,从而对黄铁矿保持较高的氧化速率。另外黄铁矿细菌氧化后浸出液的pH值会降低,这可能也是黄铁矿氧化速率较快的一个重要原因。同时电化学测量结果也表明,A.f菌的存在能显著提高黄铁矿电极的腐蚀电流密度。通过对黄铁矿在无菌及有菌体系中的交流阻抗的测量,发现氧化亚铁硫杆菌的存在不仅加速了黄铁矿中铁离子的浸出,更重要的是能将富集在黄铁矿表面的硫元素进一步氧化,从而使黄铁矿的氧化程度进行得比较彻底。在黄铁矿细菌氧化的中后期,黄铁矿中铁元素的浸出速率非常快,而对黄铁矿氧化速度起控制作用的步骤是矿物表面硫膜的氧化过程。在无菌体系中,黄铁矿表面富集的硫元素很难被氧化,从而会在矿物表面形成一层钝化层,限制着黄铁矿的进一步氧化。而且黄铁矿氧化前后的表面化学性质及形貌的观察也证实了这一点。利用电化学方法研究硫酸溶液中TETA对黄铁矿氧化的钝化效果。结果表明,TETA是能有效的抑制黄铁矿的化学氧化,经包膜处理后的黄铁矿电极阴极还原速率和阳极氧化速率都会受到不同程度的抑制。且其对黄铁矿氧化的抑制效率会随其浓度的增加而增大。Tafel极化曲线的测量结果显示:TETA浓度由1%增加到5%时其对黄铁矿的钝化效率也相应的由42.08%增加到80.98%。这个结果与EIS法测得的结果有很好的一致性（EIS结果为43.09% to 82.55%）。另外由Tafel极化曲线也可得知TETA是属于混合型的钝化剂,它可以同时对发生在矿物表面的的阴极还原及阳极氧化过程产生抑制作用。而TETA之所以能降低黄铁矿的化学氧化速率,主要原因是它可以通过化学吸附牢固的吸附在黄铁矿表面而形成一层比较稳定的保护层。最后,TETA抑制黄铁矿生物氧化的能力也通过电化学方法进行了测量。用黄铁矿碳糊电极作为指示电极监测钝化和未钝化的黄铁矿底物受A.f菌氧化时的氧化速率。通过比较黄铁矿碳糊电极在不同体系中的电化学活性随时间的变化,发现TETA在有菌体系中也能显著降低黄铁矿的氧化速度。TETA钝化法不但能同时抑制黄铁矿的化学和生物氧化,还具有操作简单、实用性强等特点。因此TETA在源头上抑制黄铁矿氧化,控制AMD污染方面具有很好的前景。更多还原

【Abstract】 Pyrite （FeS2） is a common iron sulfide mineral in tailings and waste rock dumps; it is also present in many valuable mineral raw materials. The oxidation of pyrite can produce acid mine drainage, which is then a cause of pollution by heavy metals and acidity. For the control of acid mine drainage at source, it’s essential to understand the oxidation mechanism of pyrite. Then we could find an effective passivation method to suppression the oxidation process of pyrite.Electrochemical analysis methods, such as open circuit potential （OCP）, cyclic voltammetry （CV）, Tafel polarization curves and electrochemical impedance spectroscopy （EIS） were used to investigate electrochemical behavior of pyrite in systems with and without bacteria, revealing the mechanism of pyrite’s chemical and biological oxidation. On these bases, the feasibility of triethylenetetramine （TETA） to inhibit the chemical and biological oxidation of pyrite had also been investigated. The major conclusions are given below:The oxidation process of pyrite in acid solution is via a two-step reaction occurring at the surface of pyrite: the first step is the dissolution of iron moiety and that a passivation film composed of elemental sulphur,polysulfides and metal-deficient sulfide is formed during the process of the first-step reaction. The second step is the further oxidation of these intermediate products to SO₄^2-. In sterile solution, Ferric iron plays an important role in the dissolution of pyrite by enhancing the direct oxidation. The Tafel polarization curves indicate that the polarization current of the pyrite electrode increases with an increase in Fe³⁺ concentration. The results of polarization curves and EIS had also been shown that the higher concentration of Fe³⁺, the more easily the pyrite can be transformed into the passivation region.The results of bioleaching tests showed that Acidithiobacillus ferrooxidans （A.f） can significantly improved the leaching rate of pyrite. At the end of the experiment, the concentration of total soluble iron in bioleaching solution was 8 times of that in sterile solution. Moreover, the leaching efficient of A.f bacteria after domestication was increased compared with that before domestication. The redox potential in the system with bacteria was increased much faster than that in sterile solution, which resulted from the fast oxidation of ferrous ions to ferric ions. The leached Fe³⁺ could in turn accelerate the oxidation of the pyrite. In addition, the pH of bioleaching solution was decreased with times. This may also be an important canse of the fast dissolution of pyrite in bioleaching system.The electrochemical behavior of a pyrite-carbon paste electrode in system with and without Acidithiobacillus ferrooxidans was also investigated. The results showed that the addition of A.f bacteria could enhance the corrosion current of pyrite electrode greatly. The corrosion of pyrite electrode became more serious with the increase of bioleaching time. The EIS responses were different with time in both inoculated and sterile solution, which suggested the kinetic processes occurring in the pyrite–solution interface were changed during the leaching process. In the initial stage of pyrite oxidation, the corrosion rate of the pyrite was mainly controlled by the process of iron moiety dissolution in both of the systems with and without bacteria, which results in the formation of some intermediate products such as elemental sulfur and polysulfide on the surface of pyrite. In the presence of bacteria, these intermediate products could be continuously oxidized to SO₄^2-. But in the sterile solution, the further oxidation of S was difficult to be detected by EIS measurement. These results were also confirmed by surface analysis and which showed that the principal advantage of the presence of microorganisms was to continuously remove the elemental sulfur from the surface of pyrite.The potential of triethylenetetramine （TETA） to inhibit the oxidation of pyrite acid solution has been investigated using the open circuit potential （OCP）, cyclic voltammetry （CV）, potentiodynamic polarization and electrochemical impedance （EIS） respectively. Experimental results indicate that TETA is an efficient coating agent in preventing the oxidation of pyrite and the inhibition efficiency is more pronounced with the increase of TETA. The data from potentiodynamic polarization show that the inhibition efficiency （η%） increases from 42.08% to 80.98% with the concentration of TETA increasing from 1% to 5%. These results are consistent with the measurement of EIS （43.09% to 82.55%）. The information obtained from potentiodynamic polarization also display the TETA is a kind of mixed type inhibitor, both cathodic and anodic process can be inhibited by the coating of TETA. The coating treatment of pyrite with TETA can be described as chemisorption of TETA molecules on the surface of sample particles and lead to the formation of a protective film, and this film prevent from the oxidation of pyrite.At the end of this paper, the feasibility of using triethylenetetramine （TETA） as protecting agent to reduce the biological oxidation of pyrite had also been studied by methods of electrochemical techniques. A pyrite-carbon paste electrode was utilized to monitor the oxidation rate of pristine and TETA coated pyrite oxidation in the presence of Acidithiobacillus ferroxidans bacterium. By comparing the changes of the electrochemical activity for the pyrite-carbon paste electrode, reflected by the measurements of open circuit potential （OCP）, cyclic voltammetry（CV）, Tafel polarization analysis and electrochemical impedance spectroscopy （EIS）, in different bioreactor with pyrite samples coated by various concentrations of TETA, we could find that TETA is an efficient coating agent in preventing the oxidation of pyrite in the presence of bacteria. Compared to other coatingt reatments, the coating by TETA can limit both the chemical and biological oxidation of pyrite; meanwhile, it could represent a simple, cost-eficient method to control the oxidation of pyrite.更多还原