【作者】 赵开乐；

【导师】 顾帼华；

【作者基本信息】 中南大学 ， 矿物加工工程， 2010， 硕士

【摘要】 随着经济的发展,矿产资源日渐贫乏,人们不得不考虑采用新的方法开发和利用低品位、难处理矿产资源。微生物冶金由于其成本低、污染小、工艺流程短等优点越来越受到研究者的关注。磁黄铁矿是有色金属硫化矿矿床中一种很常见的硫铁矿,其常与有价金属(如镍、钴、铜、锌等)伴生。研究磁黄铁矿在微生物浸出过程中的氧化溶解机理,对微生物浸出低品位硫化矿,有效回收有价金属有重要意义。本文采用A.ferrooxidans菌、L.ferriphilum菌和A.caldus菌,在讨论磁黄铁矿晶体性质及其浸出体系热力学分析的基础上,通过Zeta电位、吸附量和表面润湿性测定,结合X射线衍射、能谱分析等表面测试方法,考察磁黄铁矿与细菌作用后表面性质的变化及细菌作用机理。以A.ferrooxidans菌和L.ferriphilum菌为试验菌种,通过摇瓶浸出试验,结合扫描电镜,研究矿浆浓度、细菌接种量、矿浆pH值等因素对磁黄铁矿浸出的影响；并运用循环伏安、静电位、塔费尔曲线、交流阻抗等电化学分析技术研究磁黄铁矿在无菌体系和有菌体系中的电化学行为,从电化学角度揭示微生物浸出体系磁黄铁矿的氧化机理。利用FeS1.12-H2O系的Eh-pH图,分析磁黄铁矿浸出过程。微生物浸出磁黄铁矿的最佳电位-pH范围是Eh为0.4-0.8V、pH为1-3；在Eh=0.36-0.8V,pH=2.28-4.0范围内,Fe3+可能主要以沉淀的形式存在。在酸性溶液中,磁黄铁矿稳定存在的区域在0.4V以下,说明磁黄铁矿稳定性很差,在较低的电位水平下就会被氧化溶解。晶体结构性质决定着磁黄铁矿氧化溶解的行为,单斜磁黄铁矿的化学稳定性较差,在酸性体系下可以快速溶解。表面性质研究结果表明：不同类型的细菌均能快速吸附在磁黄铁矿表面,而矿驯化细菌具有更强的吸附能力。不同类型的细菌吸附后,磁黄铁矿的等电点朝细菌的等电点方向偏移,但偏移幅度不同。且不同的菌种浸出磁黄铁矿过程中,体系中生成和富集的产物不同,从而导致矿物表面接触角有不同的变化规律。研究表明：磁黄铁矿生物浸出初期以酸溶为主；微生物生长所需能源是决定其在浸出体系的作用机理关键因素,氧化亚铁细菌的微生物冶金过程中的作用机理是间接作用,硫化矿物被溶液中Fe3+氧化；氧化硫细菌的作用机理是直接作用,硫化物在细菌的参与下被O2所氧化。有菌和无菌酸性体系下磁黄铁矿氧化的电化学研究结果表明：磁黄铁矿表面首先在0.2V附近氧化产生三价铁沉淀和元素S,电位大于0.6V后,铁沉淀部分溶解,元素S被氧化生成S042-,钝化膜部分溶解,极化电流显著增加；交流阻抗研究进一步表明,随着电位由低到高,磁黄铁矿的氧化经历了钝化膜的形成和消除过程；细菌不改变磁黄铁矿的氧化机理,只对磁黄铁矿的腐蚀起加速作用,添加细菌后,磁黄铁矿的腐蚀电位降低,腐蚀电流增大,促进了腐蚀反应的发生,提高了腐蚀速率,磁黄铁矿发生化学反应的速率加快且此时电极氧化还原反应可逆性降低。摇瓶浸出研究结果表明：细菌的存在促进磁黄铁矿的溶解,在L.ferriphilum菌浸出体系中,浸出7天,全铁浸出率可达38.35%,高于相同条件下的无菌浸出；浸出体系温度是磁黄铁矿浸出的主要影响因素,磁黄铁矿极易氧化,浸出过程中体系电位一直高于0.3V,磁黄铁矿在细菌作用下被氧化生成Fe2+和5042-,以氧化亚铁为能源的细菌浸出磁黄铁矿的作用机理是间接作用；增大矿浆浓度抑制磁黄铁矿的溶解,矿浆浓度过大会影响溶氧量、增大矿粒间的剪切力从而影响细菌的生长；提高接种量和每天调整矿浆pH至初始值有利于细菌生长,促进磁黄铁矿浸出。本论文得到国家自然科学基金创新研究群体项目(50321402)和国家重点基础研究发展973项目(2010CB630903、2004CB619204)的资助。更多还原

【Abstract】 With the development of economy, the mineral resources are reducing greatly. As a result, we ought to turn to use new methods to process mineral resources of low grade. Bioleaching technology now attracts more attention than ever before for its low cost, environmental acceptance and simplicity. Pyrrhotite is a common iron sulfide in nature and is usually associated with various useful components, such as nickel, cobalt, copper, zinc and other valuable metals. Therefore, the study of the oxidation dissolution of pyrrhotite in bioleaching process means a lot in comprehensive utilization of low grade sulfide minerals and the extraction of valuable metals.On the basis of property of pyrrhotite crystal and its leaching thermodynamics, the variation of surface properties of pyrrhotite after biological conditioning with Acidithiobacillus ferrooxidans, Leptospirillum ferriphilum and Acidithiobacillus caldus was evaluated by zeta-potential, adsorption and contact angle measurements. The effect of slurry concentration, the amount of bacteria, pH value, etc. on pyrrhotite leaching in the presence of A.ferrooxidans and L.ferriphilum were conducted with SEM; the electrochemistry behavior of pyrrhotite with and without bacteria were conducted by electrochemical analysis methods (cyclic voltammetry (CV), Electrostatic potential, polarization curves and electrochemical impedance spectroscopy) to disclose the oxidation mechanism of pyrrhotite in microbic leaching system.The leaching process of pyrrhotite was analysed by the figure of Eh-pH of FeS1.12-H2O.The best conditions of bioleaching of pyrrhotite are Eh=0.4-0.8V and pH=1-3. When the system Eh is between 0.36-0.8V, pH is in 2.28-4.0, the ferric ion may mainly exist in the form of precipitates.In acidic solution, the stable existing zone is blow 0.4V, which means that pyrrhotite would be oxidized and dissolved at very low potential. The characteristics of pyrrhotite crystal determines the oxidization dissolution rate, and the polymorphism of monoclinic system is likely to present unstable chemistry property and be easily oxidized by acid and other oxidants.The results of research on surface properties showed that all types of bacterium adhered to pyrrhotite surface rapidly, but the pyrrhotite adapted bacteria had the stronger adsorption ability. The pyrrhotite isoelectric point (IEP) shifts towards the cell isoelectric point after interacting with bacteria cells, indicating the adsorption of cells on the pyrrhotite surface, and the shift degree was different. After treatment by different bacteria, due to the formation of sulfur membrane or the ferric ion was relatively enriched on the pyrrhotite surface, the change of contact angle and surface hydrophobicity were not the same. The results indicate that the pyrrhotite dissolution may be dominated by the acid dissolution during the initial bioleaching, the energy source for the microorganism growth determines its function mechanism in the bioleaching system. The iron-oxidizing bacteria offer an indirect mechanism function (sulfide mineral was oxidized by dissolved Fe3+) and the sulfur-oxidizing bacteria offer a direct mechanism function (sulfide mineral was oxidized by O2 in bioleaching process).The electrochemical study of oxidation of pyrrhotite in the presence and absence of bacteria in acidic system showed that pyrrhotite was firstly oxidized to sulfur or iron (ⅲ) complex at the potential of 0.2V, which covered the electrode and made electrode passivated; as the scanning potential rising, S was oxidized to SO42-, making the passive film dissolved. The result of AC impedance further showed within the electrode potential region of 0.2-0.7V, the oxidation of pyrrhotite firstly formed passive film and then passive film dissolved. In the solution with bacteria, the mechanism of pyrrhotite oxidation didn’t changed, but the corrosion potential and corrosion current of pyrrhotite increased, which showed bacteria promoted the oxidation of pyrrhotite.The results of bioleaching experiments showed that bacteria can improved the leaching rate of pyrrhotite; at the 7th day of bioleaching experiment, the total-iron extraction reached 30.14%, much higher than that in sterile solution. The temperature of reaction system is the main factor for pyrrhotite leaching, and pyrrhotite can be easily oxidized. The system electric potential of leaching keeps above 0.3V and pyrrhotite was oxidized to Fe2+ and SO42-.The iron-oxidizing bacteria offer an indirect mechanism function. Increasing the mineral concentration can depress the dissolution of pyrrhotite; increasing inoculation amount and adjusting the pH value to initial number are beneficial to the growth of pyrrhotite and thus promoted the leaching of pyrrhotite.The dissertation was supported by "National Basic Research Program" (2010CB630903,2004CB619204) and "National Nature Science Foundation of China" (50621063).更多还原