【作者】 胡可婷；

【导师】 顾帼华；

【作者基本信息】 中南大学 ， 矿业工程， 2014， 博士

【摘要】 摘要：中温菌浸出黄铜矿的速度慢,浸出率低,严重制约着生物浸出技术在实际生产中处理黄铜矿的应用。高温菌对黄铜矿显示出好的浸出效果,其浸矿潜力及浸矿机制越来越受到生物冶金领域研究者的重视。本论文在热力学分析基础上,采用吸附量、动电位、接触角测定等方法研究了中温菌和高温菌对黄铜矿表面性质的影响及与溶解机制的关系；并运用X射线衍射、拉曼光谱、扫描电镜和能谱等检测方法,以及电化学分析等手段,详细考察和比较了中温菌及高温菌作用下黄铜矿浸出过程的差别,深入讨论了导致黄铜矿浸出效果差异的原因及影响黄铜矿溶解机理的因素,从而揭示微生物浸出过程中黄铜矿的分步溶解机制。本文提出了黄铜矿的浸出是一个分步溶解过程,在低氧化还原电位下可转化为次生铜,次生铜的生成是深度溶解的关键,促进浸出,这是导致中温菌和高温菌浸出差异的关键原因之一。高温菌浸出过程中,Fe3+离子易于转化为铁矾沉淀,而高温菌氧化亚铁的速率远远低于其生成的速率,从而导致体系的氧化还原电位保持在较低的水平,黄铜矿可以转化为次生铜,有利于浸出；而中温菌浸出的过程中,体系的电位基本保持在高电位下,次生铜难以生成,浸出速度缓慢。而浸出过程中生成的硫膜、黄钾铁矾沉淀不是制约黄铜矿溶解的本质原因。论文的主要结论如下：(1)热力学分析结果表明：酸性条件下,黄铜矿可转化为Cu5FeS4, CuS, Cu2S的铜硫化合物,最终释放出Cu2+离子,不同温度条件下各组分优势区间的范围相近。高温酸性条件下,Fe3+离子更容易生成KFe3(SO4)2(OH)6沉淀；另外,溶液中离子浓度升高也促进了Fe3+离子转化为KFe3(SO4)2(OH)6沉淀。Fe3+离子的沉淀过程可降低浸出体系的氧化还原电位,从而影响黄铜矿的分解。(2)尽管不同能源物质培养的细菌在黄铜矿表面吸附的速度及程度有所差别,但中温菌和高温菌在黄铜矿表面的初步吸附及对其表面性质的影响规律相似,因此不是造成这两类细菌浸矿差异的主要因素。而随着微生物对黄铜矿作用时间的延长,黄铜矿接触角的变化与其溶解机制密切相关,溶解过程中会生成疏水的单质硫、铜硫化物及亲水的铁矾等,从而改变了矿物表面的接触角大小。中、高温菌作用下,黄铜矿接触角变化规律存在差异。(3)浸出体系的氧化还原电位决定了黄铜矿是否能生成次生铜,次生铜易氧化分解,从而促进浸出。中温菌浸出过程中,仅在浸出的最初几天电位较低,之后一直保持在较高的数值(550mV vs. SCE)以上。与之对应,浸出前几天的浸渣能检测到次生铜Cu2S,浸出速度相对较快；当电位达到较高数值时,次生铜的生成受到抑制,浸出速度缓慢。然而,黄铜矿的高温菌浸出过程中,体系的氧化还原电位一直保持在较低的水平(380-450mV vs. SCE),可生成Cu2S,此时的浸出效果较中温菌浸出大幅提高。(4)微生物浸出过程中,微生物的主要作用是氧化铁或者氧化硫。因此,高温菌和中温菌对黄铜矿显示出不同的浸出效果应该是基于其氧化铁或者硫的能力的差异。以单质硫为能源物质培养的高温菌氧化铁的能力明显弱于可溶性亚铁培养的中温菌。另外,温度升高,Fe3+离子易转化为铁矾沉淀而消耗。这是造成中温菌和高温菌浸出体系氧化还原电位差异的主要因素。(5)电化学研究结果表明：温度的变化和细菌的加入不改变黄铜矿的分解机理,但温度的升高和细菌的加入反应速度增大。另外,中温菌的浸出过程中,5天后黄铜矿电极的开路电位大幅降低,之后升高并保持在较高的电位值；而高温菌的浸出过程中,黄铜矿的开路电位迅速下降后一直保持在较低的水平；可见在中温菌浸出黄铜矿时,仅在浸出的前几天矿物易分解,之后浸出困难；而高温菌浸出的整个过程中,黄铜矿均易分解。(6)黄铜矿的浸出过程中,硫膜、黄钾铁矾沉淀不是制约黄铜矿溶解的本质原因。中温菌浸出中,铁氧化菌L. ferriphilum菌浸出黄铜矿的体系中加入硫氧化菌A. thiooxidans菌后,导致硫膜的消失,但铜浸出率提高不显著。而浸出中生成的铁矾疏松且脱落后黄铜矿表面没有铁矾沉积,不会阻碍浸出。另外,高温菌的浸出效果较中温菌浸出大幅提高,但浸渣中检测到硫和黄钾铁矾,进一步说明其不是制约黄铜矿溶解的本质原因。更多还原

【Abstract】 Abstract:The speed of chalcoprite bioleaching by mesophilic bacteria and the leaching rate are slow and low, which largely restricts the application of bioleaching in the processing of chalcopyrite. On the contrary, chalcopyrite bioleached by thermophilic bacteria can be significantly improved, the mechanism in which has attracted increasingly attention from researchers. Based on thermomechanical analysis, this paper studied the effects of mesophile and thermophile on surface properties of chalcopyrite by using adsorption, zeta-potential, contact angle and bioleaching tests. XRD, Raman, SEM/EDS analysis and electrochemical experiments were employed to compare the different bioleaching process by mesophile and thermophile, deeply investigate the reasons for the different leaching efficiencies, further analyze the influencing factors of chalcopyrite decomposition mechanism, and reveal the stepwise dissolution mechanism of chalcopyrite.This paper presented the reason for different leaching efficiencies when chalcopyrite bioleached by mesophile and thermophile. The decomposition mechanism of chalcopyrite does not have a direct relation to the changes of bacteria or temperature. The dissolution of chalcopyrite is stepwise, and it can be transformed into Cu2S. Cu2S accelerated leaching process, which is the main reason for the different leaching efficiency. During leaching process by thermophilic bacteria, Fe3+is easy to be converted into jarosite, which can result in and keep a low redox potential, promoting the formation of Cu2S and leaching. While bioleaching by mesophilic bacteria, the redox potential maintaining on a high level hinders the generation of Cu2S and bioleaching. However, the generation of sulfur, jarosite precipitation is not the restraints for chalcopyrite dissolution.The main conclusions are as follows:(1) The thermodynamic analysis results show that chalcopyrite can be converted into Cu5FeS4, CuS, Cu2S copper sulfur compounds under the acidic conditions, eventually release the Cu2+ions. The existence range of components is nearly the same under different temperature conditions. In the acidity condition at high temperature, Fe3+ions are likely to generate KFe3(SO4)2(OH)6precipitation. In addition, the high ion concentration in the solution also promotes Fe3+ions converting into KFe3(SO4)2(OH)6precipitation. The precipitation process can reduce the redox potential of leaching system, which affects the decomposition of chalcopyrite.(2) Due to a similar impact to chalcopyrite surface, the effect of mesophile and thermophile on chalcopyrite surface properties is not the key factor to influence the different leaching efficiency. While in the leaching system, the changes of contact angle have a tight connection with the stepwise dissolution mechanism of chalcopyrite. Due to the formation of hydrophobic elemental sulfur, copper sulfides and hydrophilic jarosite, the contact angle of chalcopyrite increased before they are reduced.(3) The key factor to reduce chalcopyrite to Cu2S is determined by the redox potential of leaching system, which restricts the leaching rate of chalcopyrite. During bioleaching by mesophile, the redox potential remained at high value (more than550mV vs. SCE) except the first few days. The leaching residue during the initial days is detected to be Cu2S and the bioleaching rate was relatively fast. However, when the potential rose to a high value, Cu2S cannot be detected in the residue, which approved that the reduction of chalcopyrite is restrained and leaching speed is hindered. Throughout the whole bioleaching process of chalcopyrite by mesophilic bacteria, the redox potential of the system keep in high value, which is not beneficial to the reduction reaction, hindering the leaching of chalcopyrite. During chalcopyrite bioleaching by thermophile, the redox potential has stabilized at a relative low level (380-450mV vs. SCE), which enhanced the leaching efficiency of chalcopyrite.(4) During microbial leaching process, the role of microbes is to determine the oxidation of ferric ions or sulfur. Therefore, mesophilic bacteria and thermophilic bacteria showing different patterns of chalcopyrite leaching effects should be based on its iron oxide or sulfur capacity differences. For thermophilic bacteria using elemental sulfur as energy material, its ability of oxidizing ferrous is significantly weaker than the ability of bacteria cultured at medium temperature. In addition, when the temperature rises, Fe3+ions are easily transformed into jarosite and Fe3+ions consumption ensues. This is the critical factor that results in different redox potential at high temperature and medium temperature leaching systems.(5) The electrochemical research results present that the changes of temperature or bacteria do not alter the decomposition mechanism of chalcopyrite, but they enhanced the decomposition. In addition, during bioleaching by mesophilic bacteria, the open circuit potential of chalcopyrite sharply declined after5days, and then rose and kept at a high value. By contrast, during the bioleaching process by thermophilic bacteria, the open circuit potential of chalcopyrite dropped rapidly and kept at lower level. Obviously, chalcopyrite can be easily decomposed only in the first few days of bioleaching by mesophile but it become tough afterwards. However, it can easy be dissolved during the whole process when bioleached by thermophile.(6) During bioleaching of chalcopyrite, sulfur and jarosite precipitation are not the restraints for chalcopyrite dissolution. During bioleaching by mesophilic bacteria, when add sulfur-oxidizing A. thiooxidans in the leaching system by iron-oxidizing L. ferriphilum, the sulfur membrane disappeared, but copper leaching rate was not significant improved. During bioleaching, the jarosite precipitate was loose and fall off from chalcopyrite surface. Hence, it cannot hinder the leaching. In addition, during bioleaching by thermophilic bacteria, the leaching effect has been largely enhanced compared to bioleaching by mesophilic bacteria, though sulfur and jarosite has been detected in the leaching residue. It further illustrates that chalcopyrite dissolution cannot be restricted by sulfur and jarosite precipitation.更多还原