Knowledge Management System Of Institute of process engineering,CAS
|Thesis Advisor||张懿 ; 王志|
|Place of Conferral||北京|
|Keyword||高铝粉煤灰 金属镓 界面改性电沉积 解耦与协同作用 过程强化|
随着科技的不断进步，金属镓在薄膜太阳能电池、磁致伸缩材料、液态金属材料以及制氢材料等方面的研究与应用日趋深入与广泛。镓及其化合物将逐渐成为太阳能、氢能及智能机器等领域的关键性材料，例如含镓化合物半导体材料，尤其是GaAs半导体，是仅次于硅的半导体材料，在光电器件与集成电路等领域有着广泛的应用。镓的主要资源分布于铝土矿、钒钛磁铁矿、闪锌矿以及粉煤灰等。目前，世界约90%的镓是从氧化铝生产过程的循环母液中回收的。高铝粉煤灰中铝、镓含量高，若实现铝-硅-镓多金属的协同提取，是目前最有可能与铝土矿抗争的提镓原料。高铝粉煤灰提镓时，由于镓富集程度低，导致镓电沉积过程中存在严重的电化学极化和浓差极化，析氢副反应极为剧烈，镓电沉积的电流效率极低，甚至难以发生；另外，提镓母液中存在多元复杂杂质，进一步降低了电沉积镓产品质量。本论文基于高铝粉煤灰铝-硅-镓多金属协同提取工艺路线，针对高铝粉煤灰中电解提镓存在的瓶颈问题，即镓电沉积反应难发生以及产物质量难调控，开展高铝粉煤灰中金属镓电解提取技术基础与应用研究。以镓电解提取过程动力学为基础，从电化学反应过程强化和产物调控两方面着手，实现低镓多元溶液体系下镓的高效电沉积。相关研究结果也可为其他金属电沉积，尤其是难还原金属电沉积提供理论指导。本论文主要取得了如下创新性进展：（1）深入分析了析氢反应伴随条件下金属镓电沉积动力学特征，揭示了电化学反应步骤及溶液传质步骤对镓电沉积影响规律。在扩散控制条件下，研究了溶液组成、电解技术以及外场强化等手段对扩散动力学参数（离子扩散系数和扩散层厚度）的作用机制。电化学反应步骤动力学计算结果表明镓电沉积的表观传递系数及交换电流密度均小于析氢反应，阴极镓电沉积过程与析氢反应相比更难进行。增加NaOH浓度，一方面减弱了阴极表面对GaO2-阴离子的电排斥作用，另一方面导致溶液黏度增加，使离子扩散系数降低。Ga浓度、脉冲电流及对流搅拌对溶液/电极表面扩散层厚度的影响不明显。超声空化作用对电极表面扩散层溶液实现强化搅拌，可使扩散层厚度由22.5 μm降低到12.9 μm，镓电沉积的反应速率系数k为无超声作用时的2.4倍。（2）采用电极活化及添加表面活性剂对电极/溶液界面进行改性，掌握了界面改性对阴极析氢和镓电沉积竞争反应的调控作用。阳极活化处理使电极表面润湿性改善、粗糙度增加，为镓电沉积提供更多的有效活性位点。经成核动力学计算，碱活化和酸活化分别使镓成核速率公式的指前因子K值增加4.1倍和20.5倍。添加全氟辛基磺酸钾使电极表面生成大量团簇状结构，电极比表面积增大，经电化学交流阻抗测试，表面活性剂使镓电沉积的电化学反应电阻降低。动力学计算发现，表面活性剂使镓电沉积的交换电流密度由0.99 mA cm-2增加到1.57 mA cm-2，因此镓电沉积的电化学极化降低，电沉积反应更容易进行。（3）证实了碱石灰烧结法碳分母液隔膜电解直接提镓、同时利用电解副反应高效回收NaOH和NaHCO3副产品的可行性。电解过程中，阳极与阴极的Na+离子浓度比随时间不断减小，加速了OH-离子反渗，使阴阳极副产物生产的电流效率降低。阳极析氧生成的H+离子存在三个竞争反应途径，分别生成产物HCO3-，CO2和H2O。阳极液组成、电流密度、阳极材料和对流搅拌等手段均会影响阳极H+离子分配，从而影响副产物生成效率。在此基础上，完成了新技术扩试规模实验验证。（4）研究了Fe(III)、V(V)等典型金属离子存在下，沉积镓表面结构和电流效率的演变规律，实现了多元离子共存体系下电沉积镓产品质量的有效调控。少量铁氧化物在阴极表面沉积使镓与电极表面的润湿性变好，同时电沉积镓易与铁氧化物形成团簇状结构，从而为镓电沉积提供更多的活性位点，使镓沉积电流效率增加。微量钒氧化物沉积在电极表面，促进了大量高氧化活性的球形镓颗粒的形成，加速了沉积镓的返溶，并使析氢反应电阻减小，抑制镓电沉积。在低电流密度下，Fe(III)对V(V)有较强的抑制作用，而在高电流密度下，Fe(III)对V(V)的抑制作用不明显。在此基础上，利用过程耦合与协同原理，对电沉积法制备CIGS四元太阳能薄膜材料及Ga电解精炼进行了实验探索。（5）研究了高硫低镓碱液中，阳极耐蚀性能及阴极镓电沉积的交互作用，实现了工业现场扩试规模技术集成与应用示范。结果表明，S2-存在使不锈钢电极表面钝化层受到破坏，导致Fe(III)溶解进入溶液，并生成大量的NaFeS2胶体物质。Fe(III)的引入使镓产品纯度降低。当S2-浓度高于2.17 g L-1时，不锈钢阳极腐蚀严重，镓电沉积过程可被完全抑制。镍阳极在含硫碱液中具有较好的耐腐蚀性能。经现场溶液扩大试验发现，采用耐硫镍阳极可在高S2-电解液中电沉积得到具有银白色金属光泽、纯度达99.96%的金属镓。
With the great progress of science and technology, the usages of Ga in thin film solar cells, magnetostrictive materials, liquid metal materials and hydrogen storage materials become increasingly mature. Ga and its compounds, especially the GaAs semiconductor, have been widely used in the photoelectric devices and integrated circuits. Ga mainly distributes in the bauxite resources, vanadium titanium magnetite, sphalerite and coal fly ash. At present, about 90% of Ga production is recycled from mother liquor of alumina production in the world. While high aluminium fly ash is most likely to compete with bauxite for raw material of Ga as its high content of aluminum and Ga. As the key subprocess, during the electrolytic recovery of Ga from high aluminium fly ash, there are serious electrochemical polarization and concentration polarization phenomenon due to the low concentration of Ga, which causes extremely low current efficiency. Meanwhile, high content impurity in the mother liquor further affects the quality of Ga products.Based on the process of Al-Si-Ga poly-metallic synergistic extraction, the paper researched the bottleneck problems of Ga electrowinning from high aluminium fly ash. With the study of electrochemical kinetics, efficient Ga electrodeposition was aimed by the means of process intensification and product decoupling control. The original results are obtained as following:(1) The kinetics of Ga electrodeposition with hydrogen evolution was analyzed, and the effect rules of electrochemical reaction and mass transfer were revealed. The influence mechanism of solution composition, electrolytic technology and outfield intensification on diffusion kinetic parameters were researched. It was found that, the values of apparent coefficients and exchange current densities of Ga electrodeposition were both less than those of hydrogen evolution. Under the control of mass transfer, the increase of NaOH concentration decreased the electric repulsion of cathode to GaO2- ions while also lessened the diffusion coefficient due to the viscosity increase. Ga concentration, pulse current and stirring could hardly affect the thickness of diffusion layer. The cavitation effect of ultrasonic produced the mix action on the solution next to the cathode, and consequently increased the reaction rate coefficient k for Ga electrowinning by decreasing the thickness of diffusion layer. (2) The competing reaction of hydrogen evolution and Ga electrodeposition at cathode were regulated by interfacial modification including the electrode activation and adding surfactant. Electrode activation improved the wettability and surface roughness of the electrode, which provided more active sites for Ga electrodeposition. From nucleation kinetic calculation, the value of pre-exponential factor (K) increased to 4.1 and 20.5 times that of none after alkaline activation and acid activation, respectively. The addition of perfluorinated surfactant promoted the formation of clustered particles on cathode surface, with the increasing of the specific surface area of cathode. From the kinetic calculation, it was found that the exchange current density of Ga electrodeposition increased from 0.99 mA cm-2 to 1.57 mA cm-2 by the addition of the surfactant. That increased the electrodeposition rate of Ga, consequently. (3) Diaphragm electrolysis of carbonated spent liquor was carried out. The NaOH and NaHCO3 by-products could be obtained while direct Ga electrodepostion through diaphragm electrolysis. The current efficiency of NaOH and NaHCO3 decreased with time due to the increase of molar ratio of Na+ ion between cathode and anode. There were three competing reactions of H+ which formed during oxygen evolution, with the formation of HCO3-, CO2 and H2O respectively. The anolyte composition, current density, anode material and stirring changed the distribution of H+ of the three reactions, and consequently affected current efficiency of the products. The expanding scale experimental verification was conducted. (4) The influence mechanism of Fe (???) and V (V) on Ga electrowinning were studied. The deposition of iron oxide enhanced the wettability of Ga with electrode surface, and caused the development of aggregated Ga particles, which might be ascribing to the difference of surface properties between Ga and impurities. The deposition of vanadium oxide catalyzed the hydrogen evolution and caused the formation of spherical Ga particles, which depressed Ga electrodeposition. The experimental exploration of the co-electrodeposition of CIGS solar film and Ga electrorefining were implemented. (5) The interactions of anode corrosion behavior and Ga electrodeposition were conducted in alkaline sulfide solutions with low Ga concentration. It was found that Ga was hardly electrodeposited using stainless steel anode due to anode corrosion. Anode corrosion introduced iron ions into Ga solutions, and Ga electrodeposition is displaced by the deposition or absorption of iron oxide. The corrosion rate of nickel is much lower than that of stainless steel due to the formation of stable passive films which consists of Ni oxide and hydroxide. Bright metal gallium with high purity is obtained by using nickel anode at high S2- concentration from online pilot plant test.
|刘玲. 高铝粉煤灰中金属镓电解提取技术基础与应用[D]. 北京. 中国科学院研究生院,2015.|
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