【作者】 魏琦峰；

【导师】 张启修；

【作者基本信息】 中南大学 ， 有色金属冶金， 2003， 博士

【摘要】 电解氧化是一种铈(Ⅲ)的廉价氧化方法，氧化过程中不使用化学氧化剂，制得的铈(Ⅳ)溶液中不引入外来杂质元素，因此人们一直在努力实现用电解方法氧化铈(Ⅲ)为铈(Ⅳ)的工业化。特别是近年来氧化铈产品价格的下跌，廉价的电解氧化生产铈产品的方法成为企业降低生产成本的一个焦点。虽然在硝酸介质中电解氧化已得到成功应用，但在硫酸介质中，由于存在硫酸稀土溶解度小、电流效率低、能耗较高以及电极材料昂贵等问题使许多尝试受挫。随着我国稀土事业的发展，硫酸介质中分离提取稀土元素已成为稀土生产的一种十分重要的工艺流程。开发一种在硫酸介质中不使用昂贵的铂材阳极及进口离子交换膜，又能保证高的电流效率和低能耗的电解氧化铈(Ⅲ)为铈(Ⅳ)的方法，既是现行工艺流程和我国稀土企业实际情况的要求，又是稀土市场日益发展成熟的必然结果。 本文通过对电解槽参数的选择，得到了适于硫酸介质中电解氧化铈(Ⅲ)为铈(Ⅳ)的电解槽结构。首次使用本文选出的铅合金和铜板分别作阳极和阴极，以国产离子交换膜为隔膜进行了系统的铈(Ⅲ)的电解氧化研究。研究结果表明：本文选择的铅合金阳极和离子交换膜完全可以代替昂贵的铂阳极和进口离子交换膜，在硫酸介质中成功地将铈(Ⅲ)电解氧化为铈(Ⅳ)，打破了使用铂阳极和进口离子交换膜带来的高投资瓶颈，为我国稀土企业实现硫酸介质中电解氧化铈(Ⅲ)工业化提供了一种现实的电极材料和膜材料。通过均匀设计的电解条件试验得出：电流密度、阳极液酸度和阳极液硫酸根浓度为影响电流效率、氧化率和槽电压的显著因素。发现阴离子膜电解体系可以在较大的阳极液酸度范围内进行铈(Ⅲ)的电解氧化，而阳离子膜电解体系则必须在[H~+]大于0.75mol／L的酸度条件下进行。在低铈(Ⅲ)浓度时采用阴离子交换膜为隔膜比阳离子交换膜有较高的电流效率。 针对电流效率随电解时间的延续而下降，造成平均电流效率低下的问题，首次提出了变电流梯度电解氧化铈(Ⅲ)为铈(Ⅳ)的方法。在电解过程中，随阳极液中铈(Ⅲ)浓度的变化逐步调节电流密度，使阳极电流效率保证在80％以上，氧化率大于98％，比现有文献资料报道的电流效率和氧化率分别提高了15％和8％左右。通过变电流梯度电解使槽电压从恒电流电解的3.0V降低到2.2-2.5V，氧化铈的能耗从1.6KW·h／t下降到0.61KW·h／t。从理论上推导出极限电流密度与阳极液中铈(Ⅲ)浓度的线性关系和极限电流密度与电解时间的半对数关系，并通过试验验证了这些关系式的正确性。在实际电解过程中可以用这些关系式指导电流密度的控制，以维持较高的电流效率。 在电解氧化铈(Ⅲ)为铈(Ⅳ)的过程中，阴极为析氢反应，阴极电流没有得到有效利用。为此首次提出：离子膜耦合电化学反应氧化铈(Ⅲ)及同时析出铜粉的电解方法，实现充分利用阴极电流的目的。为此，首次进行了离子交换膜电解制备铜粉的试验。虽然在电解中使用了离子交换膜，使槽电压增高，但由于有高的电流效率和成粉率，铜粉的直流电能耗与无隔膜电解相近。 离子膜祸合电化学反应氧化饰(m)同时析出铜粉的电解方法不仅没有使电解体系复杂化，反而使槽电压得到进一步降低，降低幅度为0.2-0.5V，使变电流梯度电解的平均槽电压再次降低到2.0v，氧化饰的能耗降低到0.SKW·b吸g左右。这一电解体系和方法的最大优点在于:1)阴阳极电流同时得到充分利用，提高了电能利用率，降低了单独电解氧化饰(m)或单独电解制备铜粉时阴极析出氢气与阳极析出氧气夹带电解液造成的环境污染;2)在保证电流效率的同时，降低了槽电压:3)在阳极得到饰(IV)的同时，在阴极得到电解铜粉，增加了产品品种;4)使电解设备得到了最大程度的利用，大幅度降低了成本，提高了经济效益。放大试验表明，放大效果良好，小试结果具有很好的指导作用， 氧化饰(m)为饰(W)的同时在阴极生产的铜粉是在既没有电解设备的投入，又没有电能消耗的条件下得到的，而且进一步降低电解氧化饰(班)为饰(W)的能耗。按现有电解铜粉的经济效益和本方法中铜粉节约的电能，在不计入电解设备投资利息、折旧、维修以及人工工资时，根据初步估算，每生产1吨氧化饰可以额外带来1000元的经济效益。 提出了电解氧化饰(m)的表面络合物一放电的电极过程机理:在电解过程中饰 (m)首先与经基化的电极表面形成表面络合物，然后饰(m)通过一O一失去电子生成饰(IV)。该机理可以解释电解氧化饰(m)过程中饰(m)浓度、酸度、硫酸根浓度等对电流效率和槽电压影响的变化规律，并可以解释阳离子膜电解体系在阳极液酸度低于0.75mol几时电极表面形成氢氧化饰(W)沉淀的现象。 随氧化饰市场的变化，对氧化饰的形貌和粒径的要求越来越多，而且对粒度的分布要求越来越严格。针对这一市场变化，本文首次提出还原一沉淀反萃的方法，从P204和P507萃取体系负载饰(W)的有机相中直接制备出能够形成不同形貌和粒径氧化饰的前驱体。该方法省去了原有工艺过程的还原反萃、反萃液酸度调节以及草酸沉淀等工序，减少了化工原辅材料的种类和用量，实现了反萃工序的闭路循环，使反萃成为稀土生产中的绿色工序。由于在反萃过程中没更多还原

【Abstract】 Industrialization of electro-oxidizing Cerium(III) to Cerium(IV) has been a important project for long time because of its low cost, no chemical oxidation agents used and no pollution to rare earths productions. Many factories focus on this method to reduce the process cost to deal with the price drop of cerium products special for recent years. The oxidation of Cerium(III) to Cerium(IV) had been unsuccessfully used in sulfuric acid solution in spite of nitric acid media for low solubility of rare earths sulfate, low current efficient, high consume of electric energy and expensive electrode material of platinum. The separation of rare earth in sulfuric acid media had been a major process with development of Chinese rare earth industry. It is requirements of present process and current situation of Chinese rare earth factories, also result of increasingly ripe for rare earth market to invent a way of electro-oxidizing Cerium(III) to Cerium(IV) in sulfuric acid media at lower cost.Structural design suitable to electro-oxidizing Cerium(IH) to Cerium(IV) in sulfuric acid had been achieved by selection of electrolysis parameters. Systematic studies of electro-oxidizing Cerium(III) to Cerium(IV) had been carried out by employed firstly lead alloy and copper as anode and cathode respectively, and with ion-exchange membranes as cell diaphragms. The results that platinum anode and ion-exchange membrane made in overseas can be replaced by lead alloy and domestic membranes broke the limit of high investment caused by platinum anode and membrane. Current density, anolyte acid and concentration of SO42" in anolyte are notable factors influencing the current efficiency, oxidation rate and cell potential. The electro-oxidation in anion exchange membrane system can be carried out in larger range of anolyte acid but cation exchange membrane system only for over 0.75mol/L. At dilute Cerium(III) solution, the anion exchange membrane system has higher current efficiency than cation exchange membrane system.Aimed at the decrease of current efficiency with the procedure of electrolysis, the method of variable current density electrolysis was put forward firstly. The oxidation rate and anode current efficiency can be kept over 98% and 80% which are higher about 8% and 15% than the values reported in the papers by variation of current density according to concentration of Cerium(III) in this electrolysis process. By the varying current density, the cell potential decreases from 3.0V for constant current electrolysis to 2.2-2.5V, consume of electric energy for CeO2 decrease from 1.6KWh/t to 0.61KWh/t. The relation between current density and electrolysis time had been induced and its correctness had been verified with the test dates.Cathode-current is wasted for deposition of H2 in the process of electro-oxidizing Cerium(III) to Cerium (IV) in the available ways. For purpose of the using electric energy, the method of electro-oxidizing Cerium(III) to Cerium(IV) on anode and simultaneous reducing Cu(II) on cathode to produce copper powder was represented firstly. So the deposition of copper powder in the membrane electrolysis system was processed firstly. The consumption of electric energy of copper powder approached to the ones without cell diaphragms because of high current efficiency and powder yield rate. Electro-oxidizing Cerium(III) to Cerium(IV) on anode and simultaneous reducing Cu( II)on cathode to produce copper powder does not make the electrolysis complicated, but reduces the cell voltage about 0.2-0.5V further. The cell voltage and energy consumption of cerium dioxide decrease to 2.0V and 0.5KWh/kg respectively.Copper powder is made without investment and consume of energy in this method. According to profit of copper powder made by available process and the decrease of energy cost, the extra profit for It CeO2 brought by copper powder is about 1000yuan RMB without counting investment interest, depreciation of equipments, service cost and worker’s salary.The surface complex-discharging kinetics and mechanism of the更多还原