【作者】 田庆华；

【导师】 郭学益；

【作者基本信息】 中南大学 ， 有色金属冶金， 2009， 博士

【摘要】 氧化钴是一类具有优良性能的重要功能材料,它是制备锂离子电池正极材料钴酸锂的主要原料,同时也被广泛应用于超级电容器、硬质合金、压敏陶瓷、无机颜料、催化剂等领域。目前,氧化钴的工业化生产方法主要采用草酸铵沉淀-热分解工艺,该方法不仅消耗氨水,同时产生大量难以回收处理的含氨废水,直接排放不仅会对环境造成严重危害,同时也是资源和能源的浪费。本研究旨在从源头上避免氨水的加入,系统研究了无氨草酸沉淀-热分解制备氧化钴及含草酸废水循环利用的工艺流程,实现了溶液闭路循环且生产过程环境友好,在有色金属清洁生产领域具有十分重要的实际应用价值和学术理论意义。本研究根据同时平衡原理和质量守恒原理,系统研究了Me2+-C2O42-Cl--H2O体系中各金属离子在水溶液中的热力学平衡模型,计算并绘制了考虑各阴离子络合作用在内的复杂体系lg[Me]-pH平衡图和各金属离子存在形式分布图,全面分析了溶液pH值及柠檬酸、酒石酸和EDTA等添加剂对该平衡体系的影响。分析得出体系中杂质Ca2+、Ni2+、pb2+、Cu2+会先于Co2+生成沉淀,而Mg2+、Fe2+、Mn2+和Zn2+类杂质离子只在pH相对较高的情况下先于Co2+形成沉淀。因此在草酸钴的生产过程中,应尽量控制这些杂质的含量和控制较低的沉淀终点pH值,以保证获得高的钴沉淀率和较好的产物品质。系统研究了无氨草酸沉淀法各工艺参数对草酸钴沉淀率及粒子形貌、粒度的影响。氯化钴溶液浓度、反应温度和草酸加料速度等因素对草酸钴晶体形貌和粒度起着决定性作用；草酸过量系数则对草酸钴沉淀率影响极大；外加超声可有效减少粒子团聚,但其空化作用也抑制了粒子生长,草酸钴形貌由长柱状变为小块状。通过全面考察,确定了无氨草酸沉淀法的优化工艺条件：以1mol/L的氯化钴溶液为原料,过量系数为1.5的草酸作为沉淀剂,反应温度60℃,正向滴加方式,加料速度10mL/min,溶液pH值5.5。可制备得到结晶形貌良好的β晶型含水草酸钴粉末粒子(β-CoC2O4-2H2O),草酸钴粉末微观形貌呈长柱簇球状,中位径为30-50μm,一次沉淀率可达95%以上。对无氨草酸沉淀法制得的草酸钴粉末进行洗涤、干燥、热分解研究,全面研究了草酸钴在氩气气氛下和空气气氛下的热分解热力学行为。通过热力学计算分析,并采用DSC-TGA曲线验证得出,在氩气等惰性气氛中,草酸钴的分解产物为金属钴；而在空气等氧化性气氛中,草酸钴在温度低于700℃时的分解产物为Co3O4,而在高于900℃时的分解产物为CoO。全面分析了草酸钴热分解行为的动力学机理,采用Coats-Redefrn方程和Ozawa法和Kissinger法推断并相互验证热分解机理函数、表观活化能和指前因子。动力学分析推断得出：草酸钴在惰性气氛中和氧化性气氛中的热分解机理函数F(α)均为[-ln(1-α)]1/3；在惰性气氛中的热分解活化能分别为129.82 kJ/mol (Ozawa法)和125.37kJ/mol (Kissinger法)；在空气气氛中生成Co3O4的热分解活化能分别为70.5kJ/mol (Ozawa法)和64.11kJ/mol (Kissinger法)；在空气气氛中高温分解生成CoO的反应表观活化能分别为1232.14kJ/mol(Ozawa法)和1276.04kJ/mol (Kissinger法)。探索了采用P350萃取分离含草酸的盐酸溶液的新方法,有效地用于草酸沉钴母液的循环利用,分离出的草酸可返回沉淀工序,盐酸则可返回含钴原料浸出工序,反萃后再生的有机相也可再次用于萃取工序,因而实现了整个工艺流程全液相的资源循环利用。采用红外光谱法分析P350萃取草酸的作用机制为氢键缔合；采用斜率法计算得到P350萃取草酸的萃合比为nP350：nH2c2O4=2：1。考察了萃取剂浓度、水相酸度、有机相和水相体积比等各工艺条件对萃取分配比的影响,通过单级萃取实验确定了萃取优化条件为：有机相中P350所占体积分数为50%,H+浓度为1.7mol/L,溶液草酸浓度为0.2mol/L-0.4mol/L,萃取达到平衡所需要时间为5分钟。运用萃取过程中的“pH值摆动效应”,选择纯水作为再生反萃剂对草酸进行反萃取,可实现草酸的再生回用。系统研究了多级逆流萃取、反萃和洗涤工艺来分离母液中的盐酸、草酸和再生有机相。采用平衡等温线法和串级模拟实验法确定优化萃取相比O/A=2.0,级数为6级,可使萃余液中草酸含量低于0.0040mol/L;采用反萃平衡等温线法确定反萃相比O/A=1.0,反萃级数为10级,草酸的反萃率可达到95%以上。更多还原

【Abstract】 Cobalt oxide is one of the most important functional materials with excellent properties, which is the main raw material for producing the lithium cobalt oxide as lithium-ion batteries cathode material. Meanwhile it is widely used in areas of super capacitor, cemented carbide, varistor ceramics, inorganic pigment and catalyst. At present, precipitation-thermolysis process with ammonium oxalate as the precipitant is the main supporting techniques for producing the cobalt oxide in industry, which consumes a lot of ammonia. And a great deal of ammonia-containing wastewater will be produced in this process. The non-treatment wastewater is directly discharged, thereby not only bringing about material loss but also polluting the environment. In this research, the addition of ammonia was avoided from the origins. Preparation of Cobalt Oxide by Precipitation-Thermolysis Process of Oxalic Acid without Ammonia and Recovery Utilization of the Mother Liquor with a great of Oxalic Acid were systematically studied. Wastewater closed circulation and reused technological process were adopted to prevent pollution. Therefore, this technique has important theoretical significance and practical value.According to the principle of simultaneous equilibrium and mass conservation, a series of thermodynamic equilibrium equations of the complex system of Me2+-C2O42--Cl--H2O were systematically studied, and the equilibrium curves of lg[Me]-pH were drawn, which indicated the equilibrium area and composites of the solutions at different complex and pH. This paper presents the comprehensive Analysis of the effect of pH value and additive such as citric acid, tartaric acid and EDTA on this Equilibrium System. It was found that the impurities such as Ca2+, Ni2+, Pb2+, Cu2+ in the solution always precipitated before Co2+, but Mg2+, Fe2+, Mn2+, Zn2+ precipitated before Co2+ only at high pH values. Therefore, reducing impurities contents and maintaining low pH value can get higher precipitation rate and better quality of cobalt oxalate in manufacture.The main factors affecting the precipitation rate, the size and morphology of the precipitated particles were investigated comprehensively. The Results show that the cobalt chloride content, temperature and the feeding speed of H2C2O4 played a decisive role in the size and morphology of cobalt oxalate. And the excess coefficient of oxalic acid had great influence on the precipitation rate. Adding ultrasonic on the process can decrease agglomeration effectively with the decrease of the particle size. But ultrasonic cavitation will hinder grains further growth, and the shape of cobalt oxalate particle became tubby and square finally and the ratio of length to diameter decreased. The optimum technological conditions were obtained as follows:using cobalt chloride as the starting material with 1mol/L, oxalic acid as coprecipitated agent with the excess coefficient(molar ratio of oxalic acid to cobalt chloride)1.5:1, positive-feed method,5.5 of pH value at 60℃, the feeding speed lOmL/min. Under these conditions, the rod-likeβ-CoC2O4-2H2O with D50 from 30μm to 50μm can be fabricated, the precipitation rate was above 95%.Washing, drying and thermal decomposition on Cobalt oxalate dehydrate (CoC2O4-2H2O) were studied. The thermal decomposition behavior of Cobalt oxalate dehydrate was studied in Ar or Air Atmosphere by Thermogravimetry analysis(TGA) and Differential Scanning Calorimetry(DSC) respectively. It was also analyzed and discussed from thermodynamics point of view in this paper. The result shows that the thermal decomposed products were mainly Cobalt Metal in Ar Atmosphere, and mainly Co3O4 with temperature below 700℃, mainly CoO with temperature above 900℃in air atmosphere. DSC-TGA curves verified the effectiveness of the thermodynamics model.This paper made an overall analysis of kinetic mechanism of the thermal decomposition behavior of cobalt oxalate.The kinetic model function, the apparent activation energy and preexponential factor were obtained by Coats-Redefrn equations, Ozawa method and Kissinger method. The most possible kinetic model function was [-ln(1-a)]1/3 in both inert atmosphere and oxidizing atmosphere. The activation energy of decomposition which was estimated by Ozawa and Kissinger in inert atmosphere were 129.82 KJ/mol and 125.37kJ/mol, respectively. And preexponential factor was 3.0533×109S-1. The activation energy of reaction from COC2O4 to Co3O4 by Ozawa and Kissinger in air atmosphere were 70.5 kJ/mol and 64.11kJ/mol, respectively. And preexponential factor was 1.2008×105S-1. The activation energy of reaction from Co3O4 to CoO by Ozawa and Kissinger in air atmosphere were 1232.14kJ/mol and 1276.04kJ/mol, respectively. And preexponential factor was 2.2103×1056S-1.A novel method of selective extraction of oxalic acid from hydrochloric acid solution by the complexing agent P350 was proposed, which was used in recycling of the mother-liquor after precipitating cobalt effectively. The oxalic acid separated from the mother-liquor can be reused in precipitation process, and the hydrochloric acid in extraction raffinate can be used for leaching of raw materials Containing cobalt. The organic Phase after back extraction can extract again. So, all the resources of this process can be recycling used.The mechanism of extraction was investigated by infrared, and there were hydrogen bond association reaction. The composition of extracted complex had been determined P350: H2C2O4=1 : 1 by means of the slope method. The influences by factors such as the extractant concentration, aqueous phase acidity, volumetric ratio of oil phase and aqueous phase on the distribution ratio were examined. The optimum technological conditions were obtained as follows:the P350 concentration in extractant 50% by volume, the concentration of hydrogen ion 1.7mol/L,the concentration of oxalic acid from 0.2mol/L to 0.4mol/L,the time of extraction equilibrium 5min. The pH swing effect was used to strip the oxalic acid from organic Phase, using pure water as stripping agent, and the reuse of oxalic acid was realized.Multi-stage countercurrent extraction, back extraction and washing were investigated in this paper. The volumetric ratio of oil phase and aqueous phase (O/A) and extraction stages were determined by the method of equilibria isotherm and the string class simulate experiment. The concentration of the oxalic acid in extraction raffinate was less than 0.0040mol/L with 6-stage extraction while O/A was 2.0.And the back extraction ratio was more than 95% with 10-stage extraction while O/A was 2.0.更多还原