弱吸波物料的微波煅烧新工艺及理论研究

【作者】 刘秉国；

【导师】 彭金辉；

【作者基本信息】 昆明理工大学 ， 冶金物理化学， 2010， 博士

【摘要】 煅烧是冶金过程关键工序之一。煅烧工艺的好坏不仅直接影响产品的优劣,而且也决定企业的经济效益。目前常规煅烧方法均存在生产周期长、能耗高等问题；微波煅烧尽管具有加热均匀,效率高,煅烧时间短等优点,但多集中于强吸波物料的煅烧,而目前在冶金工业和核能工业中存在大量的难处理弱吸波物料,将微波应用于弱吸波物料的煅烧则研究甚少。因此,探寻煅烧的新工艺和新技术,扩大微波冶金的应用领域,对促进节能降耗、加快我国冶金和铀核燃料生产能力和技术水平的提高,实现冶金和核能工业的可持续发展具有重要的意义。本论文针对我国冶金和核能工业中急需煅烧的弱吸波物料碱式碳酸钴、偏钒酸铵和铀化学浓缩物的煅烧现状,提出了配加强导电相物质实现弱吸波物料的微波煅烧新途径；探索了异质材料在微波场中的吸波特性变化规律；通过将响应曲面设计优化方法引入煅烧工艺,获得了弱吸波物料碱式碳酸钴、偏钒酸铵和铀化学浓缩物的微波煅烧新工艺和关键控制参数。1.颗粒物料的热分解机理研究利用TG/DTG分析技术研究了碱式碳酸钴和偏钒酸铵颗粒物料的热分解过程,分析了物料的热分解特性；针对碱式碳酸钴和偏钒酸铵的热分解属于多步分解反应,若采用模型法来计算该种复杂反应体系的动力学,则难以揭示中间过程的反应机理；本论文采用非模型法详细研究了碱式碳酸钴和偏钒酸铵的热分解反应动力学,获得了随转化率变化的反应活化能,揭示了反应机理。结果表明,在493-625K范围内,碱式碳酸钴无水盐分解过程的平均活化能为109.63kJ/mol,在0.1≤α≤0.3范围内,活化能随转化率变化显著,而在0.4≤α≤0.9范围内,活化能变化很小。偏钒酸铵热分解过程为三步分解,在0.1≤α≤0.9范围内,第二分解阶段反应活化能随转化率变化较小,而第三、四分解阶段活化能均变化显著,各分解阶段对应的反应活化能平均值分别为E1=96.39kJ/mol, E2=139.24kJ/mol,E3=121.04kJ/mol.2.弱吸波物料的微波煅烧关键技术研究针对弱吸波物料的微波煅烧难题,基于异质材料等效媒介理论,利用微波谐振腔法探讨了异质材料在微波场中的吸波特性变化规律,提出了配加强导电相物质实现弱吸波物料的微波煅烧,开辟了弱吸波物料的微波煅烧新途径。研究表明,碱式碳酸钴、偏钒酸铵、三碳酸铀酰铵和重铀酸铵对微波的吸收性能都很差,属于弱吸波物质,而四氧化三钴、五氧化二钒和八氧化三铀对微波的吸收性能较强；碱式碳酸钴异质材料和偏钒酸铵异质材料随配加材料四氧化三钴和五氧化二钒配比的增大微波吸收峰出现明显的蓝移,通过配加少量四氧化三钴和五氧化二钒以及八氧化三铀强导电相微波煅烧碱式碳酸钴、偏钒酸铵和铀化学浓缩物是可行的；物料在微波场中的升温速率与微波输出功率成正比例增大,而与物料量成反比关系。3.颗粒物料常规煅烧工艺参数优化研究采用基于中心组合设计的响应曲面法,建立了具有多个交叉项的超空间响应曲面方程,系统考察了煅烧温度、煅烧时间和物料量各影响因子及其交互作用对碱式碳酸钴和偏钒酸铵煅烧分解率以及对铀化学浓缩物煅烧产物八氧化三铀中总铀和U4+含量的影响规律。获得了常规煅烧碱式碳酸钴、偏钒酸铵、三碳酸铀酰铵和重铀酸铵的优化工艺参数。研究表明,响应曲面法建立的碱式碳酸钴、偏钒酸铵和铀化学浓缩物常规煅烧回归数学模型高度显著,拟合度良好；煅烧温度、煅烧时间以及物料量对碱式碳酸钴和偏钒酸铵的分解率影响显著；煅烧温度和煅烧时间以及二者的交互作用对铀化学浓缩物煅烧产物八氧化三铀中总铀和U4+含量影响显著。响应曲面法优化得到的碱式碳酸钻和偏钒酸铵常规煅烧最佳工艺条件分别为煅烧温度666.00K和669.71K,煅烧时间32.00min和35.09min,物料量3.32g和4.25 g。在此条件下,碱式碳酸钴和偏钒酸铵的分解率分别为99.99%和99.71%,与实测值接近。响应曲面法优化得到的三碳酸铀酰铵和重铀酸铵常规煅烧最佳工艺条件分别为煅烧温度962K和932K,煅烧时间28min和24min,物料量37.86g和43.9g。在此条件下,三碳酸铀酰铵和重铀酸铵煅烧产物中总铀和U4+含量分别为84.17%,29.06%和84.46%,28.36%,与实测值接近。4.弱吸波物料微波煅烧工艺参数优化研究针对常规煅烧存在煅烧时间长、生产成本高等弊端,论文基于中心组合设计的响应曲面法,在可控温度条件下选取分别配加20%四氧化三钴的碱式碳酸钴、,配加15%的五氧化二钒的偏钒酸铵和配加20%八氧化三铀的铀化学浓缩异质材料开展微波煅烧研究。探讨了各影响因子及其交互作用对响应值的影响规律,在方差分析、多元回归和模型拟合的基础上,优化得到碱式碳酸钴、,偏钒酸铵和铀化学浓缩物异质材料的微波煅烧工艺参数。结果表明,响应曲面法建立的碱式碳酸钴、偏钒酸铵和铀化学浓缩物异质材料微波煅烧回归数学模型高度显著,拟合度良好,煅烧温度和煅烧时间对碱式碳酸钴和偏钒酸铵分解率以及对铀化学浓缩物煅烧产物中总铀和U4+含量有显著影响；响应曲面法优化得到的碱式碳酸钴和偏钒酸铵异质材料微波煅烧最佳工艺条件分别为煅烧温度643.00K和645K,煅烧时间9.00min和9.5min,物料量4.34g和4.3g。在此条件下,碱式碳酸钴和偏钒酸铵的分解率分别为99.62%和99.33%；响应曲面法优化得到的三碳酸铀酰铵和重铀酸铵异质材料微波煅烧最佳工艺条件分别为煅烧温度942.75K和911.020K,煅烧时间9min和8min,物料量44g和39g。在此条件下,三碳酸铀酰铵和重铀酸铵异质材料煅烧产物中总铀和U4+含量分别为82.07%,31.33%和84.42%,32.74%,与实测值接近与常规煅烧方法相比,在产品满足质量要求的前提下,微波煅烧碱式碳酸钴、偏钒酸铵和铀化学浓缩物的优化工艺参数中煅烧温度降低约20K,煅烧时间缩短约2/3。综上,论文依据TG/DTG分析技术,采用非模型法探讨了颗粒物料的热分解特性,通过研究随转化率变化的活化能变化,揭示了其热分解机理；基于异质材料等效媒介理论,依据异质材料在微波场中的吸波特性变化规律,提出通过在弱吸波物料中添加强导电相物质解决了弱吸波物料的微波煅烧这一难题；在可控温度条件下,采用响应曲面优化设计系统研究了各影响因素及其交互作用对响应值的影响规律,获得了弱吸波物料微波煅烧新工艺和关键工艺参数。本论文研究成果为弱吸波物料的微波煅烧开辟了新途径,对促进我国紧缺战略资源钴、钒的提取和铀核燃料生产及技术水平的提高具有较高的实际应用价值和重要的现实意义。更多还原

【Abstract】 The calcination is one of the key metallurgy processes. The technique quality not only influences product quality, but also it also decides enterprise’s economic efficiency. However, the present conventional calcination method has questions such as long production cycle and high energy consumption. The microwave calcination has the advantages of even heating, high efficiency, short calcination time short and so on, but the present microwave calcination usually concentrates in calcination of well microwave adsorption materials, less on the weak microwave adsorption materials. However in the metallurgical industry and the nuclear power industry, there are massively weak microwave adsorption materials waiting for treatment urgently. Therefore, to discover new technique and technologies of calcination, especially to the materials with week microwave adsorption ability, has great meaning to promote energy conservation, speed up our country metallurgy and uranium nucleus fuel productivity and the technical level enhancement in order to realize the sustainable development of metallurgy and the nuclear power industry.In this paper, aiming at the materials with weak microwave adsorption which are needed in the calcinations of metallurgy and nuclear power industry, for example:basic carbonate cobalt, ammonium metavanadat and ammonium uranyl carbonate and ammonium diurante, the microwave calcinations by the addition of electric conduction material is realized, the pellet material thermal decomposition process is analyzed, which promulgated the thermal decomposition mechanism. The changing rules of the materials with weak microwave adsorption in microwave field are explored; the calcinations techniques are designed for optimization by the utilization of RSM. The new techniques and key parameters of microwave calcinations of basic carbonate cobalt, ammonium metavanadat and ammonium uranyl carbonate and ammonium diurante are obtained.1. Study on mechanism of thermal decomposition of granuleThe thermal decomposition processes of basic carbonate cobalt and ammonium metavanadat are analyzed by using TG/DTG. It is difficult to investigate the complex reaction system kinetics parameter using fitting-model method because pilot process. The decomposition reaction kinetics of basic carbonate cobalt and ammonium metavanadat was studied using the free-model method. The material thermal decomposition characteristic is analyzed, the decomposition mechanism is discussed, and the response activation energy of basic carbonate cobalt and ammonium metavanadat is obtained basing on free-model method. The result indicated that in the range of 493-625K, the average activation energy of basic carbonate cobalt decomposition process is 109.63kJ/mol, in the range of 0.1≤α≤0.3, the activation energy changes apparently with the conversion rate, however, in the range of 0.4≤a≤0.9, the activation energy changes little; The thermal decomposition process of ammonium metavanadat is by three steps. In the range of 0.1≤α≤0.9, the activation energy in the second decomposition step changes little with the change conversion rate, but it changes apparently in the third and the fourth step, the average energy are E1=96.39kJ/mol, E2=139.24kJ/mol, E3=121.04kJ/mol in each step respectively.2. Key technology of microwave calcination for weak microwave adsorption materialsBasing on the neterogeny material equivalent medium theory, the microwave adsorption changing rules of neterogeny materials is discussed using the microwave resonant cavity small perturbance theory. The microwave calcinations for weak microwave adsorption materials are solved by adding electric conduction inside, and the elevation of temperature in the microwave field is studied. The result indicated that basic carbonate cobalt, ammonium metavanadat, ammonium uranyl carbonate and ammonium diurante could not absorb the microwave well, however CO3O4, V2O5 and U3O8 are just on the opposite, they could absorb the microwave well. With the increasing proportion of Co3O4, and V2O5 inside, the microwave absorption peak of neterogeny material appears an obvious blue shift. The property of microwave adsorption of basic carbonate cobalt, ammonium metavanadat neterogeny materials increase with the increasing proportion of Co3O4 and V2O5 add inside the materials. The calcinations of basic carbonate cobalt, ammonium metavanadat and ammonium uranyl carbonate and ammonium diurante are available by adding little Co3O4, V2O5 and U3O8 inside, the temperature in the microwave field increases with the increasing of microwave power output in proportion, but in reverse proportion with materials quantity.3. Optimization of conventional calcination parameter for granuleThe CCD design of RSM is used in the study, the influences of calcination time, calcination temperature, mass of sample and interaction between each factor on the decomposition rate of basic carbonate cobalt, and ammonium metavanadat, as well as on the content of U and U4+ of U3O8 by calcination from ammonium uranyl carbonate, and ammonium diurante. The parameters were optimized for the calcination of basic carbonate cobalt, ammonium metavanadat, ammonium uranyl carbonate, and ammonium diurante by conventional heating. The result indicated that the return mathematical model obtained by RSM fits well, the calcination time, calcination temperature, mass of sample has great influences on the decomposition of basic carbonate cobalt, ammonium metavanadat; the calcination time, calcination temperature and the correlations between has great influences on the content of U and U4+of U3O8.The optimum technique parameters to prepare for Co3O4 and V2O5 by calcination from basic carbonate cobalt, and ammonium metavanadat are calcination time of 32.00min and 35.09min, calcination temperatures of 666.00K and 669.71K, mass of sample of 3.32g and 4.25g, the decompositions rate of the two materials are 99.99% and 99.71% respectively. The optimum technique parameters to prepare for U3O8 by calcination from ammonium uranyl carbonate and ammonium diurante are calcination time of 28min and 24min, calcination temperatures of 962K and 932K, mass of sample of 37.86g and 43.9g, and the content of U and U4+ of U3O8 by calcination from the ammonium uranyl carbonate and ammonium diurante are 84.17%,29.06% and 84.46%,28.36% respectively, which are close to the actual experimental value.4. Optimization of microwave calcination parameter for weak microwave adsorption materialsAiming at the problems of long calcination time and high production cost in conventional calcinations, basic carbonate cobalt-Co3O4 mixture of composition 20%, ammonium metavanadat-V2O5 mixture of composition 15%, and the ammonium uranyl carbonate and ammonium diurante-U3O8 mixture of composition 20% are taken as raw materials for the study of microwave calcination in the paper. The influences rules of the factors are discussed, on the base of variance analysis, multiple regression and model fitting, the microwave calcination parameters are obtained. The result indicated that the return mathematical model obtained by RSM fits well. The calcination time, calcination temperature have great influences on the decomposition rate of basic carbonate cobalt, ammonium metavanadat, as well as on the content of U and U4+ of U3O8 by calcination from ammonium uranyl carbonate, and ammonium diurante. The optimum technique parameters for microwave calcination of basic carbonate cobalt and ammonium metavanadat are calcination time of 9min and 9.5min, calcination temperature of 643K and 645K, and mass of sample of 4.34g and 4.3g, the decomposition rate of the two materials are 99.62% and99.33% respectively. The optimum technique parameters for the microwave calcination of ammonium uranyl carbonate and ammonium diurante are calcination time of 9min and 8min, calcination temperature of 942.75K and 911.020K, mass of sample of 44 and 39g, and the content of U and U4+ of U3O8 by calcination from the ammonium uranyl carbonate and ammonium diurante are 84.17%,29.06% and 84.46%,28.36% respectively, which are in good agreement with the actual experimental value. Comparing with conventional methods, under the conditions of good quality of the products, the temperatures of microwave calcinations of basic carbonate cobalt, ammonium metavanadat and ammonium uranyl carbonate and ammonium diurante more low, the calcination time is reduced for 2/3.Above all, according to TG/DTG analysis, the materials with weak microwave adsorption thermal decomposition characteristic is analyzed, the decomposition mechanism is discussed, the response activation energy is obtained basing on free-model method; According to the effective medium theory of heterogeneous materials and the microwave adsorption changing rules of neterogeny materials, the microwave calcinations for weak microwave adsorption materials is solved by adding electric conduction inside; under the condition of controllable temperature, RSM is used for the study the influence rules of different factors and the correlations between, new technique and methods are obtained for the calcinations of weak microwave adsorption materials. This paper discovers a new way for the calcinations of weak microwave adsorption materials, which has great meaning and application value for the extraction of cobalt and vanadium resources and the nuclear fuel productivity and technical level enhancement.更多还原