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Microwave Calcination Process Of Weakly Absorbing Materials And Theoretical Research

Posted on:2011-03-07Degree:DoctorType:Dissertation
Country:ChinaCandidate:B G LiuFull Text:PDF
GTID:1111330332478739Subject:Metallurgical physical chemistry
Abstract/Summary:PDF Full Text Request
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.
Keywords/Search Tags:Weak microwave adsorption materials, Thermal decomposition kinetics, Neterogeny material, Microwave adsorption property, Rising of temperature behavior, RSM, Microwave calcination
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