Microwave Enhanced To Restore The New Techniques And Theoretical Study Of The Low-grade Titanium Concentrates

New carbothermic reduction processes of low TiO2 grade ilmenite concentrate strengthened by microwave irradiation were developed in this thesis, aiming to solve the existing problems in the direct solid reduction process of Panzhihua ilmenite concentrate. The parameters of microwave carbothermic reduction and mechanical activation followed by microwave reduction were optimized. On the basis of above researches, the phases transformation, microstructure, metal Fe grain growing morphology and kinetics of reduced products by microwave heating and conventional heating were investigated comparatively to elucidate the microwave strengthening mechanism. The effect of mechanical force on the structure and characteristics of carbothermic reduction were investigated systematically to elucidate the strengthening mechanism of mechanochemical activation, and the isothermal and non-isothermal apparent kinetics of milled ilmenite concentrate reduced by conventional and microwave heating were studied, respectively, in order to elucidate the cooperative strengthening mechanism.(1) The distribution and dissociation degree of metal mineral in ilmenite concentrate were investigated, the microtopography change of ilmenite before and after oxidation were compared. Terminal Open Coaxial Reflection Method (TOCRM) and Vector Network Analyzer (VAN) were employed to measure the amplitude and phase position of reflection coefficient of different TiO2 grade ilmenite concentrate, and then the dielectric properties i.e. Specific Inductive Capacity (SIC)ε, Dielectric Dissipation Factor (DDF)εand Loss Tangent (LT) tanδwere calculated through Genetic Algorithm (GA) and Finite Element Analysis (FEA). Based on above researches, the temperature rising characteristics of ilmenite concentrate and associated materials in microwave field were studied, and the effect of chemical compositions, reaction heat and thermal radiation on the temperature rising rates were analyzed.(2) The effect of pre-oxidation, proportion of coke, sort of additives, reduction temperature and holding time on the Fe metallization of reduced ilmenite were investigated, and the processing parameters of microwave reduction of coke bearing ilmenite pellets were optimized, and the mathematical model was built up according to the relationship between Fe metallization response value and three independent variables.(3) By using of comparative studies of conventional and microwave reduction of ilmenite concentrate pellets, the strengthening mechanisms of microwave irradiation were concluded as follow:reducing the solid solution of Fe2+in isomorphism, shortening the crystal nucleus formation period of metal Fe grain, increasing the initially crystal nucleus of metal Fe, promoting the quick growing of metal Fe grain, forming many of thermal stress cracks, pushing the formation of crystal stock due to selective heating, and decreasing the interface diffusion barrier. The grain growth activation energy E, nucleus formation activation energy En and grain growth activation energy Ee of Fe grain under conventional heating and microwave heating were obtained by using K-S and A-E models.(4) The effect of mechanical force on the structure and characteristics of reduction reaction of ilmenite were investigated. The results show that the peaks intensity of ilmenite were decreased and the full width at half maximum (FWHM) were increased. The activity of ilmenite was increased due to fining of particle and grain size, coming of new surface, disordering of structure and defect of lattice strain. The dissociation degree of Ti and Fe elements in ilmenite concentrate were also increased. The carbothermic reduction temperature was decreasing and the reaction rate was significant increasing due to the increase of activity and the close contact of ilmenite and graphite.(5) The dielectric properties of milled ilmenite were measured. The effect of milling time, reduction temperature and holding time on the Fe metallization of reduced ilmenite were investigated. The processing parameters of ball milling and followed by microwave reduction were optimized, and the mathematical model was built up according to the relationship between Fe metallization response value and three independent variables.(6) The isothermal apparent kinetics of unmilled and activated ilmenite for different time reduction by conventional heating was studied. The reaction control mechanisms were analyzed and the experimental data were found to fit well to the Jander's and Ginstling's model for different samples respectively. The reduction reaction constant rates of different samples were compared, and the activation energies of unmilled and activated ilmenite for different time were obtained respectively. A non-isothermal microwave apparatus was set up to investigate the non-isothermal apparent kinetics of carbothermic reduction of activated ilmenite. The relationship between reduction degree and temperature under 320,640 and 960 W microwave power were analyzed. The reaction control mechanisms were analyzed and the apparent activation energies of ilmenite milled for 1～8 under 320,640 and 960W microwave power levels were obtained respectively. The cooperative strengthening effect was proved through comparing the kinetics parameters under tow heating ways.Generally, the available TiO2 grade in ilmenite concentrate are reduced to 37～39% by using the new processes techniques developed. The development of the present thesis is of great significance to the formation of new strengthening reduction process by microwave and mechanochemistry, perfecting the strengthening reduction theory of microwave and mechanochemistry, and broadening the application fields of microwave and mechanochemistry.