微波强化还原低品位钛精矿新工艺及理论研究

【作者】 雷鹰；

【导师】 彭金辉；

【作者基本信息】 昆明理工大学 ， 有色金属冶金， 2011， 博士

【摘要】 针对攀枝花钛精矿固相还原方面存在的问题,本文提出微波强化还原低品位钛精矿新工艺。论文以金属化率为考察指标,优化了微波强化还原钛精矿配碳球团以及微波强化还原机械活化预处理钛精矿的新工艺。在此基础上,采用常规加热和微波加热对比的方法,研究了还原产物相组成、显微结构、铁晶粒生长形态和铁晶粒生长动力学等,揭示了微波强化低品位钛精矿碳热还原的过程反应机理,详细考察了机械力对钛精矿结构及反应特性的影响,并系统研究了机械活化后钛精矿的常规加热等温还原表观动力学和微波加热非等温还原表观动力学,揭示了机械活化-微波对低品位钛精矿协同强化还原的过程反应机理。(1)研究了钛精矿金属矿物分布、解离情况,以及氧化前后钛精矿的微观形貌变化。测定了不同TiO2品位钛精矿的介电特性。采用终端开路同轴线反射法,通过矢量网络分析仪测定了不同TiO2品位钛精矿的反射系数幅值｜Γ｜和相位中变化,并运用遗传算法和有限元来反演出被测物料的介电系数ε’、损耗因子ε’’。测定了钛精矿及相关物质的微波升温特性,分析了化学成分、化学反应热和热辐射对升温速率的影响规律。(2)探索了氧化条件、配碳量、添加剂种类、还原温度和保持时间等因素对微波还原钛精矿配碳球团产物铁金属化率的影响规律,在此基础上建立了还原温度、保持时间和配碳量等可信因子与响应值金属化率的数学模型。(3)采用常规加热和微波加热对比,揭示了微波对低品位钛精矿碳热还原过程的强化机理。微波加热可减少Fe2+固溶,缩短铁晶粒形核期,增加铁晶粒初晶数量,驱动铁晶粒快速长大,使微区出现应力裂纹,并能促进铁连晶形成,降低铁晶粒生长界面扩散能垒；以铁晶粒大小和金属化率大小为研究对象,分别采用K-S模型和A-E模型拟合计算得到常规和微波加热条件下铁晶粒的生长激活能、形核活化能和生长活化能。(4)研究了机械力对钛精矿结构及反应特性的影响。机械活化使钛精矿颗粒及晶粒细化,出现大量新表面,其x衍射特征峰峰强降低,半高宽增加,导致晶格应变和结构无序化并可能出现畸变,使钛精矿活性提高,同时活化处理增加了钛铁矿与石墨的紧密接触。以上原因是导致钛精矿碳热还原过程温度降低、速率提高的主要原因。(5)测定了不同球磨活化时间下钛精矿与石墨混合物介电常数和损耗正切随频率变化关系,探索了球磨活化时间、还原温度和保持时间等因素对产物铁金属化率的影响规律,在此基础上建立了上述可信因子与响应值金属化率的数学模型。(6)系统的研究了未活化和活化1-8h钛精矿的常规加热等温还原表观动力学,分析了反应过程控制机理,对比了还原反应速率常数,拟合得到了常规等温还原反应表观活化能；建立了微波非等温表观动力学实验装置,测定了320-960w不同微波功率下活化钛精矿的还原度曲线和温度变化曲线,分析了反应过程控制机理,拟合计算得到微波非等温还原反应表观活化能。对比了两种加热条件下活化能等动力学参数的不同,揭示了机械活化-微波对低品位钛精矿碳热还原过程的协同强化机理。新工艺将可利用钛精矿的Ti02品位降低至37-39%。论文工作的开展对形成微波和机械活化强化还原新工艺、完善微波和机械活化强化还原理论及拓宽微波和机械活化应用领域等具有重要意义。更多还原

【Abstract】 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.更多还原