Basic And Applied Research On Carbothermal Chlorination Of Low-grade High-calcium-magnesium-titanium Slag

Titanium tetrachloride（TiCl₄）is the main raw material for the production of metallic titanium and titanium dioxide,and it is at the core of the titanium industry chain.China is the largest country with reserves of titanium resources in the world,but it is dominated by composite symbiotic titanium magnetite,which is characterized by high calcium and magnesium impurities and low Ti O₂ grade.The intermediate product titanium slag cannot be directly used in the boiling chlorination process to prepare TiCl₄.In this paper,in accordance with the demand for efficient development and utilization of titanium resources in china,low-grade titanium slag was used in the molten salt chlorination process to prepare TiCl₄.The physical and chemical properties,reaction mechanism of molten salt that restrict the chlorination reaction efficiency and reaction process stability control are not clear.The researches on the characteristics of low-grade titanium slag materials,the thermodynamics of the multiphase reaction of titanium slag carbochlorination,the molecular dynamics simulation and reaction mechanism of the carbochlorination process,the physical properties of the NaCl-based molten salt system and industrial practical applications were systematically carried out.To explore a new idea for the efficient and high-value utilization of titanium resources in my country,which has important academic significance and industrial practical value.Firstly,the characteristics of low-grade titanium slag materials were analyzed by means of chemical composition analysis,X-ray diffractometer,mineral dissociation analyzer,and scanning electron microscope.The results show that the low-grade titanium slag is mainly composed of M₃O₅ phase and rutile,and the M₃O₅ crystal is doped with impurity elements such as Mg,Ca,Al,Si,Mn.On this basis,the 131 chemical reactions that may occur in the carbothermal chlorination process are sorted out.Based on the related thermodynamics theory,the relationship between the Gibbs free energy of each reaction and the temperature was systematically analyzed and calculated.There are 26 main reactions will occur under the temperature of 700℃～800℃.Dominant area diagrams of M-O-C-Cl（M=Ti,Fe,Ca,Mg,Mn,Al,V）system were drawn.The saturated vapor pressure value of the pure substance of chlorination products were also calculated.Thermodynamic study results showed that the carbochlorination tendency of each component was:Ca O>Fe₂O₃>Fe₃O₄>Fe O>Mg O>Fe₂Ti O₅>V₂O₅>Ca O*Ti O₂>Mn O>Fe Ti₂O₅>Mg Ti₂O₅>Ti O₂>Al₂O₃>Si O₂.SiCl₄,VOCl₃,TiCl₄,AlCl₃,FeCl₃ in the chlorinated products are extremely volatile and will enter into the crude TiCl₄ product,while the saturated vapor pressure values of FeCl₂,MnCl₂,CaCl₂ and MgCl₂are small,and they will enter into the residues.With the help of density functional theory and molecular dynamics simulation methods,molecular dynamics simulation of the chlorination process behavior of the main phases of M₃O₅,Ti O₂,Ca O and intermediate product COCl₂ in the titanium slag is carried out,and the actual reaction was analyzed based on the calculation results.The reaction process and product morphology and properties under the conditions.The simulation calculation results show that during the chlorination process,Cl atoms are important chlorination intermediates,Cl atoms formed on the surface of C are an important source of active chlorine atoms,andCl₂ molecules on the surface of C and Ti O₂are dissociated.Cl atoms bonding with Ti and free C can independently deprive the O in the surface Ti O₂ to form CO and CO₂molecules,while the cluster state C is difficult to deprive O atoms from the Ti O₂system.AsCl migrates from Ti atoms to Mg,the energy ofCl atoms on the surface of Fe atoms decreases,and the chlorinatedCl atoms preferentially bond with Mg and Fe in the black titanium stone,which in turn leads to faults in the Mg Ti₄Fe O₁₀ structure.The simulation results explain the thermodynamic conclusion that black titanium in titanium slag is easier to chlorinate than Ti O₂.The intermediate product COCl₂ is adsorbed on rutile and dissociated into CO andCl atoms,which continue to undergo chlorination as one of the chlorine sources.The Ca-O bond is broken under the action ofCl atom and C atom,and O is taken away by C to form CaCl₂.NaCl was selected as the molten salt diluent and regulator in the process of carbothermal chlorination of low-grade titanium slag.The phase diagram of the composite molten salt system of multi-element NaCl-MgCl₂-FeCl₂-CaCl₂ and the physical properties such as density,viscosity and tension were developed systematically.The research results show that:a low melting point homogeneous mixed molten salt system can be formed at700℃～800℃,and the NaCl-based molten salt system can have a wider holding capacity of MgCl₂ and CaCl₂;the density of the system increases with the increase of CaCl₂ and MgCl₂,and The NaCl content increases and decreases,the viscosity of the system increases with the increase of CaCl₂,MgCl₂,and the surface tension of the NaCl-MgCl₂-CaCl₂ molten salt system decreases with the increase of temperature.The content of MgCl₂ and CaCl₂ in a preferred molten salt system should be less than 26.3%,10%,and NaCl in molten salt should be greater than 38.5%.Based on theoretical analysis and calculation results,experimental studies on low-grade titanium slag carbochlorination were carried out,and the influencing factors and laws of the chlorination rate of each component were obtained.The experimental results showed that the chlorination rate of each component in the titanium slag varies with The temperature increases,the chlorination time increases,the carbon ratio increases,the titanium slag particles decrease,and the chlorine concentration increases.The better carbothermal chlorination process parameters are:molten salt temperature 750℃～780℃,chlorination time should be more than 60min,chlorine concentration is 85%～90%,C:Ti O₂ratio was 0.2～0.25.The corresponding chlorination rate of each component is Ti-96.1%,Ca-98.5%,Mg-98.3%,Fe-99%,V-97.8%,Mn-97.6%,Al-61%,Si-2.3%.The chlorination residue is mainly composed of residual C,hard-to-chlorinate Al₂O₃ and Si O₂.The reaction mechanism of low-grade titanium slag carbochlorination in NaCl-based molten salt medium is proposed.The carbochlorination process mainly includes:（1）The dissociation ofCl atoms;（2）Ca and Mg in black titanium stone that can be preferentially carbochlorinated over Ti O₂ Selective chlorination of components such as,Fe,Mn;（3）Carbothermal chlorination of Ti O₂;（4）Partial chlorination of Al/Si oxides,the hard-to-chlorinate component,in four stages;in the process of carbothermal chlorination,O and Free C reacts to form CO₂ or CO,and the formation of a multi-component mixed molten salt system dominated by NaCl and Na₂MgCl₄.Low-grade titanium slag was used in industrial practice,through the application of molten salt chlorination,industrial test chlorination residue and crude titanium tetrachloride product characterization,crude TiCl₄ purification and purification,and application practice of refined TiCl₄ in the production of sponge titanium and titanium dioxide Research has further established a technical solution for industrial application of low-grade titanium slag.The research results show that:under the conditions established by the experiment,the chlorination process can achieve stable control of the molten salt temperature and the molten salt composition during the chlorination process.The chlorination rate of titanium can reach 95.5%～97.6%,the actual chlorine The smaller the chemical effect is better,and the actual output of crude TiCl₄ is 90～102t/d.The purity of the refined TiCl₄ obtained after sedimentation,vanadium removal and rectification is greater than 99.9%,and it has been successfully used in the production and preparation of O_A-grade high-quality sponge titanium and chlorinated titanium dioxide,opening up the high-efficiency and high-value application of low-grade titanium resources in China.