Study On The Chlorination Reaction Law And Melt Structure Of High Calcium Magnesium Titanium Slag Molten Sal

Titanium is widely used in chemical and aerospace industries due to its unique physical and chemical properties.China is rich in titanium resources.However,the resource characteristics of low Ti O₂ grade,high Ca O,Mg O content and the environmental standards of cleaner production,energy conservation,put forward stricter requirements for titanium extraction process.The molten salt chlorination process reduces by-products in Ti Cl₄ product,avoids the destruction of the reaction bed,improves the extraction efficiency of titanium,and basically solves the problem of utilization of titanium resources with high calcium and magnesium in China.However,in molten salt chlorination process,the catalytic chlorination mechanism of titanium slag by by-products and the composition control range of molten salt medium are unclear,which restricts the further improvement of reaction efficiency and process stability.With the support of the National Natural Science Foundation of China,the key issues such as by-product synergistic catalysis mechanism,melt structure and physical property of molten salt are explored,hoping to provide theoretical support for high-efficient and large-scale utilization of titanium resources.The thermodynamic of possible reactions in the carbochlorination process of titanium slag with high calcium and magnesium was systematically calculated.Thermodynamic calculation shows that all oxides in titanium slag can be effectively chlorinated;Volatile chlorinated products such as Si Cl₄,VOCl₃,Al Cl₃ and Fe Cl₃ are condensed together with Ti Cl₄ and then enter into crude titanium tetrachloride,while non-volatile chlorinated products such as Fe Cl₂,Mn Cl₂,Mg Cl₂,Ca Cl₂ form a multicomponent molten salts system with Na Cl molten salt media.The behaviors of concomitant chlorides in carbochlorination processes,gaseous Al Cl₃ and Fe Cl₃,liquid Ca Cl₂ and Mg Cl₂,were emphatically studied.Gaseous Al Cl₃ and Fe Cl₃ have chlorination effect on various components in titanium slag to varying degrees,while non-volatile Ca Cl₂ and Mg Cl₂ cannot directly chlorinate Ti O₂.Ca Cl₂ and Mg Cl₂ mainly affect the microstructure and physicochemical properties of molten salt medium.The influence of Mg and Fe oxides doping on the stability of titanium slag structure was clarified from the microscopic view.Mg Ti₄Fe O₁₀ was selected to simulate the structure of titanium slag based on the phase and chemical composition.The results of binding energy and electronic properties showed that the addition of Mg and Fe reduced the stability of the system to some extent,which was attributed to the relatively weak Mg-O ionic bond and Fe-O ionic covalent bond.Therefore,the presence of Mg and Fe is helpful to titanium extraction from titanium slag.The catalytic chlorination behavior of Al Cl₃ and Fe Cl₃ was investigated using the first principles and experimental research.（1）Al Cl₃（g）molecule is adsorbed on titanium slag surface by chemical adsorption after structural optimization,and its planar triangular structure is destroyed.The strong covalent bond between Al in Al Cl₃（g）molecule and O bond on the surface is the main reason for the strong chemical adsorption.The catalytic chlorination of Al Cl₃ is reflected in two aspects:it has a strong destructive effect on the structural surface of titanium slag and provides an chlorine for the chlorination of titanium slag.The experiments show that Na Cl-Al Cl₃ molten salts can effectively extract titanium from titanium slag.The catalytic essence of Al Cl₃ can be summarized as follows:The carbochlorination of Al₂O₃ to Al Cl₃ realizes Cl storage,and the chlorination of titanium slag by Al Cl₃ realizes Cl transfer,move in cycles.（2）Fe Cl₃（g）molecule is also adsorbed on titanium slag surface by chemical adsorption after structure optimization.However,the adsorption strength is weaker than that of Al Cl₃（g）system.In addition to lowering the partial pressure of oxygen,C is also a reaction catalyst.When C and Fe Cl₃ co-adsorb on the surface,C promotes the dissociation of Fe Cl₃ into Fe Cl₂ and Cl,and Cl can be used as the chlorinating agent for chlorination of titanium slag.The experiment also found that Fe Cl₃ can effectively break the dense structure of titanium slag and promote the chlorination of titanium slag in the presence of C.Therefore,the catalytic nature of Fe Cl₃ is that the chlorination of Fe Cl₂ and the dissociation of Fe Cl₃ in the presence of C bring Cl to the surface of titanium slag to realize rapid chlorination of titanium slag.The change mechanism of microstructure and physicochemical properties of Na Cl-Mg Cl₂-Ca Cl₂ ternary molten salts with different compositions was calculated.The presence of large ionic clusters,such as Ca Cl₇^5-,Ca Cl₆^4-,Mg Cl₅^3-,is the main reason for the poor fluidity of molten salts.The complexation degree of ion clusters and shear viscosity of molten salts increase as the content of Ca Cl₂ and Mg Cl₂ in the molten salt increase.However,the effect of Mg Cl₂ on melt structure and physical properties is far less than that of Ca Cl₂.With the increase of Na Cl content,free Cl^-ions will be released with the following reaction takes place,Mg Cl₅^3-→Mg Cl₄^2-+Cl^-,Ca Cl₇^5-→Ca Cl₆^4-+Cl^-,Ca Cl₆^4-→Ca Cl₅^3-+Cl^-,which facilitates the inter-phase mass transfer during the chlorination of titanium slag.Based on theoretical research,the Mg Cl₂ and Ca Cl₂ content in the actual production process should be kept at about 44.4 wt.%.An industrial test with a Ti Cl₄capacity of 100 tons/day was conducted in proposed molten salts system,and the extraction rate of titanium can reach 97.53%.