Fundamental Research On Modification Of Molten Titanium Slag From Electric Furnace And Removal Of Calcium And Magnesium Impurities

The products of titanium metallurgy mainly contain two types:titanium white and metallic titanium,both of which are produced from TiCl₄.The fluidized bed chlorination is the main process of producing TiCl₄.The content of CaO and MgO in titanium-rich material for fluidized bed chlorination is required to be as low as possible,usually less than 1.50%to avoid deteriorating the steady state of the fluidized bed.Therefore,the preparation of qualified titanium-rich materials that meet the production of titanium and titanium dioxide is an important part of titanium metallurgy.Titanium slag in Panxi area plays an important role in the domestic titanium-rich material market.However,high content of CaO and MgO has prevented it from being utilized by the fluidized bed chlorination.Therefore,the development of a new technology for removal of calcium and magnesium impurities in titanium slag with low cost and high efficiency has important industrial and practical significance.The idea of modification of molten titanium slag from electric furnace and removal of calcium and magnesium impurities is proposed in this paper.The sensible heat of molten titanium slag is utilized to save a lot of heat.The result of this paper provides a new way to remove calcium and magnesium impurities in titanium slag with low cost and high efficiency.Based on the properties of titanium slag and anosovite solid solution,the favorable conditions for the modification of molten titanium slag were determined.Firstly,the thermodynamic calculation software FactSage6.3 was used to clarify the thermodynamic principles of modification of molten titanium slag and removal of calcium and magnesium impurities.Secondly,the experimental study was carried out to determine the influence of process parameters on the removal of calcium and magnesium impurities in titanium slag.The suitable process parameters were determined.Subsequently,the mechanism of modification of molten titanium slag and removal of calcium and magnesium impurities was described by means of characterization methods such as EPMA.Finally,the structural parameters and transport properties of molten titanium slag containing B₂O₃ were studied by molecular dynamics simulations to clarify the principle of B₂O₃ promoting the conversion of low valence titanium into rutile in molten titanium slag.?1?The properties of titanium slag and anosovite solid solution were studied to determine the favorable conditions for modification of molten titanium slag.Most of Ca and Si elements in raw material titanium slag are distributed in the silicate.Most of Mg and Ti elements are distributed in anosovite solid solution.Al,Fe and Mn elements are distributed in the two phases.Anosovte is a kind of solid solution with high chemical stability.It is not feasible to remove the impurities in the solid solution by direct leaching with dilute acid.Controlling the crystallization?additive,cooling atmosphere,etc.?of molten titanium slag to suppress the formation of anosovite solid solution and convert calcium and magnesium impurities into an acid-soluble phase is a feasible solution for removing the calcium and magnesium impurities in titanium slag.?2?Thermodynamic calculation software FactSage6.3 was used to clarify the thermodynamic principles of modification of molten titanium slag and removal of calcium and magnesium impurities.In the process of cooling and crystallization of molten titanium slag,the oxidizing atmosphere can promote the conversion of anosovite solid solution to rutile.During the cooling crystallization of molten titanium slag,CaO preferentially reacts with B₂O₃ to form Ca₂B₂O₅,MgO preferentially reacts with B₂O₃to form Mg₃B₂O₆,and Ti₂O₃ preferentially reacts with O₂ to form rutile.Borates are easily chemically reacted with acids and rutile is not soluble in acids.The leaching of hydrochloric acid can achieve the purpose of removing the calcium and magnesium impurities in modified titanium slag and enriching the TiO₂.?3?The influence of process parameters on the removal of calcium and magnesium impurities in titanium slag was studied to determine the suitable process parameters.When the additive?B₂O₃?amount increases from 0%to 2%,the content of calcium and magnesium impurities in titanium slag decreases remarkably.The continuous addition of B₂O₃ do not significantly reduce the content of calcium and magnesium impurities in titanium slag.The effects of hydrochloric acid concentration?5%?,leaching temperature?80°C?and leaching time?30 min?on the content of calcium and magnesium impurities in titanium slag show a similar law with the additive?B₂O₃?amount.Considering the removal effect of calcium and magnesium impurities in titanium slag and the utilization efficiency of raw materials?energy?,suitable process parameters were determined.The process parameters are:additive?B₂O₃?amount 2%,hydrochloric acid concentration5%,leaching temperature 80°C,leaching time 30 min.The final calcined product contains 86.77%TiO₂,1.23%?CaO+MgO?and 0.91%SiO₂,which meets the requirement of the fluidized chlorination process for calcium and magnesium impurities in the raw materials.?4?The effects of B₂O₃ on the phase composition,surface morphology,element migration and valence state of titanium were studied by means of EPMA and other characterization methods to clarify mechanism of the modification of molten titanium slag and the removal of calcium and magnesium impurities.In the process of modification of molten titanium slag,B₂O₃ acts to combine the calcium and magnesium impurities to form borate?Ca₂B₂O₅ and Mg₃B₂O₆?and to promote the formation of rutile.During the cooling crystallization of molten titanium slag containing B₂O₃,Ti element and Ca,Mg and B elements migrate and enrich to different regions,forming rutile and borate.The elements that are have no time to migrate stay at the boundary of the two enriched regions to form“residual”anosovite solid solution.With the additive?B₂O₃?amount increasing,the element migration is more complete and thorough.During the acid leaching of the modified titanium slag,the borate is dissolved into solution.The anosovite solid solution and rutile are not dissolved,remaining in the slag phase.The calcium and magnesium impurities in modified titanium slag are effectively removed and the titanium element is further enriched.?5?The molecular dynamics simulations was used to study the microstructure and transmission properties of molten titanium slag,which laid a foundation for mastering the structure and properties of molten titanium slag from electric furnace.In the TiO₂-CaO-MgO-SiO₂ system,the order of the self-diffusion coefficients of ions is:Mg²⁺>Ca²⁺>Ti⁴⁺>O^2->Si⁴⁺.As the content of calcium and magnesium impurities increased from 3.50%to 31.5%,the self-diffusion coefficient of each ion increases,the order does not change,and the viscosity of the melt decreases from 0.098Pa s to0.064Pa s.As the content of calcium and magnesium impurities increases,the Mg-O bond partially replaces the Ti-O bond.The variation results in a decrease in the strength of the structure,increases the self-diffusion coefficient,and decreases the melt viscosity.The structural and transport properties of molten titanium slag containing B₂O₃were studied by molecular dynamics simulations to clarify the principle of B₂O₃promoting the conversion of low valence titanium into rutile in molten titanium slag.In B₂O₃-TiO₂-CaO-MgO-SiO₂ system,the self-diffusion coefficient of ions is in this order:Mg²⁺>Ca²⁺>B³⁺>Ti⁴⁺>O^2->Si⁴⁺.As B₂O₃ content increases from 0%to 24%,the self-diffusion coefficient of each ion increases,the order does not change,and the viscosity of the melt decreases from 0.079 Pa s to 0.032 Pa s.In this system,the BO₃planar triangular structure is the main body in the BO_p polyhedron.The BO₃ plane triangle belongs to the layered two-dimensional structure.There is a weak molecular force between the layers.Therefore,the addition of B₂O₃ reduces the overall structure strength of molten titanium slag containing B₂O₃ and increases the self-diffusion coefficient of each ion,reducing the viscosity.These variations increase the contact of Ti³⁺with O₂ in molten titanium slag,which is favorable for the oxidation of low valence titanium in molten titanium slag.