Fundamental Theory Research On Blast Furnace Smelting With Ultra-high Ratio Vanadium Titanomagnetite

Vanadium titanomagnetite is a typical precious,complex and refractory mineral resource.It is not only rich in vanadium（V）and titanium（Ti）strategic metal elements but also associated with rare metal elements with high added value,such as chromium（Cr）,nickel（Ni）,cobalt（Co）,gallium（Ga）,scandium（Sc）.After more than half a century of exploration and development,China has established a complete iron and steel metallurgy process based on"blast furnace-converter"process,vanadium metallurgy process and titanium metallurgy process based on electric furnace process with vanadium titanomagnetite as raw material,and realized the extraction and utilization of iron（Fe）,vanadium（V）and titanium（Ti）.However,although the smelting process of vanadium titanium magnetite by"blast furnace-converter"has high production efficiency and large scale,there are still many problems to be improved.For example,the enrichment rate of vanadium（V）and titanium（Ti）is low,the utilization of titanium bearing blast furnace slag is difficult,and the comprehensive recovery and utilization rate of vanadium is low;moreover,the problems of slag,foam and slag iron in the process of blast furnace smelting of vanadium titanium magnetite have not been fundamentally solved,which seriously hamper the deep development and efficient utilization of vanadium titanium resources in China.From the perspective of solving the problems encountered in the smelting process of vanadium titanium magnetite in blast furnace and improving the enrichment rate and recovery rate of vanadium and titanium resources,it is of great practical significance to improve the proportion of vanadium titanium ore in blast furnace smelting process.The key core of vanadium titanomagnetite blast furnace smelting has returned to"all vanadium titanomagnetite blast furnace smelting technology",which has always been the goal pursued by engineering technicians and scientific and technological workers engaged in vanadium titanomagnetite blast furnace smelting.It is also the"original intention"and"mission"of predecessors engaged in vanadium titanomagnetite smelting scientific research for decades.From the point of view of improving enrichment rate and resource recovery,smelting high proportioning vanadium titanomagnetite in the blast furnace has practical significance to solve this problem.The key core returns to"blast furnace smelting technology with pure vanadium titanomagnetite",which has always been the goal pursued by the engineering and technical personnel engaged in vanadium titanomagnetite blast furnace smelting,and also the"original intention"of the scientific research predecessors in the past decades.On the premise of existing technical and economic indicators,it is undoubtedly very difficult to realize high-efficiency smelting of all vanadium titanomagnetite blast furnace.Through a large number of literature reviews,this paper puts forward a new concept of slagging based on"replacing Ca O with Mg O",focuses on the influence of TiO₂ content and Mg O/Ca O mass ratio on the physicochemical properties and structure of ultra-high TiO₂ blast furnace slag,reveals the relationship between slag composition,structure and properties,and puts forward the slagging technical scheme under the smelting condition of ultra-high ratio vanadium titanium magnetite blast furnace,It is expected to contribute to the comprehensive utilization of vanadium and titanium resources and the development of iron and steel metallurgy in China.The main conclusions are as follows:（1）In this study,titanium in titanium bearing blast furnace slag melt exists in the form of four coordination and six coordination,but the content of six coordination titanium is relatively low,and titanium mainly exists in the form of four coordination.The addition of TiO₂will not only affect the Ti_xO_y^z-structure,but also affect the Si_xO_y^z-structure.The increase of TiO₂content will increase the mole fraction of Ti₂O₆^4-（chain）structural unit and O-Ti-O structural unit,and there will be more hexacoordinated titanium in the system.For Si_xO_y^z-structure,the increase of TiO₂content will reduce the mole fraction of Si₂O₇^6-（dimer）,the mole fraction of Si₂O₆^4-（chain）increases first and then decreases,while the content of Si₂O₅^2-（sheet）decreases.With the increase of Mg O/Ca O mass ratio from 0.32 to 0.65,the mole fraction of Si₂O₅^2-（sheet）does not change significantly,the mole fraction of Si₂O₆^4-（chain）decreases gradually,while the mole fraction of Si₂O₇^6-（dimer）does not change significantly at first,but increases when the Mg O/Ca O mass ratio exceeds 0.5.For Ti₂O₆^4-（chain）and Si O₄^4-（monomer）structural units,due to the overlap of their characteristic peak positions,the spectral bands are generated near 850 cm^-1,so they cannot be separated and discussed separately.（2）In an inert atmosphere,the viscosity of ultra-high TiO₂ blast furnace slag decreases significantly with the increase of TiO₂ content;"Replacing calcium with magnesium"will slightly increase the viscosity of slag,but still meet the requirements of slag fluidity in the blast furnace smelting.The increase of TiO₂ content will significantly increase the liquidus temperature of slag,reaching about 1404 K when the TiO₂ content is 26 wt.%;With the increase of Mg O/Ca O mass ratio from 0.32 to 0.57,the slag liquidus temperature decreases obviously,and the decrease range is about50℃.Among the viscosity models,Reddy-Lv,NPL and Zhang models are more reliable in predicting the viscosity of ultra-high TiO₂ blast furnace slag,with average errors of 20.3%,20.6%and 23.5%,respectively.With the increase of TiO₂ content,the sulfur capacity of slag decreases;With the increase of Mg O/Ca O mass ratio,the sulfur capacity of slag increases first and then decreases,and a turning point occurs when the Mg O/Ca O mass ratio is 0.43.The slag density decreases with the increase of TiO₂content,and"replacing calcium with magnesium"will slightly increase the density of ultra-high TiO₂ blast furnace slag.The slag surface tension decreases significantly with the increase of TiO₂ content,while"replacing calcium with magnesium"will increase the slag surface tension.When the temperature is 1500℃,the increase of TiO₂ content from 20 wt.%to 30 wt.%will reduce the surface tension of blast furnace slag from 422m N/m to 406 m N/m.The high temperature physicochemical properties of slag are closely related to the degree of polymerization of slag structure.The viscosity,density,surface tension and sulfur capacity of slag will be affected by the degree of polymerization of silicate network structure(DOP-Si_xO_y^z-)and the degree of polymerization of tixoyz structure（DOP-Ti_xO_y^z）.Determining the correlation between slag physicochemical properties and structure is helpful to clarify the internal factors and scientific truth of slag properties changing with its composition.The above research provides a reference for slag optimization in the blast furnace smelting process with ultra-high proportion of vanadium titanomagnetite.（3）With the increase of TiO₂ content from 20 wt.%to 34 wt.%,the maximum weight loss rate of non-isothermal reduction of slag and carbon gradually increases from 9.11%to 21.03%,which means that the increase of TiO₂ content in slag will deepen the degree of carbothermal reaction between slag and carbon.When the mass ratio of Mg O/Ca O increases from 0.32 to 0.73,the reduction time required for non-isothermal reduction of slag and carbon is slightly prolonged.Under the condition of long enough reaction time,the maximum weight loss rate of slag carbothermal reaction has no obvious change with the increase of Mg O/Ca O mass ratio,which is about 17.5%.When the binary basicity of slag is controlled,increasing Mg O content to improve the ternary basicity of slag（（Mg O+Ca O）/Si O₂）will not only reduce the maximum reduction degree of carbothermal reaction but also reduce the rate of carbothermal reaction,so as to inhibit the carbothermal reactivity of titanium bearing blast furnace slag.With the increase of TiO₂ content from 20 wt.%,the bubble rate has no obvious change,the rate is very large,and the bubble height reaches the maximum within 150 seconds.The maximum height of foam increases with the increase of TiO₂content,and when the TiO₂ content exceeds 26 wt.%,it is stable.From the foam defoaming situation,the increase of TiO₂ content will reduce the foaming defoaming rate,which means that the foam is stable and is not easy to defoam.The more the TiO₂content is,the more serious the foaming problem of blast furnace slag is.With the increase of Mg O/Ca O mass ratio,the maximum height of foam decreases gradually,that is,the foaming rate decreases.This means that"magnesium replacing calcium"can significantly reduce the maximum foaming height,slow down the foaming rate and inhibit the foaming of slag.（4）Considering the requirements of slag iron separation,slag desulphurization and slag carbon thermal reactivity and foaming in the blast furnace smelting vanadium titanomagnetite process,the blast furnace slagging system with ultra-high vanadium titanomagnetite ratio is determined.The specific slag composition range is（18～24wt.%）Ca O-（19～21wt.%）Si O₂-（28～32wt.%）TiO₂-（10～14wt.%）Mg O-（16～17wt.%）Al₂O₃.