Fundamental Study On Mechanism And Application Of Vanadiun And Titanium In The Molten Iron/semi-steel Desulfurization Process

Vanadium-bearing titanomagnetite is mainly composed of iron and is paragenetic and associated with titanium,vanadium and other elements.Its reserves rank the third in China.Among them,vanadium resources account for 53%and titanium resources account for 95%in China.Vanadic titanomagnetite is the raw material of low-alloy high-strength steel,heavy rail steel,vanadium battery,aerospace materials and other important national basic industries,and its strategic position is very prominent.The comprehensive utilization of V-Ti magnetite mainly includes "blast furnace" and "non blast furnace"."Blast furnace-pretreatment-converter-refining-continuous casting" process is the most important form at present.The desulfurization process of molten iron/semi-steel using vanadium-titanium magnetite as raw material is complicated.The desulfurization of molten iron has some problems,such as high final sulfur,much resulfurization,large iron loss and large temperature drop.And the desulfurization of semi-steel has problems of large iron loss and difficulty in removing slag and so on.Moreover,the mechanism of vanadium-titanium on the desulfurization process is not clear.In view of the above problems,the mechanism of vanadium,titanium and their oxides on desulphurization of molten iron/semi-steel was studied,the influence of slag containing vanadium and titanium oxides on desulfurization and resulfurization control were analyzed,and the temperature drop of desulfurization process was explored in this paper.It provided a theoretical basis for improving the pre-desulfurization of vanadium titanium hot metal/semi steel.The main research contents and results are as follows:(1)Based on thermodynamic model of V-Ti-C-O-S,and high temperature desulfurization experiments,the effect of vanadium and titanium on the equilibrium content of sulfur in CaO desulfurization was analyzed.The mechanism of titanium on sulfur mass transfer was elucidated.Titanium reacted with oxygen that was in CaO to form TiO2 and CaTiO3 with high melting point to cover the CaO surface.It decreased the mass transfer of sulfur in the desulfurization product layer.Titanium reacted with carbon to form carbides,which increased solid particles and reduced the diffusion rate of sulfur in the iron liquid.(2)The role of top slag in the process of pre-desulfurization was studied by the experiment of slag desulfurization based on the theoretical model of desulfurization kinetics.It was found that the amount of top slag desulfurization accounts for 10-15%of the total amount of desulfurization.At the late stage of injection,sulfur in the top slag transferred to the molten iron.This is one of the important reasons why it was difficult to reach the calculated value in jet desulfurization.The suggestion to adjust the composition of desulfurization agent of molten iron was given:3?6%Al2O3 and 3-5%Na2O.(3)Based on the coexistence theory of molecular and ionic in slags,the effect of VOx and TiO2 on the sulfur distribution ratio in pre-desulfurization process was studied.Through the desulfurization experiments of vanadium titanium slag,the mechanism of vanadium and titanium influencing on properties of desulfurization slag was revealed:in the high basicity slag,V2O3 and TiO2 were acidic and combined with O2-in the slag to consume free CaO.The basicity model of sulfur distribution ratio(Ls)of V2O3-TiO2-FeO semi-steel desulfurization slag was proposed,and vanadium-titanium oxides were included in this model.(4)According to Young's model and KTH model,the sulfur capacity model containing vanadium and titanium oxides was established.This model predicted the amount of resulfurization in the process of slagging-off better.Based on the comprehensive analysis of the relationship among sulfur capacity,melting point and viscosity of the desulfurization slag,a formula of slag-adjusting agent for improving the performance of hot metal desulfurization slag was put forward:45-55%CaO,10-12%SiO2,5-8%Al2O3,15-20%B2O3,5-10%Na2O.(5)Based on the principle of thermal balance and material balance,a theoretical model of pre-desulfurization temperature drop was built.The calculated values were quite consistent with the factory production data,and the qualification rate of ±5 K is 85%.It was found that the most main factor of desulfurization costs of molten iron was iron loss,accounting for more than 50%.Desulfurization agent was the most main factor in the costs of semi-steel desulfurization,accounting for more than 40%.