Study On Viscosity Characteristic And Microstructure Of Blast Furnace Titanium Slag With Boron

It is of great importance to the effect of blast furnace slag on blast furnaceironmaking process, particularly process of smelting titanomagnetite bearing vanadiumores. In comparison with blast furnace slag with titanium free, the properties of titaniumslag are quite different for containing certain TiO₂. For example, viscosity of slagincreases, stabilization lowers, desulfurization performance is poor and so on. One ofthe most effective instruments for improving performance of Ti bearing blast furnaceslag is to adjust the composition of the slag. The fluid property of high titania slag fromPangang is much improved by adding certain CaF₂to the slag. However, fluoride cancorrode furnace wall and equipment, and volatiles and acidizing of the fluorine canmake evironment pollutant, endanger a person’s health. Therefore, the key of smeltingtitanomagnetite bearing vanadium ores successfully is to find a right slag compositionpossessing good viscosity characteristic. According to research, B₂O₃is helpful tomelting of slag and it can be used as a substitute for CaF₂. Hence, major concerns for allthe metallurgical workers are to effectively improve the fluid property to meet the needof production by making full use of the function of boron on titanium Slag.Based on Ti-bearing blast furnace slag from the southwestern steel plant of China,integrate with the current status of charge structure, the properties such as viscosity,break temperature and mineralogical constitution of different BF slag were mainlyinvestigated. The effects of boron, titanium and other compositions on performance andmicrostructure of titanium Slag were discussed. And the relationships of the fluidproperty and mineralogical constitution of different titanium Slag were achieved.Moreover, the predicting model among viscosity, temperature and composition oftitanium slag with boron was built based on Arrhenius equation. The results providedimportant references for increasing the ratio of vanadium–titanium ores, improving theproperties of titanium slag, rising the effectiveness in the use of titanomagnetite bearingvanadium ores and enriching the theory of titanomagnetite bearing vanadium ores.In this study, the fluid properties of normal titanium slag were investigated firstly.The results are:â‘ The short-slag behaviors of viscosity–temperature curves of slags areobserved during the cooling process when TiO₂content in slag varies between18.65%and26.45%. TiO₂content in slag and temperature have no obvious influence on the slagviscosity under high temperature. The viscosity rapidly increases with decreasingtemperature. Especially below the break temperature, viscosities rises rapidly up to 4.0Pa.s. The higher TiO₂content in slag, the higher the break temperature is, the quickerthe slag viscosities increase. The relationship of viscosity and temperature accords withArrhenius equation.â‘¡The short-slag behaviors of viscosity–temperature curves ofslags are observed too during the cooling process when CaO/SiO₂varies between1.06and1.20. The slag viscosities alter little with temperature at high temperature. However,the influences of temperature and CaO/SiO₂ratio on the viscosity are very markedbelow1360℃. Moreover, the higher CaO/SiO₂ratio is, the higher break temperature ofthe slag is.â‘¢the viscosity and break temperature of titanium slag increase with MgOconten when MgO content varies between8.65%and11.62%. But the increase slowsquickly after MgO content in slag acceeds9.64%.According to the experimental study of the viscosity chatacteristic of titanium slagwith boron, and comparison between titanium slag with boron or free, the results are:â‘ adding B₂O₃into slag can effectively decrease the break temperature when TiO₂contentis in the range of23.48%～27.38%and B₂O₃content is in the range of1%～4%. MoreB₂O₃in slag, less viscosity is, Which is vitally important to separate slag–iron, improvereaction kinetics conditions and short the smelting time of production.â‘¡the normaleffect of higher and higher TiO₂content on slag viscosity gradually triumph over theside effect of lower B₂O₃content when TiO₂content and B₂O₃content in slagsimultaneously varied. In contrast, viscosity decreases rapidlly with B₂O₃content whenTiO₂content is higher. TiO₂can lead to the increase of break temperature and more TiO₂content results in more increase. Adding more B₂O₃into slag causes more decrease ofbreak temperature at a fixation of TiO₂content.â‘¢As previously mentioned, slagviscosity can increase with basicity and more basicity leads to more obvious changes.However, the viscosity drops even lower with more and more B₂O₃content, which isadvantage to the slag fluidity.â‘£We substitute B₂O₃for CaF₂to improve the slagproperty is feasible, which is good to prolong the life of BF wall and imoroveenvironment.The influence of boron on slag structure was analized by NBO/T and Q parameterand calculation formula of NBO/T parameter was corrected based on the experimentalresults. Then mineralogical constitution of normal titanium slag and titanium slag withboron were analyzed by XRD and SEM etc.â‘ the kind and amount of mocrostructuralunit of slag changed, which reduced the extent of networking, thus viscosity decreased.â‘¡Minerals deposited from normal titanium slag are mainly CaO·SiO₂·TiO₂, CaO·TiO₂and so on. Minerals in low Ti bearing slag are mainly melilites and those in middle,high Ti bearing slag are mainly perovskite, However, Minerals in titanium slag with boron include some borates such as CaO·B₂O₃，MgO·B₂O₃etc and amount of perovskitein the slag reduced. More B₂O₃, better effect. In this study borates in slag is not more forless B₂O₃addition.â‘¢more perovskite and other high melting point minerals, higherslag viscosity and break temperature. More B₂O₃in slag, less perovskite and otherminerals with high melting temperature. So viscosity and break temperature decreased.Thermodynamic calculation model of CaO-SiO₂-TiO₂-Al₂O₃-MgO-B₂O₃system isbuilt up with experimental data based on coexistence theory. The slag structure isdiscussed in theory. Results appear below: CaO and SiO₂probably exist as Ca₂SiO₄,and MgO May exist in the form of CaMgSiO₄, and CaO and TiO₂expect as CaTiO₃、Ca₃Ti₂O₇，and CaOå’ŒB₂O₃May exist in the form of Ca₂B₂O₅å’ŒCa₃B₂O₆, which areconsistent with results from Mineral phase analysis. In addition, the changes of Freeenthalpy and Free energy with components are calculated. They reduce with B₂O₃concentration. However, Free enthalpy and Free energy with TiO₂and B₂O₃concentration Changes faster than those with basicity and B₂O₃concentration, which iseasy to react into more Calcium borate when more CaO and B₂O₃are added into slag.According to experimental data from the study and Arrhenius formula, parametersA and B in the predicting model were given revision. The results were good throughcomparision between calculated and measured viscosities of boron-free and boronbearing blast furnace titanium slag using the present model. However, the model shouldbe further perfected in the future.The innovative research works are as follows:â‘ The effects of boron and titanium on the fluidity of titanium slag were obtainedby experiment.â‘¡The caculation formular of NBO/T was corrected to reflect the changing trendof slag viscosity based on considering the influence of various acid and alkalineoxide（CaO, MgO and Al₂O₃etc） on polymerization of slag.â‘¢The relationship between slag performance and slag structure is clarifiedaccording to mineralogical constitution and theoretical analyses by thermodynamiccaculation model to redirect smelting special ores in blast furnace by SEM and XRD.