Study On The High-temperature Physicochemical Properties Of Barium-bearing Blast Furnace Slag And Preparation Of Glass-ceramics

China is the largest manufacturer of steel product,and the crude steel output in 2020 reached 1.065 billion tons,accounting for 56.7% of world’s total production.The iron ore grade in China is usually low,which makes about 80% of the iron ore used in ironmaking depends on importing from Australia,Brazil,South Africa,etc.However,with the the degradation of high-quality iron ore and the increasing cost of raw materials for ironmaking,the further development and utilization of the domestic low-grade ores is quite necessary for the iron and steel enterprises to achieve the sustainable development.The ironmaking raw materials in Jiuquan steel plant of China mainly include the surrounding barite-bearing ores,cooperation with some imported ores.For the sinter production,barite will decompose into BaO,and then enter into ferrite phase and silicate phase.After entering blast furnace,BaO,acid gangue,basic fluxes and ash content from coal powder and coke generate the molten slag gradually through a series of reactions.Considering the further utilization of barite-bearing ores,BaO content in the blast furnace slag increases inevitably,which will affect its high-temperature physicochemical properties,such as viscosity,desulphurization ability,crystallization behavior,etc.In addition,blast furnace slag contains a large content of CaO、SiO₂、MgO、Al₂O₃,and is the one of the ideal raw materials for preparing the glass-ceramics.Simultaneously.BaO and alkali oxides in the slag are also the common fluxes,which can decrease extra addition for the fluxes owing to the utilization of this slag.As a result,carrying out the study on the high-temperature physicochemical properties of BaO-bearing blast furnace slag and the preparation of glass-ceramics will make great significance not only for further utilization of barite-bearing ores,but also for the subsequent treatment of hot slag and its comprehensive utilization acted as the solid waste resources.The viscosity variations of blast furnace slag are essentially attributed to its network structure evolution,which affects greatly the gas flow distribution,slag-iron separation,desulfurization behavior and so on in the smelting process.In this work,the effect of BaO on the viscosity and structure of CaO-SiO₂-MgO-Al₂O₃-BaO slag with different CaO/SiO₂ ratios is investigated systematically by combining with Fourier transform infrared,Raman spectroscopy,XPS,²⁷Al magic angles pinning nuclear magnetic resonance and molecular dynamic simulation.The effect of BaO is from the competitive action of Ba²⁺ and O^2-.Ba²⁺ has a higher priority for compensating[AlO₄]structure,and can inhibite its transformation towards higher-coordinated Al-based units,which helps to increase the complexity of network structure.The O^2-from BaO intereacts with bridged oxygen to form non-bridged oxygen,destroying the connection bonds between tetrahedron units and depolymerizing the polymerized network.For the basicity of 1.1,the existence of BaO induces the higher complexity of[SiO₄]and[AlO₄]structure,leading to a rise of viscosity.When the basicity is 0.9,the viscosity and polymerization degree reduce with BaO increasing from 0 to 1%,and increase slightly with further addition of BaO.As the basicity reduces to 0.7,an increase in BaO decreases the trough of[SiO₄]-tetrahedra stretching bands and Si-O-Al bending,and increases the amount of[AlO₅],[AlO₆],free oxygen and non-brodged oxygen,leading to a decrease in viscosity of the slag.Sulphur is the harful element,which usually causes the hot-shortness of steel production.In the smelting process,most of sulphur from iron-bearing furnace burdens,coke,and coal powder enters blast furnace slag.In this study,the sulfide capacity of the slag is measured,and the influence of MnO、BaO/CaO substitution and BaO is discussed based on the activity of O^2-and activity coefficient of S^2-.The results show that S^2- has a larger affinity with Ca²⁺ and it existes in the slag in form of CaS.With an increase in MnO content,the O^2-concentration and the difference between logacao and logycas increase,which helps to enhance the sulfide capacity.After substituting CaO with BaO,Ba²⁺will preferentially compensate Al³⁺ owing to its lower field strength,releasing some Ca²⁺ to absorb S^2-,which is conducive to improve the desulphurization ability.However,because BaO has the larger relative molecular mass,after substitution the total mole number of basic components,the corrected optical capacity and the the difference between logacao and logycas decrease,eventually making the sulfide capacity reduce.When keeping the basicity constant,an increment of BaO content will increase the total mole number of basic components and the difference between logaCaO and logγCaS,consequently improving the desulfurization capacity.The crystallization of molten slag can decrease the hydration activity,affecting its utilization value.The crystallization behavior of the slag under different conditons is observed by a confocal laser scanning microscope.The theoretical calculation and experimental verification are used to analyze the crystal precipitation behavior in the cooling process.The results indicate that,in the isothermal crystallization process,BaO existence has little effect on the crystal morphology and growth mode at low temperature,and crystal morphology changes from lamellar to columnar as a function of basicity.Increasing BaO content and decreasing basicity result in a decrease in the initial crystallization temperature for the continuous cooling process,and extend the incubation time for isothermal crystallization process,indicating that the crystallization behavior is inhibited,which can help recover more heat while obtaining glassy slag.For the crystal precipitation behavior,increasing BaO content and basicity can promote merwinite generation at 1350℃.Melilite is main phase and its amount reduces at 1250℃ and 1000℃.along with a slight increase of merwinite.Using blast furnace slag to prepare the glass-ceramics can broaden its application scope and further improve the application value.The diopside-based glass-ceramics is prepared successfully using BaO-bearing slag,and the influence of BaO on the netwotk structure,microstructure and physicochemical properties is studied.The results show that,as BaO content increases from 1% to 3%,the viscosity and degree of polymerization reduce,the number of crystals increases,and the crystal size and glass content decrease,leading to the higher crystallization degree and denser structure.With BaO content exceeding 3%.the viscosity of melt increases and the number of crystals decreases.Expecially for BaO content of 7%,the grain grows abnormally and the microstructure of glass-ceramics becomes looser markedly.The glass-ceramics with BaO content of about 3% presents the better comprehensive performances with the density of 3.115g/cm³,flexural strength of 153.56MPa,Vickers hardness of 7.69GPa,and the corrosion resistance more than 96%.