Study On The Effect Of Coal Gangue On The Phase Structure Of Steel Slag In Converter

China emits about 100m tonnes of steel slag a year,but uses only about 20 per cent of it.Compared with developed countries,there is still a certain gap.A large amount of unused steel slag will inevitably cause environmental pollution and waste of resources.Based on this phenomenon,this topic by adding coal gangue to change the phase structure of steel slag,to improve the utilization rate of converter slag.At the same time,because the converter slag contains free calcium oxide（f-CaO）,it will lead to the expansion and hydration of steel slag as subgrade material,and the coal gangue contains more than 50%Si O₂,which can be considered as having the potential ability to dissolve f-CaO in the converter slag.In addition,coal gangue also contains a lot of element C,which can reduce the iron oxide in the converter slag at high temperature,and can extract metal iron materials.If the coal gangue and the converter slag can be treated synchronously under the actual field conditions,it will greatly improve the utilization rate of the converter slag on the road,and can also recover the metal iron elemental from the converter slag.Thus,the iron oxide in steel slag is consumed and its hardness is reduced.In this thesis,the Fact Sage thermodynamic software is used for theoretical calculation and high temperature experiment in the laboratory.The phase microstructure of coal gangue converter slag mixture was analyzed by XRF,X-ray diffraction analysis and field emission electron scanning microscope.Then the content of f-CaO in converter slag was determined by glycol titration.The conclusions of this study are as follows:（1）According to the calculation of Fact Sage thermodynamic software,the liquid phase area of the converter slag system gradually increases with the increase of temperature.It can also be seen that the melting point of the compound containing Al in the slag is lower than that of the compound containing Mg.With the increase of Si O₂,（Ca,Mg）₂Si O₄,Ca₂（Al,Fe）₂O₅,Monoxide and Spinel in slag present a tendency of increasing firstly and then decreasing.When the temperature is 1723K and w（Si O₂）=25%,the size and shape of the liquid phase zone of the converter slag are greatly affected.（2）Through laboratory experiments,when 20%coal gangue is added,the digestion rate of free calcium oxide in converter slag reaches 45.83%.At 1550℃,coal gangue has the best digestion effect of free calcium oxide,up to 55%.Through XRD and SEM combined with coal gangue modified steel slag mixture,calcium aluminite,magnesium pyroxene,calcium aluminite,calcium aluminite spinel,magnesium iron spinel,magnesium aluminite spinel,in which the increase of calcium aluminite and the decrease of f-CaO are correlated.（3）In the high temperature experiment,the microscopic morphology of the converter slag was observed by SEM.With the increase of temperature,the area of metal iron phase became larger and larger.When the temperature is 1600℃and the amount of coal gangue is 20%,it is found that the content of elemental iron precipitated from the converter slag is the highest.It can be inferred that the C element in the gangue and the iron oxide in the converter slag have redox reaction.The metal iron was replaced.Thus the metal iron material can be extracted from the slag of the converter.