Influence Of Basicity On Composition And Structure Of Molten Mixed Slag Of Blast Furnace Slag And Steel Slag

China’s steel production has increased year by year,and the accumulated stock of steel slag is large,which causes great pressure on the environment.However,the comprehensive utilization rate of steel slag in China is not high,only 25%.Self-pulverization of steel slag will become the most effective way to achieve high value-added utilization of steel slag.In this thesis,a new idea of mixing low basicity blast furnace slag with high basicity steel slag to realize self-pulverization of mixed slag is proposed,in order to develop an efficiency and low-cost new technology of steel slag self-pulverization,and achieve the goal of green and low carbon coordinated utilization of two solid wastes.Due to the complex composition of blast furnace slag and steel slag,it may affect the self-pulverization of mixed slag.Therefore,it is necessary to conduct in-depth study on the composition and structure of molten mixed slag of blast furnace slag and steel slag.Firstly,the chemical compositions of steel slag and blast furnace slag,two solid wastes of Baotou Steel Group,are detected,and the mineral phase compositions are analyzed by XRD and SEM.The results show that the mineral phase compositions of steel slag are mainly dicalcium silicate,magnesium-iron solid solution,rose pyroxene and calcium ferroaluminate;the mineral phase composition of blast furnace slag is mainly calcium aluminate feldspar.Secondly,by combining XRD,SEM and Factsage7.1 thermodynamic simulation,the influence mechanism of special components CaF₂ and CeO₂ in blast furnace slag and P₂O₅ in steel slag on the crystal transformation of calcium silicate C₂S is experimentally studied.Pure C₂S samples are prepared with n（Ca O）:n（Si O₂）=2:1,and then mixes with different mass fractions of pure reagents CaF₂,CeO₂ and Ca₃（PO₄）₂,respectively.The samples are calcined at1450°C for 1 h and then cool with the furnace to explore the effect of CaF₂,CeO₂ and Ca₃（PO₄）₂ on the crystal transformation of C₂S.The results show that the pure C₂S sample is seriously pulverized after high temperature calcination;when CaF₂ content is more than 2.5%,CeO₂ or Ca₃（PO₄）₂ content is more than 0.5%,the crystal transformation fromβ-C₂S toγ-C₂S and its self-pulverization is inhibited.The mixed slags with different basicity（1.6～2.4）and MgO content（0%～4.0%）are calcined at 1450°C for 1 h and then take out with furnace cooling.The mineral phase composition and structure of the calcined samples are studied by XRD,SEM and EDS;The influence of basicity of mixed slag on its melting performance is studied by combining hemispherical melting point measurement with thermodynamic simulation.The results show that when the basicity of mixed slag is 2.0,the content of C₂S in slag is the highest,and the melting temperature of mixed slag increases with the increase of basicity.MgO content has no positive effect on the formation and pulverization of C₂S in the mixed slag.