Study On Dephosphorization Of High Phosphorus Hot Metal Based On CaO-SiO₂-Al₂O₃-Fe₂O₃ Slag System

With the steady declining of high-quality iron ore resources,the utilization of low grade iron ore has been increasingly emphasized.Partial substitution of high-quality iron ore with low grade iron ore can be used to reduce cost of production by iron and steel enterprises.However,the impurities of low-grade ore,especially the high content of phosphorus,will increase the phosphorus content of hot metal and form a large number of high-phosphorus hot metal.In order to solve the problem of dephosphorization of high-phosphorus hot metal,this paper studied the effect of CaO-SiO₂-Al₂O₃-Fe₂O₃ slag composition and partial substitution of CaO-SiO₂-Al₂O₃-Fe₂O₃ slag component with Al₂O₃,Na₂O,Li₂O,B₂O₃ and other oxides on the dephosphorization of high-phosphorus hot metal.In addition,the dissolution behavior of lime in slag system based on CaO-SiO₂-Al₂O₃-Fe₂O₃ we also studied.The main conclusions are as follows:?1?When the basicity is between 2.5 and 4.5,melting temperature and dephosphorization rate of the dephosphorisation agent increases rapidly with an increase of basicity,and the viscosity decreases slightly.When the basicity of dephosphorizing agent increases above 5.0,the dephosphorization rate decreases slightly.When the Fe₂O₃ content of dephosphorization agent is controlled at44%⁶4%,the melting temperature and viscosity of dephosphorization agent decrease gradually and the dephosphorization rate shows a gradually increasing trend with the increase of Fe₂O₃ content.When the content of Al₂O₃ is between 1%and 3%,the melting temperature decreases slightly,while the dephosphorization rate increases slightly.Then,with the further increase of Al₂O₃ content,the melting temperature increases gradually,and the dephosphorization rate decreases gradually.?2?When the content of B₂O₃ varies from 1%to 9%in CaO-SiO₂-B₂O₃-Fe₂O₃slag system,the dephosphorization rate decreases gradually,and remains near 64%in the range of 7%to 9%.When Li₂O varies from 1%to 9%in CaO-SiO₂-Li₂O-Fe₂O₃slag system,the dephosphorization rate increases gradually.When CaO in the CaO-SiO₂-Al₂O₃-Fe₂O₃ slag system is partially replaced by Na₂O,the dephosphorization rate of the slag system is continuously increased as the proportion of Na₂O in the slag system is continuously increased.Comparing the dephosphorization effect of different flux,it can be found that CaCl₂,Al₂O₃,B₂O₃,CaF₂,Li₂O show different dephosphorization rate,from high to low in order.?3?When lime dissolutes in CaO-Al₂O₃-Fe₂O₃-SiO₂-5%MgO-5%MnO-5%P₂O₅slag system,forming four regions along the lime cylinder:transition layer of calcium ferrite diffusion into lime cylindrical gap,white calcium ferrite layer,C₂S-C₃P solid solution layer and slag layer.With the increase of alkalinity of slag,the dissolution rate of lime is gradually decreasing.The increase of Fe₂O₃ content can promote the dissolution of lime.The addition of a small amount of Al₂O₃ contributes to the dissolution of lime,and if too much of Al₂O₃ is added,it will inhibit the dissolution of lime.As the dissolution time goes on,the lime gradually dissolves and diffuses into the slag,causing the basicity of the slag to rise.Therefore,the dissolution rate of lime decreases gradually.