Study On Dephosphorization Kinetics Of High-phosphorus Hot Metal By CaO-SiO₂-FeTo-Na₂O(Al₂O₃)slag

Many domestic steel mills have participated in the iron ore negotiations, but there is no substantial progress in the issue of leading the price. As the price of iron ore keeps increasing, cost pressure has forced the domestic companies to make a good use of the domestic iron ore. Therefore, the exploitation of domestic high-phosphorus iron ore is putting on the agenda. But the use of high-phosphorus iron ore certainly will lead to a relativity high content of phosphor in the hot metal. Fortunately, we got inspiration from the successful use of Duplex Steelmaking Technology for Converter in steel works of Japan and BAO Steel and the Duplex Steelmaking Technology for Converter has a bright future of exploiting the domestic high-phosphorus iron ore.To improve the dephosphorization efficiency, both domestic and foreign researchers have done a lot of research on the dynamics of dephosphorization, but the kinetics of dephosphorization of high phosphorus hot metal is rarely reported. Considering the damage of fluoride and the manufacture of fertilizers with dephosphorization slag, little(2⁶%)Na₂O and Al_<sub>2O₃ are added in dephosphorization agent instead of CaF₂ to ensure the effect of slag's melting. At the temperature of dephosphorization in the converter, this paper studies the effect of high oxidative CaO-SiO₂-FetO slag on the dephosphorization kinetics of high phosphorus hot metal in the laboratory and a modified model of Robertson is established to simulate the dephosphorization process of high phosphor hot metal. After this a series of studies, the following conclusions is are obtained:â‘ When small amounts(2⁶%)of Na₂O and Al_<sub>2O₃ were added, the melting point of dephosphorization agent can be reduced to below 1200℃, meeting the temperature requirement of dephosphorization in the converter. Therefore, Na₂O and Al_<sub>2O₃ can be used as a substitute for CaF₂. However, Na₂O and Al_<sub>2O₃ content should be controlled within a certain range. The optimum content of Na₂O and Al_<sub>2O₃ is both around 6%.â‘¡The addition of small amounts of Al_<sub>2O₃ and Na₂O in CaO-based dephosphor- ization agent have accelerated ephosphorization rate. As the addition of Na₂O, rephosphoriation in the later stage of the reaction is inhibitted. The perfect ratio of BOF slag in the dephosphorization agent is 20%, and the dephosphorization rate can reach 95% or more, LP is up to 184.6.â‘¢.Assumed the phosphorus tranfer between the slag and metal is under the control of liquid phase mass transfer in both pahses, the dephosphorization dynamic equation of the high phosphorus molten iron is establishd,and use this equation to analysis the actual dephosphorization experiment. The range of the apparent dephosphorization rate constant kP is 0.868⁸.602×10^-3 cm²Â·s. kP is inversely proportional to LP and R. The range of the overall mass ransfer coefficient kO is 0.005⁰.024cm/s. The range of the mass ransfer parameter A·kO at 120s is 0.08 0.37cm3/s.With the increasing of Na₂O and Al_<sub>2O₃, the overall mass-transfer coefficient kO increase. The velocity of dephosphor is influenced by the phosphor transfer in hot metal and slag, especially in the hot metal. If LP relatively small, the reaction rate is determined by the mass transfer in both liquid pahses, if LP is large, the kinetics of phosphorus tranfer is limited by the metal phase mass tranfer.â‘£Using the modified Robertson model to analyse the dynamic process of high phosphorus hot metal dephosphorization. The initial [%Si] content in hot metal, the slag-iron (FeO) ratio, the flux component, have an obvious effect on aO* during dephosphorization reaction. The aO* is proportional to the slag-iron (FeO) ratio and inversely proportional to the initial [%Si] content, but the influence of the slag-iron (FeO) ratio is stronger. The[%Si],(%FeO),quantity of slag have an obvious effect on the moment of the decrease of aO*.