Development Of A Rare Earth-containing Oxide Slag System For Oxidative Dephosphorization Of Ferromanganese Alloys

Ferromanganese is the most consumed ferroalloy in the production of steel,and it is used extensively as a deoxidizing and alloying agent.Since ferromanganese is late additives in the steelmaking process,the impurities in ferromanganese have significant influences on the cleanness of liquid steel.Blast furnace ferromanganese typically has a high content of phosphorous,i.e.0.4 %⁰.6 %,the phosphorous content in ferromanganese should to be reduced to lower than 0.2 % for the phosphorous content of clean steel.However,conventional CaO-based slags cannot obtain desire dephosphorization results,the dephosphorization efficiency of BaO-based slags is sensitive to the content of silicon in ferromanganese,and the dephosphorization efficiency of alkalis slags is still not well.In this project,the idea of dephosphorization of ferromanganese using rare earth oxide containing slags is proposed.The phosphates of rare earth are highly stable in natural environment;and rare earth oxides,likely La2O3 and Ce2O3,have higher optical basicity than CaO and BaO.Therefore,the thermodynamic conditions for dephosphorization using rare earth oxide containing slags are expected to be desire.The thermal physical properties,dephosphorization thermodynamics and dephosphorization performances of rare earth oxide containing slags have been investigated,and the composition ranges of slags with low liquidus temperature and viscosity,high phosphate capacity,and insensitive to silicon content in ferromanganese have been determined.The specific conclusions are as follows:1)When the values of binary basicity were 1.05 and 0.97,the melting temperature decreased firstly and then increased with the increase of rare earth oxide.When the content of rare earth oxide was 6 %,the melting temperature reached minimum values,respectively.The viscosity of slags decreased all the time with the increase of rare earth oxide when the value of binary basicity was 0.97,and when the content of rare earth oxide was larger than 6 %,the downtrend of viscosity was not obviously.When the content of rare earth oxide lower than 9 % for the slags with binary basicity was 1.05,the viscosity of slags decreased with the increase of rare earth oxide.When the content of rare earth oxide reached 12 %,the value of viscosity increased significantly.Combining with the melting properties and viscosity of rare earth oxide containing slags,the slags contained 6 % rare earth oxide were selected for subsequent phosphorus distribution ratio experiment.2)The phosphorus distribution ratio and phosphate capacity of slags decreased all the time when the temperature increased.However,the phosphorus distribution ratio and phosphate capacity of slags rose when the content of rare earth oxide increased,but the trend was not obvious when the content of rare earth oxide larger than 6 % for the slags with binary basicity was 1.05.The phosphorus distribution ratio almost no change when the content of silicon lower than 0.25 % in ferromanganese,and when the content of silicon reached 0.62 %,the values of phosphorus distribution ratio decreased significantly.The phosphorus distribution ratio rose with the oxygen partial pressure increased.Combining with the results and discussion,determined the optimal conditions of dephosphorization thermodynamics: dephosphorization temperature was 1350 ℃,the content of rare earth oxide in slags was 6 %,and the content of silicon in ferromanganese was lower than 0.25 %.3)The dephosphorization efficiency increased firstly and then decreased,and the manganese loss of rare earth oxide containing slags decreased firstly and then increased when the dephosphorization temperature increased.The quantity of dephosphorization slags and the content of rare earth oxide in dephosphorization slags increased were beneficial to ferromanganese dephosphorization,but the manganese loss increased as well.When the content of silicon in ferromanganese increased,the dephosphorization efficiency decreased,and the manganese loss decreased firstly and then increased.4)On the assumption that ferromanganese dephosphorization was controlled by mass transfer of slags and gold system.The ferromanganese dephosphorization dynamic equation was established according to the double film theory.The measured results and the fitting results of the mass fraction of phosphorous in ferromanganese were matched well,and the correlation coefficient of fitting function were greater than 0.96,that instructed ferromanganese dephosphorization was controlled by mass transfer of phosphorous.5)According to the optimal dephosphorization thermodynamics,combining with the discussion of dephosphorization kinetics,determined the optimal conditions of ferromanganese dephosphorization: dephosphorization temperature was 1350 ℃,residence time was 16 minutes,the quantity of dephosphorization slags was 10 %,the content of rare earth oxide in slags was 6 %,and the content of silicon in ferromanganese was lower than 0.25 %.6)The optical composition of rare earth oxide containing slags for ferromanganese dephosphorization developed in the experiment as follows: 38.54 %CaO-36.66 %SiO2-18.80 %MnO-6 %RE₂O₃ and 34.78 %CaO-35.72 %SiO2-23.50 %MnO-6 %RE₂O₃.