Experimental Study On Dephosphorization Of Niobium-bearing Hot Metal

The present work aims at the problem of high efficiency utilization of Nbresource in poor complex symbiotic ore in Bayan Obo.The kinetic mechanism ofremoval of P from hot metal contained Nb were investigated by thermal dynamicanalysis and high-temperature simulation experiment in process of microalloyedsteel making which were melted by the method of "blast furnaceironmaking-removal of P and S during pretreatment of hot metal-convertersteelmaking" The oxidation law of Nb and P was explored when CaO and BaObased slage were used. The present work provides theoretical evidence for highefficiency utilization techniques of Nb resource. And after a series study, thefollowing conclusion can be obtained:⑴The metallurgical thermodynamic analysis showed that when CaO and BaObased slag were used to removal of P，the level of balance oxygen potential ofniobium oxidation was lower than the level of balance oxygen potential ofdephosphorization reaction，and the oxidation of Nb was ahead of phosphorus’s. Thehigher of the phosphorus content of equilibrium, the easier of the oxidation of Nb.⑵when the CaO based slag was used, the dephosphorization balanceexperiment in hot metal containing niobium showed that: When Nb₂O₅was added into the slag, the oxidation of Nb can be restrained and the dephosphorization rate wasreduced. When MnO₂was added, the dephosphorization rate was increased slightlyand the oxidation rate of niobium was unchanged. In the flux, niobium presents inthe state of Ca-Nb compound in slag and the reason why niobium was oxidized wasthat the existence of CaO reduces the Nb₂O₅activity in slag.⑶when the BaO based slag was used, the dephosphorization balanceexperiment in hot metal containing niobium showed that: when ω（Fe₂O₃）＞10%, thebasicity was the key factor of the oxidation of phosphorus and the oxidation rate ofphosphorus decreased with the basicity reduce. The oxidation rate of Nb increasedwith the oxid-ability of slag increase and had little relation to the basicity of slag.Low temperature has a good favor for dephosphorization, and the oxidation of Nbcan be restrained. It is appropriate to carry out the dephosphorize of hot metalcontaining Nb. when using BaF₂instead of BaCl₂as the flux, the dephosphorization rate.⑷The two-film theory was applicate to establish the oxidation model of Nband P, and by fitting the experimental data of dephosphorization in the BaO-basedslag system, the controlling step of dephosphorization is the mass transfer in the slagand molten iron while the controlling step of the oxidation of Nb is the mass trasferin the molten iron. Under these experimental conditions, the mass transfercoefficient of phosphorus during the dephosphorization process was about3.00⁹.60×10-3g/cm²·s while the mass transfer coefficient of niobium was between2.12⁶.57×10-3g/cm²·s.