Research On Dephosphorization Reaction Process And Efficient Dephosphorization Of Multi-Phase Slag

At present,the production process of Chinese steel plant is mainly blast furnace-converter long process,with advantages of large output,low production costs,wide varieties of smelting and so on.The current dephosphorization technology of converter can meet the requirements of most steels.However,with the progress of society,people put forward higher demands for high-end varieties of steel,which needing to have characteristics of low or even ultra-low phosphorus.Japanese scholars proposed the theory of "multi-phase flux dephosphorization" to deeply remove phosphorus of hot metal using 2CaO·SiO2(C2S)solid of slag.However,research of dephosphorization reaction process of the multi-phase slag is not thoroughness and comprehensive.How to improve the dephosphorization effect by generating more small particles of phosphorus-enriched phase in reaction between C2S and slag;by increasing C2S content of multi-phase slag as well as through BaO addition to improve the multi-phase slag dephosphorization effect and other aspects need further reasearch.In present study,the dephosphorization reaction process of the solid phase in multi-phase slag was firstly investigated,and the reaction behaviour between C2S and molten slag was explored;then the influence of the C2S content and temperature in the multi-phase slag on the dephosphorisation behaviour was investigated through the reaction between the multi-phase slag and hot metal.The viscosity and structure evolution of the liquid phase of the multi-phase slag were analyzed.The phosphorus partition ratio between the solid and liquid phases of the multiphase slag,and that between multi-phase slag containing barium and hot metal were discussed,respectively.The following conclusions were obtained:(1)The relationship of between the thickness of the phosphorus diffusion layer h(mm)at the interface between C2S flake and slag and the erosion time t(s)at 1723 K temperature was given by h=171.8t1/2.The diffusion coefficient of phosphorus was 4.44×10-9 m2·s-1 at the interface between the C2S and CaO-SiO2-FeO-P2O5 slag.The surfaces of the generated solid solution layer and shed small particles were irregular and showed some gully shapes,thereby leading to a height difference on the particles’ surfaces after adding big C2S particles to CaO-SiO2-FeO-P2O5 slag.And the phosphorus content of the upper gully shapes was lower than that on the bottom.It was observed through the reaction between barium-containing slag and the C2S particles that the presence of elemental Ba within the solid solution,the enlarged cell structure of the C2S solid solution,the reduced stability of the crystals,and the numerous small particles by decomposing of the 120-250μm C2S particles,which were favourable to improve the effect of phosphorus removal of C2S solid solution.(2)The dephosphorization of multi-phase slag was best at 1723 K when the C2S content was 51.31%,with the phosphorus partition ratio(Lp)of 19.47.In the range of 1573～1723 K,the maximum phosphorus partition ratio(Lp)between slag and hot metal was 22.50 at 1673 K.While the maximum phosphorus partition ratio(L’p)between the solid and liquid phases was 5.82 at 1673 K temperature.(3)The viscosity of CaO-SiO2-FeOt-(BaO)slag and CaO-SiO2-FetO-Al2O3(BaO)slag decreased with the increasing BaO content in slag.The viscosity of CaO-SiO2-FeOt-(Al2O3)-BaO slag increased with the increasing Al2O3 content in slag.The addition of BaO in slag disrupt the network structure of the[SiO4]tetrahedra and the connection between the[SiO4]and[AlO4]tetrahedra,facilitating the conversion of Q2 and Q3 to Q0 and Q1,increasing the relative content of O0,increasing the relative cowtent of O-and O2-,and decreasing the viscosity of the slag.In contrast,the addition of Al2O3 in slag resulted in more complex structure of[SiO4]symmetric tetrahedra and[AlO4]asymmetric tetrahedra,increasing the degree of polymerisation(DOP)of the slag network and slag viscosity.(4)The phosphorus content in the phosphorus-enriched phase increased from 4.16%to 5.27%with the addition of 0-15%BaO in the multiphase slag,and the phosphorus partition ratio between the solid and liquid phases increased from 8.49 to 18.82.With BaO content in the C2S-Fe2O3-BaO slag increased from 5%to 20%,the phosphorus partition ratio between the slag and iron increased from 216.67 to 352.89,an increase of 63%.The phosphorus partition ratio significantly increased by the addition of BaO in the multi-phase slag during the simulated steel blowing of 5 kg iron.The dephosphorization effect of the multi-phase slag was clearly improved by the addition of BaO.