Study On Kinetic Behavior Of Molten Steel Slag Reduced By Aluminium Ash

Steel slag is a solid waste produced in the process of steelmaking,and it's one of the most discharged metallurgical slag in iron and steel enterprises.However,its utilization rate of resources is low,and improper treatment will not only occupy land and pollute the environment,but also cause serious waste of resources.Compared with the carbon-thermal reduction of steel slag,the new process of molten steel slag reduction with aluminum ash has many advantages,such as complete reduction,high metal yield and low smelting cost,which can make full use of the residual heat of steel slag and complete the extraction and recovery of valuable components in steel slag and stabilizing of tailings.However,the dissolution kinetics of the main components in the ash and the reduction kinetics in the ash reduction process were not investigated systemically under smelting conditions.Considering the research status of reduction reaction and dissolution kinetics of steel slag at abroad,The effects of slag composition change and slag basicity on the dissolution of main components of aluminum ash and different slag temperatures on the reduction reaction were investigated during the high temperature kinetic experments.The dissolution kinetics model of Al2O3 and the reduction kinetics model of FeO in molten steel slag were established,and the restrictive links of dissolution and reduction process were determined.The dissolution mechanism of Al2O3 was discussed based on the experimental results and the microstructure analysis of dissolution interface.The main conclusions of this paper are as follows.(1)At 1550?,the composition of molten slag and basicity of molten slag had an important effect on the dissolution amount and conversion rate of Al2O3 in aluminum ash.With the increasing of FeO reduction degree in slag,the dissolution amount and dissolution conversion rate decreased gradually.When FeO reduction degree in slag was 0%,the dissolution conversion rate of Al2O3 was 2.21?3.13 times as much as that of high FeO reduction degree.Al2O3 solubility and conversion rate were increased with the basicity of molten slag decreasing.The conversion rate of molten slag with basicity 2.99 was 1.18 times higher than that with basicity 3.49.The effect of basicity on the conversion rate and conversion rate of molten slag was smaller than that of FeO reduction in slag.(2)It was found that there was no enrichment zone in the solution interface in the initial slag.With the reduction reaction,when the FeO reduction degree is more than 50%,Mg enrichment zone will be formed at the slag-alumina solution interface,and the main phases in the enrichment zone are CaAl2O4 and MgAl2O4.The distribution of MgAl2O4 phase in the enrichment zone is relatively dispersed,which does not affect the diffusion of each component in the slag and has little influence on the dissolution rate of Al2O3.Therefore,the MgAl2O4 phase formed in the enrichment zone will not be a restrictive link of dissolution.(3)With the progress of reduction reaction,the dissolution mechanism of Al2O3 will change,while the change of slag basicity alone will not change the dissolution mechanism of Al2O3 spheres.The whole dissolution process of Al2O3 is as follows:when Al2O3 components diffuse into the slag,the components in the slag also rapidly diffuse into Al2O3 balls,that is,the Al2O3 component dissolves into the molten slag with the infiltration of the slag.(4)Based on the shrinkage model of product-free layer,the dissolution kinetics model was established.Combined with the experimental results,it was found that the dissolution of Al2O3.spheres in the initial molten steel slag was mainly controlled by the diffusion and mass transfer in the boundary layer and the interfacial reaction.When the reduction degree of FeO in molten slag reaches 50%and 100%,the boundary layer diffusion mass transfer is the limiting factor.However,under different basicity of molten slag,the diffusion and mass transfer in the boundary layer are the limiting factors for the dissolution of Al2O3.The interfacial chemical reaction rate constant decreases from 2.21×10-6 m/s to 2.06 × 10-6 m/s and the boundary layer diffusion rate constant decreases from 4.92 × 10-9 m2/s to 4.35 × 10-9 m2/s when the reduction degree of FeO in molten slag increases from 0%to 100%.When the basicity of molten slag decreases from 3.49 to 2.99,the rate constant of chemical reaction increases from 2.12 × 10-6 m/s to 2.15 ×10-6 m/s,and the rate constant of boundary layer diffusion increases from 4.48 × 10-9 m2/s to 4.73 × 10-9 m2/s.This shows that the reduction reaction will gradually hinder the dissolution of Al2O3 in aluminum ash into slag.(5)Temperature has a significant effect on the reduction of molten steel slag.The higher the temperature is,the better the reduction of FeO in molten steel slag is.The reduction rate and reduction rate of FeO in molten steel slag at 1600? are 1.18?1.58 times of those at 1550?,and the reduction rate of FeO in molten steel slag at 600 s is over 95%,and the reduction is relatively complete.In the whole reduction process,the reduction reaction rate is much higher than the dissolution rate of aluminum ash components.(6)The reaction of FeO in molten slag by smelting reduction of aluminum ash was first-order reaction.Based on the droplet reaction model,kinetic model for reduction of molten steel slag by aluminum ash was established,According to the kinetic model and the experimental data,the comprehensive rate constant of the reaction increases with the increase of temperature.When the temperature rises from 1550? to 1600 ?,the comprehensive rate constant of the reduction reaction increases from 1.10 × 10-6 m/s to 1.43 × 10-6 m/s,and the activation energy of the reaction is 143.25 kJ/mol.Therefore,the reduction reaction is mainly controlled by the diffusion and mass transfer of Al2O3 in molten slag.