Study On Inhibition Of Desilication Slag Foaming During Hot Metal Pretreatment

During the process of hot metal dephosphorizing pretreatment, Si binds more easily with oxygen in hot metal than P. when ω[Si]>0.2%, the dephosphorization efficiency will be subject to greater influence and constraints. In order to enhance the dephosphorization efficiency, desiliconization pretreatment in hot metal is needed before dephosphorization. However, during the process of desiliconization, C can be easily oxidized, so a large number of CO gases will be produced and induce slag foaming. It leads to hot metal ladle overflow and affects the continuity of continuous steelmaking process. Therefore the study on foaming performance of desiliconization slag is necessary.According to the analyzing the mechanism of slag foaming, there are two ways to reduce the foaming property of desiliconization slag:first, by adjusting the desiliconization slag composition, slag foaming capacity could be reduced; second, reducing the production of gas.In this paper, the basic physical performance of blast furnace type slag, such as foaming height, viscosity and surface tension are measured under the temperature of1450℃, and the foaming regularity of molten slag of different composition are analyzed, too. Refer to the composition of molten slag with the relatively weak foaming performance, slag composition during the desiliconization process can be adjusted accordingly. The main results are as follows:1. The measurement of foaming performance in the low melting point zone and some relative performance on the CaO-SiO2-Al2O3-MgO slag shows:the role of slag composition on the viscosity is significant, viscosity decreases with the slag basicity and co(MgO) increasing in slag, when ω(Al2O3) is0.15～0.20, the basicity of the molten slag effects little on the viscosity; slag composition on the surface tension is significant, surface tension increases significantly with the increasing content of CaO and MgO, but when co(MgO) reaches10%, surface tension begins to decline; slag composition on the density is not significant, the experimental slag density is around 2.8～2.9g/cm3.2. The slag has lower foaming performance when R=0.9～1.0, ω(MgO)=5～10%, co(A1203)=10%～15%for CaO-SiO2-MgO-Al2O3slag system3. For the CaO-SiO2-MgO-Al2O3-CaF2slag system,ω(CaF2) is around0～6%. When co(CaF2) is0～2%, with the increase of CaF2, slag foaming performance is enhanced, and when co(CaF2) is2to6%, the slag foaming performance is rapidly declined;4. Within experimental slag system, the slag foaming index is proportional to viscosity, foaming index is inversely proportional to surface tension. Because the density of experimental slag system varies little, the effect of density to foam index is not significant;4. According to the analysis of desiliconization mechanism and relative experimental verification, the dynamic factor is the restrictive condition of desiliconization. Under the control of desiliconization agent size to16meshes, the iron bath fully stirred, and flux addition and other measures, dynamic condition is improved. So the addition of desilication agent is reduced, thereby drastically reducing the amount of gas produced, and inhibiting the slag foaming.