Research On The Mechanism Of Foaming For The Blast Furnace Slag Bearing High Titania

There has been a long time for the smelting of V-Ti magnetite in Pan steel. Althoughit encountered a lot of problems, with the joint efforts of metallurgists, the blast furnacecan work normally and various indexes are good by adding the common ore to replacethe V-Ti magnetite which reduces the mass fraction of TiO₂in slag. However, thecontent of vanadium in hot metal will be reduced and the economic costs will rise withthis method. So it is not a good way. Therefore, considering the comprehensiveutilization of V-Ti ore resource and the improvement of economic benefit, it isnecessary to carry out the smelting of improve the V-Ti ore or whole V-Ti ore. But itwould increase the mass fraction of TiO₂in slag by using this method, and the massfraction of TiO₂in slag will be more than25%and reach about30%. Then the slagfoaming appeared. Therefore, if the Pan steel want to improve the V-Ti magnetite, theslag foaming must be resolved.In this paper, on the base of proper investigation of the present research developmentabout the slag foaming for the blast furnace slag bearing high TiO₂, the followingresearch works were finished aimed at the slag foaming in laboratory by using themethod combined the cold-state simulation with high temperature experiments. Fromthe research, the following conclusions are obtained:①The foaming properties of slag are influenced by the slag viscosity, surfacetension and the size of bubbles. There is a duality to the effect of slag viscosity on slagfoaming. The proper improvement of slag viscosity is in favour of the formation of slagfoaming, but a higher slag viscosity will lead to the decrease of foaming height. Theincrease of surface tension and size of bubbles have a negative effect on the slagfoaming which can restrain the formation of slag foaming. And the solid particles andbubbles size have predominance in the factors which have effects on the slag foaming,while the influence of slag viscosity and surface tension is small.②The appearance of solid particles in slag has an obvious effect on the foamingproperties of slag. The formation of solid particle increases the slag viscosity and resultin the transformation of melt from the common solution to suspension liquid. The moresolid particles appear in slag and the smaller particle size, the easier slag foaming forms.③The TiC, TiN and Ti（C,N） formed in BF slag bearing high TiO₂are diffuselydistributed in slag, therefore, the slag viscosity will increase, which in turn, adding the intensity of bubble films. The formation of solid particles can also lead to the decreaseof slag surface tension at the same time, which in turn, adding the adsorption effect ofslag for bubbles. So the bubbles in slag are more stable, therefore, the slag foaming willbecome aggravated.④The TiC and TiN have a good wettability with the slag bearing high TiO₂,therefore, the solid particle will hinder the drainage and attenuation of liquid film,which in turn, being in favour of the stability of bubbles. On the other hand, the goodwettability between slag and solid particle will result in the transformation of slag-cokefrom to non-wetting to wetting. This transformation will let the formation of CO gas inslag become easier relative to the interface between slag and coke. So there are a lot ofbubble embryos in slag which is a potential dangerous for slag foaming.⑤The surface tension of slag decreased with increasing mass fraction of TiO₂inslag, and the increase of TiO₂is beneficial to the formation of Ti（C,N）. Then the slagfoaming will become more aggravated, therefore, the content of TiO₂in slag should becontrolled strictly.⑥There is a distinction for the gas source of slag foaming between in the blastfurnace and outside the blast furnace. In the blast furnace, the gas source comes fromthe interactive reaction between slag-coke and slag-metal, the TiO₂and FeO are reducedby carbon and then generate the CO gas. Outside the blast furnace, the gas source comesfrom the reaction between TiO₂and TiC.⑦The primary cause of slag foaming is the formation of heterogeneous particlewith a high melting point in slag. The slag properties change due to the formation ofparticle, which in turn, enhancing the stability of bubbles and being beneficial to thebubbles retention in slag. Therefore, the key link for the inhibition of slag foaming is tocontrol the content of TiO₂in slag and prevent the TiO₂from being reduced excessive inorder to restrain the formation of Ti（C,N）.