Effect Of P₂O₅ And MnO On Lime Dissolution Process In CaO-SiO₂-FeO_t Slag System

With the overcapacity of iron and steel production,domestic iron and steel enterprises in recent years began to adopt"double-slag+slag remaning"or duplex melting process for smelting.The point of"double-slag+slag remaning"or duplex melting process is to use low temperature to realize efficient dephosphorization,so the quick and full dissolution of lime at low temperature is the key of this process.At the same time,the insufficient dissolution of lime and the high content of free calcium oxide in the slag will also cause the difficulty in comprehensive utilization of steelmaking slag.How to realize the rapid and full dissolution of lime at low temperature is not only a concern of steelmaking workers at present,but also a key point to be solved in the future development of steel-making technology in China.In order to explore the dissolution mechanism of lime,promote the rapid and full dissolution of lime,and improve the comprehensive utilization of steel slag,In this paper,the mechanism of lime dissolution was explored by changing the contents of Fe O,P₂O₅ and Mn O in Ca O-Si O₂-Fe O-P₂O₅ and Ca O-Si O₂-Fe O-P₂O₅-Mn O slag,researching the influence of Fe O,P₂O₅and Mn O contents on the process of lime dissolution.The following conclusions are drawn:(1)Lime dissolution process is mainly a bidirectional diffusion between Ca O in solid lime and Si O₂,Fe O,P₂O₅ and Mn O in liquid slag.Fe O and Mn O with smaller radius and faster diffusion rate form Ca O-Fe O layer near the side of solid lime.Si O₂and P₂O₅ with larger radius and slower diffusion rate generate C₂S/C₂S-C₃P layer near the liquid slag.In the Ca O-Si O₂-Fe O slag,the Ca O-Fe O permeable layer is formed on the side near the solid lime,and the C₂S permeable layer is formed on the side near the slag.Ca O-Fe O permeable layer is also formed in the Ca O-Si O₂-Fe O-P₂O₅ slag near the solid lime side,but the C₂S-C₃P permeable layer with higher melting point is replaced the C₂S layer near the slag side in Ca O-Si O₂-Fe O-P₂O₅ slag.In the Ca O-Si O₂-Fe O-P₂O₅-Mn O slag,Ca O-Fe O permeable layer is formed near the side of solid lime,and this layer is enriched with Mn O component and generates low melting point Mn Fe₂O₄phase,while the side near the slag is still C₂S-C₃P permeable layer.(2)The total thickness of Ca O-Fe O layer and C₂S/C₂S-C₃P layer increases gradually with the prolonging of reaction time.The increase of Fe O and Mn O content will reduce the thickness of the permeable layer,while the increase of P₂O₅ content will increase the thickness of the permeable layer.The increase of Fe O content will accelerate the dissolution rate of lime,its effect is mainly to increase the activity of Fe O component in the slag,improve the penetration ability of the slag and generate Ca O-Fe O phase with low melting point.The increase of P₂O₅ content will slow down the lime dissolution rate,mainly because the formation of C₂S-C₃P dense phase with high melting point seriously hinders the material transfer in the lime dissolution process.The increase of Mn O content will accelerate the dissolution rate of lime,and its mechanism is similar to that of Fe O By reducing the viscosity of liquid slag,the penetration of molten slag is increased,and at the same time,low melting point solid phase Mn Fe₂O₄spinel is generated to reduce the formation of high melting point phase.(3)Under the experimental conditions,the lime dissolution is affected by Ca O diffusion into the slag.The dissolution of lime in slag is mainly affected by Ca O saturation concentration,mass transfer coefficient and slag viscosity.The increase of Fe O content in the slag will increase the driving force?(Ca O)of lime dissolution and decrease the slag viscosity.However,too high Fe O content will lead to the decrease of mass transfer coefficient,which is not conducive to the rapid dissolution of lime.The increase of P₂O₅ content in slag system will increase the viscosity and density of slag,affect the mass transfer in the melting process,and reduce the dissolution rate of lime.The increase of Mn O content in slag system will decrease the viscosity of slag and accelerate the dissolution rate of lime.