Study On Desulfurization Performance Of High Alkalinity CaO-Al 2 O 3 -SiO 2 -MgO-TiO 2 -Na 2 O Six-component Slag System

The red mud by Bayer process of Pingguo Guangxi Aluminum Plant has its own feature for containing Fe、Si、Al、Ca and valuable Ti、V、Sc、Ta as well as rare earth elements.As a type of precious and abundant secondary resource,it has extremely high comprehensive application value.Comprehensive use of the red mud of Pingguo Guangxi Aluminum Plant can be realized through three links.Firstly,by employing COREX smelting reduction ironmaking process to deal with ferric red mud,Fe,V and Ta in red mud can be reduced to obtain pig iron,while Al and Sc enter reducing slag;secondly,the reducing slag is dissolved out by wet grinding to recycle Al₂O₃ with sodium carbonate solution;in the end,precious metal Sc gathers in leaching residues and it can be recycled through extraction method..Among these three metallurgical process（reduction,leaching and extraction）,smelting reduction process is the chief link.The metallurgical properties of reducing slag is of great importance to smelting and the desulfurization performance has direct influence on the quality of reduced iron.Hence,this paper intends to conduct integrated research on the desulfurization performance of high-alkalinity and high aluminum slag system of CaO-Al₂O₃-SiO₂-MgO-TiO₂-Na₂ O.The research results would provide theoretical foundation for the utilization for red mud and other similar metallurgical resources.Firstly,this paper conducts single factor desulfurization experiments and studies the influence of each constituent component on the desulfurization performance of this slag system;the thermodynamic model were established based on molecular ion coexistence theory and sulfur capacity separately.Also we inspect the application of theoretical thermodynamic model on this slag system.In the end,we build mathematical regression model between slag constituent component and distribution ratio of sulfur by uniform design experiments.The results are listed below:1)By conducting single factor desulfurization experiments on high-alkalinity and high aluminum slag system of CaO-Al₂O₃-Si O₂-MgO-TiO₂-Na₂ O,we find that distribution ratio of sulfur between slag and iron increases with the basicity of slag within experimental limits.When basicity of slag is above 2.9,the distribution ratio of sulfur between slag and iron are all over 140,indicating that this slag system processes rather good desulfurization performance.When the basicity is set at a fixed value,MgO has little influence on distribution ratio of sulfur,while both TiO₂ and Al₂O₃ lower the distribution ratio of sulfur,among which Al₂O₃ has rather obvious effect.The distribution ratio of sulfur increases with the amount of Na₂ O and a spot of Na₂ O cansignificantly improve the desulfurization ability of slag.2)This paper builds mass concentration equation of structural unit or ion pairs of CaO-Al₂O₃-SiO₂-MgO-TiO₂-Na₂ O slag system and thermodynamic models of distribution ratio of sulfur between CaO-Al₂O₃-SiO₂-MgO-TiO₂-Na₂ O slag system and carbon saturated smelted iron based on molecular-ion coexistence theory.By comparing the calculated value with measured value,the calculated influence laws of the the influence of separate factors on sulfur distribution ratio resembles experimental ones with certain discrepancy between them,for thermodynamic equilibrium of theoretical models are not reached in experiments.Hence the molecular-ion coexistence theory can not satisfy the demand of forecasting practical sulfur distribution ratio.3)This paper builds thermodynamic model of distribution ratio of sulfur between slag and carbon saturated smelt iron based on theoretical model of Young sulfur capacity.By comparing the calculated distribution ratio value of sulfur of thermodynamic model with experimental value,we find that that calculated value is much higher than that of measured.We can get the conclusion that this thermodynamic model can not satisfy the demand of forecasting practical sulfur distribution ratio either.4)This paper firstly builds mathematical regression model between slag constituent component and distribution ratio of sulfur by conducting uniform design experiments with partial least square.By comparison calculated value with measured value,we find that the mathematical regression model can predict the influence rule of components on distribution ratio of sulfur for CaO-Al₂O₃-SiO₂-MgO-TiO₂-Na₂ O slag system.It lays reliable theoretical foundation for smelting reduction process of red mud.