Kinetics Of Desulfurization And CaO Thermodynamic Properties Of CaO-Al₂O₃-SiO₂-MgO-TiO₂-Na₂O Slags

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.Through the COREX smelting reduction the iron-making process handling Pingguo red mud.By reducing smelting recovery of iron;wet milling elution recovery of aluminum,sodium from the calcium aluminum slag which is obtained through reduction;rare metals were enriched in the leach residue for further recycling.Therefore three metallurgical process?reduction,leaching and extraction?can be linked up by COREX process,providing technical and economic support for comprehensive use of red mud.Among these three metallurgical process,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.The research on the viscosity and desulfurization performance of high-alkalinity slag system of CaO-Al₂O₃-SiO₂-MgO-TiO₂-Na₂O had done.The results indicated that the viscosity of the slag fully meet the requirements of actual industrial operation and the slag has stronger desulfurization ability,the small increase of Na₂O content can improve the desulfurization ability of the slags.It is well known that Na₂O would escape from the slag at high temperature.The physicochemical properties and desulfurization ability would be changed due to the sodium oxide volatilization.Hence,the systematic studies have been carried out to study the evaporation kinetics of Na₂O oxides in the molten slag;A mathematical model has been developed which enables the effect of decrease in Na₂O content over time due to evaporation to be taken into consideration.The calculated results of the rate desulfurization of molten iron using this model are in reasonable accord with the experimental data;Due to the activity of CaO in the slag has direct influence on the desulfurization reaction at the high temperature,the chemical equilibrium method of the Slag-Sn-CO have been used in this paper,the influence of slag components on the CaO activity also carried out in this study.The results indicated that:1)The evaporation ratio increased with increasing the temperature.Higher basicity,larger amount of Na₂O,Al₂O₃ concentrations were also found to increase theevaporation ratio of Na₂O.While MgO addition only slightly enhances the evaporation ratio.With TiO₂ content increasing,the evaporation ratio first increased and then decreased.The evaporation rate of Na₂O appears to be controlled by chemical reaction at the slag/gas interface in the beginning,followed by a mixed reaction-mass transfer regime,and finally a liquid-phase mass transport step.2)The rate of desulfurization increases by increasing the Na₂O,MgO content and basicity in slag,decreasing Al₂O₃ and TiO₂ content,and increasing the temperature.A mathematical model has been developed which enables the effect of decrease in Na₂O content over time due to evaporation to be taken into consideration.The calculated results of the rate desulfurization of molten iron using this model are in reasonable accord with the experimental data.The activation energy of the apparent rate coefficient was found to be 172.58 kJmol-1,the mass transfer coefficient of the slag phase hardly changes with temperature.It was concluded that the desulfurization of molten iron using the present slag system is controlled by the slag phase mass transfer.3)The activity of CaO increases by increasing the MgO content and basicity,decreasing Al₂O₃ and TiO₂ content in slag.Various factors on the influence law of the activity of CaO agreed with the model calculation value and the law of the predecessors researching.It indicated that the activity of CaO of high basicity slag in this experiment is reasonable and credible,it also provided a reliable theory basis for the smelting reduction process of red mud.