Research On Calcification-Carbonation Process And Kinetics Of Red Mud In Bayer Process

In 2015 alumina production of China reached 60 Mt,the bauxite resources have been on the verge of exhaustion.At this stage,China's bauxite resources have a high,the degree of external dependence has increased year by year,which has been more than 50%,China's alumina industry is facing severe shortage of resources.Bayer alumina production is merely suitable for high-grade bauxite,and red mud has the problem of high alumina and sodium oxide.To solve the problems above,our team put forward a new process named"calcification-carbonation process" which can be used to utilize low-grade bauxite and red mud.In this paper,the thermodynamics,process conditions and kinetics of the calcification-carbonization process were studied,and the specific contents and results are as follows:(1)Thermodynamic study on the reaction between TCA and sodium silicate showed that when the temperature was between 50 ? and 300 ?,hydrogarnet with higher silicon saturation coefficient tend to react first.With the increase of temperature,the formation of hydroganet was easier.Thermodynamic study on carbonation decomposition process showed that Al2O3·SiO2 could be formed probably and the lower temperature was,the easier Al2O3·SiO2 could be formed.Another product of carbonation decomposition process was Al2O3·2SiO2,which would not be formed if the temperature was higher than 300? or the silicon saturation coefficient of hydroganet was more than 1.2.(2)The single factor experiments on calcification of red mud showed that if the red mud was treated at following conditions:calcifying temperature was 120?,calcium-silicate ratio was 2.5:1,liquid-solid ratio was 4:1.holding time was 2 h,Na2O content can be reduced to 1.26 wt.%.The single factor experiments on carbonation of red mud showed that if the red mud was treated at following conditions:carbonizing temperature was 120?,CO;pressure was 1.2 MPa,liquid-solid ratio was 8:1,holding time was 90 min,NaOH free;leaching temperature was 60?.NaOH concentration was 100 g L-liquid-solid ratio was 10:1,holding time was 60 min,Na2O content can be reduced to 1.16 wt.%and alumina-silicon ratio can drop to 0.635.(3)Experiments on kinetics of reaction between TCA and sodium silicate showed that with the increase of temperature,both of the diffusion resistances in boundary layer and in product boundary decreased gradually.The chemical reaction resistance also decreased with temperature,but chemical reaction resistance was much more higher than the other two resistances,so the whole process was controlled by chemical reaction.The relationship between k,and T was established through function fitting.(4)The main factor that affected the carbonization process of the pure hydrogarmet was the mass transfer rate from the liquid phase to the surface of the particles.On the premise of constant pressure,the increase of temperature led to the concentration of carbon dioxide dissolved in the liquid phase decreased and the mass transfer rate also had a sharp decline,therefore the higher the carbonation temperature was,the lower the apparent reaction rate was.(5)The main factors that affected the carbonization process of red mud were the mass transfer rate from the liquid phase to the surface of the particles and the surface chemical reaction rate.At the low temperature stage(60?100?),the rate of the whole carbonization process was controlled by the surface chemical reaction process.When the temperature was about 100?,the whole carbonization process was hybrid controlled.At the high temperature stage(100?160?),the rate of the whole carbonization process was controlled by the mass transfer rate from the liquid phase to the surface of the particles.