Research On Bayer Process Red Mud Dealkalization And Iron Recovery

Bayer red mud is a kind of alkaline solid waste product generated in the production of alumina by the Bayer process.The research on the comprehensive utilization of Bayer red mud has always been the focus of many researchers.If the problem of high alkali content of red mud can be effectively solved and valuable metals such as iron and aluminum can be recovered,it will be of great practical significance for the resource utilization of large amounts of red mud stockpiled in China.In this paper,the mechanism of adding calcium oxide to Bayer red mud to remove alkali and reducing roasting to recover iron by magnetic separation is analyzed.The optimum conditions were determined by studying the effect of adding calcium oxide to Bayer red mud under different experimental conditions.The optimum conditions were determined through the experimental study on the effects of reduction roasting process and magnetic separation process on iron recovery.The main results are as follows:1)The dealkalization process on adding CaO to red mud is to change the sodium silicon slag in red mud into calcium silicon slag?3CaO·Al ₂O₃·nSiO₂·?6-2n?H₂O?under hydrothermal condition.The Na₂O in sodium silicon slag was enter the solution to achieve the goal of dealkalization.Except for the main reaction,the other alkali components in red mud,such as Na₂CO₃,Na₂SiO₃ and so on,can also react with Ca?OH?₂ to form insoluble substances and enter red mud.2)The lattice alkali and alkali between the crystals are exposed to the surface of the red mud particles by mechanical activation,the sodium is more distributed in particle size below 48 microns.We find the iron phase is mainly distributed in red mud below 75 microns by the results of XRD and SEM-EDS.In addition,the sample of red mud with particle sizes less than 75 microns have distinctly irregular cylinders and spicules.3)The kinetic analysis shows that the kinetic equation of the dealkalization process can be described by k_ct=1-2?/3-?1-??^2?3.The apparent activation energy of the reaction is 23.55 kJ/mol.The reaction kinetics model of bayer process belongs to the contraction unreacted nuclear membrane type controlled by internal diffusion.The leaching process was controlled by internal diffusion.4)The results showed that the increase of leaching temperature,reaction time and CaO content was beneficial to dealkalization.The dealkalization rate of red mud increased to a certain extent and then decreased with the increase of liquid-solid ratio.The dealkalization rate of red mud could reach 92.44%and the content of Na₂O could reach 0.61%under the condition of reaction time of 5h,CaO/Na₂O=6.5,leaching temperature 95?.In addition,the dealkalization rate can reach about 97%,the content of Na₂O after alkali removal is about 0.30%under the condition of high temperature and high pressure.Roasting treatment could not improve the dealkalization rate of adding calcium oxide to remove alkali.5)The best tablet pressing conditions determined by tablet pressing experiment were 7g red mud and 2ml adhesive?PVP ethanol?.6)The optimization conditions for magnetic separation recycling of reduction roasting is:the calcination temperature 1450?,the roasting time 60 min,charcoal powder adding quantity 1%,roasting mineral grinding after 70 s,magnetic field intensity is 0.19 T,pulp density,50 ml/g by studying mineral particle size,magnetic field intensity,pulp density,roasting temperature and roasting time,adding amount of active carbon,CaO adding amount on the influence of reduction roasting magnetic separation process.The iron recovery rate is about 78%,and the iron concentrate grade is about 75%under these conditions.