Study On De-alkaliization Of Red Mud Ferric Sulfate With Bayer Process

Red mud is a large amount of solid waste generated in the alumina process.Because red mud has strong alkalinity,it will pollute groundwater and surrounding soil during storage.Red mud desalting is a key pretreatment process for resourceization and soilization.The water consumption of water-eluted alkali is large,and the combined alkali in red mud cannot be removed,and the cost of pickling is high.However,when using salts to dealkalize red mud,the red mud can be modified according to the characteristics of different salts to promote the subsequent reuse of red mud.As a wide range of iron-based coagulants,iron sulfate has the characteristics of low price.In this study,the red mud was dealkalized by the acid hydrolysis of ferric sulfate.In the dealkalization process,Fe was enriched into the red mud,the iron grade of the red mud was improved,the agglomeration of the red mud was increased,and it was convenient for the subsequent resource and soil utilization.By examining the optimized conditions for red mud dealkalization,combined with XRD,SEM and other characterizations,the form of Fe transfer to red mud and its effect on red mud morphology changes were clarified,and the mechanism and kinetics of red mud Dealkalization were studied.The conclusion is as follows;(1)Among iron-based sulfates,because the hydrolysis effect of Fe³⁺is better than Fe²⁺,the debasing effect of iron sulfate is significantly higher than that of ferrous sulfate.Temperature has little effect on the dealkalization rate of red mud.The mass ratio of red mud ferric sulfate is 1:1,After dealkalization at room temperature for 1h,the dealkalization rate is 70%,When the ratio of Na/Fe is more than 1:1,the dealkalization rate hardly changes.After the red mud is roasted,the effect of water elution can be improved.When iron sulfate and red mud are mixed and roasted,the effect of alkali removal decreases with the increase of roasting temperature,because the component of alkali removal content decreases with the thermal decomposition of iron sulfate.The reuse of supernatant and alkali residue has a low effect on the alkali removal rate and Fe enrichment rate,and the expected alkali removal effect and iron enrichment rate can be achieved after the first alkali removal.SO₄^2-,Fe in the supernatant were almost consumed up 30 min before desalination,and the Fe concentration in the supernatant was significantly correlated with p H R²=0.998.The Fe enrichment rate could be used to evaluate the alkali dissolution effect of red mud.(2)Based on the results of the above study,the characterization analysis before and after the dealkalized red mud.In the process of red mud alkalinization by ferric sulfate,Fe³⁺is hydrolyzed to form complexes such as Fe(OH)₃,which can promote the agglomeration and sedimentation of red mud particles.Fe₂O₃ formed after alkali residue dehydration has certain water stability,which strengthens the structural strength of aggregates,and the size of red mud can be concentrated in the range of 5.02um.SO₄^2-mainly reacts with Ca CO₃ in red mud to form Ca SO₄ and enters red mud;Iron grade of red mud increased from 8%to 18%.The bound Na in red mud is mainly fixed in the three-dimensional framework of Al-O-Si bonds of silicates such as Na₆(Al Si O₄)₆,so it is difficult to remove such bound alkali by washing;The hydrolysis process of ferric sulfate produces H and SO₄^2-,H weakens the Al-O-Si bond by adhering to the arc electron pair of oxygen,and SO₄^2-then reacts with Al-containing groups,thus destroying the crystal structure of Na₆(Al Si O₄)₆,and achieving the effect of binding alkali release in red mud.The alkali removal from red mud by ferric sulfate conforms to the kinetics characteristics of multiphase liquid-solid region reaction.The dissolution kinetics of Na from red mud by ferric sulfate was analyzed using Avrami equation.The activation energy Ea=9.94 k J/mol was obtained by fitting.In the leaching process of different red mud ferric sulfate mass ratio,the characteristic parameter n=0.151,the reaction series N=0.7207,and the pre-index factor k₀=536.2 were obtained.The leaching process was controlled by diffusion.