Recovery Of Alumina And Iron From High-Iron-Content Red Mud From Bayer Process

Red mud is the waste of the alumina production process,and over 60 million t red mud is discharged in 2006.It troubles the alumina industry that red mud causes alkalization of land and pollution of groundwater and the loss and waste of the available resources.The recovery of alumina and iron of high-iron-content red mud containing 32.52%(mass fractions) total Fe from Bayer process by sintering process is studied under different conditions(sintering temperature,sintering time,alkali ratio,etc.).The objective is to determine the suitable process condition and to get a higher recovery rate of aluminium.And then the residue is treated by magnetic separation after clinker is leached and the dependence of magnetic field intensity on the iron grade and recovery ratio of the magnetic concentrate is also studied. The results indicate that:1.The results of recovery of alumina of high-iron-content red mud from Bayer process show that:To incease the sintering temperature or to prolong the sintering time can promote the growth of alumina extraction rate of clinker sintered under 1050℃and for less than 90min;Expanding time to 120min,active carbon burns up,so a series of reactions occur between Fe₂O₃ and calcium silicate to generate CaO·SiO₂,and CaO·SiO₂ reacts with Na₂O·Al₂O₃ to generate the ternary phase insoluble compounds to reduce the alumina extraction rate;Active carbon burns up quickly from 1050℃to 1075℃,and a series of reactions occur between Fe₂O₃,CaO and Na₂O·Al₂O₃ to form massive Na₂O·Fe₂O₃,so liquid phase appears in clinker to cause the alumina extraction rate bringing down sharply.[C]/[S]enhances alumina extraction rate from 1.6 to 2.0,but degrades alumina extraction rate from 2.0 to 2.2.And alumina extraction rate increases with alkali ratio from 0.8 to 1.0 at 1050℃,but decreases with alkali ratio from 1.0 to 1.2 at 1050℃.Proportion of active carbon promotes the growth of alumina extraction rate.Suitable sintering conditions of the high-iron-content red mud from Bayer process are as follows:sintering temperature is 1050℃,sintering time is 90min,C/S is 2.0,N/A is 1.0,and the proportion of carbon added is 20%.Clinker prepared under those conditions is leached by the Na₂O_k 60g/L,α_k 1.6 sodium aluminate solution at 80℃for 20min,and the alumina extraction rate reaches 89.71%.2.The results of recovery of alumina of high-iron-content red mud from Bayer process show that:Grade of iron and recovery rate is improved with the proportion of active carbon increasing.The recovery rate increases with reinforcing of magnetic field intensity,but the iron grade of the magnetic concentrate decreases.The residue is treated by magnetic separation in 48 KA/m after recovery of alumina under suitable sintering process conditions.The iron grade of magnetic concentrate achieves 61.78%,and the iron recovery ratio is 60.67%.The composition of the magnetic concentrate mainly are Fe,Fe₃O₄,CaO·TiO₂ by XRD analysis.