Fundamental Research On Recovery Of Iron From Andradite-type Red Mud By Fluidized Pre-reduction And Smelting

Red mud is a kind of solid waste with complex components produced in alumina production by Bayer process.The alumina enterprises mainly adopt the way of dam construction for storage treatment.It not only occupies a large amount of land,but also causes environmental pollution.At the same time,the metal iron in red mud is not fully utilized,which causes great waste of resources.In this paper,the ’pre-reduction-melting separation iron extraction ’ technology is proposed to improve the recovery and utilization of iron in red mud.In this paper,calcium iron garnet type high iron red mud as the research object.By means of chemical analysis,XRD,SEM-EDS and BET pore structure,the changes of chemical composition,crystal structure,morphology,pore size and specific surface area of the products in different stages of pre-reduction melting process were studied.At the same time,combined with the thermodynamic calculation and analysis of the reaction characteristics of various minerals,the reaction characteristics of minerals in the pre-reduction melting process and the influence of reduction conditions on the reduction products were studied,and scientific results were obtained.Theoretical analysis of thermodynamics shows that when the temperature is lower than 570℃,the iron oxide is reduced in the order of Fe2O3→Fe3O4→Fe.When the temperature is higher than 570℃,the iron oxide is reduced in the order of Fe2O3→Fe3O4→FeO→Fe.When the temperature is higher than 690℃.It is reduced to metallic iron in the order of Ca3Fe2Si3O12→Fe3O4→FeO→Fe.The dynamic experiments show that,The kinetic mechanism function model of fluidized pre-reduction reaction of garnet red mud is A1/4 model of random nucleation and one-dimensional growth.The differential form is f(α)=1/4(1-α)[-ln(1-α)]-3 and the integral form is G(α)=[-ln(1-a)4],The apparent activation energy Ea=98.928kJ/mol,pre-exponential factor A=13214.8965s-1,It indicates that the random nucleation and growth of new-phase metallic iron is limiting link in the fluidized pre-reduction reaction process of garnet-type red mud.Experimental study on single factor condition optimization of fluidization prereduction shows that the optimum conditions of fluidized pre-reduction process are roasting temperature 800℃,roasting time 30min,total gas volume 800mL/min,CO concentration 85%.Under the optimum conditions,the TFe grade of the pre-reduction product was 44.21%,the metallization rate was 68.08%and the reduction degree was 78.72%.The experimental study on iron extraction by melting separation showed that the optimum conditions of melting separation process were reduction temperature of 1450℃,reduction time of 30min,coal blending amount of 15%,and binary alkalinity of 0.8.Under the optimal conditions,good indexes of iron phase with TFe grade of 90.37%,metallization rate of 98.56%and iron recovery rate above 99%can be obtained.The TFe grade in slag phase is generally lower than 1%,and the effect of slag iron separation is remarkable.The change rule of pore structure in the pre-reduction melting process shows that the specific surface area of pre-reduction products is significantly increased compared with that of raw ore.With the increase of temperature,the average pore diameter increases,and the specific surface area and total pore volume decrease.With the extension of time,the specific surface area,total pore volume and average pore diameter can be increased.The analysis of phase transformation and microscopic morphology changes showed that:in the fluidized pre-reduction process,XRD phase analysis showed that:increasing the reduction temperature,reducing agent CO concentration or prolonging the roasting time will help to convert hematite and perovskite into magnetite,ferrous oxide and metallic iron step by step.In the process of smelting separation,the recovery of iron in the slag and the aggregation and growth of iron particles are promoted by adjusting the binary alkalinity,coal blending amount,reduction temperature and time.Cracks will appear in the sample during pre-reduction.The change rule of the pore structure during the pre-reduction process shows that the specific surface area of the pre-reduction product is significantly increased compared with the original ore.As the temperature increases,the average pore diameter increases,and the specific surface area and total pore volume decrease;as time goes by,the specific surface area,total pore volume,and average pore volume gradually increase.