Fundamental Study On New Process Of Effective Separation Iron And Alumina And Comprehensive Utilization Of High Iron Gibbsite Ore

The high iron gibbsite ore in Guangxi region is the largest gibbsite bauxite resource of China,which features high iron content,high silica content,low alumina content and low A/S.The content of iron and alumina fail to meet each industrial grade requirement.Meanwhile,the composition and microstructure of the ore are very complicated,making one of the most refractory ore resources.In order to reach the comprehensive utilization of high iron gibbsite ore,many researches have been carried out home and aboard.And several treatments have been presented successively,including physical separating iron and alumina,first leaching alumina and then smelting iron,first smelting iron and then leaching alumina,and reduction roasting method.Owing to the disseminated agglutination and paragenesis of iron,alumina and silica in high iron gibbsite ore,separating iron and alumina from high iron gibbsite ore is extreme difficulty.Up to now,high iron gibbsite ore still do not get the industrial scale development and utilization.It is of important strategic significance to research the comprehensive utilization of high iron gibbsite ore since it is an important iron and alumina resource.Based on the summary of published work,a new process of metallized reduction-magnetic separation iron from high iron gibbsite ore-applying magnetic product to steelmaking-using non-magnetic product prepare primary Al-Si alloy was put forward.For the key steps of new process,the high iron gibbsite ore got from Guigang City,Guangxi region was taken as the research object.These processes,such as metallized reduction-magnetic separation iron from fine particles of high iron gibbsite ore,metallized reduction-magnetic separation iron from high iron gibbsite ore-coal hot briquette,were mainly researched.Also,the process of preparing primary Al-Si alloy from non-magnetic product was explored.Meanwhile,the carbothermic reduction thermodynamics,non-thermal decomposition kinetics of high iron gibbsite ore,valuable element migration patterns of new process were studied.The results of metallized reduction-magnetic separation iron from fine particles of high iron gibbsite ore show that,the process could separate iron and alumina from high iron gibbsite ore effectively.At the conditions of carbon ratio 2.00,reduction temperature 1400℃,reduction time 180 min,ore particle size less than 2.00 mm,magnetic field intensity 40 kA/m,the recovery ratio of iron and alumina are 89.24%and 86.09%,respectively.The Fe content and metallization ratio in metallic iron are 78.23%and 97.56%,respectively.While the Al₂O₃ content in non-magnetic product is 53.32%.In the reduction process,the phase transition of iron-bearing minerals are obtained as follows:FeOOH → Fe₂O ₃→FeO·AlO₃ → Fe,and also that of aluminum minerals are as follows:Al（OH）3/AlOOH/n（Al₂O₃）·SiO₂·nH₂O → Al₂O₃ → FeAl₂O₄-Al₂O₃/Al₆Si₂O₁₃.The reduction stage takes over most of the time of metallic iron particles forming process.The reaction limiting the reduction rate of iron oxide minerals to metallic iron is as follow,FeAl₂O₄ + CO = Fe + Al₂O₃ + CO₂.The lower reduction conditions and higher iron removal could be achieved with adopting ore-coal composite agglomerates and adding catalyst.The results obtained from the research on preparation and optimization of high iron gibbsite ore-coal hot briquette（indexed as Al-CCB）show that,increasing coal ratio,diminishing ore particle size and coal particle size in a certain range could improve the crushing strength of Al-CCB.The effect of process parameters on the crushing strength of Al-CCB from big to small is coal addition ratio,ore particle size and coal particle size.A quadratic polynomial model is built to predict the crushing strength of Al-CCB by using response surface methodology.Y=-2094.611 + 254.562 x1 + 0.522 x2 + 6.316 x3-0.612 x1 x2-0.150 x1 x3-0.007 x2 x3-2.930 x12 + 0.029 x2 2-0.018 x32.The correlation coefficient of mathematical model established was 0.9589,and the model could optimize the preparation process parameters of Al-CCB.The results of metallized reduction-magnetic separation iron based on Al-CCB show that,the process could separate iron and alumina from high iron gibbsite ore effectively.Compared to the process of metallized reduction-magnetic separation iron from fine particles of high iron gibbsite ore,the reduction temperature and reduction time are decreased obviously,when the recovery ratio of iron and alumina between two processes are almost the same.At the conditions of Al-CCB carbon ratio 1.00,reduction temperature 1350 ℃,reduction time 70 min,the recovery ratio of iron and alumina are 87.01%and 86.21%,respectively.The Fe content and metallization ratio in metallic iron are 78.46%and 91.29%,respectively.While the Al₂O₃ content in non-magnetic product is 55.03%.The optimization researches on catalytic reduction-local nucleation substituted show that,combining catalytic reduction by Li₂CO₃ with local nucleation alternative by metallic iron could promote the reduction,nucleation,aggregation and growth of iron particles,thereby improve the recovery ratio of iron and alumina.At the conditions of adding 2.00%Li₂CO₃,4.00%metallic iron powder,carbon ratio 1.0,reduction temperature 1350 ℃,reduction time 70 min,the recovery ratio of iron and alumina are 94.21%and 90.16%,respectively.The Fe content and metallization ratio in metallic iron are 90.37%and 94.38%,respectively.While the Al₂O₃ content in non-magnetic product is 55.03%.The metallic iron could apply to steelmaking,while the non-magnetic product enrich in alumina and silica could be used as the high quality materials of the aluminum industry.The research results got from carbothermic reduction thermodynamics of FexOy-Al₂O₃-SiO₂ system indicate that,the reducibility from high to low of the iron-bearing species generated in the carbothermic reduction process of high iron gibbsite ore at the temperature 300.0～1800.0 K are Al₂Fe₂O₆,FeSiO₃（ferrosilite）,Fe₂SiO₄（fayalite）,Fe₃Al₂Si₃O₁₂,FeAl₂O₄ and Fe₂AlaSi₅O₁₈.Controlling the reaction temperature could generate solid-phase raection product owing good reducibility.Meanwhile,increasing the CO partial pressure could enhance the reduction thermodynamic potential of iron-bearing species,which could separate iron from Al₂O₃ and SiO₂ as much as possible.The critical conditions for carbothermic reduction of high iron gibbsite ore are reduction temperature 1501.2 K and CO partial pressure 92.1%,respectively.The reaction limiting the reduction rate of iron oxide minerals to metallic iron is as follow,FeAl₂O₄ + CO = Fe +Al₂O₃ + CO₂.The research on non-isothermal thermal decomposition kinetics show that,the most probable mechanism function is the there-dimensional diffusion model of Jander equation.The integral form and differential form are G（α）=[1-（1-α）1/3]₂ and f（a）=（3/2）（1-α）_2/3[1-（1-α）1/3]-1,respectively.And the mechanism code is D3.The activation energy E and pre-exponential factor A for thermal decomposition of high iron gibbsite ore calculated by the KAS method,FWO method and Popescu method are 59.46～75.36 kJ mol-1 and 1.51×105 s-1,respectively.The results of thermodynamic analysis on preparing primary Al-Si alloy from non-magnetic product show that,the carbothermic reduction of Al₂O₃ and SiO₂ together for preparing primary Al-Si alloy should carry out at higher temperature.The proper conditions are reaction temperature 2100～2200℃ and carbon ratio 1.00.The reaction mechanisms of preparing primary Al-Si alloy from non-magnetic product are as follows:SiO₂ + 3 C = SiC + 2 CO,2 Al₂O₃ + 9C=Al₄C₃ + 6CO,3SiO₂ + 2 Al4C3 = 8A1 + 3 Si + 6 CO,3 SiC + Al₂O₃ = 2A1 + 3 Si +3 CO.The primary Al-Si alloy prepared in exploring experiments is consisted of Al-Si-Fe,SiC,and a small amount of oxide phase.The new process put forward in the paper could enrich the comprehensive utilization technology and theory of high iron gibbsite ore.Meanwhile,it could provide important theoretical basis for the design and exploitation of comprehensive utilization process of high iron gibbsite ore,and also for its industrialization applications.Thereby it could drive the development of comprehensive utilization technologies of high iron gibbsite ore.