Study On Extraction Of Iron And Aluminum From High-iron Bauxite

With sustained and rapid development of metallurgical industry in China,supply of iron ore and bauxite resources are increasingly tense,so comprehensive utilization of complex mineral resources is getting more and more attention.High iron bauxite ore is a kind of refractory ores,neral separation process cannot obtain qualified iron concentrate and aluminum concentrate,unable to realize efficient use of aluminum and iron.Therefore,the study on extraction of valuable elements from high iron bauxite is of great significance.This thesis aims at extracting iron powder and aluminum from high-iron bauxite.Hydrogen and carbon powder were used as reducing agent to reduce iron oxide into iron metal in heating condition.After reduction,reduced samples were crushed in order to take magnetic separation.Iron metal was enriched into magnetic material and aluminum was enriched into nonmagnetic material which was called aluminum-rich slag.Then aluminum was extracted from aluminum-rich slag by ammonium sulfate roasting.After leaching,Al2O3 was obtained,which can be used for preparation of alumina.On this basis,with thermal analysis techniques,mechanism functions that iron oxide in high-iron bauxite was reduced by hydrogen were determined.The apparent activation energy E,pre-exponential factor A and the kinetic equation in reaction were obtained by calculating.In the experiment of hydrogen reducing,the effects of reducing temperature,reducing time,granularity were investigated.Optimum reductive conditions are found as reducing temperature:800℃;reducing time:120min;granularity:55-74μm.Approximately 99%of iron oxide is effectively reduced.After magnetic separation,iron exists as form of metal iron in magnetic material,aluminum and silicon are enriched into nonmagnetic material.In the experiment of carbon powder reducing,the effects of reducing temperature,reducing time,reducing agent ratio,additive ratio were investigated.Optimum reductive conditions are found as reducing temperature:1200℃;reducing time:150min;reducing agent ratio:9.19%;additive ratio:17.86%.After magnetic separation,approximately 87.63%of iron is obtained,composition of aluminum in nonmagnetic material is 40.57%.With low reducing temperature（1000℃）,2CaO·Al2O3·SiO₂ is compounded by CaO-Al2O3-SiO₂ system.When reducing temperature comes to 1250℃,2CaO·Al2O3·SiO₂ completely transforms into CaO·Al2O3·2SiO₂.FeO·Al2O3 tends to be compounded by iron and aluminum,and enriched into nonmagnetic material,resulting in decrease of iron recovery rate.In the experiment of ammonium sulfate roasting,roasting temperature,roasting time,ammonium sulfate/aluminum-rich slag ratio were investigated.Optimum roasting conditions are found as roasting temperature:400℃;roasting temperature time:120min;ammonium sulfate/aluminum-rich slag ratio:2.Approximately 98%of aluminum is effectively extracted.Main composition of roasting sample are Al2SO4,SiO₂,CaSO4,and a little of Fe3O4.There is only Al2SO4 can be dissolved in water,hence aluminum can be separated from others.The reaction order with ammonium sulfate is:FeO·Al2O3>CaO·Al2O3·2SiO₂>Al2O3.With Coats-Redfern method and experimental data,reaction mechanism functions of Hydrogen reductive reaction on iron oxide were determined.When reducing temperature is between 35-100℃,reaction mechanism function is g（α）=[-ln（1-α）]3/2,and the apparent activation energy E=73.344kJ·mol-1,the pre-exponential factor A= 2.15x109,the kinetic equation is dα/dT=2.15×109exp（-73344/RT）×2/3（1-α）[-ln（1-α）]-1/2.When reducing temperature is between 570-670℃,reaction mechanism function is g（α）=[-ln（1-α）]3/4,the apparent activation energy E=357.758kJ·mol-1,the pre-exponential factor A= 6.28×1018,the kinetic equation is dα/dT=6.28×1018exp（-357758/RT）×3/4（1-α）[-ln（1-α）]1/4.