The Dissolution Process And Kinetics Of High Iron Gibbsitic Bauxite Under Atmospheric Pressure

High iron gibbsitic bauxite(HIGB)is a special kind of import bauxite resource,which contains more than 30 wt%iron oxide and is valuable for comprehensive recovery and utilization.This kind of bauxite is processed by Bayer process at present.But the red-mud contains higher Na2O in the traditional Bayer process and is hard to be utilized.The atmospheric pressure dissolution process of HIGB is systematic studied in this paper including mineral structure,dissolution property,kinetics,property of sodium aluminate solution,the property and utilization of the solid residue.The research results would provide theoretical guidance for the industrial application of HIGB.The modern testing methods such as XRD,SEM,EDS,TEM,BET,IR,TG-DSC were used to study the mineral species,contents,crystal structures,and relationships between minerals.Gibbsite crystal shapes is found to be flake,layer and multilayer.Goethite and hematite crystal shapes are scattered granulate,needle-like and clavate.Gibbsite crystals are covered by the aggregate goethite and hematite.TEM images show that gibbsite crystals are polycrystalline.The BET,pore volume and pore diameter of the HIGB are 9.26 cm2/g,0.03 cm3/g and 12.57 nm,respectively.The atmospheric pressure dissolution property of the HIGB is studied.Gibbsite dissolution rate is inversely proportional to the mineral granularity and direct proportion to stirring speed,liquid-solid ratio,NaOH concentration,and temperature.The dissolution temperature and NaOH concentration have a greater influence on the dissolution rate.The dissolution property of HIGB decreased with the increasing goethite and hematite content.The dissolution speed of synthetic gibbsite is lower than that of HIGB for the differences of crystal diameter,crystalline and interplanar spacing.Unreacted shrinking core model was selected to study the dissolution kinetics of HIGB and synthetic gibbsite.The results show that the rate-controlling step of HIGB is diffusion and that of synthetic gibbsite is dissolution chemical reaction.The pre-exponential factor A and the activation energy E of HIGB decreases with the reducing content of iron oxide.The dissolution kinetic equation of HIGB is calculated to be:1-2?/3-(1-?)2/3=1.32×1015×(cNaOH)1.70×(d)-0.36×(r)0.74×exp[-117485/(RT)]×t.The dissolution ratio equation of middle iron content HIGB and low iron content HIGB to be:1-2?/3-(1-?)2/3=2.42×1012×exp[-99144/(RT)]×t and 1-2?/3-(1-?)2/3=1.75×1012×exp[-98928/(RT)]xt,respectively.The dissolution ratio equation of synthetic gibbsite to be:1-(1-?)1/3=3.85×1014×exp[-115149/(RT)]× t.The sodium aluminate solution property of atmospheric pressure dissolution is studied.When ?k of the solution are 1.50 and 3.00,the relation between boiling point(y)and sodium oxide concentration(x)are calculated to be:y2=101.94+0.016x2+8.77×10-5x22 and y3=104.16+4.50×10-4x3+1.38×10-4x32,respectively.The dynamic viscosity and kinematic viscosity of the sodium aluminate solution decrease faster in low temperature area(20?50 ?)and the decreasing rates of them decrease slowly with the increasing temperature.When the ak are 1.60 and 2.00,the relation between the highest metastable equilibrium concentration of SiO2(y)and Al2O3 concentration(x)are calculated to be:ys1=-3.59+0.101xA1,yS2=-1.91+0.088xA2.The main chemcical compositions and mineral constitutions of high iron content red-mud are goethite and hydrous hematite.The sodium oxide content in red mud of atmospheric pressure dissolution is about 1.25%,which is only one third of the content in high pressure dissolution red mud.The hydrous hematite is produced by the dissolution process of hematite in raw bauxite.High iron content red-mud has the better magnetic separation effect when the magnetic field intensity is 6000 GS,the output ratio of concentrate is 46.42%and the iron(elemental)content of concentrate is 52.84%,which can be used for raw material of iron.The SEM and BET analysis show that the magnetic separation particles are larger and have denser structures;the tailing particles are smaller and have relatively loose structures.The properties and applications of the calcification and sodium roasting of desilication product(DSP)are studied.DSP crystals are dense cored aggregate particles;the width of strips on the particle surface is about 180 nm.The IR characteristic absorption peaks of DSP are 711 cm-1,968 cm-1 and 1136 cm-1.High calcium ratio is suitable for DSP sintered clinkers and the best calcium ratio is 2.10?2.20.The standard dissolution ratios of Al2O3 and Na2O are both above 93%with the best sintering conditions.DSP can be used to produce 4A zeolite through sodium roasting and hydrothermal conversion technology and the 4A zeolite has better crystal and the volume of calcium exchange is 300 mg/g,median size is 2.24 ?m.In this paper,the research results indicate that the dissolution ratio of Al2O3 can be ensured by suitable dissolution temperature and NaOH concentration.The desilication reaction can also be restricted in the atmospheric pressure dissolution process of HIGB.The iron oxide can be utilized because of the low sodium content in the red-mud.DSP no longer needs to be mixed with the red-mud and can be recycling easily.The atmospheric pressure dissolution is an excellent alumina extracting technique for the HIGB with low energy consumption,high efficiency,low cost and less residue.