Fundamental Research On The New Process Of Comprehensive Utilization Of High Iron Gibbsite-Type Bauxite Ores

With the rapid development of metallurgical industry in China, the consumption of the ore resources raises greatly. While the shortage of domestic bauxite and iron ores is becoming more and more severe, the amount of imported bauxite ores is increasing year by year; therefore, it is of a great significance to utilize domestic high iron bauxite ores. High iron gibbsite-type bauxite is a kind of refractory ores, and it has a large reserve in China and the rest of Southeast Asia countries. In this thesis, a basic research of a new process for the comprehensive utilization of iron, aluminum, silicon, vanadium, gallium etc. was carried out by using Guangxi high-iron gibbsite bauxite as raw materials.Measurement methods, including optical microscope, X-ray diffraction (XRD), Scanning electronic microscope (SEM) and electronic probe, etc. were used to study process mineralogy of the ore. Results obtained show that, iron element mainly occurs in goethide, and aluminum element mainly occurs in gibbsite, goethite contains aluminium and silicon elements, the content of A12O3within the goethide varies from17%to39%; and gibbsite also contains iron and silicon elements, the contents of Fe2O3within the gibbsite varies from15%to25%; the crystalline size of the aluminiferrouse minerals embedded in goethide and the ferrouse minerals embedded in gibbsite are less than5μm.Therefore, it is difficult to separate Fe, Al, Si from the ore by physical methods.The thermodynamics of CaO-Fe2O3-Al2O3-SiO2system indicates that it is impossible to separate aluminum, iron, silicon ingredients in oxidizing atmosphere. Reduction thermodynamics studies show that the sodium salts are capable of reacting with Al2O3and SiO2and forming sodium aluminosilicate, sodium silicate, sodium aluminate in turn; Na2SO4is easily reduced to Na2SO3, while unstable Na2SO3is easy to decompose into Na2S; the reaction of Na2SO3has the same regulation as Na2CO3and Na2SO4when reacting with Al2O3and SiO2; Na2S does not react directly with A12O3and SiO2, but it is capable of reacting with them in the presence of FeO. Based on the fundamental investigations, the new process of reduction roasting-magnetic separation-acid leaching for comprehensive utilization of high iron gibbsite-type bauxite ores was proposed and studied. The effect of the process parameters on the separation of iron, aluminum and silica was studied by reduction roasting and magnetic separation, the results show that aluminum and iron is capable of be separated under the condition of15%mass ratio Na2SO4,2%mass ratio borax,25%mass ratio Na2CO3, reduction roasting temperature of1050℃, reduction roasting time of60min, grinding pulp concentrate of50%, particle size of-0.074mm varies form95.5～96.0%and magnetic field intensity of975Gs; a magnetic product with TFe93.73%and Al2O31.21%, and a non-magnetic product with Al2O340.56%and TFe6.73%are obtained under above conditions; the magnetic separation recovery of iron reaches93.07%.Mechanism research shows that sodium salts promote the growth of metallic iron grain and enhance the separation of Al and Fe. Chemical analysis and XRD analysis show that the reduced pellet is mainly composed of metallic iron and sodium aluminosilicate, and main composition of the magnetic material is metallic iron, while main composition of nonmagnetic material (high-aluminium slag) is sodium aluminosilicate.The technologies recovering Al, Si and Na from nonmagnetic material were studied further. Sulfuric acid leaching is found to be one of effective methods. The optimum technological conditions of leaching high-aluminum slag in laboratory are obtained as H2SO4concentration30%, leaching temperature30℃, leaching time30min, liquid-solid ratio10:1, stirring speed200r/min. Under these conditions, the recovery of89.37%for Al2O3,89.12%for SiO2and96.46%for Na2O were achieved. The conditions of SiO2separation from the leaching solution is found to be H2SO4dosage70%, temperature90℃, time120min, liquid-solid ratio10:1, stirring speed500r/min, the recovery of SiO2is98.32%at the conditions.It has been found that gallium in high-iron bauxite goes into metallic iron, while more than80%of the vanadium goes into the nonmagnetic material and can be recycled from the leaching residue.On the basis of above investigations, a new process of comprehensive utilization of iron, aluminum, silicon, gallium and vanadium was first put forward. The process has many advantages such as short flowsheet, low investment cost, low waste disposal and high recovery efficiency over the process of First-Iron-then-Aluminium already published.The results provide a new way for the comprehensive utilization of high iron bauxite ores.