Multi-element comprehensive utilization of high-silicon bauxite by roasting pretreatment and two-stage leaching

As a potential ore resource to produce alumina in industry, the complex symbiotic relationship between the aluminum-, silicon- and iron-bearing minerals in the high-silicon bauxite and severe desilication reactions during digestion process restrict its application. In this paper, a novel zero-waste process consisting of a roasting pretreatment and two-stage leaching was proposed to comprehensively utilize the high-silicon bauxite, and the phase transition mechanism and leaching properties of the roasting solid were systemically studied. When the roasting temperature is over 310 °C, the diaspore and kaolinite in the bauxite lose the crystal water, and gradually transform to alumina and metakaolin respectively. As the roasting temperature rises to above 950 °C, the metakaolin decomposes to an amorphous aluminosilicate phase and silica. The crystallinity of decomposed alumina and silica increases with the increase of roasting temperature and duration, but the excessive temperature and duration deteriorate the extraction property of the roasted bauxite. The optimal roasting conditions for the atmospheric-pressure leaching of silica and high-pressure leaching of alumina are 1050 °C for 30 min, and the corresponding extraction efficiencies of Al2O3 and SiO2 are above 94 % and 88 % respectively. The Fe2O3 and Na2O contents in the final leaching product are 55.23 % and 0.23 %, and can be directly used as iron concentrate in the ironmaking process.