The chemical composition of bauxite is mainly Al2O3SiO2Fe2O3TiO2H2O + the total amount of the five elements accounts for more than 95% of the composition, generally> 98%. The main ingredients are SCaOMgOK2ONa2OCO2MnO2 organic matter, carbon, etc., and the trace ingredients are GaGeNbTaPCoZrVPCrNi. Al2O3 mainly occurs in aluminum minerals-diaspore, boehmite, gibbsite, and secondly in silicon minerals (mainly kaolinite minerals).
Under endogenous conditions, due to the widespread existence of silica, Al2O3 and SiO2 are often closely combined into various types of aluminosilicate minerals. These minerals generally have an aluminum-silicon ratio of less than 1 and industry generally requires Al2O3≥40% Al / Si > 1.82.6 Therefore, industrial aluminum deposits are rarely formed under endogenous conditions.
At present, domestic and foreign industrial bauxites are known to be formed under supergene conditions. There are two main types of bauxite formation under the supergene conditions: namely, weathering-residual (surplus) ore (laterite ore) and weathering -Transportation-accumulation or weathering-reformation-re-depositional ore-forming (accumulation ore-forming) weathering-residual (remaining) ore-forming is an aluminum-bearing parent rock with favorable topography (such as residual mounds, Low mountains and terraces) Due to the weathering and decomposition of water, CO2 and organisms, the soluble materials KNaCaMg and SiO2 in the parent rock are leached and discharged, and the less active material AlFeTi remains to form laterite-type bauxite. Weathering-handling-accumulation mineralization is aluminum-bearing rock, red earth weathered crust or formed laterite deposit. Under the action of gravity, water and natural acids (sulfuric acid, carbonic acid, organic acid), etc., it is mechanically or chemically weathered, eroded, Transportation and other physical and chemical transformation effects formed bauxite in hillside depressions, valleys, offshore lake basins or coastal lakes, and limited sea basins, and sedimentary bauxite was formed in an aqueous medium environment.
Bauxite ore contains useful components such as gallium, vanadium, niobium, tantalum, titanium, cerium and radioactive elements. These valuable associated components can be recovered comprehensively. The sulfur and CO2MgOP2O5 in the ore are harmful components, which is conducive to aluminum smelting and recycling.
Bauxite ore is divided into gibbsite type, boehmite type and diaspore type according to the main aluminum-bearing minerals it contains. Foreign bauxite ores are mainly gibbsite type, followed by boehmite type, and diaspore type bauxite is rare. But our country is mainly diaspore-type bauxite, and gibbsite-type bauxite is rare.
Foreign gibbsite type bauxite has the characteristics of high aluminum, low silicon and high iron. The quality of the ore is good, suitable for the treatment of Bayer method with low energy consumption. The diaspore-type bauxite mine in China is characterized by high aluminum, high silicon, low sulfur, low iron, medium and low aluminum to silicon ratio, poor ore quality, and difficult processing. The production of alumina uses a joint method with high energy consumption .
The production of aluminum includes the production of alumina from ore and the production of aluminum from alumina. The main production methods of alumina include Bayer method, soda lime sintering method, and Bayer-sintering combined method. The production method of aluminum metal is mainly cryolite-alumina molten salt electrolysis.