Details of the production of alumina raw materials: bauxite
So far, the production of alumina in two main raw materials: one is to use natural or sintered bauxite fused directly into corundum, alumina corundum, corundum-white; the other is to use commercial alumina fused or sintered as corundum, dense corundum, tabular alumina, sintered corundum and so on. While industrial use more than 95% of alumina bauxite extraction. Bauxite is an important raw material visible corundum. With alunite and nepheline can be extracted alumina.
Also known as bauxite bauxite or bauxite, the main mineral is a boehmite (Al2O3 · H2O) and gibbsite (Al2O3 · 3H2O). Depending on the structure of a boehmite, can be divided into a diaspore (α-Al2O3 · H2O or diaspore) and a boehmite (γ-Al2O3 · H2O or boehmite, Baume stone) . Bauxite mineral name is not called, but a diaspore, a boehmite and gibbsite mixture, the main chemical ingredient Al2O3, typically at 40% to 80%. Natural chemical composition of bauxite magazine big changes, in addition to Al2O3, there are SiO2, TiO2, Fe2O3, CaO, MgO, K2O, Na2O, these chemical composition of the following minerals: gibbsite, a boehmite, and sillimanite-based mineral (ie, sillimanite, andalusite, kyanite, the chemical formula (Al2O3 · SiO2), kaolinite (Al2O3 · SiO2 · H2O), rutile (TiO2) and dickite and iron minerals. bauxite mainly oolitic, lenticular, debris and cryptocrystalline (mashed) structure, as well as earthy, dense block structure and from white to ocher of everything between colors, generally red high iron, low iron content was gray, because of the different cementation material, a large color change, the advantages of red-brown spots. Exterior features of bauxite complex, but there are rules to follow generally the same level, with similar characteristics.
Our bauxite mainly in Henan, Shanxi, Guangxi, Guizhou and Shandong provinces. The main mineral is a diaspore and kaolinite, followed by a boehmite, gibbsite, rutile, dickite and iron minerals. Which is characterized by containing high Al2O3, SiO2 containing also high, containing Fe2O3 low, Al2O3 / SiO2 is low, mostly 4-7. In addition to Pingguo bauxite, the majority containing Fe2O3 are below 5%, quality bauxite Al2O3 / SiO2≥10 also less. For ore types, the vast majority of a diaspore - kaolinite type, commonly known as a high silicon and low iron diaspore bauxite, also known as a high aluminum high silicon and low iron diaspore - kaolinite bauxite. Pingguo bauxite can be called a high-speed rail diaspore - kaolinite bauxite. Diaspore and kaolinite these two minerals in different proportions composed of a series of different Al2O3 content of bauxite. Only Fujian, Guangdong has a small amount of gibbsite, but Al2O3 / SiO2 are relatively low, Guangxi and Shandong as well as a considerable number of bauxite.
Foreign mostly gibbsite, but a Europe with boehmite type mostly Greece is a diaspore - a boehmite type. From the chemical composition see, SiO2 content of most foreign bauxite lower, Al2O3 / SiO2 high Fe2O3 content and are generally higher.
Al2O3 is the main component of bauxite, and its content as high as possible, the current requirements for the production of industrial aluminum Al-Si is not less than 3.0 to 3.5. Other oxides are regarded as impurities, SiO2 is harmful alkaline alumina production impurities in the SiO2 content of bauxite, corundum smelting will, or the efficiency of industrial production and lower production of alumina, an increase in impurities. Bauxite containing Fe2O3 high, although most can be removed, but has a certain impact on product quality. If TiO2 containing high product quality is also unfavorable, containing K2O and Na2O high quality of the product greater impact.
Whether smelting corundum, or aluminum production industry, the quality of bauxite have strict requirements. Of GB / T3497-1983 bauxite by chemical composition, use classification table:
|Project||First Grade||Second Grade||Grade III||Four products||Five items||Six products||First Grade|
|Al2O3/SiO2(not less than)||12||9||7||5||4||3||6|
|Al2O3/%(not less than)||73||69||66||60||71||67||64||50||69||66||62||62||58||54||48|
|Example Uses||Corundum abrasive materials, high alumina cement||Alumina||Alumina||Alumina||Alumina cement, alumina||Alumina||Alumina||Alumina||Alumina||Alumina||Alumina||Alumina||Alumina||Alumina||Alumina|
|Note: The product is suitable for one to six diaspore ores; seven product applies gibbsite type ore|
Corundum smelting must be calcined bauxite. Aluminous clinker after not only improve the taste, the electric corundum smelting consumption decreased, and the furnace conditions stabilize and improve production efficiency. Bauxite occurs during heating a series of physical and chemical changes, not only to study the production of alumina, smelting corundum, white corundum is important, but also the manufacturing base of high alumina refractories. Changes bauxite heating can be divided into three stages, namely the decomposition stage, the second stage Mullite, recrystallization sintering stage.
High temperature calcined bauxite by product, called high bauxite, the main raw material is high alumina refractories, smelting alumina can also be used, in particular white corundum smelting. High bauxite clinker demanding, not only requires Al2O3 content is high, and difficult to restore oxide content as low as possible.
China is the world's countries rich bauxite resources, but due to the impact of the formation of deposits in the laws of nature, its distribution is not concentrated ore grade, mining mechanization level mixed serious, plus natural type of ore complex, difficult to strictly hierarchical. In recent years, from the point of view of the refractory bauxite we were more experimental work, and achieved gratifying results. The future of synthetic materials will further work, the formation of high-quality refractory materials products with Chinese characteristics.