Bauxite ore is the most important source for aluminium in the world. Bauxite ore is a mixture of aluminium and iron oxides, silica, titanium dioxide, alumina and calcium containing clay minerals. Bauxite ore is formed as a residual product in the weathering of igneous rocks, such as gabbro, basalt and granite, and is found in tropical and subtropical regions near highly weathered soils.
Bauxite ore has a wide range of chemical composition with a pronounced variation in the content of alkalis and silicon dioxide. It is basically mixtures of iron oxides, hydrated alumina and some clay minerals. The main mineral content of the bauxite ore includes gibbsite (alumina), diaspore and boehmite, which all have different chemical compositions. It also contains small amounts of quartz, kaolinite, montmorillonite, feldspar and organic matter.
The typical chemical composition of bauxite ore used in the production of aluminium is as follows. It has a specific gravity of 2.45–2.85, and its colour ranges from yellowish to reddish brown.
Aluminium Oxide (Al2O3): 47.3-54.1 percent
Silica (SiO2): 6.0-12.0 percent
Iron Oxides (Fe2O3): 17.90- 21.70 percent
Titanium Oxide (TiO2): 0.80-3.0 percent
Calcium Oxide (CaO): 1.50-3.50 percent
Magnesium Oxide (MgO): 1.90-2.20 percent
Sodium Oxide (Na2O): 0.30-1.00 percent
Potassium Oxide (K2O): 0.20-0.50 percent
The amount of alumina in bauxite ore is dependent on the availability of the other minerals in the ore. The complete chemical composition of the ore affects the strength of the ore during the processing stages. Thus, bauxite ore which has higher aluminium content is preferred for the production of aluminum.
Bauxite ore also has to meet certain chemical requirements before it can be used in the production of aluminium. These requirements are given below:
Aluminium Oxide (Al2O3): 40-54 percent
Silica (SiO2): 4-15 percent
Iron Oxide (Fe2O3): less than 7.5 percent
Titanium Oxide (TiO2): 0.3-3.0 percent
Sodium Oxide (Na2O): 0.2-2.0 percent
Calcium Oxide (CaO): 0.5–3.5 percent
Magnesium Oxide (MgO): 0.3–3.3 percent
Trace Elements: 0.1-0.3 percent
The trace elements in the ore can be divided into minor and major elements. Minor elements include lead (Pb), zinc (Zn), copper (Cu) and manganese (Mn). Major elements include iron (Fe), nickel (Ni), cobalt (Co) and chrome (Cr).
Finally, the quality of bauxite ore must meet certain requirements to be suitable for use in aluminium production. Before being put to use in the production of aluminium, bauxite ore must pass tests such as water leaching test, alkali leaching test and other tests to check for the presence of contaminants and toxic minerals. The acceptable limits for metals such as lead, chromium, zinc, nickel and other metals in bauxite ore should be less than 0.1 percent.
In conclusion, bauxite ore is an important source for the production of aluminium. The chemical composition of bauxite ore varies widely depending on its origin and processing. To use this ore in the production of aluminium, the ore must meet certain chemical requirements. It should contain a good amount of aluminium oxide and should be free from contaminants and toxic minerals. Thus, the chemical composition of bauxite ore is important in ensuring the quality of the ore and its suitability for use in the production of aluminium.
