The bauxite is purified by the Bayer Process. First the ore is mixed with a hot concentrated solution of sodium hydroxide. The NaOH will dissolve the oxides of aluminum and silicon but not other impurities such as iron oxides, which remains insoluble. The insoluble materials are removed by filtration.

Bauxite is the primary ore of aluminum, and it often contains impurities such as iron oxide, silica, and titania. The purification of bauxite involves the removal of these impurities to obtain pure aluminum oxide, also known as alumina. The process of purifying bauxite can be carried out through the following steps:


The most commonly used method for purifying bauxite is the Bayer process. It was developed in the late 19th century by Austrian chemist Karl Bayer and has since become the standard method for producing alumina.


The first step in the Bayer process is digestion, in which crushed bauxite is mixed with a sodium hydroxide solution under high temperature and pressure. The purpose of digestion is to dissolve the aluminum-containing minerals in bauxite, leaving behind the impurities as solid residues.


After digestion, the mixture is allowed to settle in a series of tanks. During settling, the solid impurities, including iron oxide, settle to the bottom of the tanks, while the dissolved alumina remains in the liquid phase. The settled impurities are then removed and discarded.


To further remove any remaining impurities, the liquid phase undergoes clarification. This step involves the addition of flocculants, such as aluminum sulfate or polyacrylamides, which cause the impurities to form larger particles that can be easily separated from the solution. The clarified solution is then ready for the next stage.


In this stage, the clarified solution is cooled, and the alumina is precipitated as hydrated particles. The addition of seed crystals helps promote the growth of the desired aluminum hydroxide particles. The precipitated hydrate is then filtered and washed to remove any remaining impurities.


The final step in the purification process is calcination, where the hydrated alumina is heated at high temperatures to drive off the water and convert it into pure alumina. The resulting product is a fine white powder of aluminum oxide, which can be used for various applications, including the production of aluminum metal.

Overall, the purification of bauxite containing impurities of iron oxide involves the Bayer process, which includes digestion, settling and separation, clarification, hydrate precipitation, and calcination. Through these steps, impurities are progressively removed, resulting in the production of high-purity alumina suitable for further processing into aluminum.

Bayer's process