What is Alumina Mineral & How's it Made?

Alumina mineral is commonly known as activated alumina and is made from bauxite ore. The numerous properties of alumina minerals make it highly useful in various industries such as ceramics, electronics, refractories, glass, construction materials, abrasives, and military equipment, among others.

Alumina & its Properties:

• It has a very high hardness level, and reasonably high melting and boiling point, which makes it perfect for ceramics.
• It is also a great option for many electrical goods because of its electrical resistivity and thermal conductivity.
• Not to forget the fact that it has mechanical and compressive strengths that are both higher than many comparable materials making it ideal for products that require hardness & strength.

Now, we have a basic understanding of what alumina mineral is! Let's learn how alumina is made.

Alumina mineral is made from bauxite ore which is an important mineral for aluminum. 

And, do you know that the sixth largest bauxite resource in the world, with a reserve base of more than 2.20 billion tonnes, is located in India? Indian bauxite is often of higher grade and is concentrated on a single plateau, because of this bulk mining is made possible and the cost of producing alumina and aluminum is significantly reduced.

Bauxite ore contains several minerals such as gibbsite, boehmite, iron oxides, iron hydroxides, quartz, and clay. The physical composition of bauxite can range from being as hard as a rock to being as soft as mud, and it can have any combination of the colors red, white, buff, pink, and yellow.

The Bayer process is the main method for converting bauxite into alumina and it was discovered in 1887 by Karl Josef Bayer. Another interesting fact about alumina production is that 2 to 3 tonnes of bauxite is required to produce 1 tonne of alumina.

Now, let’s understand the process of making alumina from bauxite in detail. The steps involved in the Bayer process are:

1. Grinding/ Milling:

Bauxite ore is taken to a processing facility where bauxite is cleaned and crushed to reduce particle size and increase surface area for the digestion stage. At the mills, lime and "spent liquor" (caustic soda that has been recovered from the precipitation step) are combined to create a pumpable slurry.

2. Desilication:

The mixture is purified to get rid of silica. Bauxites that are high in silica (SiO2) are processed to get rid of this impurity because silica does not dissolve, can create scaling, and impact the quality of the finished product.

3. Digestion:

The sodium aluminate supersaturated solution, also known as "pregnant liquor," is created by dissolving the aluminum-bearing minerals in bauxite (gibbsite, böhmite, and diaspore) in a hot caustic soda (NaOH) solution.

The bauxite ore's characteristics are taken into consideration when adjusting the digester's conditions (caustic concentration, temperature, and pressure). The slurry is subsequently cooled to around 106°C at atmospheric pressure and by flashing off steam in a succession of flash tanks.

4. Filtration:

Again the mixture goes through a purification stage. All other substances in bauxite, besides alumina and silica, do not dissolve. The solids (bauxite residue) from the pregnant liquor (sodium aluminate remains in solution) via sedimentation are separated.

Using several security filters, the pregnant liquor is further separated from the bauxite residue. The security filters prevent pollutants from contaminating the finished product.

The materials that cannot be dissolved settle as red mud on the bottom of the water. After that, the red muck is often removed from the solution using a rotary sand trap.

5. Precipitation:

Hot exchangers are used to transferring the remaining, clear mixture from heat to cold liquor before it is added to precipitators. Due to heating, silica precipitates out of the mixture. In this step, aluminum hydroxide crystals are found. A small amount of aluminum hydroxide that was found in this step is employed as a chemical for water treatment.

6. Classification:

Size ranges are used to categorize the precipitated gibbsite crystals. Vacuum filtration is used to remove the coarse-sized crystals from the spent liquid, and the solids are then washed with hot water. The fine crystals are returned to the precipitation stage as fine seeds to be agglomerated after being cleaned to remove organic contaminants.

7. Calcination:

Alumina solids are created by roasting the filter cake in calciners at temperatures as high as 1100°C to remove free moisture and chemically linked water. There are several calcination technologies in use, including rotary kilns, fluidized bed calciners, and gas suspension calciners.

This stage's output is alumina, a white powder that is the finished product of the Bayer Process and is prepared for final shipping.

We hope this gives you a detailed understanding of what alumina mineral is & the Bayer process that is used for the manufacturing of Alumina mineral. Connect with us via call at + 91 - 637 797 0211 or mail us at info@aryantiles.com to get the latest quotes about Alumina mineral TODAY!