Production of Alumina

Alumina is essentially a form of occurrence of Al2O3, aluminium oxide. Commercial varieties of alumina serve as a raw material for the production of industrial abrasive, wearproof and refractory materials.

Pure alumina can occur as corundum and it is also a part of minerals and rocks, such as bauxites, alunites, kaolins and nephelines.

 Production of Alumina from Various Types of Raw Materials

The ore containing bauxites, or a clay rock consisting of various modifications of aluminium hydroxide, oxides of iron, silicon, titanium, sulfur, gallium, chrome, vanadium and carbonate salts of calcium, iron and magnesium is widely used to produce alumina. The produced technical alumina looks like a homogeneous crystalline white powder.

Alumina can be produced using alkaline and acid methods. The most common method is the Bayer’s alkaline technology, which is suited to separate alumina oxide from high-quality bauxites with a low content of silicon oxide, SiO2.

To treat other types of rock, a method of sintering can be used. It permits to obtain alumina from bauxites of various types, nepheline concentrates and ores, Bayer’s muds, kaolins, alumo-calcium slags and other materials.

Technologies of Alumina Production

The process of alumina production by the Bayer’s hydrochemical method consists in decomposition (hydrolysis) of alkali-aluminate solutions at high temperatures followed by the separation of aluminium hydroxide. The impurities, contained in bauxites, remain in the non-dissolved residue.

The sequence of operations to produce alumina by the Bayer’s method:

  • preparing bauxite ore by crushing and milling;
  • adding lime and caustic alkali to the processed material;
  • treating bauxites with alkali liquor;
  • splitting the mud and aluminate liquor by washing;
  • decomposing the resulting aqueous aluminate solution;
  • receiving ready-made aluminium hydroxide by isolating it from the solution;
  • ignition and calcination (dehydration) of aluminium hydroxide.

Alumina, produced using this method, is characterized by a stable chemical compound. The resulting aluminium oxide is high-melting (melting temperature is 2050°C).

The technology of alumina production by sintering involves ore sintering in furnaces till solid aluminate appears. The resulting aluminate is leached using water or soda solution. Aluminate solution decomposes using carbon dioxide to obtain aluminium hydroxide.

The quality, performance and application capacities of the resulting alumina depend on the phase of the materials, technologies and raw materials used to produce it. MICROINTECH offers our customers to buy alumina for various purposes in any volume they may need.