Bauxite

Bauxite is a lateritic rock, white, red or grey, characterised by a strong content in alumina Al2O3 and iron oxides. This rock is the main ore enabling aluminium production.
It is formed by continental alteration in wet and hot climate. With varied structure, it contains in variable proportions alumina hydrates, kaolinite, silica and iron oxides which often gives it a red color.
 

The main bauxite producers are Australia, China, Guinea and Brazil, but we also find bauxite in many other countries in Europe as in France (the bauxite name is coming from the village "Baux de Provence" where it has been discovered), Greece, Italy...
 

Simplified process (Bayer process)
First, bauxite is grinded. During particle size reduction, Neyrtec Minéral's hydrocyclones are used in the closed grinding circuits to separate the fine particles from the coarse ones, the coarse particles will be resent in the grinding circuit. The grinded ore undergo an attack by a soda solution. A solid-liquid separation by settling enables to separate the liquor containing the aluminates in solution from the solids residues called red muds. The aluminates are precipitated in alumina which will be transfomed in aluminium. Neyrtec Minéral's hydrocyclones are very used in this step of alumina trihydrate separation. Indeed only the particles >50µm will be used for the aluminium, the particles <50µm wil be resent in the Bayer process where they are used as nucleus to create new trihydrate particles.
 

Red muds (residues of the chemical attack with high content in iron) are sent in washing line which main aim is to wash the muds reducing the caustic soda concentration. The recovered liquor is reinjected in the process upstream and thickened muds are rewashed at the next step. At the last step, the muds, highly thickened have a soda concentration <5g/l and are no more considered as pollutant or dangerous. They are then put in lagoon.

The hydrocyclone with small inner diameters 50 to 100 mm are particularly suitables for trihydrate aluminium classification.
We have many references in trihydrate alumina classification as well as in grinding lines, mainly in China and in India.
High quality polyurethane used for hydrocyclones' manufacturing enables a high durability of our equipments even in the difficult conditions of the alumina (high temperature, causticity of the solution, high abrasiveness). All our hydrocyclones are manufactured in France.
Our muds compactor, the Tasster, has been especially developped for red muds processing. It enables to obtain concentrated red muds up to 900g/l. In the sites where our Tasster are used they offer performances beyond the competitors' equipments  (Vimetco, CVG Bauxilum).

The hydrocyclones enable an hydraulic classification and are used :
- In closed circuits of bauxite grinding.
- For grain size alumina separation.
- To remove the sand (>100µm) after bauxites' digestion.

1) At the end of washing line : red muds after washing are thickened and compacted with an equipment TASSTER type. This equipment enables to increase mud concentration up to 900g/l.
Which enable to :
- Reduce the final muds volume to store.
- Improve the soda recovery.
- Decrease the discharge in the environment of polluted waters.
 

2) In the washing line : By more concentrating the red muds, the TASSTER enable to improve muds' washing. At each step the soda volume contained in the muds is reduced because of a more important muds' concentration.