The Pechiney process in precipitation has been used in the plant of "Aluminium de Grèce" since 1988.
A description of this process with very high solid content, up to 1,000 grams hydrate per liter of slurry, is applied, particularly with addition of a chemical in precipitators.
Further, the improvement of precipitation yield with an innovating interstage cooling in precipitation, is described.
It is shown that combination of this process with the interstage cooling in precipitation allows us to obtain, on a very regular basis, a consistent sandy alumina with the main following characteristics:
- Soda content lower than 3,300 ppm.
- Particle smaller than 45 µm less than 8% of weight.
That is achieved with a precipitation yield up to 91 grams per liter of pregnant liquor, with a short residence time.
The technical results of some smelters show the excellent compatibility of this alumina with the most recent smelting technology.