En construction
Aluminium metal production comes from the electrolysis of alumina : a white
powder with the following chemical formula Al2O3. The most common process for
alumina production consists of dissolving alumina from bauxite ore through a
chemical attack with caustic soda. Concentrated caustic liquor is mixed up with
the crushed ore, under high pressure and temperature. After elimination of
insoluble matter through a filtration stage, the caustic liquor is cooled down
to allow precipitation of alumina hydrate. The alumina hydrate is collected and
dehydrated in a very high temperature calciner. The alumina powder can then be
exported to the smelter for final aluminium production. On the other side, the
caustic liquor is concentrated through evaporation and purified before being
recycled.
Although Kestner is specialised in evaporation and
crystallisation technologies, its know-how in the alumina industry covers many
aspects, including :
Caustic liquor concentration
Bayer liquor
purification
Depending on the quality of bauxite used, some caustic liquors
need to be purified before being recycled to the digestion stage. Kestner
proposes an evapo-crystallisation unit, in order to remove mineral impurities
(‘’ salting-out’’ units) as well as organic impurities (super concentration for
‘’ liquor burning’’, oxalate precipitation).
In 2004, GEA acquired the
subsidiary MESSO Switzerland (former Sulzer Escher Wyss), also well known to
the Alumina Producers, especially in multi flash technology.
Kestner
and Messo AG have installed more than 80 spent liquor evaporation plants and
are able today, as world market leaders, to offer all evaporation and
crystallisation technologies for the alumina industry.