Alumina production

Alumina is produced from bauxite by a classic Bayer process within the Organizational Unit Alumina Plant, where crushed bauxite is mixed with caustic soda solution (NaOH) in grinding mills, and resulting slurry is directed to autoclaves where useful component Al2O3 is diluted and transformed to slurry of sodium aluminate solution under high pressure and increased temperatures. Slurry of sodium aluminate solution is treated in settlers at the settlement facility, where liquid (useful) component – aluminate solution and solids – red mud- are separated.

Red mud is further directed to washing (in washers), then to filtration and afterwards to the red mud pond.

Useful component –aluminate solution- is directed to red filtration where impurities contained therein (mud particles) are removed, and such filtrated aluminate solution is directed to heat exchange where it is cooled down to desired temperature, while its heat gets transfered to media (washwater and spent liquor) whose temperature needs to be increased for more efficient process. Following heat exchange, aluminate solution is mixed with seeding agent and such hydrate slurry is directed to the series of precipitators for precipitation, where Al2O3 from aluminate solution is transformed into hydrate. This slurry is further directed to I° of white filtration, where hydrate and spent liquor are seperated on disk filters.

Following heat exchange, spent liquor is directed to evaporation where its concetration is increased and new soda added, after which it is returned into the process for leaching in mills and autoclaves.

Hydrate from first step of white filtration is directed to second step of white filtration where hydrate is washed, and such washed filtrate is further directed to the calcining furnace.

Upon exiting the calcining furnace, alumina is stored in silos from which it is then transported to the Smelter.

Organizational unit Alumina Plant temporarily stopped alumina production on 24 April 2009.