The tailings at Paragominas are stored in dedicated tailing ponds, where the particles settle. Separated water is transferred to a clarification dam before it is reused in the process. There is a minor run-off to the river downstream of the tailings, which is required to maintain an ecological flow. The run-off is monitored, and the water quality meets the requirements set by the authorities.
The current tailing ponds are reckoned to be full by 2015-2020. The area will then be reforested. The total production of tailings in 2011 was 5.9 million metric tons (mt). The Paragominas' mine produced 8.2 million mt bauxite in 2011.
Bauxite residue, also known as red mud, is a by-product of the alumina refining process. Alunorte uses the Bayer process, which includes the use of caustic soda. The residue is washed with water to lower the alkalinity and recover caustic soda to be reused in the process. The residue is dry-stacked, which means it is transformed into a clay-like solid with a low moisture content. Alunorte is in the process of reducing the moisture further through conversion to pressure filtration.
The bauxite residue deposit at Alunorte was extended in 2011. In total, 6.4 million mt were disposed in 2011. When the deposits are full, we have a plan for replanting of the area.
Bauxite residue from Alunorte is being tested as a raw material for bricks and paving stones, but even with an optimistic market estimate, this production will only use a small fraction of the total residue. The remaining residue is disposed and replanted.
After a spillage in 2009 of storm water from the bauxite residue deposits at Alunorte, corrective actions have been taken, including strengthening the drainage system and improving the surveillance of the water treatment facility. A need for better emergency handling, including information to the local community, was also identified. There are still legal issues pending following the incident, such as individual lawsuits filed by local residents who claim compensation for damages caused by the spillage. So far all of the claims have been dismissed. There is also a negotiation in place with the public prosecutor, who claims compensation for the environmental damages caused by the spillage. If an agreement is not reached with the public prosecutor, a class action lawsuit can be filed against Alunorte in this regard.
For detailed information about Hydro's waste production, see Hydro's Annual Report 2011 page 79.