Red mud

Red mud is a waste product of the alumina production by the Bayer process. He falls as the water-insoluble residue in the extraction of aluminum - in the form of water-soluble sodium Na [ Al (OH ) 4] - from bauxite with sodium hydroxide solution to. The remaining red mud containing iron and titanium oxides, various silicates, and many heavy metals ( such as mercury and arsenic). The characteristic red color is derived from iron hydroxide (III). How much red mud per ton of aluminum is obtained, depends on the quality of the bauxite used: in tropical bauxite 1.6t, at European bauxite 3.2-3.7 t wet red mud.

The highly alkaline sludge was previously landfilled without further precautions or conducted in rivers, resulting in significant environmental impacts. Today, the sludge is stored in sealed landfills until the present as a dispersion hydroxides and silicates have discontinued. The exiting caustic soda is recycled. Subsequently, the landfill is covered with sand and soil and revegetated. More recently, purified red mud is also used as filler in road construction and as a starting material for ceramics.

One of the biggest red mud disposal in Germany is located near Stade in Lower Saxony between Bützflethermoor and Stader bog, 10 km north- west of Stade. For her by the former VAW (United aluminum plants Stade ) was washed, the caustic soda from the red mud prior to landfilling.

Dangerousness

The short-term hazard of the red mud is primarily based on the content of caustic soda lye ( sodium hydroxide dissolved in water ). A long-term harm resulting from the levels of toxic heavy metals, depending on the origin and nature of the bauxite. Heavy metal oxides and Schwermetallhydroxide are in basic medium usually only very slightly soluble. Landfilled red mud contains about 1 % of soluble Schwermetallhydroxiden. However, when anions present toxic components such as fluorides, arsenates, vanadates and chromates can also be washed in basic medium out of the mud. If the sodium hydroxide of the red mud is neutralized by strong dilution or access of acids, it can also lead to formation of soluble compounds of other heavy metals and thus to environmental hazards. Why should red mud both a surface coverage as well as protection against contact with groundwater have.

Environmental hazards

Improper disposal or the deliberate introduction of red mud in rivers and lakes it comes to serious environmental problems. Also during the storage of red mud can cause accidents.

So came on 4 October 2010 at Kolontár - dam failure in Hungary 700000-1 million cubic meters of red mud from the memories of an aluminum plant in Ajka Hungarian settlements from.

In one of the largest bauxite mines in Brazil, Porto Trombetas in the Amazon basin, red mud is introduced into the Lake Batata. This had an enormous extinction of species in the lake result in environmental organizations such as Save the Rainforest eV even speak of a complete extinction of the ecosystem. Moreover, the water of the lake and the adjacent Rio Sapone can no longer be used as drinking water.