ALFERROCK

Endpoint summary

Description of key information

Aluminium is the most relevant metal constituent released from "Neutralisation and reduction products of bauxite residue from refinement". It is the most abundant metal in the lithosphere and is characterized by a complex biogeochemical cycle. Aluminium persists in the environment irrespective of the chemical species formed as a result of hydrolysis, although it may form insoluble aluminium hydroxides which precipitate.

The existing information suggest aluminium does not bioaccumulate/ biomagnify across trophic levels. In addition, the existing information shows the tendency of Al to exhibit biodilution at higher trophic levels in the food chain.

Al is only released at very low amounts (max. 0.5 mg/L after 28 days, 100 mg/L loading). Therefore, the substance as such cannot be tested for adsorptive properties. The adsorption/desorption from the soluble fraction of Al³⁺generated in contact with water is influenced and at the same time also superimposed by other effects occurring in soil.

 

Additional information

"Neutralisation and reduction products of bauxite residue from refinement process" is an inorganic substance hence cannot undergo biological degradation. It is hardly soluble and releases only low amounts of Al in the transformation/dissolution test (up to ca. 500 µg/L after 28 days, 100 mg/L loading; see IUCLID section 4.8).

Aluminium is the most abundant metal in the earth's crust, but it is never found free in nature. All naturally occurring aluminium forms compounds with other elements or molecules, like oxygen, hydroxides or sulphates. More than 8 % of the earth's crust is composed of aluminium, and aluminium is present in more than 270 different minerals. Aluminium is characterised by a complex biogeochemical cycle, it can participate in hydrolysis reactions, thereby forming a number of monomeric and polymeric Al-hydroxides, and this process is highly dependent on pH. The transport and partitioning of aluminium in the environment is determined by its chemical properties, as well as the characteristics of the environmental matrix that affect its solubility. At a pH > 5.5, naturally occurring aluminium compounds exist predominantly in an undissolved form such as gibbsite, Al(OH)₃.

As an element, aluminium cannot be degraded in the environment, but may undergo various precipitation or ligand exchange reactions. Aluminium in compounds has only one oxidation state (+3) and would not undergo oxidation-reduction reactions under environmental conditions. Aluminium can be complexed by various ligands present in the environment (e.g., fulvic and humic acids). The solubility of aluminium in the environment will depend on the ligands present and the pH.