Geochemistry of rare earth elements in acid mine drainage
Día: Jueves 20 de Junio a las 12:15 h
Lugar: Departamento de Ingeniería Civil y Ambiental, Modulo D2-Aula CIHS, Planta Baja
The REE concentrations in AMD are several orders of magnitude higher than the rest of surface waters and could be a future supplementary source of some highly valuable REE. Precipitation of schwertmannite and to basaluminite occurs due to mixing of acid (and REE-rich) and alkaline streams. The REE fractionation between AMD and the solid phases has been investigated in several localities from the Odiel-Tinto (SW Spain) and Arroyo del Val (N Spain) basins. The behavior of REE during the mixing is conservative at low pH (pH<3), whereas they are scavenged by the flocculates at near neutral pH. The validity and limitations of a recently proposed thermodynamic model of REE sorption on schwertmannite and to basaluminite has been tested by comparing its predictions with the observations made. Finally, some observations suggest that Sc behaves differently from the rest of REE. According to the model, sorption of Sc onto schwertmannite at pH lower than 4 could also occur. . As a practical consequence, REE are preferentially accumulated in the basaluminite sludge of AMD treatments, but a significant fraction of Sc from the AMD can be also found in the schwertmannite residue.