Rare earth elements (REE) are strategic raw materials due to their increasing demand in current society and their shortage of supply. Their concentrations are several orders of magnitude higher in acid mine drainage (AMD) than in natural river waters, which could make them a complementary source of REE. In the Iberian Pyrite Belt (South of Spain), the Odiel river water is acidified (pH about 3 to 4) by AMD discharges. When the Odiel river meets seawater at the estuary, the pH increases due to water mixing along with a notorious change in the water chemistry. This pH increase leads to precipitation of schwertmannite (Fe8O8(OH)6SO4) and basaluminite (Al4SO4(OH)10 x 5H2O) (pH = 3 and = 4.5-8, respectively), which are responsible for the REE scavenging in this area. Recent studies on retention mechanisms of REE on basaluminite and schwermannite show that adsorption is significant at pH = 6–6.5 in both minerals, and it can be enhanced by increasing the SO42- concentration in solution. However, both phases are metastable and tend to age to nanobohemite (AlOOH) in the case of basaluminite and goethite (FeOOH) in the case of schwertmannite with a dependence on the SO42- concentration in solution. The objective of the present work is to study the release (desorption) of lanthanides, yttrium and scandium from basaluminite and schwertmannite over the pH range of 4 to7 at room temperature in order to emulate estuary conditions. To this end, desorption experiments on REE-enriched synthetic basaluminite and schwertmannite were performed over a three month period and in presence of SO42-. Ageing of the solid sample occurred during this period, yielding a release of REE.

REE desorption from Al and Fe hydroxysulfates (basaluminite and schwertmannite) under estuary conditions

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.