Arsenic Scavenging by Aluminum-Substituted Ferrihydrites in a Circumneutral pH River Impacted by Acid Mine Drainage

Areej Adra (1) , Guillaume Morin (1) , Georges Ona-Nguema (1) , N. Menguy (1) , Fabien Maillot (1, 2) , Corinne Casiot (3) , Odile Bruneel (3) , Sophie Lebrun (1) , Farid Juillot (1) , Jessica Brest (1)

1 IMPMC - Institut de minéralogie, de physique des matériaux et de cosmochimie
2 Department of Earth and Planetary Sciences [St Louis]
3 HSM - Hydrosciences Montpellier

Ferrihydrite (Fh) is a nanocrystalline ferric oxyhydroxide involved in the retention of pollutants in natural systems and in water-treatment processes. The status and properties of major chemical impurities in natural Fh is however still scarcely documented. Here we investigated the structure of aluminum-rich Fh, and their role in arsenic scavenging in river-bed sediments from a circumneutral river (pH 6−7) impacted by an arsenic-rich acid mine drainage (AMD). Extended X-ray absorption fine structure (EXAFS) spectroscopy at the Fe K-edge shows that Fh is the predominant mineral phase forming after neutralization of the AMD, in association with minor amount of schwertmannite transported from the AMD. TEM-EDXS elemental mapping and SEM-EDXS analyses combined with EXAFS analysis indicates that Al3+ substitutes for Fe3+ ions into the Fh structure in the natural sediment samples, with local aluminum concentration within the 25−30 ± 10 mol %Al range. Synthetic aluminous Fh prepared in the present study are found to be less Al-substituted (14−20 ± 5 mol %Al). Finally, EXAFS analysis at the arsenic Kedge indicates that As(V) form similar inner-sphere surface complexes on the natural and synthetic Al-substituted Fh studied. Our results provide direct evidence for the scavenging of arsenic by natural Al-Fh, which emphasize the possible implication of such material for scavenging pollutants in natural or engineered systems.

Domaines: Environnement et Société

Areej Adra, Guillaume Morin, Georges Ona-Nguema, N. Menguy, Fabien Maillot, et al.. Arsenic Scavenging by Aluminum-Substituted Ferrihydrites in a Circumneutral pH River Impacted by Acid Mine Drainage. Environmental Science and Technology, 2013, 47, pp.12784-12792. ⟨10.1021/es4020234⟩. ⟨hal-01018033⟩