Adra A., Morin G., Ona-Nguema G., Menguy N., Maillot F., Casiot C., Bruneel Odile, Lebrun S., Juillot Farid, Brest J.
Source
Environmental Science and Technology, 2013,
47 (22), p. 12784-12792 ISSN 0013-936X
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 K-edge 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.
Plan de classement
Sciences fondamentales / Techniques d'analyse et de recherche [020]
;
Pollution [038]
;
Géologie et formations superficielles [064]
