Publications des scientifiques de l'IRD

Maillot F., Morin G., Juillot Farid, Bruneel Odile, Casiot C., Ona-Nguema G., Wang Y. H., Lebrun S., Aubry E., Vlaic G., Brown G. E. (2013). Structure and reactivity of As(III)- and As(V)-rich schwertmannites and amorphous ferric arsenate sulfate from the Carnoules acid mine drainage, France : Comparison with biotic and abiotic model compounds and implications for As remediation. Geochimica et Cosmochimica Acta, 104, p. 310-329. ISSN 0016-7037.

Titre du document
Structure and reactivity of As(III)- and As(V)-rich schwertmannites and amorphous ferric arsenate sulfate from the Carnoules acid mine drainage, France : Comparison with biotic and abiotic model compounds and implications for As remediation
Année de publication
2013
Type de document
Article référencé dans le Web of Science WOS:000314664500020
Auteurs
Maillot F., Morin G., Juillot Farid, Bruneel Odile, Casiot C., Ona-Nguema G., Wang Y. H., Lebrun S., Aubry E., Vlaic G., Brown G. E.
Source
Geochimica et Cosmochimica Acta, 2013, 104, p. 310-329 ISSN 0016-7037
Poorly ordered nanocrystalline hydroxysulfate minerals of microbial origin, such as schwertmannite, Fe8O8(OH)(6)SO4, are important arsenic scavengers in sulfate-rich acid mine drainage (AMD) environments. However, despite the fact that As(III) and As(V) have been shown to sorb on schwertmannite, little is known about the actual mechanism of arsenic scavenging processes after microbial Fe(II) oxidation in AMD environments. The major focus of the present study is to determine the molecular-level structure of poorly ordered As(III) and As(V) bearing Fe oxyhydroxysulfate minerals from the Carnoules AMD, France, which exhibits exceptional As(III) concentrations. Powder X-ray diffraction (XRD) and extended X-ray absorption fine structure (EXAFS) spectroscopy were used to compare field samples with a large set of synthetic analogs prepared via biotic or abiotic pathways, with As/Fe ratios typical of minerals and mineraloids ranging from nanocrystalline schwertmannite to amorphous hydroxysulfate compounds. Our results yield further evidence for the poisoning effect of As(V) in limiting the nucleation of schwertmannite. For initial dissolved As(V)/Fe(III) molar ratios >= 0.2, amorphous Fe(III)-As(V) hydroxysulfate forms, with a local structure consistent with that of amorphous ferric arsenate. EXAFS data for this amorphous material are consistent with corner-sharing FeO6 octahedra to which AsO4 tetrahedra attach via double-corner C-2 linkages. For As(V)/Fe(III) molar ratios lower than 0.2, As(V) binds to schwertmannite via C-2 surface complexes. In contrast with the As(V)-containing samples, As(III) has a lower affinity for schwertmannite following its nucleation, as this mineral phase persists up to an initial As(III)/Fe(III) molar ratio of 0.6. EXAFS data indicate that during the precipitation process, As(III) forms dominantly C-2 surface complexes on schwertmannite surfaces, likely on the sides of double-chains of Fe(III)(O, OH)(6) octahedra, with a smaller proportion of edge-sharing E-2 surface complexes at the apexes of these chains. Importantly, dissolved As(V) concentrations in contact with As(V)-schwertmannite or ferric arsenate were found to be similar to 10 times lower than dissolved As(III) concentrations in contact with As(III)-schwertmannite for similar As/Fe ratios in the solid phase. Consequently, remediation of As-rich AMD environments is greatly improved by oxidation of As(III) to As(V).
Plan de classement
Géologie et formations superficielles [064]
Description Géographique
FRANCE
Localisation
Fonds IRD [F B010058984]
Identifiant IRD
fdi:010058984
Contact