title: Arsenic Incorporation in Pyrite at Ambient Temperature at Both Tetrahedral S-Iand Octahedral FeIISites: Evidence from EXAFS-DFT Analysis.
abstract: Pyrite is a ubiquitous mineral in reducing environments and is well-known to incorporate trace elements such as Co, Ni, Se, Au, and commonly As. Indeed, As-bearing pyrite is observed in a wide variety of sedimentary environments, making it a major sink for this toxic metalloid. Based on the observation of natural hydrothermal pyrites, As-Iis usually assigned to the occupation of tetrahedral S-Isites, with the same oxidation state as in arsenopyrite (FeAsS), although rare occurrences of AsIIIand AsIIhave been reported. However, the modes of As incorporation into pyrite during its crystallization under low-temperature diagenetic conditions have not yet been elucidated because arsenic acts as an inhibitor for pyrite nucleation at ambient temperature. Here, we provide evidence from X-ray absorption spectroscopy for AsII,IIIincorporation into pyrite at octahedral FeIIsites and for As-Iat tetrahedral S-Isites during crystallization at ambient temperature. Extended X-ray absorption fine structure (EXAFS) spectra of these As-bearing pyrites are explained by local structure models obtained using density functional theory (DFT), assuming incorporation of As at the Fe and S sites, as well as local clustering of arsenic. Such observations of As-Iincorporation at ambient temperature can aid in the understanding of the early formation of authigenic arsenian pyrite in subsurface sediments. Moreover, evidence for substitution of AsII,IIIfor Fe in our synthetic samples raises questions about both the possible occurrence and the geochemical reactivity of such As-bearing pyrites in low-temperature subsurface environments.
authors.affiliation: Institut de Minéralogie, de Physique des Matériaux et de Cosmochimie (IMPMC), UMR CNRS 7590, UPMC-IRD-MNHN, Sorbonne Universités , Campus Jussieu, 4 place Jussieu, 75252 Paris cedex 05, France.
authors.forename: Pierre
authors.initials: P
authors.lastname: Le Pape
authors.affiliation: Institut de Minéralogie, de Physique des Matériaux et de Cosmochimie (IMPMC), UMR CNRS 7590, UPMC-IRD-MNHN, Sorbonne Universités , Campus Jussieu, 4 place Jussieu, 75252 Paris cedex 05, France.
authors.forename: Marc
authors.initials: M
authors.lastname: Blanchard
authors.affiliation: Institut de Minéralogie, de Physique des Matériaux et de Cosmochimie (IMPMC), UMR CNRS 7590, UPMC-IRD-MNHN, Sorbonne Universités , Campus Jussieu, 4 place Jussieu, 75252 Paris cedex 05, France.
authors.forename: Jessica
authors.initials: J
authors.lastname: Brest
authors.affiliation: Institut de Minéralogie, de Physique des Matériaux et de Cosmochimie (IMPMC), UMR CNRS 7590, UPMC-IRD-MNHN, Sorbonne Universités , Campus Jussieu, 4 place Jussieu, 75252 Paris cedex 05, France.
authors.forename: Jean-Claude
authors.initials: JC
authors.lastname: Boulliard
authors.affiliation: Institut de Minéralogie, de Physique des Matériaux et de Cosmochimie (IMPMC), UMR CNRS 7590, UPMC-IRD-MNHN, Sorbonne Universités , Campus Jussieu, 4 place Jussieu, 75252 Paris cedex 05, France.
authors.forename: Maya
authors.initials: M
authors.lastname: Ikogou
authors.affiliation: Institut de Minéralogie, de Physique des Matériaux et de Cosmochimie (IMPMC), UMR CNRS 7590, UPMC-IRD-MNHN, Sorbonne Universités , Campus Jussieu, 4 place Jussieu, 75252 Paris cedex 05, France.
authors.forename: Lucie
authors.initials: L
authors.lastname: Stetten
authors.affiliation: Institut de Minéralogie, de Physique des Matériaux et de Cosmochimie (IMPMC), UMR CNRS 7590, UPMC-IRD-MNHN, Sorbonne Universités , Campus Jussieu, 4 place Jussieu, 75252 Paris cedex 05, France.
authors.forename: Shuaitao
authors.initials: S
authors.lastname: Wang
authors.affiliation: Synchrotron SOLEIL , F-91192 Gif Sur Yvette, France.
authors.forename: Gautier
authors.initials: G
authors.lastname: Landrot
authors.affiliation: Institut de Minéralogie, de Physique des Matériaux et de Cosmochimie (IMPMC), UMR CNRS 7590, UPMC-IRD-MNHN, Sorbonne Universités , Campus Jussieu, 4 place Jussieu, 75252 Paris cedex 05, France.
authors.forename: Guillaume
authors.initials: G
authors.lastname: Morin
mesh_terms: D001151:Arsenic; D005296:Ferrous Compounds; D007501:Iron / Q000737:chemistry; D010084:Oxidation-Reduction; D013696:Temperature; D056928:X-Ray Absorption Spectroscopy
chemical_list: D005296:Ferrous Compounds; D007501:Iron; D001151:Arsenic