Quick Search:    advanced search

GSW Home   GeoRef Home   My GSW Alerts   Contact GSW   About GSW   Journals List   Help

This Article Résumé Full Text (PDF) Submit a response Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in Web of Science Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Web of Science (15) Citing Articles via Google Scholar Google Scholar Articles by Morin, G. Articles by Borensztajn, S. Search for Related Content GeoRef GeoRef Citation

EXAFS evidence of sorbed arsenic(V) and pharmacosiderite in a soil overlying the Echassières geochemical anomaly, Allier, France

Guillaume Morin¹, Delphine Lecocq¹, Farid Juillot¹, Georges Calas¹, Philippe Ildefonse, Stéphanie Belin², Valérie Briois², Philippe Dillmann², Pierre Chevallier², Christophe Gauthier³, Armando Sole³, Pierre-Emmanuel Petit³ and Stephan Borensztajn⁴

¹ Laboratoire de Minéralogie-Cristallographie, UMR CNRS 7590, Universités Paris 6 et 7, et IPGP 4 Place Jussieu, 75252 Paris cedex 05, France.
² Laboratoire pour l’Utilisation du Rayonnement Synchrotron, LURE, CNRS/CEA/MEN, Bat. 209 D, 91405 Orsay cedex, France.
³ European Synchrotron Radiation Facility, ESRF, BP20, Grenoble, France.
⁴ Laboratoire de Physique des Liquides et Electrochimie, Université Paris 6, France.

Abstract

At Echassières (Allier, France), arsenic speciation was determined in a soil developed over a micaschist where Hercynian hydrothermal mineralization, including arsenopyrite FeAsS and löllingite FeAs₂, has lead to a regional As anomaly. The overlying soils which have developed from long term weathering exhibit As levels as high as 900 ppm in the richest area, where the saprolite contains up to 5200 ppm As. Analysis by powder XRD, µ-X-ray diffraction on the 20µm scale, SEM-EDS and electron micro-probe analyses revealed that As, released from arsenopyrite and/or löllingite alteration, is concentrated in a secondary iron arsenate, pharmacosiderite, (Ba_x,K_2-2x) (Fe,Al)₄ (AsO₄)₃ (OH)₅ • 6H₂O. Quantitative mineralogical analysis by Rietveld refinement indicates that the proportion of As hosted by this mineral decreases systematically from the saprolite to the topsoil (from 70 % to 30 % of the total bulk As content, respectively). EXAFS spectroscopy indicates that the main form of the As occurring with pharmacosiderite, consists of As(V) ions sorbed on iron oxides. Sorption processes, which dominate As speciation in the topsoil horizons, appear as a key mechanism able to delay As dissemination from soils to plant and surface waters, provided that pH and Eh conditions remain sufficiently acidic and oxidizing, respectively.

Key Words: Arsenic • Soils • Speciation • EXAFS • Iron-oxides

This article has been cited by other articles:

				S. R. Walker, M. B. Parsons, H. E. Jamieson, and A. Lanzirotti ARSENIC MINERALOGY OF NEAR-SURFACE TAILINGS AND SOILS: INFLUENCES ON ARSENIC MOBILITY AND BIOACCESSIBILITY IN THE NOVA SCOTIA GOLD MINING DISTRICTS Can Mineral, June 1, 2009; 47(3): 533 - 556. [Abstract] [Full Text] [PDF]

				M. F. Lengke, C. Sanpawanitchakit, and R. N. Tempel THE OXIDATION AND DISSOLUTION OF ARSENIC-BEARING SULFIDES Can Mineral, June 1, 2009; 47(3): 593 - 613. [Abstract] [Full Text] [PDF]

				G. Morin and G. Calas Arsenic in Soils, Mine Tailings, and Former Industrial Sites Elements, April 1, 2006; 2(2): 97 - 101. [Abstract] [Full Text] [PDF]

				S. R. Walker, H. E. Jamieson, A. Lanzirotti, C. F. Andrade, and G. E.M. Hall THE SPECIATION OF ARSENIC IN IRON OXIDES IN MINE WASTES FROM THE GIANT GOLD MINE, N.W.T.: APPLICATION OF SYNCHROTRON MICRO-XRD AND MICRO-XANES AT THE GRAIN SCALE Can Mineral, August 1, 2005; 43(4): 1205 - 1224. [Abstract] [Full Text] [PDF]