title: Evolution of uranium distribution and speciation in mill tailings, COMINAK Mine, Niger.
abstract: This study investigated the evolution of uranium distribution and speciation in mill tailings from the COMINAK mine (Niger), in production since 1978. A multi-scale approach was used, which combined high resolution remote sensing imagery, ICP-MS bulk rock analyses, powder X-ray diffraction, Scanning Electron Microscopy, Focused Ion Beam--Transmission Electron Microscopy and X-ray Absorption Near Edge Spectroscopy. Mineralogical analyses showed that some ore minerals, including residual uraninite and coffinite, undergo alteration and dissolution during tailings storage. The migration of uranium and other contaminants depends on (i) the chemical stability of secondary phases and sorbed species (dissolution and desorption processes), and (ii) the mechanical transport of fine particles bearing these elements. Uranium is stabilized after formation of secondary uranyl sulfates and phosphates, and adsorbed complexes on mineral surfaces (e.g. clay minerals). In particular, the stock of insoluble uranyl phosphates increases with time, thus contributing to the long-term stabilization of uranium. At the surface, a sulfate-cemented duricrust is formed after evaporation of pore water. This duricrust limits water infiltration and dust aerial dispersion, though it is enriched in uranium and many other elements, because of pore water rising from underlying levels by capillary action. Satellite images provided a detailed description of the tailings pile over time and allow monitoring of the chronology of successive tailings deposits. Satellite images suggest that uranium anomalies that occur at deep levels in the pile are most likely former surface duricrusts that have been buried under more recent tailings.
authors.affiliation: Institut de Minéralogie, de Physique des Matériaux et de Cosmochimie, Case 115, 4 place Jussieu, 75005 Paris, France; Université Paris Diderot - Paris VII, 5 rue Thomas Mann, 75013 Paris, France. Electronic address: adrien.dejeant@normalesup.org.
authors.forename: Adrien
authors.initials: A
authors.lastname: Déjeant
authors.affiliation: Institut de Minéralogie, de Physique des Matériaux et de Cosmochimie, Case 115, 4 place Jussieu, 75005 Paris, France; Université Pierre et Marie Curie - Paris VI, 4 place Jussieu, 75005 Paris, France.
authors.forename: Laurence
authors.initials: L
authors.lastname: Galoisy
authors.affiliation: AREVA Mines - Geoscience Department, Tour AREVA, 1 place Jean Millier, 92084 Paris, La Défense, France.
authors.forename: Régis
authors.initials: R
authors.lastname: Roy
authors.affiliation: Institut de Minéralogie, de Physique des Matériaux et de Cosmochimie, Case 115, 4 place Jussieu, 75005 Paris, France; Université Pierre et Marie Curie - Paris VI, 4 place Jussieu, 75005 Paris, France.
authors.forename: Georges
authors.initials: G
authors.lastname: Calas
authors.affiliation: Institut de Minéralogie, de Physique des Matériaux et de Cosmochimie, Case 115, 4 place Jussieu, 75005 Paris, France; Université Pierre et Marie Curie - Paris VI, 4 place Jussieu, 75005 Paris, France.
authors.forename: Flora
authors.initials: F
authors.lastname: Boekhout
authors.affiliation: AREVA Mines - R&D Department, BAL 0414C-2, Tour AREVA, 1 place Jean Millier, 92084 Paris, La Défense, France.
authors.forename: Vannapha
authors.initials: V
authors.lastname: Phrommavanh
authors.affiliation: AREVA Mines - R&D Department, BAL 0414C-2, Tour AREVA, 1 place Jean Millier, 92084 Paris, La Défense, France.
authors.forename: Michael
authors.initials: M
authors.lastname: Descostes
mesh_terms: D004784:Environmental Monitoring; D008906:Mining; D009548:Niger; D063809:Satellite Imagery; D012990:Soil Pollutants, Radioactive / Q000032:analysis*; D014501:Uranium / Q000032:analysis*
chemical_list: D012990:Soil Pollutants, Radioactive; D014501:Uranium
keywords: Focused Ion Beam–Transmission Electron Microscopy; ICP-MS bulk rock analyses; Mill tailings; Mine waste; Monitoring; Powder X-ray diffraction; Radioactive waste management; Remote sensing; Scanning Electron Microscopy; Xanes