Solid-phase speciation of arsenic in abandoned mine wastes from the northern Puna of Argentina using X-ray absorption spectroscopy

2016 ◽  
pp. 265-267
Author(s):  
N Nieva ◽  
L Borgnino ◽  
M García
Keyword(s):  
Absorption Spectroscopy ◽  
Solid Phase ◽  
Abandoned Mine ◽  
Mine Wastes ◽  
X Ray ◽  
X Ray Absorption

scholarly journals Melting of iron determined by X-ray absorption spectroscopy to 100 GPa

2015 ◽  
Vol 112 (39) ◽  
pp. 12042-12045 ◽  
Author(s):  
Giuliana Aquilanti ◽  
Angela Trapananti ◽  
Amol Karandikar ◽  
Innokenty Kantor ◽  
Carlo Marini ◽  
...  
Keyword(s):  
Melting Temperature ◽  
Absorption Spectroscopy ◽  
Inner Core ◽  
Solid Phase ◽  
Melting Curve ◽  
X Ray ◽  
Core Boundary ◽  
Diamond Anvil ◽  
Laser Heated ◽  
X Ray Absorption

Temperature, thermal history, and dynamics of Earth rely critically on the knowledge of the melting temperature of iron at the pressure conditions of the inner core boundary (ICB) where the geotherm crosses the melting curve. The literature on this subject is overwhelming, and no consensus has been reached, with a very large disagreement of the order of 2,000 K for the ICB temperature. Here we report new data on the melting temperature of iron in a laser-heated diamond anvil cell to 103 GPa obtained by X-ray absorption spectroscopy, a technique rarely used at such conditions. The modifications of the onset of the absorption spectra are used as a reliable melting criterion regardless of the solid phase from which the solid to liquid transition takes place. Our results show a melting temperature of iron in agreement with most previous studies up to 100 GPa, namely of 3,090 K at 103 GPa.

scholarly journals Solid-phase arsenic speciation in aquifer sediments: A micro-X-ray absorption spectroscopy approach for quantifying trace-level speciation

2017 ◽  
Vol 211 ◽  
pp. 228-255 ◽  
Author(s):  
Sarah L. Nicholas ◽  
Melinda L. Erickson ◽  
Laurel G. Woodruff ◽  
Alan R. Knaeble ◽  
Matthew A. Marcus ◽  
...  
Keyword(s):  
Absorption Spectroscopy ◽  
Solid Phase ◽  
Arsenic Speciation ◽  
Trace Level ◽  
X Ray ◽  
Aquifer Sediments ◽  
X Ray Absorption

scholarly journals Uranium (VI) Adsorbate Structures on Portlandite [Ca(OH)2] Type Surfaces Determined by Computational Modelling and X-Ray Absorption Spectroscopy

Minerals ◽  
2021 ◽  
Vol 11 (11) ◽  
pp. 1241
Author(s):  
Christopher A. Lee ◽  
Arjen van Veelen ◽  
Katherine Morris ◽  
J. Fred W. Mosselmans ◽  
Roy A. Wogelius ◽  
...  
Keyword(s):  
Absorption Spectroscopy ◽  
Density Functional ◽  
Solid Phase ◽  
Computational Modelling ◽  
Potential Of Mean Force ◽  
Atomic Scale ◽  
Ex Situ ◽  
Geological Disposal ◽  
X Ray ◽  
X Ray Absorption

Portlandite [Ca(OH)2] is a potentially dominant solid phase in the high pH fluids expected within the cementitious engineered barriers of Geological Disposal Facilities (GDF). This study combined X-Ray Absorption Spectroscopy with computational modelling in order to provide atomic-scale data which improves our understanding of how a critically important radionuclide (U) will be adsorbed onto this phase under conditions relevant to a GDF environment. Such data are fundamental for predicting radionuclide mass transfer. Surface coordination chemistry and speciation of uranium with portlandite [Ca(OH)2] under alkaline groundwater conditions (ca. pH 12) were determined by both in situ and ex situ grazing incidence extended X-ray absorption fine structure analysis (EXAFS) and by computational modelling at the atomic level. Free energies of sorption of aqueous uranyl hydroxides, [UO2(OH)n]2-n (n = 0–5) with the (001), (100) and (203) or (101) surfaces of portlandite are predicted from the potential of mean force using classical molecular umbrella sampling simulation methods and the structural interactions are further explored using fully periodic density functional theory computations. Although uranyl is predicted to only weakly adsorb to the (001) and (100) clean surfaces, there should be significantly stronger interactions with the (203/101) surface or at hydroxyl vacancies, both prevalent under groundwater conditions. The uranyl surface complex is typically found to include four equatorially coordinated hydroxyl ligands, forming an inner-sphere sorbate by direct interaction of a uranyl oxygen with surface calcium ions in both the (001) and (203/101) cases. In contrast, on the (100) surface, uranyl is sorbed with its axis more parallel to the surface plane. The EXAFS data are largely consistent with a surface structural layer or film similar to calcium uranate, but also show distinct uranyl characteristics, with the uranyl ion exhibiting the classic dioxygenyl oxygens at 1.8 Å and between four and five equatorial oxygen atoms at distances between 2.28 and 2.35 Å from the central U absorber. These experimental data are wholly consistent with the adsorbate configuration predicted by the computational models. These findings suggest that, under the strongly alkaline conditions of a cementitious backfill engineered barrier, there would be significant uptake of uranyl by portlandite to inhibit the mobility of U(VI) from the near field of a geological disposal facility.

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