Silver in geological fluids from in situ X-ray absorption spectroscopy and first-principles molecular dynamics

Pokrovski, Gleb S.; Roux, Jacques; Ferlat, G.; Jonchiere, Romain; Seitsonen, Ari P.; Vuilleumier, Rodolphe; Hazemann, Jean‐Louis

doi:10.1016/j.gca.2012.12.012

Cited by 47 publications

(24 citation statements)

References 106 publications

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“…For all compositions, the fit parameters included the number of neighboring atoms, N, around the central Br atom, the average distance, d, to the central Br atom, the Debye-Waller factor, σ 2 , characterizing the degree of disorder present in the signal, the amplitude reduction factor, S 0 2 , and the difference between the initial model nearest neighbor distance and the real distance, ΔE 0 . All the fits were conducted with a kweighting of 1 and 2 to decrease correlations between N and σ 2 (Pokrovski et al, 2013). The fits were also performed assuming that the theoretical backscattering amplitude and phase shift functions could The water content was determined after calculating the ratio, R w/s , between the "silicate" region's area, A s, and the "water" region's area, A w , as R w/s = A w / A s , then correlating it with the empirical calibration of Losq et al (2012).…”

Section: Exafs Data Analysismentioning

confidence: 99%

Bromine speciation in hydrous silicate melts at high pressure

et al. 2015

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International audienceBr speciation in hydrous silicate melts at high pressure has been investigated up to 7.6 GPa using X-ray Absorption Spectroscopy (XAS) at the Br K-edge in a Paris-Edinburgh press. Br in silicate melts is surrounded by an average of 6 Na cations, a number slightly increasing with pressure (5.8 to 6.6), with a Br-Na distance increasing from 3.49 to 3.72 Å. Two oxygens, either from a water, an –OH molecule or from the tetrahedral silicate network, with an average Br-O distance of 1.80 Å, form the closest coordination shell around Br ions. The persistence of an alkali shell around Br, in a structure similar to crystalline NaBr, throughout the pressure range investigated shows that Br can be retained in the melt structure at relatively high pressure and supports the idea of its deep recycling. Finally, our results confirm that Br could be efficiently degassed with water at low pressures and that Br may also have been efficiently degassed along with water during the early stages of an oxidized magma ocean

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Section: Exafs Data Analysismentioning

confidence: 99%

Bromine speciation in hydrous silicate melts at high pressure

et al. 2015

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“…However, they conclude that there remain major challenges, both experimental and in modelling, to fully understand vapour transport of ore components, a status comparable to that of liquid solution transport decades ago . Regimes for various hydrothermal fluids compared to the densities and critical curve for water, the heavy line up to the critical point of water at 344.7 ºC, 215.4 bars (modified from Pokrovski et al, 2013).…”

Section: Metal Complexes Referencesmentioning

confidence: 99%

Hydrothermal Processes: The Development of Geochemical Concepts in the Latter Half of the Twentieth Century

Barnes¹

2015

Geochem. Persp.

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“…Enabled by advances in computing power and algorithms, molecular dynamics simulations have been applied increasingly to the study of metal speciation in hydrothermal liquids (e.g., Cu(I)-Cl -, [13,14]; Au(I)-HS -, [15]; Ag(I)-Cl -, [16,17]; Au(I)-HS -/OH -/S 3 -, [18,19]; Cu(I)-HS -/Cl -, [20]; Au(I)-Cl -, [14]; Pd(II)-Cl -/HS -, [21]; Zn(II)-Cl -/HS -, [22,23]; Ag(I)-HS -/OH -, [24]; Cu(I)-Ac -, [25]). These studies have demonstrated the importance of MD in understanding metal complexation at the molecular-level and, in some cases, have provided complementary information that helped resolve apparent discrepancies in the interpretation of experimental results [13,22].…”

Section: Introductionmentioning

confidence: 99%

CuCl Complexation in the Vapor Phase: Insights from Ab Initio Molecular Dynamics Simulations

et al. 2018

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We investigated the hydration of the CuCl 0 complex in HCl-bearing water vapor at 350 ∘ C and a vapor-like fluid density between 0.02 and 0.09 g/cm 3 using ab initio molecular dynamics (MD) simulations. The simulations reveal that one water molecule is strongly bonded to Cu(I) (first coordination shell), forming a linear [H 2 O-Cu-Cl] 0 moiety. The second hydration shell is highly dynamic in nature, and individual configurations have short life-spans in such low-density vapors, resulting in large fluctuations in instantaneous hydration numbers over a timescale of picoseconds. The average hydration number in the second shell (m) increased from ∼0.5 to ∼3.5 and the calculated number of hydrogen bonds per water molecule increased from 0.09 to 0.25 when fluid density (which is correlated to water activity) increased from 0.02 to 0.09 g/cm 3 ( H 2 O 1.72 to 2.05). These changes of hydration number are qualitatively consistent with previous solubility studies under similar conditions, although the absolute hydration numbers from MD were much lower than the values inferred by correlating experimental Cu fugacity with water fugacity. This could be due to the uncertainties in the MD simulations and uncertainty in the estimation of the fugacity coefficients for these highly nonideal "vapors" in the experiments. Our study provides the first theoretical confirmation that beyond-first-shell hydrated metal complexes play an important role in metal transport in low-density hydrothermal fluids, even if it is highly disordered and dynamic in nature.

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Silver in geological fluids from in situ X-ray absorption spectroscopy and first-principles molecular dynamics

Cited by 47 publications

References 106 publications

Bromine speciation in hydrous silicate melts at high pressure

Bromine speciation in hydrous silicate melts at high pressure

Hydrothermal Processes: The Development of Geochemical Concepts in the Latter Half of the Twentieth Century

CuCl Complexation in the Vapor Phase: Insights from Ab Initio Molecular Dynamics Simulations

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