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

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 2O-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 ( f H 2O 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. Finally, 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.
Authors:
ORCiD logo [1] ; ORCiD logo [2] ; ORCiD logo [3] ; ORCiD logo [4] ;  [5]
  1. Commonwealth Scientific and Industrial Research Organization (CSIRO), Clayton, VIC (Australia); Monash Univ., Melbourne, VIC (Australia). School of Earth, Atmosphere and Environment
  2. Commonwealth Scientific and Industrial Research Organization (CSIRO), Clayton, VIC (Australia)
  3. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
  4. Monash Univ., Melbourne, VIC (Australia). School of Earth, Atmosphere and Environment
  5. McGill Univ., Montreal, QC (Canada). Earth and Planetary Sciences
Publication Date:
Report Number(s):
LA-UR-17-31093
Journal ID: ISSN 1468-8115
Grant/Contract Number:
AC52-06NA25396
Type:
Accepted Manuscript
Journal Name:
Geofluids
Additional Journal Information:
Journal Volume: 2018; Journal ID: ISSN 1468-8115
Publisher:
Wiley
Research Org:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Sponsoring Org:
Australian Research Council (ARC); USDOE; CSIRO Office of the Chief Executive (OCE)
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES; Earth Sciences; Copper chloride; AIMD; hydrothermal; vapor transport
OSTI Identifier:
1440484