Rigorous analysis of non-ideal solubility of sodium and copper chlorides in water vapor using Pitzer-Pabalan model

Velizhanin, Kirill A.; Alcorn, Christopher; Migdisov, Artas; Currier, Robert P.

doi:10.1016/j.fluid.2020.112731

Cited by 8 publications

(4 citation statements)

References 24 publications

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“…2b). Thus, above a hydration number between 3 and 6, which depends on the metal of interest (Au, Ag, Cu, and Mo), the energy of hydration (per water molecule added) approaches a constant similar to that calculated using theoretical models for water molecule cluster formation (Mejías and Lago, 2000;Velizhanin et al, 2020). Below, we use the observations described above to simulate metal transport in the continuum between vapor-like fluids and those of intermediate density.…”

Section: Limitations Of the Numerical Simulationsmentioning

confidence: 96%

Are Vapor-Like Fluids Viable Ore Fluids for Cu-Au-Mo Porphyry Ore Formation?

2021

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Ore formation in porphyry Cu-Au-(Mo) systems involves the exsolution of metal-bearing fluids from magmas and the transport of the metals in magmatic-hydrothermal plumes that are subject to pressure fluctuations. Deposition of ore minerals occurs as a result of cooling and decompression of the hydrothermal fluids in partly overlapping ore shells. In this study, we address the role of vapor-like fluids in porphyry ore formation through numerical simulations of metal transport using the Gibbs energy minimization software, GEM-Selektor. The thermodynamic properties of the hydrated gaseous metallic species necessary for modeling metal solubility in fluids of moderate density (100–300 kg/m3) were derived from the results of experiments that investigated the solubility of metals in aqueous HCl- and H2S-bearing vapors. Metal transport and precipitation were simulated numerically as a function of temperature, pressure, and fluid composition (S, Cl, and redox). The simulated metal concentrations and ratios are compared to those observed in vapor-like and intermediate-density fluid inclusions from porphyry ore deposits, as well as gas condensates from active volcanoes. The thermodynamically predicted solubility of Cu, Au, Ag, and Mo decreases during isothermal decompression. At elevated pressure, the simulated metal solubility is similar to the metal content measured in vapor-like and intermediate-density fluid inclusions from porphyry deposits (at ~200–1,800 bar). At ambient pressure, the metal solubility approaches the metal content measured in gas condensates from active volcanoes (at ~1 bar), which is several orders of magnitude lower than that in the high-pressure environment. During isochoric cooling, the simulated solubility of Cu, Ag, and Mo decreases, whereas that of Au reaches a maximum between 35 ppb and 2.6 ppm depending on fluid density and composition. Similar observations are made from a compilation of vapor-like and intermediate-density fluid inclusion data showing that Cu, Ag, and Mo contents decrease with decreasing P and T. Increasing the Cl concentration of the simulated fluid promotes the solubility of Cu, Ag, and Au chloride species. Molybdenum solubility is highest under oxidizing conditions and low S content, and gold solubility is elevated at intermediate redox conditions and elevated S content. The S content of the vapor-like fluid strongly affects metal ratios. Thus, there is a decrease in the Cu/Au ratio as the S content increases from 0.1 to 1 wt %, whereas the opposite is the case for the Mo/Ag ratio; at S contents of >1 wt %, the Mo/Ag ratio also decreases. In summary, thermodynamic calculations based on experiments involving gaseous metallic species predict that vapor-like fluids may transport and efficiently precipitate metals in concentrations sufficient to form porphyry ore deposits. Finally, the fluid composition and pressure-temperature evolution paths of vapor-like and intermediate-density fluids have a strong effect on metal solubility in porphyry systems and potentially exert an important control on their metal ratios and zoning.

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Section: Limitations Of the Numerical Simulationsmentioning

confidence: 96%

Are Vapor-Like Fluids Viable Ore Fluids for Cu-Au-Mo Porphyry Ore Formation?

2021

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“…Numerous experimental studies on the solubility of salts in water vapors, dating back to the 1960s, have shown that the measured solubilities are many orders of magnitude greater than those calculated based on the salt volatility. For example, the solubility of sodium chloride is controlled by NaCl·(H 2 O) n rather than NaCl. − …”

Section: Introductionmentioning

confidence: 99%

“…Quasi-chemical theory (QCT), which views water clusters as a quasi-reaction between water molecules and ion pairs (also known as neutral molecular salts), is one way to describe these hydrated metal clusters. − In principle, QCT can describe solution thermodynamics and phase equilibrium on the basis of fully defensible statistical mechanics developed from electronic structure calculations. ,− The focus of rigorous QCT is usually on characterization of compact hydration clusters in water and can use numerical data from any source, including molecular simulations. ,− Recently, a classical form of QCT based on a Pitzer–Pabalan model was applied to both NaCl and CuCl and successfully reproduced the available experimental data for the partial pressure of CuCl-bearing water clusters as a function of water fugacity in high-temperature vapor phases. Interestingly, experimentally derived estimates of the CuCl hydration number ( n ) at 553, 573, and 593 K show either a constant value of n in the range of 6–7.5 or a small increase with increasing water fugacity (which at constant temperature corresponds to increasing density and/or pressure) .…”

Section: Introductionmentioning

confidence: 99%

First-Principles Simulations of CuCl in High-Temperature Water Vapor

et al. 2021

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Experimental data suggest that the solubility of copper in high-temperature water vapor is controlled by the formation of hydrated clusters of the form CuCl(H2O) n , where the average number of water molecules in the cluster generally increases with increasing density [Migdisov, A. A.; et al. Geochim. Cosmochim. Acta 2014, 129, 33–53]. However, the precise nature of these clusters is difficult to probe experimentally. Moreover, there are some discrepancies between experimental estimates of average cluster size and prior simulation work [Mei, Y. Geofluids 2018, 2018, 4279124]. We have performed first-principles Monte Carlo (MC) and molecular dynamics (MD) simulations to explore these clusters in finer detail. We find that molecular dynamics is not the most appropriate technique for studying aggregation in vapor phases, even at relatively high temperatures. Specifically, our MD simulations exhibit substantial problems in adequately sampling the equilibrium cluster size distribution. In contrast, MC simulations with specialized cluster moves are able to accurately sample the phase space of hydrogen-bonding vapors. At all densities, we find a stable, slightly distorted linear H2O–Cu–Cl structure, which is in agreement with the earlier simulations, surrounded by a variable number of water molecules. The surrounding water molecules do not form a well-defined second solvation shell but rather a loose network of hydrogen-bonded water with molecular CuCl on the outside edge of the water cluster. We also find a broad distribution of hydration numbers, especially at higher densities. In contrast to previous simulation work but in agreement with experimental data, we find that the average hydration number substantially increases with increasing density. Moreover, the value of the hydration number depends on the choice of cluster definition.

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“…20 Finally, we will also perform electronic structure calculations to help parameterize and validate semi-empirical solubility models. 21 We will continue to build on our experience simulating aqueous electrolytes. Our earlier work on dynamic properties 22 as well as an evaluation of many of the common classical force field for aqueous NaCl 23 has given us a good foundation from which to proceed.…”

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confidence: 99%

Salts in Hot Water: Developing a Scientific Basis for Supercritical Desalination and Strategic Metal Recovery

Maerzke

Patel

Yoon

2020

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Given the steady growth in world population and the ever-increasing fresh water demand, the only sustainable water supply option is desalination. Conceptually, desalination is very simple-just separate dissolved salts from water. While desalination research programs have existed since the 1960s and have resulted in a multitude of approaches, realizing affordable desalination has proven to be a challenge. Our goal is to meet this challenge using low cost heat sources to drive a liquid-discharge-free desalination process that can be co-mingled with the extraction of economically valuable co-products. High temperatures and pressures will be used to manipulate water's properties, such as the dielectric constant, and hence its ability to solvate ions. Selective precipitation/recovery of valuable metal co-products creates new revenue streams (i.e., cost offsets). We will develop the scientific understanding necessary to control salt precipitation from supercritical seawater, inland brines, and water commonly co-produced with oil and gas. Atomistic simulations will be used to understand at a molecular level the changes in hydrogen bonding and ion solvation that occur as we increase the temperature and/or pressure and change the density and ion concentration. Our simulation results will also aid in the interpretation of experimental data and guide the development of applied thermodynamic models for engineering design calculations. Technical Description: Affordable desalination should include the use of less-expensive energy and comingle desalination with other profitable ventures. Specifically, if a desalination method could be driven with less expensive thermal energy sources and include the recovery of strategic metals as co-products that offset costs, it would be game changing. Our proposed method (LDRD 20190057DR) accomplishes this by selectively precipitating salts from supercritical water. This innovative method (a) exploits molecular properties of water under supercritical (SC) conditions, (b) recovers valuable metals (e.g., lithium and rare earth elements), and (c) can be powered by inexpensive energy sources (e.g., thermal energy). By controlling temperature and density, the properties of water can be manipulated. Water essentially acts as a dielectric to screen ionic charges, which is central to its role as a solvent. However, the dielectric constant degrades significantly above the critical point (TC=647 K, PC=218 atm, C=0.322 g/cm 3). Under SC conditions, dielectric properties are altered dramatically as the thermal energy associated with the higher temperature randomizes the water dipole orientations and disrupts the hydrogen bond network. Under lower density SC conditions, water's ability to solvate ions and ionic complexes is degraded and it becomes a surprisingly poor solvent for ions. 1-4 Salt precipitation under SC conditions is well documented. For example, measurements of NaCl solubility in SC water 5, 6 show its solubility to be below the limit required for drinking water. Salt precipitation from SC ...

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Rigorous analysis of non-ideal solubility of sodium and copper chlorides in water vapor using Pitzer-Pabalan model

Cited by 8 publications

References 24 publications

Are Vapor-Like Fluids Viable Ore Fluids for Cu-Au-Mo Porphyry Ore Formation?

Are Vapor-Like Fluids Viable Ore Fluids for Cu-Au-Mo Porphyry Ore Formation?

First-Principles Simulations of CuCl in High-Temperature Water Vapor

Salts in Hot Water: Developing a Scientific Basis for Supercritical Desalination and Strategic Metal Recovery

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