Equations of state for aqueous solutions under mantle conditions

Zhang, Zhigang; Zhang, Chi; Geng, Ming

doi:10.1007/s11430-016-5299-3

Cited by 5 publications

(3 citation statements)

References 75 publications

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“…Sverjensky et al (2014a) found a good correlation between dielectric constant and H 2 O density, which enabled them to extend the HKF model to 6 GPa and 1200°C, becoming the Deep Earth Water (DEW) model. More than being applicable to a broader range of temperature and pressure, the DEW model incorporates hundreds of molecular and ionic species and can address fluid interaction with solid phases, and is one of the most important developments in the field of deep fluids (Zhang et al, 2016). Still, polymerized Si-Al-Na species are still not covered in the DEW database, which hinders its applicability to silicate-rich fluids (Huang and Sverjensky, 2019).…”

Section: Methods For Slab Fluid Chemistrymentioning

confidence: 99%

Dehydration at subduction zones and the geochemistry of slab fluids

2020

Sci. China Earth Sci.

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Subducting oceanic slabs undergo metamorphic dehydration with the increase of temperature and pressure during subduction. Dehydration is an essential step for element recycling, and slab fluids are critical agents for mediating slab-mantle interaction. Dehydration is mainly controlled by the thermal structure of subduction zones and the stability of hydrous minerals. At fore-arc depths, slab dehydration produces aqueous fluid with dissolved salts such as NaCl. As subduction proceeds deeper, the content of silicate components increases. At sub-arc and post-arc depths, a hydrous silicate melt is likely to form, or a supercritical fluid could arise from complete miscibility between silicates and H 2 O. The partitioning of elements between slab fluid and the residual solid rock is controlled by the type of fluid, and generally it is the supercritical fluid that is the most capable of mobilizing trace elements, being an effective carrier even for high field strength elements. Understanding the chemistry of slab fluids relies on sophisticated integration of experiments, theoretical computation and investigation of natural rock samples. This contribution focuses on the content and speciation of key volatiles, including carbon, nitrogen and sulfur, in slab fluids as well as important fluid properties such as oxygen fugacity and acidity. The properties of slab fluids show complicated variation under the control of mineral assemblages and T-P conditions. Slab fluids at great depths of subductions have been inferred to be modestly alkaline and not necessarily very oxidizing as often assumed. Further progress in the research of slab dehydration and the chemistry and properties of slab fluids demands urgently the development of innovative experimental and computational technology including in situ analytical methods at high T-P.

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Section: Methods For Slab Fluid Chemistrymentioning

confidence: 99%

Dehydration at subduction zones and the geochemistry of slab fluids

2020

Sci. China Earth Sci.

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“…Since the 1970s, many thermodynamic models have been proposed for N 2 in geological fluids, and most of them are EOS. ,, Despite this, thermodynamic models with a simple or compact form, high or acceptable accuracy, and a wide valid range are still scarce for N 2 , although some of them have one or two of the three features.…”

Section: Introductionmentioning

confidence: 99%

Molecular Dynamics Simulations and a Quintic Equation of State for Nitrogen in a Wide P–T Range, with Validation of a Reference Model up to Ultrahigh P–T Conditions

Guo

Jiang

et al. 2022

J. Chem. Eng. Data

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Pressure−density−temperature data of nitrogen (N 2 ) at 589 state points are obtained by molecular dynamics simulations at 1573.15−3273.15 K and 500−3500 MPa (using NPT ensemble) or 0.2−0.5 g•cm −3 (using NVT ensemble). The results agree well with those of experiments at high temperatures and pressures, and the Helmholtz free energy model of Span et al. [J. Phys. Chem. Ref. Data 2000, 29, 1361−1433. The model of Span et al. is confirmed to be valid to at least 6000 K and 30000 MPa (or 2.0 g•cm −3 ) using the new and previous data, as well as thermodynamic analysis. Using this model as a reference, a quintic equation of state (EOS) is developed for supercritical N 2 . Compared to the reference model, the volume deviations of the EOS are within 0.21% at 273−4273 K, 0−4300 MPa, and 0−1.035 g•cm −3 . The EOS compares well with the new simulation results and previous experimental and simulated data at high pressures and temperatures. It is capable of accurate prediction of fugacity coefficient, residual enthalpy and entropy, and other properties. It can also be extrapolated to lower temperatures or higher temperatures and densities, but with lowering of accuracy.

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“…[10] are generally smaller than the results obtained by Zhang and Duan's EOS [11] in 2009, which was designed for C-O-H fluids in Earth's mantle. It was recently reported [25] that for CO 2 -H 2 O binary systems, the EOS in Ref. [10] performs better than the one in Ref.…”

Section: Introductionmentioning

confidence: 99%

Large Presence of Carbonic Acid in CO₂-Rich Aqueous Fluids under Earth’s Mantle Conditions

Stolte

Pan

2019

J. Phys. Chem. Lett.

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The chemistry of carbon in aqueous fluids at extreme pressure and temperature conditions is of great importance to Earth's deep carbon cycle, which substantially affects the carbon budget at Earth's surface and global climate change. At ambient conditions, the concentration of carbonic acid in water is negligible, so aqueous carbonic acid was simply ignored in previous geochemical models. However, by applying extensive ab initio molecular dynamics simulations at pressure and temperature conditions similar to those in Earth's upper mantle, we found that carbonic acid can be the most abundant carbon species in aqueous CO 2 solutions at ∼10 GPa and 1000 K. The mole percent of carbonic acid in total dissolved carbon species increases with increasing pressure along an isotherm, while its mole percent decreases with increasing temperature along an isobar.In CO 2 -rich solutions, we found significant proton transfer between carbonic acid molecules and bicarbonate ions, which may enhance the conductivity of the solutions. The effects of pH buffering by carbonic acid may play an important role in water-rock interactions in Earth's interior. Our findings suggest that carbonic acid is an important carbon carrier in the deep carbon cycle.

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Equations of state for aqueous solutions under mantle conditions

Cited by 5 publications

References 75 publications

Dehydration at subduction zones and the geochemistry of slab fluids

Dehydration at subduction zones and the geochemistry of slab fluids

Molecular Dynamics Simulations and a Quintic Equation of State for Nitrogen in a Wide P–T Range, with Validation of a Reference Model up to Ultrahigh P–T Conditions

Large Presence of Carbonic Acid in CO₂-Rich Aqueous Fluids under Earth’s Mantle Conditions

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Equations of state for aqueous solutions under mantle conditions

Cited by 5 publications

References 75 publications

Dehydration at subduction zones and the geochemistry of slab fluids

Dehydration at subduction zones and the geochemistry of slab fluids

Molecular Dynamics Simulations and a Quintic Equation of State for Nitrogen in a Wide P–T Range, with Validation of a Reference Model up to Ultrahigh P–T Conditions

Large Presence of Carbonic Acid in CO2-Rich Aqueous Fluids under Earth’s Mantle Conditions

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Large Presence of Carbonic Acid in CO₂-Rich Aqueous Fluids under Earth’s Mantle Conditions