Brine System Research Articles

Influence of Chitosan Salt on Capillary Pressure and Interfacial Tensions of CO2/Brine and H2/Brine Systems

Influence of Chitosan Salt on Capillary Pressure and Interfacial Tensions of CO₂/Brine and H₂/Brine Systems

CO2 geological storage in subsurface aquifers as a function of brine salinity: A field-scale numerical investigation

Subsurface aquifers demonstrate a broad range of salinities and salt compositions, affecting the physicochemical characteristics of the CO2/brine/rock systems, which in turn, influence the CO2 trapping of the aquifer formation. Available simulation studies generally focus on single NaCl systems and do not adequately account for the variations in salt types. In this study, the impact of salinity and salt type on several key parameters, including wettability, interfacial tension, brine properties, diffusion, and capillary pressure, were considered within the context of underground CO2 storage. We conducted pore network modeling to assess the impact of salinity (i.e., pure water, 1 M (molality), 3 M, and 5 M) and salt type (i.e., NaCl, CaCl2, and MgCl2) on the residual trapping behaviors. Subsequently, these findings were utilized in field-scale simulations to assess the influence of various salinities and salt types on the CO2 trapping capacity in a single salt brine system. The pore network modeling results showed that residual CO2 saturation decreases in higher salinity conditions, with the lowest value in MgCl2 brine system. In field-scale simulations incorporating residual trapping alone, the residual trapping capacity decreases in higher salinity NaCl brine systems. However, in high salinity MgCl2 brine, increased viscosity and density lead to a widespread CO2 plume, leading to an increased residual trapping capacity. This plume spread difference also influences the amount of dissolved CO2 in scenarios considering dissolution trapping alone. When considering both trapping mechanisms, our observations indicate that a decrease in dissolution trapping under high salinity and divalent cations conditions leads to enhanced residual trapping (e.g., ∼51.56% for 5 M MgCl2) - suggesting an interplay or codependency between these two mechanisms. The influences of diffusion and capillary pressure on the CO2 geo-storage trapping capacity are also investigated. Overall, an aquifer containing lower salinity brine composed of monovalent ions exhibits lower residual trapping, greater dissolution trapping, and lower mobile CO2. Especially, the pure water system exhibits the lowest percentage of mobile CO2 (∼13.72%). We also highlight that this impact is not governed by the corresponding wettability shift alone; rather, the physical properties of native brine (i.e., viscosity and density) play a part too. The findings help evaluate the CO2 storage potential of aquifers and thus assist in de-risking large-scale storage projects.

Predicting CO2 and H2 Solubility in Pure Water and Various Aqueous Systems: Implication for CO2–EOR, Carbon Capture and Sequestration, Natural Hydrogen Production and Underground Hydrogen Storage

The growing energy demand and the need for climate mitigation strategies have spurred interest in the application of CO2–enhanced oil recovery (CO2–EOR) and carbon capture, utilization, and storage (CCUS). Furthermore, natural hydrogen (H2) production and underground hydrogen storage (UHS) in geological media have emerged as promising technologies for cleaner energy and achieving net–zero emissions. However, selecting a suitable geological storage medium is complex, as it depends on the physicochemical and petrophysical characteristics of the host rock. Solubility is a key factor affecting the above–mentioned processes, and it is critical to understand phase distribution and estimating trapping capacities. This paper conducts a succinct review of predictive techniques and present novel simple and non–iterative predictive models for swift and reliable prediction of solubility behaviors in CO2–brine and H2–brine systems under varying conditions of pressure, temperature, and salinity (T–P–m salts), which are crucial for many geological and energy–related applications. The proposed models predict CO2 solubility in CO2 + H2O and CO2 + brine systems containing mixed salts and various single salt systems (Na+, K+, Ca2+, Mg2+, Cl−, SO42−) under typical geological conditions (273.15–523.15 K, 0–71 MPa), as well as H2 solubility in H2 + H2O and H2 + brine systems containing NaCl (273.15–630 K, 0–101 MPa). The proposed models are validated against experimental data, with average absolute errors for CO2 solubility in pure water and brine ranging between 8.19 and 8.80% and for H2 solubility in pure water and brine between 4.03 and 9.91%, respectively. These results demonstrate that the models can accurately predict solubility over a wide range of conditions while remaining computationally efficient compared to traditional models. Importantly, the proposed models can reproduce abrupt variations in phase composition during phase transitions and account for the influence of different ions on CO2 solubility. The solubility models accurately capture the salting–out (SO) characteristics of CO2 and H2 gas in various types of salt systems which are consistent with previous studies. The simplified solubility models for CO2 and H2 presented in this study offer significant advantages over conventional approaches, including computational efficiency and accuracy across a wide range of geological conditions. The explicit, derivative–continuous nature of these models eliminates the need for iterative algorithms, making them suitable for integration into large–scale multiphase flow simulations. This work contributes to the field by offering reliable tools for modeling solubility in various subsurface energy and environmental–related applications, facilitating their application in energy transition strategies aimed at reducing carbon emissions.

Radiolytic support for oxidative metabolism in an ancient subsurface brine system

Abstract Long-isolated subsurface brine environments (Ma-Ga residence times) may be habitable if they sustainably provide substrates, e.g. through water-rock reaction, that support microbial catabolic energy yields exceeding maintenance costs. The relative inaccessibility and low biomass of such systems has led to limited understanding of microbial taxonomic distribution, metabolism, and survival under abiotic stress exposure in these extreme environments. In this study, taxonomic and metabolic annotations of 95 single cell amplified genomes (SAGs) were obtained for one low biomass (103–104 cells/mL), hypersaline (246 g/L), radiolytically enriched brine obtained from 3.1 km depth in South Africa’s Moab Khotsong mine. The majority of SAGs belonged to three halophilic families (Halomondaceae (58%), Microbacteriaceae (24%), and Idiomarinaceae (8%)) and did not overlap with any family-level identifications from service water or a less saline dolomite aquifer sampled in the same mine. Functional annotation revealed complete metabolic modules for aerobic heterotrophy (organic acids and xenobiotics oxidation), fermentation, denitrification and thiosulfate oxidation, suggesting metabolic support in a microoxic environment. SAGs also contained complete modules for degradation of complex organics, amino acid and nucleotide synthesis, and motility. This work highlights a long-isolated subsurface fluid system with microbial metabolism fueled by radiolytically generated substrates, including O2, and suggests subsurface brines with high radionuclide concentrations as putatively habitable and redox-sustainable environments over long (ka-Ga) timescales.

Distribution and Evaporation Characteristics of Rb and Cs in Complex Salt Brine Systems

The brine in salt lakes is rich in resources, including not only K, Mg, and B, but also valuable trace elements. During the enrichment and extraction of trace elements (Rb, Cs) from sodium sulfate subtype salt lake brines, the process is significantly influenced by the presence of other coexisting ions such as Li+, K+, and Mg2+.The physical and chemical properties of K+ are extremely similar to those of Rb+ and Cs+, and its impact on the extraction of Rb+ and Cs+ is particularly significant. When K+, Rb+, and Cs+ coexist, they can form solid solutions such as [(K, Rb)2SO4], [(K, Cs)2SO4], and [(Rb, Cs)2SO4]. The formation of these solid solutions can lead to severe losses of Rb and Cs during the evaporation process of the brine, resulting in low yield. In response to the aforementioned issues regarding the evaporation process of Rb and Cs, this paper uses the aqueous-salt system phase diagram as a guide and combines experimental research with simulation calculations to study the enrichment patterns of trace elements Rb and Cs in the Na+, K+//Cl-, CO32-, SO42--H2O aqueous-salt system, as well as the migration mechanism of Rb and Cs.

Kinetics of CO2 hydrate formation in clayey sand sediments: Implications for CO2 sequestration

Hydrate-based CO2 sequestration beneath oceanic sediments is an emerging technique that involves the injection of CO2 into the hydrate stability zone (HSZ) beneath the seabed, forming hydrate cap that structurally traps the injected CO2 and reduces the risk of leaking CO2 from the storage sediment. Gas hydrates are adequately stable in sand sediments saturated with fresh water; however, the salinity of oceanic water impairs hydrate formation kinetics, stability, and CO2 storage capacity. In addition to sandstones, marine sediments are composed of many clay minerals that could affect hydrate formation. Therefore, this study experimentally simulates CO2 injection into sand and clayey sand sediments to assess the potential of CO2 hydrate formation. CO2 hydrates are formed inside a high-pressure reactor, which contains unconsolidated sediment bed/pack (silica sand; mixed sand with bentonite clay: 5 wt% and 10 wt%), saturated with de-ionized water or brine (3.3 wt% NaCl). Hydrate formation experiments were performed at 4 MPa pressure and 274.15 K temperature. Results show that CO2 hydrate formed within the sand sediment, with induction times of 6 and 8.5 h, for the de-ionized and brine systems, respectively. CO2 gas mole uptake in the de-ionized system was 71.54 mmol/mol however, in the brine system the gas uptake was 56.95 mmol/mol. Hence this 20.4% reduction in the gas uptake indicated the inhibition effect of salinity. In contrast, in the brine-saturated 5 wt% clay-sand sediment, the induction time was 6.5 h, indicating the promoting effect of the nano-sized clay particles. However, the gas uptake in this brine-saturated clay-sand sediment was reduced by 45.51% compared to the brine-saturated sand sediment. Increasing the clay content to 10 wt% prevented CO2 hydrate formation due to porosity reduction. Moreover, de-ionized water in clayey sand sediments prevented hydrate formation due to clay swelling. Finally, CO2 hydrate formation at the end of each experiment was visually confirmed.

Rock Wettability and Its Implication for Caprock Integrity in CO2–Brine Systems: A Comprehensive Review

Rock Wettability and Its Implication for Caprock Integrity in CO₂–Brine Systems: A Comprehensive Review

Geochemical Characteristics and Genesis of Brine Chemical Composition in Cambrian Carbonate-Dominated Succession in the Northeastern Region of Chongqing, Southwestern China

Deeply situated brine is abundant in rare metal minerals, possessing significant economic worth. To the authors’ knowledge, brine present within the Cambrian carbonate-dominated succession in the northeastern region of Chongqing, Southwestern China, has not been previously reported. In this investigation, brine samples were collected from an abandoned brine well, designated as Tianyi Well, for the purpose of analyzing the hydrochemical characteristics and geochemical evolution of the brine. Halide concentrations, associated ions, and their ionic ratios within the sampled brine were analyzed. The brine originating from the deep Cambrian aquifer was characterized by high salinity levels, with an average TDS value of 242 ± 11 g/L, and was dominated by a Na-Cl facies. The studied brine underwent a moderate degree of seawater evaporation, occurring between the saturation levels of gypsum and halite, accompanied by some halite dissolution. Compared to modern seawater evaporation, the depletion of Mg2+, HCO3−, and SO42− concentrations, along with the enrichment of Ca2+, Li+, K+, and Sr2+, is likely primarily attributed to water–rock interactions. These interactions include dolomitization, combination of halite dissolution, upwelling of lithium- and potassium-bearing groundwater, calcium sulfate precipitation, biological sulfate reduction (BSR), and the common ion effect within the brine system. This research offers valuable insights into the genesis of the brine within the Cambrian carbonate succession and provides theoretical backing for the development of brine resources in the future.

Influence of nitrogen cushion gas in 3-phase surface phenomena for hydrogen storage in gas condensate reservoirs

Recent research has primarily focused on 2-phase systems for hydrogen storage in porous media. However, the impact of cushion gases mixed with hydrocarbon fluids, such as n-octane, in depleted condensate-type reservoirs remains poorly understood. This study addresses the gap by evaluating the effects of pressure (500–3000 psi), temperature (30–70 °C), and NaCl brine salinities (2–20 wt%) by measuring the contact angles (CAs) between n-octane and substrates (for Quartz and Wolf camp shale) in brine, and interfacial tensions (IFTs) between brine and n-octane while injecting pure H2 gas (base case) and a mixture of 60% H2 and 40% cushion gas (30% N2 + 5% CH4 + 5% CO2). The CA results revealed that pressure had a relatively minor impact on the system with pure H2 injection, compared to temperature and salinity. However, when 40% cushion gas was added, the CA increased with pressure and salinity but decreased with rising temperature. It was observed that CAs for pure H2 gas were lower than those for the H2 + cushion gas mixture. Also, the equilibrium IFTs showed a consistent reduction with increasing pressure and temperature, while they increased with higher salinity. Comparing the IFTs of the 3-phase (H2 + cushion)/n-octane/brine system to those of the 2-phase (H2 + cushion)/brine system revealed that n-octane could effectively reduce the system's IFT by approximately 33%. Overall, this study provides valuable data for hydrogen storage in depleted gas condensate reservoirs containing hydrocarbon fluids like n-octane.

Inaccuracy principle and dissolution mechanism of lithium iron phosphate for selective lithium extraction from brines

The electrochemical lithiation/delithiation (ELD) method with the typical active materials being LiFePO4 and LiMn2O4, is the next generation technique for the selective lithium extraction from slat-lake brines owning to the advantages of high selectivity and excellent capacity and feasibility. However, the dissolution of LiFePO4/FePO4 (LFP/FP) during the ELD is seldom studied and an inaccurate measurement method for dissolution may result in obtaining an incorrect feasible application range for LFP/FP. Here, electrochemical workstation-electrochemical quartz crystal microbalance (EW-EQCM) is first utilized in the brine system to acquire the in-situ dissolution behavior of LFP/FP redox couple and verify the inaccuracy principle of the dissolution measurement. Both experimental results and thermodynamic calculations demonstrated that the accurate dissolution ratios can only be obtained by iron ions and phosphates at pH < 2.7 and pH < 5.3, respectively, which is induced by the narrow soluble range of iron ions and the formation of Ca5(PO4)3OH and Mg3(PO4)2 precipitation. In addition, the stable pH range of LFP and FP is 4 to 10 and 3 to 5, respectively, and the dissolution is caused by the formation of thermodynamically more stable metal ions, metal ion complexes, and metal ion hydroxides. At the optimum pH, the capacity can maintain 35 mg/g with average dissolution ratios of the cathode and anode lower than 0.1 %. This research sheds light on the accurate dissolution measurement range and method, dissolution mechanism and feasible application range of the LFP/FP redox couple.

Permafrost Hydrogeology of Taylor Valley, Antarctica: Insights From Deep Electrical Resistivity Tomography

AbstractGlobal warming has prompted globally widespread permafrost thawing, resulting in enhanced greenhouse gas release into the atmosphere. Studies conducted in the Northern Hemisphere reveal an alarming increase in permafrost thawing. However, similar data from Antarctica are scarce. We conducted a 2‐D Deep Electrical Resistivity Tomography (DERT) survey in Taylor Valley, Antarctica, to image the distribution of permafrost, its thicknesses, lower boundaries, and hydrogeology. Results show resistive, discontinuous domains that we suggest represent permafrost units. We also find highly conductive layers (5–10 Ω·m), between 300–350 m and 600–650 m below ground level and a shallower (∼50–100 m depth) conductive layer. The combined data set reveals a broad brine system in Taylor Valley, implying multi‐tiered groundwater circulation: a shallow, localized system linked with surface water bodies and a separate deeper, regional circulation system. The arrangement of these brines across different levels, coupled with the uneven permafrost distribution, underscores potential interplay between the two systems.

Preparation of high-purity magnesia spinel refractory raw materials with spinel-wrapped periclase structures using bischofite from salt lake

A large amount of bischofite is produced in the process of potassium extraction from salt lake, which seriously affects the ionic balance of brine system. In this study, a high-purity magnesia spinel refractory raw material with a spinel-wrapped periclase structure was directly prepared using bischofite by a precipitation-sintering approach. A coupling process of one-time crude magnesium chloride solution recrystallization and three-time precipitates washing was employed to remove crucial impurities (sodium, potassium, boron, etc.) and prepare the magnesium hydroxide precipitates with a high purity of 99.37 %. The lightly calcined magnesia gained from the high-purity magnesium hydroxide precipitates and white corundum were then employed for preparing the refractory raw materials. The effects of particle size and dosage of white corundum on the phase distribution, microstructure, and physical properties of the materials were thoroughly studied. The results illustrated that the prepared refractory raw materials were mainly composed of periclase and spinel phases, showing a distinct spinel-wrapped periclase structure that could enhance the physical properties. Therefore, the prepared refractory raw materials showed a high bulk density of 3.46 g·cm−3, a low apparent porosity of 2.46 %, and a linear shrinkage rate of 12.33 %, under the optimum conditions of white corundum particle size of 3.00 μm and alumina/magnesia mass ratio of 3:10.

Preface to the Special Issue on "The Hydrochemistry and Isotope Geochemistry of Alkaline Lakes and Brine Systems": A Tribute to Paolo Censi

Preface to the Special Issue on "The Hydrochemistry and Isotope Geochemistry of Alkaline Lakes and Brine Systems": A Tribute to Paolo Censi

CO2 solubility in aqueous solution of salts: Experimental study and thermodynamic modelling

AbstractThere are many economic obstacles and complex engineering problems associated with CO2 capture and storage in saline aquifers that need to be addressed. Overcoming such challenges requires precise knowledge on the fluid phase equilibria of CO2‐brine systems. Having accurate CO2 solubility data over a wide range of temperature and pressure can greatly assist in resolving these obstacles by improving the performance and accuracy of the thermodynamic modeling and subsequent CCS engineering success.CO2 solubility in pure water and NaCl solutions has been widely studied in the literature, however, there is a lack of data on CO2 solubility at lower temperatures (below 298 K). Furthermore, limited phase equilibria data are available for CO2 solubility in CaCl2, MgCl2, and KCl solutions at elevated temperatures (i.e., T &gt; 323.15 K).In this work, the phase equilibria of CO2 and brine systems are investigated experimentally and theoretically. In this study, solubilities of CO2 in pure water and various concentrations of NaCl (10, 15, 20, and 22 wt%), KCl (10, 15, and 22 wt%), CaCl2 (7.5, 10, 15.7, and 23.4 wt%), and MgCl2 (6.7, 11, 18, and 29 wt%) aqueous solutions are reported. All CO2 solubilities were measures at 323.15, 373.15, and 423.15 K and over various pressure ranges, while solubilities in 10 and 20 wt% NaCl aqueous solutions were also measured over the temperature range of 263 to 298 K and pressures up to the hydrate dissociation pressure of each system. Equation of state modelling using the PC‐SAFT and the Cubic Plus Association equations of state, is performed in the theoretical part of the study to validate the measured solubility data. © 2024 The Author(s). Greenhouse Gases: Science and Technology published by Society of Chemical Industry and John Wiley &amp; Sons Ltd.

Thermodynamic description of U(IV) solubility and hydrolysis in chloride systems: Pitzer activity model for the system U4+–Na+–Mg2+–Ca2+–H+–Cl––OH––H2O(l)

This study presents updated chemical, thermodynamic, and activity models for the system U4+–Na+–Mg2+–Ca2+–H+–Cl––OH––H2O(l) derived using the Pitzer formalism and a strict ion interaction approach. The models build on comprehensive solubility datasets in dilute to concentrated NaCl, MgCl2, and CaCl2 solutions. The Nuclear Energy Agency-Thermochemical Database (NEA-TDB) selection of solubility and hydrolysis constants in the reference state were taken as anchoring point, and were extended further with the solid nanocrystalline phase UO2∙H2O(ncr) and the ternary complex Ca4[U(OH)8]4+. The former was identified in long-term solubility experiments at ambient conditions, whereas the latter has been selected in analogy to Th(IV), Np(IV), and Pu(IV) considering experimental evidences available for these An(IV) in alkaline, concentrated CaCl2 solutions. These models represent an improved tool for the calculation of U(IV) solubility and aqueous speciation in a variety of geochemical conditions including concentrated brine systems relevant in salt-based repositories for nuclear waste disposal.

Surface charge change in carbonates during low-salinity imbibition

Optimizing the injection water salinity could present a cost-effective strategy for improving oil recovery. Although the literature generally acknowledges that low-salinity improves oil recovery in laboratory-scale experiments, the physical mechanisms behind it are controversial. While most experimental low-salinity studies focus on brine composition, this study investigated the influence of carbonate rock material on surface charge change, wettability alteration, and spontaneous imbibition behavior. Zeta potential measurements showed that each tested carbonate rock material exhibits characteristic surface charge responses when exposed to Formation-water, Seawater, and Diluted-seawater. Moreover, the surface charge change sensitivity to calcium, magnesium, and sulfate ions varied for the tested carbonate materials. Spontaneous imbibition tests led to high oil recovery and, thus, wettability alteration towards water-wet conditions if the carbonate-imbibing brine system’s surface charge decreased compared to the initial zeta potential of the carbonate Formation-water system. In the numerical part of the presented study, we find that it is essential to account for the location of the shear plane and thus distinguish between the numerically computed surface charge and experimentally determined zeta potential. The resulting model numerically reproduced the experimentally measured calcium, magnesium, and sulfate ion impacts on zeta potential. The spontaneous imbibition tests were history-matched by linking surface charge change to capillary pressure alteration. As the numerical simulation of the laboratory-scale spontaneous imbibition tests is governed by molecular diffusion (with a time scale of weeks), we conclude that molecular diffusion-driven field scale wettability alteration requires several hundred years.

Thermodynamic Predictions of Hydrogen Generation during the Serpentinization of Harzburgite with Seawater-derived Brines

Salty aqueous solutions (brines) occur on Earth and may be prevalent elsewhere. Serpentinization represents a family of geochemical reactions where the hydration of olivine-rich rocks can release aqueous hydrogen, H2(aq), as a byproduct, and hydrogen is a known basal electron donor for terrestrial biology. While the effects of lithological differences on serpentinization products have been thoroughly investigated, effects focusing on compositional differences of the reacting fluid have received less attention. In this contribution, we investigate how the chemistry of seawater-derived brines affects the generation of biologically available hydrogen resulting from the serpentinization of harzburgite. We numerically investigate the serpentinization of ultramafic rocks at equilibrium with an array of brines at different water activities (a proxy for salt concentration in aqueous fluids and a determinant for habitability) derived from seawater evaporation. Because the existing supersaturation of aqueous calcium carbonate, a contributor to dissolved inorganic carbon (DIC) in natural seawater, cannot be captured in equilibrium calculations, we bookend our calculations by enabling and suppressing carbonate minerals when simulating serpentinization. We find that the extent of DIC supersaturation can provide an important control of hydrogen availability. Increased DIC becomes a major sink for hydrogen by producing formate and associated complexes when the reacting fluids are acidic enough to allow for CO2. Indeed, H2(aq) reduces CO2(aq) to formate, leading to a hydrogen deficit. These conclusions provide additional insights into the habitability of brine systems, given their potential for serpentinization across diverse planetary bodies such as on Mars and ocean worlds.

Mutual Diffusivities of Mixtures of Carbon Dioxide and Hydrogen and Their Solubilities in Brine: Insight from Molecular Simulations.

H2-CO2 mixtures find wide-ranging applications, including their growing significance as synthetic fuels in the transportation industry, relevance in capture technologies for carbon capture and storage, occurrence in subsurface storage of hydrogen, and hydrogenation of carbon dioxide to form hydrocarbons and alcohols. Here, we focus on the thermodynamic properties of H2-CO2 mixtures pertinent to underground hydrogen storage in depleted gas reservoirs. Molecular dynamics simulations are used to compute mutual (Fick) diffusivities for a wide range of pressures (5 to 50 MPa), temperatures (323.15 to 423.15 K), and mixture compositions (hydrogen mole fraction from 0 to 1). At 5 MPa, the computed mutual diffusivities agree within 5% with the kinetic theory of Chapman and Enskog at 423.15 K, albeit exhibiting deviations of up to 25% between 323.15 and 373.15 K. Even at 50 MPa, kinetic theory predictions match computed diffusivities within 15% for mixtures comprising over 80% H2 due to the ideal-gas-like behavior. In mixtures with higher concentrations of CO2, the Moggridge correlation emerges as a dependable substitute for the kinetic theory. Specifically, when the CO2 content reaches 50%, the Moggridge correlation achieves predictions within 10% of the computed Fick diffusivities. Phase equilibria of ternary mixtures involving CO2-H2-NaCl were explored using Gibbs Ensemble (GE) simulations with the Continuous Fractional Component Monte Carlo (CFCMC) technique. The computed solubilities of CO2 and H2 in NaCl brine increased with the fugacity of the respective component but decreased with NaCl concentration (salting out effect). While the solubility of CO2 in NaCl brine decreased in the ternary system compared to the binary CO2-NaCl brine system, the solubility of H2 in NaCl brine increased less in the ternary system compared to the binary H2-NaCl brine system. The cooperative effect of H2-CO2 enhances the H2 solubility while suppressing the CO2 solubility. The water content in the gas phase was found to be intermediate between H2-NaCl brine and CO2-NaCl brine systems. Our findings have implications for hydrogen storage and chemical technologies dealing with CO2-H2 mixtures, particularly where experimental data are lacking, emphasizing the need for reliable thermodynamic data on H2-CO2 mixtures.

Molecular dynamics simulation studies elucidating interaction mechanisms and structures of salt–brine interfacial systems derived from magnesium sulfate subtype salt lakes

Salt–brine interfacial systems widely occur in the process of salt crystallization and separation, where the interfacial interaction plays a crucial role in influencing salt crystal growth, product purity and brine recovery rates. In the present study, molecular dynamics simulations were employed to investigate the interaction mechanisms and structures of salt–brine interfacial systems derived from the magnesium sulfate–subtype salt lakes. The results indicate that the type of salts was the key factor that affects salt–brine interfacial interactions. The strength of interfacial interaction in hydrated salt–brine systems was found to be more than twice that of ionic salt–brine systems. This can be attributed to two characteristics observed in hydrated salt–brine systems: the incompact and undulating surface structure of hydrated salts and the hydrogen bonding between water molecules on hydrated salt and brine surfaces. In all the seven interfacial systems, no accumulation of Li+ ions at the interface was observed, and there were no significant structure changes in bulk brines except the variations in hydration numbers of K+ ions. These findings provide insights into atomic-level mechanisms governing the interfacial interactions between different types of salts and brines, thus providing a theoretical guidance for enhancing the salt crystallization and separation process.

Effect of equilibrium contact angle on water equilibrium film thickness for the carbon dioxide–brine–mineral system based on surface force theory

The thickness of the thin wetting film depends on disjoining pressure forces, and it evolves with pH evolution due to brine acidification at the physical and chemical conditions of geological carbon dioxide storage becoming thinner in response to dewetting. In the literature, molecular dynamic simulation (MDS) studies have been employed to understand the effect of pressure/capillary pressure on the thin wetting film evolution. In this paper, a theoretical approach based on the Frumkin–Derjaguin Equation (FDE), models of electric double layer repulsion, and van der Waals forces have been used for the calculation of the wetting film thickness. The approach excluded hydration forces contribution to disjoining pressure forces due partly to its poorly understood nature, and partly to the high salinity conditions encountered in geological carbon storage. Due to its promising global storage capacity compared to other lithologies, the carbon dioxide–brine–silica systems was chosen to simulate sandstone saline aquifers. The validation of the model benefited much from literature resources on data and a universal model of carbon dioxide–brine interfacial tension. Calculated results confirm pH-induced dewetting and they follow trends controlled by pH and pressure as found in the literature. The novelty of the paper can be seen from the fact that it has demonstrated a theoretical supplement to MDS studies in addition to justifying the fundamental utility and versatility of the FDE. Moreover, the paper links for the first time, a transcendental equation to the thin wetting film theory encountered in the carbon dioxide–solid–brine system found in geological carbon storage.