Search Results (25)

The rising levels of Co(II) in aquatic environments present considerable risks, thereby necessitating the development of effective remediation strategies. This study introduces an innovative pre-hydration method for synthesizing carbonated calcined clay dolomite (CCCD) to efficiently remove Co(II) from contaminated water. This pre-hydration treatment successfully reduced the complete carbonation temperature of the material from 500 °C to 400 °C, significantly enhancing energy efficiency. The Co(II) removal performance was systematically investigated by varying key parameters such as contact time, initial Co(II) concentration, pH, and solid/liquid ratio. Optimal removal was achieved at 318 K with pH of 4 and a solid/liquid ratio of 0.5 g·L⁻¹. Continuous flow column experiments confirmed the excellent long-term stability of CCCD, maintaining a consistent Co(II) removal efficiency of 99.0% and a stable effluent pH of 8.5 over one month. Isotherm and kinetic models were used to empirically describe concentration-dependent and time-dependent uptake behavior. The equilibrium data were best described by the Langmuir model, while kinetics followed a pseudo-second-order model. An apparent maximum removal capacity of 621.1 mg g⁻¹ was obtained from Langmuir fitting of equilibrium uptake data. Mechanistic insights from Visual MINTEQ calculations and solid phase characterizations (XRD, XPS, and TEM) indicate that Co(II) removal is dominated by mineral water interface precipitation. The gradual hydration of periclase (MgO) forms Mg(OH)₂, which creates localized alkaline microenvironments at particle surfaces and drives Co(OH)₂ formation. Carbonate availability further favors CoCO₃ formation and retention on CCCD. Importantly, this localized precipitation pathway maintains a stable, mildly alkaline effluent pH (around 8.5), reducing downstream pH adjustment demand and improving operational compatibility. Overall, CCCD combines high Co(II) immobilization efficiency, strong long-term stability, and an energy-efficient preparation route, supporting its potential for scalable remediation of Co(II) contaminated water. Full article

Natural gas hydrate (NGH) is a clean resource characterized by abundant potential reserves, clean combustion, and high energy density. Although significant progress has been made in the development of NGH resources all around the world, challenges still exist that hinder commercial exploitation, such as a low daily gas production rate and short steady production periods. One significant reason lies in the complex gas–liquid–solid phase transitions occurring within the formation during production, which lead to changes in flow capacity. Understanding the phase change mechanism of NGH reservoirs will help to further reveal the production increase mechanism. To address the phase transitions’ effect on production, this paper establishes a numerical simulation model for the depressurization exploitation of natural gas hydrates in order to investigate phase transition characteristics at the field scale. First, the phase equilibrium calculation method is presented and the phase equilibrium curve is modified by considering the capillary effect, soluble salt, and surface adsorption. Then, the phase transition model is successfully characterized in a simulation and the numerical simulation model is established based on the first test project parameters in the Shenhu area. The production characteristics of different sediment types (montmorillonite, South China Sea sediments, kaolin, and silt) are analyzed under the effects of water content and salinity. It is shown that lower initial water content and higher salinity result in higher gas production. The results provide a better understanding of the effects of phase transition parameters on NGH production at the field scale. Full article

Salt lakes are a rich source of metals used in various fields. Rubidium is found in small amounts in salt lakes, but extraction technology on an industrial scale has not been developed completely. Clathrate hydrates are crystalline compounds formed by the encapsulation of guest molecules in cage-like structures made of water molecules. One of the most important properties for engineering practices of hydrate-based technologies is the comprehension of the phase equilibrium conditions. Phase equilibrium conditions of CO₂ hydrate in rubidium chloride aqueous solution with mass fractions of 0.05, 0.10, 0.15 and 0.20 were experimentally investigated in the pressure range from 1.27 MPa to 3.53 MPa, and the temperature was from 268.7 K to 280.6 K. The measured equilibrium temperature in this study decreased roughly in proportion to the concentration of the RbCl solution from the pure water system. This depression is due to the lowering of the chemical potential of water in the liquid phase by the dissolution of RbCl. Experimental results compared with other salt solution + CO₂ hydrate systems showed that the equilibrium temperatures decreased to a similar degree for similar mole fractions. Full article

Natural gas hydrate is a kind of low-carbon and clean new energy, so research on its efficient extraction in terms of theory and technology is particularly important. Combined thermal injection and depressurization is an effective method for extracting natural gas hydrate. In this study, the classical local heat equilibrium model was modified, and a pore-scale fully coupled unsteady heat transfer model for hydrate reservoirs was set up by considering multiple forms of heat flow accompanying hydrate’s decomposition and gas–liquid flow. Based on this model and the basic geological information of the X2 hydrate reservoir in the western Pacific Ocean, a numerical model of gas hydrate extraction using combined heat injection and depressurization was constructed to simulate the production performance of the hydrate reservoir. The results were fully compared with the results obtained by the depressurization method alone. The results indicated the hydrate extraction via a combined heat injection and depressurization would have a cumulative gas production of 31.609 million m³ and a cumulative water production of 1.5219 million m³, which are 72.57% higher and 31.75% lower than those obtained by depressurization alone, respectively. These study results can provide theoretical support for the industrial extraction of gas hydrate in seas. Full article

The aim of this study was to determine the influence of four inorganic salts, KCl, NaCl, KBr and NaBr, on the thermodynamic conditions of methane hydrate formation. In order to achieve this, the vapor–liquid water-hydrate (VL_WH) equilibrium conditions of methane (CH₄) hydrate were measured in the temperature range of 274.15 K–282.15 K by the isothermal pressure search method. The results demonstrated that, in comparison with deionized water, the four inorganic salts exhibited a significant thermodynamic inhibition on CH₄ hydrate. Furthermore, the inhibitory effect of Na⁺ on methane hydrate is more pronounced than that of K⁺, where there is no discernible difference between Cl⁻ and Br⁻. The dissociation enthalpy ($∆H_{diss}$) of CH₄ hydrate in the four inorganic salt solutions is comparable to that of deionized water, indicating that the inorganic salt does not participate in the formation of hydrate crystals. The Chen–Guo hydrate model and N–NRTL–NRF activity model were employed to forecast the equilibrium conditions of CH₄ hydrate in electrolyte solution. The absolute relative deviation (AARD) between the predicted and experimental values were 1.24%, 1.08%, 1.18% and 1.21%, respectively. The model demonstrated satisfactory universality and accuracy. This study presents a novel approach to elucidating the mechanism and model prediction of inorganic salt inhibition of hydrate. Full article

Accurately predicting the phase behavior and physical properties of carbon dioxide (CO₂) in pure water/NaCl mixtures is crucial for the design and implementation of carbon capture, utilization, and storage (CCUS) technology. However, the prediction task is complicated by CO₂ liquefaction, CO₂ hydrate formation, multicomponent and multiphase coexistence, etc. In this study, an improved method that combines Benedict–Webb–Rubin–Starling equation of state (BWRS EOS) + hydrate thermodynamic theories was proposed to predict CO₂ solubility and phase equilibrium conditions for a mixed system across various temperature and pressure conditions. By modifying the interaction coefficients in BWRS EOS and the Van der Waals–Platteeuw model, this new method is applicable to complex systems containing two liquid phases and a CO₂ hydrate phase, and its high prediction accuracy was verified through a comparative evaluation with a large number of reported experimental data. Furthermore, based on the calculation results, the characteristics of CO₂ solubility and the variation of phase equilibrium conditions of the mixture system were discussed. These findings highlight the influence of hydrates and NaCl on CO₂ solubility characteristics and clearly demonstrate the hindrance of NaCl to the formation of CO₂ hydrates. This study provides valuable insights and fundamental data for designing and implementing CCUS technology that contribute to addressing global climate change and environmental challenges. Full article

Stability condition is of critical importance for methane hydrate exploitation, transportation, and reserves. This study measured the stability conditions of methane hydrate in fine-grained sediment with different dry densities (${\rho }_d$ = 1.40, 1.50 and 1.60 g/cm³) and various initial water saturations by the multi-step heating method. The experimental result showed that the methane hydrate formation in fine-grained sediment required lower temperature and/or higher pressure compared to that in bulk state. At the same time, it is found that the deviation degree of P–T conditions of methane hydrate in fine-grained sediment with different dry density and initial water saturation are completely different from that in pure water. In addition, according to the nuclear magnetic resonance technique (NMR), the changes in NMR signal intensity during the formation and decomposition of methane hydrate in silt were analyzed. Regardless of formation and dissociation stages, liquid water always distributes in the small sediment pores. An empirical formula is developed to address the capillary suction of water and hydrate with respect to the unhydrated water within sediment. Furthermore, a phase equilibrium model is proposed to predict the stability conditions of hydrate-bearing fine-grained sediment. Full article

The purpose of this paper is to present a one-dimensional model that simulates the thermo-physical processes for methane hydrate decomposition in porous media. The mathematical model consists of equations for the conservation of energy, gas, and liquid as well as the thermodynamic equilibrium equation for temperature and pressure $\left(P-T\right)$ in the hydrate stability region. The developed model is solved numerically by using the implicit finite difference technique on the grid system, which correctly describes the appearance of phase, latency, and boundary conditions. The Newton–Raphson method was employed to solve a system of nonlinear algebraic equations after defining and preparing the Jacobean matrix. Additionally, the proposed model describes the decomposition of methane hydrate by thermal catalysis of the components that make up the medium through multiple phases in porous media. In addition, the effect of thermodynamic processes during the hydrate decomposition on the pore saturation rate with hydrates a7nd water during different time periods was studied in a one-dimensional model. Finally, in a one-dimensional model over various time intervals, $t=1,\hspace{0.17em}10,\hspace{0.17em}50\hspace{0.17em}\mathrm{s}$, the pressure and temperature distributions during the decomposition of methane hydrates are introduced and investigated. The obtained results include more accurate solutions and are consistent with previous models based on the analysis of simulations and system stability. Full article

Cloud point extraction is a versatile method aimed at separating compounds from complex mixtures and arouses great technological interest, particularly among the biochemical industries. However, one must have deep knowledge of the liquid–liquid equilibrium behavior of systems to properly use the method. Thus, we used thermodynamic parameters to evaluate the effect of citrate, sulfate, and tartrate anions on the phase separation of water + Triton X-114^® mixtures at 283.2 K, 293.2 K, and 303.2 K. In these systems, increasing the temperature and the anion molar fraction expanded the biphasic region in the following order: ${\mathrm{C}}_6{\mathrm{H}}_5{\mathrm{O}}_7^{3-}$> ${\mathrm{SO}}_4^{2-}$ > ${ \mathrm{C}}_4{\mathrm{H}}_4{\mathrm{O}}_6^{2-}$. Unlike other studies based on the Hofmeister series, the Gibbs free energy of micellization correlated the anion effect on the biphasic region with the spontaneity of the micelle formation. The water molecules structured around these anions were evaluated according to the shell volume of the immobilized water by electrostriction, volume of water around the hydration shell, Gibbs free energy of hydration, and Gibbs free energy of electrostriction ($\Delta {\mathrm{G}}_{\mathrm{el}12}$). The citrate anion presented a higher $\Delta {\mathrm{G}}_{\mathrm{el}12}$ of −1781.49 kJ mol⁻¹, due to the larger number of electrons around it. In addition, the partition coefficient of the surfactant in the two liquid phases revealed a linear dependence upon the anion mole fractions by following the previous anion sequence and temperature in the phase separation. Full article

Thermo-responsive (TR) gels of the LCST (lower critical solution temperature) type swell in water at temperatures below their volume phase transition temperature $T_{\mathrm{c}}$ and collapse above the critical temperature. When water is partially replaced with an organic liquid, these materials demonstrate three different types of equilibrium solvent uptake diagrams at temperatures below, above, in the close vicinity of $T_{\mathrm{c}}$. A model is developed for equilibrium swelling of TR gels in binary mixtures of solvents. It takes into account three types of phase transitions in TR gels driven by (i) aggregation of hydrophobic side groups into clusters from which solvent molecules are expelled, (ii) replacement of water with cosolvent molecules in cage-like structures surrounding these groups, and (iii) replacement of water with cosolvent as the main element of hydration shells around backbone chains. The model involves a relatively small number of material constants that are found by matching observations on covalently cross-linked poly(N-isopropylacrylamide) macroscopic gels and microgels. Good agreement is demonstrated between the experimental data and results of numerical analysis. Classification is provided of the phase transition points on equilibrium swelling diagrams. Full article

Supercritical water desalination (SCWD) shows great potential in the treatment of high-salt wastewater with zero liquid discharge. To investigate the salt precipitation behavior and mechanism in supercritical water, experiments and molecular dynamics simulations (MDs) were used to study the salting-out process of different salts in supercritical water. The equilibrium concentrations of NaCl, KCl, CaCl₂, Na₂SO₄, and Na₂CO₃ in supercritical water were experimentally measured. When the temperature exceeded 693 K, the salt equilibrium concentration measured in the experiment was less than 130 mg/L. The solubility decreased in the order of KCl > NaCl > CaCl₂ > Na₂SO₄ > Na₂CO₃. To elucidate the effects of different cations and anions in supercritical water on salt dissolution and precipitation behavior, the potential energy, radial distribution function (RDF) and coordination number in the system were obtained via molecular dynamics simulation. Experimental and MD results showed that salt solubility has significant positive correlation with systemic potential energy and hydration number. MD results indicated that a small ionic radius, large ionic charge, and low hydration coordination number are favorable for inorganic salts to precipitate and crystallize since these factors can strengthen the interaction between free ions and salt clusters. Moreover, due to the formation of multilayer coordination structure, polyatomic ions can achieve a lower equilibrium concentration than that of the corresponding monatomic ions. Full article

The water content of the upper layers of the surface of Mars is not yet quantified. Laboratory simulations are the only feasible way to investigate this in a controlled way on Earth, and then compare it with remote and in situ observations of spacecrafts on Mars. Describing the processes that may induce changes in the water content of the surface is critical to determine the present-day habitability of the Martian surface, to understand the atmospheric water cycle, and to estimate the efficiency of future water extraction procedures from the regolith for In Situ Resource Utilization (ISRU). This paper illustrates the application of the SpaceQ facility to simulate the near-surface water cycle under Martian conditions. Rover Environmental Monitoring Station (REMS) observations at Gale crater show a non-equilibrium situation in the atmospheric H₂O volume mixing ratio (VMR) at night-time, and there is a decrease in the atmospheric water content by up to 15 g/m² within a few hours. This reduction suggests that the ground may act at night as a cold sink scavenging atmospheric water. Here, we use an experimental approach to investigate the thermodynamic and kinetics of water exchange between the atmosphere, a non-porous surface (LN₂-chilled metal), various salts, Martian regolith simulant, and mixtures of salts and simulant within an environment which is close to saturation. We have conducted three experiments: the stability of pure liquid water around the vicinity of the triple point is studied in experiment 1, as well as observing the interchange of water between the atmosphere and the salts when the surface is saturated; in experiment 2, the salts were mixed with Mojave Martian Simulant (MMS) to observe changes in the texture of the regolith caused by the interaction with hydrates and liquid brines, and to quantify the potential of the Martian regolith to absorb and retain water; and experiment 3 investigates the evaporation of pure liquid water away from the triple point temperature when both the air and ground are at the same temperature and the relative humidity is near saturation. We show experimentally that frost can form spontaneously on a surface when saturation is reached and that, when the temperature is above 273.15 K (0 °C), this frost can transform into liquid water, which can persist for up to 3.5 to 4.5 h at Martian surface conditions. For comparison, we study the behavior of certain deliquescent salts that exist on the Martian surface, which can increase their mass between 32% and 85% by absorption of atmospheric water within a few hours. A mixture of these salts in a 10% concentration with simulant produces an aggregated granular structure with a water gain of approximately 18- to 50-wt%. Up to 53% of the atmospheric water was captured by the simulated ground, as pure liquid water, hydrate, or brine. Full article

Experimental and field observations evidence the effects of capillarity in narrow pores on inhibiting the thermodynamic stability of gas hydrates and controlling their saturation. Thus, precise estimates of the gas hydrate global inventory require models that accurately describe gas hydrate stability in sediments. Here, an equilibrium model for hydrate formation in sediments that accounts for capillary inhibition effects is developed and validated against experimental data. Analogous to water freezing in pores, the model assumes that hydrate formation is controlled by the sediment pore size distribution and the balance of capillary forces at the hydrate–liquid interface. To build the formulation, we first derive the Clausius–Clapeyron equation for the thermodynamic equilibrium of methane and water chemical potentials. Then, this equation is combined with the van Genuchten’s capillary pressure to relate the thermodynamic properties of the system to the sediment pore size distribution and hydrate saturation. The model examines the influence of the sediment pore size distribution on hydrate saturation through the simulation of hydrate formation in sand, silt, and clays, under equilibrium conditions and without mass transfer limitations. The results show that at pressure–temperature conditions typically found in the seabed, capillary effects in very fine-grained clays can limit the maximum hydrate saturation below 20% of the host sediment porosity. Full article

Understanding of CO₂ hydrate–liquid water two-phase equilibrium is very important for CO₂ storage in deep sea and in submarine sediments. This study proposed an accurate thermodynamic model to calculate CO₂ solubility in pure water and in seawater at hydrate–liquid water equilibrium (HL_WE). The van der Waals–Platteeuw model coupling with angle-dependent ab initio intermolecular potentials was used to calculate the chemical potential of hydrate phase. Two methods were used to describe the aqueous phase. One is using the Pitzer model to calculate the activity of water and using the Poynting correction to calculate the fugacity of CO₂ dissolved in water. Another is using the Lennard–Jones-referenced Statistical Associating Fluid Theory (SAFT-LJ) equation of state (EOS) to calculate the activity of water and the fugacity of dissolved CO₂. There are no parameters evaluated from experimental data of HL_WE in this model. Comparison with experimental data indicates that this model can calculate CO₂ solubility in pure water and in seawater at HL_WE with high accuracy. This model predicts that CO₂ solubility at HL_WE increases with the increasing temperature, which agrees well with available experimental data. In regards to the pressure and salinity dependences of CO₂ solubility at HL_WE, there are some discrepancies among experimental data. This model predicts that CO₂ solubility at HL_WE decreases with the increasing pressure and salinity, which is consistent with most of experimental data sets. Compared to previous models, this model covers a wider range of pressure (up to 1000 bar) and is generally more accurate in CO₂ solubility in aqueous solutions and in composition of hydrate phase. A computer program for the calculation of CO₂ solubility in pure water and in seawater at hydrate–liquid water equilibrium can be obtained from the corresponding author via email. Full article

In order to prevent solids from forming during the transportation and handling of liquid propane, C₃H₈(l), the fluid is dehydrated to a level below the water dew point concentration for the coldest operating temperature. Thus, accurate calculation of the saturation water content for C₃H₈ is important to determine the designed allowable concentration in liquid C₃H₈. In this work, we measured the water content of liquid C₃H₈ in the presence of the structure II hydrate from p = 1.081 to 40.064 MPa and T = 241.95 to 276.11 K using a tunable diode absorption spectroscopy technique. The water content results were modelled using the reference quality reduced Helmholtz equations and the Sloan et al. model for the non-hydrate and hydrate phases, respectively. Calculations show a good agreement (an average difference of less than 12 ppm) when compared to our measurements. Furthermore, the model was also used for calculating the dissociation temperatures for three phase loci, where a relative difference greater than 5 K was observed compared to the literature, hence our previously model reported by Adeniyi et al. is recommended for three phase loci calculations. Full article