Equilibrium Curve Research Articles

Experimental measurements and thermodynamic modeling of hydrate dissociation conditions for CO2 + THF + MgCl2 + water systems

• Experimental hydrate dissociation conditions for (CO2 + THF + MgCl2 + Water) system are reported. • A thermodynamic model has been developed and its results are in acceptable agreement with the experimental data. • The addition of low-medium concentration THF to the system has a promotion effect. • The addition of MgCl2 has an inhibition effect In this study, experimental and thermodynamic modeling on hydrate dissociation conditions of CO 2 + water systems in the absence/presence of MgCl 2 + THF aqueous solutions at various concentrations were investigated. The ternary systems, including different aqueous solutions of tetrahydrofuran and magnesium chloride (0.05 mass fraction of MgCl 2 , 0.05 mass fraction of THF: solution A; 0.15 mass fraction of MgCl 2 , 0.05 mass fraction of THF: solution B; 0.05 mass fraction of MgCl 2 , 0.20 mass fraction of THF: solution C; 0.15 mass fraction of MgCl 2 , 0.20 mass fraction of THF: solution D) were conducted in the temperature range between 280.9 to 292.9 K and pressure ranges 0.92 to 3.89 MPa. An isochoric pressure–search method was applied to undertake all measurements. The results demonstrated that MgCl 2 acts as an inhibitor in all experiments, while THF acts as a promoter. Comparing mentioned data with the same system in the absence of MgCl 2 , a shift is observed toward the left in the equilibrium curve that this kind of shifting left is more observable at high pressures. In addition, a thermodynamic model was developed utilizing the Peng-Robinson equation of state with classical mixing rules and the UNIQUAC activity coefficient model to predict the equilibrium conditions of the aforementioned system. The model results implied a reasonable agreement with the experimental dissociation data with an average absolute deviation of pressure below 0.3%.

A Study on crystallization temperature and rate of ammonium salt in the high-pressure hydrogenation heat exchanger

Ammonium salt crystallization corrosion failure is an essential problem in the failure of high-pressure hydrogenation heat exchangers. The crystallization equilibrium curves of NH4Cl and NH4HS under different pressures were established according to the ammonium salt crystallization process in the high-pressure hydrogenation heat exchange unit, and the crystallization equilibrium temperatures of NH4Cl and NH4HS were obtained based on Aspen Plus. In addition, a prediction model for the crystallization temperature of ammonium salt was established, then the relationship between crystallization temperature and rate of ammonium salts was elaborated. The results indicate that the initial crystallization temperatures of NH4Cl and NH4HS are respectively 198.95°c and 134.45°c when the system pressure is 10MPa, and the temperature is 433.15K. The maximum crystallization rate of NH4Cl and NH4HS occur at the initial crystallization temperature, respectively 0.104kg/h and 29.23kg/h. The crystallization rate of NH4HS is three orders of magnitude higher than that of NH4Cl.

A Speech Cryptosystem Using the New Chaotic System with a Capsule-Shaped Equilibrium Curve

A Speech Cryptosystem Using the New Chaotic System with a Capsule-Shaped Equilibrium Curve

The light curve simulations of the 2021 anomalous event in SS Cygni

Abstract The prototype dwarf nova SS Cyg unexpectedly exhibited an anomalous event in its light curve in the early few months of 2021 in which regular dwarf nova-type outbursts stopped, and only small-amplitude fluctuations occurred. Inspired by this event, we have performed numerical simulations of light curves of SS Cyg by varying mass transfer rates and varying viscosity parameters in the cool disk. We have also studied the effect of gas-stream overflows beyond the outer disk edge in the light curve simulations. We have confirmed that the enhanced mass transfer is not likely to be responsible for the 2021 anomalous event or its forerunner. We have found that the enhancement of the viscosity in the disk may reproduce the forerunner of that event but may not be sufficient to explain the 2021 anomalous event, although the latter result might be particular to the thermal equilibrium curve we used. Within our simulations, a model of the gas-stream overflow with a slightly higher mass transfer rate than that of our standard model reproduces light curves similar to the 2021 anomalous event. We suggest that the gas-stream overflow is necessary to reproduce that event. The gas-stream overflow may also be responsible for the abnormally high X-ray flux during the normal quiescent state in SS Cyg.

Dynamics of a Mechanical System with Curve of Equilibria: Cosymmetry and Multistability

We analyze the effects of extreme multistability in a mechanical system which describes the movement of an idealized ball over a surface like a Mexican hat. The mathematical model is given by a system of autonomous ordinary differential equations with parameters. In particular cases of rotational symmetry and cosymmetry, the system has a curve of asymptotically stable equilibria. The symmetry gives a circle of equilibria with identical stability spectra, whereas the cosymmetry produces an ellipse of equilibria with nonidentical properties. The destruction of both symmetry and cosymmetry leads to a finite number of equilibria (multistability). We study the dynamics for conservative (without dissipation) and dissipative (linear damping) cases using analytical methods and computer simulation. We found interesting effects caused by extreme multistability: nontrivial selection of equilibria of the family, high sensitivity to initial data because of memory about conservative chaos, and essential difference in dynamics in rotational symmetry and cosymmetry cases.

The Influence of Plant Extract on the Phase Equilibrium of Structure I Gas Hydrate in a Simulated Offshore Environment

Gas hydrate inhibitors, especially those used in offshore environments, are chemicals. These chemicals are synthetic in nature and pose both technical and environmental risks. This study emphasizes the influence of a Plant Extract (PE) on the phase behavior and equilibrium of structure I (SI) gas hydrate and its inhibition efficiency. The PE was screened using a mini flow loop. From the pressure-temperature phase diagram, the various weight percentages of the PE were able to disrupt the thermodynamic equilibrium conditions of the water and gas molecules to lower temperatures and increase pressures, which caused a shift in the equilibrium curve to an unstable hydrate formation zone. The pressure versus time plot as well as the inhibition efficiency plots for the PE and Mono Ethylene Glycol (MEG) were evaluated. Overall, the inhibition efficiency of the PE was higher than that of MEG for 1 wt% (60.53%) and 2 wt% (55.26%) but had the same efficiency at 3 wt% (73.68%). The PE at 1 wt% had the greatest inhibition effect and adjudged the optimum weight percent with a well-regulated phase equilibrium curve. This shows that PE is a better gas hydrate inhibitor than MEG, which is toxic to both human and aquatic life; therefore, it is recommended for field trials.

Microcosmic mechanism and correction of moisture effect on furfural diffusion and equilibrium in oil‐paper insulation

AbstractFurfural content in oil is considered as an effective parameter to evaluate the ageing state of oil‐immersed transformers. In previous thermal ageing experiments at 130°C, we found that moisture increment in oil‐paper system makes more furfural distribute in oil. However, the microcosmic mechanism of moisture effect on furfural diffusion from paper to oil is still unknown, and the furfural equilibrium law at transformers' typical operating temperatures is also unclear, resulting in the unreliability of the existed furfural evaluation model. To elucidate the above problems, molecular dynamics simulation and furfural equilibrium experiments at 60°C were carried out at different moisture contents. The results show that high moisture content makes part of furfural diffuse from paper to oil indeed. Supposing moisture content increases from 1% to 2%, mass fraction of furfural in oil may increase from 32.98% to 49.83%, leading to furfural content in oil increases from 0.76 mg/L to 1.06 mg/L when the degree of polymerisation of insulation paper is about 524, which increased by 39.5%. The increase in moisture content makes cellulose form hydrogen bonds with H2O preferentially, decreasing the hydrogen bonds interaction between cellulose and furfural. Thus, partial furfural falls off cellulose and diffuses into oil, leading to an increase in furfural content in oil. To eliminate the moisture interference, a corrected furfural assessment model based on the moisture equilibrium curve has been constructed, which can accurately evaluate the ageing state of insulation paper regardless of the moisture influence.

Photochemistry and Heating/Cooling of the Multiphase Interstellar Medium with UV Radiative Transfer for Magnetohydrodynamic Simulations

We present an efficient heating/cooling method coupled with chemistry and UV radiative transfer that can be applied to numerical simulations of the interstellar medium (ISM). We follow the time-dependent evolution of hydrogen species (H2, H, H+), assume carbon/oxygen species (C, C+, CO, O, and O+) are in formation–destruction balance given the nonsteady hydrogen abundances, and include essential heating/cooling processes needed to capture the thermodynamics of all ISM phases. UV radiation from discrete point sources and the diffuse background is followed through adaptive ray tracing and a six-ray approximation, respectively, allowing for H2 self-shielding; cosmic-ray heating and ionization are also included. To validate our methods and demonstrate their application for a range of density, metallicity, and radiation fields, we conduct a series of tests, including the equilibrium curves of thermal pressure versus density, the chemical and thermal structure in photodissociation regions, H i-to-H2 transitions, and the expansion of H ii regions and radiative supernova remnants. Careful treatment of photochemistry and cosmic-ray ionization is essential for many aspects of ISM physics, including identifying the thermal pressure at which cold and warm neutral phases coexist. We caution that many current heating and cooling treatments used in galaxy formation simulations do not reproduce the correct thermal pressure and ionization fraction in the neutral ISM. Our new model is implemented in the MHD code Athena and incorporated in the TIGRESS simulation framework, for use in studying the star-forming ISM in a wide range of environments.

Rhenium-molybdenum separation in an alkaline leaching solution of a waste superalloy by N263 extraction

The recovery of rhenium from waste superalloys has always been a research focus. This study focuses on the performance of extraction of rhenium and its separation with molybdenum in alkali leaching solution of waste superalloy by methyl trioctylammonium chloride (N263). Minitab 17 Statistical Software (Trial version, Techmax, USA) was used to create a four-factor (N263 concentration, sec-octyl alcohols concentration, extraction time and organic to aqueous ratio (O/A ratio)) two-level orthogonal experiment table. According to the orthogonal experiment results of rhenium extraction and rhenium molybdenum separation coefficient, rhenium extraction model, rhenium molybdenum separation coefficient model and the corresponding regression equation were established. The rhenium extraction performance of N263 was investigated by the rhenium equilibrium curve and NaSCN concentration. It was found that the N263 concentration was the main factor affecting rhenium extraction, and the regression equation of rhenium extraction was Re extraction/% = 0.672 + 9.880 [N263]. Moreover, N263 concentration and O/A ratio are the main factors affecting rhenium molybdenum separation coefficient. The regression equation of rhenium molybdenum separation coefficient is βRe/Mo = 37.5 + 116.88* [N263] −24.3 *(O/A ratio) −20.62 [N263]*(O/A ratio). At the same concentration of the rhenium stripping agent, the rhenium stripping efficiency is perchloric acid > nitric acid > sodium thiocyanate. However, the strong oxidability of perchloric acid and nitric acid destroys the organic phase, making the organic phase produce visible destruction. The rhenium stripping was about 75.8 % with 40 times the theoretical amount of sodium thiocyanate. The results showed that Re was easy to be extracted in the alkali solution, but it was not easy to be stripped from the loaded N263 phase.

Methane and Carbon Dioxide Hydrate Formation in the Presence of Metal-Based Fluid

Hydrate-based technology has yet to find its way to commercial applications due to several issues, including formation conditions and slow kinetics. Several solid particles were introduced to speed up hydrate formation. However, these solid compounds have given contradictory results. This study investigated the effect of high thermal conductive metallic nanofluids of silver (Ag) and copper (Cu) on CH4 and CO2 hydrates. The solid particles were suspended in a 0.03 wt% SDS aqueous solution, and the results were compared with the 0.03 wt% SDS and deionized water samples. A stirred tank batch reactor was used to conduct the thermodynamic and kinetic experiments. The thermodynamic study revealed that 0.1 wt% of solid particles do not shift the equilibrium curve significantly. The kinetic evaluation, including induction time, the initial rate of gas consumption, half-completion time, t50 and semi-completion time, t95, gas uptake, and storage capacity, have been studied. The results show that the Ag and Cu promote CH4 hydrates while they inhibit or do not significantly influence the CO2 hydrates formation. A predictive correlation was introduced to get the apparent rate constant of hydrate formation in the presence of metal-based fluid at the concentrations range of 0.005-0.1 wt%.

Separation of phosphoric acid and magnesium from wet process phosphoric acid by solvent extraction

ABSTRACT Wet process phosphoric acid (WPA) contains a high concentration of metal cations. Our research group developed a P-15 extractant that can effectively remove metal cations in WPA. Different metal cations supported by the extractant are stripped and recycled by different stripping agents. In this study, ammonium sulfate is used as a stripping agent to separate magnesium ions from the extractant. So that phosphoric acid and magnesium ions can be separated and separately prepared into their own products. To determine the optimal operation parameters of the magnesium ion stripping process, single factor experiments are conducted. Under the reaction temperature of 333.15 K, stirring speed of 300 rpm, phase ratio (A/O) of 1/2, ammonium sulfate concentration of 3.305 mol/L, and reaction time of 30 min, the stripping efficiency reaches 75%. A stripping equilibrium curve at 333.15 K is plotted to determine the optimal reaction order for countercurrent stripping. Through two-stage countercurrent stripping, the magnesium ion concentration in the extractant could be reduced to approximately 0.0018 mol/L when A/O = 1/2. Magnesium ion concentration in extraction can be reduced from 0.0419 mol/L to 0.0026 mol/L through two-stage stripping countercurrent cascade. The concentration of each kind of impurity ion in ammonium magnesium sulfate crystals is all below 500 ppm.

The Unique Magnetic Signature of Sickle Red Blood Cells: A Comparison Between the Red Blood Cells of Transfused and Non-Transfused Sickle Cell Disease Patients and Healthy Donors.

Sickle cell disease (SCD) is an inherited blood disorder that affects millions of people worldwide, especially in low-resource regions of the world, where a rapid and affordable test to properly diagnose the disease would be highly valued. Magnetophoresis is a technique that could simultaneously analyze, quantify, and potentially separate the patient's sickle red blood cells (RBCs) from healthy RBCs, but the magnetic characteristics of sickle RBCs have yet to be reported. In this work, we present the single cell magnetic characterization of RBCs obtained from SCD patients. Sufficient single cells are analyzed from patient samples undergoing transfusion therapy and not yet having transfusion therapy (TP and NTP, respectively), such that means and distributions of these single RBC mobilities are created in the form of histograms which facilitated comparison to RBCs from healthy donors (HD). The magnetic characterization is obtained using a technique known as Cell Tracking Velocimetry (CTV) that quantitatively characterizes the RBC response to magnetic and gravitational fields. The magnetic properties of RBCs containing oxygenated, deoxygenated hemoglobin (Hb) and methemoglobin (oxyHb-RBCs, deoxyHb-RBCs, and metHb-RBCs) are further determined. The NTP samples reported the highest magnetic character, especially when compared to oxyHb-RBCs from HD, which implies impaired oxygen binding capabilities. Also, the oxygen-Hb equilibrium curves are obtained to estimate the magnetic character of the cells under intermediate oxygen levels. Our results confirm higher magnetic moment of SCD blood (NTP) under intermediate oxygen levels. These data demonstrate the potential feasibility of magnetophoresis to identify, quantify and separate sickle RBCs from healthy RBCs.

The removal of Cr3+ using a vertical rotating micro-channel extractor with gas intensification and parallel model

A gas-liquid-liquid three-phase co-current vertical rotating micro-channel device is designed in this work to further strengthen the extraction process. The Cr3+-2-ethylhexyl phosphoric acid-2-ethylhexyl ester (EHEHPA) system was chosen to evaluate the new rotating micro-channel device in parallel mixing mode. The equilibrium distribution of Cr(Ⅲ) in the aqueous and organic phases has been indicated for the first time, which depends on the variation of Cr3+ concentration and the pH of the aqueous. And then, the effect of gas intake quantity (Qg) and parallel flow pattern has been studied. Meanwhile, in the state of the gas phase adding, the impacts on the extraction efficiency are investigated, which include the distance between inner cylinder and outer wall (D), rotational inner cylinder speed (R) and volumetric flow rate (Qaq, Qo). The calculated stage efficiency, material balance(operating) line and equilibrium curve also have been studied, which demonstrates that the extraction of Cr3+ in one vertical rotating micro-channel in parallel model is equivalent to two traditional extractors.

Microwave-assisted synthesis of l-aspartic acid-based metal organic aerogel (MOA) for efficient removal of oxytetracycline from aqueous solution

Developing advanced adsorption materials is of great significance for removing antibiotics from wastewater owing to the increasingly severe issue of antibiotic contamination. Herein, a novel bio-based metal organic aerogel (FLAM) adsorbent with macroscopic shapeability, formed through the coordination of l-aspartic acid (L-AA) and Fe salt, was fabricated for the first time via the microwave-assisted synthesis method. Subsequently, the FLAM was used to remove oxytetracycline (OTC) from aqueous solution, and the result indicated FLAM exhibited ultrahigh adsorption capacity for OTC with a record-high value of 1566 mg·g−1, which greatly outperformed the reported adsorbents. The adsorption equilibrium curve and adsorption thermodynamics followed the pseudo-second-order kinetics model and the Freundlich model respectively, which indicated multilayer adsorption and chemisorption dominated the adsorption process. Significantly, the adsorbent also enabled efficient decontamination of tetracycline (TC) and chlortetracycline hydrochloride (CTC). Such an excellent adsorption capability of FLAM can be attributed to multiple factors, i.e., electrostatic interaction, surface complexation and hydrogen bonding. Coexisting experiments demonstrated that the FLAM possessed excellent application ability in treating practical antibiotic wastewater. Ultrahigh adsorption capacity and fast-synthesis method prefigured its broad prospect for OTC-related wastewater remediation.

Experimental investigation on the phase behaviour for gas hydrates in CO2 rich gas mixtures & multiphase system

Almost 40% of undiscovered hydrocarbon reserves have high CO2 and H2S concentrations around the globe. So it is crucial to understand these hydrocarbon systems’ thermophysical properties for the excellent design of production facilities. An experimental investigation is conducted in this study to understand and evaluate the thermodynamic conditions of gas hydrate formation in natural gas systems with high CO2 levels gas and dominant multiphase (high CO2 level gases, deionized water, and crude oil). Three gas mixtures were chosen in this study to simulate natural gas with high CO2 content. The experiments are conducted within the critical pressure of the selected gas to avoid any phase change due to pressure. The impact of high CO2 levels in gas systems on the thermodynamic conditions of the gas hydrates was first explored. Then, the effect of a multiphase system was investigated after the addition of the oil phase into the system. The thermodynamic equilibrium conditions obtained from experiments were used to construct the Hydrate liquid–vapour Equilibrium (HLVE) curves, and the phase behaviour was studied. The details about the temperature variance and enthalpy are also clearly discussed. It has been discovered that gas mixtures with a higher CO2 content tend to promote compared to the pure methane gas system but inhibit compared the pure CO2 system. But in the multiphase system, all the gases show an inhibition effect compared to their respective pure gas system results.

How land use functions evolve in the process of rapid urbanization: Evidence from Jiangsu Province, China

The continuous urbanization of the world is exacerbating the severe situation of insufficient supply of land resources. Therefore, realizing the synergy between urbanization and land use functions is the key to regional sustainable development. Our purpose is to discuss the synergistic state of land use functions and the transition characteristics of dominant functions under specific urbanization conditions. The theoretical framework of urbanization and land use functions is constructed from the four dimensions of “systems-elements- process-relationship”, entropy method, mechanical equilibrium model and curve estimation model are specifically considered. The results indicated that: (1) The comprehensive urbanization clearly shows characteristics of “Southern Jiangsu > Central Jiangsu > Northern Jiangsu” from 1997 to 2018, and the dominant type of urbanization has gradually shifted from population urbanization to economic urbanization. (2) The deviation index of land use functions is between 0.0055 and 0.2101, which is significantly higher in Southern Jiangsu than in Northern Jiangsu, and the dominant function of land use is gradually transformed into production function. (3) There is an obvious positive correlation between urbanization and land use functions from multiple dimensions, and when the production function becomes dominant, the urbanization development level of Southern Jiangsu reaches 0.5038, correspondingly, Northern Jiangsu is 0.2791. This research can provide a quantitative reference and policy decision basis for rationally regulating land use functions at different stages of urbanization.

Molecular Dynamics Study of CO2 Phase Change Transport in the Near-Critical Region: Model Parameter Optimization

The technical development of supercritical CO2, energy systems, CO2 capture, and other applications has become a hot topic in recent years. Therefore, molecular dynamics simulation (MD) of CO2, especially the investigation at the CO2 supercritical region is urgently needed. This study focused on the optimization of common CO2 potential model EPM2 (elementary physical model—2) combined MD forcefield OPLS-AA (optimized potentials for liquid simulations—all atom) and CHARMM (chemistry at Harvard macromolecular mechanics for MD simulation). Through adjusting angle parameters according to EPM2, vapor-liquid equilibrium curve, critical point and supercritical region could be well corresponding with experiments, which can be more accurate than previous approaches. The simulated results using 179.63° in OPLS-AA forcefield can not only correspond to supercritical phase of near-critical region (within ±10% error range under CO2 is at 468 kg/m3, 304.2–320 K, 7.2–10.0 MPa), but also be consistent with actual CO2 properties in gas phase of near-critical region (temperature range can reach 304.2–350 K while the density scope can reach 15–168 kg/m3). Besides, optimized potential model also has a certain reliability on the investigation of CO2 diffusion properties. The values simulated have the same order of magnitude as literature values, especially simulated diffusion coefficient values at gas phase. The CO2 property of heat capacity is also simulated, and the errors are within ±15%. That is to say, the optimized CO2 potential parameter also has a certain accuracy to analyze CO2 heat transfer. The angle value optimized in this study may be useful for the fundamental understanding of the supercritical state and it can well be applied in the further investigation of CO2 systems.

Red blood cell magnetophoresis as a function of oxygen partial pressure

Red blood cell (RBC) magnetophoresis is a function of the concentration of dissolved oxygen (O2) in normal RBCs measured by cell tracking velocimetry (CTV). The hemoglobin (Hb) magnetic susceptibility changes from diamagnetic (when fully oxygenated, oxyHb) to paramagnetic (when fully deoxygenated, deoxyHb) resulting in a small shift in the normal RBC diamagnetic susceptibility from lower to higher than that of water (-9.05 × 10-6). To date, the RBC magnetophoretic motion analyses have been limited to only two quaternary states of the Hb-O2 complexes, fully oxygenated RBCs (i.e. 100 % O2 saturation of Hb inside RBCs) and fully deoxygenated RBCs (0 % O2 saturation of Hb inside RBCs). In this work, the RBC magnetophoretic velocity is measured at small pO2 intervals for the entire physiological range of 0–160 mmHg. The changes in the RBC magnetophoresis as a function of the O2 partial pressure in solution (pO2) agreed with the theoretical predictions based on the RBC-O2 equilibrium curve (OEC, measured by Hemox Analyzer and Blood Oxygen Binding System, BOBS™) and the Adair O2-Hb cooperative binding theory. The results provide a scientific basis for future designs of a “magnetic filter” based on the precise control of the RBC magnetic moment by carefully controlling the pO2 of the RBC suspension.

Thermodynamic and kinetic synergetic separation of CO2/C2H2 in an ultramicroporous metal-organic framework

The selective removal of carbon dioxide (CO2) from acetylene (C2H2) is an important separation process in the petrochemical industry, but is challenging due to the similar physicochemical properties of the two gases. Using CO2-selective adsorbents that have preferential affinity for CO2 over C2H2 in pressure swing adsorption was deemed a promising separation method for the separation of CO2/C2H2 mixtures. Herein, we report an ultramicroporous metal-organic framework, Y-bptc, to achieve efficient separation of CO2/C2H2 through thermodynamic and kinetic synergetic effects. The unique cage-type structure interconnected by small windows exhibits high adsorption capacity for CO2 while efficiently impeding adsorption diffusion of C2H2, which was proved by the single-component equilibrium and kinetic adsorption curves. Grand canonical Monte Carlo (GCMC) molecular calculations further show that the µ3-OH− of the framework have a stronger adsorption affinity for CO2 through forming hydrogen bonds. Breakthrough experiments using Y-bptc as a CO2-selective adsorbent proved that high-purity C2H2 (>99%) could be directly produced from one-step separation of CO2/C2H2 (1/1, v/v) mixtures, which greatly reduced the separation process and energy consumption. In addition, the structure of Y-bptc due to the high charge density of the Y6 cluster has high stability under humid and high-temperature conditions adding to the application possibility in industry.

Calcium leaching from cement hydrates exposed to sodium sulfate solutions

Calcium leaching from cement hydrates to pore solution increases the porosity and reduces the bonding strength of cement hydrates, accelerating the degradation of concrete. Calcium leaching can be quantified by solid–liquid equilibrium curves, which have been studied in deionized water or ammonium nitrate. The research of solid–liquid equilibrium curve of calcium under sulfate attack is limited and its mechanism is poorly understood. Reported here provide insights into the dissolution process of calcium from cement hydrates exposed to the sodium sulfate solution. The experimental programme examines the effects of sulfate ion concentration and temperature. An external sulfate attack (ESA) model considering the influence of calcium leaching is established and validated. The results show that, compared to deionized water, sulfate ions impact strongly the leaching process. Qualitatively, the dissolution of calcium in cement hydrates is accelerated by increasing the concentration of sulfate ions and decreasing the environmental temperature. Quantitatively, the presence of sulfate ions modifies the equilibrium curve describing calcium leaching in deionized water. In addition, the prediction results of the ESA model considering the influence of calcium leaching are in good agreement with the experimental results.