Gibbs Energy Minimization Software Research Articles

Effect of CO2 Mineralization on the Composition of Alkali-Activated Backfill Material with Different Coal-Based Solid Wastes

Research focusing on waste management and CO2 mineralization simultaneously has been a popular topic in the mining community, and a common approach is to mineralize CO2 with coal-based solid waste (CSW, e.g., gangue (CG), fly ash (FA), coal gasification slag (CGS)) produced by mining activities. Despite the understanding of CO2 mineralization by cementitious materials, the mineralization capacity of alkali-activated CSWs remains unknown. Therefore, the mineral composition evolution and mineralization capacity of different alkali-activated materials (prepared with CG, FA, CGS, and sodium hydroxide (which works as the alkali-activator), respectively) are investigated with the adoption of Gibbs Energy Minimization Software (GEMS). The results indicate that the abovementioned three alkali-activated CSWs are majorly composed of calcium silicate hydrate, magnesium silicate hydrate, kaolinite, sodium zeolite, and liquid. Due to the difference in the chemical composition of different CSWs, the amount of hydration products varies. Specifically, the alkali-activated CSWs made with CGS have the maximum calcium silicate hydrate (C-S-H), while those prepared with FA enjoy the lowest porosity. In addition, the CO2 mineralization process will result in the formulation of carbonate and, theoretically, the maximum quantity of mineralized CO2 is less than 20% of the binder used. Furthermore, compared with CG and CGS, FA is characterized with the highest mineralization capacity. The findings in this study contribute to the understanding of CO2 mineralization with alkali-activated CSWs.

Thermodynamic equilibrium approach to predict the inorganic interactions of ash from biomass and their mixtures: A critical assessment

Process simulation approaches based on thermodynamics calculations can provide good capabilities to predict the ash behavior of biomasses and their mixtures. In the present work, a critical assessment of such simulations was performed in the field of biomass ashes, and experimentally checked to be at equilibrium. Two commercial thermodynamic databases, FToxid and GTOX, were used together with the FactSage Gibbs energy minimization software. For the first time in literature, a comparison was performed between the calculated phase equilibria using the recent market versions of the two databases. The predicted results were then compared to those measured on various ash samples of straws and barks along with their ash mixtures, highlighting the lingering need for improvements for the recent versions of these commercial databases.The phase diagram approach showed excellent capabilities in predicting the physical state of the ash (solid, liquid, or solid-liquid mixture) using both databases. Global simulations using the FToxid database showed better prediction capabilities for single biomass ash than those using the GTOX database. Unfortunately, predictions using the former were significantly limited in the case of ash mixture samples, whereas using the latter were a total failure. Nevertheless, both databases showed correct volatilization prediction capabilities but failed to forecast the solidus and liquidus characteristic temperatures. Further work is still needed to enhance the prediction capabilities of this tool.

Study on the Strength and Hydration Behavior of Sulfate-Resistant Cement in High Geothermal Environment.

The hydration process and compressive strength and flexural strength development of sulphate-resistant Portland cement (SRPC) curing at 20 °C, 40 °C, 50 °C, and 60 °C were studied. In addition, MIP, XRD, SEM, and a thermodynamic simulation (using Gibbs Energy Minimization Software (GEMS)) were used to study the pore structure, the types, contents, and transformations of hydration products, and the changes in the internal micro-morphology. The results indicate that, compared with normal-temperature curing (20 °C), the early compressive strength (1, 3, and 7 d) of SRPC cured at 40~60 °C increased by 10.1~57.4%, and the flexural strength increased by 1.8~21.3%. However, high-temperature curing was unfavorable for the development of compressive strength and flexural strength in the later period (28~90 d), as they were reduced by 1.5~14.6% and 1.1~25.5%, respectively. With the increase in the curing temperature and curing age, the internal pores of the SRPC changed from small pores to large pores, and the number of harmful pores (>50 nm) increased significantly. In addition, the pore structure was further coarsened after curing at 60 °C for 90 d, and the number of multiple harmful pores (>200 nm) increased by 17.9%. High-temperature curing had no effect on the types of hydration products of the SRPC but accelerated the formation rate of hydration products. The production of the hydration products C-S-H increased by 13.5%, 18.6%, and 22.8% after curing at 40, 50, and 60 °C for 3 d, respectively. The stability of ettringite (AFt) reduced under high-temperature curing, and its diffraction peak was not observed in the XRD patterns. When the curing temperature was higher than 50 °C, AFt began to transform into monosulfate, which consumed more tricalcium aluminate hydrate and inhibited the formation of “delayed ettringite”. Under high-temperature curing, the compactness of the internal microstructure of the SRPC decreased, and the distribution of hydration products was not uniform, which affected the growth in its strength during the later period.

Effect of waste corn stalk ash on the early-age strength development of fly ash/cement composite

To alleviate the challenges from the early-age strength shortage of fly ash/cement system, the corn stalk ash, an agricultural waste, was used to expedite the early-age strength development of the fly ash/cement system. The mechanical property was tested and the microstructure was analyzed to understand the hydration mechanism of this system. Besides, the Gibbs Energy Minimization Software (GEMS) was applied to further understand the hydration process. It can be deduced from the results that the corn stalk ash accounted for the increase of the content of the amorphous phase and the reduction of the calcium hydroxide.

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

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

Evaporation of materials from the molten salt reactor fuel under elevated temperatures

The release of fission product and salt compounds from a molten salt reactor fuel under accident conditions was investigated with coupled computer simulations. The thermodynamic modeling of the salt and fission product mixture was performed in The Gibbs Energy Minimization Software GEMS and the obtained compound vapor pressures were exchanged with the severe accident code MELCOR, where the evaporation from a salt surface located at the bottom of a confinement building was simulated. The fuel salt considered in the simulations was LiF-ThF4-UF4 with fission products Cs and I. The composition of the fuel salt material was obtained from an equilibrium fuel cycle simulation of the salt using the EQL0D routine coupled to the Serpent 2 code. The results were compared to simulations using pure compound vapor pressures in the evaporation simulations. It was observed that by modeling the salt mixing the release of fission products and salt materials was reduced when compared to the pure compound simulations. The mixing effects in the salt, when compared to the pure compound simulation also affected evaporation temperatures and therefore the timing of the release of compounds. In an additional simulation in which the depressurization of the confinement was considered, the total evaporated mass of compounds increased due to increased mass transfer at the salt surface. The simulation process described in this paper can be used for a more comprehensive accident analysis of molten salt reactors once the detailed description of the reactor confinement and accident sequences are available and more fission product elements have been added to the analysis.

Thermodynamic modeling of Portland cement without mineral additives

The paper deals with thermodynamic modeling of Portland cement hydration as a complex system, which describes the clinker dissolution, diffusion, and surface phenomena that occur on phase nuclei at different water/cement ratio and depend on the curing time and temperature of the whole process. Using Gibbs Energy Minimization Software (GEMS) and the hydration model proposed by Parrot and Killoh, thermodynamic modeling allows a longterm detection of the amount of both original clinker and nucleating phases such as cement paste, ettringite, Portlandite, and others. The paper presents results of GEMS modeling the phase composition during Portland cement hydration in terms of the Parrot and Killoh model and using the Rietveld refinement technique. Alite, belite, ferrite, and aluminate phases predominate in the cement paste. In order to get the Gibbs free energy of Portland cement in the vicinity of the cement system equilibrium, GEMS modeling considers a balance between the dissolution rate of clinker phases and the deposition of solid solutions of individual phases using thermodynamic parameters at different stages of cement hardening. At the initial stages of hydration, the aqueous solution is oversaturated relative to the amount of elements which determine the Portlandite and ettringite compositions. During the hydration process, the formation of stable complex hydrated silicates occurs, and pH value decreases. It is found that the main components of hardening Portland cement are calcium–silicate–hydrate (C–S–H) and Portlandite which are used herein as reference phases for the identification of their content in Portland cement. Major phases of Portland cement after 5-month curing are studied using the Rietveld method as a tool of the quantitative phase analysis. As a result, the following phase composition is identified: 47.72% tobermorite amorphous phase, 37.40% ettringite, 5.12% portlandite, 0.30% alite and 7.96% belite. The obtained experimental data are in good agreement with theoretical calculations. Ab initio assessments of the binding energy prove the lattice stability in detected major phases.

Thermodynamic assessment of ZnO-SiO2 system

Abstract ZnO-containing slags are common in pyrometallurgical processing of the base metals and steel. This caused the interest to the thermodynamics of the ZnO-SiO2 system. A complete literature survey, critical evaluation of the available experimental data and a thermodynamic optimization of the phase equilibria and thermodynamic properties of the system ZnO-SiO2 at 1.013×105 Pa are presented. The molten oxide was described as an associate solution. The properties of liquid were reassessed and enthalpy term of the Gibbs energy of solid Zn2SiO4 was re-fitted to be compatible with the new data in the willemite primary phase field. The thermodynamic data set agrees well with the recent experimental observations. It can be used for predicting, e.g., the thermodynamic properties and the domains of the phase diagram, like critical point of the liquid miscibility gap, with a better accuracy than using the previous assessments. A set of optimized model parameters were obtained, reproducing the reliable thermodynamic and phase equilibrium data within their experimental errors from 298 K to liquidus temperatures, over the entire composition range. The created database can be used in a Gibbs energy minimization software to calculate the thermodynamic properties and the phase diagram sections of interest.

Hydration characteristics and modeling of ternary system of municipal solid wastes incineration fly ash-blast furnace slag-cement

Municipal solid waste incineration fly ash (MSWI FA) can be reused as an admixture in preparing various types of cementitious materials. In this work, MSWI FA was used as a supplementary cementitious material in combination with ordinary Portland cement and ground-granulated blast furnace slag (GGBFS). Mixture design modeling and Gibbs Energy Minimization Software (GEMS) were adopted to discuss the compressive strength and hydration characteristics of binary and ternary systems, respectively. A toxicity characteristic leaching procedure test of total Cr and Cr(VI) was conducted to analyze the environmental risk of MSWI FA-containing samples. The experimental data and the results of mixture design modeling suggested that, with an increase in MSWI FA in GGBFS-MSWI FA binary, the compressive strength exhibited an inverted ‘V’ shape. GGBFS could be activated by chloride and sulfate in MSWI FA to form ettringite and Friedel’s salt in the GGBFS-MSWI FA binary system, according to the results of GEMS and X-ray diffraction. At nearly 0.55 of MSWI FA proportion in the GGBFS-MSWI FA system, the compressive strength and the modeling volume of ettringite and Friedel’s salt reached their maximum. The concentration of leached Cr and Cr(VI) indicated that the hydrates from the solidified mixtures could reduce the leaching rate of total Cr and Cr(VI).

Thermodynamic database for multicomponent oxide systems

A state-of-the-art thermodynamic database has been developed for multicomponent oxide systems. It can be used in combination with FactSage software to calculate the properties of metallurgical slags, glasses, ceramics, refractories, minerals, cements, etc. The database has been developed by collecting all available structural, thermodynamic, and phase equilibria data for a particular chemical system, critical evaluation of this information, developing a thermodynamic model for each solution phase and optimization of model parameters to reproduce the experimental data. Then the models are used to estimate the thermodynamic properties of multicomponent solutions from the properties of lower-order subsystems. Oxide phases often exhibit complex structures and strong interactions between components, which require more sophisticated models than are normally used, for example, for metal alloys. Short-range ordering is rather common and random mixing is often not a good approximation. The models for multicomponent liquid and solid solutions have been developed within the Modified Quasichemical Formalism and Compound Energy Formalism. Optimized model equations are consistent with thermodynamic principles and fully characterize a chemical system, requiring much less experimental work to achieve this goal since only a few measurements are needed in higher-order systems to validate the model estimates. The database can be readily used in conjunction with the FactSage Gibbs energy minimization software to calculate any stable or metastable phase equilibria and phase diagrams. The present article outlines the major components and phases that are currently available in the oxide database, as well as the most important features of the models that have been developed. The model and database have also been developed for the viscosity of oxide melts and glasses. The model links the viscosity to the structure of the liquid phase, which is estimated using the thermodynamic database.

Scheil–Gulliver Constituent Diagrams

During solidification of alloys, conditions often approach those of Scheil–Gulliver cooling in which it is assumed that solid phases, once precipitated, remain unchanged. That is, they no longer react with the liquid or with each other. In the case of equilibrium solidification, equilibrium phase diagrams provide a valuable means of visualizing the effects of composition changes upon the final microstructure. In the present study, we propose for the first time the concept of Scheil–Gulliver constituent diagrams which play the same role as that in the case of Scheil–Gulliver cooling. It is shown how these diagrams can be calculated and plotted by the currently available thermodynamic database computing systems that combine Gibbs energy minimization software with large databases of optimized thermodynamic properties of solutions and compounds. Examples calculated using the FactSage system are presented for the Al-Li and Al-Mg-Zn systems, and for the Au-Bi-Sb-Pb system and its binary and ternary subsystems.

Contribution of limestone to the hydration of calcium sulfoaluminate cement

Calcium sulfoaluminate (CSA) cements can be blended with mineral additions such as limestone for properties and cost optimization. This study investigates the contribution of limestone to the hydration of a commercial CSA clinker regarding the hydration kinetics, hydrate assemblage and compressive strength. Nine formulations were defined at M-values of 0, 1.1 and 2.1 (M=molar ratio of anhydrite to ye’elimite) without and with medium and high limestone contents.Calorimetric results indicate that limestone accelerates the hydration reaction especially at M=1.1, probably due to the filler effect. The phase assemblages were calculated by thermodynamic modeling using Gibbs Energy Minimization Software (GEMS). With increasing limestone content the formation of ettringite and calcium monocarboaluminate is predicted at the expense of calcium monosulfoaluminate. With increasing M-value more ettringite is predicted at the expense of the monocarbonate and less calcite takes part in the hydration reactions.The modeled results compare well with the experimental data after 90d of hydration, except that calcium hemicarboaluminate was found instead of monocarbonate, which is assumed to be due to kinetics considerations.The lowest compressive strength occurs in ternary formulations, whereas in the absence of calcium sulfate, strength is significantly higher.The results presented here indicate that in CSA cements, limestone accelerates early hydration kinetics, takes part in the hydration reactions at M<2, and has a positive effect on strength development in systems without anhydrite.

A Thermodynamic Model for the NH4+, K+ // H2PO4-, H2P2O72-, NO3-, Cl- - H2O System

We have developed a quantitative thermodynamic description of the NH4H2PO4-(NH4)2H2P2O7-KH2PO4-K2H2P2O7-NH4NO3-KNO3-NH4Cl-KCl-H2O system, which is of great importance for fertilizers applications. The liquid phase and all solid solutions were modeled using the Modified Quasichemical Model for short-range ordering. The liquid model includes the reaction of dimerization of AH2PO4 (where A = NH4+ or K+) according to: 2 AH2PO4(liquid) ↔ A2H2P2O7(liquid) + H2O(liquid or gas). The model parameters are mainly obtained by the critical evaluation and optimization of available thermodynamic and phase equilibrium data for the lower-order subsystems. The model is then used to estimate the properties of multicomponent salts from these assessed parameters for the lower-order subsystems, using interpolation methods along with Gibbs energy minimization software. When used in conjunction with thermodynamic databases for solids, solid solutions, and gases, these databases permit the calculation of complex multiphase equilibria in multicomponent systems, using the FactSage thermochemical software. In particular, calculations of interest for the production and storage of fertilizers may be performed.

A Density Model Based on the Modified Quasichemical Model and Applied to the NaF-AlF3-CaF2-Al2O3 Electrolyte

A theoretical model for the density of multicomponent inorganic liquids based on the modified quasichemical model has been presented in a previous article. In the present article, this model is applied to the NaF-AlF3-CaF2-Al2O3 electrolyte. By introducing in the Gibbs energy of the liquid phase, temperature-dependent molar volume expressions for the pure fluorides and oxides, and pressure-dependent excess parameters for the binary (and sometimes higher-order) interactions, it is possible to reproduce, and eventually predict, the molar volume and the density of the multicomponent liquid phase using standard interpolation methods. All available density data for the NaF-AlF3-CaF2-Al2O3 liquid were collected and critically evaluated, and optimized pressure-dependent model parameters have been found. This new volumetric model can be used with Gibbs energy minimization software, to calculate the molar volume and the density of cryolite-based melts used for the electroreduction of alumina in Hall–Heroult cells.

Stability of calcium carbonate and magnesium carbonate in rainwater and nitric acid solutions

Carbonation of magnesium and calcium silicates has emerged as an interesting option for long term storage of captured CO 2 . However, carbonated minerals are not stable in acidic environments. This study was conducted to determine if synthetically carbonated minerals dissolve in acidic rain and release CO 2 . Synthetic magnesium and calcium carbonates were leached in nitric acid solutions of various acidities, as well as rainwater, and the stability of the minerals was investigated with various methods. The experimental study was complemented with thermodynamic equilibrium calculations using Gibbs energy minimization software (HSC 4.0). The leaching of base ions from the two carbonate minerals was found to behave similarly and depend mainly upon the acidity of the solution. The fraction of Mg and Ca dissolved after several days of stabilization in separate solutions with initial pH 1 was 9% for both carbonates, while the fraction of dissolved minerals in a solution with initial pH > 2 was less than 1%. FT-IR analyses of the reactor atmosphere revealed that CO 2 gas was more rapidly released from calcium carbonate than from magnesium carbonate. However, only 1.5% of the CO 2 stored in the calcium carbonate was released as gas at pH 1 against 0.0% for magnesium carbonate. No notable CO 2 release occurred when leaching magnesium and calcium carbonates in solutions of pH 2. The solid residue analyses showed that the fixed CO 2 content of the carbonates that had been exposed to nitric acid was even higher than before the treatment.

Thermodynamic Modeling of Zinc Distribution Among Matte, Slag and Liquid Copper

Recently a thermodynamic database was developed to calculate equilibria involved in copper production. Zinc has now been included in the database for the matte, slag and blister copper phases, thereby permitting calculations in the 8-component system Zn-Pb-Cu-Ca-Fe-Si-O-S. Thermodynamic and phase equilibrium data from the literature have been critically assessed and optimized with the modified quasichemical model. When used with the Gibbs energy minimization software and other databases of the F*A*C*T thermodynamic computing system, this database can be used to calculate the distribution of zinc among the matte, slag, copper and gas phases during copper smelting and converting, or under various conditions which are difficult to study experimentally. The calculations predict that the presence of zinc increases the solubility of copper in the fayalite slag.Récemment, nous avons développé une banque de données thermodynamiques afin de calculer des équilibres de phases propres aux procédés d'élaboration du cuivre. Nous venons d'ajouter le zinc à cette banque de données, pour la matte, le laitier, et la phase métallique. Il est donc possible de faire des calculs pour le système à huit composants: Zn-Pb-Cu-Ca-Fe-Si-O-S. Des données sur les propriétés thermodynamiques et les équilibres de phases, prises de la littérature, ont été évaluées et optimisées en utilisant le modèle quasichimique modifié. On peut utiliser cette banque de données, avec les autres banques de données et les logiciels de minimisation de l'énergie de Gibbs du système informatisé F*A*C*T / F*A*I*T, afin de calculer la distribution du zinc entre la matte, le laitier et l'alliage lors du smeltage et du convertissage du cuivre, ou pour des conditions qui sont difficiles à réaliser expérimentalement. Les calculs prévoient que la présence du zinc sert à augmenter la solubilité du cuivre dans le laitier fayalitique.

Thermodynamic modeling of lead distribution among matte, slag, and liquid copper

Recently, a thermodynamic database was developed for the calculation of equilibria involved in the production of copper. The present study is concerned with the further development of the thermodynamic models and the database of model parameters for the matte, slag, and blister copper phases with a view to including Pb in the database and permitting calculations in the seven-component system Pb-Cu-Ca-Fe-Si-O-S. Thermodynamic and phase equilibrium data available in the literature are reviewed, critically assessed, and optimized with the modified quasi-chemical model. When used with the Gibbs energy minimization software and other databases of the FACT thermodynamic computing system, the database developed in the present study can be used for the calculation of matte-slag-copper-gas phase equilibria during copper smelting and converting.

Thermodynamic modeling and phase equilibrium calculations in nuclear materials

Abstract