Experimental Measurements of Carbon Dioxide Solubility in Na–Ca–K–Cl Solutions at High Temperatures and Pressures up to 20 MPa

International audienceExperimental CO 2 solubility data in brine at high pressures and high temperatures are needed in different technologies such as carbon dioxide storage or geothermal process. A lot of data have been acquired in single-salt solutions, whereas data for mixed-salt solutions remain scarce. In this study, new carbon dioxide solubility data in salt solutions have been measured. Two synthetic brines have been studied at 323, 373, and 423 K from 1 to 20 MPa. The brine 1 is composed of a mixture of NaCl and CaCl 2 and the brine 2 is made from a mixture of NaCl, CaCl 2 , and KCl. Measurements have been carried out by conductimetric titration. In this study, 6 isotherms presenting 48 new solubility data have been reported. These results have been obtained in an original range of temperature, pressure, and salinity. In these conditions of temperature and pressure, we verified that an increase of the temperature or the salinity involves a decrease of the CO 2 solubility. On the other hand, an increase of the pressure implies an increase of the CO 2 solubility. Then, the obtained results were compared with the values calculated using PhreeSCALE and PSUCO2 models. The comparison between experimental and calculated values revealed a good agreement

Thermodynamic Modelling of the Excess Properties of Natural and Industrial Brines

Les saumures naturelles sont des ressources en eau de plus en plus convoitées et utilisées par les industriels, que ce soit pour la production d’eau potable (dessalement de l’eau de mer…) ou pour la récupération de substances valorisables (le lithium, le potassium, le magnésium, la silice …). Les saumures industrielles sont aussi souvent utilisées dans différents procédés comme fluides caloporteurs ou lors d’extraction de minerai (phosphore, alumine…). Cependant, ces solutions aqueuses complexes présentent des propriétés thermodynamiques qui s’écartent de celles des solutions aqueuses diluées (dites idéales). Des approches de calcul spécifiques sont alors nécessaires pour pouvoir déterminer ces propriétés. Cette étude s’intéresse au calcul des propriétés thermodynamiques d’excès (coefficient osmotique, capacité calorifique, densité …) de ces systèmes. Celles-ci dépendent toutes de la dérivée de l’énergie libre de Gibbs d’excès (G^ex) par rapport à la concentration en sels dissous, à la température ou à la pression. Suite à une revue bibliographique des différents modèles thermodynamiques permettant de calculer l’énergie libre de Gibbs d’excès, le modèle de Pitzer a été sélectionné pour décrire les propriétés d’excès d’un système contenant c cations, a anions et n espèces neutres. Les propriétés thermiques et volumiques ont été, dans un premier temps, établies pour un système contenant des espèces neutres avant d’être implémentées dans le logiciel PhreeqC, logiciel de géochimie qui permettait déjà le calcul du coefficient osmotique, de l’activité de l’eau et du coefficient d’activité. Le logiciel issu de cette modification, PhreeSCALE, permet désormais, lorsque les paramètres d’interaction de Pitzer sont connus, de calculer les propriétés d’excès telles que le coefficient osmotique, la capacité calorifique ou la densité d’une saumure en tenant compte de la spéciation exacte de la solution. Dans le cas où les paramètres d’interaction sont à déterminer, PhreeSCALE peut être couplé à des logiciels d’optimisations pour établir de nouveaux jeux de paramètres, calés sur les propriétés mesurées des solutions. Les applications de cette étude s’appuient sur plusieurs systèmes qui sont soit des saumures industrielles, soit des saumures naturelles. Le système NaOH-H2O a été sélectionné en raison des salinités élevées dans l’eau (jusqu’à 29 mol.kgw-1 à 25°C). Pour représenter au mieux l’ensemble des propriétés sur toute la gamme de concentrations, la dissociation partielle de l’espèce NaOH a dû être prise en compte. Les autres systèmes étudiés sont des saumures chlorurées, plus caractéristiques des saumures naturelles. Une approche par étape a permis d’établir les paramètres d’interaction pour cinq systèmes binaires (NaCl, KCl, CaCl2, MgCl2 et BaCl2). Puis, des systèmes ternaires et un système quinquénaire composés de ces cinq électrolytes, ont été étudiés. Dans chaque cas, la capacité calorifique et la densité ont été déterminées. Finalement des abaques, tenant compte des conditions de température et de pression, ont pu être tracées pour le système NaCl-H2O.Natural brines are water resources that are increasingly sought and used by industrialists both to produce drinking water (e.g. seawater desalinisation) or retrieve economically exploitable substances (lithium, potassium, magnesium, silica, etc.). Industrial brines are often used in various processes as coolants or in ore processing (phosphorus, alumina, etc.). However, the thermodynamic properties of these complex aqueous solutions differ somewhat from those of so-called "ideal" diluted aqueous solutions. Specific calculation methods must therefore be used to determine these properties. This study focuses on calculating the thermodynamic excess properties of these systems (osmotic coefficient, heat capacity, density, etc.). All of these depend on the derivative of the excess Gibbs free energy (G^ex) in relation to the concentration of dissolved salt, temperature or pressure. A literature survey of thermodynamic models capable of calculating excess Gibbs free energy was done and the Pitzer model was chosen to describe the excess properties of a system containing c cations, a anions and n neutral species. Thermal and volumetric properties were determined for a system containing neutral species and these were then added to PhreeqC, a geochemical model that makes it possible to calculate the osmotic coefficient, water activity, and the activity coefficient. The resulting model, PhreeSCALE, now makes it possible, when the Pitzer interaction parameters are known, to calculate excess properties such as the osmotic coefficient, the heat capacity, and the density of a brine, taking into account the precise speciation of the solution. If the interaction parameters must be determined, PhreeSCALE can be coupled with optimisation software to determine new parameter sets based on properties measured in solution. The applications of this study are based on several systems that are either industrial or natural brines. The NaOH-H2O system was chosen because of its high salinities in water (up to 29 mol.kgw-1 at 25 °C). To best represent all of the properties over the entire range of concentrations, the partial dissociation of the NaOH species had to be considered. The other systems studied are chloride brines, which are more like natural brines. A multi-step approach made it possible to determine the interaction parameters for five binary systems (NaCl, KCl, CaCl2, MgCl2, and BaCl2). Ternary systems and one quinary system made up of all five electrolytes were then studied. In each case, the heat capacity and the density were determined. Charts taking into account temperature and pressure conditions were drawn for the NaCl-H2O system

Thermodynamics of aqueous solutions at high ionic strength using the Pitzer model.

International audienceMore and more attention is paid to the description of brine chemistry for various reasons. Natural brines are extensively exploited for the reserves of valuable chemical elements or chemical products they contain (such as lithium, potash, potassium, magnesium and other various salts). Geothermal energy currently uses hot deep brines. Greenhouse gases like CO2 are forecasted to be stored in deep geological reservoirs containing saline solutions. The number of desalination plants is increasing with the fresh water demand, leading to increasing amounts of highly saline waste. Geochemical modelling is one of the numerical tool needed to predict the properties and the behavior of such systems. Different approaches can be used but one of the most relevant is the Pitzer [1] model. Since more than 20 years, our team is working on developing and improving the modelling of multicomponent saline systems, using the Pitzer approach. Our efforts focus on both the development of a database for specific interaction parameters and a numerical code. We propose a Pitzer database for several chemical systems in order to deal with lithium chemistry [2,3] , phosphate systems, chloride systems (Na+, K+, Ca+2 and Mg+2)-Cl between 0-100°C [4] , and nitrate-sulfate systems [5] at 25°C, both in acidic and basic conditions. These implementations in the database allow dealing with topics such as the optimisation of lithium extraction process from salars brines or the improvement of phosphate production from WPPA process. Next evolution perspectives of this database are the extension to high temperatures (above 150°C) and the addition of trace elements (aluminium and radionuclides for instance). The description of these complex aqueous solutions requires the development of specific tools, like PhreeSCALE [6] , after the geochemical code PHREEQC [7]. In this new tool, computation of heat capacities, excess enthalpy and density was implemented in coherence with Pitzer and HKF [8] models. Consequently, the heat capacity or density of a geothermal fluid can be computed according to its exact chemical composition. References: (1) Pitzer, K. S. 1991 Activity Coefficients in Electrolyte Solutions (2) Lassin, A.; et al. Am. J. Sci. 2015, 315, 204–256 10.2475/03.2015.02. (3) Lassin, A.; et al. CALPHAD accepted. (4) Lach, A.; et al. J. Chem. Eng. Data 2017, 62 (10), 3561–357610.1021/acs.jced.7b00553. (5) Lach, A.; et al. J. Chem. Eng. Data 2018, in press 10.1021/acs.jced.7b00953. (6) Lach, A.; et al. Comput. Geosci. 2016, 92, 58–69 10.1016/j.cageo.2016.03.016. (7) Parkhurst, D. L.; Appelo, C. A. J. 2013 Description of Input and Examples for PHREEQC Version 3 (8) Helgeson, H. C.; et al. Am. J. Sci. 1981, 281, 1249–1516 10.2475/ajs.281.10.1249

Darapskite solubility in basic solutions at 25 °C: A Pitzer model for the Na NO 3 SO 4 OH H 2 O system

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Thermodynamics of saline aqueous solutions

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Geochemical modelling at high temperature.

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THERMODYNAMIC MODELING IN THE Na-NO3-SO4-Cl-OH-H2O CHEMICAL SYSTEM AT 25 °C

International audienceIn the French concept for radioactive waste disposal, long-lived intermediate-level waste (bituminous waste, for instance) and radiferous waste contain large amounts of soluble salts which are essentially composed of nitrate and sulfate. Because of their high solubility, these salts will dissolve into the pore solution coming from the concrete barrier after the closure of the disposal. Then, under repository conditions, the resulting increased ionic strength brine could migrate by diffusion through the cement barrier, potentially reach the surrounding rock and impact the physical and chemical behavior of the constituents of the host material. The extent of this impact, including the spatial extent of the saline plume, is unknown. To determine how much of an issue this is, a first step consists of correctly describing the aqueous solutions' properties and mineral solubility in the nitrate-sulfate system. This study focuses on the Na-NO 3-SO 4-Cl-OH-H 2 O system and, in particular, on the computation of its thermodynamic properties (e.g., water activity or osmotic coefficient, and ion activity coefficients). To this end, we use the semi-empirical thermodynamic Pitzer model [1], which was developed to extend the field of application of the Debye-Hückel equations [2] only valid for a low range of molalities. The Pitzer model relies on the description of specific interactions between aqueous species that become dominant over ionic strength as concentrations increase. For one electrolyte, hypothetically totally dissociated in water, the model involves three adjustable interaction parameters (β (0) c/a , β (1) c/a and C φ c/a). In the quaternary system, two additional specific interactions are involved and the related interaction parameters can be determined: θ c/c' or a/a' and ψ c/c'/a or a/a'/c. For more complex systems, no supplementary parameters are necessary. In case the electrolyte is considered partially dissociated, neutral species, n, can be present in the aqueous solution, which implies new additional specific interactions. Thus new binary and ternary interaction parameters can be determined (λ nc , ζ nca …). Consequently a step-by-step approach is necessary to study a complex chemical system. First, all the binary subsystems are studied and binary interaction parameters are optimized, mainly on the basis of experimental osmotic coefficient data. Then, the ternary interaction parameters are determined from solubility data. Finally, quaternary systems or more can be studied. In the case of the system of interest in this study, NaNO 3 , Na 2 SO 4 and NaCl are considered totally dissociated whereas the partial dissociation of NaOH must be taken into account, due to its high solubility (28.3 mol • kg-1 at 25 °C) [3]. So in addition to interaction parameters for NaOH-H 2 O, the dissociation constant of NaOH 0 (aq) is required. The binary interaction parameters relative to the aforementioned binary systems are provided by previous studies [3–6], while ternary interaction parameters are determined in this study. Without supplementary data the phase diagram of the quaternary system Na-NO 3-SO 4-OH-H 2 O is determined (Figure 1). The comparison of numerical results with experimental observations is tricky since few data exist on this specific system [7]. Consequently, to show the coherence of the proposed parametrization on the Na-NO 3-SO 4-OH-H 2 O system, the model is extended to study the quaternary Na-NO 3-SO 4-Cl-H 2 O system. Finally, after checking binary and ternary parameters of this last system the model can correctly represent the experimental data of the Na-NO 3-SO 4-Cl-H 2 O system. This check confirms the coherence of the proposed parametrization and the accuracy of the calculations for the Na-NO 3-SO 4-OH-H 2 O system. This chemical system of interest for the waste radioactive storage was recently published [8]

L'extraction du lithium des saumures naturelles et des salars - Modélisation thermodynamique des systèmes électrolytiques et l'établissement des séquences évaporitiques

International audienceThe recovery of minerals from saline waters has been practiced since the antiquity and salt is still of great value for man needs and technological developments. Seawater contains large quantities of valuable minerals, some of them being very scarce and expensive in their land-based form. Brines from salted lakes, salars, oil and geothermal reservoirs contain high concentrations of valuable metals (i.e., Li, Zn, Cu, Zn, Mg, K, Br, B, REE, etc.). Brine mining is becoming an attractive option mainly because of the depletion of high-grade ores exploited by land-based mining industries. However, up to now, only few minerals are mined from natural brines. Among the numerous valuable elements issued from natural brines, the lithium is one of the most attractive. Indeed, large amounts of lithium are found in the salars of the Altiplanos in South America, mostly in Chile, Argentina and Bolivia. Many other sources of lithium exist in saline lakes, geothermal and oil brines in other countries. Regardless of the sources and geochemical cycle of lithium in hydrogeological systems, an understanding of its thermodynamic properties and its geochemical behavior is a prerequisite for its exploration, extraction and exploitation. Indeed, it can reach abnormally high concentrations in aqueous solutions due to the very high solubility of the lithium salts. Comprehensive and consistent thermodynamic models are then needed to accurately predict lithium aqueous chemistry (like speciation) and associated lithium mineral solubilities in highly saline waters. The development of such approach is a prerequisite for developing and optimizing extraction processes. Numerical simulations of the thermodynamic properties of the brines and salt solubilities allow establishing the specific evaporation sequence and estimating the amounts of valuable precipitated solids (LiCl, Li2CO3, etc.) to be recovered from the exploited brines taking into account the salinity of the brine, the exploitation conditions (temperature, evaporation rate, etc.). This allows identifying the family of minerals and their maximal precipitable amounts depending on the rate of its precipitation and the reaction paths constrained by some internal loops. A global overview of the state of the art will be presented with some challenges for Lithium extraction from salars

CHEMICAL BEHAVIOR OF NITRATE IN CEMENTITIOUS MATERIALS AND SALINE AQUEOUS ENVIRONMENTS

International audienceIn the context of radioactive waste disposal, long-lived intermediate-level waste (bituminous waste, for instance) and radiferous waste contain large amounts of soluble salts which are essentially composed of nitrate. Because of their high solubility, these salts will dissolve into the pore solution coming from the concrete barrier. Then, under repository conditions, the resulting increased ionic strength brine could migrate by diffusion through the cement barrier, potentially reach the surrounding rockand impact the physical and chemical behavior of the constituents of the host material. The extent of this impact, including the spatial extent of the saline plume, is unknown. To determine how much of an issue this is, the first step consists of correctly describing the aqueous solutions’ properties and mineral solubilities in the nitrate system. This study focuses on the Na-K-Ca-NO3 quaternary system

Thermodynamic study of the ternary system LiCl-Li2CO3-H2O

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