Environmentally Friendly Process for Producing Magnesium-Enriched

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A New Environmentally Friendly Process for Producing Magnesium-enriched Salt Charlotte Coussine, Lidia M. Casás, Jean-Paul Serin, François Contamine, Pierre Cézac, Karine Dubourg, and Jean Cambar Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.8b03114 • Publication Date (Web): 04 Oct 2018 Downloaded from http://pubs.acs.org on October 4, 2018

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Industrial & Engineering Chemistry Research

A New Environmentally Friendly Process for Producing Magnesium-enriched Salt Charlotte Coussine, Lidia Casás*, Jean-Paul Serin, François Contamine and Pierre Cézac. Univ Pau & Pays Adour/ E2S UPPA, Laboratoire de Thermique, Energétique et Procédés-IPRA EA1932, 64000, Pau, France. Karine Dubourg and Jean Cambar. Institut du Thermalisme, Université de Bordeaux, 8 rue Sainte Ursule, 40100, Dax, France. ABSTRACT A new production process to obtain magnesium-enriched salt from natural mineral water is described. The main purpose of this study was to develop a reproducible process for the production of salt of known and fixed compositions without the addition of chemicals. The first step involved the prediction of the evaporite sequence from the studied spring water composition. This simulation was accomplished with a numerical model previously developed by our team. From the theoretical evaporite sequence of the salt water, the specifications of the pilot could then be established and analytical devices were chosen: chromatographic modules for measuring concentrations and an electronic densimeter to monitor the density of the solution. Later, the experimental study of these tools was performed: operating principle, protocol, repeatability. Finally, the new experimental laboratory scale apparatus was validated. 1. Introduction

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Salts are mineral compounds used in many areas, particularly in food processing, cosmetics and chemical industries. They are available naturally in solid form or dissolved in aqueous solutions named salt (or saline) water: brines, sea water, thermal / mineral water or salt lakes. Thus, there are as many salt compositions as salt springs. By and large, natural salt is predominantly sodium chloride. However, this product may contain many other constituents such as calcium, potassium or magnesium. In addition, the salt and the associated salt saturated water, called mother liquor, can also be used in cosmetics and medicine, particularly in thermal treatments. That is why the produced salt is often referred as thermal salt. Indeed, certain minerals included in the salt have interesting properties for the human body1-3. Crystallization of salt is achieved by evaporation of saline water. Since prehistoric times, salt production is performed by humans. The oldest production process was discovered in Lunca, Romania and dated from the sixth millennium BC4. Since then different production techniques were developed and exploited; including salines, vacuum pans and evaporators. Salt production is substantial around the world. In 2017, world production was estimated at 280 million tonnes5. However, the production of mother liquor and salts enriched in other minerals with a constant and known composition is currently little mastered. The study carried out in our group focuses on the design of a method for producing value-added mother liquor and salt from a natural mineral water as raw material, specifically a strong sodic chlorinated mineral water- without the addition of any chemicals. In particular, the objective of this study was to produce a magnesium-enriched salt and / or mother liquor because of the wellbeing therapeutic properties and health benefits of this mineral. Thus, this element is the fourth most abundant cation in the human body and aside from its important role in clinical medicine, it has de-stressing, relaxing properties and is also used as a body-detoxifying product6-8. During the production process, brines are concentrated by evaporation until reaching the saturation and therefore precipitation of salts. The order of precipitated salts is called evaporite 2


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sequence and it is conditioned to the initial composition of the saline water. Salt crystallization process is considered as a unit operation of separation in dynamic mode. This is a system in phase equilibrium (vapor-liquid-solid) which evolves over time. In a previous work9, a general dynamic model for multiphase electrolytic systems has been developed in order to simulate the behaviour of aqueous solution involving liquid, solid and vapor phases. A numerical resolution method was used to solve the nonlinear differential system composed by the mass and energy balances, electroneutrality and evaporation equations, and the equilibrium equations. First simulations, whereby activity coefficients and solubility was modeled, were successful. Then, the model was used to simulate the evaporite sequence of salt water, as seawater, also achieving satisfactory results. In the present research, the general model was again applied to simulate the evaporite sequence of salt water with a mineral composition similar to those thermal spring water existing in the southwest of France. From the first results obtained by simulation, whereby magnesium-enriched salt precipitates at the end of the evaporite sequence and a literature review of salt production processes, the specifications of the experimental pilot were established. The analysis devices were then selected for an optimal monitoring of the process. Then, various experiments were conducted by varying the operation parameters. This experimental pilot has allowed verifying the feasibility of the process of producing mother liquor and magnesium-enriched. 2. Model Section As it has been described in our previous paper9, our general triphasic model is based on a thermodynamic description of the macroscopic physical-chemical phenomena involved in a vapor-liquid-solid system, supposed perfectly stirred and under heating. Thus, the appearance or disappearance of various solid and vapor phases should be taken into account in modelling, as

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well as the difficulties due to the presence of electrolytes and the consequent non-ideality of the solution. The main equations of the developed model are the following ones. • Chemical equilibria. In this kind of aqueous solutions only dissociation equilibria are involved: n species

∏

ν

a i i , j − mK dis j (T ) = 0

(1)

i =1

where i and j refer to the species and equilibrium, respectively. • Physical equilibria. They are fundamentally solid-liquid and vapor-liquid equilibria (Eq. 2 and 3, respectively): n species

∏

ν

(T ) = 0 ai i , j − mK SLE j

(2)

i =1

yi ·φiV (T , P, y )·P − xi ·γ i (T , P, x)· f i 0 L (T , P ) = 0

(3)

• Mass balance. Both, global and partial balances have been considered as follows: n solids dU dni +V + ∑ =0 dt dt i =1

(4)

  n solids yi dn dU  dxi  + n vapor ·V  + ∑ bi j · i = 0 bi ·U · + xi · ∑ dt  dt i =1 ∑i =1 yi  i =1 dt 

n species

j

(5)

Here we have chosen to work with partial mass balances on atoms, so bij is the number of atoms j in species i. The first term concerns to the liquid and vapour phase, and the second one refers to the solids. • Charge balance. The principle of electroneutrality must be respected: n ions

∑ z ·m i

i

=0

(6)

i =1

• Energy balance.

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dh dU n solids dhci dn U · 1 + h1· + ∑ ni · + hci · i + V ·H v − Q = 0 dt dt dt dt i =1

(7)

• Evaporation flow. It is calculated through the Carrier’s correlation10: n vapor

V − (0.089 + 0.40782·vel )·A·

∑ i =1

y i ·P − y ai ·P ∆H LVi (T )

=0

(8)

where vel and yai are the velocity of the air below the reactor and the vapor molar fraction of compound i in this air, respectively; A is the evaporation area of the vessel. All these equations are solved simultaneously by means of a numerical procedure, Gear’s method11. In the first stage of our work, initial simulations have been carried out with our studied raw material, a salt water whose composition is comparable to a natural mineral water from Béarn region (France), specifically a strong sodic chlorinated mineral water. Because each underground water has different physical-chemical characteristics, the choice of operating conditions in our pilot is conditioned to its composition. Thus, the general dynamic model for multiphase electrolytic systems has been used in order to simulate the sequence of salt precipitation from this raw material, based on the main parameters of the process: initial composition, temperature and pressure. According to this simulation, magnesium salt precipitates at the end of the sequence. These results are only guaranteed to our composition. Each kind of mineral water represents a particular case and would need its own modelling. 3. Experimental Section Our first modelling results showed that magnesium salts precipitate at the end of the evaporite sequence, whatever were the process parameters. Therefore, it is possible to isolate magnesium salts separating first salts produced in the process from those obtained by the end of the evaporite sequence. Keeping these results in mind, a literature review on salt production process from salt

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waters12-15 was conducted to devise the experimental pilot to obtain the magnesium enriched salts, in accordance with the best available technology. 3.2 Process description The process consists in two evaporative crystallizers placed in series. Batch stirred tank reactors (BSTR) were chosen to ensure a homogeneous solution. A filter system is placed between two reactors. First process step is carried out in the reactor 1. By evaporation and thus concentration of the solution, various salts precipitate; primarily calcium and sodium salts. When transferring from the first to the second reactor, the precipitated salts in reactor 1 are separated from the mother liquor which flows into reactor 2. Then, the solution recovered in the second reactor is enriched in magnesium and other compounds, such as potassium, because the salts formed by these species have not yet precipitated. Figure 1 shows the scheme of the final experimental pilot. Both crystallizers are made of glass and their volumes are 4 L and 500 mL, respectively. Inside of each reactor a 316-stainless steel mechanical stirring system is placed to ensure the homogeneity of temperature and compositions. A compressed air bubbling can also be introduced into each reactor in order to promote the evaporation of water. Then air flow is regulated using a tantalum ball flow meter (SHO-RATE R6-15-A) and a manual valve (Rexroth). In this case, the mechanical stirring system is not necessary for a good homogenization of the solution, which is then performed by the bubbling system. The two crystallizers are equipped with a double envelope. A PT100 sensor is placed in each of them and connected to a thermostatic bath Fisher Scientific Polystat 37 in order to regulate the temperature of the system by controlling the operation of a bath resistance. The setpoint can be external with a temperature regulation in the reactor or internal with a regulation of the thermal fluid temperature. The thermal fluid used is water because temperature during experiments was always less than 373.15 K. The uncertainty of the temperature measurement is 6


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estimated to ± 0.3 K. A filtration system is set up between two reactors in order to separate the saturated solid salts precipitated in the first reactor. The glass filter consists of a basket made of polypropylene homopolymer and a 5-micron porous polypropylene disc. Its effective volume is 1 L. The valves and the piping between two reactors are insulated and the filter is also composed of a double jacket in order to prevent a decrease in temperature and thus the precipitation of salts by cooling during the passage of the solution in the filtration system. Filtration is carried out in vacuum using a diaphragm pump to promote the separation process. Recovery of the vapor phase is performed by means of a glass condenser installed on the top of each reactor. The cold fluid used is also water. Condensate is recovered in the condenser outlet. The volumes of glass collecting containers for reactors 1 and 2 are 5 L and 1 L, respectively. A pressure gauge and an electro-valve have the function of displaying and controlling the pressure of two reactors. Vacuum is created by the diaphragm pump at the inlet of each collecting containers to promote the recovery of vapors from the condensers. Acquisition of temperature and pressure is executed by a display / controller equipped with a USB port for data recovery. The operating conditions in temperature and pressure of these equipments were fixed between 283.15 and 373.15 K and from 103 to 105 Pa, respectively. The sampling system consists of a movable 316-stainless steel tube connected to a valve and a syringe. The tube is introduced at the top of each reactor and can be moved vertically in order to reach the supernatant liquid in the reactor. This assembly allows sampling liquid phase for analysis by limiting the disturbance of the media in both reactors. The principle of the process is as follows. The salt water is introduced into the first reactor. Then temperature rises and / or pressure decreases to reach their fixed setpoint values. After this transitional phase, the solution is concentrated by evaporation of water promoted by air bubbling. As soon as the saturation point for one of the species in the solution is reached, the corresponding salt precipitate. When the system approaches the desired concentration, the valve of the first reactor is opened manually. Crystals of precipitated salts are recovered in the filter installed 7



between the first and the second reactor. Those are mainly sodium chloride and calcium sulfate. Then the second reactor is filled with the saturated solution. The evaporation goes on in this second reactor in the same operating conditions as previously in the first reactor. The evolution of the aqueous solution over time is followed through sample analysing by ion chromatography in order to determine the concentrations of the species and by electronic densimeter to evaluate the density of the solution. At the end of the experiment, the salts precipitated in each reactor are redissolved in ultra pure water and the aqueous solutions obtained were analysed by ion chromatography to determine the solid composition. The operating parameters to optimize in order to improve the quality of the obtained salt are mainly temperature and agitation. In addition, temperature, evaporation rate, which is also dependent on temperature and pressure, and stirring affect the crystal size and thus the crystallization step16. 3.3 Analysis The concentration of the ionic species in solution and the composition of salts, after dilution in ultrapure water, were measured by ion chromatography modules. It is thus possible to monitor the concentration of anions, cations and carbonates over time. The principle of the ion chromatography technique is based on the different affinities of ions for the stationary phase, the resin, in the presence of a carrier liquid phase called eluent. Ions move through the column at different speeds according to their affinities for the stationary phase. The affinity of the ions depends on their charges, their sizes and their polarizations. The anion and cation columns are made of an ion exchange resin and carbonate column consists of an ion exclusion resin. In the case of cationic and anionic modules, a guard column is located before the resin to capture contaminants and remove particles that could damage the separation column. The electrical conductivity of the ions is measured during their passage in the conductivity cell of the chromatograph. The conductivity measurement allows a qualitative and 8


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quantitative analysis of ionic species from the onset time of conductivity signal and the value of this signal, respectively. A suppressor is also connected in order to reduce the conductivity of the eluent and therefore increase the detection sensitivity of ionic species. Regeneration of suppressor is required during operation. In our case, we use a chemical regeneration with dilute sulfuric acid for anions and regeneration by electrolysis for cations. Suppressor is not necessary in the carbonates module because pure water is used as eluent and its conductivity is small. More details about modules and operation conditions are given in Table 1. Table 2 shows all the ionic species that can be analyzed with the three assemblies in order of appearance in the outlet of the separation column. Their respective retention times are the result of the eluent chosen and its flow. The reliability of the analysis results depends mainly on the calibration quality. In order to obtain a reliable calibration curve, we prepare five solutions at different known concentrations; each being injected 3 times. The stock solutions are standard solutions ICP CertiPUR® 1000 mg·L-1. Calibration solutions are prepared by dilution these stock solutions in 100 mL flasks using a micropipette. They can contain simultaneously multiple standards with the same sign (anions or cations). Thereby we prepare 5 anionic, 5 cationic and 5 carbonate standard solutions at different concentrations. Using the software Chromeleon© calibration curves of each species are then created. These curves give the surface or height of the peak as a function of the concentration. In this study, straight lines are used as calibration curves. For good accuracy peaks and in order to avoid column saturation, our highest concentration of each ion is 400 mg·L-1. For this reason, we also dilute the samples with ultrapure water to be lower than this value of concentration. Knowing the repeatability of the analysis device is necessary to determine the experimental measurement uncertainties and give a confidence interval of the results obtained. For that purpose, a solution was injected 20 times under the same measurement conditions. The resulting standard deviation gave the repeatability of the apparatus. This deviation is less than 3% for most 9



of the ionic species. However, in the case of magnesium, the standard deviation is 8%. This value can be explained partly by a relatively low concentration of the species, and secondly, by the proximity of magnesium and calcium peaks. The integration of these peaks has then more uncertainty. Throughout the results section, all measurements made by ion chromatography will be presented with a maximum uncertainty of 10%. Determining the density of the solution is necessary for conversion of molarity results, obtained by ionic chromatography, in molality (concentration unit used in this study). It was carried out using an electronic densimeter Mettler Toledo DM40, with an accuracy of 10-4 g·cm-3. This device is constituted by an oscillating U-tube of borosilicate glass. Density is evaluated by measuring the oscillation frequency, which is directly proportional to the density of the injected liquid. A Peltier thermostat is placed into the device to control temperature. The homogeneity of the cell is ensured by an automatic detection of air bubbles or solid particles in the sample. Calibration of the unit is done using two fluids at 293.15 K: air and ultrapure water. In the same manner as for the ion chromatography apparatus, repeatability of measurements was performed. Thus, a salt water solution was injected 20 times in the device. The resulting standard deviation is 0.03%. The electronic densimeter has therefore a very good repeatability. 4. Results and discussion First of all, a validation of the experimental pilot was conducted. On the one hand, we have verified here the proper operation of the pilot and sampling techniques for the monitoring of the system over time. On the other hand, the reproducibility of the experimental results was tested. This last step was essential because the purpose of this study is to produce a salt and / or valueadded mother liquor of constant compositions. The validation step also allowed to verify the main hypothesis of this study, the precipitation of magnesium salt at the end of the evaporite sequence whatever the initial conditions of the process. 10


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In order to confirm all these points, we have studied the evaporation of a brine containing the predominant existent species in natural solutions. The composition of the artificial salt water, concentrated in magnesium is given in Table 3. The experiments were carried out in the second reactor (500 mL) at 323.15 K and atmospheric pressure with a compressed air flow of 700 L·h-1 (at 298.15 K). Experimental molality values were followed over time by ion chromatography. In order to check the reproducibility of the pilot, three experiments were carried out under the same conditions of work. Then, each experimental sample was also injected three times in the ion chromatography device to verify that the three results from the same point were within the measurement uncertainty. Moreover, these results allow identifying globally the evaporite sequence. Indeed, when a salt precipitates, a change in the tendency of the curves is observed, for example a step or a decrease of the ion concentration. Figure 2 displays the obtained results for the molality of magnesium ions. Figures 3.a to 3.d represent the evolution of molality over time of other predominant ions of the salt solution: sodium, potassium, magnesium and chloride, respectively. All experimental values are within the measurement error bar. In this process, ion chromatography has been chosen to enable the monitoring of the evolution of the molalities over time In this work, the analytical technique has proved suitable, obtaining reproducible results. Indeed, molality follows the same trend in the three experiments. Moreover, the change in the curve, which corresponds to the precipitation of a magnesium salt, appears at the same time in the three experiments, at the end of the evaporite sequence. In these figures, data points shown are the average of the measurements. Error bars of the experimental points correspond to measurement uncertainty17. We have considered the maximum uncertainty that we could have on a species, 10%, and this value was used for all measurements made by ion chromatography. Lines are the data obtained by simulation. The error in obtained 11



results from the model is relatively large for the species potassium, magnesium and chloride, especially for high concentrations at the end of evaporite sequence. However, the general model, with the calculation of activity coefficients by Pitzer18 predicts the evolution of molality over time and the appearance of different salts at time t, making possible the determination of the evaporite sequence of natural salt waters. In these figures, the appearance of certain salts can be observed. Thus, the precipitation of sodium chloride NaCl(s) is detected by the decreasing of the molality of sodium ions and a plateau on the curve of chloride ions after 20h. Similarly, we note the precipitation of potassium salts at about 30h. However, in the simulation results, the precipitation of potassium and magnesium salts does no appear because it occurs at the end of evaporite sequence when there is almost no more water. In this experimental study, it is difficult to accurately determine the evaporite sequence. In fact, the precipitation of certain salts is not necessarily visible, especially when the amount of dissolved salt is low. Furthermore, with the monitoring of molalities, we do not know whether precipitated salts are hydrated or not. Thus, the experimental evaporite sequence is NaCl(s), KCl(s) and MgCl2(s). The simulation tool is then used to complete these experimental results. The evaporite sequence obtained with the model is as follows: calcite CaCO3(s), anhydrite CaSO4(s), halite NaCl(s) sylvite KCl(s) and bischofite MgCl2·6H2O(s). Thus, the main hypothesis of this study is verified: magnesium salts precipitate at the end of the evaporite sequence. After validating the model developed, we have focused our interest on the thermal spring from Salies-de-Béarn, which is a strong sodic chlorinated natural mineral water available in the South West region of France. We have studied the possibility of producing value-added salt from an artificial water of the same composition as water from Salies-de-Béarn at atmospheric pressure and three temperatures: 303.15, 323.15 and 353.15 K. Composition of the studied salt water is given in Table 4. This study also combined experimental and simulation aspects. 12


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The experiments were performed in the whole laboratory pilot consisting of the two evaporators crystallizers in series; the initial salt solution being fed to reactor 1. An initial mass of 4.7 kg was tested after measuring the density at 298.15 K (1.18 ±0.02 kg·L-1). The compressed air flow in reactor 1 and reactor 2 were 1980 L·h-1 and 540 L·h-1 (at 298.15 K), respectively. In these experiments, the emptying of reactor 1 to reactor 2 was carried out when the overall volume of solution and precipitated salts was one litre. We arbitrarily selected this volume in order to have a sufficient amount of liquid when transferring from reactor 1 to reactor 2. Then we followed the molality experimentally over time by ion chromatography technique. Each experimental sample was also injected three times in the apparatus. Experiments at three temperatures, 303.15, 323.15 and 353.15 K, were conducted in order to evaluate the effect of temperature on evaporite sequence, mother liquor’s magnesium enrichment, quantity of value-added salt. Figure 4 shows the evolution over time of molalities of the major ions present in the solution: sodium, chloride, potassium and magnesium, at 303.15 K. As above, data points shown are the average of the measurements of experimental samples, error bars represent an uncertainty of 10% and lines (normal or dash) are the data obtained by the model. In the first part of the curves, the reactor used is the BSTR 1; then after transferring the solution from reactor 1 to reactor 2, the experience continued in the BSTR 2. The time of the experimental transfer is indicated on each graph with a vertical dash line. Figures 5 and 6 present the evolution of the molalities of the same species at 323.15 and 353.15 K, respectively. At the three working temperatures, the curves of composition follow the same evolution. Thus, the molalities of chloride and sodium ions increase until the precipitation of halite starts. It happens in approximately 8 hours at 303.15 K, 4 h at 323.15 K and 1 h at 353.15 K. As can be observed in graphs 5, 6 and 7, molalities remain almost constant or their evolution is negligible 13



up to about 100 h at 303.15 K, 30 h at 323.15 K and 8 h at 353.15 K. From these respective times, the sodium ion concentration decreases while the concentrations of chloride, potassium and magnesium ions increase. From this moment transferring the solution from reactor 1 to reactor 2 can be advantageous. These results allow establishing the evaporite sequence. As in the previous experiment, we can not give the complete experimental evaporite sequence because the precipitation of calcite is still not visible even though the precipitation of anhydrite was detected this time. The experimental evaporite sequence and that predicted by the model remains in the same order that in the experiment before. Furthermore, this accurate agreement between simulations by the general model and experimental results equally stands out in the experiment at 303.15 K, whereby the model predicts the precipitation of halite earlier than anhydrite that can be also observed experimentally. The salts precipitated in reactors 1 and 2 were dried and then redissolved in ultrapure water in order to measure the final compositions of the solid phase by ion chromatography. Table 5 shows the experimental and model results for the three temperatures studied. At 303.15 K, we obtained experimentally in reactor 2 about 100 g of salt containing 10% of magnesium salts. At 323.15 K, we recovered about 50 g of salt with 20% of magnesium salts. Finally, at 353.15 K, salts mass was 45 g containing 22% of value-added salts. At 303.15 and 353.15 K, results obtained by modelling are close to experimental values. We note that at 323.15 K, the error is quite large. The experiment carried out at 323.15 K was the first in this series. The transfer protocol was then adjusted according to this first test. Uncertainty of the experimental results is therefore more important for this case. The experimental and simulation results obtained on operating time, quantity of magnesium salt and magnesium salt enrichment are given in Table 6, for the three temperatures studied. Magnesium enrichment is calculated by the following equation: 14


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enrichment =

% magnesium salt in reactor 2 % magnesium salt obtained with a single reactor

(9)

It is important to highlight that the results gathered in Table 6 are conditioned by the fact that we have chosen to do the transfer from reactor 1 to reactor 2 when one litre was left. Other experiments with a different signal for emptying reactor 1 are possible and should be carried out in a future work. In thoses cases, the obtained salts in reactors 1 and 2 may have a different composition and could be optimised. According to the experimental results from Salies-de-Béarn natural mineral water with the studied operation conditions, the use of the proposed pilot makes possible the production of magnesium salts and an enrichment of 12, 24 or even 26 times with magnesium relative to the salt obtained with a single crystallizer, depending on temperature. From an environmental point of view, not only the production process is enhanced but also it represents an eco-friendly improvement by the fact that no addition of chemicals is necessary. 5. Conclusion A new experimental pilot to produce mother liquor and / or salt enriched in magnesium from natural salt water is presented. In order to design the experimental process a simulation model developed previously was used to predict the evaporite sequence. The first obtained results showed that it was possible to isolate the magnesium salts at the end of the evaporite sequence using a two-crystallizing process in series. From these results and a bibliographic study of the existing processes, the specifications of the laboratory pilot were then established. In parallel, a method of analysis of the aqueous phase by ion chromatography was put in place to follow salt concentrations over time. This monitoring of the composition is complemented by a density measurement. The experimental results are necessary to verify the feasibility of the pilot and this study but also to validate the simulation model developed. First experiments were carried out

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three times. The obtained results demonstrate that the process is reproducible. A comparison of these results with those from simulation made possible to experimentally validate the process for the production of value-added salt. In the second part, a study of the process at three different temperatures (303.15, 323.15 and 353.15 K) was carried out with, as raw material, artificial water with a composition similar to that of Salies-de-Béarn thermal water. This study made possible to verify and demonstrate the possibility of obtaining a salt enriched in magnesium using a strong sodium chloride-containing mineral water. Finally, we were able to evaluate the magnesium enrichment and the quantity of salts that could be obtained. From an environmental perspective, we have developed an eco-friendly process whereby no additional chemicals are involved. Future works could be dedicated to improve the process making a rational use of the energy by optimising the air flow and the working temperature, and reducing the time of the experiment. The further step then would be the use of solar energy to provide the necessary power. Other technical aspects to explore are the influence of the operating parameters on the quality of the final salt (shape, size).

Corresponding Author •

Phone: +33 (0) 559 40 79 46. E-mail: [email protected]

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References (1) Houston, M. C.; Harper, K. J. Potassium, magnesium, and calcium: their role in both the cause and treatment of hypertension. J. Clin. Hypertens. 2008, 7(2), 3-11. (2) Carretero, M. I.; Pozo M. Clay and non-clay minerals in the pharmaceutical and cosmetic industries. Part II. Active ingredients. Appl. Clay Sci. 2010, 47, 171–181. (3) Pan, W.-H.; Lai, Y.-H.; Yeh, W.-T.; Chen, J.-R.; Jeng, J.-S.; Bai, C.-H.; Lin, R.-T.; Lee, T.H.; Chang, K.-C.; Lin, H.-J.; Hsiao, C.-F.; Chern, C.-M.; Lien, L.-M.; Liu, C.-H.; Chen, W.H,; Chang, A. Intake of potassium-and magnesium-enriched salt improves functional outcome after stroke: A randomized, multicenter, double-blind controlled trial. American J. Clin. Nutr. 2017, 5(1), 1267-1273. (4) Weller, O. Aux origines de l’exploitation du sel et des techniques de briquetage : pour un élargissement chronologique et géographique des problématiques, L’exploitation du sel dans la France protohistorique et ses marges, Table ronde des Comité des Salines de France, Paris, France, May 18, 1998. (5) U.S. Department of the Interior and U.S. Geological Survey. Mineral commodity summaries 2018; U.S. Geological Survey: Reston, Virginia, 2018. (6) Volpe, L. Magnesium in Disease Prevention and Overall Health. Adv. Nutr. 2013, 4, 378S383S. doi:10.3945/an.112.003483. (7) Serefko, A; Szopa, A; Piotr Wlaz, P.; Nowak, G.; Radziwon-Zaleska, M.; Skalski, M.; Poleszak, E. Magnesium in depression. Pharmacol. Rep.. 2013, 65, 547-554. (8) Boyle, N.B. ; Lawton, C.L.: Dye, L. The effects of magnesium supplementation on subjective anxiety. Magnesium Res. 2016, 29, 120-125.

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(9) Coussine, C.; Serin, J. P.; Cézac, P.; Contamine, F.; Reneaume, J. M.; Dubourg, K.; Knorst, A.; Cambar, J. A general dynamic model for multiphase electrolytic systems. AIChE Journal.

2012, 58 (12), 3832-3840. (10)

Asdrubali, F. A scale model to evaluate water evaporation from indoor swimming pools.

Energy Build. 2009, 41, 311-319. (11)

Antia, H.M. Numerical Methods for Scientists and Engineers. Boston, Basel, Berlin:

Birkhäuser Verlag, 2002. (12)

Gornitz V. Encyclopedia of Paleoclimatology and Ancient Environments; Springer: The

Netherlands, 2009. (13)

Cézac P.; Serin J. P. Modélisation thermodynamique d’un procédé de fabrication d’un sel

thermal enrichi en magnésium ; Rapport Innovation CCI A0802003B, 2008. (14)

Warren J.K. Evaporites: Sediments, Resources and Hydrocarbons; Springer: The

Netherlands, 2006. (15)

Copin-Montégut G. Propriétés physiques de l’eau de mer. Techniques de l’Ingénieur.

2002, K170. (16)

Boistelle R.; Dugua J. ; Klein J. P. Cristallisation industrielle – Aspects pratiques.

Techniques de l’Ingénieur. 1994, J2788. (17)

Ellison, S. L. R.; Williams, A. Quantifying Uncertainty in Analytical Measurement, 3rd

Edition (2012); Eurachem/CITAC guide, 2012. http://www.eurachem.org (18)

Pitzer, K. S. Thermodynamics of Electrolytes. I. Theoretical basis and general equation. J.

Phys. Chem. 1973, 77, 268-277.

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Table of Contents Graphic and Synopsis Here

19



Figure 1. Scheme of the experimental pilot: 1 and 2 are reactor 1 and 2, respectively, 3 is the thermostatic bath, 4 corresponds to the filtration system, 5 and 6 are the glass condensers, 7 and 8 are the containers for condensate recovery and 9 is the vacuum pump.

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Page 21 of 33

10 Exp. 1 Exp. 2 Exp. 3

8

Mg2+/mol·kg-1H2O

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


6

4

2

0 0

5

10

15

20

25

30

35

time/h Figure 2. Experimental results for the evolution of molality of Mg2+ over time. Error bars of the experimental points correspond to measurement uncertainty.

21



3.0

a

Na+/mol·kg-1H2O

2.5

2.0

1.5

1.0

0.5 0

5

10

15

20

25

30

35

20

25

30

35

time/h

0.5

b 0.4

K+/mol·kg-1H2O

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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0.3

0.2

0.1

0.0 0

5

10

15

time/h

22


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7

c 6

Mg2+/mol·kg-1H2O

5

4

3

2

1

0 0

5

10

15

20

25

30

35

time/h

14

d 12

10

Cl-/mol·kg-1H2O

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


8

6

4

2 0

5

10

15

20

25

30

35

time/h

Figure 3. Experimental (points) and simulation (line) results for the evolution of molality of ions over time: a) Na+, b) K+, c) Mg2+, d) Cl-. Error bars represent the measurement uncertainty. 23



9.0

7.5

6.0

4.5

molalities/mol·kg-1H2O

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 24 of 33

3.0

1.5

2.5

2.0

1.5

1.0

0.5

0.0 0

25

50

75

100

125

150

time/h

Figure 4. Evolution of molalities of ions over time: Na+ (experimental - black circles, model – black dash lines), Cl- (experimental - grey circles, model - grey dash lines), K+ (experimental - black triangles, model – black lines), Mg2+ (experimental - grey triangles,

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model - grey lines), at 303.15 K. The measurement uncertainty is represented by error bars. Vertical short-dash line represents experimental transfer.

25



9.0

7.5

6.0

4.5

3.0


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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1.5

3.0

2.4

1.8

1.2

0.6

0.0 0

10

20

30

40

50

time/h


26


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27



9.0

7.5

6.0

4.5

3.0


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 28 of 33

1.5

3.6

3.0

2.4

1.8

1.2

0.6

0.0 0

2

4

6

8

10

12

time/h


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Page 30 of 33

Table 1. Material and operating conditions of the ion chromatopraphy modules. Eluent

Module

Regenerant Flow / - V/ Concentration Concentration mL·min µL Solution Formula 1 / mmol·L-1 / mmol·L-1

Solution

Formula

Methanesulfonic acid (MSA)

CH3SO2OH

20

Sodium carbonate

Na2CO3

8

Anions

Sodium hydrogencarbonate

NaHCO3

1

Carbonates

Water

H2O

-

Cations

Sulfuric acid

H2SO4

11

-

Table 2. Ionic species detected by ion chromatography modules. Ion Sodium Potassium Magnésium Calcium Chloride Sulfate Carbonate

Formula Mean retention time / min Cationic module + Na 4.7 K+ 6.9 2+ Mg 11.4 Ca2+ 14.6 Anionic module Cl 5.0 SO4212.6 Carbonate module 27.5 CO3

30


1

10

1

10

1.5

100

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Table 3. Composition of the artificial brine studied. Species NaCl MgCl2 Na2SO4 KCl CaSO4 NaHCO3

Molality / mol·kg-1 H2O 1 1 10-1 10-1 10-2 2·10-3

Table 4. Composition of the artificial water comparable to Salies-de-Béarn thermal water. Molality / mol·kg-1 H2O 5.556 5.08·10-2 2.989·10-2 2.659·10-2 2.359·10-3

Species NaCl KCl MgCl2 CaSO4 NaHCO3

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Industrial & Engineering Chemistry Research 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47

Page 32 of 33

Table 5. Masses and composition of the salts obtained at all temperatures studied. T = 303.15 K T = 323.15 K T = 353.15 K Reactor 1 Reactor 2 Reactor 1 Reactor 2 Reactor 1 Reactor 2 Exp. Model Exp. Model Exp. Model Exp. Model Exp. Model Exp. Model 1077 Mass of salt / g % Sodium salts 99 1 % Calcium salts % Potassium salts % Magnesium salts

1059 99 1 -

103 76 1 13 10

121 79 2 11 8

1129 99 1 -

32

1087 99 1 -


51 53 26 20 1

93 74 14 11 1

1135 99 1 -

1134 99 1 -

45 47 1 30 22

46 47 1 30 22

Page 33 of 33 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Table 6. Comparison of the results obtained at all temperatures studied.

T/K 303.15 323.15 353.15

Operating time / h Exp. 136 46 11

Model 128 43 11

Mass of magnesium enriched salt / g Exp. Model 103 121 51 93 45 46

33


Magnesium salt enrichment Exp. Model 12 10 24 13 26 26

Environmentally Friendly Process for Producing Magnesium-Enriched

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