Chloride Brine Research Articles

Selective sodium removal from lithium chloride brine with novel inorganic ion exchanger

Natrium superionic conductor (NASICON) ceramics present interesting sensitive and selective properties against alkaline cations due to their structure. The powder of Li1.4La0.4Zr1.6(PO4)3 has been synthesized by a solid phase reaction. The removal of sodium was studied in an extensive series of tests involving different ionic exchange process variables such as time and temperature. The results indicated that its exchange capacity is very high, even reach 41.3 mg/g. The Na/Li ion exchange reaction rate increased obviously with increasing temperature, and the kinetic data fitted well to the equation of Johnson-Mehl-Avrami-Kolmogorov with a regression coefficient value of above 0.99. KEY WORDS: Brine, Lithium chloride, Sodium, Separation Bull. Chem. Soc. Ethiop. 2013, 27(2), 241-248.DOI: http://dx.doi.org/10.4314/bcse.v27i2.9

Effect of structure on the sorption properties of chlorine-containing form of double aluminum lithium hydroxide

The effect exerted by composition and specific structural properties of commercial batches of granular sorbent based on chlorine-containing form of double aluminum lithium hydroxide on its sorption properties in lithium extraction from magnesium chloride brines was determined. Deficiency in lithium chloride in the sorbent structure and structural defects are responsible for the selectivity of granular sorbent. It was shown that sorbent is selective for lithium even in the presence of high concentrations of magnesium chloride in brine and the borate ions exhibit adverse effect on the technological process.

Ultrasonic attenuation and speed of sound of cornstarch suspensions

The goal of this study is to contribute to the physics underlying the material properties of suspensions that exhibit shear thickening through the ultrasonic characterization of suspensions of cornstarch in a density-matched solution. Ultrasonic measurements at frequencies in the range of 4 to 8 MHz of the speed of sound and the frequency-dependent attenuation properties are reported for concentrations of cornstarch in a density-matched aqueous (cesium chloride brine) suspension, ranging up to 40% cornstarch. The speed of sound is found to range from 1483 ± 10 m/s in pure brine to 1765 ± 9 m/s in the 40% cornstarch suspension. The bulk modulus of a granule of cornstarch is inferred to be 1.2(± 0.1) × 1010 Pa. The attenuation coefficient at 5 MHz increases from essentially zero in brine to 12.0 ± 1.2 dB/cm at 40% cornstarch.

Application of a Re–Pd bimetallic catalyst for treatment of perchlorate in waste ion-exchange regenerant brine

Concentrated sodium chloride (NaCl) brines are often used to regenerate ion-exchange (IX) resins applied to treat drinking water sources contaminated with perchlorate (ClO4−), generating large volumes of contaminated waste brine. Chemical and biological processes for ClO4− reduction are often inhibited severely by high salt levels, making it difficult to recycle waste brines. Recent work demonstrated that novel rhenium–palladium bimetallic catalysts on activated carbon support (Re–Pd/C) can efficiently reduce ClO4− to chloride (Cl−) under acidic conditions, and here the applicability of the process for treating waste IX brines was examined. Experiments conducted in synthetic NaCl-only brine (6–12 wt%) showed higher Re–Pd/C catalyst activity than in comparable freshwater solutions, but the rate constant for ClO4− reduction measured in a real IX waste brine was found to be 65 times lower than in the synthetic NaCl brine. Through a series of experiments, co-contamination of the IX waste brine by excess NO3− (which the catalyst reduces principally to NH4+) was found to be the primary cause for deactivation of the Re–Pd/C catalyst, most likely by altering the immobilized Re component. Pre-treatment of NO3− using a different bimetallic catalyst (In–Pd/Al2O3) improved selectivity for N2 over NH4+ and enabled facile ClO4− reduction by the Re–Pd/C catalyst. Thus, sequential catalytic treatment may be a promising strategy for enabling reuse of waste IX brine containing NO3− and ClO4−.

Influence of Sodium Chloride, pH, and Lactic Acid Bacteria on Anaerobic Lactic Acid Utilization during Fermented Cucumber Spoilage

Cucumbers are preserved commercially by natural fermentations in 5% to 8% sodium chloride (NaCl) brines. Occasionally, fermented cucumbers spoil after the primary fermentation is complete. This spoilage has been characterized by decreases in lactic acid and a rise in brine pH caused by microbial instability. Objectives of this study were to determine the combined effects of NaCl and pH on fermented cucumber spoilage and to determine the ability of lactic acid bacteria (LAB) spoilage isolates to initiate lactic acid degradation in fermented cucumbers. Cucumbers fermented with 0%, 2%, 4%, and 6% NaCl were blended into slurries (FCS) and adjusted to pH 3.2, 3.8, 4.3, and 5.0 prior to centrifugation, sterile-filtration, and inoculation with spoilage organisms. Organic acids and pH were measured initially and after 3 wk, 2, 6, 12, and 18 mo anaerobic incubation at 25 °C. Anaerobic lactic acid degradation occurred in FCS at pH 3.8, 4.3, and 5.0 regardless of NaCl concentration. At pH 3.2, reduced NaCl concentrations resulted in increased susceptibility to spoilage, indicating that the pH limit for lactic acid utilization in reduced NaCl fermented cucumbers is 3.2 or lower. Over 18 mo incubation, only cucumbers fermented with 6% NaCl to pH 3.2 prevented anaerobic lactic acid degradation by spoilage bacteria. Among several LAB species isolated from fermented cucumber spoilage, Lactobacillus buchneri was unique in its ability to metabolize lactic acid in FCS with concurrent increases in acetic acid and 1,2-propanediol. Therefore, L. buchneri may be one of multiple organisms that contribute to development of fermented cucumber spoilage. Microbial spoilage of fermented cucumbers during bulk storage causes economic losses for producers. Current knowledge is insufficient to predict or control these losses. This study demonstrated that in the absence of oxygen, cucumbers fermented with 6% sodium chloride to pH 3.2 were not subject to spoilage. However, lactic acid was degraded by spoilage microorganisms in reduced salt, even with pH as low as 3.2. Efforts to reduce salt in commercial brining operations will need to include control measures for this increased susceptibility to spoilage. Lactobacillus buchneri was identified as a potential causative agent and could be used as a target in development of such control measures.

The study of the hydrogeological setting of the Chamshir Dam site with special emphasis on the cause of water salinity in the Zohreh River downstream from the Chamshir Dam (southwest of Iran)

Dissolution of evaporite formations, emergence of salty water springs, and intrusion of deep saline waters are important causes in changing the quality of surface water. The study area is part of the reservoir and downstream of Chamshir Dam, which is located in watershed of the Zohreh River 20 km southeast of Gachsaran City (southwest Iran). To construct powerhouse and related structures for supplying water to agricultural lands located in downstream of dam, water quality of Zohreh River was studied by eight sampling stations in the study area. Early studies showed that water quality of the Zohreh River decreases severely downstream of the Chamshir Dam. Spatial variations diagram of major ions, Piper and composition diagrams of water samples in selected stations mark the presence of two slight and major contaminating zones at sampling station R4 and R5. In these zones, concentration of Ca, SO4 and Na, Cl ions increase suddenly. Results of hydrogeological, hydrochemical, lithological and tectonics studies showed that even though there are several low discharges springs in the contaminated zone they cannot be related to surface dissolution of evaporate layers by Zohreh River. There is an important fault zone including Chamshir faults I and II in the contamination zones through which intrusion of sulfate brackish and chloride brine waters occur along the fault zone and then enter Zohreh River below its base level. In the absence of any surface evidence, the fault zone is the main cause of salinity. Evaluation of water balance salinity in contaminated zones shows that the discharge rate of saline waters to the river is not low and cannot be separated. These findings show that there are serious restrictions upon the purposes of the project.

Effects of Cooking Conditions on the Protein Quality of Chub Mackerel Scomber japonicus

The effects of cooking method (grilling, frying, steaming, and microwaving) on the proximate composition and protein quality of chub mackerel Scomber japonicus treated with 2, 6, and 10% sodium chloride (NaCl) brine were investigated. Moisture content decreased in all cooked samples from 60.22% in the raw sample to 48.7% in the fried samples. Brine (10% NaCl) treatment recorded the highest moisture loss. All cooked samples showed a decrease in fat content, except fried samples. Protein content increased in all cooked samples, from 47.21% in the raw sample to 63.87% in the grilled sample. Brine treatment resulted in the highest degree of fat oxidation (thiobarbituric acid-reactive substances), which was highest in the fried samples and lowest in the microwaved samples. The trypsin inhibitor (TI) concentration was highest in the microwaved samples and lowest in the fried samples. In all samples, 6% salt treatment caused the lowest TI level and the highest in vitro protein digestibility. In vitro digestibility increased from 79.4% in the raw sample to 86.43% in the fried samples. The total essential amino acids of all cooked samples increased. Results suggested that grilling and steaming had beneficial effects on the protein quality of chub mackerel.

Efficacy of NaCl brine for treatment of ballast water against freshwater invasions

Currently, all transoceanic vessels entering the Great Lakes must perform ballast water exchange or saltwater flushing, procedures designed to reduce the risk of new biological invasions from ballast water. Vessels not in compliance with these regulations presently have limited, often costly, and/or time-consuming alternatives available. Treatment with sodium chloride brine at an initial concentration of 230‰ has been proposed as an emergency ballast water management option and is examined here. Six shipboard trials were conducted under operational conditions to determine the efficacy of brine ballast water treatment. Trials were conducted on three vessels with full ballast tanks and on three vessels with only residual ballast water. Brine distribution in tanks was adequate, noting that vessel movement was essential to ensure mixing into ballast water or ballast residuals. Once mixing has occurred, approximately 25hour exposure to 45‰ brine or 1 hour exposure to 115‰ brine is required to effectively exterminate freshwater zooplankton. Brine appears to be a cost-effective and relatively safe procedure that could be implemented immediately for emergency treatment of non-compliant ballast water to reduce risk of new invasions in the Great Lakes.

Flow Drag and Heat Transfer Reduction Characteristics of Organic Brine (Potassium Acetate) and Inorganic Brine (Calcium Chloride) Solutions with Nonionic Surfactant

Flow drag and heat transfer reduction effects are useful in heat energy transportation systems and can lead to lower pumping energy requirements. The purpose of this research is to describe the flow drag and heat transfer reduction characteristics of organic (potassium acetate) and inorganic (calcium chloride) brine solutions. The nonionic surfactant oleyl dihydroxyethyl amine oxide (ODEAO) is used as a drag-reducing additive. The pipe friction coefficient and heat transfer coefficient are investigated experimentally in a straight pipe for each type of solution with ODEAO. These coefficients are found to be lower than those of water in the turbulent flow range. However, the rod-like micelles of ODEAO, which are necessary to induce the flow drag reduction effect, are not readily formed in these solutions. Hence, the flow drag and heat transfer reduction effects are measured only under limited conditions and it is difficult to apply these solutions practically as heat transfer media.

The fate of minor alkali elements in the chemical evolution of salt lakes

Alkaline earth elements and alkali metals (Mg, Ca, Na and K) play an important role in the geochemical evolution of saline lakes as the final brine type is defined by the abundance of these elements. The role of major ions in brine evolution has been studied in great detail, but little has been done to investigate the behaviour of minor alkali elements in these systems despite their similar chemical affinities to the major cations. We have examined three major anionic brine types, chloride, sulphate, and bicarbonate-carbonate, in fifteen lakes in North America and Antarctica to determine the geochemical behaviour of lithium, rubidium, strontium, and barium. Lithium and rubidium are largely conservative in all water types, and their concentrations are the result of long-term solute input and concentration through evaporation and/or sublimation. Strontium and barium behaviours vary with anionic brine type. Strontium can be removed in sulphate and carbonate-rich lakes by the precipitation of carbonate minerals. Barium may be removed in chloride and sulphate brines by either the precipitation of barite and perhaps biological uptake.

CONTRIBUTIONS TO THE IMPROVEMENT OF POLLUTION CONTROL IN LAKES AND AN APPLICATION FOR THE GOVORA LAKE

In this paper, the mathematical model is improved by considering the density variations of the liquid from the pollution source vs. pollutant s concentration of this liquid and by including the sorption-desorption term (SDT), which takes into account this physical process, played by a first-order decay model defined by two coefficients and an exponent. In order to practically use this improved mathematical model, the authors inferred the calculating relationships from automatic processing of monitored data during the process of pollution, so that to assess the three SDT function parameters and properly enhance the computer programming code Storage_Lake_ Zero.m. Thus, at the resumption of the numerical simulation of the same real case of pollution, there was a significant improvement in line with the experimental concentration. Using the same numerical results for the SDT, different scenarios of chloride brine pollution in the Govora accumulation lake can be numerically simulated, with increased accuracy.

Experimental and Numerical Modeling of Three-Phase Flow Under High-Pressure Air Injection

Summary In this paper, an improved characterization of three-phase flow under high-pressure-air-injection (HPAI) conditions was achieved on the basis of experimental results and numerical reservoir simulation. A three-phase coreflood experiment was conducted at reservoir conditions, using 37°API stock-tank oil, an 84% nitrogen and 16% carbon dioxide flue-gas mixture, and 3% potassium chloride brine. The aim of the test was to evaluate the effects that the highly liquid-saturated front produced by the thermal reactions has on the mobility of each phase. Departing from connate-water saturation and reservoir pressure and temperature, sequential injection of water, gas, and oil was carried out, followed by a final gasflood to residual liquid saturation. Other two- and three-phase tests performed on this rock specimen were published elsewhere (Niz-Velásquez et al. 2009). Numerical history matching was employed to determine oil/water and liquid/gas relative permeability (kr) curves for both imbibition and drainage cases. A combustion-tube (CT) test was simulated using conventional kr curves and a set that included hysteresis. The degree of hysteresis observed during the coreflood test was maintained for the CT simulation. History matching of the coreflood showed that kr to the gas phase is much smaller during liquid reimbibition than during drainage. The use of gas-phase hysteresis for the CT test allows for a better matching of liquid volumes and pressure drop. Analysis of the simulated data suggests that the reduction in gas-phase mobility encourages an early increase in the oil rate, which is more consistent with experimental data than what is predicted by a model with conventional kr. The analysis also reveals that water distilled below the saturated steam temperature plays an important role in the increase of liquid saturation and oil mobilization. The improved characterization of relative permeability considering gas-phase hysteresis for simulating HPAI enhances the predictive capability of available commercial simulators, providing a more certain method to evaluate the technical and economical feasibility of a project. The ability to predict an early increase in oil rate, consistent with experimental observations, results in improved economics for the project.

Brine-induced mortality of non-indigenous invertebrates in residual ballast water

All transoceanic vessels entering the Great Lakes are required to manage ballast water and ballast tank residuals with ballast water exchange and tank flushing, respectively. While these management procedures effectively reduce the density and richness of biota in ballast waters and thereby reduce the risk of transferring non-indigenous species, some ships are unable to uniformly manage all tanks. Laboratory experiments were conducted to evaluate sodium chloride brine as an emergency treatment for ballast tanks with non-compliant residuals. Invertebrate communities collected from i) Detroit River, ii) exchanged ballast tanks arriving in the Great Lakes, and iii) North Sea ports, were exposed to a range of brine concentrations (15–115‰) until complete mortality was reached. Results indicate that a 1-h exposure to 115‰ brine is a broadly effective treatment (>99.9% mortality) regardless of treatment temperature, taxonomic group, or species’ source habitat salinity. A median of 0.00% (range 0.00–5.33) of individuals are expected to survive treatment and the expected number of viable individuals released after treatment is within Canadian and proposed international discharge standards. Before implementation, validation with ship-scale trials is recommended.

Silver–antimony deposits of Central Asia: physico-chemical model of formation and sources of mineralisation

Questions on the origin of Ag–Sb deposits are considered for several large economic ore districts in Central Asia: southeast Pamir (Tajikistan), Talas in northern Tien Shan (Kyrgyzstan), southeast Altai and northwest Mongolia, and Verkhoyansk province (Yakutia). The Ag–Sb mineralisation of Central Asia is spatially and temporally associated with alkaline mafic magmatism, and occasionally with coeval granitoid magmatism. Ag–Sb deposits have close spatial and temporal relationships with granitoid and alkaline mafic magmatism. The Ag–Sb deposits were formed in the temperature range 50–280°C, from Ag-specific reduced two-phase hydrothermal fluids containing a highly concentrated chloride solution (NaCl > FeCl2 > CaCl2 > KCl > MnCl2) and a high-density CO2+ CH4 ± N2 gaseous phase. Fluid salinities range widely from 40 to 0.1 wt% NaCl equiv. Geochemical specialisation of Ag–Sb ore is caused by chemical features of chloride brines enriched in Ag, Sb, Pb and Cu, with a relatively low Au content (≤10−6 mol/kg) within a pH of 3.5–4. The highest temperatures, concentrations of solutions and ore elements in the ore fluids were found in early quartz of siderite–tetrahedrite veins from below-ore level of the ore-forming system. Vertical zonation of the Ag–Sb mineralisation is caused by precipitation of different mineral associations from the same solution with temperatures decreasing towards the upper parts of the system. Sufficient vertical range of mineralisation (600–800 m) and relatively low Ag contents in the ore (300–600 ppm) result from the temperature decrease and absence of geochemical barriers. Higher temperature gradient and dilution of magmatogenic fluid with meteoric water was a geochemical barrier for the Ag-rich ore formation in a narrow (about 400 m) main ore deposition zone. Lateral zonation of Ag–Sb mineralisation is related to a staged development of the ore-forming process and deposition of different stage mineral associations at the beginning and end of the hydrothermal process. The Ag–Sb deposits are polygenic in terms of sources of ore elements and ore-forming fluids. Ore elements may have been inherited from magmatic and terrigenous host-rocks of different ages. Temporal correlation of the Ag–Sb mineralisation with alkaline mafic magmatism, He isotope composition and Hg contents in the ores confirm participation of a mantle source in the formation of the Ag–Sb deposits.

DMFC with Hydrogen Peroxide Cogeneration

The process of generation in the direct methanol fuel cell (DMFC) composed of the “Black Pearls 2000” gas-diffusion cathode, washed by sodium chloride brine or sea water for electroreduction and the half-membrane-electrode assembly with the Nafion 115 cation-exchange membrane, hot-pressed on one side with the carbonaceous gas-diffusion anode impregnated by Pt/Ru catalyst for methanol oxidation, has been developed. The effect of NaCl concentration in the catholyte, methanol and the KOH concentration in the anolyte, electrolyte temperature, and circulation flow rate on the generated cell voltage, current, and current efficiency have been studied in 2 h trials. An 87–95% current efficiency for generation with a rate and at current density was achieved in the DMFC with 1 M KOH in the anolyte and NaCl in the catholyte.

Generation of Hydrogen Peroxide in DMFC

The novel process of H2O2 generation in the direct methanol fuel cell (DMFC) composed from the "Black Pearls 2000" gas-diffusion cathode (GDE), washed by sodium chloride brine or sea water for O2 electro-reduction and the half-membrane-electrode assembly (MEA) with the Nafion 115® cation-exchange membrane (CEM), hot pressed on one side with the carbonic gas-diffusion anode impregnated by Pt/Ru catalyst for methanol oxidation, has been developed. The effect of NaCl concentration in the catholyte, methanol and the KOH concentration in the anolyte, electrolyte temperature and circulation flow rate on the generated cell voltage, current and H2O2 current efficiency have been studied in 2 hour trials. 87-95 % current efficiency for H2O2 generation with a 5.286 -9.44 mg h-1 cm-2 rate and at 15 mA cm-2 current density was achieved in the DMFC with 1 M CH3OH +7M KOH in the anolyte and 30 g L-1 NaCl in the catholyte.

Electrochemical Oxidation of Hydrogen Sulfide in Polluted Brines Using Porous Graphite Electrodes under Geothermal Conditions

Hydrogen sulfide contaminates the geothermal brines that are encountered in the drilling of wells. It promotes the corrosion of the drilling equipment, pipelines, vessels, forms sulfide scales, which plug tubulars, and degrades the quality of the produced oil. This work aims to study the feasibility of electrochemical removal of H2S from such brines by anodic oxidation. Porous graphite electrode was used to achieve electrochemical oxidation of sulfide ions in chloride brines in an autoclave under high temperature and pressure. The X-ray photoelectron spectroscopy (XPS) and Energy Dispersive Spectroscopy (EDS) proved that sulfur was identified as the final reaction product under various potentials and temperatures. In low temperature, the sulfur was detected on the electrode surface, while in high temperature the resulting sulfur flows out in the electrolyte so that it is not detected on the electrode surface. The rate of sulfide oxidation depends on the potential, temperature and the sulfide concentration. The obtained limiting currents are lower than those predicted from mass transfer correlations, which result from the effects of the deposited sulfur on the internal surface of the porous graphite electrode. The large internal surface area of the used electrodes improved the removal efficiency of sulfide ions and this is very clearly noticed from the current transient's results. In high temperature, the limiting current is re-increased due to the liberation of sulfur from the electrode surface, which reactivates electrode surface and the rate of oxidation is increased again.

Modeling acid-gas generation from boiling chloride brines.

BackgroundThis study investigates the generation of HCl and other acid gases from boiling calcium chloride dominated waters at atmospheric pressure, primarily using numerical modeling. The main focus of this investigation relates to the long-term geologic disposal of nuclear waste at Yucca Mountain, Nevada, where pore waters around waste-emplacement tunnels are expected to undergo boiling and evaporative concentration as a result of the heat released by spent nuclear fuel. Processes that are modeled include boiling of highly concentrated solutions, gas transport, and gas condensation accompanied by the dissociation of acid gases, causing low-pH condensate.ResultsSimple calculations are first carried out to evaluate condensate pH as a function of HCl gas fugacity and condensed water fraction for a vapor equilibrated with saturated calcium chloride brine at 50-150°C and 1 bar. The distillation of a calcium-chloride-dominated brine is then simulated with a reactive transport model using a brine composition representative of partially evaporated calcium-rich pore waters at Yucca Mountain. Results show a significant increase in boiling temperature from evaporative concentration, as well as low pH in condensates, particularly for dynamic systems where partial condensation takes place, which result in enrichment of HCl in condensates. These results are in qualitative agreement with experimental data from other studies.ConclusionThe combination of reactive transport with multicomponent brine chemistry to study evaporation, boiling, and the potential for acid gas generation at the proposed Yucca Mountain repository is seen as an improvement relative to previously applied simpler batch evaporation models. This approach allows the evaluation of thermal, hydrological, and chemical (THC) processes in a coupled manner, and modeling of settings much more relevant to actual field conditions than the distillation experiment considered. The actual and modeled distillation experiments do not represent expected conditions in an emplacement drift, but nevertheless illustrate the potential for acid-gas generation at moderate temperatures (<150°C).

A Phase-Partitioning Model for CO2–Brine Mixtures at Elevated Temperatures and Pressures: Application to CO2-Enhanced Geothermal Systems

Correlations are presented to compute the mutual solubilities of CO2 and chloride brines at temperatures 12–300°C, pressures 1–600 bar (0.1–60 MPa), and salinities 0–6 m NaCl. The formulation is computationally efficient and primarily intended for numerical simulations of CO2-water flow in carbon sequestration and geothermal studies. The phase-partitioning model relies on experimental data from literature for phase partitioning between CO2 and NaCl brines, and extends the previously published correlations to higher temperatures. The model relies on activity coefficients for the H2O-rich (aqueous) phase and fugacity coefficients for the CO2-rich phase. Activity coefficients are treated using a Margules expression for CO2 in pure water, and a Pitzer expression for salting-out effects. Fugacity coefficients are computed using a modified Redlich–Kwong equation of state and mixing rules that incorporate asymmetric binary interaction parameters. Parameters for the calculation of activity and fugacity coefficients were fitted to published solubility data over the P–T range of interest. In doing so, mutual solubilities and gas-phase volumetric data are typically reproduced within the scatter of the available data. An example of multiphase flow simulation implementing the mutual solubility model is presented for the case of a hypothetical, enhanced geothermal system where CO2 is used as the heat extraction fluid. In this simulation, dry supercritical CO2 at 20°C is injected into a 200°C hot-water reservoir. Results show that the injected CO2 displaces the formation water relatively quickly, but that the produced CO2 contains significant water for long periods of time. The amount of water in the CO2 could have implications for reactivity with reservoir rocks and engineered materials.

Experimental investigation of the stability and evaporation of sulfate and chloride brines on Mars

We have investigated the evaporation of concentrated magnesium and ferrous sulfate, and magnesium and ferric chloride brines as possible sources for liquid water on the surface of Mars, with special emphasis on the effect of freezing and crystallization of solutions. Experimental evaporation rates range from 0.04 mm h − 1 for 25 wt.% MgSO 4 at 271.9 K, to 0.19 mm h − 1 for 18 wt.% FeSO 4 at 270.5 K. For chloride solutions, evaporation rates range from 0.09 mm h − 1 for 40 wt.% FeCl 3 at 261.34 K, to 0.43 mm h − 1 for 20 wt.% MgCl 2 at 267.2 K. These evaporation rates are significantly lower than for pure water, i.e. 1.35 mm h − 1 at 273 K. Using the Pitzer ion interaction model, we show that the decrease in evaporation rate is due to lower water activity in concentrated solutions, down to 0.91 for saturated MgSO 4 and 0.97 for saturated FeSO 4, at their eutectic temperatures. For saturated MgCl 2 and FeCl 3, the calculated water activities are 0.57 and 0.60 at their respective eutectic temperatures. In addition, we show that the water activity drops significantly when salts are crystallizing, down to 0.17 and 0.21 for MgSO 4 and FeSO 4, respectively. Our experiments and calculations show that the water activity and evaporation rate are dependent on the hydration state of the precipitating salt, which is in turn controlled by the temperature and the relative humidity. Low-hydration state salts precipitate at lower humidity, with lower evaporation rates. Our study suggests that martian brines could remain stable for longer periods of time, at low temperatures and low humidity, than previously thought. Brines formed from these salts would be a more stable source of water on Mars, thus beneficial for any putative martian life, past and/or present.