Aqueous Solutions Of MgCl2 Research Articles

Evaluation of bubble column dehumidifier using magnesium chloride desiccant

With growing emphasis on indoor air quality and energy conservation, the development of sustainable and efficient dehumidification systems has become increasingly crucial across various industries. Liquid desiccant dehumidification system (LDDS) offers a more efficient alternative to conventional methods by utilizing low-grade waste heat. Most direct-contact liquid dehumidification systems use expensive desiccants such as LiCl and LiBr. Our research focuses on exploring MgCl2, prevalent in saltwater bitterns, as a cheaper, less toxic alternative. The core principle of this system involves passing air through a column filled with the MgCl2 aqueous solution, leveraging the hygroscopic properties of MgCl2 to remove moisture from the air stream effectively. Various parameters such as hole size, air flow rate and desiccant concentration are investigated. We further developed a numerical model for the dehumidification process considering the rise time of the bubbles in the desiccant solution and mass transfer in the bubble. After dehumidification, the diluted desiccant solution can be revived using low-grade heat. Use of seawater bitterns, with major component as MgCl2, shows potential for building an environmentally friendly and cost-effective dehumidification system.

CO2 solubility in aqueous solution of salts: Experimental study and thermodynamic modelling

AbstractThere are many economic obstacles and complex engineering problems associated with CO2 capture and storage in saline aquifers that need to be addressed. Overcoming such challenges requires precise knowledge on the fluid phase equilibria of CO2‐brine systems. Having accurate CO2 solubility data over a wide range of temperature and pressure can greatly assist in resolving these obstacles by improving the performance and accuracy of the thermodynamic modeling and subsequent CCS engineering success.CO2 solubility in pure water and NaCl solutions has been widely studied in the literature, however, there is a lack of data on CO2 solubility at lower temperatures (below 298 K). Furthermore, limited phase equilibria data are available for CO2 solubility in CaCl2, MgCl2, and KCl solutions at elevated temperatures (i.e., T > 323.15 K).In this work, the phase equilibria of CO2 and brine systems are investigated experimentally and theoretically. In this study, solubilities of CO2 in pure water and various concentrations of NaCl (10, 15, 20, and 22 wt%), KCl (10, 15, and 22 wt%), CaCl2 (7.5, 10, 15.7, and 23.4 wt%), and MgCl2 (6.7, 11, 18, and 29 wt%) aqueous solutions are reported. All CO2 solubilities were measures at 323.15, 373.15, and 423.15 K and over various pressure ranges, while solubilities in 10 and 20 wt% NaCl aqueous solutions were also measured over the temperature range of 263 to 298 K and pressures up to the hydrate dissociation pressure of each system. Equation of state modelling using the PC‐SAFT and the Cubic Plus Association equations of state, is performed in the theoretical part of the study to validate the measured solubility data. © 2024 The Author(s). Greenhouse Gases: Science and Technology published by Society of Chemical Industry and John Wiley & Sons Ltd.

Application of deep learning through group method of data handling for interfacial tension prediction in brine/CO2 systems: MgCl2 and CaCl2 aqueous solutions

Capillary/residual CO2 trapping is one of the main mechanisms of CO2 storage in underground formations. Therefore, it is required to estimate the brine/CO2 interfacial tension under different conditions. Although many methods have been proposed so far, the error of estimation is still high. This paper proposes a novel deep learning method to estimate the brine/CO2 interfacial tension at various temperatures, pressures, and salinities. The proposed method is a neural network with the Group Method of Data Handling (GMDH) learning method. The GMDH has the advantage of handling the structural and parametric optimization of the network automatically. The proposed method is tested on an experimental dataset of brine/CO2 interfacial tension with CalCl2 and MgCl2 salts. The results of the proposed method were compared with four of the best performing methods in the literature. The Average Absolute Percentage Error (AAPE) of the method on the training, testing and all data was 1.3 %, 2.95 %, 1.73 %, respectively, while the best method from the literature could reach an AAPE of 8.16 % on all data. Therefore, the proposed method performs far better than the existing methods. Also, a sensitivity analysis was done to determine the most influential inputs to estimate the output. The contribution of this work is to show the applicability of the GMDH method to construct more optimal data-driven models to estimate the brine/CO2 interfacial tension. Also, the utilized dataset is collected under a wide range of pressure, temperature and salinity conditions that increases the generality of the model.

Probing molecular interactions of an anti-epileptic drug, sodium valproate in aqueous MgCl2 solutions

Study of the physicochemical properties of anti-epileptic drugs in the presence of cosolutes in aqueous solutions has been a subject of interest of researchers because of their interaction with biological membranes to employ their effect. Such properties provide complete information regarding solute-solute and solute-solvent type interactions. As electrolytes are essential components of biological systems, therefore the study of drug-electrolyte chemistry is important to understand the mechanism of drug action at the molecular level and hence useful in drug design and development processes. Therefore, in the current report, the density and sound velocity of an anti-epileptic drug sodium valproate (SV) in aqueous and in aqueous solutions of an electrolyte viz. MgCl2 (mB = 0.024, 0.047, 0.070 mol kg−1) at different temperatures (288.15, 298.15, 308.15, and 318.15 K) and at a pressure of 0.101 MPa were measured along with 1H NMR spectroscopy. Various volumetric and acoustical parameters such as apparent molar volume (Vφ) and isentropic compressibility (Kφ) of the solute, apparent molar volume (Vφ°) and isentropic compressibility (Kφ°) of solute at infinite dilution, apparent molar expansibility (Eφ°) and their double derivatives (∂2Vφ°/∂T2)P, transfer volumes (∆trVφ°), hydration number (nH), acoustic impedance (Z), intermolecular free length (Lf), Wada's constant (W) and Rao's constant (R) were calculated from density and sound velocity data. The variation in all these parameters with cosolute concentration indicates the existence of hydrophilic/ionic-ionic interactions at lower concentrations but hydrophobic-ionic interactions at higher concentrations of MgCl2. The 1H NMR spectroscopic results also support the existence of hydrophobic-ionic interactions at higher concentrations of MgCl2. The decrease in electrostriction but increase in hydrophobic hydration of solute molecules has also been seen with rise in temperature.

Comparative Investigation of the Microstructure of MgCl2 Aqueous Solutions Using Different X-ray Scattering Sources, Raman Spectroscopy, and Atomistic Simulations.

Aqueous solutions of magnesium chloride (MgCl2(aq)) are often used to test advances in the theory of electrolyte solutions because they are considered an ideal strong 2:1 electrolyte. However, there is evidence that some ion association occurs in these solutions, even at low concentrations. Even a small ion-pairing constant can have a significant impact on the chemical speciation of ions, so it is important to determine whether ion pairing actually occurs. In this study, MgCl2(aq) with concentrations ranging from 1 to 35% was studied using three methods: X-ray scattering (XRS) with the Shanghai Synchrotron Radiation Facility (SSRF) and silver-anode laboratory sources, Raman spectroscopy, and molecular dynamics (MD) simulations with the COMPASS-II and Madrid force fields. XRS results were analyzed in the framework of PDF theory to obtain the reduced structure function F(Q) and the reduced pair distribution function G(r). The F(Q) values from synchrotron radiation and laboratory sources both showed that the tetrahedral hydrogen bonds in bulk water were destroyed with the increased MgCl2 concentration. The results of G(r) indicated that the main peaks centered at 2.05 and 2.80 Å can be ascribed to the interactions of Mg-O and O-O, respectively. The peak at 3.10 Å is attributed to the combined effect of O-O and Cl-O. By comparing the structural information on MgCl2 solution obtained from the two light sources, it was found that both SSRF and silver-anode laboratory sources can reflect the above-mentioned structural information on MgCl2 solution. The radial distribution function (RDF) obtained from MD simulations of MgCl2 solutions assigned the peaks at 2.0, 2.8, and 3.2 Å to the Mg-O, O-O, and Cl-O interatomic pairs, respectively. The decrease in the O-O coordination number confirms that the hydrogen-bonding network of water is disrupted by increasing MgCl2 observed by X-ray scattering. The proportion of Mg-Cl contact ion pairs gradually increases with MgCl2 concentration as does the coordination number. Raman spectroscopy results show that the bond type changes from double donor double acceptor (DDAA) to single donor-single acceptor (DA) with increasing concentration, providing explicit details of the hydrogen-bond evolution in the aqueous solution.

Cathodic Polarization Behavior of Steel in Aqueous MgCl2 Solutions Containing Zn2+

So far, we have revealed that the dissolution rate of zinc is accelerated in relative high concentrations of MgCl2 in the corrosion process of galvanic couples consisting of zinc and steel. In this study, we investigated the cathodic polarization behavior of steel in MgCl2 solution containing Zn2+ and the effect of Zn2+ dissolved in the solution on the oxygen reduction reaction and hydrogen evolution reaction.The specimens used in the experiments were carbon steel SS400 (Fe-0.12C-0.60Mn-0.011P-0.019S) machined into a 1.5×1.5×0.3 cm3. One side of the specimen was polished with SiC abrasive paper up to #2000 grit and degreased in acetone before being used for the experiment. The test solution was mixtures of 0.25 M MgCl2 + x mM ZnCl2 (x = 2.5, 5 mM, Mg/Zn molar ratio: 100, 50) at room temperature under a naturally aerated condition. As a comparison solution, 0.5 M NaCl + y mM ZnCl2 (x = 5, 10 mM, molar ratio of Na/Zn: 100, 50) with the same chloride ion concentrations were used. Cathodic polarization curves of steel were measured using a three-electrode method with a platinum wire as the counter electrode and an Ag/AgCl electrode (saturated KCl, SSE) as the reference electrode. The potential sweep rate was 0.5 mV/s. After the polarization test, the specimen surfaces were observed with a scanning electron microscope and analyzed for corrosion products formed during cathodic polarization with XRD and laser Raman spectroscopy.The cathodic polarization behavior of steel in MgCl2 solution without Zn2+ was investigated and compared with that of NaCl solution without Zn2+. Diffusion-limited currents of dissolved oxygen reduction (ORR) were observed at -0.6 V to -0.8 V in MgCl2 and NaCl solutions. Furthermore, cathodic polarization in MgCl2 and NaCl solutions showed an increase in current due to hydrogen evolution reaction (HER), and the cathodic current due to HER on steel was larger in the MgCl2 solution than in the NaCl solution. To investigate the difference in HER in both solutions, the steel surface was observed after constant polarization at -1.0 V for 20 min. Mg(OH)2 deposition was observed on the steel surface in the MgCl2 solution, but not in the NaCl solution. This indicates that the increase in pH due to ORR and HER is mitigated by the formation of Mg(OH)2 during cathodic polarization. Therefore, due to the pH buffering action of Mg2+ associated with the formation of Mg(OH)2, it can be considered that a larger HER current flowed in the MgCl2 solution than in the NaCl solution when compared at the same potential.On the other hand, cathodic polarization curves for steel in MgCl2 and NaCl solution containing Zn2+ were investigated. As a result, ORR and HER were observed at potentials down to -1 V in the MgCl2 and NaCl solutions containing Zn2+; the cathodic current due to ORR and HER in the MgCl2 and NaCl solutions containing Zn2+ was reduced compared to the solutions without Zn2+. The inhibition of ORR and HER can be attributed to the precipitation of Zn corrosion products.These results suggest that in solution environments containing Mg2+ and Zn2+, the promotion of HER by the effect of Mg2+ and the inhibition of HER and ORR by Zn corrosion products occur simultaneously.

Positively charged thin-film composite hollow fiber nanofiltration membrane via interfacial polymerization and branch polyethyleneimine modification for Mg2+/Li+ separation

It is a vital technical challenge to extract lithium from salt-lake brine which has very high Mg2+ / Li+ mass ratio via green and low-cost methods, as these two cations have quite similar ionic hydration radius. Positively charged nanofiltration membranes can separate Li+ and Mg2+ through Donnan exclusion. In this work, a kind of hollow fiber nanofiltration membrane with positively charged skin layer was successfully fabricated via interfacial polymerization followed by a surface modification with branched polyethyleneimine (BPEI). The resultant membrane has a large number of amine groups, and thus shows positively charged surface with high rejection for divalent cation ions via Donnan exclusion. This gives it very high selectivity for the separation of Li+ ions from salt-lake brine. Under optimized conditions, it achieves a water permeance of up to 126.2 L m-2 h-1 MPa−1 at a transmembrane pressure difference of 4 bar, and a MgCl2 rejection of 94.6% with 2000 mg L-1 aqueous MgCl2 solution as feed. Meanwhile, it achieves a Mg2+ / Li+ selectivity of nearly 24 for MgCl2 and LiCl salt mixture solution with an overall concentration of 2000 mg L-1 and a Mg2+ / Li+ mass ratio of 150 : 1 as feed, which is high as compared with most of the literature, demonstrating its potential in the practical application of Mg2+ and Li+ separation.

Effect of Ion Size on Pressure-Induced Infiltration of a Zeolite-Based Nanofluidic System.

A nanofluidic system consists of a nano-porous medium and functional liquid, which demonstrates a higher energy absorption density compared to conventional systems for energy absorption. Alterations in the composition of the functional liquid can significantly impact the properties of a nanofluidic system. In this paper, the widely used zeolite ZSM-5 was chosen as the porous medium to establish a nanofluidic system. Three distinct electrolyte solutions, namely KCl aqueous solutions, NaCl aqueous solutions and MgCl2 aqueous solutions were employed as functional liquids while pure water served as the reference condition for configuring four kinds of nanofluidic systems. Pressure-induced percolation experiments were performed on the four zeolite-based systems. The difference in the infiltration process between the electrolyte solution systems and the deionized water system has been ascertained. The effect of the ion size on the infiltration and defiltration process has been determined. The results show that the introduction of ions induces a hydration effect, resulting in a higher critical infiltration pressure of the electrolyte solution system compared to an aqueous solution system. The magnitude of cation charge directly correlates with the strength of the hydration effect and the corresponding increase in critical infiltration pressure. Upon entering the nanochannel, the liquid infiltrates primarily in the form of ions rather than a cation hydration form. The larger the ion size, the shallower the penetration depth after entering the nanopore channel and the larger the corresponding relative outflow rate. The present work will provide valuable theoretical complementary and experimental data support for nanofluidic system applications.

Distinct hydrolysis kinetics and catalytic mechanism of CaMg2, CaMg2X0.1(X= Ni, Zn, Ti) ternary alloys

In this experiment, the as-cast CaMg2, CaMg2Ni0.1, CaMg2Zn0.1, CaMg2Ti0.1 ternary alloys have been successfully developed through vacuum melting induction method. The phase compositions and microstructures of these alloys were characterized using X-ray diffraction and scanning electron microscopy. Subsequently, we investigated the kinetics and microscopic mechanism of hydrolysis in MgCl2 aqueous solution for both as-cast and hydrogenated alloys. The hydrogen production curves were fitted at different temperatures using the nucleation-growth Avrami model, which exhibited a good fit to the hydrolysis kinetics. Our findings revealed that the hydrides obtained through H2 absorption exhibited fast hydrolysis reaction rates. Notably, CaMg2Ti0.1 alloy demonstrated excellent hydrolysis properties, with a yield of 1020 mL/g and an activation energy of 37.77 kJ/mol. The activation energy of H–CaMg2Ti0.1 alloy decreased to 15.66 kJ/mol, attributed to the synergistic catalytic effect of TiH2 phase and Ca4Mg3H12 phase. These hydrides exhibited ease of hydrolysis, releasing H+ ions to generate H2 gas. Furthermore, the hydrolysis properties of the as-cast alloys were observed that ranked as CaMg2Ti0.1 > CaMg2Zn0.1 > CaMg2 > CaMg2Ni0.1. However, the order of hydrogenated alloys changed to CaMg2Ti0.1 > CaMg2Zn0.1 > CaMg2Ni0.1 > CaMg2, indicating the synergistic catalytic effect between the Mg phase and Mg2NiH4. Among the Mg-based alloys, Ca–Mg-based alloy hydrolysis showed a research trend towards improving the kinetic properties through alloying.

An X-ray and Neutron Scattering Study of Aqueous MgCl2 Solution in the Gigapascal Pressure Range

The structure of electrolyte solutions under pressure at a molecular level is a crucial issue in the fundamental science of understanding the nature of ion solvation and association and application fields, such as geological processes on the Earth, pressure-induced protein denaturation, and supercritical water technology. We report the structure of an aqueous 2 m (=mol kg−1) MgCl2 solution at pressures from 0.1 MPa to 4 GPa and temperatures from 300 to 500 K revealed by X-ray- and neutron-scattering measurements. The scattering data are analyzed by empirical potential structure refinement (EPSR) modeling to derive the pair distribution functions, coordination number distributions, angle distributions, and spatial density functions (3D structure) as a function of pressure and temperature. Mg2+ forms rigid solvation shells extended to the third shell; the first solvation shell of six-fold octahedral coordination with about six water molecules at 0 GPa transforms into about five water molecules and one Cl− due to the formation of the contact ion pairs in the GPa pressure range. The Cl− solvation shows a substantial pressure dependence; the coordination number of a water oxygen atom around Cl− increases from 8 at 0.1 MPa/300 K to 10 at 4 GPa/500 K. The solvent water transforms the tetrahedral network structure at 0.1 MPa/300 K to a densely packed structure in the GPa pressure range; the number of water oxygen atoms around a central water molecule gradually increases from 4.6 at 0.1 MPa/298 K to 8.4 at 4 GPa/500 K.

Room temperature phosphorescence from natural wood activated by external chloride anion treatment

Producing afterglow room temperature phosphorescence (RTP) from natural sources is an attractive approach to sustainable RTP materials. However, converting natural resources to RTP materials often requires toxic reagents or complex processing. Here we report that natural wood may be converted into a viable RTP material by treating with magnesium chloride. Specifically, immersing natural wood into an aqueous MgCl2 solution at room temperature produces so-called C-wood containing chloride anions that act to promote spin orbit coupling (SOC) and increase the RTP lifetime. Produced in this manner, C-wood exhibits an intense RTP emission with a lifetime of ~ 297 ms (vs. the ca. 17.5 ms seen for natural wood). As a demonstration of potential utility, an afterglow wood sculpture is prepared in situ by simply spraying the original sculpture with a MgCl2 solution. C-wood was also mixed with polypropylene (PP) to generate printable afterglow fibers suitable for the fabrication of luminescent plastics via 3D printing. We anticipate that the present study will facilitate the development of sustainable RTP materials.

Incorporation of Functionalized Halloysite Nanotubes (HNTs) into Thin-Film Nanocomposite (TFN) Nanofiltration Membranes for Water Softening

Incorporating nanoparticles (NPs) into the selective layer of thin-film composite (TFC) membranes is a common approach to improve the performance of the resulting thin-film nanocomposite (TFN) membranes. The main challenge in this approach is the leaching out of NPs during membrane operation. Halloysite nanotubes (HNTs) modified with the first generation of poly(amidoamine) (PAMAM) dendrimers (G1) have shown excellent stability in the PA layer of TFN reverse-osmosis (RO) membranes. This study explores, for the first time, using these NPs to improve the properties of TFN nanofiltration (NF) membranes. Membrane performance was evaluated in a cross-flow nanofiltration (NF) system using 3000 ppm aqueous solutions of MgCl2, Na2SO4 and NaCl, respectively, as feed at 10 bar and ambient temperature. All membranes showed high rejection of Na2SO4 (around 97-98%) and low NaCl rejection, with the corresponding water fluxes greater than 100 L m-2 h-1. The rejection of MgCl2 (ranging from 82 to 90%) was less than that for Na2SO4. However, our values are much greater than those reported in the literature for other TFN membranes. The remarkable rejection of MgCl2 is attributed to positively charged HNT-G1 nanoparticles incorporated in the selective polyamide (PA) layer of the TFN membranes.

Molecular interactions of local anesthetics in aqueous MgCl2 solutions: A volumetric, acoustic and spectroscopic analysis

Investigations of the physicochemical properties of drugs in the presence of co-solutes in aqueous solutions have always been a keen interest of the researchers. Such properties are very important to derive the information about solute–solute and solute–solvent type interactions. Therefore, in this communication, various physicochemical properties of two local anesthetics viz. Procaine hydrochloride (PC) and Tetracaine hydrochloride (TC) in aqueous and in aqueous solutions of MgCl2 (mB = 0.024, 0.047, 0.070 mol kg−1) have been studied using density and sound velocity measurements at different temperatures (288.15, 298.15, 308.15, and 318.15 K) along with 1H NMR spectroscopy. Various parameters like apparent molar volume (V) and isentropic compressibility (Ks) of solutes, apparent molar volume (V°) and isentropic compressibility (Ks°) of solutes at infinite dilution, apparent molar expansibility (E°) and their double derivatives (∂2V°/∂T2)P have been evaluated using density and sound velocity data. The transfer volumes (ΔtrV°) of PC and TC drugs from water to aqueous MgCl2 solutions and the various acoustical parameters like acoustic impedance (Z), intermolecular free length (Lf), and relative association (RA) have also been computed. All these parameters have been used to throw light on the effect of temperature as well as the effect of co-solute (MgCl2) concentration on the various solute–solvent/co-solute interactions with the help of co-sphere overlap model. The structure breaker/or maker ability of both local anesthetics in the presence of MgCl2 has also been analyzed. The spectroscopic results indicate the presence of hydrophobic–ionic interactions at higher concentrations of co-solute.

Regeneration of As(V) loaded granular activated carbon through desorption in FeCl3, CaCl2 and MgCl2 aqueous solutions

As(V) adsorption on granular activated carbon (GAC) and subsequent desorption in dH2O was modeled using the pseudo-first and pseudo-second order kinetic models. Regeneration was achieved by immersing loaded GAC in NaCl, FeCl3, CaCl2 and MgCl2 aqueous solutions. As(V) detection after desorption was highest for NaCl but subsequent adsorption was lowest. Regeneration was highest in FeCl3 solution of pH 2 followed closely by pH 3, but As(V) precipitation appeared superior at pH 3. Molar ratios of Fe, Ca and Mg to As were tested in the range of 0.75:1 to 12:1 where a logarithmic relation was found between the molar ratio and As(V) desorption as diluted in HNO3 and H2O and subsequent adsorption. Precipitation was nearly complete in FeCl3, limited in MgCl2 at a ratio of 12:1 and not observed in CaCl2. While kinetic values were lower than in previous tests, the pseudo-first and pseudo-second order models could accurately describe desorption in CaCl2 and MgCl2 but not in FeCl3 due to precipitation. Desorption in FeCl3 was most effective in precipitating As(V), being highest at a molar ratio of 6:1, but regeneration was slightly higher at a molar ratio of 12:1.

Analysis and information content of quadrupolar NMR in glasses: 25Mg NMR in vitreous MgSiO3 and CaMgSi2O6

The static wideline and high-resolution magic angle spinning (MAS) 25Mg NMR lineshapes measured for isotopically enriched enstatite and diopside glasses indicate a wide distribution of the electric-field gradient (EFG) components at the 25Mg position caused by disorder. The correct characterization of this distribution requires simulations with special attention paid to the experimental parameters. Here, both the static spectra obtained by wideband excitation and the MAS-NMR spectra obtained via rotor-synchronized Hahn spin echo acquisition were successfully simulated with the Czjzek distribution model, using one consistent set of parameters. Average nuclear electric quadrupole coupling constants near 8 MHz and a distribution width around 4 MHz were obtained for both materials, which suggests that earlier results on these glasses need to be re-examined. The results of this study outline a general strategy for characterizing the local environments of strongly coupled quadrupolar nuclei in amorphous and glassy materials. Despite the discrepancies between the interaction parameters extracted from our data and those published in earlier NMR work, the best fit to the data indicate an average isotropic chemical shift near 13 ppm (vs. aqueous MgCl2 solution) for both the enstatite and diopside glasses. Assuming the applicability of the current database relating the 25Mg chemical shifts with coordination numbers in crystalline compounds, this value suggests that the Mg2+ ions are six-coordinated. This conclusion, however, is based on the simplifying assumption that the 25Mg spectrum comprises a Czjzek distribution centered at a single isotropic chemical shift value and stands in contrast to the results of recent isotope-selective neutron diffraction studies which give an average Mg-O coordination number of 4.4–4.5 for both glasses. However, reasonable fits to the MAS-NMR spectra can also be obtained when constraining the average isotropic chemical shift to 50 ppm, a value typical of four-coordinated Mg. We conclude that multiple Mg sites with different coordination numbers may well be present and that, in the present glasses, 25Mg NMR at typically used spinning rates and magnetic field strengths (20 kHz, 14.1 T) is not capable of resolving them due to excessive broadening by quadrupolar interactions.

Molecular dynamics study of water and ion behaviors of mixed salts solutions on extended quartz surface

The adoption and evolution of water molecules and ions in mixed electrolytes at the surface play vital roles in the physical properties and chemical reactions of SiO2-like corrosion. The effect of salt type and concentration on the structure and dynamics of water molecules and ions at silica surfaces are studied using all-atom molecular dynamics simulations taking the case of the NaCl, MgCl2, and NaCl–MgCl2 aqueous solutions. The ability of ion hydration is in the order of Mg2+ > Na+ > Cl−, being opposite to their hydration Gibbs free energies, which directly influence the weak interaction in the solution and the diffusion rate of the particles. Mg shows stronger destruction to weak interactions than Na does, and ionic hydration of Mg2+ decelerates the self-diffusion coefficient of water molecules significantly due to the enhanced Coulomb effect and the interruption of solution continuity. Meanwhile, the self-diffusion coefficient of particles decreases with the concentration improvement in the single salt solution as increased ionic hydration. In the mixed salt solution, the order of diffusion rate is Cl− > Na+ > Mg2+ as a result of the different confinement effects of the protonated pore. Interestingly, a small amount of Na+ addition can promote the self-diffusion of Mg2+, but a great many of Na+ addition slows the diffusion of Mg2+. This work provides comprehensive insight into the behavior of mixed salt solutions at silica surfaces, shedding light on the practical applications of geological sciences, cultural relics protection, and colloidal sciences.

Monitoring MgCl2 hydrate formation from aqueous solutions using terahertz time-domain spectroscopy.

The interaction of MgCl2 with H2O is heavily involved in biological and chemical processes. In this work, freezing-induced hydrate formation from MgCl2 aqueous solution was monitored using terahertz time-domain spectroscopy. At low temperatures, two phase transitions from brine to hydrate formation could be clearly observed, and the formation of hydrate was accompanied by the emergence of new THz fingerprint peaks at 1.02, 1.56, and 1.84 THz, respectively. Integrating XRD and quantum chemical calculations, we attributed the absorption peaks to the vibrational modes of the formed MgCl2·12H2O. This demonstrates the potential of THz spectroscopy for application in the detection of biological processes in low-temperature environments, such as cell freezing.

Hydrogen production from hydrolysis of magnesium wastes reprocessed by mechanical milling under air

Magnesium-based wastes were reprocessed by mechanical milling under air atmosphere and used to produce hydrogen by hydrolysis on a laboratory scale. The evolution of the material during reprocessing and the generation of hydrogen in a 0.6 M MgCl2 aqueous solution at 24 °C are reported. The morphology, microstructure and phase abundance change with milling time. During mechanical processing, (i) particle size and crystallite size reduce, (ii) microstrain accumulates in the material, (iii) Al dissolves in Mg, (iv) the amount of Mg17Al12 (β-phase) increases and (v) small quantities of Fe from the milling tools are incorporated in the material. By hydrolysis, hydrogen yields in the 70–90% range after 30 min of reaction have been obtained, depending on milling time. Reactants are not exhausted during the hydrolysis reaction in the saline solution, due to the formation of a Mg(OH)2 layer that produces a passivating effect. Higher generation has been observed for larger particles and for materials reprocessed for longer milling times. Reaction kinetics also improves with milling time, with faster rates observed for the smaller particles. The shape of the hydrolysis curves can be fitted with a model that corresponds to a reaction limited by a three dimensional geometric contraction process. Mg17Al12 and Fe favor hydrogen production by acting as micro-galvanic cathodes during the reaction.

Kinetics and mechanism of MgH2 hydrolysis in MgCl2 solutions

In the present work we systematically studied the hydrolysis of magnesium hydride in MgCl2 aqueous solutions, which was used as a process promotor. The initial hydrolysis rate, the pH of the reaction mixture, and the overall reaction yield are all found to be linearly dependent of the logarithm of MgCl2 concentration. The phase-structural and elemental compositions of the formed precipitates showed that they do not contain chlorine ions and solely consist of Mg(OH)2. The size of the Mg(OH)2 crystallites increased with increasing content of MgCl2 in the aqueous solution.The best agreement between the observed and modelled hydrolysis kinetics was achieved by applying a pseudo-homogeneous model that describes the process rate as increasing with H+ ions concentration. The deposition of Mg(OH)2 which is impermeable to water and blocks the surface of the remaining MgH2 however simultaneously and partially suspends this reaction. We therefore propose a mechanism of MgH2 hydrolysis in the presence of MgCl2 that is based on the comparison of the kinetic dependencies, variations of solutions pH and the structural and elemental analysis data for the solid deposits formed during the interaction. We furthermore define the kinetic model of the process, and the equation that describes the variation in pH of solutions containing chloride salts. Hydrolysis efficiency increased with increased relative MgCl2 amount; the best performance being achieved for the stoichiometric ratio MgH2+0.7MgCl2 (MgCl2/MgH2 weight ratio of 12.75/100). This provided a hydrogen yield of 1025 mL (H2)/g MgH2. Maximum hydrogen yield peaked at 89% of the theoretical H2 generation capacity, and was achieved within 150 min of hydrolysis start, 35% of hydrogen being released in the first 10 min after start, the hydrogen generation rate being as high as 800 mL min−1·g−1 MgH2.

Effect of additive concentration on water solution under vacuum ambient: A molecular dynamics simulation study

In order to explore the effect of different concentrations of additives on aqueous solution in vacuum ambient, this paper uses molecular dynamics simulation method to study different concentrations of magnesium chloride (MgCl2) aqueous solution, ethylene glycol aqueous solution and nano iron oxide (nano-Fe3O4) aqueous solution. The radial distribution function of atoms, the water molecules’ self-diffusion coefficient and the type and number of hydrogen bonds are analyzed in detail. The dynamic behavior between water molecules and chloride and alcohol molecules in the solution is revealed. The results show that the additives affect the crystallization of the solution by inhibiting the self-diffusion rate of water molecules, and the iron oxide nanoclusters exhibit the most obvious behavior. Meanwhile, the added additives can also restrain the formation of hydrogen bonds between water molecules in solution. This suppresses the hydrogen bonds between two water molecules. At the same time, it reduces the diffusivity of water molecules. These effects weaken the tendency of water molecules to migrate to the nucleus, and can curb the nucleation and growth of ice crystals in the aqueous solution to a certain extent. This research will provide reference value in the selection of ice-making working fluid. Nano-iron oxide has better performance than MgCl2, and glycol solution is not conducive to vacuum ice making.