Alkaline Earth Hydroxides Research Articles

Generating sustainable cement material from seawater with low-cost ultrafiltration (UF) membrane electrolysis

Membrane electrolysis offers a promising avenue for in-situ generation of hydroxide ions (OH−), facilitating the recovery of magnesium (Mg2+) and calcium (Ca2+) ions from seawater as alkaline earth hydroxide precipitates. This process paves the way for an alternative greener method in the production of raw materials for cement manufacturing compared to limestone mining. Despite its potential, the application of conventional ion migration membranes, such as anion exchange membrane (AEM) and cation exchange membrane (CEM), is hampered by their high cost and low mechanical quality, posing significant barriers to industrial scalability. In this work, we introduce the utilization of commercially available high mechanical strength ultrafiltration (UF) membrane within a two-chamber electrochemical system, repurposing it as an ion migration membrane due to its distinct advantages in terms of simplicity and relative cost-efficiency than conventional AEM. This research demonstrates that the UF membrane exhibited a comparable performance to AEM in terms of OH− production. Both membranes achieved 97–99 % removal of Mg2+ and Ca2+ within 3 h at a current density of 8 mA/cm2 and maintained comparable migration rate of SO42− ion. Compared to AEM, a notable distinction of the UF membrane is its reduced migration rate of Cl− ions, resulting in lower membrane discoloration/oxidation. Furthermore, the investigation reveals that utilizing a Na2SO4 solution as an alternative anolyte, despite being slower for OH− production, offers economic advantages and facilitates higher selective recovery of Mg2+ over Ca2+. The end products of this process, MgO and CaO, are viable raw materials for cement production, underscoring a sustainable and low carbon approach compared to conventional limestone mining of cement production.

Increasing Al-Pair Abundance in SSZ-13 Zeolite via Zeolite Synthesis in the Presence of Alkaline Earth Metal Hydroxide Produces Hydrothermally Stable Co-, Cu- and Pd-SSZ-13 Materials

Replacing alkaline for alkaline-earth metal hydroxide in the synthesis gel during the synthesis of siliceous SSZ-13 zeolite (Si/Al~10) yields SSZ-13 with novel, advantageous properties. Its NH4-form ion-exchanges higher amount of isolated divalent M(II) ions than the conventional one: this is the consequence of an increased number of Al pairs in the structure induced by the +2 charge of Sr(II) cations in the synthesis gel that force two charge-compensating AlO4− motives to reside closer together. We characterize the +2 state of Co(II) ions in these materials with infra-red spectroscopy and X-ray absorption spectroscopy measurements and show their utility for NOx pollutant adsorption from ambient air: the ones derived from SSZ-13 with higher Al pair content contain more isolated cobalt(II) and, thus, perform better as ambient-air NOx adsorbers. Notably, Co(II)/SSZ-13 with an increased number of Al pairs is significantly more hydrothermally stable than its NaOH-derived analogue. Loading Pd(II) into Co-SSZ-13(Sr) produces an active NOx adsorber (PNA) material that can be used for NOx adsorption from simulated diesel engine exhaust. The critical issue for these applications is hydrothermal stability of Pd-zeolites. Pd/SSZ-13 synthesized in the presence of Sr(OH)2 does not lose its PNA capacity after extremely harsh aging at 850 and 900 °C (10 h in 10% H2O/air flow) and loses only ~55% capacity after hydrothermal aging at 930 °C. This can be extended to other divalent metals for catalytic applications, such as copper: we show that Cu/SSZ-13 catalyst can survive hydrothermal aging at 920 °C without losing its catalytic properties, metal dispersion and crystalline structure. Thus, we provide a new, simple, and scalable strategy for making remarkably (hydro)thermally stable metal-zeolite materials/catalysts with a number of useful applications.

Method to prevent accidental ruthenium volatilization from high-level liquid waste using alkaline earth hydroxide

Method to prevent accidental ruthenium volatilization from high-level liquid waste using alkaline earth hydroxide

Degradation of poly-L-lactic acid biopolymer films in Ca(OH)2-dosed fresh human urine collected in source-separating sanitation systems

Alkaline dehydration is a promising technology for producing organo-mineral fertiliser from source-separated human urine, but potential risks to users from handling alkaline earth hydroxides at source and carbonation of hydroxides during dehydration limit its implementation in real-life settings. These issues could be addressed by enclosing chemicals in bio-derived polymers. In this study, we investigated degradation and erosion of poly-L-lactic acid (PLLA) biopolymer films of different thicknesses (0.05, 0.1 and 0.25 mm) in Ca(OH)2-dosed fresh urine and Milli-Q water at two temperatures (20 °C and 45 °C). Evaluation of degraded films by XRD, GPC and SEM showed changes in crystallinity, reduction in molecular weights and change in surface morphology, respectively. SEM/EDX, FTIR and ICP-OES data indicated that L-CaL2, L-lactides and lactic acid were formed in urine. Overall, we found that thinner films, higher temperature and higher pH accelerated PLLA degradation in urine.

Barium Hydroxide Nanoparticle–Phosphoric Acid System for Desalination and Consolidation of Tomb Murals

Tomb murals are an important component of cultural heritage, but the extant majority of burial murals are severely damaged. There are various causes behind the deterioration of tomb murals, among which the detrimental effects of sodium sulfate on murals are some of the most difficult to treat. In the past decades, the application of alkaline earth metal hydroxides (such as Ba(OH)2, Ca(OH)2, and Ma(OH)2) for the conservation and consolidation of murals has become more common. However, there are some problems, such as large particles, poor permeability, and potential for surface whitening. In response to this issue, we investigated a facile method for the synthesis of nano barium hydroxide (N-Ba(OH)2), from which we developed a barium hydroxide nanoparticle–phosphoric acid (N-Ba(OH)2/H3PO4) multisite in situ consolidation system. The results show that N-Ba(OH)2/H3PO4 consolidation material has good permeability and mechanical properties compared with commercial Ba(OH)2 and other common consolidation materials. This material performs very well in both salt resistance and desalination tests, the color difference change is minimal, and the technique is suitable for the practical manipulation of outdoor artifact conservation work. Recently, it has even been used in the desalination and consolidation of tomb murals in Jiangxi, China, the results of which opened a new way of thinking about the long-term conservation of tomb murals.

One-Step Solvometallurgical Process for Purification of Lithium Chloride to Battery Grade

The use of lithium in manufacturing of lithium-ion batteries for hybrid and electric vehicles, along with stringent environmental regulations, have strongly increased the need for its sustainable production and recycling. The required purity of lithium compounds used for the production of battery components is very high (> 99.5%). In this work, a solvometallurgical process that exploits the differences in solubility between LiCl and other alkali and alkaline-earth chlorides and hydroxides in ethanolic solutions has been investigated for the purification of LiCl to battery grade at room temperature. A closed-loop flowsheet based on the green solvent ethanol is proposed for purification of LiCl, a precursor for battery-grade LiOH·H2O. High-purity LiCl solution (> 99.5% Li) could be obtained in a single-process step comprising the simultaneous selective dissolution of LiCl and the precipitation of Mg(OH)2 and Ca(OH)2 using LiOH·H2O in 95 vol% ethanol. However, the analogous process in aqueous solution resulted in impure LiCl (typically less than about 75%).Graphical

A First-Principles Study on the Electronic, Thermodynamic and Dielectric Properties of Monolayer Ca(OH)2 and Mg(OH)2.

We perform first-principles calculations to explore the electronic, thermodynamic and dielectric properties of two-dimensional (2D) layered, alkaline-earth hydroxides Ca(OH) and Mg(OH). We calculate the lattice parameters, exfoliation energies and phonon spectra of monolayers and also investigate the thermal properties of these monolayers, such as the Helmholtz free energy, heat capacity at constant volume and entropy as a function of temperature. We employ Density Functional Perturbation Theory (DFPT) to calculate the in-plane and out-of-plane static dielectric constant of the bulk and monolayer samples. We compute the bandgap and electron affinity values using the HSE06 functional and estimate the leakage current density of transistors with monolayer Ca(OH) and Mg(OH) as dielectrics when combined with HfS and WS, respectively. Our results show that bilayer Mg(OH) (EOT∼0.60 nm) with a lower solubility in water offers higher out-of-plane dielectric constants and lower leakage currents than does bilayer Ca(OH) (EOT∼0.56 nm). Additionally, the out-of-plane dielectric constant, leakage current and EOT of Mg(OH) outperform bilayer h-BN. We verify the applicability of Anderson’s rule and conclude that bilayers of Ca(OH) and Mg(OH), respectively, paired with lattice-matched monolayer HfS and WS, are effective structural combinations that could lead to the development of innovative multi-functional Field Effect Transistors (FETs).

Thermodynamics and Kinetics of pH-dependent Dissolution of Sparingly Soluble Alkaline Earth Hydroxides in Source-Separated Human Urine Collected in Decentralised Sanitation Systems

Alkaline earth hydroxides are widely used in water and wastewater treatment. Within the emerging niche of source-separating sanitation, these chemicals have found a new application—to prevent urease-catalysed degradation of urea present in freshly excreted human urine. However, little is known about the dissolution behaviour of these hydroxides in biological fluids like human urine. Herein, we investigate the solubility of Mg(OH)2 and examine factors that govern its dissolution in different types of urine (real fresh urine, synthetic fresh urine, synthetic dephosphatised fresh urine and real fresh urine concentrated by CO2-free drying). We report experimentally determined as well as thermodynamically simulated data on Mg(OH)2 solubility, dissolution kinetics, and chemical speciation in urine. We find that it takes between 6 and 16 min for Mg(OH)2 to dissolve and the average solubility in real fresh urine at 25°C to be 650 mg L−1. We show that solubility is influenced mainly by concentration of organic compounds, soluble phosphate, and magnesium excreted in fresh urine. When fresh urine is supersaturated with Mg(OH)2, the pH increases to >10.5 and urease-catalysed degradation of urea is inhibited for >14 days. Removing 95% water present in urine increases the solubility of Mg(OH)2 to 16,240 mg L−1 but reduces pH to < 10. Because relative increase in Mg(OH)2 solubility decreases as more water is removed and the solubility is retrograde with respect to temperature, to increase the urine pH to >10 and prevent enzymatic ureolysis, the temperature must be kept < 29°C at 75% water removal and < 22°C at 95% water removal. We find this dissolution behaviour of Mg(OH)2 in concentrated urine solutions to be unlike other alkaline earth hydroxides. These findings have significant implications for the design of new sanitation systems that separately collect and recycle plant-essential nutrients present in human urine.

On the effect of Alkaline Earth Metal Cations in the Hydrogenolysis of Glycerol over Pt/C – an Experimental and Theoretical Study

AbstractGlycerol can be converted to propylene glycol via metal and base catalyzed hydrogenolysis. The nature of the base has a profound influence on the outcome of the reaction. We have tested a range of alkaline (LiOH, NaOH and CsOH) and alkaline earth (Mg(OH)2, Ca(OH)2, Sr(OH)2 and Ba(OH)2) metal hydroxides in combination with Pt/C. The data reveal that alkaline earth metal hydroxides exhibit a much higher activity and improved selectivity. DFT calculations confirm that the coordination of reactive intermediates to divalent cations is responsible for the observed behavior. In the study, the effect of the cation on hydrogenolysis was elucidated for the first time.

Ex-situ mineral carbonation – A parameter study on carbon mineralisation in an autoclave as part of a large-scale utilisation process

The exothermic carbonation reaction includes the degradation of alkaline earth metal (mainly Mg-, Ca-) oxides, hydroxides or silicates under participation of carbon dioxide under aqueous conditions and the formation of stable carbonates with long-term storage of carbon dioxide. The extent of reaction depends on different influencing factors, which significantly affect the economic and ecological feasibility of this technology. With special regard to the possibilities of upscaling and balancing in the context of life cycle analyses for the carbon capture and usage approach, various material-specific and process-related parameters and also combinations of these have been tested experimentally and evaluated. Hereby, significant differences in the carbonation extent were identified with achieved carbonation degrees from below 5 up to 60%, corresponding to 305 kgCO2/tfeed. This study is a comprehensive investigation of those material-specific and process-related parameters and their combination and aims to ensure the economic viability of enhanced weathering by increasing the degree of carbonation.

Direct conversion of alkaline earth metal hydroxides and sulfates to carbonates in ammonia solutions

Direct conversion of alkaline earth metal hydroxides and sulfates to carbonates in ammonia solutions

Anionic Tuning of Zeolite Crystallization

Zeolites are of great industrial relevance as catalysts, adsorbents, and ion-exchangers and typically synthesized under hydrothermal conditions. Rational regulation of their crystallization process...

Effect of Alkali Metals and Alkaline Earth Metals Hydroxides on the Structure of Wool Fibers

ABSTRACT Wool is sensitive toward the effect of alkaline solutions which are usually used in the dissolution of wool fibers to regenerate keratin. In this investigation, the effect of different alkalis on the chemical composition and the secondary structure of wool was studied. Wool was treated with equivalent amounts of alkali metal hydroxides (lithium, sodium, and potassium hydroxides) as well as alkaline earth metal hydroxides (strontium and barium hydroxides). The effect of these alkalis on wool was monitored using amino acid analysis, elemental analysis, carboxylic content, acid, and base combining capacity, urea-bisulfite and alkali solubility, and FTIR spectroscopy. Further structure elucidation was conducted by thermo-gravimetric analysis, differential scanning calorimetry, and X-ray diffraction pattern. Scanning electron microscopy was used to assign the alteration of the fiber morphology of the alkali-treated wool. The results of this investigation indicate that the effect of the used alkalis on wool is not similar. Cystine, glycine, and the basic amino acids are the most affected species in the treated wool. Some elimination reactions were involved during alkaline treatment of wool; namely decarboxylation, desulphydration, and deamination. The secondary structure of wool treated with Sr(OH)2 and Ba(OH)2 was changed from the α-helical structure into the β-sheet form.

Recent Advances in Thermochemical Energy Storage via Solid–Gas Reversible Reactions at High Temperature

The exploitation of solar energy, an unlimited and renewable energy resource, is of prime interest to support the replacement of fossil fuels by renewable energy alternatives. Solar energy can be used via concentrated solar power (CSP) combined with thermochemical energy storage (TCES) for the conversion and storage of concentrated solar energy via reversible solid–gas reactions, thus enabling round the clock operation and continuous production. Research is on-going on efficient and economically attractive TCES systems at high temperatures with long-term durability and performance stability. Indeed, the cycling stability with reduced or no loss in capacity over many cycles of heat charge and discharge of the material is pursued. The main thermochemical systems currently investigated are encompassing metal oxide redox pairs (MOx/MOx−1), non-stoichiometric perovskites (ABO3/ABO3−δ), alkaline earth metal carbonates and hydroxides (MCO3/MO, M(OH)2/MO with M = Ca, Sr, Ba). The metal oxides/perovskites can operate in open loop with air as the heat transfer fluid, while carbonates and hydroxides generally require closed loop operation with storage of the fluid (H2O or CO2). Alternative sources of natural components are also attracting interest, such as abundant and low-cost ore minerals or recycling waste. For example, limestone and dolomite are being studied to provide for one of the most promising systems, CaCO3/CaO. Systems based on hydroxides are also progressing, although most of the recent works focused on Ca(OH)2/CaO. Mixed metal oxides and perovskites are also largely developed and attractive materials, thanks to the possible tuning of both their operating temperature and energy storage capacity. The shape of the material and its stabilization are critical to adapt the material for their integration in reactors, such as packed bed and fluidized bed reactors, and assure a smooth transition for commercial use and development. The recent advances in TCES systems since 2016 are reviewed, and their integration in solar processes for continuous operation is particularly emphasized.

Effect of Solid Bases Catalyst on Conversion of Acrylonitrile into Acrylic Acid by Hydrothermal Reaction

This study aims at the shortcomings of the current industrial application of acrylonitrile wastewater treatment, using alkali-catalyzed hydrothermal technology to convert acrylonitrile into acrylic acid for achieving resource utilization. In this study, alkali metal, alkaline earth metal hydroxide and composite solid base were used as catalysts to investigate catalytic effects of these solid based on the hydrothermal reaction. The results show when using the alkali and alkaline-earth metal hydroxides as catalysts, the best effect of treatment was KOH and the highest yield of acrylic acid reached 56.60%. It was also found that, among the three kinds of solid base catalysts (Ca-O-Mg, K-O-Al, K-O-Si) adopted with the same mass and various loading capacity, K-O-Si (15%) was the most effective catalyst for the conversion of acrylonitrile, and the highest yield of acrylic acid reached 57.78%. This process provides an environmentally friendly method toward the synthesis of useful acrylic acid from acrylonitrile within a very short time.

Near room temperature synthesis of perovskite oxides

Perovskite oxides ABO3 (A = Sr, Ba, B = Ti, Zr, Hf) were prepared at around room temperature using the reaction between alkaline earth hydroxides and metal oxide hydrous gels. The products of the reaction crystallized without any calcination. High-symmetry perovskite oxides, such as cubic perovskite, were obtained at lower temperatures. The Madelung energy of each perovskite oxide was calculated from the crystal structure and the lattice parameter obtained by XRD measurement. The calculated Madelung energy change in the synthesis reaction showed a linear relationship with the synthesis temperature. A rise in the synthesis temperature increased the change of the Madelung energy. The results thus confirmed that the synthesis temperature depended on the symmetry of the perovskite oxide in this study. Drawing from these results, we concluded that the synthesis temperature could be estimated by considering the crystal structure and Madelung energy change in the synthesis reaction.

Ab initio molecular dynamics studies of hydroxide coordination of alkaline earth metals and uranyl.

Ab initio molecular dynamics (AIMD) simulations of the Mg2+, Ca2+, Sr2+ and UO22+ ions in either a pure aqueous environment or an environment containing two hydroxide ions have been carried out at the density functional level of theory, employing the generalised gradient approximation via the PBE exchange-correlation functional. Calculated mean M-O bond lengths in the first solvation shell of the aquo systems compared very well to existing experimental and computational literature, with bond lengths well within values measured previously and coordination numbers in line with previously calculated values. When applied to systems containing additional hydroxide ions, the methodology revealed increased bond lengths in all systems. Proton transfer events (PTEs) were recorded and were found to be most prevalent in the strontium hydroxide systems, likely due to the low charge density of the ion and the consequent lack of hydroxide coordination. For all alkaline earths, intrashell PTEs which occurred outside of the first solvation shell were most prevalent. Only three PTEs were identified in the entire simulation data of the uranium dihydroxide system, indicating the clear impact of the increased charge density of the hexavalent uranium ion on the strength of metal-oxygen bonds in aqueous solution. Broadly, systems containing more charge dense ions were found to exhibit fewer PTEs than those containing ions of lower charge density.

Synthesizing Alkaline Earth Metal Hydroxides Nanoparticles through an Innovative, Single-Step and Eco-Friendly Method

The objective of this paper is to introduce a patented and eco-friendly method to synthesize aqueous suspension of all types of alkaline-earth metal hydroxides nanoparticles (NPs). This method is based on an ion exchange process; the exchange takes place at ambient temperature/pressure, starts from cheap or renewable reagents and, in one single step, results in the creation of the crystalline desired nanoparticles in only a few minutes. In terms of structural and morphological features, the synthesized nanoparticles are characterized by means of XRD-Rietveld refinement, FTIR, and TEM. In particular, we obtained pure and crystalline magnesium and calcium hydroxide suspensions, showing the typical brucite crystal structure with a hexagonal lamellar morphology and dimensions generally <100 nm. With respect to the strontium and barium hydroxide suspensions, we observed different kinds of hydroxides (either anhydrous and hydrate forms), characterized by orthorhombic or monoclinic crystal lattices with rod-like nanostructured morphologies. Despite the different morphologies, all synthesized nanoparticles appear constituted by a superimposition of primary nanoparticles, of dimensions ranging from a few to 15 nm, correlated to the increase in the atomic number of the alkaline earth metal.

Structures and Heats of Formation of Simple Alkaline Earth Metal Compounds II: Fluorides, Chlorides, Oxides, and Hydroxides for Ba, Sr, and Ra.

Geometry parameters, vibrational frequencies, heats of formation, bond dissociation energies, cohesive energies, and selected fluoride affinities (difluorides) are predicted for the late alkaline earth (Sr, Ba, and Ra) oxides, fluorides, chlorides, and hydroxides at the coupled cluster theory CCSD(T) level. Additional corrections (scalar relativistic and pseudopotential corrections, vibrational zero-point energies, and atomic spin-orbit effects) were included to accurately calculate the total atomization energies and heats of formation following the Feller-Peterson-Dixon methodology. The calculated values are compared to the experimental data where available. In some cases, especially for Ra compounds, there are no experimental results, or the experimental energetics and geometries are not reliable or have very large error bars. All of the Sr, Ba, and Ra difluorides, dichlorides, and dihydroxides are bent structures with the OMO bond angles decreasing going down the group. The cohesive energies of bulk Be dihalides are predicted to be quite low, while those of Ra are relatively large. The fluoride affinities show that the difluorides are moderately strong Lewis acids and that such trifluorides may form under the appropriate experimental conditions.

Mechanochemical Synthesis of Double Tin and Alkaline Earth Metal Hydroxides

Mechanochemical Synthesis of Double Tin and Alkaline Earth Metal Hydroxides