Magnesium Ion Concentration Research Articles

Evaluation of water hardness treatment methods using sodium hydroxide and their impact on water quality

Hard water is an environmental and technical challenge caused by high concentrations of calcium (Ca²⁺) and magnesium (Mg²⁺) ions, leading to scale formation that affects the efficiency of household and industrial appliances and increases maintenance and treatment costs. Additionally, hard water can pose health risks and reduce its quality for daily use. This study aims to evaluate the effectiveness of different doses of sodium hydroxide (NaOH) in treating water hardness and improving water quality by reducing total hardness (TH) and adjusting the physicochemical properties of water. Three main dosages were tested: the first dosage (5 g/L of NaOH), which assessed the basic effectiveness of sodium hydroxide; the second dosage (2.5 g/L of NaOH and 2.5 g/L of Na₂CO₃ with HCl and acid), aimed at balancing hardness reduction with mineral retention; and the optimized dosages (10, 20, and 30 mg/L of NaOH), which proved to be the most effective and balanced. The optimized doses successfully reduced total hardness to levels compliant with Algerian standards while maintaining calcium and magnesium concentrations within acceptable ranges. Furthermore, electrical conductivity (EC) remained within safe limits without significant increases, ensuring the water did not become oversaturated with dissolved salts. The slight increase in sodium (Na⁺) concentration also remained within permissible levels, enhancing the water's suitability for drinking and other uses. Based on these results, the optimized NaOH dosages are the optimal solution for water hardness treatment, achieving a balance between reducing hardness and ensuring water quality in compliance with local standards.

Comparing clinical and biochemical characteristics of febrile seizures in children with and without COVID-19: a retrospective study

BackgroundTransmission of COVID-19 is now normalized. There is an association between it and increased incidence of febrile seizures in children. Exploring whether COVID-19 has a specific effect on the clinical and biochemical features of febrile seizures is critical for the development of clinical treatment and prevention strategies. This study is to compare the differences in clinical features, hematological features, and cerebrospinal fluid characteristics between COVID-19 and non-COVID-19 children with febrile seizures and to provide a new perspective for further exploring the impact of COVID-19 on the nervous system of children.MethodsThis was a retrospective case–control study. The cases included children with COVID-19 and non-COVID-19 febrile seizures admitted to Xiamen Children’s Hospital from December 2022 to December 2023. The age, gender, length of hospital stay, peak body temperature, presence or absence of other viral infections, hematological characteristics, and cerebrospinal fluid characteristics were compared between children with COVID-19 febrile seizures and non-COVID-19 febrile seizures.ResultsA total of 50 COVID-19 children with febrile seizures and 192 non-COVID-19 children with febrile seizures were enrolled in this study. Multivariate analysis showed that age (OR = 0.715, P = 0.031), blood urea nitrogen (OR = 0.454, P = 0.029), platelet count (OR = 0.987, P = 0.009) and magnesium ion concentration (OR = 0.109, P < 0.001) were negatively correlated with COVID-19 febrile seizures. Albumin (OR = 1.840, P < 0.001) was positively correlated. The concentration of potassium ion in cerebrospinal fluid (OR = 0.334, P = 0.012) was negatively correlated with COVID-19 febrile seizures, and the concentration of sodium ion (OR = 4.383, P = 0.022) was positively correlated with COVID-19 febrile seizures.ConclusionThere were differences in age, blood urea nitrogen, platelet count, magnesium ion concentration, albumin, potassium ion concentration in cerebrospinal fluid, and sodium ion concentration in the cerebrospinal fluid between children with COVID-19 febrile seizures and non-COVID-19 febrile seizures. This study may provide valuable insights into the potential mechanisms of COVID-19 damage to the nervous system in children, and the long-term neurological prognosis of these children requires long-term follow-up.

Positive effects of magnesium supplementation in metabolic syndrome.

Recent data show that magnesium supplementation decreases systolic and diastolic blood pressure values depending on the blood pressure levels and improves metabolic parameters in cardiovascular disease. In this context, we conducted a prospective, randomized, double-blind study on serum and ionized magnesium, systolic and diastolic blood pressure values, interleukin-6, vitamin D, and metabolic profile in 27 patients (13 male/14 female, age: 60.2±12.5 years) with metabolic syndrome. All patients received 400 mg of oral magnesium supplementation daily. Parameters were measured before and after 6 and 12 weeks of treatment. 27 patients served as controls without additional magnesium treatment (10 male/17 female, age: 64.6±13.2 years). There was no significant change in serum magnesium after 6 and 12 weeks of magnesium supplementation and in controls. Ionized magnesium significantly increased from 0.56±0.05 to up to 0.63±0.08 mmol/L (mean ± SD) (p < 0.01). The ionized Ca++/Mg++ ratio was significantly increased at baseline in about 32% of all patients; after 12 weeks of magnesium supplementation, the Ca++/Mg++ ratio decreased significantly from 2.32±0.22 to 2.04±0.24 at the end of the study (mean ± SD, p<0.05). In the magnesium-treated group, there was a significant decrease in systolic and diastolic blood pressure values after 12 weeks (systolic: 134.6±6.8 to 126.3±5.6 mmHg, diastolic: 84.1±3.9 to 79.4±1.6 mmHg) (mean ± SD) (p<0.01). Additional magnesium supplementation decreased interleukin-6 values significantly from 4.94±3.30 to 4.53±6.89 pg/mL after 6 weeks to 3.01±1.32 pg/mL after 12 weeks (mean±SD) (p<0.01). In the control group, interleukin-6 was 3.73±4.36 pg/mL before the start of the supplementation, 4.87±4.35 pg/mL after 6 weeks, and 4.41±3.15 pg/mL after 12 weeks (means ± SD) (n.s.). In patients receiving magnesium supplementation, vitamin D levels significantly improved from 17.93±8.96 to 24.41±10.20 ng/mL (mean±SD) (p < 0.05). HbA1c and serum cholesterol values improved under magnesium therapy, but the improvement did not reach significance. For statistical analysis, Mann-Whitney-U-Test was used. Using supplementation with 400 mg magnesium for 12 weeks in patients with metabolic syndrome, ionized magnesium concentrations significantly increased, while serum magnesium did not change significantly. Both systolic and diastolic blood pressure values decreased significantly in the magnesium-treated group. Magnesium supplementation also significantly decreased interleukin-6 levels and increased vitamin D in patients. HbA1c and cholesterol levels improved with magnesium supplementation, but the improvement did not reach significance. The anti-inflammatory effects of magnesium as well as anti-arteriosclerotic effects of magnesium therapy are beneficial for patients with metabolic syndrome at high risk of cardiovascular disease and mortality.

Hardness properties of calcium and magnesium ions in drinking water

The drinking water parameter - water hardness - is defined as the sum of calcium and magnesium ion concentrations. In this study, their precipitation during boiling was investigated, using water of different hardnesses, calcium to magnesium ratios, natural tap and bottled waters. During boiling, pH value, conductivity, and calcium and magnesium concentrations were measured. Further, the morphology and composition of precipitates were analyzed. Boiling tests with durations of 30 min showed only a decrease of calcium concentration by precipitation. Longer boiling of water with a high proportion of magnesium showed decreasing magnesium concentrations once the calcium precipitation was completed. Calcium carbonate precipitated as calcite and aragonite crystals with aragonite needles occurring in the presence of high magnesium concentrations. Magnesium hydroxide formed during precipitation was identified as hydromagnesite crystals with different crystallization morphologies. Unexpectedly, for a water with low and equimolar concentrations of calcium and magnesium only magnesium precipitated at the relatively low pH 8.7. In summary, calcium ions in drinking water are evaluated as being of considerably higher relevance for the hardness properties than the magnesium ions. However, the precipitation of both minerals depends on their concentrations and ratio as well as on the pH value and the water matrix.

Regulation of magnesium ion transport in Escherichia coli: insights into the role of the 5’ upstream region in corA expression

ABSTRACT In Escherichia coli, transport of magnesium ions across the cellular membrane relies on MgtA and CorA transporters. While the expression of mgtA is controlled by the two-component system PhoQ/PhoP and 5’ upstream region elements, corA expression is considered to be constitutive and not to depend on cellular factors. Importantly, the 5’ upstream region of corA is predicted to fold into structures highly similar to the magnesium-sensing mgtA 5‘ upstream region. Here using biochemical and genetic assays, we show that the intracellular concentration of magnesium ions affects corA expression. Similarly to mgtA, we find that the effect of magnesium ions on corA expression is mediated by the 5’ upstream region. We demonstrate that the RNA structure is important for regulation and that the Rho transcription factor is involved in the modulation of transcription termination. Consistent with previous studies, we find that translation of corL, a short ORF located within the 5’ upstream region, is important for corA regulation. Our data indicate that the efficiency of corL translation is inversely proportional to corA expression, similar to what has been described for mgtA and corA in Salmonella enterica. Using a novel assay to control the import of magnesium ions, we show that while the expression of mgtA is regulated by both extra- and intracellular magnesium ions, corA is regulated by variations in intracellular magnesium ions. Our results support a model in which the expression of corA is regulated by the 5’ upstream region that senses variations of intracellular magnesium ions.

Effects of amino alcohols-intercalated MgAl-LDH nanocomposites on the properties of sulfoaluminate cement-based materials

Sulfoaluminate cement-based materials (SCBMs) have low mechanical properties in the early stages when they are used in grouting reinforcement engineering. The mechanical properties of cement-based materials can be improved by nanotechnology. Hydrotalcite is a layered anionic clay with adjustable interlayer anions and nanometer spacing. To date, the effect of amino alcohols (ethanolamine (MEA), diethanolamine (DEA), and triethanolamine (TEA))-intercalated MgAl-layered double hydroxides (LDH) nanocomposites (denoted as MgAl-LDH-TEA, MgAl-LDH-DEA, and MgAl-LDH-MEA) on the properties of SCBMs have not been studied. Herein, we demonstrate that intercalated MgAl-LDH exhibit a decrease in crystallinity, an increase in particle size, and improved early mechanical properties compared to unmodified LDHs. MgAl-LDH modified by TEA, DEA, and MEA all have a nucleation effect and provide nucleation sites for ettringite. Simultaneously, the intercalated hydrotalcite can release higher concentrations of magnesium ions into the slurry, forming a magnesium-containing ettringite phase and accelerating the hydration of SCBMs. Modified MgAl-LDH can also release amino alcohols, affecting the hydration process of the paste. The modified LDHs affect the hydration and compressive strength of SCBMs owing to the combined action of the nucleation of LDHs and the release of magnesium ions and amino alcohols compounds.

Rapid method for screening of both calcium and magnesium chelation with comparison of 21 known metal chelators

Chelation is the rational treatment modality in metal overload conditions, but chelators are often non-selective and can, hence, cause an imbalance in the homeostasis of physiological metals including calcium and magnesium. The aim of this study was to develop an affordable, rapid but sensitive and precise method for determining the degree of chelation of calcium and magnesium ions and to employ this method for comparison on a panel of known metal chelators. Spectrophotometric method using o-cresolphthalein complexone (o-CC) was developed and its biological relevance was confirmed in human platelets by impedance aggregometry. The lowest detectable concentration of calcium and magnesium ions by o-CC was 2.5 μM and 2 μM, respectively. The indicator was stable for at least 110 days. Four and seven out of twenty-one chelators strongly chelated calcium and magnesium ions, respectively. Importantly, the chelation effect of clinically used chelators was not negligible. Structure–activity relationships for eight quinolin-8-ols showed improvements in chelation particularly in the cases of dihalogen substitution, and a negative linear relationship between pKa and magnesium chelation was observed. Calcium chelation led to inhibition of platelet aggregation in concentrations corresponding to the complex formation. A novel method for screening of efficacy and safety of calcium and magnesium ion chelation was developed and validated.Graphical abstract

Calcium-activated chloride channels. Role of potassium ions

Using the patch-clamp method in the whole-cell configuration, it was shownthat external potassium ions play an important role in the regulation of calcium-activated chloride currents. A clear dependence of the amplitude of chloride currents on changes in the concentration of external potassium is shown. Changes in concentration of sodium, magnesium and calcium ions from membrane outside have no so significant effect, like outside potassium ions. The effect of potassium on the amplitudes of chloride currents is significantly greater than the effect it has on other cell ionic currents — sodium, potassium, cation. There is reason to believe that a change in the amplitudes of chloride currents contributes to the pathophysiological processes characteristic of hypokalemia and hyperkalemia.

Sustainable agriculture through qanat systems in Karabakh: Water and soil characteristics in the context of climate change

This study investigates the water quality and soil characteristics associated with qanat systems in the Cebrail district of the Karabakh region, Azerbaijan. Qanat systems, traditional underground channels designed for water transport, play a crucial role in providing reliable water sources for drinking and irrigation. Water and soil samples were collected from seven qanat systems and analyzed for various physicochemical properties. Water quality parameters included pH, electrical conductivity, hardness, mineralization, and concentrations of calcium, magnesium, sodium, and other ions. Soil analyses focused on pH, electrical conductivity, organic matter content, salinization degree, and the presence of key ions like sulfate and nitrate. The results indicated that qanat water is generally of high quality, with pH levels suitable for both drinking and irrigation. However, some qanat systems exhibited high electrical conductivity and mineralization levels, suggesting potential salinity issues for sensitive crops. Soil samples showed favorable conditions for agriculture, with good pH levels, low salinity, and high organic matter content. The analysis revealed a significant interaction between water quality and soil characteristics, emphasizing the importance of integrated management practices. In the context of climate change, the sustainability of qanat systems is critical. Recommendations include regular monitoring of water and soil quality, soil amendments to mitigate salinity, efficient irrigation techniques, and the use of climate-resilient infrastructure. This study underscores the importance of qanat systems in arid and semi-arid regions and provides practical recommendations for sustainable land and water resource management, enhancing the socio-economic well-being of local communities.

The Neuroprotective and Anxiolytic Effects of Magnesium Sulfate on Retinal Dopaminergic Neurons in 6-OHDA-Induced Parkinsonian Rats: A Pilot Study.

This study investigates the protective effects of magnesium sulfate on dopamine neurons in the retinas of rats with 6-hydroxydopamine (6-OHDA)-induced Parkinson's disease (PD). Rapidly progressing cognitive decline often precedes or coincides with the motor symptoms associated with PD. PD patients also frequently exhibit visual function abnormalities. However, the specific mechanisms underlying visual dysfunction in PD patients are not yet fully understood. Therefore, this study aims to investigate whether magnesium homeostasis affects dopaminergic neurons in the retina of PD rats. Thirty-six rats were divided into four groups: (1) control, (2) control with magnesium sulfate (control/MgSO4), (3) Parkinson's disease (PD), and (4) Parkinson's disease with magnesium sulfate (PD/MgSO4). The apomorphine-induced (APO) rotation test assessed the success of the PD models. The open-field experiment measured the rats' anxiety levels. Tyrosine hydroxylase (TH) and glutamate levels, indicators of dopamine neuron survival, were detected using immunofluorescence staining. Protein levels of solute carrier family 41 A1 (SCL41A1), magnesium transporter 1 (MagT1), and cyclin M2 (CNNM2) in the retina were analyzed using Western blot. Results showed that, compared to the PD group, rats in the PD/MgSO4 group had improved psychological states and motor performance at two and four weeks post-surgery. The PD/MgSO4 group also exhibited significantly higher TH fluorescence intensity in the left retinas and lower glutamate fluorescence intensity than the PD group. Additional experiments indicated that the protein levels of SLC41A1, MagT1, and CNNM2 were generally higher in the retinas of the PD/MgSO4 group, along with an increase in retinal magnesium ion content. This suggests that magnesium sulfate may reduce glutamate levels and protect dopamine neurons in the retina. Thus, magnesium sulfate might have therapeutic potential for visual functional impairments in PD patients.

Impact of Strontium, Magnesium, and Zinc Ions on the In Vitro Osteogenesis of Maxillary Sinus Membrane Stem Cells.

Human Maxillary Sinus Membrane Stem Cells (hMSMSCs) contribute significantly to bone formation following maxillary sinus floor augmentation (MSFA). The biological behavior of mesenchymal stem cells is notably influenced by varying concentrations of magnesium (Mg2+), strontium (Sr2+), and zinc (Zn2+) ions; however, their specific effects on hMSMSCs have not been comprehensively studied. We isolated hMSMSCs and identified their mesenchymal stem cell characteristics by flow cytometry and multilineage differentiation experiments. Subsequently, the hMSMSCs were cultured in media containing different concentrations of these metal ions. The proliferation and viability of hMSMSCs were assessed using CCK-8 and Calcein AM/PI staining. After osteogenic induction, cells were evaluated for alkaline phosphatase (ALP) activity, ALP staining, and Alizarin Red staining. Additionally, qRT-PCR was used to detect differences in osteogenic gene expression, and immunofluorescence staining was used to observe variations in OCN protein levels. The results indicated that 1 mM Mg2+, 0.01 mM Sr2+, and 0.001 mM Zn2+ significantly improved the proliferation and activity of hMSMSCs. These concentrations also notably enhanced ALP secretion, increased bone-related gene expression, and augmented osteocalcin expression and formation of extracellular calcium nodules, thereby improving osteogenic differentiation. However, higher concentrations of Mg2+, Sr2+, and Zn2+ decreased cell viability and osteogenic differentiation. Mg2+, Sr2+, and Zn2+ promote osteogenic differentiation and proliferation of hMSMSCs in a concentration-dependent manner, indicating that the type and concentration of ions in the extracellular environment can significantly alter hMSMSCs behavior, which is a crucial consideration for material design in maxillary sinus elevation applications.

CRISPR-Cas12a exhibits metal-dependent specificity switching.

Cas12a is the immune effector of type V-A CRISPR-Cas systems and has been co-opted for genome editing and other biotechnology tools. The specificity of Cas12a has been the subject of extensive investigation both in vitro and in genome editing experiments. However, in vitro studies have often been performed at high magnesium ion concentrations that are inconsistent with the free Mg2+ concentrations that would be present in cells. By profiling the specificity of Cas12a orthologs at a range of Mg2+ concentrations, we find that Cas12a switches its specificity depending on metal ion concentration. Lowering Mg2+ concentration decreases cleavage defects caused by seed mismatches, while increasing the defects caused by PAM-distal mismatches. We show that Cas12a can bind seed mutant targets more rapidly at low Mg2+ concentrations, resulting in faster cleavage. In contrast, PAM-distal mismatches cause substantial defects in cleavage following formation of the Cas12a-target complex at low Mg2+ concentrations. We observe differences in Cas12a specificity switching between three orthologs that results in variations in the routes of phage escape from Cas12a-mediated immunity. Overall, our results reveal the importance of physiological metal ion conditions on the specificity of Cas effectors that are used in different cellular environments.

STUDY OF THE EFFECT OF THE SCUTELLARIA BAICALENSIS GEORGI EXTRACT ON THE CONTENT OF MINERALS IN THE BLOOD SERUM OF RATS UNDER "SOCIAL" STRESS

Background. The study of the influence of "social" stress on biogenic elements involved in mineral metabolism and playing an important role in the life of the human body, the search for agents that have a leveling effect on their content, is an urgent problem of modern pharmacological science. Purpose. To study changes in the content of biogenic elements in the course of mineral metabolism in the blood serum of rats under conditions of "social" stress and under the influence of Scutellaria baicalensis Georgi extract. Materials and methods. Experimental studies were carried out on 96 mature male non-linear rats weighing 295±12.17 g at the age of 7-9 months. The first stage of the experiment involved the study of mineral metabolism in the norm. Individuals of the first group of animals were injected with water; the second was an extract of Scutellaria baicalensis Georgi (100 mg/kg/day); the third – medicinal product (MP) "Mebicar®" (25 mg/kg/day) and the fourth - MP "Phezam®" (45 mg/kg/day). At the second stage of the experiment, “social” stress was reproduced on animals, in groups of which aggressors and victims were identified after the formation of inter-male confrontations for 21 days. These individuals received the solutions used earlier (stage I) for two weeks. The content of sodium and potassium ions in plasma was determined by flame photometry; the level of total calcium - by the photometric method; the concentration of phosphorus and magnesium - by biochemical analysis; the amount of chloride ions - by mercurimetric titration. Statistical data processing was performed using the Statistica 10 package. Results. It was found that the introduction of the extract of Scutellaria baicalensis Georgi, MP "Mebikar®" and "Phezam®" normally does not affect the content of minerals in plasma. It has been shown that modeling of "social" stress in control animals with both dominant and submissive types of character contributes to a significant decrease in the concentration of calcium, phosphorus and magnesium ions compared with individuals of the intact group. A statistically significant difference in the content of chloride ions was proved only in the case of a group of victims. Comparable values of mineral metabolism parameters of the group that received the extract under stress conditions were obtained with the first stage of the experiment in the norm of both intact and experimental animals, as a result of which the leveling effect of the extract of Scutellaria baicalensis Georgi was substantiated. Statistically significant differences in the concentration of magnesium ions in the group of victims exposed to "social" stress under the influence of the type of behavior were determined. Conclusion. The analysis of the data obtained forms an idea of the mineral composition of blood plasma in normal conditions and under conditions of "social" stress. The results of the study characterize the extract of Scutellaria baicalensis Georgi as a remedy that has a leveling effect in conditions of anxiety-depressive state caused by inter-male confrontations.

Evaluation of mechanical properties and potential environmental applications of biomimetic mineralized composites

With the growing emphasis on environmental protection, there has been extensive research on new green cementitious materials suitable for different conditions. This study focuses on the influence of key environmental factors on proposed biomimetic mineralized composites (BMC) using polyacrylic acid (PAA) as a modifier, based on the biomimetic chemistry induced carbonate precipitation (BCICP) method. The environmental factors examined include the cementing matrices type, the magnesium ions concentration, and the cementing solution pH. The samples treated under various conditions were evaluated for their unconfined compressive strength (UCS) and calcium carbonate content, and their microstructure was characterized using scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results demonstrate that the BMC treatment could achieve high-strength cementation for both Toyoura sand and Fujian quartz sand, with a more pronounced enhancement observed for Toyoura sand. Magnesium ions reduce the cementation effect, and they cannot fully replace calcium ions in participating in the cementation process. Moreover, the cementing solution pH significantly influences the cementation effect, with the best acid-base condition for PAA to modify BMC sand samples found at a pH of 11.5. Overall, the BMC exhibits high performance under various environmental conditions. These findings could provide valuable insights into the influence of environmental factors and the potential applications of BMC in diverse environments.

Understanding the Thermodynamics of Magnesium Binding to RNA Structural Motifs.

Divalent magnesium ions (Mg2+) serve a vital role in defining the structural and catalytic chemistry of a wide array of RNA molecules. The body of structural information on RNA motifs continues to expand and, in turn, the functional importance of Mg2+ is revealed. A combination of prior work on the structural characterization of magnesium binding ligands with inner- and outer-sphere coordination modes, with recorded experimental binding energies for inner- and outer-sphere contacts, demonstrates the relative affinity and thermodynamic hierarchy for these sites. In turn, these can be correlated with cellular concentrations of free available magnesium ions, allowing the prioritization of populating important functional sites and a correlation with physiological function. This paper summarizes some of the key results of that analysis and provides predictive rules for the affinity and role of newly identified Mg binding sites on complex RNA structures. The influence of crystal packing on magnesium binding to RNA motifs, relative to their solution form, is addressed and caveats made.

Research on Carbon Dioxide-Assisted Electrocoagulation Technology for Treatment of Divalent Cations in Water

In the external drainage water of Xinjiang Karamay Petrochemical Company, the calcium and magnesium ion contents are as high as 630 mg/L and 1170 mg/L, respectively. These ions are subsequently scaled at large quantities in water treatment equipment, which greatly reduces the efficiency of the process. This study used a coupled chemical precipitation (CP) and electrocoagulation (EC) method to deal with external drainage water. The results show that the removal rates of calcium and magnesium were 94.71% and 96.33%, respectively, when the pH was adjusted with sodium silicate and EC was introduced after saturating the water samples with CO2. In this study, a quadratic polynomial equation was developed for predicting the removal of calcium and magnesium ions using this coupled technique under three factors of current density (CD) (15, 20 and 25 mA/cm2), reaction time (RT) (30, 40 and 50 min) and pH (10.0, 10.5 and 11.0). It was found that these three variables have a significant effect on the removal of both the abovementioned ions. The response surface method based on a Box–Behnken design showed that the average removal rates of calcium and magnesium ions could be 96.57% and 98.66% at a CD of 22 mA/cm2, RT of 46 min and pH of 11. This study confirmed the presence of calcium carbonate in the solid product through XRD and SEM analysis. The results indicate that this study is promising, and the developed technique can also be used to remove the high concentrations of calcium and magnesium ions from different wastewaters.

The impact of seawater ions on urea decomposition and calcium carbonate precipitation in the MICP process

As an environmentally friendly biotechnology, the microbial induced calcium carbonate precipitation (MICP) provides a new approach to repair concrete cracks. Most existing studies focused on finding a suitable environment for bacteria to induce as much calcium carbonate as possible, but the effect of actual concrete service environment on the repair of concrete cracks was usually ignored. This work compared the repair quality of cracked specimens via MICP with the original Sporosarcina (Sp.) pasteurii strain and salt-tolerant Sp. pasteurii strain in the deionized water and simulated seawater. Then the adverse effects of seawater ions on the MICP process was investigated. The results showed that the permeability coefficient of repaired specimens was 175.7 % higher, and the bond strength between the calcium carbonate and concrete surface was lower in the simulated seawater as compared with the deionized water environment. The high concentration of sodium, chloride, magnesium, and sulfate ions in the seawater led to the decrease of the urea decomposition rate and calcium carbonate yield rate, which further induced the decreased super-saturation of calcium carbonate and the conversion of the calcium carbonate crystal form from calcite to vaterite. Besides, the salt-tolerant strain with a high salt adaptability showed a higher repair ability in the simulated seawater as compared with the original strain.

Effects of hydrotalcites with different laminate element composition on the properties of sulfoaluminate cement-based materials

Sulfoaluminate cement-based materials (SCBMs) are widely used for grout reinforcement. It is common to use a large water-to-binder ratio in the construction of sulfoaluminate cement-based materials (SAGMs) to obtain good workability and permeability, which results in poor early strength. Nanotechnology has been increasingly employed to enhance the mechanical properties of cementitious materials. Nano Zn-Mg-Al hydrotalcite-like (LDHs) and nano Mg-Al LDHs increased the early compressive strength, while nano Zn-Al LDHs had the opposite effect. However, the reason for this observation remains unclear. In this study, the influence of LDHs structures with different laminar element compositions on the hydration and hardening processes of SCBMs was analysed. The results showed that nano-ZnAl-LDHs, ZnAl-LDHs, and MgAl-LDHs could provide nucleation sites for ettringites. The three hydrotalcite-like materials slowly released different concentrations of zinc and/or magnesium ions and carbonate ions in the cement paste. Zinc ions entered the hydration product of ettringite and aluminum gel and promoted the transformation of amorphous aluminum gel to bayerite, which inhibited the hydration reaction of SCBMs. Magnesium ions could also enter the ettringite, and carbonate ions promoted the formation of calcium carbonate, which facilitated the hydration reaction of SCBMs. The nucleation effect and the release of zinc and/or magnesium ions and carbonate ions acted synergically to influence the hydration rate, pore size distribution, and compressive strength of SCBMs.

Excess-sulphate phosphogypsum slag cement blended with magnesium ion: Part Ⅱ-the long-term microstructure characterisation and phase evolution

Magnesium ions, as the most destructive ions in seawater, significantly affect the durability of cement-based structure. Excess-sulphate phosphogypsum slag cement (ESPSC) with great resistance to chemical attack, exhibits a potential application in marine engineering. As a continuation of previous research, the long-term performance development and microstructure evolution of ESPSC mixed with water including various magnesium ion concentrations (0–0.5 mol/L), are investigated in this study. The results indicate that incorporating magnesium ions within 0.2 mol/L has optimised the later compressive strength, as well as the pore structure. Furthermore, the components and nanostructure of C-(A)-S-H gels change due to the charge balance and cation compensation caused by magnesium ions. The phase evolution of AlⅣ to AlⅥ and an increase in hydration degree have been detected, where the aluminium phase tends to exist stable as ettringite. The M-S-H gel production is detected in samples incorporating 0.5 mol/L magnesium ions at early stage, which is detrimental to the gelatinous structure and strength development of ESPSC. From the perspectives of technological feasibility and environmental requirements, ESPSC production is an effective method for CO2 emission reduction and phosphogypsum utilisation with scalable potential. Introducing magnesium ions through seawater is also regarded as a modification to enhance the mechanical performance of ESPSC.

Membrane pre-concentration as an efficient strategy to enhance the enrichment of rare earth by MgO precipitation

Taking advantage of the environmentally-friendly properties of a magnesium salt leaching agent, magnesium oxide (MgO) was used as a precipitant to enrich rare earth (RE) from leaching liquor in the magnesium salt system. This approach not only tackles the issue of ammonia–nitrogen pollution but also enables efficient magnesium recycling. However, due to the high concentration of magnesium ions and the low concentration of RE ions in the leaching solution, the precipitation kinetics of RE concentrates are sluggish, leading to low RE purity in the resulting precipitated product. In this work, we proposed a novel strategy that combines complexation-ultrafiltration (UF) pre-concentration with subsequent MgO precipitation to enhance the hydrolysis of MgO, promoting the precipitation of RE. We further improved the RE enrichment efficiency by optimizing membrane type, complexing agent selection, concentration levels, precipitation temperature, and MgO dosage. Under the conditions of concentrating the leaching solution using optimal UF membrane and employing glyphosate as the complexing agent, the RE ions concentration increased from 101 to 3940 mg/L, and we successfully separated magnesium ions with a separation factor of 36.4. A comparison between direct MgO precipitation and the pre-concentration approach revealed an 80 % reduction in precipitation time and an 80 % decrease in MgO usage with pre-concentration. Furthermore, this combined process led to an 8 % increase in RE recovery and a 2.8-fold enhancement in RE purity, and similar results were obtained when using actual mine leaching solutions. Additionally, the glyphosate present in the UF permeate and the precipitated mother liquor can be efficiently reclaimed through resin adsorption. This proposed process holds significant potential for engineering applications aimed at enriching RE.