Bestimmung der Oberflächenzusammensetzung von Calcit in Mg2+-haltigen Ca-45-markierten Lösungen

The Mg²⁺ ion content in the surface layer of calcite in relation to the Mg²⁺ ion content in Ca-45 labelled solution was determined by Ca²⁺-Mg²⁺ ion exchange process. It was found that the increase of the molar ratio Mg/Ca in the surface due to increase of Mg²⁺ concentration in solution is decreasing significantly when approaching ratios of Mg/Ca ～ 1 and ～ 3. The experimental exchange isotherm can be used to relate the Mg/Ca molar ratio of solutions to that of the surface layers of calcite.     

Effect of agar hydrogel and magnesium ions on the biomimetic mineralization of calcium carbonate

Here, agar hydrogel was selected as diffusion medium and template to control the biomimetic mineralization of calcium carbonate (CaCO₃). Due to three dimensional network structures and abundant functional groups (such as, hydroxyl groups), Ca²⁺ ions were uniformly distributed in the network and electrostatically attracted. The diffusion speed and range of CO₃^2? ions were mediated by the concentration of hydrogel medium. Under the synergistic effect of Mg²⁺ ions, the crystal CaCO₃ was induced by gas phase diffusion method in the hydrogel system. The results showed that the concentrations of Mg²⁺ ions and agar hydrogel had no obvious effect on the calcite phase of CaCO₃, but the morphologies and sizes changed with concentrations of medium and Mg²⁺ ions. Attribute to template effect, the crystallization behavior and growth rate of CaCO₃ crystals were regulated. Since Mg²⁺ ions were easily adsorbed on the surfaces of unit cell, the unique structure of CaCO₃ was precisely controlled. This study provides a useful reference and inspiration for the understandings of the contributions of ion supply rate in bio-mineralization and hydrogel medium in biomimetic mineralization.     

Influence of ionic composition in aqueous solution on wettability of rock surface-experiment and economics evaluation

In this study, the influence of different ionic composition in aqueous solution on the minerals surface wettability was studied. The differences effect of monovalent ion and divalent ions onto the wettability alteration were studied. The anions were Cl^- and SO₄^2-. The SO₄^2- could make the minerals surface more hydrophilic. Besides, the influence of NaCl, MgCl₂, CaCl₂, Na₂SO₄, K₂SO₄ and MgSO₄ on the mineral wettability alteration were studied. The results indicated that divalent ions showed significant impact on the minerals wettability alteration, compared with monovalent ion. The reasons were due to the fact that divalent ions showed higher ions adsorption than monovalent ion, and divalent ions have higher effect on compressing the electric double layer. The static contact angle and dynamic contact angle were measured. Different heavy oils were studied, including heavy oil with 100 ppm, heavy oil, heavy oil without resins, heavy oil without asphaltenes. The results showed that the asphaltenes would make it difficult for the heavy oils to liberate from minerals, thus decreasing the oil drops contact angle. Then the resins would decrease the heavy oil contact angles. CaCl₂/MgCl₂ and K₂SO₄ have synergistic effect on the change of the minerals surface wettability. Atomic force microscope (AFM) measurement indicated that the ions would effectively decrease the interaction force on the surface of heavy oil-minerals, which was beneficial to the heavy oil liberation. The roughness measurement indicated that the different ions would effectively increase the minerals surface wettability.     

Thermogravimetric analysis of selected group (II) carbonateminerals — Implication for the geosequestration of greenhouse gases

The precursors of carbonate minerals have the potential to react with greenhouse gases to form many common carbonate minerals. The carbonate bearing minerals, magnesite, calcite, strontianite and witherite, were synthesised and analysed using a combination of thermogravimetry and evolved gas mass spectrometry. The DTG curves show that as both the mass and the size of the metal cationic radii increase, the inherent thermal stability of the carbonate also increases dramatically. It is proposed that this inherent effect is a size stabilisation relationship between that of the carbonate and the metal cation. As the cationic radius increases in size, the radius approaches and in the case of Sr²⁺ and Ba²⁺ exceeds that of the overall size of the carbonate anion. The thermal stability of these minerals has implications for the geosequestration of greenhouse gases. The carbonates with the larger cations show significantly greater stability.     

Wettability alteration of carbonate rocks from strongly liquid-wetting to strongly gas-wetting by fluorine-doped silica coated by fluorosilane

Wettability alteration is an important mechanism to increase recovery from oil and gas reservoirs. In this study, effect of fluorine-doped silica coated by fluorosilane nanofluid on wettability alteration of carbonate rock was investigated. The nanoparticle synthesized by sol-gel method was characterized using XRD, FTIR, SEM, and DLS. Adsorption of nanoparticle on rock was characterized by FESEM, and composition of rock after treatment was determined by EDXA. Effect of nanofluid on wettability was investigated by measuring static, advancing, and receding contact angle and surface free energy, imbibition of water, crude oil, and condensate of untreated and treated carbonate rock. Also, stability of contact angle and thermal stability of nanofluid were studied. ?Results show that contact angles for water, condensate, and crude oil were altered from 37.95°, 0°, ?and 0° to 146.47°, 145.59°, and 138.24°. In addition, water, condensate, and oil imbibition ?decreased more than 87, 88, and 80%, indicating that wettability was altered from strongly oil wet, ?condensate wet, and water wet to strongly gas wet. The ultraoleophobic and ultrahydrophobic stability were >48 hours and 120 minutes. Surface free energy of treated rock for water, crude oil, and condensate was ?2.24, 1.17, and 1.47mN/m. Thermal stability of nanofluids and adsorbed nanoparticle was up to 150°C.     

Cation exchange, interlayer spacing, and thermal analysis of Na/Ca-montmorillonite modified with alkaline and alkaline earth metal ions

Na-montmorillonites were exchanged with Li⁺, K⁺, Rb⁺, Cs⁺, Mg²⁺, Ca²⁺, Sr²⁺, and Ba²⁺, while Ca-montmorillonites were treated with alkaline and alkaline earth ions except for Ra²⁺ and Ca²⁺. Montmorillonites with interlayer cations Li⁺ or Na⁺ have remarkable swelling capacity and keep excellent stability. It is shown that metal ions represent different exchange ability as follows: Cs⁺?>?Rb⁺?>?K⁺?>?Na⁺?>?Li⁺ and Ba²⁺?>?Sr²⁺?>?Ca²⁺?>?Mg²⁺. The cation exchange capacity with single ion exchange capacity illustrates that Mg²⁺ and Ca²⁺ do not only take part in cation exchange but also produce physical adsorption on the montmorillonite. Although interlayer spacing d ₀₀₁ depends on both radius and hydration radius of interlayer cations, the latter one plays a decisive role in changing d ₀₀₁ value. Three stages of temperature intervals of dehydration are observed from the TG/DSC curves: the release of surface water adsorbed (36?C84?°C), the dehydration of interlayer water and the chemical-adsorption water (47?C189?°C) and dehydration of bound water of interlayer metal cation (108?C268?°C). Data show that the quantity and hydration energy of ions adsorbed on montmorillonite influence the water content in montmorillonite. Mg²⁺-modified Na-montmorillonite which absorbs the most quantity of ions with the highest hydration energy has the maximum water content up to 8.84%.     

Effect of Native Reservoir State and Oilfield Operations on Clay Mineral Surface Chemistry

An understanding of clay mineral surface chemistry is becoming critical as deeper levels of control of reservoir rock wettability via fluid–solid interactions are sought. Reservoir rock is composed of many minerals that contact the crude oil and control the wetting state of the rock. Clay minerals are one of the minerals present in reservoir rock, with a high surface area and cation exchange capacity. This is a first-of-its-kind study that presents zeta potential measurements and insights into the surface charge development process of clay minerals (chlorite, illite, kaolinite, and montmorillonite) in a native reservoir environment. Presented in this study as well is the effect of fluid salinity, composition, and oilfield operations on clay mineral surface charge development. Experimental results show that the surface charge of clay minerals is controlled by electrostatic and electrophilic interactions as well as the electrical double layer. Results from this study showed that clay minerals are negatively charged in formation brines as well as in deionized water, except in the case of chlorite, which is positively charged in formation water. In addition, a negative surface charge results from oilfield operations, except for operations at a high alkaline pH range of 10–13. Furthermore, a reduction in the concentrations of Na, Mg, Ca, and bicarbonate ions does not reverse the surface charge of the clay minerals; however, an increase in sulfate ion concentration does. Established in this study as well, is a good correlation between the zeta potential value of the clay minerals and contact angle, as an increase in fluid salinity results in a reduction of the negative charge magnitude and an increase in contact angle from 63 to 102 degree in the case of chlorite. Lastly, findings from this study provide vital information that would enhance the understanding of the role of clay minerals in the improvement of oil recovery.     

Über die Bildung von röntgenamorphem Eisen(III)-hydroxid durch Luftoxydation von Eisen(II)-hydroxid und Eisen(II)-carbonat

In the presence of certain foreign cations (Ca²⁺, Mg²⁺), amorphous iron(III) hydroxide may be obtained from Fe^II hydroxide or carbonate by air oxidation.     

Oberflächenzusammensetzung,Löslichkeit und Ionenaktivitätsprodukt von Calcit in fremdionenhaltigen Lösungen

Surface Composition, Solubility, and the Ion Activity Product of Calcite in Solutions with Auxiliary Ions Using the method of simultaneous ion and isotope exchange the chemical composition of the surface layer of calcite powder in equilibrium with solutions of varying Me/Ca molar ratios is determined (Me = Mg²⁺, Co²⁺, Ni²⁺, and Fe²⁺ ions). The ion exchange isotherms show a marked bend in the surface reactivity when a surface molar ration of ～1 and ～3 is reached. The solubility of calcite initially decreases on the addition of Co²⁺ or Ni²⁺ ions to the solution whereas it increases in the presence of Mg²⁺ or Fe²⁺ ions. The activity product of the pseudo compound, Ca_xMe_(1–x)CO₃, decreases in the Ni²⁺, Co²⁺ or Fe²⁺ exchange experiments, however, it increases considerably in those with Mg²⁺ ions.     

Some aspects of the surface chemistry of calcite and aragonite Part I: An electrokinetic study

Summary Zeta potential measurements made on calcite and aragonite in the presence of Cat²⁺ and Mg²⁺ have shown that both ions were specifically adsorbed as they increased the positive charge on the mineral's surfaces. Measurements made in the presence of sodium carbonate and sodium sulphate showed that charge reversal occurred at low electrolyte concentrations, suggesting that C03/2– and to a lesser extent S04/2– ions, are also adsorbed at the Stern Plane. All of the ions, in particular the Cat+ ions,. were adsorbed more strongly by aragonite than calcite. Except for glucose, all of the organic substances examined caused charge reversal, showing that they had been adsorbed by the two polymorphs. With the exception of agar, which caused bridging flocculation, the adsorbed organic additives stabilised the mineral suspensions by steric and double layer repulsions.

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Zusammenfassung Die bei Gegenwart von Ca²⁺ und Mg²⁺ an Kalzit und Aragonit unternommenen Zetapotentialmessungen haben gezeigt, daß die beiden Ionen spezifisch absorbiert werden, indem sie die positive Ladung auf den Oberflächen der Mineralien erhöhten. Die bei Gegenwart von Natriumcarbonat und Natriumsulfat unternommenen Messungen haben gezeigt, daß bei niedrigen Elektrolytkonzentrationen Ladungsumkehrung auftritt, was darauf hindeutet, daß CO2/3– Ionen und in geringerem Ausmaß S04/2– Ionen ebenfalls auf der Sternschen Fläche absorbiert werden. Alle Ionen, insbesondere die Ca²⁺ Ionen, wurden mehr durch Aragonit als durch Kalzit absorbiert. Mit Ausnahme von Glykose verursachen alle untersuchten organischen Substanzen die Ladungsumkehrung, was zeigt, daß sie durch die beiden Polymorphe absorbiert werden. Ausgenommen Agar-Agar, das Flocken verursacht, stabilisieren die absorbierten organischen Zusatzstoffe die Mineralsuspensionen durch sterische und Doppelschicht-Abstoßung.

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With 5 figures and 2 tables     

Synergistic effect of water layer and divalent metal ions in a model oil sand on bitumen liberation from solids surface

In this work, we offer a direct evidence to illustrate the synergistic effect of water layer and divalent metal ions in oil sands on bitumen liberation from solids surface. A model oil sand was constructed by coating bitumen on the glass surface with a water layer containing divalent metal ions inserted between them. The bitumen liberation behaviors were investigated by placing the model oil sands in various pH solutions. It was found that the water layer facilitated the bitumen liberation, while the presence of Ca²⁺ or Mg²⁺ in the water layer played a different role on the bitumen liberation depending on the solution pH. It was believed that the variation of the bitumen liberation was attributed to the changes of surface wettability arising from the adsorption of natural surfactants on the solids and bitumen surfaces. The preferential adsorption of Ca²⁺ or Mg²⁺ on the solids and bitumen surfaces acted as either a barrier to disturb the cationic surfactants adsorbing or a bridge to anchor the anionic surfactants. The findings in this work are important for understanding the bitumen liberation behaviors and give a guideline of how controlling the water chemistry when processing the oil sands by water-based bitumen extraction processes.     

Untersuchungen an Oxidischen Katalysatoren. XXX [1] Charakterisierung der Me2+ -Kationenlokalisierung in CaNaY-, MgNaY- und CaMgNaY-Zeolithen

Studies on Oxide Catalysts. XXX. Characterization of the Me²⁺ Localization in Zeolites CaNaY, MgNaY, and CaMgNaY Data for exchange of the cations Ca²⁺, Mg²⁺, as well as Ca²⁺ and Mg²⁺ into the zeolite NaY have been determined. From this it was concluded on the localization of Me²⁺ cations in hydrated samples. The adsorption of ammonia in the temperature region of 420 to 670 K, the determination of the heats of immersion in water and nitromethane and the Me²⁺ ? CO-interaction indicated by IR spectroscopy yielded informations on the localization of cations in dehydrated samples. The results show that cations Ca²⁺ more selectively than cations Mg²⁺ occupy positions in the small cages. In the case of the competitive cation exchange this fact causes a site directed distribution of cations in zeolite cages.     

High-Resolution Continuum Source Atomic Absorption Spectrometry with Microwave-Assisted Extraction for the Determination of Metals in Vegetable Sprouts

The goal of this study was to investigate the enrichment of garden cress (Lepidium sativum), mung beans (Vigna radiata), and soybeans (Glycine max) with minerals. Hydroponic nutrient solutions were enriched with Zn²⁺,Cr³⁺, Ca²⁺, Mg²⁺, and Se²⁺. Morphological assessment was based on monitoring changes that occurred as a function of the concentrations of elements in the medium. The growth of the plant, as a result of a stimulating or inhibitory effect of the identity and concentration of elements on the germination process, was characterized. Microbiological contamination was identified and catabolic profiles of two bacterial strains were performed. High-resolution continuum source atomic absorption spectrometry (HR-AAS) was used to determine Zn²⁺, Cr³⁺, Ca²⁺, Mg²⁺, and Se²⁺ in dried plant material after sample pretreatment using microwave-assisted extraction. The limits of detection were 0.010, 0.029, 0.013, 0.151, and 0.030 milligram per liter for Ca²⁺, Cr³⁺, Mg²⁺, Se²⁺, and Zn²⁺, respectively. Recoveries were higher than 98 percent and the relative standard deviation was less than 5 percent. The accuracy of the procedure was estimated by analyzing certified reference materials. The results showed that biofortification of garden cress by zinc holds the highest promise for the creation of designer foods. Garden cress was found to have the highest bioconcentration factor among the investigated plants; at 50 parts per million, plant growth was stimulated without contamination by microorganisms.     

Effect of ionic charge on energy contributions to the interaction of an ion with a polar molecule: ab initio calculations for M⋯H2O (M = Mg,Mg+, Mg2+, Ca,Ca+, Ca2+)

For M?H₂O (M = Mg, Mg⁺, Mg²⁺, Ca, Ca⁺, Ca²⁺) various energy contributions (first-order, induction and charge-transfer, dispersion) are compared. Near the minimum, stability due to the first-order energy decreases and that due to dispersion increases from M²⁺ to M⁰. For M²⁺, dispersion represents only 1–7% of the total energy; it may reach 25% with M⁺ and is largely responsible for stability of the neutral complex.     

Modification and characterization of polystyrene surfaces used for cell culture

Surfaces of polystyrene Petri dishes used for cell culture were chemically modified by 5% fuming sulfuric acid. The sulfonation was performed at room temperature for various times. Formation of polar groups takes place essentially on the surface of the polymer. Wettability and ionic character of the modified surfaces were determined by contact angle measurements and surface conductivity measurements, respectively. Radioactive calcium (⁴⁵Ca) adsorption at these surfaces was investigated by means of radiotracer techniques. The chemical composition (concentration of polar sites produced) of these modified polystyrene surfaces was thus determined. It was found that the wettability of these surfaces is directly related to the concentration of sulfonate groups. The cation-exchange capacity of treated surfaces with inorganic cations (Na⁺, Mg²⁺, Ca²⁺, and Al³⁺) were determined by the radiotracer technique.     

Significant enhancement of luminescence intensity of CaTiO3:Eu3+ red phosphor prepared by sol–gel method and co-doped with Bi3+ and Mg2+

In this study, red phosphors Ca_1?n Mg _n TiO₃:Eu³⁺,Bi³⁺ were prepared by the sol?Cgel method and the impact of single dopant, co-dopants and solid solutions on the photoluminescence of the samples has been also investigated. Our results show that the crystal structure of the host does not have distinct changes when doped with Eu³⁺, Bi³⁺ and/or Mg²⁺. The emission intensity at 615?nm of Eu³⁺ increased at the presence of Bi³⁺ ions owing to the energy transfer from Bi³⁺ ion to Eu³⁺ ion. Moreover, with the addition of Mg²⁺, the red emission of the phosphor was further enhanced due to the stronger absorption at 399 and 467?nm, which match well with the emission of near-UV (395?C400?nm) and blue-LED (450?C470?nm), respectively. Under the near-UV (399?nm) or blue light (467?nm) excitation, the fluorescence quantum yield of the optimal composition Ca_0.9Mg_0.1TiO₃:0.18Eu³⁺,0.018Bi³⁺ is 0.36 and 0.41, respectively, which possesses the higher photoluminescence intensity than CaMoO₄:0.2Bi³⁺,0.05Eu³⁺ and the commercially available Y₂O₂S:Eu³⁺ phosphors under near-UV excitation. Based on these results, we are currently considering the potential application of Ca_0.9Mg_0.1TiO₃:Eu³⁺,Bi³⁺ as a near-UV or blue-chip convertible red-emitting phosphor.     

The binding of Ca2+ and Mg2+ to human serium albumin: A calorimetric study

The binding of calcium and magnesium to human serum albumin has been studied in the pH region 2.5–8.0 by a calorimetric procedure. Both metal ions bind to the carboxylate groups of albumin. 36 and 44 carboxylate groups appear to be involved in the binding of Ca²⁺ and Mg²⁺, respectively. Based on previously reported results that twelve Ca²⁺ ions are the maximum which can bind to albumin, the results given here support previous X-ray crystallographic evidence that three carboxylate groups can be involved in the binding of a Ca²⁺ by a protein. The data also confirm that Ca²⁺ and Mg²⁺ binding is competitive. Binding of the cations to the carboxylate groups appears to involve the breaking of carboxylate-imidazole hydrogen bonds in the protein. Log K, ΔH and ΔS values obtained for the binding of metal ions to albumin in aqueous solution at 25°C are 2.72 ± 0.02, 0.0 ± 0.1 kcal/mole, and 12.4 ± 0.3 cal/mole K for Ca²⁺ and 1.12 ± 0.05, ?0.2 ± 0.1 kcal/mole, and 4.5 ± 0.3 cal/mole K for Mg²⁺, respectively.     

Evaluation of Metal Ions and Surfactants Effect on Cell Growth and Exopolysaccharide Production in Two-Stage Submerged Culture of Cordyceps militaris

During the two-stage submerged fermentation of medicinal mushroom Cordyceps militaris, it was found that K⁺, Ca²⁺, Mg²⁺, and Mn²⁺ were favorable to the mycelial growth. The EPS production reached the highest levels in the media containing Mg²⁺ and Mn²⁺. However, Ca²⁺ and K⁺ almost failed to increase significantly exopolysaccharides (EPS) production. Sodium dodecyl sulfate (SDS) significantly enhanced EPS production compared with that of without adding SDS when SDS was added on static culture stage of two-stage cultivation process. The presence of Tween 80 in the medium not only simulated mycelial growth but also increased EPS production. By response surface methods (RSM), EPS production reached its peak value of 3.28?g/L under optimal combination of 27.6?mM Mg²⁺, 11.1?mM Mn²⁺, and 0.05?mM SDS, which was 3.76-fold compared with that of without metal ion and surfactant. The results obtained were useful in better understanding the regulation for efficient production of EPS of C. militaris in the two-stage submerged culture.     

Comparison of Ca2+ and Mg2+ binding to calmodulin. An enthalpy,entropy, and gibbs free energy analysis

A consistent set of G _B , H _B , and S _B parameters have been determined from ion specific electrode, calorimetric, and spectrophotometric studies for the binding of Ca²⁺ and Mg²⁺ to bovine calmodulin at pH=7.0 and an ionic strength I of 0.113M. A non-linear least squares analysis of calcium specific ion electrode data yields, on a molar basis, four calcium dissociation constants: 10^–7 for the first site, 10^–5 for the fourth site, and two constants between these values. Both calorimetric experiments and an indicator method provide evidence that Mg²⁺ binds to calmodulin, probably at the same sites as Ca²⁺, but with affinities about 100 times smaller: 4×10^–5 for the first site and 2×10^–3 for the fourth. Calorimetric titrations on Ca²⁺ binding to calmodulin in three buffers are consistent with 0.46 protons released upon binding at all four sites and yield an average H _B per site of 5.6 and 7.9 kJ-mol^–1 for Ca²⁺ and Mg²⁺, respectively. The entropy of the system increases by 524 and 361 J-K^–1-mol^–1 when Ca²⁺ and Mg²⁺, respectively, bind to four sites on calmodulin, i.e., the selectivity of calmodulin for Ca²⁺ is primarily derived from entropy effects. Further analysis based on elimination of the entropy term for the metal ions demonstrates that calmodulin bound to Ca²⁺ has a larger entropy than the unbound calmodulin; the opposite is true for calmodulin bound to Mg²⁺. These analyses are consistent with the hypothesis that Ca²⁺ forms tight complexes at all sites on calmodulin and that release of waters of hydration upon binding is the source of the increase of entropy in the system.     

A thermodynamic study of the complexation reaction of beryllium(II), magnesium(II) and calcium(II) with 3-hydroxy-2-naphtoic acid

The thermodynamic stability constants and thermodynamic parameters for the complexation reaction of Be²⁺, Mg²⁺ and Ca²⁺ with 3-hydroxy-2-naphthoic acid have been determined pH metrically in a 70% v/v dioxane-water medium in the presence of potassium nitrate. The study showed the formation 1:1 and 1:2 complexes of Be²⁺, Mg²⁺ and 1:1 complex of Ca²⁺ with 3-hydroxy-2-naphthoic acid. The order of overall stability is Be²⁺>Mg²⁺>Ca²⁺.