Alkaline Earth Content Research Articles

Synthesis of aluminophosphate molecular sieves with AFI topology substituted by alkaline earth metal and their application to solid acid catalysis

Metalloaluminophosphate molecular sieves with AFI topology, in which a part of aluminum is substituted isomorphously to alkaline earth metals: Mg, Ca, Sr, and Ba (MAPO-5; M = Mg, Ca, Sr and Ba), were synthesized by hydrothermal synthesis (HTS) method and two types of dry–gel conversion (DGC) methods: vapor-phase transport (VPT) and steam-assisted conversion (SAC) methods, using triethylamine (Et 3N) as a structure-directing agent (SDA). Systematic studies were carried out by varying the synthesis parameters such as gel composition including content of alkaline earth metals and SDA, amount of external bulk water, and heating time. It has been observed that MO/Al 2O 3 ratio of starting gel plays an important role in the crystallization of the molecular sieves. The ratios from 0.025 to 0.10 gave pure MAPO-5 with AFI topology; however, MAPO-34 with CHA topology was observed as an impurity with further increase of the Mg content. The amount of Et 3N also played important role for the crystallization: Et 3N/Al 2O 3 ratios from 0.38 to 0.76 gave pure MgAPO-5 and CaAPO-5, whereas SrAPO-5 and BaAPO-5 were obtained as pure phase from 0.76 to 1.52. MAPO-5 molecular sieves were crystallized even in the absence of external bulk water. Period for crystallization was studied from 3 to 48 h; the highest intensities were observed between 12 and 18 h for all cases. The occluded SDA was removed by calcination at 550 °C. The molecular sieves were characterized by XRD, ICP, TG-DTA, SEM, FT-IR, N 2 and pyridine adsorption, and NH 3-TPD. Alkaline earth metals, at least a part of them, are isomorphously substituted in the framework of AFI topology judging from NH 3-TPD, unit cell parameters, and their FT-IR spectra of adsorbed pyridine. The substitution of alkaline earth metal with aluminum produced acidic sites in the molecular sieves: substitution of Al 3+ to Mg 2+ enhanced the appearance of strong acidity; however, only weak acidities appeared for CaAPO-5, SrAPO-5, and BaAPO-5 in small amount. The isopropylation of benzene and biphenyl was examined over MAPO-5 by VPT method to characterize their acidic properties. Their catalytic activity decreases in the order: MgAPO-5 ≫ CaAPO-5 ⩾ SrAPO-5 ⩾ BaAPO-5; ≫ APO-5; moderate to good selectivity for 4,4′-DIPB was observed in the level of 50–70% for all MAPO-5. These catalytic properties support strongly the incorporation of alkaline earth metals in the AFI framework.

Reciclagem química de zeólitas comerciais desativadas

Pyro and hydrometallurgical processes were applied to the treatment of spent commercial zeolites (a molecular sieve and a ZSM-5 sample). Both catalysts were employed in pilot plant units. They were kept in their original shape, they were not regenerated and were not subjected neither to mechanical stress nor to overheating zones during their time on-stream. Two recycling processes were tested: (i) direct solubilization of samples in mixtures of HF + H2O2 (60 oC, 1 h). Although silicon was solubilized, insoluble matter was found in both samples, particularly in the molecular sieve, due to its high amounts of alkaline and alkaline-earth metals; (ii) fusion with KHSO4 (5 h, 600 oC) with KHSO4/zeolite mass ratio 6:1. After fusion the solid was solubilized in water (100 oC), leaving silicon as SiO2 residue. In both processes, solubilized metals were isolated by conventional selective precipitation techniques. Analysis of final products by common analytical methods shows that metals present in the original catalysts were recovered with very high yields except when the molecular sieve was treated with HF + H2O2. This reactant mixture proved to be suitable for processing zeolites with a low alkaline and alkaline-earth metal content whereas fusion with KHSO4 appeared to be adequate for all types of zeolites.

Radiation induced capacitance in barium aluminoborate glasses

Impedance analysis (IA) was applied to study the effect of electrically charged radiation-induced point defects on the dielectric properties of barium aluminoborate glasses. Changes observed in the real component ε ′ of the dielectric constant after X-ray irradiation have been investigated by comparing the dipolar contributions from the induced electrical charges, with those already present in the glass before irradiation. In this paper the results of impedance spectroscopy are presented and analyzed for the glass systems (1− x)((1/7)Al 2O 3 · (6/7)B 2O 3) · xBaO(A x) and (1− x)((2/7)Al 2O 3 · (5/7)B 2O 3) · xBaO(B x), where x represents the molar fraction of the alkaline earth oxide in the sample for x=0.3(A x) and x=0.2, 0.3, and 0.4(B x). It is suggested that the most important contributions in the observed increase of ε ′ at room temperature are provided by the dipoles formed by a boron–oxygen hole center and a non-paramagnetic boron electron center (BEC 2−, BOHC +), those composed by a BOHC and a neighboring Fe 3+ impurity cation which has trapped an electron ([Fe 2+] −, BOHC +), and those composed by a BOHC and an alkaline earth electron center (AEEC −, BOHC +). For glasses of high alkaline earth content it was observed a decrease of ε ′ and a model is suggested for the mechanism of this behavior.

Distributions of alkali and alkaline earth metals in several agricultural plants

Several agricultural plants were collected from an experimental field and the concentrations of alkali and alkaline earth metals were determined in different plant components. The concentrations of Cs in older leaves of rice and cabbage plants were higher than those in younger ones. The K concentrations in rice leaf blades decreased with withering, and these were similar in cabbage leaves. The distribution pattern of K. concentrations in the plant components was similar to that of Rb, however that of Cs was different. The distributions of Ca, Ba and Sr concentrations in the rice leaf blades followed a relatively similar pattern, whereas that of Mg was different. The concentrations of alkaline earth metals in older leaves of a cabbage plant were higher than those in younger ones. The percentage distributions of Cs and Sr in non-edible plant components were 93 and 99 % in rice plants, and 77 and 91 % in cabbage leaves, respectively. These results showed that the non-edible plant components were important for understanding the transfer of the alkali and alkaline earth metals and radionuclides in the soil-plant system. These elements could serve as natural analogues to predict the distributions of 137 Cs and 90 Sr in different plant components.

Structural studies and electrical properties of recycled glasses from glass and incinerator wastes

The electrical behaviour of different glass compositions obtained from mixing waste glass deriving from a community glass recycling program and silicate waste from the incineration of municipal solid residues (from Reggio Emilia city) have been investigated as a function of temperature and frequency. The electrical and dielectric properties were related to structural studies performed on the same glassy materials. As the amount of incinerator wastes increases, on account of lower alkali and higher alkaline-earth content in the final glass composition, conductivity and dielectric losses decrease approaching the behaviour of type E glass fibres, so envisaging a possible use of waste-containing glasses in the production of high voltage insulators.

Variations in K +–Na + ion exchange depth in commercial and experimental float glass compositions

We report the results of ion-exchange experiments conducted on 17 commercial soda–lime–silicate (SLS) float glass and 8 experimental SLS glass compositions. A significant variation in the depth of K + penetration with relatively small changes in composition was observed. The data were fit to a multiple regression model in which the major oxides are the independent variables and depth of K + is the dependent variable. The model indicates that increased depth of exchange (increased interdiffusion coefficient) correlates predominantly with increased K 2O and/or Na 2O content of the glass, with a decreased total alkaline earth content and with the ratio of CaO/MgO.

Synthesis of MgO–SiO 2 and CaO–SiO 2 amorphous powder by sol–gel process and ion exchange

The processing of binary or ternary metal–oxide spherical powders often provides ideal starting materials for the preparation of ceramics or glasses, and the use of these powders can lead to excellent properties. Amorphous spherical powders composed of SiO 2 and MgO or CaO were synthesized by using Na 2O–SiO 2 spherical powder as a starting material and then conducting ion-exchange between the magnesium or calcium ions and the sodium ions in the Na 2O–SiO 2 powder. The maximum amount of magnesium or calcium in the powder was Mg/Si=0.5 or Ca/Si=0.8. The ratios of Mg/Si and Ca/Si were then determined by controlling the alkaline-earth concentration of the suspension used for the ion exchange. The ratio of Mg 2+ or Ca 2+ to consumed Na + as a result of the ion exchange was estimated to be 1.0, and it was found that OH − around Si–ONa also participates in the ion exchange. The ratio of water to ethanol in the reaction mixture also influenced the ion exchange.

Sintering behavior and mechanism of Sr-doped lanthanum chromites with A site excess composition in air

Sintering characteristics and mechanisms of lanthanum strontium chromites, (La 1− x Sr x ) 1+ y CrO 3 (0≤ x≤0.3, 0≤ y≤0.02), in air are discussed in comparison with the results for Ca-doped lanthanum chromites. The sinterability of La 0.9Sr 0.1+ y CrO 3 increased with increasing alkaline earth (AE) content, but was much lower than that of La 0.9Ca 0.1+ y CrO 3. It was found that the ratios of AE to Cr formed a second phase in the sample in the region 0.5< x<3 for Ca/Cr and in the range 10< x<15 for Sr/Cr. The ratios of Ca to Cr entered in the composition range, forming a low melting point (≥1050°C) system. On the other hand, the second phase formed by the Sr/Cr ratios might be in the composition range of the solid state at firing temperatures of 1600°C. An attempt was made to fully sinter 10 mol% Sr-doped lanthanum chromites with 2 mol% sintering aids. After heating at 1600°C in air, the relationship between the ionic field strength of the sintering aids and the relative density for La 0.9Sr 0.1CrO 3 with 2 mol% sintering aid was clarified. With increasing ionic field strength, that is with decreasing basicity, the relative density of the doped La 0.9Sr 0.1CrO 3 perovskites decreased.

Effect of substitution of La by alkaline earth metal on the thermoelectric properties and the phase stability of γ-La3S4

The Seebeck coefficient, electrical resistivity, and thermal conductivity of La3−xAxS4 with the Th3P4-type structure (the γ-phase) for A=Ca, Ba, and x=0–0.8 have been measured as a function of alkaline earth metal content and temperature to determine the optimum dopant concentration and doping agent by calculating the corresponding figure of merit (Z). With an increase of x, the Seebeck coefficient and electrical resistivity increase, while the thermal conductivity decreases. The decrease of thermal conductivity is ascribed to the decrease of the electron concentration and the increase of the phonon scattering accompanying the substitution for La by an alkaline earth metal. As a result, La2.2Ca0.8S4 has a maximum value of Z of 2.3×10−4 °C−1 at 700 °C. We also have examined the long term stability of γ-La3−xAxS4. The substitution for La by alkaline earth metal of La3S4 stabilized the Th3P4-type structure at high temperature.

Ｌａ３−ｘＡｘＳ４（Ａ＝Ｂａ，Ｃａ）の熱電特性

The effectiveness of substitution for La by Ba or Ca on the physical properties of rare earth chalcogenide La3S4 was examined. Cubic γ -phase (Th3P4-type) was obtained in the range of 0≤x≤1 in La3-xAxS4 (A=Ba, Ca). The lattice parameter in La3-xBaxS4 system increased, while that in La3-xCaxS4 system decreased with an increase of x, which is ascribed to the difference of the radius among the ions. The thermoelectric power (α) and the electrical resistivity (ρ) of La3-xAxS4, which are functions of the electron concentration, increased with an increase of the temperature and the alkaline earth metal content x. A maximum value of the power factor (p=α2/ρ) at high temperature above 750K was obtained at x=0, i.e., La3S4. On the other hand, the thermal conductivity (κ) decreased with an increases of x. In result, a maximum value of the figure of merit (Z=α2/(ρκ)) was obtained at large value of x (x≈0.6 in La3-x, BaxS4 and x≈0.8 in La3-xCaxS4).

A study by density measurements and indentation tests of a calcium silicophosphate bioactive glass with different MgO or SrO contents

Vickers and Knoop indentation techniques and density measurements have been employed to study the structure of two series of glasses in the system CaOROSiO 2P 2O 5CaF 2 (R = Sr, Ca, Mg) with: (a) constant alkaline earth oxide content, but using different cations (Ca, Ca + Sr, Ca + Mg), and (b) increasing alkaline earth concentration (Mg and/or Ca). Samples have been prepared by melting the raw materials at 1400°C, and pouring the liquid on a steel plate. From the experimental data, microhardness, H V, fracture toughness, K IC, and values for mean atomic volume, V A, and ionic volume fraction, V F, were obtained. The last parameter is proposed as a suitable one for the analysis of variations in cationic coordination numbers, n. The results show that Mg, Ca and Sr have similar values of n. The value of n is proposed to be six.

Thermal behaviour of bioactive alkaline-earth silicophosphate glasses

The thermal behaviour (sinterability and first crystallization) of a series of alkaline-earth silicophosphate glasses has been studied by differential thermal analysis (DTA), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The samples were prepared from a base bioactive glass of the system CaO−P2O5−SiO2−CaF2, by (a) slightly changing the F/O ratio; (b) replacing part of the CaO by SrO or MgO; and (c) increasing the total alkaline earth concentration by MgO additions. The results show that the addition of MgO is the most effective way of improving sinterability. In these samples, a decrease of the glass transition temperature, together with an increase in the temperature of the first crystallization, is observed. The difference between both temperatures is proposed to be an adequate indicator of the sinterability. The initial stages of the first crystallization (which produces an oxo-fluorapatite), and its composition dependence, are discussed in terms of the results of sinterability, and the classical theory of nucleation.

Studies on Tanzanian Acacia gums. Part 3. Some properties of gum exudates from the series Vulgares and Gummiferae

Some properties of gum exudates from Tanzanian Acacia Senegal var. leiorhachis, A. polyacantha ssp. campylacantha and A. tortilis ssp. spirocarpa are presented, and compared with Sudanese commercial Acacia gums. Some properties of the gum exudates from A. Senegal var. leiorhachis and A. polyacantha ssp. campylacantha show significant differences from Sudanese Acacia gums by having a higher proportion of insoluble gel fraction, lower magnesium content and higher viscosity. Furthermore, the methoxyl content of A. polyacantha spp. campylacantha gum is higher than previously reported. The viscosity of A. tortilis ssp. spirocarpa gum, on the other hand, is similar to that of Sudanese Acacia gums at the same concentration. However, the nitrogen content is higher, whereas its alkaline earth metal content is lower.

The reaction of nitrogen with dilute solutions of barium in liquid lithium: electrical resistivity, X-ray phase analysis, kinetic and thermal analysis studies

The reaction of nitrogen with liquid lithium containing dissolved barium which follows a solution–precipitation mechanism has been studied. Initially, nitrogen dissolves in the liquid metal to form an homogeneous solution; the reaction is first order with respect to nitrogen with an activation energy of 33.6 kJ mol–1. Subsequently, it reacts to form a precipitate of Li3N; the Li3N crystallisation face is dependent on the barium content of the solution, nitrogen solubility rising with increasing barium content. The ternary nitride, LiBaN, is only formed on cooling the solution; there is no evidence for Ba2N or Ba3N2 formation. This behaviour contrasts with that in the corresponding Na–M–N (M = Sr or Ba) systems where the solubility is directly proportional to the alkaline-earth metal content of the solution and the precipitating phase is the alkaline-earth metal subnitride. M2N (M = Sr or Ba). Analysis of the crystallisation fields of Li, Li4Ba, LiBaN and Li3N indicated they are separated by monovariant curves which fall from the binary eutectics (Li–Ba, xBa= 0.105 and 416 K; Li–N. degenerate at 453.5 K, Li3N–LiBaN, unknown) through a quasi-peritectic equilibrium involving liquid, lithium, Li4Ba and LiBaN (372 K) to a ternary eutectic point based on liquid, lithium. Li3N and LiBaN (368 K).

Sampling and Analysis of KGa-1B Well-Crystallized Kaolin Source Clay

AbstractAdditional well-crystallized kaolin from Washington County, Georgia, has been supplied to the Clay Minerals Society Source Clay Repository to replace the exhausted supply of KGa-1. This kaolin is called KGa-1B and is from a geographic location and stratigraphic position close to where KGa-1 was collected. Slight mineralogical and chemical differences are observed between KGa-1 and KGa-1B. KGa-1B crude appears slightly better crystalline than KGa-1, and it has a slightly higher titania content than KGa-1. The Al2O3, SiO2, Fe2O3, alkali, and alkaline earth contents appear similar for both samples. KGa-1 has a slightly coarser particle size than KGa-1B crude. More intensive post-depositional alteration may have cleansed and crystallized the KGa-1B material to a slightly greater degree than the KGa-1 material.

Behavior of Surfactants in a Highly Loaded Coal–Water Slurry. II. Effects of Coal Properties on the Behavior of a Surfactant

Abstract The roles and behaviors of two kinds of anionic surfactants were investigated in order to clarify their influence on the properties of a highly loaded coal water slurry (CWM) prepared from six kinds of coals. It was confirmed that the adsorbed surfactants on coal particles and their presence in water were both required for preparing practical CWMs of every type of coal. The ion concentrations of alkaline earth metals and protons derived from coal increased the adsorption of surfactants; the amounts of the adsorbed surfactants varied from coal to coal. A surfactant of molecular weight around 5000 was found to be preferentially adsorbed, and thus the most effective for controlling the properties of the CWM.

Synthesis, air sintering and properties of lanthanum and yttrium chromites and manganites

A new combustion process, the Glycine-Nitrate Process (GNP), is used for synthesizing ultra-fine, single- or multi-phase electrically conducting oxide powders. The resulting powders are crystalline, homogenous, softly agglomerated, and vary in size between 1 and 100 nm depending upon composition and synthesis parameters. The process is simple, rapid, low-cost and environmentally compatible. GNP synthesized yttrium and lanthanum chromite powders can be air-sintered to high density below 1550°C. The air-sintering mechanism are functions of alkaline-earth concentration, cation ratio, vapor loss and liquid-phase formation. Sintered densities increase with increasing alkaline-earth substitution and with increasing (La+Sr)/Cr and (Y+Ca)/Cr ratios. Large changes in air sinterability can occur with small changes in these cation ratios. Vaporization of Cr appears to be a major influence in La 1− x Sr x CrO 3 air-sintering. Liquid-phase sintering appears to be a major factor in the sintering of Y 1− x Ca x CrO 3. The electrical conductivity and thermal expansion also increase with ncreasing alkaline-earth substitution for the lanthanum or yttrium chromites and manganites. In addition, the electrical, thermal and structural properties of these perovskite materials are also influenced by the synthesis and processing conditions as well as by thermal cycling and heat treatment in air.

Phase relation in the system (La1−xAx)1−yMnO3+z (A=Sr and Ca)

Abstract The phase relation in the system, (La1−xAx)1−yMnO3+z (A=Sr and Ca), has been investigated by XRD method. The system showed the A site deficiency in ABO3 perovskite structure, and the range, y, was less than 0.1 when x=0, which decreased with increasing alkaline earth content, x. Three single phases with different structure were observed in this system; two orthorhombic structures based on the orthoferrite GdFeO3 type and a rhombohedral structure based on the LaAlO3 type. The latter has more oxygen in the structure than the former two. The electrical conductivity was measured for Sr doped samples up to 1000°C. In spite of the large composition dependent conductivity at room temperature, all the samples showed the almost same values of 60–90 Scm−1 at 1000°C.

Bioremediation of metal‐contaminated surface and groundwaters

Abstract Microorganisms immobilize, mobilize, or transform metals by extracellular precipitation reactions, intracellular accumulation, oxidation and reduction reactions, methylation and demethylation, and extracellular binding and complexation. Nearly all of these microbe/metal interactions occur within the wetlands approach to acid mine drainage treatment, a process that is rapidly gaining support as a low‐maintenance, cost‐effective approach to solving an important environmental problem. Several proprietary processes, which employ nonliving microorganisms that are immobilized in polymer matrixes, are entering the water treatment market. These processes take advantage of negatively charged functional groups on cell walls and exopolymers of microorganisms that bind cationic metals. These biosorbents effectively remove low concentrations (<1 to about 20 mg/L) of heavy metal cations in the presence of high concentrations of alkaline earth metals (Ca2+ and Mg2+) and organic contaminants to levels lower than...

Major elements in manganese and iron oxides precipitated from seawater

manganese and iron oxides precipitated from aerated well-seawater at aquaria in Japan were analyzed for their mineralogy and alkaline earth and alkali metal contents. Todorokite-rich manganese oxides were enriched in Na and Ca and depleted in K and Mg relative to birnessite-rich manganese oxides. The concentrations of alkaline earths and alkali metals in the iron oxide were lower than in the manganese oxides; this is especially true of the alkali metals. On the basis of these results, mineralogical control on the major element composition and the charge-balancing cations of marine ferromanganese oxide deposits are discussed.