Calcium Ion Exchange Research Articles

Fabrication and characterization of sol–gel derived hydroxyapatite/zirconia composite nanopowders with various yttria contents

Homogeneous composite nanopowders of hydroxyapatite/30 wt% yttria-stabilized zirconia (HA–YSZ) containing 0, 3, 5, and 8 mol% Y 2O 3 (namely; HA–0YSZ, HA–3YSZ, HA–5YSZ, and HA–8YSZ) were successfully synthesized using the sol–gel method. Simultaneous thermal analysis (STA), X-ray diffraction (XRD), X-ray fluorescence spectroscopy (XRF), Fourier transformed infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM) techniques were utilized to characterize the prepared nanopowders. Analyses of HA–YSZ composite nanopowders showed the successful formation of desirable phases. HA unit cell volume in the composites increased as a result of ion exchange of calcium and zirconium between HA and zirconia. Results revealed the formation of HA particles with irregular morphology (40–80 nm) and spherical yttria-stabilized zirconia particles (20–30 nm). Segregation of yttrium ions at the grain boundaries of ZrO 2 particles retarded the grain growth of zirconia particles and the presence of ZrO 2 nanoparticles among the hydroxyapatite particles resulted in grain growth inhibition of HA particles. This process can be used to synthesize HA–YSZ composite nanopowders with improved properties, which are much needed for hard tissue repair and biomedical applications.

Octacalcium phosphate: Osteoconductivity and crystal chemistry

Octacalcium phosphate (OCP), which is structurally similar to hydroxyapatite (HA), is a possible precursor of bone apatite crystals. Although disagreement remains as to whether OCP comprises the initial mineral crystals in the early stage of bone mineralization, the results of recent biomaterial studies using synthetic OCP indicate the potential role of OCP as a bone substitute material, owing to its highly osteoconductive and biodegradable characteristics. OCP tends to convert to HA not only in an in vitro environment, but also as an implant in bone defects. Several lines of evidence from both in vivo and in vitro studies suggest that the conversion process could be involved in the stimulatory capacity of OCP for osteoblastic differentiation and osteoclast formation. However, the osteoconductivity of OCP cannot always be secured if an OCP with distinct crystal characteristics is used, because the stoichiometry and microstructure of OCP crystals greatly affect bone-regenerative properties. Osteoconductivity and stimulatory capabilities may be caused by the chemical characteristics of OCP, which allows the release or exchange of calcium and phosphate ions with the surrounding of this salt, and its tendency to grow towards specific crystal faces, which could be a variable of the synthesis condition. This paper reviews the effect of calcium phosphates on osteoblastic activity and bone regeneration, with a special emphasis on OCP, since OCP seems to be performing better than other calcium phosphates in vivo.

Mineralogy and Chemical Composition of High-Calcium Fly Ashes and Density Fractions from a Coal-Fired Power Plant in China

To understand the formation mechanism of high-calcium fly ashes, the mineralogical, physical, and chemical properties of several high calcium fly ashes and their different density fractions (<1.0, 1.0−2.5, 2.5−2.89, and >2.89 g/cm3) from a coal-fired power plant were characterized by X-ray diffractometry (XRD), field scanning electron microscopy equipped with energy dispersive X-ray analysis (FSEM-EDX), and X-ray fluorescence spectroscopy (XRF). The occurrence of calcium in coal was determined using sequential extraction tests. The results show that the carbonate-bonded calcium is the dominant species in Xiaolongtan coal, and the ion-exchangeable calcium only occupies 19.2% of total calcium. The major calcium-bearing minerals in low temperature ash (LTA) of the feed coal, lignite from the Yunnan province, include calcite, bassanite, and dolomite. The fly ashes examined contained aluminosilicates with a high concentration of calcium oxide. The major minerals include mullite, quartz, lime, anhydrite, and gehlenite, and the minor minerals are comprised of hematite, magnetite, akermanite, portlandite, and larnite. Minerals in the density faction less than 1.0 g/cm3 consist of lime, calcite, anhydrite, and clay; between 1.0−2.5 g/cm3, quartz, mullite, anhydrite, and gehlenite; between 2.5−2.89 g/cm3, anhydrite, lime, gehlenite, hematite, and quartz; and greater than 2.89 g/cm3, larnite, gehlenite, anhydrite, brownmillerite, and some heavy minerals. In accordance with the microstructural characteristics of the fly ash particles, high-calcium fly ash can be classified into several groups, namely hollowed smooth particles, dense particles, agglomerate particles, porous particles, plerosphere, and other particles with complex surface characteristics. On the basis of chemical composition, high-calcium fly ashes can be classified into four groups namely: calcium oxide, calcium sulfates, Ca−Al−Si compounds, and Ca−S−X (X: Fe, Al, Si, Mg, etc.) compounds. Calcium oxide and calcium sulfates are mainly derived from the original calcium-bearing minerals in coal, whereas Ca−Al−Si and Ca−S−X compounds are formed by the secondary reaction of CaO and CaSO4.

Synthesis of Zeolite of Type A from Bentonite by Alkali Fusion Activation Using Na2CO3

Optimization studies were carried out for the synthesis of zeolite A by a hydrothermal method using alkali-activated bentonite as raw material. The process of alkali fusion activation and optimization of the composition were studied by TG-DTA, XRD, and calcium ion exchange capacity. It was found that a mixture of additional alumina (aluminum hydroxide) and bentonite was converted to highly reactive sodium silicate, sodium aluminate, and aluminosilicate by alkali fusion activation using Na2CO3 at high temperature. Zeolite A with a maximum crystallinity of 82.7% and calcium ion exchange capacity of 302 mg of CaCO3/g was obtained at optimized conditions.

Surface enrichment of biomimetic apatites with biologically-active ions Mg 2+ and Sr 2+: A preamble to the activation of bone repair materials

The surface activation of calcium phosphate-based biomaterials for bone repair is an emerging route for improving bone regeneration processes. One way for such activation is through the exchange of surface calcium ions with biologically-active cations such as Mg 2+ or Sr 2+. In this work, the interactions of non-carbonated and carbonated nanocrystalline apatites with Mg 2+ and Sr 2+ were investigated by means of ion exchange experiments in solution. Langmuir-type isotherms were determined. For both Sr and Mg, a greater uptake was observed on the carbonated sample, and on both types of apatites the maximum strontium uptake was greater than that of magnesium. Inverse exchanges showed that the proportion of reversibly fixed ions after surface exchange was close to 85% for Mg and 75–80% for Sr. The results are related to the presence of a surface hydrated layer on the nanocrystals and possible exchange mechanisms are discussed. Our results favor the hypothesis of hetero-ionic surface exchanges (Mg 2+↔Ca 2+, Sr 2+↔Ca 2+) within the hydrated layer, and some analogy with octacalcium phosphate (OCP) is considered. This work should prove helpful for the control and understanding of the activation of synthetic apatite-based powders or scaffolds with bioactive elements, as well as for the global understanding of biomineralization processes.

Long-term shear strength of geosynthetic clay liners

Geosynthetic clay liners (GCLs) often have a sandwich-like multilayer structure, e.g. bentonite encased between two geotextile layers connected by fibers or yarns, either by needle-punching or stitch-bonding. Therefore, the internal shear strength of the GCL depends on the strength of reinforcing fiber bundles or yarns and their anchoring strength in the cover and carrier geotextiles. When used on long and steep slopes and covered with thick soil layers, the GCL is permanently exposed to a combined action of compressive and shear stress. Such load conditions are characteristic for landfill covers and the slope stability of the overall cover system in the long run strongly depends on the long-term internal shear strength of the GCL. A new test method was developed to study this long-term shear behavior. The focus was not only on creep, as it is normally done, but on aging effects. The shear test devices allow the measurement of creep curves and times-to-failure at elevated temperatures in different media (tap water and de-ionized water). In this publication, the main findings of the experiments on needle-punched GCLs with and without thermal treatment are summarized. Tap water as a test medium was essential to ensure sodium to calcium ion exchange in the bentonite layer. Under this condition extremely long test durations without failure were achieved. Sliding failure occurred when de-ionized water was used. Two failure modes were observed: brittle failure of the GCLs with thermal treatment and slow disentanglement of fiber bundles for untreated GCLs. Short-term shear strength (e.g. peel strength) is unrelated to the actual long-term shear strength, i.e. to the times-to-failure achieved in long-term shear strength test. Hence, short-term shear strength alone will not provide reliable dimensioning data for product design and choice of resins. Therefore, the often suggested approach, namely, restriction to short-term tests only and application of factors of safety, is challenged by these results.

The temperature dependence of the exchange enthalpy of calcium and sodium ions on polymethacrylic and polyacrylic cationites

The influence of temperature on the exchange of calcium and sodium ions from solutions of 2.3–2.8 g-equiv/l concentrations on KB-2e4 gel polyacrylic cationite, KB-4P2 and KB-4 gel polymethacrylic cationites, and Purolite C104 polyacrylic cationite was studied over the temperature range 273–400 K. It was shown that, simultaneously with a substantial increase in selectivity with respect to calcium ions, the differential enthalpy of the ion exchange reaction increased linearly on all polyacrylic and polymethacrylic cationites as the temperature grew.

WHAT IS THE BEST TREATMENT FOR HYPERKALAEMIA IN A PRETERM INFANT?

A 720 g neonate in the intensive care unit develops severe hyperkalaemia with cardiac arrhythmia. The specialist registrar decides to give a calcium gluconate bolus and start an insulin and...

Correlation of Sorption Behavior of Nitrogen, Oxygen, and Argon with Ca2+ Locations in Zeolite A: A Grand Canonical Monte Carlo Simulation Study

The adsorption isotherms for nitrogen, oxygen, and argon in various NaCaA zeolite samples were calculated theoretically using the grand canonical Monte Carlo simulation method. The adsorption capacity, selectivity, and heat of adsorption of nitrogen increase with an increasing number of calcium cations in zeolite A. The heat of adsorption of nitrogen showed a sudden increase when the calcium ion exchange to zeolite A was around 60%. Adsorption isotherms, determined experimentally by the volumetric adsorption method, support theoretically predicted isotherms. These observations have been explained in terms of the interaction of the nitrogen molecule with Ca2+ ions and their locations in zeolite A.

Preparation of 5A zeolite monolith granular extrudates using kaolin: Investigation of the effect of binder on sieving/adsorption properties using a mixture of linear and branched paraffin hydrocarbons

A zeolite monolith extrudates using kaolin is synthesized, and effect of binders on sieving/adsorption properties of the prepared zeo- lite is reported. The monolith extrudates of 4A zeolite powder produced as the precursor of 5A zeolite in the first stage of synthesis pro- cess was prepared using different percentages of kaolin powder and carboxymethylcellulose (CMC) as binding agent. The average particle size distribution of produced 4A zeolite was between 20 and 40 US standard mesh sizes equivalent to 0.841 mm and 0.420 mm, respectively. The extrudate was calcined at 600 � C, and the kaolin content of extrudates was converted to type A zeolite through ion exchange by immersing the extrudates in caustic soda solution. The 4A zeolite extrudate samples were converted to 5A type through ion exchange process using calcium chloride solution. The 5A zeolite samples were characterized using XRD, SEM, and EDX instrumental analytic methods. Sieving test was carried out using samples of 5A zeolite and a special cut of kerosene containing C10-C13 saturated hydrocarbons using a simple dead-end fixed bed. Results show that the highest purity of 5A zeolite, highest rate of calcium ion exchange, and best sieving results are obtained when 30 wt% of binder (kaolin) is used, and use of small amounts of CMC as an organic binder along with inorganic kaolin binder has a pro- found effect on the adsorption properties of the synthesized 5A zeolite. This profound effect is attributed to de-clogging of the cylindrical pores due to CMC gasification in final calcinations of the extrudates.

Optimization of an Iron Intercalated Montmorillonite Preparation for the Removal of Arsenic at Low Concentrations

AbstractA series of iron intercalated montmorillonites (Fe‐Monts) were prepared using (i) ion exchange of native sodium and calcium ions with iron ions, (ii) base hydrolysis of inserted iron ions in montmorillonite suspension, and (iii) insertion of pre‐hydrolyzed iron colloid in montmorillonite. The materials were characterized by X‐ray diffraction and gas adsorption‐desorption techniques. The basal d(001)‐spacing and BET specific surface area increased after the intercalation of iron species in montmorillonite. Local iron structure studied by X‐ray absorption fine structure (XAFS) spectroscopy showed an unsaturation of the Fe···Fe coordination number (N 2.5) of the intercalated iron species as compared to the bulk iron oxyhydroxides (N 6). The Fe‐Monts were employed for arsenic removal from aqueous solutions at low concentration (0.2–16 mg/L). Among the Fe‐Monts, the one prepared by the hydrolysis of inserted iron ions, was the best in performance. The saturation adsorption amount of the optimized iron‐montmorillonite was 4 and 28 times higher for the removal of arsenite and arsenate, respectively, as compared to bulk iron oxyhydroxide (goethite). Compared with bulk iron oxyhydroxide, the Fe‐Monts were superior for arsenate uptake and comparable for arsenite. In addition, arsenite adsorbed on the Fe‐Monts was found to be oxidized to arsenate based on XAFS spectroscopy.

Removal of Perfluorooctanoic Acid and Perfluorooctane Sulfonate from Wastewater by Ion Exchange

Recent studies have demonstrated that fully fluorinated surfactant molecules have a tendency to accumulate in biological tissues. As a result, the Environmental Protection Agency has sought to reduce the usage of these chemicals and limit their discharge into the environment. Perfluorooctanoic acid (PFOA) is used in the manufacture of fluoropolymers and fluoroelastomers and is present as a component of some top-antireflective coating (TARC) materials. Perfluorooctane sulfonate (PFOS) is a component of some TARCs and photoacid generators used by the semiconductor industry in its fabrication processes. The purpose of this study is to determine effective and economically feasible methods to treat PFOA/PFOS contaminated process wastewater. A treatment screening study was performed investigating activated carbon adsorption, adsorption onto calcium fluoride solids, evaporation, ion exchange, and liquid-liquid extraction. Ion exchange was determined to be the best technology for treatment of PFOA/PFOS wastewater. Batch equilibrium isotherm experiments and a continuous-flow column study were performed to determine a feasible design. In addition, a model based upon equilibrium multicomponent chromatography theory was employed for prediction of column breakthrough curves.

Investigation of the effects and degree of calcium exchange on the Atterberg limits and swelling of geosynthetic clay liners when subjected to wet–dry cycles

In the field, particularly in landfill cover system applications, a geosynthetic clay liner may be exposed to inorganic cations such as calcium, magnesium and aluminium which can alter the performance of the GCL bentonite component especially if accompanied by drying and re-wetting as a result of seasonal changes in temperature and rainfall. To investigate the impacts of wetting and drying, the Atterberg limits of the GCL bentonite component and swelling of the GCL were determined under wet–dry cycling with calcium chloride solution used for the wetting cycles. From the quantities of calcium chloride added at each wetting stage, estimates were made of the degree of ion exchange of calcium for sodium on the clay. The authors recognise that there is a substantial literature on the effects of inorganic salts such as calcium chloride on the behaviour of bentonite. However, so far as they are aware, the results of such tests involving cation exchange have not been investigated in terms of the degree of exchange achieved. In the tests two calcium chloride solutions were used: 0.0125 and 0.125 M. This allowed a detailed investigation of the effects of the degree of sodium–calcium exchange on the bentonite and some, though more limited, consideration of the effects of ionic strength of the pore fluid. It is shown that for Atterberg limit tests, even using 0.125 M calcium chloride solution, full calcium exchange could not be achieved as the amount of liquid added to bring the bentonite to the liquid or plastic limit did not contain sufficient calcium ion for full exchange. For the swell tests, much higher liquid-to-solid ratios were used so that near full exchange could be achieved though only after several wet–dry cycles. Using these data the paper develops a methodology for estimating the position of the cation exchange equilibrium and shows how complex this analysis can become. It also shows that on occasion only limited cation exchange may be achieved in laboratory tests whereas near full exchange may occur in the field. If the effects of full/near full exchange are to be investigated, laboratory procedures must be specially designed to achieve high degrees of exchange, for example, by using multiple exchange cycles, large liquid-to-solid clay ratios or by permeating the clay with the cation exchange liquid—though such permeation procedures may take a very substantial time.

Development of polysaccharide gel-coated pellets for oral administration: 2. Calcium alginate

Calcium alginate gel-coated pellets were developed by forming an insoluble gel coat on extruded–spheronized pellets by interfacial complexation. Experiments were designed to investigate the effect of pellet size, alginate type, alginate concentration, and dissolution medium on swelling and drug release behavior. Low swelling in acidic media was related to proton–calcium ion exchange forming insoluble acid gels. In contrast, partial formation of soluble sodium alginate in 0.1 M NaCl induced water uptake, resulting in greater swelling. Drug release from coated pellets showed a lag time when the gel coat hydrated and swelled, followed by a zero-order release. Significantly slower release was observed when either the pellet size or the alginate concentration was increased. Alginate with high guluronic acid content gave the slowest release. Different types of alginate with high mannuronic acid content showed different release behaviors that are probably due to the different monomer sequences and botanical sources. The faster drug release in acidic media and 0.1 M NaCl compared to water is probably due to reduced calcium cross-linking in the gel. These results suggest that the pellet size, alginate type and concentration and dissolution medium influenced the swelling and drug release behavior of calcium alginate gel-coated pellets.

Calcium Ion Exchange in Crystalline Gelsolin

Gelsolin is a calcium and pH-sensitive modulator of actin filament length. Here, we use X-ray crystallography to examine the extraction and exchange of calcium ions from their binding sites in different crystalline forms of the activated N and C-terminal halves of gelsolin, G1-G3 and G4-G6, respectively. We demonstrate that the combination of calcium and low pH activating conditions do not induce conformational changes in G4-G6 beyond those elicited by calcium alone. EGTA is able to remove calcium ions bound to the type I and type II metal ion-binding sites in G4-G6. Constrained by crystal contacts and stabilized by interdomain interaction surfaces, the gross structure of calcium-depleted G4-G6 remains that of the activated form. However, high-resolution details of changes in the ion-binding sites may represent the initial steps toward restoration of the arrangement of domains found in the calcium-free inactive form of gelsolin in solution. Furthermore, bathing crystals with the trivalent calcium ion mimic, Tb3+, results in anomalous scattering data that permit unequivocal localization of terbium ions in each of the proposed type I and type II ion-binding sites of both halves of gelsolin. In contrast to predictions based on solution studies, we find that no calcium ion is immune to exchange.

Influence of morphology and topography on potentiometric response of magnesium and calcium sensitive PEDOT films doped with adenosine triphosphate (ATP)

Poly(3,4-ethylenedioxythiophene) (PEDOT) films doped with adenosine triphosphate (ATP) are used to study the biologically relevant competitive magnesium and calcium ion-exchange at ATP membrane sites. It is shown, by atomic force microscopy (AFM) and scanning electron microscopy (SEM), that the surface topography and morphology of the PEDOT–ATP films determines the quality of their potentiometric response. More smooth and less rough films result in better potentiometric characteristics, particularly in a faster response. The topography/morphology of the PEDOT–ATP films is influenced by conditions during electrodeposition (electrochemical method of deposition, pH, concentration of electrolytes) and post-deposition soaking (including net-time of soaking), as evidenced by X-ray photoelectron spectroscopy (XPS) and energy dispersive analysis of X-rays (EDAX).

Synthesis and crystallization of macroporous hydroxyapatite

Macroporous hydroxyapatite Ca 10(PO 4) 6(OH) 2 was synthesized using ordered polystyrene sphere templates that were impregnated with a calcium phosphate precursor solution which was allowed to solidify followed by sintering from 500 to 1000 °C in flowing oxygen to remove the polymer and crystallize the phosphates. Using a combination of diffraction and imaging the face-centered cubic macroporous framework was shown to have pore diameters of 0.8–0.9 μm and to be composed of hydroxyapatite (80–98 wt%) and X-ray diffraction amorphous material (14–55%), the proportions dependent on the duration and temperature of heat treatment. At lower sintering temperatures the HAp is calcium deficient. Ion exchange of calcium by cadmium demonstrated the potential of this material for hazardous waste remediation.

Influence of minerals and added calcium on the pyrolysis and co-pyrolysis of coal and biomass

AbstractThe pyrolysis behaviour was studied of two types of biomass (pine and wheat) and a Polish lignite (Turow) in the presence of minerals and ion-exchanged calcium using a variety of laboratory-scale methods including pyrolysis–gas chromatography–mass spectrometry (py–GC–MS) and thermogravimetric analysis coupled to a FTIR spectrometer (TGA–FTIR). Ion-exchange worked well for all samples, but particularly for the biomass, and the wt% Ca introduced followed the order wheat (4·17 wt%) > pine (1·74 wt%) > coal (0·80 wt%). The degree of catalysis displayed by the calcium during pyrolysis of the ion-exchanged samples varied with the fuel used. Significant catalysis by calcium was observed in pyrolysis of pine, but only a small effect was seen for wheat and very little for coal. The inherent minerals also play a catalytic role in all the samples studied, but potassium is by far the most important in the pyrolysis of the raw wheat straw. The gases and light volatiles are influenced by the presence of catalyt...

A Study of the Competitive Equilibrium in Ion Exchange of Calcium(II) on Zirconium Phosphate in Multicomponent Salt Solutions

A sorption technology for stabilization of multicomponent salt solutions (wines) subject to calcium clouding is being developed on the basis of an inorganic cation-exchanger of Termoksid-3A brand. In this connection the ion-exchange equilibrium on a zirconium(IV) phosphate of Termoksid-3A brand in multicomponent solutions at pH 2.5 – 3.0 was studied. The selectivity series of the sorbent were determined in relation to the solution composition.

Effect of soil composition on adsorption of lead as reflected by a study on a natural forest soil profile

The adsorption characteristics of lead on each genetic horizon of a natural brown forest soil profile were studied to recognize the possible immobilizing effect of a mineralogical diverse soil profile in the case of a possible lead contamination. Lead adsorption experiments were carried out on whole soil samples, soil clay fractions, as well as on their carbonate and organic matter free variant. TEM-EDS analyses were performed to characterize the adsorption capacity of individual mineral phases. The most important lead adsorbents in order of importance are the organic matter, the clay minerals, and the iron oxides. The most significant process is the ion exchange of calcium by lead with the respect to adsorption. The organic matter adsorbs more lead than clay minerals, and clay fractions adsorb more lead as compared to the whole soil samples. Among mixed layer clay minerals, those containing swelling component have the highest lead adsorption capacity, but the exact distinguishing of the individual clay mineral particles with the respect to their adsorption capacity is not possible. The calcite influences the lead adsorption through its buffering capacity: high calcite content results in lead precipitation. Soils characterized by high amount of organic matter, swelling clay mineral accumulation horizon and calcareous subsoil are suitable medium to immobilize a significant lead pollution.