Type Of Interlayer Cation Research Articles

Intercalation of CO2 Selected by Type of Interlayer Cation in Dried Synthetic Hectorite.

Clay minerals are abundant in caprock formations for anthropogenic storage sites for CO2, and they are potential capture materials for CO2 postcombustion sequestration. We investigate the response to CO2 exposure of dried fluorohectorite clay intercalated with Li+, Na+, Cs+, Ca2+, and Ba2+. By in situ powder X-ray diffraction, we demonstrate that fluorohectorite with Na+, Cs+, Ca2+, or Ba2+ does not swell in response to CO2 and that Li-fluorohectorite does swell. A linear uptake response is observed for Li-fluorohectorite by gravimetric adsorption, and we relate the adsorption to tightly bound residual water, which exposes adsorption sites within the interlayer. The experimental results are supported by DFT calculations.

The effect of layer charge origin and density, type of interlayer cations, and occupancy of the octahedral sheet of smectites on the adsorption of pyocyanin

Inactivation of pyocyanin, a virulence compound produced by Pseudomonas aeruginosa, has been proposed as a novel alternative approach to combat the multi-drug resistant Pseudomonas aeruginosa infections. It has been shown that montmorillonite was able to bind pyocyanin. Yet, the adsorption mechanism and the influence of the structural properties of smectites — type of interlayer cation, charge density, source of charge, and occupancy of the type of octahedral sheet — on the adsorption of pyocyanin is not clear. Batch adsorption experiments, variable-temperature X-ray diffraction, UV spectroscopic measurements, and electron dispersive spectroscopy analysis were conducted to investigate the role of several smectite structural properties on pyocyanin adsorption — affinity (K), capacity (Qmax), the adsorption mechanism, and the transformation of pyocyanin on smectite surface. The results indicated that interlayer adsorption of pyocyanin in smectite occurred by two types of adsorption mechanisms. 1) protonation of zwitterionic pyocyanin (PYO) and ion-exchange of PYOH+ for interlayer cations. This mechanism was dominant in alkali and alkaline-earth metal smectites. 2) direct coordination of zwitterionic PYO with interlayer cations. This mechanism was dominant for transition/heavy metal smectite. Among the structural factors investigated, 1) the type of interlayer cation showed the greatest effects on pyocyanin adsorption. Except for Cu2+, Qmax was similar for all the cation-saturated smectites (∼0.30–0.56 mol/kg) while the affinity K was higher in monovalent cations compared to the divalent cations. The Cu-smectite recorded the highest Qmax of ∼0.70 mol/kg. 2) smectites with different layer charge densities showed similar Qmax but the K was higher in low charge density smectite suggesting the importance of hydrophobic domain for pyocyanin adsorption. 3) It appeared that the layer charge source or the types of octahedral occupation did not show distinct effects on pyocyanin adsorption, but the presence of accessory minerals may mask the effects.

A quantitative and mechanistic model for the coupling between chemistry and clay hydration

It is proposed here to describe smectite water vapor desorption isotherms using an exchange formalism that quantitatively accounts for the different hydration states and thus different water contents. This approach makes it possible to reproduce both desorption isotherms and relative proportions of the different hydration states as determined by X-ray diffraction. The method is numerically robust and easy to implement in most reactive transport codes. The formalism is satisfactory from a phenomenological point of view and accounts for the influence of external parameters such as interlayer cation composition and solution cation composition and salinity on clay hydration. Furthermore, in contrast to most solid solution models, this approach focuses on the clay reactivity according to the charge and type of interlayer cation rather than on its solubility and therefore does not require the overall thermodynamic properties of the clay. In addition, such an explicit distinction of the hydration/cation exchange processes from the thermodynamic stability of smectite 2:1 layer allows the use of kinetics driving slow dissolution/precipitation rates if the number of exchange sites is related to the amount of clay minerals.

Different level of fluorescence in Raman spectra of montmorillonites

The paper presents the study of selected montmorillonite standards by Raman spectroscopy and microscopy supported by elemental analysis, X-ray powder diffraction analysis and thermal analysis. Dispersive Raman spectroscopy with excitation lasers of 532nm and 780nm, dispersive Raman microscopy with excitation laser of 532nm and 100× magnifying lens, and Fourier Transform-Raman spectroscopy with excitation laser of 1064nm were used for the analysis of four montmorillonites (Kunipia-F, SWy-2, STx-1b and SAz-2). These mineral standards differed mainly in the type of interlayer cation and substitution of octahedral aluminium by magnesium or iron. A comparison of measured Raman spectra of montmorillonite with regard to their level of fluorescence and the presence of characteristic spectral bands was carried out. Almost all measured spectra of montmorillonites were significantly affected by fluorescence and only one sample was influenced by fluorescence slightly or not at all. In the spectra of tested montmorillonites, several characteristic Raman bands were found. The most intensive band at 96cm−1 belongs to deformation vibrations of interlayer cations. The band at 200cm−1 corresponds to deformation vibrations of the AlO6 octahedron and at 710cm−1 can be assigned to deformation vibrations of the SiO4 tetrahedron. The band at 3620cm−1 corresponds to the stretching vibration of structural OH groups in montmorillonites.

Radiation-induced defects in clay minerals: A review

Extensive information has been collected on radiation effects on clay minerals over the last 35years, providing a wealth of information on environmental and geological processes. The fields of applications include the reconstruction of past radioelement migrations, the dating of clay minerals or the evolution of the physico-chemical properties under irradiation.The investigation of several clay minerals, namely kaolinite, dickite, montmorillonite, illite and sudoite, by Electron Paramagnetic Resonance Spectroscopy has shown the presence of defects produced by natural or artificial radiations. These defects consist mostly of electron holes located on oxygen atoms of the structure. The various radiation-induced defects are differentiated through their nature and their thermal stability. Most of them are associated with a π orbital on a Si–O bond. The most abundant defect in clay minerals is oriented perpendicular to the silicate layer. Thermal annealing indicates this defect in kaolinite (A-center) to be stable over geological periods at ambient temperature. Besides, electron or heavy ion irradiation easily leads to an amorphization in smectites, depending on the type of interlayer cation. The amorphization dose exhibits a bell-shaped variation as a function of temperature, with a decreasing part that indicates the influence of thermal dehydroxylation. Two main applications of the knowledge of radiation-induced defects in clay minerals are derived: (i) The use of defects as tracers of past radioactivity. In geological systems where the age of the clay can be constrained, ancient migrations of radioelements can be reconstructed in natural analogues of high level nuclear waste repositories. When the dose rate may be assumed constant over time, the paleodose is used to date clay populations, an approach applied to fault gouges or laterites of the Amazon basin. (ii) The influence of irradiation over physico-chemical properties of clay minerals. An environmental application concerns the performance assessment of the engineered barrier of nuclear waste disposals. In case of a leakage of transuranic elements from the radioactive waste form, alpha recoil nuclei can amorphize smectite after periods of the order of 1000years according to a worst case scenario, whereas amorphization from ionizing radiation is unlikely. As amorphization greatly enhances the dissolution kinetics of smectite, the sensitivity of the smectites must be taken into account in the prediction of the long term behavior of engineered barriers.

Effect of extensive drying on the cation exchange capacity of bentonites

AbstractExtensive drying of smectites can cause the interlayer space to break down (collapse). This can affect the properties of bentonites as geotechnical barriers of HLRW (highly radioactive waste) repositories. If and to what extent the collapse occurs depends strongly on the type of interlayer cation. In particular K is known to lead to ready dehydration, in contrast to Ca and Mg. In the present study, various bentonites and one illite/smectite clay were dried/heated at 90ºC for 1.5 a and in a different experiment at 120ºC for 4.5 a and investigated with respect to mineralogical and geochemical changes of the smectite.Smectite alteration after extensive drying was restricted to changes of the exchangeable cations. The CEC decreased by 9% (90ºC test) and 14% (120ºC test). A slight decrease of exchangeable Na+ was observed following the 90ºC test. No significant further decrease was observed after the 120ºC test. In contrast, the larger cation exchange capacity (CEC) decrease after the 120ºC test could be explained by increased Ca/Mg fixation. A possible mechanism for the observations is presented.

Electrical and magnetic properties of ion-exchangeable layered ruthenates

An ion-exchangeable ruthenate with a layered structure, K 0.2RuO 2.1, was prepared by solid-state reactions. The interlayer cation was exchanged with H +, C 2H 5NH 3 +, and ((C 4H 9) 4N +) through proton-exchange, ion-exchange, and guest-exchange reactions. The electrical and magnetic properties of the products were characterized by DC resistivity and susceptibility measurements. Layered K 0.2RuO 2.1 exhibited metallic conduction between 300 and 13 K. The products exhibited similar magnetic behavior despite the differences in the type of interlayer cation, suggesting that the ruthenate sheet in the protonated form and the intercalation compounds possesses metallic nature.

Hydrothermal Reactivity of Saponite

AbstractSaponite crystallizes from amorphous gel having an ideal saponite composition within 7 days at all experimental temperatures between 300° and 550°C at 1 kbar pressure. Reactions subsequent to this initial crystallization vary in type and degree, depending on the temperature of reaction and the type of interlayer cation. Above 450°C, the intitially crystallized K-saponite dissolves, and talc and phlogopite nucleate and grow as discrete phases. At 450°C the initial K-saponite reacts to form talc and phlogopite layers, but the reaction proceeds via intracrystalline layer transformations rather than via dissolution and precipitation, producing a mixture of fully ordered, interstratified talc/saponite and fully ordered saponite/phlogopite. The K-saponite shows subtle signs of reaction at 400°C after 200 days: this temperature is at least 150°C lower than experimental reaction temperatures previously reported for saponites. No reactions beyond the initial crystallization of saponite were observed below 400°C. K-saponite reacts more rapidly than either Na-saponite or Ca-saponite above 400°C, and the Na-saponite and Ca-saponite produce no mica layers during their transformation to mixed-layer clays. Interstratified talc/saponite formed in the Na-saponite system, and the Ca-saponite system produced both talc/saponite and chlorite/saponite.

Precise Identification of Illite/Smectite Interstratifications by X-Ray Powder Diffraction

AbstractThe thickness of the two-layer ethylene glycol complex of dioctahedral smectites varies under room conditions between 17.3 and 16.5 Å because of such factors as layer charge density, type of interlayer cation, and relative humidity. Neglecting this variability can give up to 30% error in the X-ray powder diffraction estimation of the smectite:illite ratio of the mixed-layer structures. Three methods have been developed for the interpretation of X-ray powder diffraction patterns of glycolated mixed-layer illite/smectite which take layer-spacing variability into account. The methods include a technique for quantifying the degree of layer ordering. In addition, the proposed techniques minimize the error due to the influence of domain size on positions of reflections. The experimental error can be kept below 5% or below 1% smectite layers, depending on the method applied, provided that the peak positions are measured with the accuracy of ± 0.02°2θ.

Diffusion of Exchangeable Cations in Vermiculite

VERMICULITE consists essentially of mica-like silicate layers separated by double sheets of water molecules carrying exchangeable cations, the cations being located midway between the water sheets in octahedral co-ordination1. In certain instances, replacement of one type of interlayer cation by another causes swelling or shrinking of the crystal lattice perpendicular to the plane of the silicate layers. These changes in the c-dimension of the unit cell are readily observable by X-ray diffraction procedures; replacement of magnesium by strontium for example, involves an increase in interlayer distance of about 0.6A., corresponding to an increase in basal spacing from 14.4A. to 15.0A. When a flake of vermiculite in which interlayer magnesium has been partly replaced by strontium is examined by X-rays, 14.4A. and 15.0A. reflexions are observed together, with the latter growing in intensity at the expense of the former as the replacement proceeds (Fig. 1).