Mineralogy and Physicochemistry of Smectites Saturated with Inorganic and Organic Cations (original) (raw)
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Characterization and properties of treated smectites
Journal of the European Ceramic Society, 2012
Two natural smectite clays named BC and AC were thermal and chemically treated. Apart from smectite, quartz and kaolinite, BC clay also contains calcite, whereas illite and higher quartz content is found in AC. Treatment at 823 K leads to a collapse of the smectite structure. Treating with H 2 SO 4 or NaOH also leads to the elimination of calcite and Al and Si ions. The higher swelling capacity of BC clay is in accordance with its higher cation exchange capacity. γ d S values for both smectites decreases with the applied treatments. The surface acid-base constants determined for BC clay are higher than those obtained for AC independently of the applied treatment. This result together with the higher nanorugosity index, has been attributed to the higher quartz of the AC clay. Moreover, it has been observed that the cationic exchange capacity increases in both clays with the acidity of the surface.
Modification of smectite structure by sulfuric acid and characteristics of the modified smectite
Journal of Agricultural Sciences, Belgrade, 2011
Bentonite samples from Petrovac and Aleksinac were treated with sulfuric acid of different molarities. Differences in structure and texture of the initial and modified bentonite were determined by chemical analysis and Xraypowder diffraction (XRPD), infra-red spectroscopy (FTIR), scanning electron microscopy (SEM) and physisorption nitrogen at −196°C. Sulfuric acid caused an exchange of Al 3+ , Fe 3+ and Mg 2+ with H + ions which led to a modification of the smectite crystalline structure. The Mg and Fe substitution in the octahedral sheet promoted the dispersion of those layers and forming of amorphous silicon. The sequence according to which the cations left the octahedral sheets was as follows: Mg 2+ >Fe 3+ >Al 3+ . The sulfuric acid activated bentonites exhibiting a lower cation exchange capacity (CEC) and а change of specific surface area (S BET ) from 6 to 387 for bentonite from Petrovac and from 44 to 1784 m 2 g -1 for bentonite from Aleksinac, positioning them as an excellent absorber in wine technology and in the protection of soil and environment.
Experimental transformation of Na,Ca-smectite under basic conditions at 150 °C
Applied Clay Science, 2004
The aim of this study is to examine the effect of various high pH solutions on smectites. The starting materials were a Na,Casmectite and two homoionic Na-and Ca-smectites. The experimental solutions were 0.01 m NaOH (pH 12), 1 m K 2 CO 3 and mixtures of 1 or 3 m KCl with 10 À 4 or 10 À 2 m KOH (pH 10 or 12). To enhance the reaction rate, all experimental investigations were carried out at 150 jC ( F 5jC max.), during 2 months. The internal pressure was 5 bars (liquid -vapour equilibrium pressure) when experiments were conducted in warm seal autoclaves and fixed to 150 bars, using standard cold seal vessels. The liquid/clay mass ratio was fixed to 10/1. Integrated data obtained by a multitechnique analytical approach [XRD, electron microprobe, transmission electron microscopy (TEM), scanning electron microscope (SEM) on run products, and inductively coupled plasma atomic emission (ICP-AES) and mass spectrometry (ICP-MS) on experimental solutions] show a distinct behaviour of smectite as a function of experimental fluid composition. In NaOH solution, run products remain low-charge smectites. In KCl + KOH solutions, crystal chemical changes concern mostly the interlayer. A significant replacement of Na by K, and a partial substitution of Ca by K are observed. The tetrahedral Si content does not change, but the total interlayer charge in smectite increases, balancing the changes occurring in the octahedral occupancy (release of Al and Fe). Low-charge smectite transforms into high-charge smectite and byproducts are quartz and feldspars. In the presence of 1 m K 2 CO 3 , homoionic Na-and Ca-smectites are unstable and in part replaced by zeolites (merlinoite), feldspars and calcium silicate hydrates (CSH), the latter being dominated by a tobermorite-like phase. The main consequences of the cement or concrete like pore fluid -bentonite contact at elevated temperature induce dissolution of smectite (at various rates), cation exchange and the formation of byproducts (quartz, feldspars, zeolites and CHS). These mineralogical changes affect the expandability and surface area of minerals, and therefore may significantly change the porosity and fluid flow diffusion in clay barriers exposed to high pH fluids. D
Equimolar cation exchange of polyacrylamide in smectite
Applied Clay Science, 2020
Smectite-polymer composites from cationic polyacrylamide (PAM S,τ40 Cl) were prepared to investigate the adsorption behavior of the smectite after the intercalation procedure. PAM S,τ40 Cl solutions with two different concentrations (γ = 5.18 g/L corresponds to 4.3 mmol/L and γ = 3 g/L corresponds to 4.3 mmol/L) were used to manufacture smectite-PAM + S,τ40 composites. The total amount of PAM + S,τ40 intercalated into the interlayer of the smectite was between 4.5 and 10%. This corresponds to coverage between 4 and 11 cmol(+)/kg, based on the cation exchange capacity (CEC) of the smectite. The smectite in the smectite-PAM + S,τ40 composites still possesses a CEC. The CEC decreased with increasing PAM + S,τ40 content. The CEC decrease was higher than the effective coverage. The amount of Na + in the interlayer decreased compared to the initial amount with increasing PAM + S,τ40 content. PAM + S,τ40 prefers the interlayer with Na +. Smectite particles in the used raw bentonite (MX-80) are large enough for a planar covering of the basal surfaces by PAM S,τ40 Cl. Furthermore, the distances between the charges at the basal surfaces of the smectite and in the oligomer are also large enough for planar covering. Evaluation of the mass spectrometer (MS) curve of m/z = 35 (Cl 2) showed that PAM + S,τ40 does not saturate all charges of the smectite per unit cell. Some charges of PAM + S,τ40 are still saturated by Cl −. The exchange of PAM + S,τ40 for Na + in the interlayer of smectite takes place equimolar.
The effect of polycationic system on the expandability of the smectite as a backfill material
Geosciences Journal, 2000
The expandability of smectite along with cation exchange reaction was investigated at 150~ Elements such as Cs +, Sr 2+ and Ba 2+ were selected as surrogates for radionuclides which can be contained in leachate from the radioactive waste repositories. Using Teflon-lined reaction vessel and Barnes-type autoclave, mixtures of purified smectite and synthetic water containing appropriate concentrations of the cations were hydrothermally treated at 150~ during 70 days. The vapor pressure was elevated to that of water vapor at 150~ Cs + showed highest tendency to be located in the interlayer sites of smectite and, at the same time, turned out to have the greatest inclination to expel K +. In the presence of Cs +, other cations (Sr 2+ and Ba 2+) remain in the interlayer at nearly constant concentration regardless of the initial concentration of Cs +. It is revealed that Ba 2+ retards the silica-releasing rate. Cation exchange reaction seems to have achieved equilibrium in short time. At the ends of the experiments, the illitization has occurred to some extent, which was confirmed by the XRD analyses of the reaction products, and the layer charges of them are qualitatively compared with that of the smectite from Osoung mine by collapsing their basal spacings by the saturation of K +. The comparison of ionic strength values of solutions before and after reactions can give information on the creation of negative charges on the 2:1 layers.
World Journal of Nano Science and Engineering, 2013
The present study was carried out on the effect of acid leaching on the modification and structure alteration of montmorillonite. A nanostructured, activated material was prepared by selective leaching of pure smectite clay with different concentrations of sulfuric acid (1 -10 N/L) at 85˚C for 120 min using a solid/liquid ratio of 1:20 and a reflux system. The Fourier transform infrared (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-Ray diffraction (XRD) techniques were used for the characterization and study of the acid-treated montmorillonite clay. Chemical structure of specimens was distinguished by FTIR. The results showed that the formation of Si-OH bonds and leaching of Al 3+ ions increased progressively with severity of the acid treatment. As the FTIR studies indicated, acid treatment led to the removal of the octahedral Al 3+ cations and an increase in the Si-OH bonds. The morphological alteration of the untreated and treated montmorillonite was investigated by using TEM and SEM. X-ray fluorescence (XRF) analysis revealed a considerable decrease in the relative content of Al by increasing the acid strength. Moreover, the XRD results showed that the treatment using highly concentrated acid resulted in the formation of an amorphous silica phase.
Advances in Civil Engineering
The use of montmorillonite in the context of engineered barriers makes it possible to minimize the spread of heavy metals from industrial and even radioactive waste. An evaluation of the performance of the mechanisms controlling the clay-environment interaction and predicting the dynamics/configuration of the interlayer space (IS) is required. This work focuses on a quantitative identification of the structural changes and porosity alteration in the case of heavy metal-exchanged montmorillonite samples (Co2+ and Cd2+ cations) undergoing mechanical stresses (uniaxial oedometric test (loading/unloading)). Relationships between mechanical stress strength, intrinsic structural response, ion exchanger efficiency, and adsorption performance fate are investigated. This goal is achieved through the correlation of in situ quantitative X-ray diffraction (XRD) analysis (under an extremely controlled atmosphere reached by varying relative humidity rate %rh) and porosity investigation (assured b...
Bulletin of the Chemical Society of Ethiopia, 2021
Solid-state intercalation was applied to prepare organo-smectites using cationic surfactants and natural clays containing smectite at various surfactant/smectite ratios. The surfactants enter the interlayers of smectites causing a swelling of the clays. The used clays were collected in Siétougou and Diabari villages located in the eastern part of Burkina Faso. The solid-state intercalation was successful for all four surfactants applied, n-dodecyltrimethylammonium bromide, (n-C12H25(CH3)3NBr), n-tetradecyltrimethylammonium bromide, (n-C14H29(CH3)3NBr), n-hexadecyltrimethylammonium bromide (n-C16H33(CH3)3NBr) and di-n-dodecyldimethylammonium bromide ((n-C12H25)2(CH3)2NBr) at different levels of the cation exchange capacity (CEC). The synthesized organo-smectites were characterized regarding relative density, structural and textural properties. XRPD data showed a systematic increase of the basal spacing of the unit cell of the smectite up to >38 Å at 2.0-CEC loading of the surfact...
Desalination and Water Treatment, 2013
The clay mineral membrane is increasingly used, as a natural geological barrier, in wastewater treatment. The variation of the environmental condition (T, P, RH, etc.) induces probably several change on the materials structure. This work aims at characterizing the link between dehydration-hydration behavior, charge location, and the ionic radius, in the case of dioctahedral smectites, exchanged with Na + and Cs + cation, which are occurred from industrial waste. A natural montmorillonite and beidellite, with different charge location (respectively, dioctahedral and trioctahedral), are selected. The exchange process is directed using Na + and Cs + cations. The hydration hysteresis is investigated "in situ" as a function of relative humidity condition rates. All samples are studied using quantitative X-ray diffraction (XRD) analysis. This method allows us to determine the structural parameters obtained from the theoretical mixed layer structure used to fit experimental XRD patterns. For both Na + and/or Cs + exchangeable cations, an increase in hydration heterogeneity degree for the tetrahedral substituted smectite layer is noted and the position of exchangeable Cs + cation induce a homogeneous hydration trend which is interpreted by a new interlamellar space organization.