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This work aims to contribute to the interpretation of soil colors; mainly to identify the pigments that generate the greenish colors in hydromorphic conditions (gley colors) in vertisols of the coastal plain of the Río de la Plata estuary. These colors are of cold hues, generally greenish (olive-gray), and occur in poorly drained soils with prolonged water accumulation. For this purpose, samples of Bssg horizons of hydromorphic vertisols from the coastal plain of the Río de la Plata estuary were analyzed using routine and chemical analyses, Mössbauer spectroscopy, determination of rocks magnetic parameters, X-ray diffraction, thermogravimetric and differential thermal analysis and petrographic-electronic microscopy. The pigments associated with the gley colors of these soils are mainly due to ferric iron content, corresponding to minerals such as ferric iron-rich smectites (nontronite/Fe-rich beidellite) and oxy-hydroxides like goethite, which colors range from green to yellow. These minerals, combined with gray or black components, e.g., manganese compounds and/or organic matter, contribute to the generation of the usual gley colors in the analyzed soils of the Pampean plain. The obtained data allows us to state that it is a mistake to assing the olive color in hydromorphic soils to the presence of ferrous iron compounds, as it is traditionally done. The oxidizing condition of iron is dominant in all the analyzed samples, integrating the composition of ferric iron-rich clay minerals and oxy-hydroxides (goethite). [ABSTRACT FROM AUTHOR]

In the adsorption process, the adsorbent structure and its interaction with wastewater are the main determinant of the process efficiency. For this reason, the correct selection of the production conditions for the produced adsorbents is critical. In this study, the reaction time and the concentration of acid, oxidant, substrate, and monomer were selected as independent variables which effect the structure of the polyaniline based composite material. These production variables of polyaniline/beidellite (PANI/BEI) composites were designed by response surface methodology (RSM). According to RSM, 46 different PANI/BEI composites were synthesized and were used as an adsorbent in the removal of acid yellow 194. Thus, the optimum PANI/BEI production conditions were determined. After the identification of the optimum PANI/BEI production conditions, the effect of adsorption conditions such as pH, mixing time, and dye concentration were studied by batch experiments. The maximum adsorption capacity was obtained as 123 (mg g−1) at the T = 25 °C, t = 24 h, pH 3, ms = 0.15 g adsorbent, Vs = 50 ml dye solution, and ω = 200 rpm. The results presented in this study revealed that the central composite design is a suitable method to optimize the production conditions of PANI/BEI and the prepared PANI/BEI composites has an important potential as an adsorbent for the removal of metal-complex dyes such as AY194. In addition, the polymerization of aniline and the removal of dye were confirmed by different analytical techniques such as BET, XRD, SEM, and EDAX. [ABSTRACT FROM AUTHOR]

The paper reports data obtained in the course of a comprehensive physicochemical study of Li-tosudite, a mixed-layer mineral from hydrothermally altered rocks in western Chukotka, Russia, whose formula was reliably established. The enthalpy of formation of Li-tosudite from Chukotka, Ca0.15(Li0.9Mg0.2Al6.0)[Si6.4Al1.6O20](OH)10 ⋅ 3.3H2O, from elements was experimentally determined by melt solution calorimetry in a high-temperature Calvet microcalorimeter: ΔfHelo(298.15 К) = -15087 ± 26 kJ/mol. The standard entropy and Gibbs free energy of formation of this mineral were evaluated. [ABSTRACT FROM AUTHOR]

Smectites are clay minerals of interest due to their natural availability, extraordinary surface properties, and high swelling capacity in the presence of water. The behaviour of smectites and other layered phyllosilicates is largely affected by the appearance of isomorphous substitutions with a lower nuclear charge in their layer structures. These substitutions are the origin of negative net layer charge, and their distribution in the mineral layer impacts on the electrostatic properties of the mineral surfaces. The present density functional theory study shows that octahedral Mg(II) and tetrahedral Al(III) substitutions in aluminium-rich dioctahedral smectites tend to avoid each other and disperse in the layer structure. This behaviour is explained and demonstrated to originate from geometry deformations around the substitutions which are larger than the unsubstituted species. [ABSTRACT FROM AUTHOR]

The surfaces of natural beidellite clay were modified with cationic surfactant, tetradecyltrimethylammonium bromide, at different concentrations. The organo-beidellites were analysed using thermogravimetric analysis which shows four thermal oxidation/decomposition steps. The first step of mass loss is observed from room temperature to 130 °C due to the dehydration of adsorbed water. The second step of mass loss between 130 and 400 °C is attributed to the oxidation step of the intercalated organic surfactant with the formation of charcoal. The third mass loss happens between 400 and 500 °C which is assigned to the loss of hydroxyl groups on the edge of clays and the further oxidation step of charcoal. The fourth step is ascribed to the loss of structural OH units as well as the final oxidation/decomposition step of charcoal which takes place between 500 and 700 °C. Thermogravimetric analysis has proven to be a useful tool for estimating loaded surfactant amount. [ABSTRACT FROM AUTHOR]

Beidellite, a low-cost, locally available and natural mineral was used as an adsorbent for the removal of lead and cadmium ions from aqueous solutions in batch experiments. The kinetics of adsorption process was tested for the pseudo first-order, pseudo second-order reaction and intra-particle diffusion models. The rate constants of adsorption for all these kinetic models were calculated. Comparison amongst the models showed that the sorption kinetics was best described by the pseudo second-order model. Langmuir and Freundlich isotherm models were applied to the experimental equilibrium data for different temperatures. The adsorption capacities ( Q°) of beidellite for lead and cadmium ions were calculated from the Langmuir isotherm. It was found that adsorption capacity was in the range of 83.3–86.9 for lead and 42–45.6 mg/g for cadmium at different temperatures. Thermodynamic studies showed that the metal uptake reaction by beidellite was endothermic in nature. Binary metal adsorption studies were also conducted to investigate the interactions and competitive effects in binary adsorption process. Based on the optimum parameters found, beidellite can be used as adsorbent for metal removal processes. [ABSTRACT FROM AUTHOR]

This study is focused on the basic mineralogical and chemical characteristics of some selected samples from Jianping (JP) and Ningcheng (NC) area, China. These were studied using X-ray diffraction (XRD), expandability, Greene-Kelly test, specific surface area, cation exchange capacity (CEC), differential thermal analysis (DTA), and chemical analysis. The bulk samples consist of mainly montmorillonites along with appreciable amounts of cristobalite and with small amounts of quartz, feldspar and calcite. The basal spacings of montmorillonites in all these examined samples show at about 1.5 nm, indicating that predominant cations were divalent. Mean crystallite thickness of the present sample lies from 0.449 to 0.710 nm (4.58-7.24 layers). As Greene-Kelly test, samples from Ningcheng area confirmed appreciable amount of beidellite component but samples from Jianping area did not contain anything about it. Surface area of samples varies from 671 to 766 m g depending on the amounts of impurities. Analyzed CEC ranges from 70.30 to 82.75 meq 100g in < 2 μm size samples. The DTA curves are considered abnormal type. Samples from Ningcheng area show relatively higher amount of SiO than those from Jianping area, possibly due to difference of parent rock type. Trace element (Y, Nb, Ce and Zr) data are plotted on acidic to intermediate composition. It is apparent that no large chemical transfer would have been necessary during alteration. [ABSTRACT FROM AUTHOR]

Beidellite was used as an adsorbent for the removal of copper ions from aqueous solutions. Batch mode studies were carried out by varying initial copper (II) concentrations (50–500 mg/l), initial pH (2.0–5.0), adsorbent particle size (0.095–0.890 mm) and temperature (293–333 K). A contact time of 60 min was required to reach equilibrium. Adsorption of the metal ion was highly pH dependent and the optimum pH for the removal was 5.0 at which the removal was maximum (25.3 mg/g). The result showed that the amount adsorbed of the metal ion increased with increasing initial copper (II) concentration and contact time. Three adsorption kinetic models, the pseudo first-order, second-order and intraparticle diffusion were applied to experimental data to predict the adsorption rate constants. A comparison of kinetic models on the overall adsorption rate showed that metal ion/adsorbent system was best described by the pseudo second-order rate model. The adsorption capacity ( Q o) calculated from the Langmuir isotherm was 71.07 mg/g for at pH 5.0, 293 K for the particle size of 0.095–0.890 mm. The experimental data yielded excellent fits with Langmuir isotherm equation. Different thermodynamic parameters viz., changes in standard free energy, enthalpy and entropy were evaluated and it was found that the reaction was spontaneous and endothermic in nature. [ABSTRACT FROM AUTHOR]

Molecular mechanics simulations, combined with X-ray powder diffraction and infrared spectroscopy, have been used in structure analysis of montmorillonite and beidellite intercalated with tetramethylammonium cations. A complex structure analysis provided us with the detailed structure model, including characterization of the disorder, the total sublimation energy and a charge distribution in the structure of intercalates. The calculated basal spacings (14.36 Å for TMA-montmorillonite and 14.12 Å for TMA-beidellite) are in good agreement with the experimental values (14.31 Å for TMA-montmorillonite and 14.147 Å for TMA-beidellite). Both intercalated structures exhibit positional and orientational disorder in the arrangement of TMA cations, and consequently disorder in layer-stacking. In the present work we analyse the effect of octahedral and tetrahedral substitutions in a 2:1 silicate layer on the arrangement of tetramethylammonium (TMA) cations in the interlayer space of montmorillonite and beidellite. The most significant difference between TMA-montmorillonite and TMA-beidellite is in the charge distribution on the TMA cations and silicate layer. The TMA-beidellite structure is highly polarized, the total charge on one TMA cation is +0.167 e−, while the total charge on the TMA cation in montmorillonite is +0.050 e−. [ABSTRACT FROM AUTHOR]

The mechanochemical adsorption of phenol by laponite, saponite, montmorillonite, beidellite and vermiculite was studied by simultaneous DTA and TG analysis. Fitting of the DTA curves showed four endothermic peaks in the r.t. −250°C temperature range. The first peak represents the melting of the excess crystalline phenol. The second peak represents the evolution of water. The third peak represents the boiling of the free phenol. The fourth peak represents the evolution of adsorbed phenol. In the DTA curves of montmorillonite the fourth peak is not observed as a separate peak but as part of the third peak. Laponite, saponite and montmorillonite show a very small exothermic effect which follows the endothermic events. Iaponite adsorbs the greatest amounts of phenol and shows a strong exothermic peak at 390°C. None of the other clays show this exothermic effect at this temperature. [ABSTRACT FROM AUTHOR]

The swelling properties of Al-pillared clays, obtained from five different smectites, were studied using X-ray diffraction. These clays, the dioctahedral beidellite and montmorillonite and the trioctahedral saponite, hectorite and laponite differ in source of isomorphic substitution and represent a series of decreasing basicity along the siloxane plane. An Al oxyhydroxy cation was inserted between the layers to form the respective pillared clays and these clays were heated incrementally to 600°C. The XRD peaks at each stage of heating were recorded as well as the same samples subsequently wetted. Basal spacings of each clay at each stage of dehydration ↭d rehydration indicated that the swelling of tetrahedrally substituted saponite and beidellite was indeed restricted, compared with the other three clays. This was attributed to greater basicity of the oxygen plane of beidellite and saponite due to tetrahedral substitution of Si by Al, resulting in an increase in the strength of hydrogen bonds between either water or the interlayer polyhydroxy cation and the clay. The data from the XRD analyses helped in addition, to clarify the thermal transformations of the Keggin ion itself. According to the changes in the d-spacings of the pillared clays it was concluded that the Keggin ion lost its structural water at ∼200°C and dehydroxylated in a range beginning at 350°C. Between 500 to 600°C this polymer cation, which is thought to form the Al2O3 oxide, did not rehydrate. [ABSTRACT FROM AUTHOR]

It is established that use of ash material within ceramic compositions based on beidellite clay makes it possible to prepare heat insulation objects with improved thermotechnical properties. [ABSTRACT FROM AUTHOR]

Heat and mass transfer is studied during firing of ceramic heat insulation objects making it possible to monitor firing taking account of a change in the effective thermal properties of an object, manufactured using burnt rocks, in the temperature range of physicochemical transformations, and also to determine rational firing regimes. It is revealed that the least value for the coefficient of effective thermal conductivity for the material corresponds to a temperature range within which the intensity of physicochemical processes is more significant. [ABSTRACT FROM AUTHOR]