Fe-rich kaolinites were synthesized at 225°C in distilled water from gels with different Fe/Al ratios (0.15, 0.25, 0.35) and with Si/(Al + Fe) = 2. X-ray diffraction patterns of the reaction products showed that kaolinite was the only long-range crystalline phase synthesized. Analytical electron microscopy analyses of individual particles and Fourier transform infrared spectra indicated that Fe3+ was isomorphously incorporated into the kaolinite octahedral sheet and that tetrahedral substitution did not occur. The Fe content hosted in the synthetic kaolinites was similar to that incorporated into its corresponding starting gel. The highest Fe content in the particles reached 30 mol.% of the octahedral occupancy. Increases in the b parameter are proportional to increases in Fe for Al substitution. The extent of isomorphic substitution of Al by Fe is the highest ever reported for both natural and synthetic samples. At the nano-scale, there is no evidence of discontinuity in the solid-solution between the Si2Al2O7 and Si2Al1.4Fe0.6O7 end-members, such as short-range disorder or clustering of Fe and Al in domains.

The synthesis of a Mg2+-Al3+-SO2−4-hydrotalcite-type compound from the acid wastewaters of the aluminum-anodizing industry has been studied as a possible means of recovering the unused Al resource materials as a useful mineral. The synthesis has been carried out from wastewaters of different concentrations (from 6.7 g Al/L to 134 mg Al/L) using the method of precipitation at constant pH, proving that all of them are suitable for such a process. The mineral was characterized using X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetric analysis, differential thermal analysis and chemical analysis, all of which indicated characteristics typical of the desired compound. Almost 100% of the Al initially present in the wastewater solutions is recovered in the form of the Mg2+-Al3+-SO42−-hydrotalcite-type compound.

Synthesis of the Li-Al-Fe layered double hydroxides was performed by the coprecipitation method at constant pH (11.0±0.2) and temperature (40±2°C). Structural features of the as-synthesized samples were investigated by X-ray diffraction (XRD), infrared (IR) spectroscopy, scanning electron microscopy and Mössbauer spectroscopy. The samples consisted of well crystallized [LiFexAl2-x(OH)6]2CO3·nH2O phases with strict ordering of M+ and M3+ cations in the sheets. However, only a proportion of Al3+ could be substituted by Fe3+ ions. The excess Fe3+ cations formed a separate ferrihydrite phase. Incorporation of Fe into the hydrotalcite-like structure resulted in an increase in the a lattice parameter determined by XRD. In addition, a shift of IR absorption bands, ascribed to the stretching vibrations of interlayer CO32− anions as well as the transitional motions of oxygen in the layers, to lower frequencies was observed. The presence of Fe3+ in the octahedral sheets caused a splitting of the band assigned to the stretching vibrations of the layer OH groups. Mössbauer experiments revealed that Fe exists in the synthesized samples in two different chemical environments. A proportion of the Fe3+ cations is incorporated as isolated ions in the [LiFexAl2-x(OH)6]2CO3.nH2O crystal structure. However, Fe3+ ions forming the ferrihydrite phase are dominant in the Fe-rich materials.

The present work deals with the synthesis of Na-A zeolite using 10 Å halloysite (collected near Grosseto, Italy) as the starting material, instead of the more expensive chemicals currently used in industry (Na aluminates and Na silicates). The process of synthesizing Na-A zeolite from 10 Å halloysite is rather simple as the reaction of halloysite with alkali occurs very readily and is achieved without prior thermal activation at high temperature. The optimal conditions of crystallization of Na-A zeolite from 10 Å halloysite are reached at 80°C. At lower temperatures, transformation of halloysite into an amorphous material requires more time, and the field within which Na-A zeolite exists overlaps that of 7 Å halloysite, G and HS zeolites. The products of synthesis at 80°C were characterized by X-ray diffraction, scanning electron microscopy, inductively coupled plasma optical emission spectrometry and infrared spectroscopy. We also propose a model to study the reaction kinetics of zeolite (Na-A and HS) nucleation and growth by real-time X-ray powder diffraction data.

Smectites are considered to be an important component in backfill barriers due to their marked swelling and high cation exchange capacity. Both properties are affected considerably when these clays transform under natural conditions. However, we have recently described a chemical interaction between high-activity radionuclide simulators and smectites which could prove to be effective at immobilizing radionuclides definitively. Investigating the efficiency of this mechanism, independent of bentonite ageing, is a challenge. For this purpose, the reactivity shown by a non-expandable layered aluminosilicate, muscovite, has been compared to that shown by an expandable one, beidellite. Both samples were treated hydrothermally with a solution of lutetium nitrate, and the transformations were studied by X-ray diffraction, nuclear magnetic resonance and scanning electron microscopy/energy dispersive X-ray analysis. Lutetium cations react with the silicon framework of both 2:1 layered aluminosilicates under hydrothermal conditions, and new phases, lutetium disilicate, kaolinite, boehmite and natrosilite are generated. The results demonstrate that the efficiency of the chemical mechanism is not determined by the swelling and the cation exchange capacity of 2:1 layered aluminosilicates. Thus, the rare earth disilicate formation might account for the success of the clay barrier, once bentonite has lost its swelling and cation exchange capacity.

To better predict the fate and mobility of surfactants in the environment, sorption and desorption of a nonionic polyoxyethylene lauryl ether surfactant (Brij 35) by two smectites (Wyoming montmorillonite and Panther Creek smectite) and two interstratified mica-vermiculites (IMVs) were investigated by batch techniques, X-ray diffraction, and infrared spectroscopy. Maximum surfactant sorption by smectites ranged from 196 to 256 g kg−1, whereas the maximum sorption by the IMVs was indeterminate over the range of concentrations employed. Sorption by smectites was best described by the Langmuir model, but sorption by the IMVs showed an S-shaped isotherm, suggesting that cooperative sorption occurred. The surfactant was more readily desorbed from the IMVs than from the smectites in an initial wash with water. After two water washes, 65–75% of the initially sorbed surfactant was retained by the smectite, and 44–51% of the surfactant sorbed to the IMVs remained with the solid phase. In this study, basal spacing of the smectites increased to ≈17.5 Å near the sorption maximum, suggesting intercalation of surfactant molecules in the interlamellar regions of the clay. X-ray data also suggested that the surfactant molecules were oriented horizontally in the interlayer spaces. Greater surfactant sorption by the Casmectites gradually diminished the intensity of the 1630 cm−1 infrared band dues to hydration water, indicating that some water had been displaced by the surfactant. The surfactant was also sorbed by the IMV clays, but only on external surfaces and probably via interactions of micelles with the solid phase.

Traditionally, land subsidence resulting from groundwater over-pumping has often been described by the theory of consolidation. The mechanism of land subsidence due to the dehydration of clay minerals has not been well addressed. Therefore, this study develops a smectite dehydration model to describe the effect of the release of water from the smectite interlayer upon land subsidence. Using a thermodynamic solid-solution model and laboratory studies of clay-water systems, a complete description of the dehydration relationships among the swelling pressure, basal spacing and mw/mc in a Na-smectite water system at 25°C under variable pressure conditions was derived. Accordingly, the evaluation model of the ‘hydration state of smectite’, and the ‘solid-solution model of smectite dehydration’ were formulated rigorously. These two models were applied to quantify the effects of smectite dehydration on the accumulated land subsidence in the Yun Lin offshore industrial infrastructure complex and in the Tai-Shi area. The result reveals that smectite dehydration is of importance in assessing and predicting land subsidence in a shallow sedimentary basin.

Seven sedimentary bentonite deposits were investigated in the Miocene series of the Pannonian Basin. The following stratigraphic and genetic characteristics were significant: (1) all deposits were formed within a transgressive series of a given Miocene sequence; and (2) it is possible that the source material of the bentonites is rhyolitic, confirmed by radiometric data proving simultaneous rhyolite tuff volcanism.

A detailed investigation on three lithologically different bentonite horizons within the same transgressive series was made at Sajoábaábony to determine the source material and to determine the causes of the differences. X-ray diffraction, differential thermal analysis and geochemical data of the different lithological types show that they all have rhyolitic source material, although in the case of the lowermost horizon the existence of reworked material from an underlying andesite tuff series is also presumed. The main difference is the degree of weathering. Considering the ratio between the amorphous phase and the montmorillonite, the amorphous volcanic glass can be regarded as the main source of the montmorillonite formation. The differences in the degree of alteration can be related to the changing characteristics of the tuff accumulation and the sedimentation. Transgression decreases the sedimentation rate allowing the optimal alteration of the amorphous phase. The increasing intensity of the tuff accumulation can also limit the bentonite formation because rapid deposition and burial present too little time for the optimal alteration of the amorphous phase.

Summarizing the results from the stratigraphic interpretation of the bentonite deposits and from the comparative analyses of the different bentonite horizons within the same transgressive systems tract, we can state that the relationship of the tectonic-related tuff accumulation and the eustasy-related sedimentation rate can affect both the possibility of bentonite formation in macro-scale and the degree of bentonitization in micro-scale.

The transformation process between palygorskite and smectite was studied by examining the morphological and structural relationships between these two minerals in an assemblage from the Meigs Member of the Hawthorne Formation, southern Georgia. Studied samples were related to an alteration horizon with a tan clay unit above and a blue clay unit below. Atomic force microscopy (AFM) and transmission electron microscopy (TEM) were used to study the mechanism of transformation.

From AFM data, both clay units contain euhedral palygorskite fibers. Many fibers are found as parallel intergrowths joined along the [010] direction to form ‘raft-like’ bundles. Degraded fibers, which are common in the tan clay, have a distinctly segmented morphology, suggesting a dissolution texture. Many of the altered palygorskite fibers in the tan clay exhibit an oriented overgrowth of another mineral phase, presumably smectite, displaying a platy morphology. This latter mineral forms along the length of the palygorskite crystals with an interface parallel to {010} of the palygorskite. The resulting grain structures have an elongate ‘wing-like’ morphology.

Imaging by TEM of tan clay material shows smectite lattice-fringe lines intergrown with 2:1 layer ribbon modules (polysomes) of the palygorskite. These features indicate an epitaxial overgrowth of smectite on palygorskite and illustrate the structural relationship between platy overgrowths on fibers observed in AFM data. The epitaxial relationship is described as {010} [001] palygorskite ‖ {010} [001] smectite.

Energy dispersive spectroscopy indicates that the smectite is ferrian montmorillonite. Polysomes of palygorskite fibers involved in these textures commonly vary and polysome widths are consistent with double tetrahedral chains (10.4 Å), triple tetrahedral chains (14.8 Å), quadruple tetrahedral chains (21.7 Å) and quintuple tetrahedral chains (24.5 Å).

The transformation of palygorskite to smectite and the resulting intergrowths will cause variations in bulk physical properties of palygorskite-rich clays. The observation of this transformation in natural samples suggests that this transformation mechanism may be responsible for the lower abundance of palygorskite in Mesozoic and older sediments.

A pseudomorphous aggregate after titanite composed of smectite, anatase and residual titanite of composition (Ca0.98,Mn0.02)(Ti0.65,Al0.35)[SiO4](O0.65,OH0.35), from a depth of 450 m in the Broken Hill South Mine, New South Wales, Australia, was investigated by electron microscopy and microanalysis to characterize the alteration products and the mobility of Ti. Examination of the pseudomorph showed randomly oriented anatase crystals dispersed throughout a matrix of beidellite, with 9% porosity. Around the periphery and along the (110) cleavage plane of titanite, alteration was most developed. The range of Ti mobility was found to be limited to ~500 nm, and the ratio between the average diameter of anatase crystals and the average distance between them is ≈1.3. This ratio is consistent with an alteration process in which Ti is conserved and the anatase crystals grow from the Ti available immediately around them. It is unlikely that Ti migrated beyond the titanite pseudomorph.