To control a vast spectrum of applications and processes, an understanding of the morphologies of clay mineral assemblies dispersed in aqueous or non-aqueous media is important. As such, the objective of this study was to verify the relationship between dispersion medium type and the size and morphology of the clay aggregates that are formed, which can increase knowledge on the assembly formation process. Scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier-transform infrared (FTIR) spectroscopy were used in an attempt to describe kaolinite platelet organization in non-aqueous media and to compare it to the organization in aqueous media or in media with or without a selection of dissolved organic polymers. The SEM images indicated that the kaolinite platelet assembly process occurs during slow evaporation of the solvent. Because the experimental procedure was rigorously identical for all cases in this study, the SEM images compared how the effects of various media and environments on kaolinite platelet interactions can lead to different morphologies. Quite spectacular morphological differences were indeed observed between samples dispersed in aqueous and non-aqueous media, particularly when the kaolinite platelets were dispersed in an organic solvent with dissolved organic polymers. For kaolinite dispersed in water, only small aggregates were observed after slow evaporation. In contrast, large kaolinite booklets or vermiform aggregates were formed by slow solvent evaporation when kaolinite was first dispersed into some organic solvents. The aggregates were particularly large when an organic polymer was dissolved in the organic solvent. For example, kaolinite aggregates dispersed in a binary cyclohexane/toluene mixture with dissolved ethyl cellulose (EC) had top apparent surface areas (i.e. stacking length × width) of more than 3,000 µm2. Other dissolved polymers, such as polystyrene or the polysaccharide, guar gum, gave similar results. Kaolinite platelet aggregation resulted from face-to-face interactions as well as edge-to-face and edge-to-edge interactions. The XRD results showed that ethyl cellulose led to the formation of smaller kaolinite platelets with an increased tendency to form larger aggregates, which is due to the ability of EC to chemically interact with silanol and/or the aluminol groups of kaolinite.

A more controllable method to synthesize particular zeolites from geopolymers is needed in order to effectively use these materials in industrial applications. In the present study, a well-crystallized zeolite P1 was synthesized from a metakaolin-based geopolymer (SiO2/Al2O3=3.2) using a hydrothermal method. The products obtained by hydrothermal treatment were identified using X-ray diffraction (XRD), scanning electron microscopy (SEM), and specific surface areas. The XRD patterns and SEM micrographs indicated that the structure and morphology of zeolite P1 could be controlled by the NaOH solution concentration, hydrothermal temperature, and the hydrothermal treatment time. The crystalline structure of the prepared zeolite P1 was refined using the Rietveld method and the crystal structure parameters were as follows: a = 10.01 Å, b = 10.01 Å and c = 10.03 Å. The optimal hydrothermal conditions to form zeolite P1 were 24 h at a hydrothermal temperature of 100°C and 2.0 M NaOH solution. Moreover, the synthesized zeolite P1 had a specific surface area of 36.56 m2/g.

Fe-rich smectite is ubiquitous in soil environments and closely linked to the fate and mobility of hazardous trace metals and particularly to the variations in the biogeochemical redox reactions of structural Fe that determine the sorption and desorption properties of clay minerals. The biotic/abiotic redox reactions of a Fe-rich smectite, nontronite (NAu-1), were performed at various reaction times using the Fe-reducing bacterium Shewanella oneidensis MR-1 at 30°C and Na-dithionite (Na2S2O4), respectively. The extent of biotic Fe-reduction of NAu-1 after 30 days of incubation reached up to 10.7% of total Fe and the range of abiotic Fe-reduction varied from 4.9–46.6% at reaction times of 5 min, 30 min, 1 h, and 4 h. The biotically and abiotically Fe-reduced NAu-1 samples were spiked with Pb concentrations of 0.07, 0.2, 0.5, and 1.0 mg/kg and incubated under aerobic or anaerobic conditions for 24 h.

The amounts of Pb in the supernatants were analyzed using an Inductively Coupled Plasma Mass Spectrometer (ICP-MS) and Multi-collector (MC)-ICP-MS. The amounts of Pb removed from the supernatants were negatively related to the extent of Fe(III) reduction in the abiotically Fe-reduced NAu-1 samples. In contrast, less Pb (~15%) was removed from the biotically Fe-reduced NAu-1 samples with a similar extent of Fe(III) reduction. Changes in the isotopic 208/204Pb ratio indicated that the lighter 204Pb isotope was preferentially adsorbed to the NAu-1 samples with less Fe reduction and indicated that variations in the net layer charge affected isotopic fractionation. Significant differences in the 208/204Pb ratios for NAu-1 samples that were biotically Fe-reduced under anaerobic conditions were measured and indicate that the reversibility of the structural/chemical modifications that occur under redox conditions can affect Pb removal and, thus, isotope fractionation. These results collectively infer that the biogeochemical properties of clay minerals should be considered in order to understand the fate of trace metals in natural environments.

The radiogenic isotope systematics of clay minerals are complex because of the intimate mixture of minerals from different origins such as detrital and authigenic sources. An important aspect of dating clays is the primary sample preparation and disintegration method. In the present study, a sample of weakly deformed Opalinus claystone from the Mont Terri underground site (Switzerland) was investigated after disintegration by three different methods. The Opalinus Clay was sedimented in the late Toarcian and early Aalenian and reached maximum temperatures of ~85°C during burial in the Cretaceous. The present study reports data from a comprehensive investigation comparing the effects of disintegration by: (1) disc milling; (2) repeated freezing and thawing; and (3) high-voltage discharges. K-Ar age values of the finest clay (<0.1 µm) released by the different disintegration methods are indistinguishable, indicating that the high-voltage liberation method does not influence grains as small as 100 nm. The K-Ar age values of particle-size separates decreased with decreasing particle size. The age values of the 2–6 µm separates correspond to the Carboniferous Period, which reflects the dominance of Paleozoic detritus in that size range. The age values of the smallest separates (<0.1 µm), on average 213 ± 4 Ma, exceed the numerical age of the formation (~177−172 Ma), which show predominance of detrital grains over authigenic grains even in the finest illite. In summary, isotope geochronology data suggest that the high-voltage method can be applied reliably for disintegrating claystones.

The removal of Co2+, Ni2+, and Pb2+ from aqueous solutions using a modified zeolite was investigated because of the need to eliminate toxic contaminants from wastewaters. In the present study the ways in which equilibrium, thermodynamics, and kinetics parameters affected the removal of heavy metals were evaluated and compared. An Iranian clinoptilolite with a Si/Al ratio of 6.5 was used as an adsorbent. In order to increase the adsorption capacity of the adsorbent, it was converted to a manganese oxide-coated zeolite (MOCZeo) using various Mn solutions. The initial concentration of metals, pH, contact time, and temperature were the variables studied and optimal conditions were established. The maximum amount of Co2+, Ni2+, AND Pb2+ adsorption on MOCZeo was ascertained. A thermodynamics study, using ΔG, ΔH, and ΔS state functions showed that adsorption of Pb2+ was more spontaneous than that of Co2+, Ni2+ ions. The adsorption of these ions on MOCZeo was an endothermic reaction. Investigation of the adsorption models revealed that the adsorption of Pb2+, Co2+, and Ni2+ on MOCZeo followed both the Langmuir and Freundlich models. Kinetics studies showed that the adsorption of Pb2+, Co2+, and Ni2+ on MOCZeo followed the pseudo-second order kinetics model with a high correlation coefficient.

In recent years KAlSiO4 polymorphs have become minerals of interest from an industrial point of view; they have various applications in technological and medical fields. The costs of synthesis processes are often significant and so, in the present study, an attempt was made to develop a new synthesis protocol using a widely available and inexpensive, natural starting material. The KAlSiO4 polymorphs synthesized here were kalsilite and KAlSiO4-01 — 01 refers to the high-temperature polymorph of KAlSiO4 (Cook et al., 1997; Gregorkiewitz et al., 2008; Kremenovic et al., 2013). KAlSiO4 polymorphs were synthesized using kaolin; the effects of time and temperature on the synthesis process were investigated. A solid-state synthesis protocol was developed which required the mixing of the calcined kaolin with K2CO3 in stoichiometric proportions at temperatures of 700 and 800°C at atmospheric pressure. Crystallization of kalsilite at 700°C was demonstrated while that of KAlSiO4-01 was revealed at 800°C. Synthetic kaliophilite H2 was found in both of the experiments as a metastable phase. The products of synthesis were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), inductively coupled plasma optical emission spectrometry (ICP-OES), infrared spectroscopy (IR), and 29Si magic-angle spinning solid-state nuclear magnetic resonance spectroscopy (29Si MAS NMR). Calculation of cell parameters (through Rietveld refinement) and the density and specific surface area of the phases synthesized was also achieved. The amount of amorphous phase in the synthesis powders was estimated by means of quantitative phase analysis using the combined Rietveld and reference intensity ratio methods. In particular, the results of the spectroscopic, chemical, and morphological characterizations are in agreement with the data available for these minerals in the literature, thus confirming the effectiveness of the experimental protocol. The quantitative phase analysis (QPA) also indicated the high purity of the powders synthesized, thus allowing for industrial applications.

The Reynolds Cup (RC) is a unique round-robin competition that was established by The Clay Minerals Society in 2000 to assess the level of precision and accuracy that is attainable for the mineralogical analysis of a wide range of complex clay-rich materials. Although the Reynolds Cup roundrobin allows any possible analysis methods, X-ray diffraction (XRD) is by far the most frequently used technique. It is not only used to identify components, but also for quantitative phase analysis (QPA). QPA means determination of the relative concentrations of the coexisting phases in a mixture, commonly as a weight percent (wt.%) or mass fraction. Several approaches allow a quantitative determination of mineral contents, such as the Rietveld method (Rietveld, 1967). The successful application of the Rietveld method for QPA requires that all components are correctly identified and that the component diffraction patterns are appropriately described, which is preferably based on structure. In addition, the quality of a Rietveld quantification also depends on suitable sample preparation and measurement conditions, as well as a correct description of instrument configurations. Results from all previous Reynolds Cup contests show that a successful quantification depends strongly on the skill of users. Although the refinement procedure itself is automatic and, therefore, user independent, the results are strongly influenced by the structural models and refinable parameters that are selected and on the limitations of those parameters. Selected examples for the successful application of Rietveld refinement as well as the limitations of the method will be discussed in this article. The goal of the present work was to demonstrate that the Rietveld method is in principle capable of quantifying all Reynolds Cup samples with a high degree of accuracy, but sample specific difficulties and analysts’ inexperience may impede successful application. Incorrect results are often not indicated simply by low residuals or good fits. All refinement results should be validated and corrected using supplementary techniques, even if the results appear acceptable.

Hydrophobicity, swellability, and dispersion are important properties for organo-montmorillonites (OMnt) and have yet to be fully characterized for all OMnt configurations. The purpose of the present work was to examine the preparation of OMnt from the reaction of Ca2+-montmorillonite (Ca2+-Mnt) with a high concentration of surfactant and to reveal the relevant properties of hydrophobicity and dispersion of the resultant OMnt. A series of OMnt samples were prepared using a small amount of water and cetyltrimethylammonium bromide (CTAB) with a concentration more than the CTAB critical micelle concentration (CMC). The relationship between OMnt microstructure and the hydrophobicity and swellability properties was investigated in detail. The resulting OMnt samples were characterized using powder X-ray diffraction patterns (XRD), Fourier-transform infrared (FTIR) spectroscopy, thermogravimetric and differential thermogravimetry (TG-DTG), water contact angle tests, swelling indices, and transmission electron microscopy (TEM). The addition of CTAB and water in the OMnt preparation affected the OMnt microstructure and properties. An increase in CTAB concentration led to a more ordered arrangement of cetyltrimethylammonium (CTA+) cations in the interlayer space of the OMnt and a large amount of CTA+ cations on the outer surfaces of the OMnt. The swelling indices and the water contact angles of OMnt samples depended on the distribution of the CTAB surfactant on OMnt and the orientation of the surfactant hydrophilic groups on the inner and on the outer surfaces of OMnt. A maximum swelling index of 39 mL/g in xylene was achieved with an average water contact angle of 62.0° ± 2.0° when the amount of CTAB added was 2 times the cation exchange capacity (CEC) of Mnt and the lowest water to dry Mnt mass ratio was 3 during the preparation of OMnt samples. The platelets of OMnt aggregated together in xylene by electrostatic attraction and by hydrophobic interactions.

Nuclear magnetic resonance (NMR) provides a powerful tool to describe local nuclear environments. In this work, unique structural information on kaolinite and on kaolinite dimethylsulfoxide (DMSO) intercalate were provided by solid-state 1H and 27Al magic-angle spinning (MAS) NMR. The interlayer chemistry of kaolinite (K) was examined by intercalating a select group of highly polar organic molecules or salts into kaolinite as a first step. Once the interlayer space is expanded, the intercalated compounds can be replaced in a second step. Intercalating DMSO into kaolinite to form the DMSO-K intercalate is, thus, a particularly useful first step toward the intercalation of a large variety of molecules, including polymers and ionic liquids. Well developed characterization methods are essential to define the structural modifications of kaolinite, and MAS NMR is a useful complement to other techniques. The use of 1H and 27Al MAS NMR for this purpose has been relatively rare. 1H NMR, nevertheless, can give unique information about kaolinite hydroxyls. Because quadrupolar interactions are sensitive to the local octahedral Al(III) geometry, solid-state 27Al NMR can follow subtle structural modifications in the octahedral sheet. In the present work, the 1H MAS NMR chemical shifts of KGa-1b were unambiguously attributed to the internal surface hydroxyls at 2.7 ppm and to the internal hydroxyls at 1.7 ppm. The 1H MAS NMR chemical shifts of the two methyl groups in DMSO-K are not equivalent and can be attributed to the 2.9 and 4.2 ppm peaks. The 27Al MAS NMR spectra of KGa-1b obtained under different magnetic fields revealed that most of the quadrupolar effects were highly reduced at 21.1 T, whereas the spectra at lower field, 4.7 T, were dominated by quadrupolar effects. The two octahedral Al(III) sites are not equivalent and can be distinguished in the low-field spectral simulation. Increased quadrupolar constants were observed and showed the major perturbations of the local Al symmetry that resulted from DMSO intercalation. Both the 1H and 27Al MAS NMR studies at different magnetic fields afforded important information about the local environments of the kaolinite hydroxyl groups and structural Al(III).

Shales have undergone a complex burial diagenesis that involved a severe modification of the pore structure. Reconstituted shales can provide new insights into the nature of the pore structure in natural materials. The effects of diagenesis on the microfabric, pore size distribution, and porosity of Opalinus shale were measured by comparing the behavior of natural and reconstituted specimens. The parent material (Opalinus shale) was reconstituted through multiple grinding operations, sedimentation from a dispersed slurry, and one-dimensional isothermal consolidation. This process produced uniform specimens that were not cemented and had replicable microfabric and engineering properties. The microfabric and mineralogy of the materials were examined using high-resolution scanning/backscattered electron microscopy (SEM/BSEM) and energy-dispersive X-ray spectroscopy (EDS) for specimens with broken and milled surfaces. Mercury intrusion porosimetry (MIP) and N2 adsorption were used to assess the pore size distributions and specific surface areas of the materials. The microstructure of natural shale was characterized to be highly heterogeneous with significant concentrations of calcareous microfossils, calcite, and quartz particles embedded within the clay matrix. The microfossils were observed to be locally infilled and rimmed by a calcite cement that showed evidence of dissolution. The reconstituted specimens showed a double-structure microfabric that evolved with the level of consolidation stress and converged into a single-structure material (comparable to the natural shale) at a consolidation stress of more than twice the estimated maximum in situ effective stress. The natural shale had a lower specific surface area in comparison to the reconstituted material, which was consolidated at large effective stresses. These differences can be attributed to cementation at a submicron pore scale and highlight chemical diagenesis effects that were not replicated in the reconstituted specimens.

The objective of this study was to explore the geological origin of glauconite, which is believed to precipitate and mature very slowly (~1 Myr) in neritic environments (shallow water, oceanic coastal zones, at water depths of 100–200 m) with very low sedimentation rates. A series of simulation experiments was designed and carried out in sealed tubes placed in an oven and heated to a constant temperature of 50°C (±2°C) for 60 or 150 d. The parent materials used for these experiments were two low-Fe montmorillonites with different crystallinities. The montmorillonites were introduced to solutions with concentrations of 0.02–0.1 mol/L Fe3+ and 0.05–0.2 mol/L K+ with various values of pH and Eh. The products were analyzed using X-ray powder diffraction (XRD), Fourier-transform infrared (FTIR) spectrometry, electron spin resonance (ESR) spectrometry, scanning electron microscopy (SEM), and Mössbauer spectroscopy. The morphological changes from parent material to product were observed under SEM, which revealed the formation of a flaky mineral (e.g. a product formed in the interstitial spaces between montmorillonite crystals). The formation of a flaky mineral indicates that the product is a layer silicate. Qualitative analysis of XRD patterns revealed that the main product phase was a mica group mineral and the d060 value was consistent with the presence of glauconite (0.152 nm) and/or Fe-illite (0.150 nm). A glauconite and Fe-illite mineral assemblage formed in a weakly acidic solution, while Fe-illite, mixed-layer Fe-illite, and montmorillonite formed in neutral and alkaline solutions. Stretching vibrations of Fe(III)Fe(III)OH-AlFe(II)OH and/or MgFe(III)OH were observed in FTIR spectra (3550–3562 cm−1) of the products formed in acidic solutions, which along with the g = 1.978 ESR signal indicated that Fe(III) entered octahedral positions in the tetrahedral/octahedral/tetrahedral layer (TOT) platelets. The AlFe(II)OH-MgFe(III)OH (3550–3562 cm−1) and AlFe(III)OH (870 cm−1) vibrations were only observed in products formed in neutral and alkaline solutions. Analysis of the Mössbauer spectra showed that Fe(III) substituted for Al and Mg in the cis octahedral sites of montmorillonite. The simulation experiments demonstrated that the pH and redox conditions (Eh) of the environment controlled the nature of the product mineral species. Results of the present study revealed that glauconitization and illitization occurred under different conditions, where glauconitization preferentially occurred in an acidic environment and illitization preferentially occurred in a nearly neutral to alkaline environment.