A detailed stratigraphic and facies reconstruction of a bentonitized acid-tuff succession, deposited within the transgressive systems tract of the Upper Miocene-Sarmatian Ser-3 eustatic cycle, at Sajóbábony, northern Hungary, was performed via petrographic, mineralogical and geochemical analyses. The purpose of the work was to analyze the degree of alteration of the volcanogenic sediments, as an indicator of the relative volcanic sedimentation rate. This may have an important role in indicating volcanic periods synchronous with sedimentation or reconstructing the volcanosedimentary paleoconditions. Sample pairs were collected from each bentonite and tuff layer, and, to facilitiate microstratigraphic relations, samples were collected every 10 cm within bentonite layers. Mineralogical analyses were performed by X-ray diffraction and geochemical analyses by inductively coupled plasma-mass spectroscopy.

The CaO/K2O and Eu/La ratios correlate with each other and with a montmorillonite/X-ray-amorphous phase ratio, reflecting Ca and Eu incorporation associated with devitrification and smectite formation. In accordance with the current literature, these mineralogical and geochemical proxies can be related primarily to the weathering processes. Considering vertical distributions in a sequence-stratigraphic context, the Ca content and Eu/La values show that local peaks and Eu anomalies characteristic of acid tuffs show minima at flooding surfaces (FS). Within a bentonite layer, representing a single transgressive period, the repeated events of dust-tuff accumulations have been determined by K2O/CaO and La/Eu peaks, confirmed also by the Eu anomalies in the rare earth element (REE) patterns, thus leading to the conclusion that the level of alteration is closely correlated with the elimination of terrigenous input and a minimum in volcanic sedimentation rate allowing more intensive alteration of the deposited volcanic material. In the case of fine tuff beds, Eu anomalies on REE patterns reflect limited alteration at the bottom and more intensive alteration in the upper parts of the beds, reflecting the effect of infiltration of sea water into the pores.

Various physicochemical characteristics of a sepiolite sample from the Eskişehir area, Turkey, were investigated to help in making predictions about possible uses of the material. The sample was examined by chemical analysis (CA), thermal analysis (DTA/TGA), X-ray diffraction (XRD) analysis, particle-size analysis (PSA), linear dilatometry (LD), scanning electron microscopy (SEM), mercury porosimetry (Hg-Por.), and low-temperature nitrogen adsorption/desorption (N2-AD) techniques. The CA and XRD data indicated that the sepiolite contains only 6% dolomite by mass. The XRD patterns showed that sepiolite anhydride, enstatite, diopside, and opal-CT form upon heating the sepiolite above 600, 800, 900, and 1200°C, respectively. The maximum rate of endothermic changes in the DTA and TGA curves were observed at 82, 287, and 491°C, corresponding to the loss of external, zeolitic, and bound water from the sepiolite, respectively. Dehydroxylation and recrystallization of the sepiolite were fastest at 845°C and 862°C, respectively. The LD curve indicated that the shrinkage began at 800°C and reached 4.0% at 1000°C. The proportion of particles with diameters of <2 µm, and the external surface area of the long-term (24 h) water-treated sepiolite were determined by PSA as 79% by volume, and 8 m2g−1, respectively. The SEM view revealed discrete bundles of sepiolite fibers of various lengths. The specific surface area found from adsorption data was 316 m2g−1. The specific micro-, meso-, macro-, and total-pore volumes obtained from the combination of Hg-Por. and N2-AD results were 0.16, 0.21, 0.45, and 0.82 cm3g−1, respectively. The average macropore and micro-mesopore radii in the sepiolite were estimated (using the Hg-Por. and N2-AD data) tobe 35 and 2.4 nm, respectively.

Palygorskite and sepiolite are fibrous clays that occur mostly in agricultural soils of arid regions. Although many investigations have examined the environmental conditions for the formation and stability of these clays, information on the transformation of these clays in the root zone (or rhizosphere) of agricultural crops is limited. In this study, changes in palygorskite and sepiolite within the rhizosphere of selected agricultural crops were determined and the ability of plants to extract Mg from these minerals compared. Alfalfa, barley, and canola were cultivated in pots under controlled conditions in a growth chamber using growth media that consisted of a mixture of Ottawa sand and clay-sized Florida palygorskite (PFl-1) or Spanish sepiolite (SepSp-1). After 100 days of cultivation, the biomass of plant roots and shoots were determined and Mg uptake measured by inductively coupled plasma analysis of the plant biomass after microwave oven digestion. The clay fraction in each pot was separated from the sand and analyzed using X-ray diffraction (XRD) and examined using transmission electron microscopy (TEM). The XRD reflection at 0.718 nm clearly indicated kaolinite in the rhizosphere after growth of the three crops. Furthermore, hexagonal kaolinite particles were observed, using TEM, and the amount of Mg extracted by the three crops was significantly greater for sepiolite than for palygorskite. Palygorskite and sepiolite kaolinization in the rhizosphere was apparently due: (1) to high acidity in the rhizosphere caused by root activity and organic matter decomposition; and (2) to fibrous clay destabilization caused by Mg uptake by plants. This study shows that kaolinite in agricultural soils of arid and semi-arid regions might be partly due to neoformation after fibrous clay dissolution and not entirely inherited from parent materials, as has been suggested in earlier literature.

Clay minerals impart important chemical properties to soils, in part, by virtue of changes in the redox state of Fe in their crystal structures. Therefore, measurement of Fe(III)/Fe(II) and partitioning of Fe(II) in different reactive sites in clay minerals (during biological and chemical Fe(III) reduction) is essential to understand their role and their relative reactivity in terms of reduction and immobilization of heavy metal contaminants such as technetium. This study had three objectives: (1) to understand the degree of dissolution of nontronite (Fe-rich smectite) as a result of chemical and biological reduction of Fe(III) in the structure; (2) to quantify partitioning of chemically and biologically produced Fe(II) into different reactive sites in reduced nontronite, including aqueous Fe2+, ammonium chloride-extractable Fe(II) (mainly from the ion-exchangeable sites, denoted as $\text{Fe}{\left(\text{II}\right)}_{{\text{NH}}_4\text{Cl}}$${\rm{Fe}}{\left( {{\rm{II}}} \right)_{{\rm{N}}{{\rm{H}}_4}{\rm{Cl}}}}$), sodium acetate-extractable Fe(II) (mainly from the surface complexation sites, denoted as Fe(II)acetate), and structural Fe(II) (denoted as Fe(II)str); and (3) to evaluate the reactivity of these Fe(II) species in terms of Tc(VII) reduction. Chemical and biological reduction of Fe(III) in nontronite (NAu-2) was performed, and reduced nontronite samples with different extents of Fe(III) reduction (1.2–71%) were prepared. The extent of reductive dissolution was measured as a function of the extent of Fe(III) reduction. Our results demonstrated that chemically and biologically produced Fe(II) in NAu-2 may be accommodated in the NAu-2 structure if the extent of Fe(III) reduction is small (< ∼30%). When the extent of reduction was >∼30%, dissolution of nontronite occurred with a corresponding decrease in crystallinity of residual nontronite. The Fe(II) produced was available for partitioning into four species: ${\text{Fe}}_{\left(\text{ab}\right)}^{2+}$${\rm{Fe}}_{\left( {{\rm{ab}}} \right)}^{2 + }$, Fe(II)acetate, $\text{Fe}{\left(\text{II}\right)}_{{\text{NH}}_4\text{Cl}}$${\rm{Fe}}{\left( {{\rm{II}}} \right)_{{\rm{N}}{{\rm{H}}_4}{\rm{Cl}}}}$, and Fe(II)str. The increase in Fe(II)acetate during the early stages of Fe(III) reduction indicated that the Fe(II) released had the greatest affinity for the surface-complexation sites, but this site had a limited capacity (∼60 µmol of Fe(II)/g of NAu-2). The subsequent increase in $\text{Fe}{\left(\text{II}\right)}_{{\text{NH}}_4\text{Cl}}$${\rm{Fe}}{\left( {{\rm{II}}} \right)_{{\rm{N}}{{\rm{H}}_4}{\rm{Cl}}}}$ indicated that the released Fe(II) partitioned into the exchangeable sites once the amount of Fe at the surface-complexation sites reached half of its maximum site capacity. The fraction of Fe(II)str decreased concomitantly, as a result of Fe(II) release from the NAu-2 structure, from 100% when the extent of Fe(III) reduction was <30% to nearly 65% when the extent of Fe(III) reduction reached 71%. The Fe(II)acetate and Fe(II)str exhibited greater reactivity in terms of Tc(VII) reduction than the $\text{Fe}{\left(\text{II}\right)}_{{\text{NH}}_4\text{Cl}}$${\rm{Fe}}{\left( {{\rm{II}}} \right)_{{\rm{N}}{{\rm{H}}_4}{\rm{Cl}}}}$. Clearly, the surface-complexed and structural Fe(II) are the desirable species when reduced clay minerals are used to reduce and immobilize soluble heavy metals in contaminated groundwater and soils. These results have important implications for understanding microbe—clay mineral interactions and heavy metal immobilization in clay-rich natural environments.

The worldwide emergence of infectious diseases, together with the increasing incidence of antibiotic-resistant bacteria, elevate the need to properly detect, prevent, and effectively treat these infections. The overuse and misuse of common antibiotics in recent decades stimulates the need to identify new inhibitory agents. Therefore, natural products like clays, that display antibacterial properties, are of particular interest.

The absorptive properties of clay minerals are well documented for healing skin and gastrointestinal ailments. However, the antibacterial properties of clays have received less scientific attention. French green clays have recently been shown to heal Buruli ulcer, a necrotic or ‘flesh-eating’ infection caused by Mycobacterium ulcerans. Assessing the antibacterial properties of these clays could provide an inexpensive treatment for Buruli ulcer and other skin infections.

Antimicrobial testing of the two clays on a broad-spectrum of bacterial pathogens showed that one clay promotes bacterial growth (possibly provoking a response from the natural immune system), while another kills bacteria or significantly inhibits bacterial growth. This paper compares the mineralogy and chemical composition of the two French green clays used in the treatment of Buruli ulcer.

Mineralogically, the two clays are dominated by 1Md illite and Fe-smectite. Comparing the chemistry of the clay minerals and exchangeable ions, we conclude that the chemistry of the clay, and the surface properties that affect pH and oxidation state, control the chemistry of the water used to moisten the clay poultices and contribute the critical antibacterial agent(s) that ultimately debilitate the bacteria.

The structural significance of micas with Na-K intermediate composition, and their chemical and structural evolution at increasing metamorphic grade have been investigated in Triassic rocks from the transition between the Maláguide and Alpujárride complexes (Internal zones of the Betic Cordillera, Spain). Micas were studied by X-ray diffraction (XRD) and by scanning and transmission electron microscopy (SEM/TEM). Three samples, belonging to the late diagenesis and to the low and medium anchizone, were selected for this study. Na-bearing mica appears as submicroscopic packets intergrown in parallel with K-mica, becoming more compositionally uniform with increasing grade. The diagenetic sample contains illite, minor paragonite, and two main populations of intermediate Na-K micas, with average compositions Ms60Prg40 and Ms35Prg65, respectively, where Ms represents muscovite and Prg, paragonite. The lattice-fringe images of mica packets with intermediate compositions suggest the presence of random mixed-layered paragonite-muscovite. Under low anchizonal conditions the amount of discrete paragonite increases and the Na-K intermediate mica has a mean composition of Ms40Prg60. The TEM images suggest that the packets with intermediate composition are solid solutions of paragonite and illite. Micas with Na-K intermediate composition are lacking in the sample with the highest metamorphic grade. In this sample, paragonite and muscovite coexist with mica, with composition intermediate between paragonite and margarite. The lattice-fringe images of these Na-Ca-bearing packets suggest that they consist of irregularly shaped domains enriched either in Na or in Ca.

Our data indicate that Na+K-bearing micas have several origins: detrital stacks of K- and Na-bearing micas coexist with authigenic phases, formed from dickite in the diagenetic, coarse-grained samples, and perhaps from smectite-bearing mixed-layers or detrital illite, in the fine-grained rocks. The changes observed at increasing metamorphic grade can be related to the influence of the lithology, the metamorphic grade, and the different geological settings. Intermediate Na-Ca mica appears to have grown from paragonite, with calcite as the source of Ca.

Stevensite-like sauconite, with the general composition: ${\text{Si}}_4\left({\text{Zn}}_{3-x}{\square }_x\right){\text{O}}_{10}{\left(\text{OH}\right)}_2{R}_{2x}^{+}$\$\end{document}, where □ is a vacant site, was synthesized. The objective was to study the possible migration of some cations (Li+ and Zn2+) within such trioctahedral smectites, under heating, following the so-called ‘Hofmann-Klemen’ (HK) effect. The initial gel was divided into five aliquots and placed in teflon-coated hydrothermal reactors with distilled water, and these were hydrothermally treated at 80, 100, 120, 150, and 200°C, respectively, over 30 days. X-ray diffraction (XRD) analysis confirmed that the samples synthesized were smectites. The number of vacant sites (x) per half unit cell (O10(OH)2) ranged from nearly 0 to 0.23 but no simple relationship was established between x and the temperature of synthesis. The samples were Li+- and Zn2+-saturated, and heated overnight at 300°C (HK treatment). Cation exchange capacity measurements were made by Fourier transform infrared spectroscopy (FTIR) on ${\text{NH}}_4^{+}$\$\end{document}-saturated samples. After LiHK treatment, the structural formula of samples could be expressed as: ${\text{Si}}_4{\text{Zn}}_{\left(3-x\right)}{\text{Li}}_x{\text{O}}_{10}{\left(\text{OH}\right)}_2{\text{NH}}_{4x}^{+}$\$\end{document}, while after ZnHK treatment, it could be expressed as: Si4Zn3O10(OH)2. Analysis by XRD and FTIR showed that the samples moved from a Zn-stevensite-like structure to Zn-talc-like structure after treatment with ZnHK. These results are interpreted asevidence that Zn2+ (and Li+) migrated into the previously vacant sites under HK treatment.

The configuration of hydroxyl groups around the octahedral cations of 2:1 phyllosilicate minerals has long been an important question in clay science. In the present study, 27Al multiple quantum (MQ) magic angle spinning nuclear magnetic resonance (MAS NMR) was applied to the local structural analysis of octahedral Al positions in a purified Na-montmorillonite. Three octahedral Al sites ([6]Ala, [6]Alb, and [6]Alc) are distinguished by 27Al 5QMAS NMR, whereas these sites are not differentiated by 27Al MAS and 3QMAS NMR. The isotropic chemical shift (δcs) and the quadrupolar product (PQ) were estimated to be 5.8 ppm and 2.6 MHz for [6]Ala, 6.2 ppm and 3.0 MHz for [6]Alb, and 6.7 ppm and 3.7 MHz for [6]Alc, respectively. The three Al sites originated from geometric isomers with cis and trans structures, which have mutually different configurations of the OH groups around the central Al3+ ions. From the view point of symmetry for the OH groups, [6]Ala and [6]Alb in the upfield region were assigned to cis sites, and [6]Alc in the downfield region was assigned to a trans site. The occurrence of multiple Al sites implies that Na-montmorillonite used in the present study has cis-vacant structure in the octahedral sheet. This is a reasonable insight, supported by the chemical composition and the differential thermal analysis data of the Na-montmorillonite.

Low-charge beidellites were synthesized by a hydrothermal treatment applied to an amorphous gel phase in basic solution. The hydrothermal conditions for the syntheses were chosen from the stability field of beidellite previously investigated in the literature. The synthetic samples were characterized chemically and structurally using X-ray diffraction, infrared spectroscopy, cation exchange capacity measurement, and chemical and thermal analyses. We compared the synthetic sample with a natural beidellite sample (SbId) from Idaho, USA, looking at chemical composition and particle size. The main difference is the octahedral site occupancy (cis- or trans-vacant layer structure). The natural SbId sample has trans-vacant layers and the synthetic sample has a preferentially cis-vacant character. This character can be modulated, using specific synthesis conditions. The cis- or trans-vacant layer structure of various synthetic beidellites was investigated at low temperature (<350°C) and pressure (<25 MPa). Depending on the pressure and/or synthesis temperature, the proportion of cis-vacant layers ranges from 20 to 100% and increases with the layer-charge deficit.

The state and dynamics of water and cations in pure and mixed Na-Cs-montmorillonite as a function of the interlayer water content were investigated in the present study, using Monte Carlo and classical, molecular-dynamics methods. While highly idealized, the simulations showed that the swelling behavior of hetero-ionic Na-Cs-montmorillonite is comparable to the swelling of a homo-ionic Na- or Cs-montmorillonite. The mixed Na-Cs-montmorillonite is characterized by intermediate interlayer distances compared to homo-ionic Na- and Cs-montmorillonites. Dry, hetero-ionic Na-Cs-montmorillonite is characterized by a symmetric sheet configuration, as is homo-ionic Cs-montmorillonite.

We found that at low degrees of hydration the absolute diffusion coefficient of Cs+ is less than for Na+, whereas at greater hydration states the diffusion coefficient of Cs+ is greaterthan for Na+. An analysis of the relative diffusion coefficients (the ratio between the diffusion coefficient of an ion in the interlayer and its diffusion coefficient in bulk water) revealed that water and Na+ are always less retarded than Cs+. With large interlayer water contents, tetralayer or more, Na+ ions preferentially form outer-sphere complexes. The mobility perpendicular to the clay surface is limited and the diffusion is equivalent to two-dimensional diffusion in bulk water. In contrast, Cs+ ions preferentially form ‘inner-sphere complexes’ at all hydration states and their two-dimensional diffusion coefficient is less than in bulk water.

The question remains unanswered as to why experimentally derived relative diffusion coefficients of Cs+ in the interlayer of clays are about 20 times less than those we obtained by classical molecular dynamics studies.

An organophilic bentonite was prepared by means of a reaction of natural Na-montmorillonite with trimethyldococylammonium which has an especially long n-alkyl chain. The addition of trimethyldococylammonium to montmorillonite was in the range 0.25–3.0 times the cation exchange capacity (CEC) of the clay (i.e. 0.23–2.82 mmol/g clay). The particle morphology in organic liquid suspensions of organoclay complexes was studied by measuring the viscosity based on Eyring’s rate process and Robinson’s relative sediment volume. In toluene, montmorillonite with 1.17 mmol/g clay trimethyldococylammonium (1.25 times the CEC) had the largest specific gel volume, relative sediment volume, and K-factor. The results of the stoichiometry for trimethyldococylammonium-montmorillonite show that practically all of the quaternary ammonium was adsorbed to montmorillonite. Maximum half widths of 001 reflections from X-ray diffraction patterns were obtained in the range 0.74–1.17 mmol/g clay, indicating a disordered arrangement of the organic cation molecules intercalated between the layers. Appreciable shifts to lower-frequency regions in the Fourier transform infrared absorption spectra as a result of CH2-stretching vibrations were observed with increasing amounts of the organic cation. When increasing the amount of organic cation added to the clay from 0.94 to 1.41 mmol/g clay, a large shift occurred to the lower-frequency side, approaching the frequency of the organic cation alone. This indicates that the interaction between adjacent hydrocarbon chains becomes progressively stronger, due to van der Waals attraction, with increases in the amount of organic cation. Interactions of the alkyl chains in trimethyldococylammonium-montmorillonite complexes with irregularly distributed and randomly arranged alkyl chains between the silicate layers were weak, and, as a result, solvation with external organic liquids occurred and gel formation developed through macroscopic swelling of the organoclay.

Samples from different depths in the Oligocene Frio formation (offshore Gulf of Mexico) were studied by X-ray diffraction (XRD), thermal analyses, and scanning electron microscopy. The experimental XRD patterns recorded from oriented and ethylene glycol (EG) solvated clay fractions of the samples were similar to those typical of random, mixed-layered illite-smectite (R0 I-S). The experimental XRD patterns recorded in air-dried (AD) and EG states were simulated using three different models. One of them corresponds to R0 I-S for which thickness and content of the interstratified layers were determined by the Środoń technique. The second model is represented by a single homogeneous I-S in which illite and smectite layers are interstratified with a tendency to segregation. The expandability of the segregated I-S model varies from 48% to 75% without any rational relationship between the smectite layer content and depth.

The third model assumes that the clay fraction is a physical mixture of smectite and an R0 I-S. In this model the I-S contains 65% illite and 35% smectite layers independent of depth, whereas the smectite content varies from 28% to 63%. This model has consistently smaller profile factors, Rp, for both EG and AD XRD scans compared with the Rp values determined for the other two models.

The mineralogical association, volcanic origin, narrow stratigraphic interval (427 m), and low maximum temperature (42°C) of the studied Frio Formation are considered. These features are completely consistent with the two-phase model and so the segregation model must be rejected. An authigenic origin of the pure smectite and an alternative detrital or authigenic origin of the R0 I-S are discussed.

Mineral chabazite has shown the unusual ability to surface template nanometal particles, especially Ag. A chabazite analog was synthesized from delaminated metakaolin. The chabazite formed retained the platy morphology of the base clay. This morphology is ideal for displaying surface-supported nanometal particles. The synthetic chabazite analog demonstrated the ability to form and support large concentrations of Ag nanoparticles, as observed in the related natural mineral. Due to greater Al content, the synthetic chabazite manifests significantly improved capacity for the formation of such Ag nanoparticles. As in the case of the mineral chabazite, surface Ag nanoparticles of high uniformity were observed in the range of 5–6 nm.

Very unusual rocks consisting of natrolite (>95 vol.%) ± pargasite (<5 vol.%) and rarealbite (<1 vol. %) have been discovered in the Kop mountain range, eastern Turkey. We propose to call these rocks ‘natrolitite’ and ‘pargasite natrolitite’. They were produced by Na Si metasomatism of dikes and stocks of diorite through replacement of the intermediate primary igneous plagioclase to produce natrolite. The metasomatic alteration produced concentric elliptical zones characterized by distinct mineral assemblages centered on intrusions of diorite. The Central Zone 1 consists of variably albitized diorite with preserved magmatic textures (albite ± andesine ± pargasite ± quartz). Transition Zone 2 comprises natrolite-bearing diorite (natrolite ± albite ± andesine ± pargasite ± calcite ± quartz). Marginal Zone 3 is a rock made up almost entirely of natrolite (natrolite ± pargasite ± albite ± calcite ± chlorite). Outer Zone 4 occurs along the boundary between the natrolitite and the surrounding serpentinite and consists of listvenite, a rock which comprises magnesite, quartz, calcite, mica, talc, and hematite, indicating a role for CO2 in the metasomatic reactions, consistent with the presence of calcite in the alteration zones. Zone 5 consists essentially of brecciated serpentinite with numerous hydrothermal quartz veins and calcite veins. Whole-rock compositions document an increase in Na2O, Al2O3, and H2O from the core (central zone) to themargin while CaO, MgO, and SiO2 decrease. Plagioclase abundance and composition also varies outwards from the central core rocks where it occurs as a primary magmatic phase (∼95 vol.% An41−38) to the alteration zones (<5 vol.% An32−37) due to partial to complete replacement of plagioclase by natrolite with or without rare albite. The natrolites exhibit little variation in Si/Al ratios, ranging between 1.45 and 1.61, and are similar in composition to those reported in the literature. Accompanying pargasitic amphibole also becomes progressively more sodic in composition from the core rocks to the marginal zone rocks. Our analysis indicates that albitization preceded the formation of natrolite and that the formation of natrolite, instead of other more typical alteration minerals (e.g. analcime and paragonite), reflects Na metasomatism at lower chemical potentials for Al2O3 and SiO2. Potential sources of Na could be hypersaline brines or leaching of country rocks, such as trondhjemites. The fluids were driven in hydrothermal convection cells set up by theintrusion of thediorites.

Feroxyhyte (δ′-FeOOH) is a relatively uncommon Fe oxide mineral and one of the few phases in the system Fe2O3-H2O for which thermodynamic properties are not known. In natural occurrences, it is always fine-grained, although samples with larger particle sizes and better crystallinity (labeled as δ-FeOOH) can be prepared in the laboratory. This contribution presents a thermochemical study on a series of feroxyhyte samples. One is fine-grained and poorly crystalline, similar to natural materials, while the other three are of better crystallinity. The enthalpy of formation of feroxyhyte at 298.15 K is −547.4±1.3kJ mol−1 for the poorly crystalline sample (surface area 88 m2/g), and −550.6±1.4, −550.9±1.3, and −552.6±1.2 kJ mol−1 for the samples with better crystallinity. The entropy of feroxyhyte can be estimated only crudely, because it is influenced to a great extent by its magnetic properties, particle size, and structural disorder. The $S_{298}^{\text{o}}$$S_{298}^{\rm{o}}$ of feroxyhyte is estimated here to be 65±5 J K−1 mol−1. The Gibbs free energy of the reaction feroxyhyte → hematite + liquid water is −7.4 to −12.6 kJ mol−1 at 298.15 K. The Gibbs free energy of formation ($\text{Δ}{G}_{\text{f}}^{\text{o}}$${\rm{\Delta }}G_{\rm{f}}^{\rm{o}}$) of the fine-grained, poorly crystalline feroxyhyte is −478.1±2.0 kJ mol−1 at 298.15 K. Since this sample is closest in its physical properties to natural feroxyhyte, this $\text{Δ}{G}_{\text{f}}^{\text{o}}$${\rm{\Delta }}G_{\rm{f}}^{\rm{o}}$ value should be used in thermodynamic modeling related to processes involving naturally occurring feroxyhyte. In terms of Gibbs free energy and enthalpy, feroxyhyte is very similar to lepidocrocite and maghemite, and, like these two phases, has no thermodynamic stability field in the system Fe2O3-H2O, except possibly at the nanoscale.

Micron-grade natural vermiculite was modified by several physical and chemical treatments in order to increase the adsorption capacity of this material for B. A thermal exfoliation (T = 600°C) of pristine material, a chemical exfoliation through reaction with hydrogen peroxide (H2O2 35%), or grafting of a specific B complexant (i.e. N-methyl-D-glucamine: NMDG) led to an increase in the uptake of B at low initial concentrations of the aqueous solutions ([B] ≈ 5 mg L−1). The more efficient material is the NMDG-grafted clay, for which the adsorption uptake is four times greater than that of raw vermiculite, and reaches 0.04 mmol g−1. For all modified materials, the effect of the pH on B adsorption and the adsorption kinetics were studied and compared to raw vermiculite. Adsorption isotherms were also plotted and fitted well with the Freundlich equation.

The present work shows the results of X-ray diffraction (XRD), Fourier transform infrared (FTIR), and thermal analysis of untreated (RMnt) and acid-treated red mud (RMa), a bauxite ore-processing waste, exchanged with Pb2+, Cd2+, and Zn2+ cations. These studies were performed in order to investigate the changes in the sorbent structure caused by the exchange with metals of different ionic radii.

The XRD pattern of RMnt, analyzed according to the Rietveld method, showed a mixture of eight different phases. However, just three phases made up 78 wt.% of the RMnt: cancrinite (33 wt.%), hematite (29 wt.%), and sodalite (16 wt.%). X-ray diffraction patterns of RMnt exchanged with Pb2+ and Cd2+ cations revealed two additional phases, namely hydrocerussite [Pb3(CO3)2(OH)2 (10 wt.%))] and octavite [CdCO3 (8 wt.%)].

These two phases probably originated from the carbonate precipitation processes which were due to the decarbonation of cancrinite. Hydrocerussite and octavite were not found in the case of acid-treated red mud samples.

In the FTIR spectra, the introduction of cations caused a distinct shift to higher wavenumbers in the peak at ∼1100 cm−1, which is attributed to the asymmetric stretch of Si-O-Al. This effect may be associated with the Pb2+, Cd2+, and Zn2+ adsorbed by the red muds which caused a deformation of the initial structure.

Thermal analysis data of the red mud samples were obtained by thermogravimetric/differential thermogravimetric analysis, and these methods were employed to evaluate the desorption behavior of water and to clarify the thermal stability of the chemical phases of the different red mud samples. The loss of metal-bound water in the red mud samples was found to depend on the size of non-framework cations and water loss consistently followed the order: Zn2+>Cd2+>Pb2+.

Late Miocene (Messinian) alluvial and lacustrine deposits characterize the so-called Kızılbayır Formation of the Aktoprak Basin (central Turkey) and consist of conglomerate, sandstone, mudstone, limestone, marl, and dolomite units. These sediments are composed mainly of feldspar, quartz, hornblende, diopside, olivine, serpentine, calcite, and dolomite with subordinate palygorskite, chlorite, smectite, and illite. Studies by scanning electron microscopy indicate that calcite and dolomite show both meniscus and micrite-sparite-type cements, characteristic of both vadose and phreatic zones. Chlorite, smectite, and illite are products of the alteration of the underlying Güney Formation with subsequent transportation by local streams into the Kızılbayır Formation, and therefore these are considered to be reworked materials. Authigenic palygorskite and dolomite formed as a result of the calcretion of mudstone-carbonate units under alkaline conditions, with high Si, Ca, and Mg activity, and low Al, originated from ophiolitic and carbonate units based on the increase in Ni and Co. The paragenesis and textural features of the minerals of the alluvial fan and lacustrine sediments determined in the study area indicate that precipitation probably occurred due to climate fluctuations ranging from arid and semi-arid to wet conditions.

Quantitative analysis of the smectite-to-illite and illite-to-muscovite transformations indicates that 17–28 wt.% SiO2 and 17–23 wt.% SiO2, respectively, are liberated during these reactions, assuming that Al is conserved. Dissolution of quartz silt in shales yields up to 6–9% SiO2 in the range up to 200°C and a further 10–15% SiO2 in the 200–500°C range. For muds altered to shales at 200°C, 14–20 wt.% silica is evolved. From 200 to 500°C, a further 18–28 wt.% silica is evolved. Additional small amounts of silica may be released in the alteration of feldspar to clay and by stylolitization of quartz silt. Thus, in the burial and temperature range of diagenesis into the epizone, major quantities of silica are released from clays and by quartz dissolution in shales. Within this range of alteration, concomitant decline of whole-rock Si/Al (SiO2/Al2O3) in the transformation of smectite to illite to muscovite suggests the liberated silica migrates from the source shale. As a result, the metamorphosed shales are more micaceous and less quartzose than their progenitor muds. In the diagenetic zone and anchizone, the evolved silica is probably a major source of quartz cement in sandstones. In the epizone, evolved silica is commonly present in quartz veins in the parent rocks. Fluid-inclusion temperatures in quartz overgrowths and fracture fillings in some sandstones suggest that some cements may have been derived from downdip basinal shales and pressure solution in sandstones.

The preparation of porous materials from clay minerals by selective leaching is of interest because it yields residues with large specific surface areas that can be used as adsorbents of contaminants or as catalysts. Grinding produces surface modifications and therefore may significantly influence the leaching behavior. The aim of this paper is to study the effect of grinding and leaching on the structure of the vermiculite from Santa Olalla, Spain, using 57Fe Mössbauer spectroscopy, X-ray diffraction, infrared spectroscopy, and specific surface area (SBET) measurements. The study shows that grinding destroys the long range order of the vermiculite, but leaves the local structure in the environment of the Fe atoms intact, at least up to a grinding time of 10 min. The Mössbauer study shows that there is no Fe3+ in the tetrahedral sheets and that grinding does not lead to a significant oxidation of the structural Fe. Vermiculite ground for 4 min and leached with 1 M HCl solution at 80°C over a 24 h period was decomposed to X-ray amorphous silica with a very large specific surface area (SBET = 720 m2g−1) and with total pore volume of 0.586 cm3 g−1, whereas an unground sample leached with the same acid concentration yielded a specific surface area of only 504 m2 g−1. Most of the Mg2+ and Al3+ are removed from the ground sample after leaching with 1 M HCl, while large percentages of Fe2O3 remain with the X-ray amorphous silica. In unground vermiculite leached with 1 M HCl, a considerable amount of vermiculite remains in the residue. A sample ground for 4 min and treated with 0.25 M HCl also shows the typical vermiculite Mössbauer spectrum with an Fe2+/Fe3+ ratio similar to that of the unground vermiculite. The samples ground for 2 or 4 min and treated with 1 M HCl solution have an orange color and, according to the Mössbauer spectra, only Fe3+ remains. Mössbauer spectra of these samples taken at 4.2 K reveal the presence of akaganéite.