A magnetic composite was prepared by wet-impregnating a powder of a natural zeolite with a magnetic Fe oxide-containing synthetic material. Both starting materials were first characterized with X-ray diffraction, scanning electron microscopy, Mössbauer spectroscopy, and by isoelectric-point using vibrating-sample magnetometry. The synthetic Fe oxide-containing material was characterized as a mixture of magnetite (Fe3O4) and goethite (α-FeOOH). From the Fe Mössbauer analysis, the relative subspectral area for magnetite corresponds to 93(2)%; the remaining spectrum is assignable to goethite. After the impregnation process, magnetite was still identified in the composite material as a magnetic layer surrounding the zeolite particles; no magnetically ordered goethite could be detected. The Mössbauer pattern for this sample indicates a much more complex structure than for the precursor material, based on Fe oxides, with some more altered magnetite and an intense central doublet of (super)paramagnetic Fe3+, probably due to small Fe (hydr)oxides and/or to a residual contribution of Fe-bearing species from the starting zeolite material. The composite preparation procedure also promoted the change of the characteristic A-type zeolite to mordenite. The resulting magnetic composite presented a magnetic coercivity of as much as 0.140 A m−1, at 77 K. The final composite is now being evaluated as an adsorbent: results to date confirm that this novel magnetic material may have applications in the remediation of contaminated water bodies.

Layered double hydroxides (LDHs) are layered ion exchangers, with a large surface-charge density, which react easily with organic anions. Various types of organics are rapidly substituted in the interlayer space of inorganic precursor LDHs. ZnAl-LDHs were intercalated with 1- to 19-carbon monocarboxylic acid anions by anion exchange of NO3-saturated LDH precursor phases in order to study the dependence of exchange reactions on synthesis parameters (temperature, pH, and interlayer anion). The carboxylic acid anion-LDHs synthesized were characterized using X-ray diffraction, infrared spectroscopy, thermal analysis, scanning electron microscopy, chemical analysis, and N2 adsorption. Carboxylic anion quantities in excess of the LDH anion exchange capacity easily replaced exchangeable nitrate anions at moderate pH. The intercalated LDH interlayer space depended on the alkyl chain length and orientation (inclination angle) of thecarboxylic-acid anion. Thelatticeparameter c0 ranged from 3.4 to 13.5 nm, but the a0 lattice parameter remained constant at 0.31 nm. Crystallographic analyses indicated a monomolecular arrangement of intercalated short-chain fatty-acid anions. At pH < 7, intercalated long-chain carboxylates showed a preferred bimolecular interlayer orientation. Carboxylic-acid anion exchange with LDHs at pH 7 resulted in the formation of two different sets of basal spacings, which indicated the coexistence of LDHs intercalated with monomolecular and bimolecular arrangements of interlayer carboxylic compounds.

Thermal treatment of the carboxylic acid anion-intercalated LDHs indicated stability up to ~140ºC. The release of interlayer water led to distortion of the crystallographic units and resulted in smaller basal spacings without collapse of the layered structure. Heat treatment re-oriented alkyl-chain carbon carboxylates (with >10 carbons) to a more upright interlayer position.

Shales and claystones in the Permian Irati Formation consist of Al-rich or Fe-Mg clay minerals in its southern/central and northern parts, respectively. The constrasting compositions indicate particular geological and paleo-environmental conditions. The purpose of this study was to determine the conditions of formation by characterizing the black shales and claystones from different sections of the northern edge of the basin, some of which reveal the presence of intruded diabase sills.

Black shales consist of saponite or saponite-talc mixed layers, talc, lizardite, nontronite, and quartz. Green claystones are nontronite-rich but also contain lizardite, talc, and quartz. The chemical compositions of the black shale and claystones, except for one sample (POR-56), exhibit a positive correlation of the TiO2, Cr, and P2O5 contents with Al2O3, which typically results from weathering processes. The presence of saponite, nontronite, and some accessory minerals (spinel, pyroxene, native silver) suggests altered basic-ultrabasic rocks as sediment sources, consistent with the rare earth element (REE) composition being less than the Post-Archean Average Shale (PAAS) or North American Shale Composite (NASC) levels and with negative Ce and Eu anomalies. Sample POR-56 consists largely of nontronite and is anomalously rich in zircon, monazite, and apatite. Chemically, sample POR-56 is different from the black shales and claystones, being richer in Al2O3-Fe2O3, MgO-poor, and having greater REE contents than the PAAS or NASC standards. The POR-56 bed is probably a bentonite resulting from the alteration of volcanic ash in sea water (strong, negative Ce anomaly). The Zr/TiO2vs. Nb/Y relation indicates that the magmatism was andesitic. During the Upper Permian, intermediate to basic volcanic activity was recorded in the Mitu Group of the Central Andes.

Close to the diabase sill, the black shales and claystones contain saponite, talc, and lizardite but nontronite is absent. Saponite and talc crystals, however, exhibit a larger coherent scattering domain size (CSDS) and are randomly oriented with respect to the sedimentary bedding. The thermal metamorphism effect is confirmed by the presence of secondary enstatite-augite and albite crystals.

The current study demonstrates how co-existing zeolite and clay minerals formed by the alteration of tephra in a closed-basin lacustrine and lake-margin environment can retain the overall composition of the original bulk tephra for many elements, even when diagenetic conditions and resulting authigenic mineral assemblages change. Zeolite and clay minerals co-exist in the closed-basin, saline-alkaline lacustrine altered tephra of Pleistocene Olduvai Gorge, Tanzania, and their diagenetic histories can be reconstructed using variations in their textures and compositions. The authigenic minerals in the altered tephra of the Olduvai paleolake form a classic ‘bull’s-eye’ pattern, with clay-dominated tephra in the distal lake margin, chabazite and phillipsite in the proximal margin, and phillipsite ± K-feldspar in the intermittently dry lake and lake center. Fifteen representative samples of altered volcanic ash lapilli (designated Tuff IF) were analyzed by X-ray diffraction (XRD), X-ray fluorescence (XRF), electron probe microanalysis (EPMA), and scanning electron microscopy (SEM) to determine their authigenic mineral assemblages and bulk compositions, and to texturally and compositionally compare their clay mineral and zeolite components.

Textural observations indicate that clay minerals formed first, followed by zeolites and finally feldspars. Clay minerals, however, persist even in the most altered samples. The overall composition of Tuff IF shows only limited change in Fe, Si, Al, and Na between fresh, clay-altered, and zeolite-dominated diagenetic environments, despite significant differences in authigenic assemblage. Where zeolites dominate the assemblage, the remaining clay minerals are rich in Mg, Fe, and Ti, elements that are not readily incorporated in zeolite structures. Where clay minerals dominate, they are more Al-rich. A ‘mixing model’ combining clay-mineral and zeolite compositions yields a close approximation of the original volcanic glass for most elements (exceptions including Mg, Ca, and K). This initial composition was preserved in part by the redistribution of elements between co-existing clay minerals and zeolites.

The Antalya Unit, one of the allochthonous units of the Tauride belt, is of critical, regional tectonic importance because of the presence of rifting remnants related to the break-up of the northern margin of Gondwana during Triassic time. Paleozoic — Mesozoic sedimentary rocks of the Antalya Unit consist mainly of calcite, dolomite, quartz, feldspar, and phyllosilicate (illite-smectite, smectite, kaolinite, chlorite, illite, chlorite-smectite, and chlorite-vermiculite) minerals. Illite-smectite (I-S) was found in all of the sequences from Cambrian to Cretaceous, but smectite was only identified in Late Triassic-Cretaceous sediments. R0 I-S occurs exclusively in early-diagenetic Triassic—Cretaceous units of the Alakırçay Nappe (rift sediments), whereas R3 I-S is present in late-diagenetic to low-anchimetamorphic Cambrian—Early Triassic units of the Tahtalıdağ Nappe (pre-rift sediments). Kübler Index (KI) values and the illite content of I-S reflect increasing diagenetic grades along with increasing depth. Major-element, trace-element, rare-earth-element (REE), and stable-isotope (O and H) compositions were investigated in dioctahedral and trioctahedral smectites and I-S samples from the pre-rift and rift-related formations. Both total layer charge and interlayer K increase, whereas tetrahedral Si and interlayer Ca decrease from smectite to R3 I-S. Trace-element and REE concentrations of the I-S are greater in pre-rift sediments than in rift sediments, except for P, Eu, Ni, Cu, Zn, and Bi. On the basis of North American Shale Composite (NASC)-normalized values, the REE patterns of I-S in the pre-rift and rift sediments are clearly separate and distinct. Oxygen (δ18O) and hydrogen (δD) values relative to SMOW (Standard Mean Oceanic Water) of smectite and I-S reflect supergene conditions, with decreasing δ18O but increasing δD values with increasing diagenetic grade. Lower dD values for these I-S samples are characteristic of rift sediments, and pre-rift sediments have greater values. On the basis of isotopic data from these I-S samples, the diagenesis of the Antalya Unit possibly occurred under a high geothermal gradient (>35ºC/km), perhaps originating under typical extensional-basin conditions with high heat flow. The geochemical findings from I-S and smectites were controlled by diagenetic grade and can be used as an additional tool for understanding the basin maturity along with mineralogical data.

Disposal facilities in deep geological formations are considered to be a possible solution for long-term management of high-level nuclear waste (HLW). The design of the repository generally consists of a multiple-barrier system including Fe-based canisters and a clay backfill material. The Fe-clay system will undergo a thermal gradient in time and space, the heat source being the HLW inside the canisters. In the present paper, the effect of a thermal gradient in space on Fe-smectite interactions was investigated. For this purpose, a tube-in-tube experimental device was developed and an 80–300ºC thermal gradient was applied to a mixture of MX80 bentonite, metallic Fe (powder and plate), magnetite, and fluid over periods of 1 to 10 months. Transformed and newly formed clay minerals were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and Mössbauer spectroscopy. The main mineralogical transformations were similar to those described for batch experiments: smectite was destabilized into an Fe-enriched trioctahedral smectite and Fe-serpentine or chlorite as a function of the experimental conditions. Newly formed clay was observed all along the walls of the gold tube. Their crystal chemistry was clearly different from the clays observed in the hot and cold part of the tubes. The thermal diffusion of elements was also observed, especially that of Mg, which migrated toward the hottest parts of the tubes. In the end, the thermal gradient affected the redox equilibria; more reduced conditions were observed in the hotter parts of the tubes.

Much attention has been paid to the adsorption of Fe(II) onto mineral surfaces as it is a crucial step in enhancing the reductive activity of Fe(II) species. The present study elucidates the role of Fe(II) adsorbed on Fe (oxyhydr)oxides (γ-FeOOH, α-FeOOH, and α-Fe2O3) for the reductive transformation of 2-nitrophenol (2-NP), using cyclic voltammetry (CV). Studies of Fe(II) adsorption and 2-NP reduction kinetics showed that an increase in pH gave rise to an elevated density of adsorbed Fe(II) on mineral surfaces, which further resulted in an enhanced reaction rate of 2-NP reduction. In addition, CV tests showed that the enhanced activity of Fe(II) species is attributed to the negative shift of peak oxidation potential (EP) of the Fe(III)/Fe(II) couple. The dependence of adsorbed Fe(II) reactivity on pH values was proven by the three linear correlations obtained (ln k vs. pH, EPvs. pH, and ln k vs. EP). The present study demonstrated that the reductive activity of adsorbed Fe(II) species can be indicated by the EP value of active Fe(II) species. Moreover, the electrochemical approach can be used as an effective tool to study the reductive activity of adsorbed Fe(II) species in subsurface environments.

The source and temporal changes of minerals transported by the world's large rivers are important. In particular, clay minerals are important in evaluating the maturity of suspended sediments, weathering intensity, and source area. To examine seasonal changes in mineralogical compositions of the Changjiang River (CR), suspended particulate matter (SPM) samples were collected monthly for two hydrological cycles in Nanjing city and then were studied using X-ray diffraction (XRD), diffuse reflectance spectrophotometry (DRS), X-ray fluorescence spectrometry (XRF), and chemical analyses. The results indicate that the concentration of CR SPM ranges from 11.3 to 152 mg/L and is highly correlated to the rate of water discharge, with a greater concentration in flood season and lower concentrations during the dry season. CaO, MgO, and Na2O increase with increasing discharge whereas Al2O3 decreases sharply with increasing discharge. Dolomite, calcite, and plagioclase show strikingly similar seasonal variations and increase with increasing discharge with maximum concentrations in the flood season. In contrast, the clay mineral content exhibits the opposite trend with the lowest concentrations in the flood season. Illite dominates the clay minerals of the CR SPM, followed by chlorite, kaolinite, and smectite. Illite and kaolinite show distinctly seasonal variations; SPM contains more illite and less kaolinite during the flood season than during the dry season. The illite chemistry index and crystallinity, as well as kaolinite/illite ratio, all indicate intense physical erosion in the CR basin during the rainy season. Total iron (FeT) and highly reactive iron (FeHR) concentrations display slight seasonal changes with the smallest values observed during the flood season. Goethite is the dominant Fe oxide mineral phase in the CR SPM and hematite is a minor component, as revealed by DRS analyses. The FeT flux and FeHR flux are 2.786×106 T/y and 1.196×106 T/y, respectively.

Allophane is a very fine-grained clay mineral which is especially common in Andosols. Its importance in soils derives from its large reactive surface area. Owing to its short-range order, allophane cannot be quantified by powder X-ray diffraction (XRD) directly. It is commonly dissolved from the soil by applying extraction methods. In the present study the standard extraction method (oxalate) was judged to be unsuitable for the quantification of allophane in a soil/clay deposit from Ecuador, probably because of the large allophane content (>60 wt.%). This standard extraction method systematically underestimated the allophane content but the weakness was less pronounced in samples with small allophane contents. In the case of allophane-rich materials, the Rietveld XRD technique, using an internal standard to determine the sum of X-ray amorphous phases, is recommended if appropriate structural models are available for the other phases present in the sample. The allophane (+imogolite) content is measured by subtracting the amount of oxalate-soluble phases (e.g. ferrihydrite). No correction would be required if oxalate-soluble Fe were incorporated in the allophane structure. The present study, however, provides no evidence for this hypothesis. Mössbauer and scanning electron microscopy investigations indicate that goethite and poorly ordered hematite are the dominant Fe minerals and occur as very fine grains (or coatings) being dispersed in the cloud-like allophane aggregates.

Allophane is known to adsorb appreciable amounts of water, depending on ambient conditions. The mass fraction of the sample attributed to this mineral thus changes accordingly; the choice of a reference hydration state is, therefore, a fundamental factor in the quantification of allophane in a sample. Results from the present study revealed that (1) drying at 105ºC produced a suitable reference state, and (2) water adsorption has no effect on quantification by XRD analysis.

The arguments of Nieto et al. (2010) in favor of the incorporation of H3O+ rather than H2O in interlayer positions of illite are disputable. Stoichiometric arguments suggest that the excess water in the Silver Hill illite is in the form of H2O. Moreover, recent thermodynamic models assuming the incorporation of interlayer H2O in illite provide reasonable estimates of temperature and water content using the AEM/TEM analyses of Nieto et al. (2010).

The arguments of Vidal et al. (2010) against the incorporation of H3O+ rather than of H2O in the interlayer position of illite are disputable. Stoichiometric arguments do indeed suggest that the excess water in the Silver Hill illite is in the formof H3O+. No reason exists to assume less water content in the IMt-2 sample than in those determined by Hower and Mowatt (1966) and confirmed by the thermogravimetric analyses of Nieto et al. (2010). The comparison between element contents calculated from end-members and those from the structural formula in figure 1 of Vidal et al. (2010) is not an experimental result, but rather a trivial mathematical artifact. The fact that thermodynamic models, based on the incorporation of interlayer H2O in illite, may provide reasonable estimates neither proves nor disproves the presence of H3O+; this is because thermodynamics is a non-atomistic, macroscopic approach.

In the paper ‘Porosity evolution of free and confined bentonites during interlayer hydration” from Clays and Clay Minerals, vol. 58, (2010), 399–414