Zeolite ZSM-5 was synthesized successfully, in situ, on pyrokaolin microspheres (PKM) under hydrothermal conditions, without the use of an organic amine template. The utility of alkali-modified pyrokaolin microspheres (AMKM) was also evaluated. The resulting products were characterized using X-ray diffraction, scanning electron microscopy (SEM) and N2-adsorption isotherm data. The material containing ZSM-5 synthesized from the system PKM-additional silica-water had a large surface area and pore volume with significant enhancements in the micropore surface area and micropore volume. The SEM images show that the synthesis of zeolite ZSM-5 from pyrokaolin microspheres (PKM) led to the formation of polycrystalline aggregates <2 μm in size. The purity of the zeolite ZSM-5 produced was affected by both the pH value of the reactant system and the reaction temperature. In the system containing AMKM-additional silica-water, very little of the synthesized zeolite resided on the kaolin microspheres.

Adsorption of the polycation chitosan on montmorillonite was studied at different pH values from 4.5 to 6.5 and at temperatures of 25, 50 and 75ºC. The amount of chitosan adsorbed increased with temperature, indicating that temperature is a decisive factor. At pH 5.0 and 25ºC the amount adsorbed was 1.18 molc kg–1, whereas it was 1.5 times higher (1.79 molc kg–1) at 75ºC. The uptake of chitosan increased significantly at higher pH. This can be attributed to the decrease in the degree of protonation. Surface charge and X-ray diffraction measurements indicate that most of the chitosan is adsorbed in the interlayer, where mono- and bilayer structures are formed.

The kinetics of chitosan adsorption also depend on temperature and pH. At ⩾ 50ºC, the adsorption mechanism of chitosan on montmorillonite is closest to the intraparticle diffusion model, whereas at lower temperature (25ºC) the adsorption process is closer to the pseudo-second order model. The pH of the solution affects the protonation degree of chitosan and the mode of adsorption on montmorillonite, but not the adsorption rate.

For chitosan-montmorillonite prepared at pH 5.0 and 75ºC, the effective anion exchange capacity (AEC) was found to be 80% (0.36 molc kg–1) of the calculated value. The relatively large AEC and the location of most of the anion exchange sites in the interlayer make chitosan-montmorillonite an interesting prospect as an adsorbent for water-purification procedures.

The Capim Kaolin District (eastern Brazilian Amazon), is one of the largest kaolin deposits in the world; with the kaolin used mainly for paper coating. The kaolin developed at the expense of Cretaceous sandy-clayey sediments of the Ipixuna formation, through intense lateritization from the Mesozoic to Cenozoic times.

This work describes the morphological, mineralogical, crystallochemical and geochemical evolution of the Capim kaolin facies. Based on the profile analysis in the open pit fronts, it encompasses X-ray diffraction, thin-section optical analysis, EDS-assisted scanning electron microscopy and transmission electron microscopy, chemical analysis, infrared and Mössbauer spectroscopies.

Six facies were defined as different stages of the supergene process. Ferruginization led to a thick duricrust on the soft kaolin, which in turn evolved from sandy-clayey sediments of the Ipixuna Formation. A subsequent deferruginization event degraded the duricrust, resulting in the flint kaolin facies.

Smectite formation in a vertisol developed from a granitic parent rock in the Kaélé region of Cameroon in a tropical, dry climate was studied by means of X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), chemical analyses, cation exchange capacity (CEC) and low temperature gas adsorption. The soil profile comprises three horizons (from base to top): (1) a saprolite, (2) an intermediate horizon, and (3) an upper dark grey horizon. In the saprolite, the progressive alteration of feldspars gave rise to the exclusive neoformation of beidellite exhibiting a typical honeycomb fabric. This process resulted in Al, Fe, Ca, Mg, Ti and Mn enrichment, a depletion of Si and Na and a significant negative Eu anomaly. In the upper horizons, beidellite evolves and is transformed into montmorillonite and kaolinite, probably through a series of smectite-kaolinite mixed layers. This transformation, from the saprolite to the upper horizons, causes the observed decrease in the CEC and the increase in specific surface area and mesoporosity of the clay. The REE patterns of the bulk soil and clay fraction display similar behaviour, indicating that the three horizons, and hence the clay minerals, have a common source in the underlying granite. Mass-balance calculations show that the intense weathering of the granite leads to a mass reduction of ~80–90%.

This study is located on the bentonite outcrop of ‘El Toril’ (Cabo de Gata, Almeria, Spain), where acid solutions have resulted in an alteration front that has caused physical, chemical and mineralogical changes in the bentonite material. The main objective is to assess these changes and to draw a model of evolution of this front in the outcrop. The most important chemical and mineralogical changes observed consist mainly of the loss of mass in the bentonite, the formation of kaolinite, the precipitation of jarosite and alunite from leachates and important changes in the rare earth element distribution pattern. No sulphurs have been identified in the pyroclastic rock at the top of the outcrop, but the presence of dissolution marks and the high concentrations of As, Pb and V in the rock overlying the bentonite point towards the existence, in principle, of these sulphurs and suggest that meteoric alteration is mainly responsible for the genesis of the outcrop.

A geochemical and mineralogical study has allowed us to address the factors controlling distribution pattern, residence and behaviour of rare earth elements (REE) during kaolinization of Variscan granitoids in NW Spain. Mineral composition of the deeply weathered samples is dominated by kaolinite, with minor amounts of quartz, muscovite-illite, alkaline feldspar and traces of resistant minerals (rutile, ilmenite, zircon and monazite). Variable amounts of Si, Na, Ca, K, Rb, Cs, Ba, U and P were lost from the weathering profile, as a result of feldspars, mica and apatite breakdown, whereas Al, Fe, Ti, Zr, Th, Hf and REE were concentrated in the residual kaolin. Chondrite-normalized REE patterns of the kaolins show an overall enrichment of light REE (LaN/SmN = 1.22–2.53), heavy REE depletion (GdN/YbN = 2.42–15.10) and a strong negative Eu anomaly (Eu/Eu* = 0.11–0.25), probably inherited from the parent granite. Nevertheless, the normalization to the parent granite reveals some REE fractionation and increasing positive Eu anomalies with advancing weathering, in response to the breakdown of feldspars. Different grain-size fractions show similar REE distribution patterns, but differ in concentration levels. Although the fine fractions are the most important REE reservoir, there is no positive correlation with clay mineralogy. The correlative behaviour among P2O5, Th and REE in the <2 mm fraction suggests that monazite plays a dominant role controlling the REE budget in the weathering profile.

Metamorphic grade, palaeothermal history and the influence of tectonic strain on clay minerals and organic matter transformation were studied in the eastern part of the Teplá-Barrandian unit in the Czech Republic. The metamorphic grade of pelitic sediments ranges from the lower anchizone (IC ~0.30–0.36Δº2θ) to the lowermost epizone (IC ~0.24–0.26Δº2θ). Increase in metamorphic grade is paralleled by the development of anastomosing cleavage and lenticular quartz grains in the anchizone which give way to slaty cleavage and dynamically recrystallized ribbon quartz grains in the lower epizone. White mica in highly strained rocks generally has greater IC values whereas chlorite displays reduced values in deformed and cleaved samples. The organic matter dispersed in the sediments represents a complex assemblage of highly matured particles of uncertain origin, pyrobitumen and ‘transitional matter’. The reflectance of organic fragments generally varies from 3.1% to 7.7% of Rmax which suggests anthracite to meta-anthracite rank progrades to semigraphite in higher-grade samples, although the overall link between Rmax and IC values is weak, if present at all. Newly formed shear-induced graphite appears abruptly near the anchizone-epizone boundary and correlates with the onset of plastic deformation and dynamic recrystallization of quartz grains in the host sediments.

Maximum metamorphic temperatures within the Neoproterozoic sequence in the range of 250–350ºC were attained during the Cadomian (Pan-African) orogeny at 540–550 Ma. Apatite fission-track analysis reveals a subsequent decrease in rock temperature over the period 340–350 Ma that persisted throughout the late Palaeozoic. The most recent episode of accelerated cooling occurred between 20 and 40 Ma, corresponding with the regional uplift of the Bohemian Massif due to the Alpine orogeny.

A mixed-layer illite-smectite, illite-rich calcareous mudstone intruded by a basaltic dyke at the Perthus Pass (southern Massif Central, France) allows us to study the transformation of clays subjected to a brief thermal gradient. X-ray diffraction, scanning electron microscopy, electron microprobe and atomic absorption spectroscopy analyses were performed on samples at variable distances from the mudstone-dyke contacts.

A roughly similar evolution is seen on both sides of the dyke: quartz, calcite, kaolinite and illite disappear; Ca-silicates, albite and saponite-beidellite form, late meteoric halloysite crystallizes in open fractures.

Chemical and mineralogical transformations are related to heat diffusion from the dyke. Theoretical calculations highlight the influence of the dyke orientation. The mineralogical reactions observed in rocks are similar to those observed in experimental conditions. The formation of new swelling phases with a high retention capacity linked to a short duration, large-temperature increase, should constitute a positive process for Repository Performance Assessment.

This study focused on the structure and physical properties of acid-treated bentonite L45 from the Lieskovec deposit (Slovakia). New applications of near infrared and visible spectroscopies were used to follow Fe-montmorillonite dissolution and layer-charge reduction. Progressive dissolution of L45 results in the formation of a protonated amorphous silica phase. The OH overtone at 7312 cm–1 revealed the creation of Si–OH groups in the mildly treated samples. The area of the Si–O–Moct band, as obtained by a peak-fitting procedure, is a sensitive indicator of the changes in the octahedral sheets. Ultraviolet-visible (UV-VIS) spectroscopy of the smectite dispersions with methylene blue (MB) is an efficient method for controlling the acid activation process of bentonites. The results reveal that acid treatment causes a substantial layer-charge reduction, probably due to prevailing dissolution of MgO4(OH)2 polyhedra in the octahedral sheets. The layer-charge reduction is proportional to the structural changes and to the extent of mineral decomposition upon acid treatment.

This study characterizes the effects of fluid migration into a predominantly shale cover which seals the active geothermal system of Mt. Amiata (Tuscany, Italy). During Alpine orogenesis the shale unit was affected by regional metamorphism at the limit of the diagenesis-anchizone. Subsequently, the phyllosilicate clay minerals of the shales underwent significant alteration at diagenetic temperatures (175±25ºC as determined by the geochemical model) by the pervasive circulation of fluids activated by the geothermal field. The overall mineralogical assemblages indicate that the main transformations consisted mostly of destabilization of illite and formation of kaolinite together with large amounts of I-S mixed layers, with higher smectite content and decreased Reichweite I-S ordering (from R3 to R1) with respect to the original, unaltered phases. Application of computer modelling indicates that the circulation of CO2-rich geothermal fluids into the shale unit was responsible for the observed phyllosilicate clay mineral transformations.

Turkey has a long tradition (starting with prehistoric civilizations) and experience in exploring for raw clay materials and processing them into ceramic products. Many of these products, such as tiles and sanitary ware, are manufactured for domestic and export markets. Kaolin is one of the raw materials of major importance for the ceramic and paper industry, as well as for a number of auxiliary applications. There is ongoing interest in applying kaolin in the construction industry as a raw material in the production of white cement clinker and as an artificial pozzolanic additive for concrete (in the form of metakaolin). This report presents results related to search, assessment and evaluation of available resources for advanced cement and concrete additives.

We have carried out optical microscopy, X-ray diffraction (XRD) and scanning and transmission electron microscopy (SEM and TEM) studies of phyllosilicates from black slates of very low to low-grade metamorphism. Such slates belong to a Middle/Late Devonian basin and an Early Carboniferous basin associated with the Porto–Tomar–Ferreira do Alentejo strike-slip shear zone (Ossa-Morena Zone, Portuguese Iberian Variscan Massif). These black slates are imbricated in an Upper Proterozoic substratum of higher metamorphic grade. Kübler Index values of white micas and mineral assemblages deduced from the XRD, SEM and TEM data (muscovite, chlorite and pyrophyllite) indicate high anchizonal and epizonal metamorphic conditions for slates from these basins. The b parameter and the phengitic contents of mica suggest the occurrence of low pressures (1–2 kbar) related to an extensional geotectonic setting. The dense fracture network shown by SEM images and the high density of crystal defects revealed by the TEM study in the eastern basin, adjacent to faults produced by shearing, suggest that their epizonal phyllosilicates were more affected during deformation than those belonging to the western basin, favouring the development of a retrograde association (siderite, kaolin group minerals and Al-smectite) on the epizonal paragenesis. Microcavities formed along phyllosilicate cleavage acted as channels for fluid transport favouring alteration under low-temperature conditions.

A series of thin clayey beds topping shallow marine cyclothems was sampled from a Turonian succession in Israel and was analysed by XRD for the mineralogical composition of its clay fraction. The main goal was to search for potential relations between short-term shallowing and possible emergence events and clay mineralogy. The bulk (<2 μm), coarse (0.2–2 μm) and fine (–0.2 μm) clay fractions of a unique clay bed, dominated by R⩾1-type I-S were analysed for their chemical composition and dated by the K-Ar method. The fine clay fraction was dated at ~5 m.y. younger and the bulk clay to be slightly older than the known stratigraphic age, which means that the clay is mostly authigenic and formed at low-temperature, near-surface conditions. This is supported by the geological history of the region and by the variability of the clay assemblages and I-S composition within ~30 m vertical distance, neither of which indicates evidence for high temperatures. The sedimentological analysis suggests that the clay bed was deposited at marginal marine marshes where evaporated sea water turned into an alkaline solution of high K concentration. This is apparently the first study to provide convincing evidence for low-temperature, early diagenetic formation and preservation of I-S with R1-type, or similar ordering.

The saponite examined occurs as two 0.1 m thick layers in a Pliocene sequence consisting of dolomite and dolomitic marl. To characterize this material, mineralogical and structural analyses (XRD, SEM and FTIR), thermal analyses (DTA, TG) and chemical analyses (ICP-ES) were performed. From XRD patterns of randomly-oriented powder samples, the first basal reflection appears as an asymmetric and broad peak with d001 values varying between 16.55 and 17.32 Å. In oriented and air-dried samples, this reflection occurs between 14.45 and 16.42 Å and is fairly symmetrical with FWHM of 2.7º2θ. Oriented and ethylene glycol-solvated samples produce a rational series of basal reflections, where 001 occurs at ~17.8 Å as an intense, narrow (1.1º2θ) and fairly symmetrical reflection. Upon solvation with glycerol, the 001 reflection shifts to ~18.7 Å.

The chemical composition of this saponite is similar to stevensite. However, the structural formula of Na0.114Ca0.013K0.003(Mg2.957Al0.004Fe0.028Ti0.004)(Si3.826Al0.174)O10(OH)2 indicates that vacancies in the octahedral sheet do not exist. The negative layer charge arises nearly entirely from the substitutions in the tetrahedral sheet, with the net layer charge of –0.148, smaller than for common smectites.

Due to the XRD characteristics and particularly the layer-charge distribution, it was concluded that this mineral is a Mg-rich saponite with low layer charge. The saponite was formed by direct precipitation in an alkaline lake environment from Mg- and Si-rich solutions at high pH.

Two soil profile sequences on paragneiss debris in the Val di Rabbi (Northern Italy) along an altitude gradient ranging from 1200 to 2400 m a.s.l. were studied to evaluate the effect of aspect on the weathering of clay minerals. All the soils had a coarse structure, a sandy texture and a low pH. Greater weathering intensities of clay-sized phyllosilicates (greater content of smectites) were observed in soils on the north-facing slope. On the south-facing slope, smectite was found only in the surface horizon of the soil profile at the highest altitude. Hot citrate treatment of north-facing soils revealed the presence of low-charged 2:1 clay minerals, the expansion of which was hindered in the untreated state by interlayered polymers. However, the hot citrate treatment encountered some problems with the samples of the south-facing soils: as confirmed by Fourier transform infrared spectroscopy, the hot citrate treatment was unable to remove all interlayer Al polymers. The 2:1 phyllosilicates were not expanded by ethylene glycol solvation in several samples, although thermogravimetric analyses indicated the presence of clay minerals with interlayer H2O. At the same time, the collapse of clay minerals to 1.0 nm following K-saturation was evident. Theoretically, this should indicate that 2:1 phyllosilicates had no evident substitution of trioctahedral cations (Mg2+, Fe2+) by dioctahedral cations (Al3+ and Fe3+). X-ray diffraction analysis of the d060 region and determination of the layer charge of clay minerals by the long-chain (C18) alkylammonium ion, however, did not confirm this. A transformation from trioctahedral to dioctahedral species was observed and low-charge clay minerals (ξ ~0.30) were identified in the surface horizons of the south-facing sites. In the south-facing soils, the podzolization process was less pronounced because of a lower water flux through the soil and probably less complexing organic molecules that would remove the interlayer polymers. Besides the eluviation process, clay minerals underwent a process of ionic substitutions in the octahedral sheet that led to the reduction of the layer charge. This process was more obvious in the north-facing sites.

Numerous studies focus on the relationships between chemical composition and OH-band positions in the infrared (IR) spectra of micaceous minerals. These studies are based on the coexistence, in dioctahedral micas or smectites, of several cationic pairs around the hydroxyl group which each produce a characteristic band in the IR spectrum. The aim of this work is to obtain the wavenumber values of the IR OH vibration bands of the (Al-Fe3+)-OH and (Fe3+-Fe3+)-OH local cationic environments of ‘pyrophyllite type’ in order to prove, disprove or modify a model of dioctahedral phyllosilicate OH-stretching band decomposition. Natural samples are characterized by powder X-ray diffraction (XRD), Fourier transform infrared (FTIR) and Raman spectroscopies and electron microprobe; the hydrothermal synthesis products are also analysed by powder XRD and FTIR after inductively coupled plasma measurements to obtain the chemical compositions of starting gel phases. Natural samples contain some impurities which were eliminated after acid treatment; nevertheless, a small Fe content is found in the pyrophyllite structure. The amount of Fe which is incorporated within the pyrophyllite structure is much more important for the synthetic samples than for the natural ones. The IR OH bands were clearly observed in both natural and synthetic pyrophyllites and assigned to hydroxides bonded to (Al-Al), (Al-Fe) and (Fe-Fe) cationic pairs. During this study, three samples were analysed by DTG to check the cis- or trans-vacant character of the layers and to determine the influence of this structural character on the OH-stretching band position in IR spectroscopy.

The colloidal state of aqueous Ca2+-montmorillonite dispersions was modified with three types of cationic end-capped poly(ethylene oxides). The macromolecules were not only adsorbed at the external surfaces but were also intercalated into the dispersed montmorillonite particles. The amounts adsorbed and the basal spacings (~1.7 nm) were comparable to the corresponding Na+-montmorillonite dispersions. The poly(ethylene oxides) protruding out of the interlayer spaces or adsorbed at the external surface determined the colloidal behaviour of the dispersions. The phase diagrams (sol-gel diagrams) of the Ca2+-montmorillonite dispersions differed from those of the corresponding Na+-montmorillonite because of the different colloidal states of both dispersions (Ca2+-montmorillonite particles vs. delaminated Na+-montmorillonite). The phase diagrams of the poly(ethylene oxide) containing Ca2+-montmorillonite dispersions showed fields of sol and flocs. Attractive gels were formed in a few cases only (TMA+-PEO 1500 and 4000, THA2+-PEO 1500, 4000 and 20,000) and with distinctly lower gel strength than in the presence of Na+ ions. On the basis of the sol-gel diagrams, conditions (type and concentration of poly(ethylene oxides), montmorillonite content) can be selected which lead to peptization of the Ca2+-montmorillonite particles into stable colloidal dispersions (sols). Addition of cationic poly(ethylene oxides) can enhance the salt tolerance up to 1000 mmol/l NaCl.

Scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS) analysis of smear slides of oriented <2 mm clay fractions is shown to be a reliable and rapid analytical technique for providing chemical data on clay mineral mixtures. Such smear slides are routinely prepared for clay mineral analysis by X-ray diffraction and the only additional treatment required for chemical analysis by EDS is carbon-coating to form an electronically conductive surface. Using standard clays, mixtures of standard clays, and sediment samples, it is shown that sample thickness, sample heterogeneity and surface roughness do not introduce significant analytical errors, although the presence of non-clay mineral phases such as calcite, dolomite, quartz and pyrite may introduce minor discrepancies. Chemical data complement the XRD analyses and increase their accuracy and reliability.

The bentonite deposits in Başören Kütahya, W Anatolia, Turkey were formed by alteration of Pliocene perlite and pyroclastic rocks. Two types of bentonites are distinguished in this area on the basis of their physical properties, chemistry and occurrence. Bentonites were examined to determine their mineralogical, chemical and physical properties. Analytical methods include X-ray diffraction (XRD), scanning electron microscopy (SEM), chemical analysis and measurement of cation exchange capacity (CEC), swelling volume, water adsorption, bleaching capacity, and firing shrinkage. Bentonites consist mainly of dioctahedral smectite. They also contain zeolite, opal-CT, cristobalite, quartz, feldspar, dolomite and calcite. The ‘Type 2’ bentonites had greater CEC, swelling volume, water adsorption and bleaching capacity than ‘Type 1’. The variation in the physical properties of the two bentonites is attributed to the differences in the non-clay mineralogy and to the chemical composition and nature of interlayer cation.