Many safety functions required of the compacted bentonite buffer in the KBS-3 concept rely on processes influenced by the composition of the pore water. Important safety-relevant processes are related to the bentonite buffer, e.g. swelling, precipitation and dissolution reactions, and transport of water, colloids and ions. One of the methods used in analysing pore water in compacted bentonite is the ‘squeezing technique’. Various possible artefacts which can occur during squeezing, such as mixing of different pore-water types, dissolution of accessory minerals and cation exchange, need special attention.

The present work describes the methodology for studying the composition of the non-interlamellar pore water by combining squeezing methods, chemical analyses, microstructure measurements and geochemical modelling. Four different maximum pressures were used to squeeze the compacted bentonite pore water. The origin of the pore water was studied by analysing the bentonite microstructure both before and after squeezing using SAXS and NMR, the cation exchange and dissolution reactions were studied by chemical analyses and geochemical modelling.

The pore-water yield increased from 32 to 48 wt.% from the initial amount of porewater in the samples when the maximum squeezing pressure was increased from 60 MPa to 120 MPa. About 35 wt.% of the water collected originated from the interlamellar (IL) pores. The ratio between IL and non-IL pore waters as well as the composition of the squeezed porewater was constant in the squeezing-pressure range used. The results of microstructural measurements by SAXS were in perfect agreement with previous studies (e.g. Muurinen & Carlsson, 2013). The dissolving accessory minerals have an effect on the ratio of the cations in the squeezed solution while the migration of anions in bentonite seems to be diffusion limited. According to geochemical modelling the chloride concentration of the non-IL pore water in compacted bentonite before squeezing was 0.34 Mgreater than in the squeezed pore water due to the mixing of two main water types.

Few reports exist on the use of Diffuse Reflectance Infrared Fourier Transform Spectrometry coupled with Mass Spectrometry (DRIFTS-MS) in situ to monitor the dehydroxylation of kaolinitic clays. The use of DRIFTS-MS in situ allows study of the effect of heat treatment on the dehydroxylation, identifying intensities and temperatures at which the hydroxyl groups are released, forming metakaolinite and meta-alunite. The effluent gases from the infrared cell were analysed by mass spectrometry. The decrease in intensity of the bands at 3694, 3669, 3650 and 3621 cm−1 associated with the −OH stretching vibration modes of AlVI−OH−AlVI of kaolinite began at 450°C. Two additional bands at 3513 and 3485 cm−1 are associated with the vibration of AlVI−OH of alunite that also began to disappear during thermal treatment. Monitoring of the fractions m/e 17 and 18 using a mass spectrometer revealed that the intensity of these fractions increased starting at 450°C. Therefore, it is possible to study the dehydroxylation process of clays during thermal treatment.Chemical and mineralogical characterization of a kaolinitic clay (KN) fromMexico showed that the clay consists of 64.8% kaolinite, 11.0% alunite and 24.4% quartz based on PXRD, EDS, TG/DTA, TEM and FTIR results, and suggested that the material might have potential for use in the manufacture of ceramics, refractory bricks or geopolymers.

The cation exchange capacity (CEC) of seven well characterized halloysite nanotubes (HNTs) in the dehydrated 7 Å form has been measured using a method based on cobalt hexammine exchange. In addition to unbuffered measurements, which varied between 2.9 and 9.3 cmol(+)kg−1, CECs were also determined over a wide pH range and proton titration measurements were conducted on two samples. The data were fitted using a constant capacitance model based on the presence of two sites: permanently charged sites and pH-dependent variable charged sites. Normalization of CEC to the average specific surface area (BET) of the halloysite samples reduces considerably the variation of CEC values for the different samples particularly over the intermediate pH range (5–9) with the average value at pH 7 equal to 8.5 cmol(+)kg−1 and a standard deviation of 1.17. Overall the CEC behaviour of the seven samples appears reasonably consistent throughout the set. Calculations based on proton titrations suggest a ratio of variable charge to basal sites for the dehydrated halloysite nanotubes of ∼3:1.

The pyroclastic carbonatitic rocks from the Catanda volcanic area (Angola) contain annite and phlogopite grains which have been affected to a significant extent by vermiculitization. A mineralogical study of these micas has revealed that the annite was altered to K-vermiculite while vermiculitization of phlogopite generated Ca-vermiculite. Intermediate alteration products such as intergrowths of phlogopite/Ca-vermiculite were also found, but interstratified crystals of phlogopite/ vermiculite, a common intermediate product during vermiculitization processes, are not reported in the Catanda rocks. The two types of vermiculitized micas show ‘accordion’ textures, related to the expansion of vermiculite. To the authors’ knowledge, the present study is the first report of expanded vermiculites described in natural rocks and not generated as a consequence of industrial processing.

The distribution of octahedral cations in the two component layers of a 7 Å–14 Å interstratified mineral with a bulk chemical composition (Fe4.122+Mg0.07Mn0.01Al1.69□0.11)(Si2.56Al1.44) O10(OH)8 was investigated using high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) in combination with the image simulations. In the 14 Å component layers, comparison between the observed and simulated images revealed that the M4 sites of the interlayer sheets were occupied preferentially by Al together with a small amount of Fe; the other M1, M2 and M3 sites were occupied by dominant Fe and residual Al in equal proportions. Two types of octahedral sheets with disordered and ordered cation distributions were recognized in the 7 Å component layers. The two types of sheets were similar to the octahedral sheet of the 2:1 layer and the interlayer sheet in the 14 Å layer above, respectively. Irregular vertical stacking and lateral contact of the different component layers in structure and chemistry characterized the interstratification, which may be caused by rapid precipitation and accretion of the component layers in hydrothermal environments.

The Barzaman Formation exposed in the United Arab Emirates was deposited as a series of fluvial sediment sequences lying along the western margin of the Hajar Mountains, part of the Oman–UAE ophiolite. This formation consists of a sequence of rocks dominated by variably cemented and altered conglomerates comprising calcareous siltstones and calcareous clays deposited during the Miocene to Pliocene under a humid climate. The conglomerates are composed largely of ultramafic and lesser-mafic clasts. The present study was undertaken in order to understand the occurrence and genesis of palygorskite and sepiolite in relation to the environmental changes including evaporitic and sabkha environments.

Sediments were collected from two trenches and a drill hole of ∼22 m depth. Samples were analysed by optical petrograpy, X-ray diffraction and scanning electron microscopy. Pedogenesis occurred at the deeper level in well cemented conglomerate which constitutes the hard crust. Post-depositional erosion started in marine phreatic or vadose zones as shown by the neoformation of serpentine from the weathering of olivine as well as of calcite and dolomite. Neoformation of palygorskite, sepiolite, dolomite and halite occurred under evaporitic conditions on calcareous silty clay facies. Relatively hot, vadose and oxidizing environmental conditions affected the calcareous siltstone facies leading to the genesis of dolomite and palygorskite by direct precipitation from solution rich in Ca, Mg, Al, Fe and Si ions.

The present study investigated the efficiency and mechanisms of aqueous Pb(II), Cd(II), Zn(II) and As(V) adsorption on natural (H), calcined (HC), and acid-activated halloysite (HA). The XRD and FTIR measurements indicated that the aluminosilicate framework was not affected by high-temperature treatment, in contrast to acid activation, which led to structural changes mainly in the tetrahedral sheet. The sorption of cations on H sample was low, though it was most effective for As(V). The X-ray photoelectron spectroscopy results suggested that removal of As(V) might be related to its reduction to As(III) involving oxidation of Fe(II) present in the mineral structure and/or iron minerals. The calcination enhanced halloysite sorption capacity for cations, while the As(V) sorption decreased. This was due to partial dehydroxylation and the subsequent formation of additional active sites. The acid treatment induced selective adsorption of Pb(II).

The milling process in the solid-state 2:1 clay minerals, montmorillonite and talc, which have different cation exchange capacities, is reported here. Several instrumental techniques were used to monitor systematically the products formed. The dehydroxylation/amorphization of the montmorillonite and talc structures occurs within 3 and 6 h of milling, respectively. Electron paramagnetic resonance spectra indicated that structural Mn2+ was oxidized more quickly in the montmorillonite structure than in talc, while the paramagnetic defects increased during milling. Nuclear magnetic resonance was also used to monitor the environmental changes for Si and Al during milling.

Compacted bentonite is to be used as a buffer material between waste canisters and the bedrock in the deep geological disposal of high-level nuclear waste in several countries. In spite of the fact that such large bentonite systems have long equilibration times, estimation of the material properties and performance in repository conditions is often based on short-term, laboratory-scale experiments. Sample-preparation procedures in these experiments may differ from the natural evolution of the bentonite in the repository, however, affecting the bentonite properties. The present study reports the influence on the structure of clay tactoids of four different preparation procedures of water-saturated, compacted MX-80 bentonite samples using four target dry bulk densities. Small-angle X-ray scattering was used to illustrate the differences between the samples. The different treatments of the bentonite samples may lead to different structural features. Clear differences between low-density samples prepared using different procedures were observed. The influence of the preparation methods was less, but still noticeable, for the high-density samples.

The advantages and limits of empirical, semi-empirical and thermodynamic methods devoted to the estimation of chlorite-formation temperature are discussed briefly. The results of semiempirical and thermodynamic approaches with different assumptions regarding the redox state of iron in chlorite are compared for a large set of natural data covering a range of pressure conditions from a few hundred bars to 18 kbar and temperature from 100 to 500°C. The T-XFe3+ evolution estimated using the thermodynamic approach of Vidal et al. (2005) shows a systematic increase in XFe3+ with decreasing temperature, which is compatible with the decrease in aO2 buffered by magnetite- or hematite-chlorite equilibrium. This trend as well as the observed increase in vacancies in chlorite with decreasing temperature is interpreted as the incorporation of Fe3+-sudoite. The standard-state properties of this endmember have been derived to reproduce the observed T-aO2-XFe3+ evolutions. It can be used to estimate T-aO2-XFe3 values with a Chl-Qtz-H2O multi-equilibrium approach. When combining our results with those of other studies published recently, it appears that thermodynamic approaches and mapping techniques developed for metamorphic rocks can be used to discuss the conditions of formation of very low-grade rocks where kinetics is much more sluggish than in metamorphic rocks. This requires use of appropriate analytical tools and techniques with a spatial resolution of a few hundred nanometres.

Diffuse reflectance (DR) spectra in the visible (VIS) and near-infrared (NIR) region of methylene blue (MB) adsorbed on clay samples of different mineral composition and varying MB/clay ratios were analyzed. This type of investigation is not affected by unadsorbed MB molecules and can be used in clay-mineral determination. When the MB dye/clay loading was increased, enhancement of bands in the DR-VIS and DR-NIR was observed. The distribution of various MB aggregates was interpreted according to mineral composition and MB loading. The NIR spectrum of H2O overtone provides insights about the intercalated MB aggregation, consistent with VIS spectra. Critical MB concentration for formation of dimeric structure was between 0.7 and 1.75 mmol/100 g followed with suppression of monomers. Different orientations of vectors of polarized light allowed calculations of the possible orientation and tilting angle of MB molecules on the surface of the clay particles in accordance with XRD data.

New insights from the recent literature are summarized and new data presented concerning the formation, structure and morphology of halloysite. Halloysite formation by weathering always requires the presence of water. Where substantial drying occurs, kaolinite is formed instead. Halloysite formation is favoured by a low pH. The octahedral sheet is positively charged at pH < ∼8, whereas the tetrahedral sheet is negatively charged at pH > ∼2. The opposing sheet charge would facilitate interlayer uptake of H2O molecules. When halloysite intercalates certain polar organic molecules, additional (hkl) reflections appear in the X-ray diffraction pattern, suggesting layer re-arrangement which, however, is dissimilar to that in kaolinite. Associated oxides and oxyhydroxides of Fe and Mn may limit the growth of halloysite particles as does incorporation of Fe into the structure. Particles of different shape and Fe content may occur within a given sample of halloysite.

The swelling and cation exchange properties of montmorillonite are fundamental in a wide range of applications ranging from nanocomposites to catalytic cracking of hydrocarbons. The swelling results from several factors and, though widely studied, information on the effects of a single factor at a time is lacking. In this study, density functional theory (DFT) calculations were used to obtain atomic-level information on the swelling of montmorillonite. Molecular dynamics (MD) was used to investigate the swelling properties of montmorillonites with different layer charges and interlayer cationic compositions. Molecular dynamics calculations, with CLAYFF force field, consider three layer charges (−1.0, −0.66 and −0.5 e per unit cell) arising from octahedral substitutions and interlayer counterions of Na, K and Ca. The swelling curves obtained showed that smaller layer charge results in greater swelling but the type of the interlayer cation also has an effect. The DFT calculations were also seen to predict larger d values than MD. The formation of 1, 2 and 3 water molecular layers in the interlayer spaces was observed. Finally, the data from MD calculations were used to predict the selfdiffusion coefficients of interlayer water and cations in different montmorillonites and in general the coefficient increased with increasing water content and with decreasing layer charge.

A synthetic protonic magadiite was used as a silica source to prepare zeolitic material (PLS-1) in the presence of tetramethylammonium hydroxide and water. The conversion of the protonic magadiite to the PLS-1 phase was achieved at 150°C after 5 days, or at 170°C after 3 days for SiO2: TMAOH:H2O molar ratios of 2.54:1:4.4. The synthesis of the pure PLS-1 phase depended also on the amounts of tetramethylammonium hydroxide and water used. Analysis by 29Si magic angle spinning nuclear magnetic resonance spectroscopy confirmed the layered character of the PLS-1 phase with a resonance at −93 ppm, and its dehydroxylation-condensation process. The chemical formula of (TMA)2Si18O33(OH)6 for PLS-1 was refined with the Rietveld method and the tetrahedron-splitting model. The later model has been proposed to describe the presence of silanol defects in the layered structure of PLS-1. Upon calcinations of the PLS-1 phase at temperatures >400°C, the removal of TMA cations and dehydroxlyation of PLS-1 layers resulted in a three-dimensional structure phase identified as the CDS-1 phase, with a chemical formula of Si18O36. The CDS-1 phase exhibited a large specific surface area of 288 m2/g and microporous character, as indicated by the nitrogen adsorption isotherms. The temperature-programmed desorption profile of ammonia indicated that CDS-1 exhibited one weak type of acid sites, confirmed, by pyridine desorption studies, as weak Lewis acid sites.

Tosudite, a regularly interstratified chlorite-smectite, crystallizes as an alteration mineral of several preexisting Al-bearing silicates (feldspars, kaolin minerals, chlorites) present in arkosic sandstones hosted in uranium deposits in Niger. X-ray diffraction patterns show a sharp superstructure at 29–29.6 Å for an air-dried state and a peak at 30.8–31.6 Å following ethylene glycol solvation. The 060 reflection at 1.507–1.509 Å indicates an overall dioctahedral character, and the very low coefficient of variation of the d00l reflections for the solvated mineral (0.03–0.13) permits validation of the regular interstratification justifying its identification as tosudite. Microprobe analysis allowed specification of the component layers of this mixed-layer mineral. The chlorite is a di-trioctahedral type analogous to sudoite (Si3Al4Mg2(OH)8), and the smectite component is a low-charge montmorillonite type Tosudite is characterized by large Al2O3 and MgO contents and small Fe content; its composition corresponds approximately to the formula where octahedral occupancy is ∼7. Scanning electron microscope (SEM) observations show that tosudite is closely associated with some uranium minerals: tosudite crystallization occurred during a late alteration event which post-dates burial diagenesis and during which uranium was remobilized by Mg-rich oxidizing fluids.

Chlorite (C)-corrensite (Co)-smectite (S) seriesminerals occur as vein constituents in the two epithermal ore veins, the Chuetsu and Shuetsu veins of the Todoroki Au-Ag deposit. The characteristics of the C–Co–S seriesminerals indicate that the clays may be products of direct precipitation from hydrothermal fluids and subsequent mineralogical transformations during and/or after vein formation. The minerals from the Chuetsu vein are characterized by ‘monomineralic’ corrensite showing an extensive distribution throughout the vein, and trioctahedral smectite occurring locally. The Shuetsu vein minerals are characterized by C-Co series minerals which can be divided into three different types: a I type including discrete chlorite with minor amounts of S layers, a II type comprising interstratified C/Co and discrete chlorite, and a III type characterized by segregation structures of C and Co layers. The C-Co series minerals show slightly different spatial distributions in the Shuetsu vein. Different epithermal environments during the vein formations and possible kinetic effects may have played a role in the formation and conversion of Co-C series at the Shuetsu vein and S-Co series at the Chuetsu vein.

Understanding the composition of clay-rich sediments and their transportation into proximal marine basins allows us to better decipher hydroclimatic changes before and within the Palaeocene–Eocene Thermal Maximum (PETM). Only a limited number of such studies exists from the North Sea Basin, which was proximal to the volcanic activity and early rifting hypothesized to have triggered the PETM. The present study examines core material from well 22/10a-4, UK North Sea, as it exhibits an exceptionally expanded and almost stratigraphically complete fine-grained sedimentary sequence suitable for high-resolution analysis.

Quantitative Newmod-for-Windows™-modelled clay mineral assemblages, rather than traditional semi-quantitative estimates, are dominated by smectite-rich, interlayered illite-smectite that probably developed from volcanogenic deposits on continental landmasses. Soil development before the PETM is consistent with the existence of a seasonal tropical climate with a prolonged dry season. A striking rise and fall of kaolinite content within the PETM onset, prior to the principal carbon-isotope excursion, is reported here. This variation is interpreted as a signal of an enhanced hydrologic cycle producing an increase in erosionally derived kaolinite, followed by a dampening of this detrital source as sea-levels rose. Global variations in PETM kaolinite concentrations are consistent with a latitudinal shift in patterns of precipitation in models of global warming.

Commercial bentonite from the Kopernica deposit, Slovakia, is currently mined by the CERTECH Company, Poland, to produce materials intended for animal-care applications and other industrial purposes. The present study aimed to assess the mineralogical, petrographic and physicochemical characteristics of three bentonite varieties from Kopernica used by the company. The X-ray diffraction, optical microscopy, field emission scanning electron microscopy (FESEM), nuclear magnetic resonance, thermal analysis, infrared spectroscopy and chemical analyses showed that the main component of the rocks is montmorillonite with the average structural formula Ca0.31K0.08Na0.04(Al3.23Mg0.54Fe0.23)[(Si7.80Al0.20)O20](OH)4. In addition, opal-C/CT, biotite, potassium feldspar and plagioclase, quartz, clinoptilolite and kaolinite are present. Key information about the textural relationships between the mineral components identified was obtained from detailed thin-section petrography and FESEM studies. The rocks studied have fragmented, eutaxitic texture. They are composed of pumice fragments collapsed into lenticular masses (fiamme) which were strongly deformed and altered, though the shard structures were retained. The compressed glass shards were moulded around pyroclastic grains such as crystal fragments of quartz, biotite and zoned plagioclases, and clasts of volcanic rocks. Observations by FESEM showed that the axes of shards and the walls of the flattened vacuoles are outlined by the inward-growing microlites of silica (axiolitic texture), whilst the interiors of shards are altered to clay. Grain-size distribution, textural properties and microscope observations of grain-size fractions reveal that the Kopernica bentonite contains montmorillonite-opal aggregates difficult to disperse in water.

Bentonite colloids generated from the backfill barrier in nuclear waste repositories may act as radionuclide carriers, if they are stable and mobile. Repository scenarios with highly saline groundwater inhibit colloid stability as particles tend to aggregate but, in the time frame of repositories, groundwater conditions may evolve, promoting particle disaggregation and stabilization. The disaggregation of FEBEX bentonite colloids by fast dilution to lower ionic strength was analysed in this study. Time-resolved dynamic light-scattering experiments were carried out to evaluate the kinetics of bentonite colloid aggregation and disaggregation processes in Na+ and Na+-Ca2+ mixed electrolytes of low ionic strength. Attachment and detachment efficiencies were determined.

Aggregation is promoted by increasing ionic strength, being more efficient in the presence of divalent cations. Once bentonite colloids are aggregated, a decrease in ionic strength facilitates disaggregation, but the process is not fully reversible as the initial size of the stable bentonite colloids at low ionic strength is not fully recovered. Particle-size distribution and concentration in suspension were analysed on disaggregated samples by single particle-counting measurements. Small colloids were measured in the disaggregated samples but their population was smaller than in the initial stable sample, especially in the presence of Ca2+.

Tubular halloysite has many applications as a nanomaterial. Spheroidal halloysite (SPH) is the other most common form of halloysite. Its mode of formation has had different explanations, including association with allophane, or more generally, following weathering of volcanic glass. Some SPHs have formed from minerals in crystalline rocks, sometimes as an early stage of evolution into plates and/or tubes of halloysite and ultimately to kaolinite. Spheroidal halloysites can show a range of Fe contents and can occur with other forms of halloysite; they have often formed in confined environments whereas tubular halloysites apparently form in more open spaces. They have also formed on microbes or where there is a significant amount of organic matter. Generally, SPHs have often formed by rapid dissolution of volcanic glass and primary minerals. The SPHs can persist over time. They have fewactive edges, so interparticle interaction is poor, causing low viscosities in clay-water suspensions, poor soil stability and low adsorption capacities.