The grain size of raw materials influences their behaviour during the technological process and affects many properties of building clay products. Over the last few years, brickworks have been technologically updated and grain size requirements have been modified to ensure good behaviour during shaping and drying. Therefore, the reference schemes used to assess the suitability of clays, such as the classic Winkler diagram, should be updated.

For this purpose, the grain-size distribution of 350 clays currently used in ~240 Italian plants was determined by X-ray monitoring of gravity sedimentation. Raw materials are basically represented by silty clays and clayey silts, while bodies present a narrower grain-size range. With reference to the Winkler diagram, most of the Italian bodies fall within the field of ‘thin-walled hollow bricks’, with no significant differentiation among the various product types.

In order to improve the grain-size characterization of bodies, a new classification scheme for Italian raw materials is proposed, based on three ranges: >10 µm, 2-10 µm and <2 µm, respectively. It allows distinction of specific grain-size features of bodies for (a) facing bricks; (b) roofing tiles; and (c) lightweight blocks, paving bricks and hollow slabs.

The Ga for A1 substitution in kaolinites and smectites was studied using clay synthesis from initial gels having an (Al + Ga)/Si ratio of kaolinites and MGa = Ga/(Ga + A1) ratio ranging from 0 to 1. Only kaolinite was obtained for MGa in the range 0-0.10. For higher MGa, synthesized clays were both kaolinite and beidellite, or pure beidellites. The evolution of b cell parameters, and the appearance of a vAI-OH-Ga absorption band at 3600 cm-1 in FFIR spectra, proves the progressive substitution of AI by Ga in kaolinite. The low substitution of AI by Ga in kaolinite can be correlated with the large difference in ionic radii between Al3+ and Ga3+ which causes a large increase in cell dimensions. By contrast, the incorporation of Ga in smectites is easy and can be complete.

Four samples of <2 µm fractions of Fe-rich bentonites from tile area of the Zvolenská kotlina Basin (Slovakia) have been investigated by MiSssbauer spectroscopy and reductive dissolution in ammonium hydrogen oxalate (pH = 2.7). Both methods have shown the presence of goethite in the samples. The relative amount of Fe bound in goethite varied more within the samples of bentonite from Zvolensk~ Slatina, which was redeposited after transport over a short distance, than in the authigenically altered bentonite from Hrochot’. The results of the fits of the reductive dissolution curves suggest size distribution, variation in Al-for-Fe substitution in goethite particles and/or different access of extracting solution to goethite particles present in the analysed fine fractions of bentonites.

More than 50 samples from a Barents Sea borehole near the Mjolnir Structure (an extraterrestrial impact feature) were used to investigate changes in the clay assemblage associated with the submarine impact. Seismic evidence, the presence of shocked quartz and a prominent Ir anomaly restricted the potential impact affected zone to a 10 m interval, straddling the Jurassic/Cretaceous boundary.

Increased abundance (up to 30 wt%) of a smectite, a randomly interstratified smectite-illite with 85% smectite layers, forms the basis for a two-layer oceanic impact clay model that differs from published terrestrial cases. The smectite is assumed to represent seawater-altered impact glass from the ejecta blanket material that was mixed with resuspended shelf sediments by the collision generated waves. The smectite-rich interval is almost 5 m thick. It is overlain by a coarser unit (~2 m thick) containing abundant smectite, shocked quartz grains, and anomalous Ix contents at its base. The smectite-rich interval may have originated as a density/turbidity current, generated by the impact and the collapse and erosion of the crater rim. Seawater alteration of volcanic glass and changes in the tectonic regime of the provenance area, or changing oceanic current circulation patterns could produce similar variations in the clay mineral assemblage. The most compelling evidence for the possible impact derivation of this clay assemblage is the direct association with the Mjolnir Impact Structure and associated mineralogical and geochemical anomalies.

Carbonate-bearing ceramic bodies are frequently used in the manufacture of bricks, roofing tiles, wall and floor tiles, pottery and tableware. During the firing of these bodies, clinopyroxene is usually formed in very small crystals, 1-5 µm in diameter or less. In the literature this phase is generally referred to as diopside, but no quantitative data are available. In order to chemically characterize these ‘ceramic’ pyroxenes, nine industrial products were analysed by XRF and XRD (bulk sample) and SEM-EDS (fracture surface). Quantitative ZAF analyses of pyroxene crystals showed a certain chemical variability: SiO2 35-50%, Al2O3 9-20%, Fe2O3 1-15%, MgO 3-14%, and CaO 16-25%. Sodium, K and Ti are always <1%, while ferrous iron is always <0.2% in the bulk sample. Overall, ‘ceramic’ clinopyroxenes present wide chemical analogies with ‘fassaite’, e.g. the abundance of aluminium and ferric iron, and the excess ofwollastonite molecules with respect to the diopside-hedenbergite series.

Infrared (IR) spectra of well-ordered kaolinites generally show four OH-stretching frequencies, near 3697, 3670, 3652 and 3620 cm-1. Raman spectra of the same kaolinites mostly show an additional band near 3686 cm-1, which, in the coarsely crystalline Keokuk kaolinite, largely replaces the 3695 cm-1 band. It is shown that the 3686 cm-1 band can be ascribed to a transverse optical crystal vibration involving the in-phase stretching vibration of the three inner-surface hydroxyl groups in the unit-cell. Raman exciting radiation, commonly of wavelength near 500 nm, can excite this crystal vibration in crystals of comparable and greater thickness.

Infrared studies are usually made on clay-size (<2 μm) particles, which have mean thicknesses of 30-150 nm. Infrared radiation of wavelength near 2.7 <m can only excite whole crystal vibrations perpendicular to the plates. The in-phase vibration of inner-surface OH groups in the whole-crystal mode lies at 3697 cm-1, which is the same frequency as that of the longitudinal optical mode in macroscopic crystals.

The layer charge characteristics of smectite from the Tertiary basins in the Pohang area, Korea have been studied in detail using the alkylammonium method. On the basis of layer charges, the smectite in the Pohang area can be classed as normal and high-charge (hc) smectite. The layer charge of the normal smectite averages 0.3, and ranges from 0.25 to 0.38/half unit-cell. The hcsmectite collapses on K saturation to become illite-like material and shows 10 Åseries reflections on X-ray diffraction. The layer charge of the hc-smectite ranges from 0.5 to 1. The layer charges do not appear to be related to stratification or to basins of occurrence. The diagenetic trend that may have existed in the region was probably disturbed by later volcanic activity. A systematic change in layer charge and geochemistry of smectite in Waeup illustrates that the heat and solutions associated with the volcanic activity may have played a role in the development of layer charge.

According to multivariate analysis, the following were established (a) kaolinite crystallinity index (KCI) values determined by XRD are highly correlated to one another and seemingly influenced by kaolin impurities; (b) kaolin minerals are concentrated mainly in the fractions <4 µm; (c) the kaolin surface area as determined by the BET (nitrogen adsorption) method is more markedly affected by kaolin impurities than by kaolin minerals themselves; (d) BET surfaces increase when kaolinite crystallinity decreases; (e) brightness is inversely correlated with kaolin impurities; (f) the more ordered the kaolinite and the greater the proportion in the <4 µm fraction of the kaolin, the greater the brightness; and (g) KCI values are particle size-distribution dependent for sedimentary-residual kaolins. The correlations obtained were better when kaolins were selected according to their origin because the kaolin minerals and their impurities, particle size-distribution and texture were more alike. The industrial properties of kaolin can not be predicted from other basic properties such as mineralogy, KCI, etc., because they are intricately related to one another.

Clay from Fourges has been selected by the Commissariat à l'Energie Atomique as a support in radioactive waste disposal studies. This material was activated by adding Na2CO3, then compacted at 60 MPa. Subsequently, its swelling behaviour was monitored at 90°C and 145°C for 330 days and at the end of this period the samples were examined by transmission electron microscopy (TEM). For this, they were embedded in a resin then sectioned with an ultramicrotome for mineralogical and chemical analyses. The initial material is essentially composed of kaolinite and smectite. Addition of Na2CO3 at room temperature induces a replacement of Ca ions by Na ions and the precipitation of finely divided carbonates on the surface of the constituents. At the end of 330 days at 90°C under a hydraulic pressure of 1 MPa, the initial particles combine and the material exerts a swelling pressure of 20 MPa. A complete reorganisation of the clay crystallites is observed without significant dissolution of the solid phases. After the same time at 145°C under a hydraulic pressure of 10 MPa, in a basic medium, the combined conditions are such that a high proportion of the clay is dissolved with formation of amorphous aluminosilicates correlated with a marked drop in the swelling pressure to 5 MPa. This work establishes the advantages of following the macroscopic properties in parallel with the microstructure variations for understanding the changes in the properties of clays.

Fifteen Swedish and Finnish soil samples from spodic B horizons containing imogolite-type materials were equilibrated with dilute NaCl and HC1 at 8°C. For the NaCl extracts, apparent equilibrium with respect to an AI(OH)3 phase was reached in one to two weeks. Equilibrium with respect to an imogolite-type phase was slower, especially at large soil:solution ratios. The results show that log *Ks (gibbsite), i.e. the logarithm of the solubility constant for reactive AI(OH)3 at 8°C was ~9.40 (8.29 at 25°C) while log *Ks (imogolite) was variable; for the soil studied in most detail it was 7.66 (6.64 at 25°C) As well-ordered gibbsite rarely forms in spodic B horizons, it is suggested that Al(OH)3 and poorly-ordered allophanic materials may be slowly converted to less soluble and less reactive imogolite-type materials.

The kinetics of structural change of a highly ordered kaolinite intercalated with potassium acetate have been studied through both intercalation and deintercalation. Deintercalation of the intercalated kaolinite, brought about by washing for different time intervals was followed by both X-ray diffraction and Raman microscopy. X-ray diffraction shows the kaolinite to be highly ordered with a Hinekley index of 1.42 and intercalated to ~90%. X-ray diffraction also showed that the intercalated kaolinite was deintercalated by 80% in the first minute of washing. An additional Raman band, attributed to the inner surface hydroxyl groups, strongly hydrogen bound to the acetate, is observed at 3605 cm-1 for the potassium acetate intercalate with the concomitant loss of intensity in the bands at 3652, 3670, 3684 and 3693 cm-1. Upon deintercalation, the intensity of the 3605 cm-1 band decreased as the 3695 cm-1 band increased. The Raman spectral changes brought about upon deintercalation mirrored the changes observed by X-ray diffraction. Deintercalation of kaolinite caused disordering of the kaolinite.

An attempt has been made to assess new potential applications for the Bailén clays, traditionally used for manufacturing bricks, based on mineralogical, chemical, particle size, plasticity and firing results. Raw materials and mixtures used by the local factory were selected and tested with the addition of some diatomite, feldspar or kaolin. Based on their properties, clay materials from Bailén might be suitable for making porous red wall tiles, clinker, vitrified red floor tiles and porous light-coloured wall tiles by pressing; the first could be manufactured from the raw materials and mixtures currently used by the local manufactures. On the other hand, stoneware shaped by extrusion, such as perforated bricks, facing bricks and roofing tiles, can be also manufactured from the mixtures used at the factory if they contain 20-25% carbonate and small amounts of iron oxides; lightweight bricks require black and yellow clays with diatomite.

Iron(II)-containing minerals are potential inorganic nitrate reductants in soils and sediments. Specifically, synthetic green rust (Fe4IIFeIII2(OH)12SO4.yH2O, GR) reduces nitrate to ammonium. The reaction of GR with two different nitrate salts, NaNO3 and Ba(NO3)2, has been compared. The reaction stoichiometry and the reaction order with respect to Fe(II) in GR does not change in the examined temperature range (15-50°C) irrespective of the nitrate salt used. Activation energies of 83.9±7.6 kJ mol-1 and 90.5±6.9 kJ mol-1 have been determined for the reaction of GR with NaNO3 and Ba(NO3)2, respectively. However, for the latter reaction the rate of reaction is increased 40 times. Based on X-ray and M6ssbauer investigations, this acceleration of the reaction rates is attributed to the forced exchange of sulphate with nitrate in GR interlayers caused by precipitation of BaSO4 outside the GR particles, a reaction which does not occur in the presence of NaNO3. This difference in anion exchange behaviour is confirmed by anion exchange experiments with the redox-inactive GR-analogue, pyroaurite. A reaction model initiated by nitrate electrostatically bound at positively charged sites of GR is proposed.

This paper aims at characterizing the structural and textural evolution of three mixed-layered clays in Ca-form from Southern and Central Tunisia, These samples contain various amounts of mixed-layer smectite-illite associated with crystallites of kaolinite. The clay fractions were prepared in the Ca-form and submitted to suction pressures increasing from 3.2 up to 1000 kPa. The structural and textural changes of the pastes obtained were studied by TEM and SAXS. The TEM observations and SAXS quantitative analysis on samples at low stress (3.2 kPa) showed that the thickness of the particles (number of layers per particle) and their lateral extension (in the plane of layers) decrease with increasing illite content. The textural evolution during drying, as described by SAXS, is controlled by the geometry of particles which is determined by the mineralogy of the structural units. With increasing illite content, the particles became shorter, rigid and had flat surfaces. This geometry increases their ability to associate face-to-face during dehydration. When the 2:1 fraction contains a high proportion of smectite, the architecture of the clay-water system at high water content (low stress) seems to be analogous to that of smectites. However, contrary to the behaviour of pure smectites reported in the literature, desiccation led first to a rupture of particles and a reorganization of the geometry of the pore system. This behaviour is due to the rigidity of particles caused by the presence of non-exchangeable K. The structural evolution showed that for an illite-rich sample a transition from the three-water layer to the one-water layer state occurred at 1000 kPa, whereas for smectite-rich materials, the hydration state of layers, i.e. three water layers, was not affected.

The interaction between phenyl salicylate and sepiolite has been studied using drugclay systems obtained by melting and grinding. The samples have been characterized by powder Xray diffraction, differential thermal and thermogravimetric analyses, and Vis-UV and FT-IR spectroscopies. ‘Free’ water molecules are steadily substituted by the drug molecules, without any chemical change as shown by FT-IR. The systems prepared improved the protecting ability of the pure sepiolite or the pure drug against ultraviolet radiation, especially in the so-called ‘C’ range (290-190 nm).

Although the kinetics of the dehydroxylation of kaolinite have been widely studied, there is no definitive explanation of its mechanism due to its dependence on a variety of parameters. In this study, the dehydroxylation of kaolinite has been studied using controlled-transformation rate thermal analysis (CRTA), allowing precise control of the reaction rate, and thus of both the temperature and pressure above the sample. Modelling of the experimental results obtained by CRTA as well as those from TEM and MAS-NMR show that two elementary processes (diffusion and firstorder) can occur in competition. At the start of the decomposition the diffusion mechanism is predominant, but as the reaction progresses, the first-order mechanism prevails. It would seem that the importance of each process depends, in particular, on the presence of defects as well as on the local vapour pressure.

Nitrogen adsorption isotherms were measured on synthetic 2-line and 6-line ferrihydrites heated to 400 K, 500 K, and 600 K under dry conditions for different times ranging from 4 to 3000 h. Evaluation of specific surface area, microporosity and fractal dimension revealed that 2-line and 6-line ferrihydrites are highly microporous powders consisting of aggregates with corrugated interior and exterior surfaces. Furthermore, the surfaces of the single particles forming the aggregates have a smaller fractal dimension, i.e. a smoother appearance, than those of the entire aggregate. The diffusion of water lost during the heating process is influenced by the size of the micropores. The initial stage of the dehydration of the ferrihydrites can be described as similar to the process of Ostwald ripening.

The Athabasca oil sands deposit in Alberta contains ~5 x 109 m3 of bitumen accessible by surface mining. During bitumen separation from the mined ore, ultra-fine (<300 nm) aluminosilicate clays only a few layers thick (U/F) are mobilized and become dispersed in the process water. In this water containing dissolved salts from natural deposits, U/F are capable of forming thixotropic gels. The consequence of this is the production of large volumes of mature fine tailings (MFT) with a high water holding capacity. For mine planning purposes, the objective of predicting and possibly mitigating MFT formation requires an understanding of the colloidal behaviour of U/F particles in salt solutions. In this work, photon correlation spectroscopy and the deuterium NMR method are used to provide an insight into the U/F floc formation process. These results are correlated with conventional analysis of settling data.

The observation of clayey matrix on a thin-section under polarized transmitted light allows the analysis of the clay particle arrangements, the measurement of their orientations in 3-D, and finally the cartography of the different orientation modes by using a simple image analysis system connected to the optical microscope. The method is based on: (1) the analysis of the shape evolution of the grey-level diagram vs. the rotating stage angles; and (2) the mathematical decomposition of these grey-level diagrams into elementary gaussian curves. For each identified orientation mode, the standard deviation of the grey values gives the dispersion index of the oriented particles around the axial plane. The 3-D representation is performed on the Wulff stereonet. The horizontal orientations are measured by simple rotation of the revolving stage and the dip angles are deduced from the peak displacements along the abscissa of the grey-level diagram during the complete rotation of the revolving stage. The quantifications (percentage, isotropy and distribution index) are performed after a thresholding operation of each orientation mode.

A dioctahedral bentonite was treated hydrothermally with KCI solutions (0.025-1 M) at different temperatures (60-200°C) and times (1-360 days) to evaluate its use as a barrier for radioactive waste disposal. Equations relating adsorbed K on smectite with initial and equilibrium K concentrations in solution, temperature and time have been obtained. These equations are useful for modelling the influence and behaviour of these variables and contribute to the performance assessment calculations for radioactive waste repositories. Likewise, the thermodynamic parameters of the K adsorption process have been calculated. Other relationships, including silica in solution and pH, are also shown.