The present study investigated the adsorption behaviour of Direct Orange 34, a highly toxic dye used in textile industries in Tunisia, on modified kaolinite-rich clays. A kaolin from the Sidi Bader (SDB) area was activated with hydrochloric acid to create the activated clay referred to hearafter as SDBa, or treated with FeSO4•7H2O to obtain its Fe-saturated form, Fe-SDB. The adsorbents were characterized by X-ray diffraction, X-ray fluorescence, transmission electron microscopy, BET surface area and zeta-potential measurements. The equilibrium adsorption data were analysed using the Langmuir and Freundlich isotherms. The estimated adsorption capacities (qm) for the dye were improved in the Fe-loaded samples. The good fit (R2 = 0.99) with a pseudo-second order expression suggests that the adsorption process could be effective following a chemisorption mechanism. At acidic pH, the optimum dye-retention rate was achieved for SDB (83%) after 60 min. The uptake decreased at neutral pH and increased again in alkaline media. This behaviour might be explained by the formation of covalent bonds between the OH radicals on the external surface and the negatively charged dye molecules. On the other hand, Fe impregnation increased the zeta potential of kaolinite, leading to a greater adsorption capacity compared to its natural and acid-activated counterparts. In addition, the adsorption rate increased when increasing the suspension temperature from 283 to 313 K. The modified kaolinite-rich materials showed satisfactory affinity for adsorbing this reactive dye.

This contribution is the second part of an in-depth study on the hydration and strength evolution of blended cement pastes at a water to binder (W/B) ratio of 0.3, cured by two different methods. The blended cement pastes showed significant hydration up to 7 days, when almost all of the hydration products had already formed; thereafter, carbonation played an important role up to, and possibly beyond, 91 days. Likewise, the hydration of alite (tricalcium silicate, Ca3SiO5, C3S) proceeded up to 14 days and then started to slow down. However, the hydration of belite (dicalcium silicate, Ca2SiO4, C2S) was affected most strongly, as it nearly ceased, under the air-curing conditions. During hydration, some of the blended cement pastes had a larger calcium hydroxide (CH) content than the unblended (plain) ones. The accelerating effects of the addition of supplementary cementitious materials (SCMs), the air-curing conditions and the low W/B ratio may explain these unusual results. Under these experimental conditions, the water incorporated into hydrates was about 50% of the total amount of water used during full hydration of the cement pastes. The pozzolanic reaction predominated during the early ages, but disappeared as time passed. In contrast, the carbonation reaction increased by consuming ∼45% of the total amount of CH produced after aging for 91 days. Only one blended cement paste reached the compressive strength of the plain cements. The blended cement pastes containing 5% of the zeolitic tuffs, Zeo1 or Zeo2, or 10% of the calcareous siltstone, Limo, developed the greatest compressive strength under the experimental conditions used in this study.

The clay mineralogy and surface charge characteristics of four basaltic soils from Western Samoa have been studied. The soils contained subordinate to dominant amounts of poorly ordered allophanic material in addition to varying amounts of crystalline free iron oxide minerals. Infrared studies revealed the presence of trace to subordinate amounts of kaolin minerals in all the soils. The surface charge-pH curves followed a constant potential model indicating the presence of substantial amounts of pH-dependent charge. Some negative charge was present, however, at pH values as low as 3.0 and small quantities of positive charge were detected at pH values as high as 9. Values for PZC ranged from 2.2 to 3.9 and these were generally higher than the pHo determined by the ΔpH method.

The exchange reaction of Na-bentonite with zirconium pillars gives products which suffer from a loss of crystallinity, with basal spacing about 18 Å and surface area of 200 m2 g–1. Aluminium introduced in different amounts in the zirconium intercalated solution leads to an improvement in the stability and crystallinity of zirconia-pillared clays (Zr-PILCs) and creates pillared clays with new properties. Adding a small amount of Al (10 molar %) leads to an increase of d001 from 18 Å to 20.5 Å and an increase of the percentage of introduced zirconium from 16.71 to 21, expressed as ZrO2 wt.%, accompanied by an increase of the Brönsted and Lewis acidic sites. The acetalization of acetone with ethylene glycol was studied in order to compare the activity of PILCs. The results show that the yield of the aforementioned reaction depends strongly of the composition and acidity of the catalyst.

Commonly streaks and rarely extra spots are observed on the selected area diffraction patterns of beidellite. The streaks are non-radial, and are restricted along the direction parallel to [11], [11], and [01]. Extra spots appear instead of streaks between the normal Bragg spots along the direction parallel to [11] and [11]. These extra spots suggest the formation of a superlattice with the a and b cell parameters twice as large as those of the beidellite lattice. Dark-field images on the strong 020 reflection reveal the presence of a network of dislocations in some of the beidellite crystallites. These dislocations suggest that the chemistry is not uniform over the successive layers in these crystallites. The structural difference between the layers seems to be accommodated by the dislocations.

A 65 m thick altered volcanic profile was studied in the Cava di Caolino (Lipari Island) in order to (1) identify the alteration event(s), (2) model these events, and (3) propose estimates of the degree of chemical alteration (CIA, chemical index of alteration). Two mineral parageneses were identified: one comprising silico-aluminous phases, with well crystallized kaolinite (type 1), and the other comprising sulphates, with kaolinite as fracture infilling (type 2). The geochemistry of fluids analysed from a local hot spring (40°C, pH ≈ 8) allowed modelling of the observed silico-aluminous paragenesis. A later fumarolic event is suggested to be responsible for the sulphate paragenesis. The main stage of hydrothermal alteration lasted for ~50 ky, was marked by an increase in the CIA from the protolith (~52) to the alterites (~98), and resulted in the alteration of a 65 m thick series. Such data could be used to predict the alteration of volcanic rocks around underground nuclear waste repositories.

Aqueous suspensions of sepiolite, tagged with fluorescent dyes, have been studied using electro-fluorescence polarization spectroscopy. The binding modes of some 37 fluorescent dyes and optical brightening agents to the rod-like sepiolite particles have been determined. Many of the dyes are found to bind with a degree of order to the clay particle's major axis. The binding geometries of the cationic dye molecules tested were found to be dependent upon molecular size. This supports the view that these cationic dye molecules are constrained within the channels which are characteristic of the mineral sepiolite. Results for uncharged and anionic dye molecules are also presented; no dependence of binding geometry upon molecular size was found. The anionic molecules are most likely to associate with the exterior cationic magnesium surface. The results indicate that some of the anionic dyes are too large to fit in the channels. Some of the uncharged molecules adopt a number of orientations upon binding which gives rise to an average geometry being observed for these dyes.

Bei der Untersuchung von 6 Glaukonitproben mit Hilfe der ‘H-Kernresonanz-Spektroskopie zeigen sich deutlich zwei verschieden gebundene OH-Gruppierungen. Wàhrend die relativ scharfen Signale A auf die in der Oktaederschicht flxierten zwei OH-Gruppen zuriickzufuhren sind, muB fiir die anderen OH-Gruppen des breiteren Signals B eine andere Bindungsnatur gefordert werden. Es ist móglich, dafl es sich bei den OH-Gruppen des Signals B ebenfalls um verschieden gebundene OH-Gruppen handelt und zwar um solche, die an Eisenhydroxid- Verunreinigungen gebunden sind und solche, die zwischenschichtlich in Form von Eisen-Hydroxo-Komplexen gebunden sind. Eine Unterscheidung zwischen letzteren beiden Mòglichkeiten ist aber nicht mòglich.

An earlier paper (McConnell, 1950), outlines a structural hypothesis according to which high-temperature water occurs in the tetrahedral layers of montmorillonite. In real crystals of montmorillonite, hydroxyl ions are presumed to be distributed at random within the Si2O5 layers in such a manner that four hydrogens substitute statistically for one silicon—the number of oxygens remaining unaltered. In an idealized model the hydroxyls are visualized as forming discrete (OH)4 tetrahedra which are linked at three vertices to other tetrahedra of the sheet in the same manner as the SiO4 tetrahedra for which they substitute.

Liberation of tetrahedral water was employed as a basis for partially explaining the second high-temperature endotherm of the differential thermal analysis, whereas it was indicated that the quantity of water liberated during the first high-temperature endotherm appears to be essentially equal to the theoretical hydroxyls required for octahedral co-ordination. The number of hydroxyl ions that occur in the silica sheets is presumed to be small but, nevertheless, sufficient to cause anomalies in rigorous calculation of the contents of the unit cell.

The gold-decoration technique of electron microscopy is used to study the surface microtopography of natural (001) surfaces of sudoite collected from a hydrothermal vein of the Berezovsk gold deposit, Central Urals, Russia. Only closed step patterns with malformed and/or nearly circular islands were observed on the (001) growth surface of sudoite crystals, implying a twodimensional nucleation mechanism. This is in contrast to the spiral step patterns commonly recognized on growth surfaces of other clay minerals, such as illite and kaolinite, formed under hydrothermal conditions. It is inferred that the crystallization of sudoite occurred under relatively higher temperatures and/or from more highly supersaturated fluids than many other hydrothermal clay minerals so far described.

Alumina-pillared fluorine micas were prepared from synthetic highly layer-charged expandable fluorine mica and polyhydroxoaluminium solutions under different solution loadings (Al mmol in solutions per 1.0 g mica) in order to clarify the effects of solution loading on thermal durability and microporous properties. The intercalated Al content of the pillared micas increased with increased solution loading. The intercalated Al content (i.e. the pillar density) of the pillared micas influenced both the thermal durability and specific surface areas of the pillared micas. The pillared micas obtained from the high solution loadings showed better thermal durability than those obtained from the low solution loadings. Through micropore formation upon heating, the pillared micas exhibit cation exchangeability due to the liberation of residual Na+ ions from steric hindrance in the interlayer pillaring space. The amount of the exchangeable ions depends on the heating temperature of the pillared micas.

Swelling deformation tests of Kunigel bentonite and its sand mixtures were performed in distilled water and NaCl solution. The salinity of NaCl solution has a significant impact on the swelling properties of bentonite, but not on its surface structure. The surface structure was characterized using the fractal dimension Ds. Based on the fractal dimension, a unique curve of the em–pe relationship (em is the void ratio of montmorillonite and pe is the effective stress) at full saturation was introduced to express the swelling deformation of bentonite–sand mixtures. In mixtures with a large bentonite content, the swelling deformation always followed the em–pe relationship. In mixtures with a small bentonite content, when the effective stress reached a threshold, the void ratio of montmorillonite em deviated from the unique em–pe curve due to the appearance of a sand skeleton. The threshold of vertical pressure for mixtures in different solutions and the maximum swelling strains were estimated using the em–pe relationship. The good agreement between estimates and experimental data suggest that the em–pe relationship might be an alternative method for predicting the swelling deformation of bentonite–sand mixtures in salt solution.

Potential secondary influences on titanium distribution should be evaluated when using ash beds as volcanic source indicators and for correlation purposes. In this study, well-correlated altered ash beds in Permian–Triassic boundary (PTB) successions of various facies in South China were investigated to better understand their use in source discrimination and stratigraphic correlation. The ash beds deposited in lacustrine and paludal facies contain significantly more Ti relative to deposits in marine facies. Neoformed anatase grains nanometres to micrometres in size are associated closely with clay minerals, whereas detrital anatase was observed in the remnants of altered ash beds of terrestrial facies. Extraction of the clay fraction of altered ash beds may exclude significantly detrital accessory minerals such as anatase and rutile added during sediment reworking, and the concentrations of immobile elements in the clay fraction may therefore be used to interpret more effectively their source igneous rocks.

Detrital, volcanic and diagenetic origins have been used to explain the smectite clay assemblage that characterizes the Upper Cretaceous Chalk of Europe. To further the understanding of how clays of different origins may have converged to this characteristic clay mineral assemblage a new approach is put forward for their investigation. This is based upon (1) the correlation that exists between the trace element and stable isotope geochemistry of the calcite cements preserved within Chalk brachiopods and the various diagenetic phases of early lithification and cementation recognized in the Chalk, and (2) an understanding of the process of late diagenetic cementation that has caused regional differences in the hardness of the Chalk. It is suggested that each phase of lithification and associated calcite cementation may preserve the different clay assemblages at various stages in their convergence to the characteristic Chalk smectite assemblage.

The retention mechanisms of metal ions during interaction of clay with metal-rich aqueous solutions is usually investigated by sorption isotherms. Although classical isotherm models may provide sufficient information about the characteristics of the solid–liquid system, they do not distinguish among the various retention mechanisms. This study presents a methodological approach of combining batch experiment data and geochemical modelling for the characterization of the interaction of Mg-Fe-rich clay materials with monometallic solutions of Pb and Cu. For this purpose, a palygorskite clay (PCM), an Fe-smectite clay (SCM) and a natural palygorskite-Fe-smectite mixed clay (MCM) were assessed for their effectiveness as metal ion sorbents. The sorption capacity of the materials follows the order MCM > SCM > PCM and ranges between 27.6–52.1 mg g–1 for Pb and 7.7–17.6 mg g–1 for Cu. Based on the experimental results that allowed the speciation calculations, fitting of sorption isotherms and the investigation of relationships between protons, Mg and the metals studied we suggest that a combination of sorption mechanisms occurs during the interaction of clay materials with metal solutions. These involve surface complexation, ion exchange and precipitation of solid compounds onto the solid surface. A three-term isotherm model was employed to quantify the role of each of the above mechanisms in the overall retention process. The superior performance of mixed clay among the materials tested is attributed to the synergetic effect of exchange in the interlayer and specific sorption on the clay edges.

The chemical composition and structural characteristics of clays from samples of eight Tuscan soils were investigated. Using simple selective dissolution method (successive boiling in 1 N HCl and 0·5 N NaOH) it was possible to distinguish two types of low charge dioctahedral vermiculite; one easily HCl soluble the other practically insoluble.

Structural formulae for the soluble type were calculated from the chemical analysis of the dissolved material; for the insoluble type it was possible to calculate only an 'average' structural formula which included the micaceous material.

Since the HCl soluble vermiculites show a high content of Fe and Mg, they can be considered either as alteration products of glauconites or biotites, or as a result of a synthesis, at least in soils derived from basic rocks which do not contain mica.

The aluminous insoluble type, present also in parent material, may be the result of an incomplete 'illitization' in a marine environment.

The Georgia, USA, kaolins contain three major occurrences of Fe-sulphide minerals, namely (1) in burrow structures, (2) as nodules associated with lignite and (3) as finely disseminated material. We have used sulphur isotope analysis and X-ray powder diffraction to understand these three occurrences in order to gain insight into the diagenetic conditions and microbial influences affecting the kaolin mineralogy. Burrows and nodules are dominated by corroded marcasite with thin pyrite overgrowths. The δ34S composition of each sulphide sample has internal fractionations (δ34Shigh – δ34Slow) ranging from 22‰ to 67‰. The secondary pyrite phase tends to be the most 34S depleted, with a low δ34S value of –47‰, whereas marcasite displays a δ34S range from 30‰ to +33‰. Early acidic environments from organic acids could have facilitated the initial marcasite crystallization, with a pH increase during later diagenesis producing pyrite overgrowths. Sulphide formation would have continued until burial restricted the diffusion of sea-water sulphate. At this point, the metabolism of sulphate-reducing bacteria would have been retarded, producing δ34S values ranging from –30‰ (open sulphate supply) to +40‰ (highly restricted sulphate supply). Under the nutrient-starved conditions of later-diagenesis, disproportionate sulphur-reducing bacteria would likely have become more dominant, yielding additional δ34Ssulphide fractionation and producing the observed fractionation (δ34Ssulphate – δ34Ssulphide) values of +67‰.