A comparative study using bentonite (BT), hexadecyltrimethylammonium-modified bentonite (BT-HDTMA) and phenyl fatty hydroxamic acid-modified bentonite (BT-PFHA) as adsorbents for the removal of Pb(II) has been proposed. These adsorbents were characterized by X-ray diffraction, X-ray fluorescence, Fourier-transform infrared spectroscopy and surface area measurement. Cation exchange capacity was also determined in this study. The adsorbent capabilities for Pb(II) from aqueous solution were investigated, and the optimal experimental conditions including adsorption time, adsorbent dosage, the initial concentration of Pb(II), pH and temperature that might influence the adsorption performance were also investigated. The experimental equilibrium adsorption data were tested by four widely used two-parameter equations, the Langmuir, Freundlich, Dubinin- Radushkevich (D-R) and Temkin isotherms. The monolayer adsorption capacities of BT, BT-HDTMA and BT-PFHA for Pb(II) were 149.3, 227.3 and 256.4 mg/g, respectively. The experimental kinetic data were analysed by pseudo-first order, pseudo-second order and intraparticle diffusion kinetics models. The experimental data fitted very well with the pseudo-second order kinetic model. Determination of the thermodynamic parameters, ΔG, ΔH and ΔS showed the adsorption to be feasible, spontaneous and exothermic.

Smectitic clays from the Sabga and Bana areas, western Cameroon were treated with sulfuric-acid solutions of various concentrations – 0.5, 0.7, 1.0 and 4.0 N – at 80°C for 2 h. The mineralogical, physicochemical and morphological characteristics of the samples treated were analysed using several techniques. The sulfuric acid caused structural modification of the dioctahedral smectite. The accessory minerals such as cristobalite, quartz, feldspars and anatase remained unaltered by the acid attack. The supernatant solutions after acid treatment contain Mg, Ca, K, Na, Si, Al and Fe as a result of partial dissolution of octahedral and tetrahedral cations. The activated clay samples exhibited a smaller cation exchange capacity (CEC) and the specific surface area (SSA) increased with increasing concentration of sulfuric acid, ranging from 65 to 134 m2/g for the sample from Bana and from 74 to 84 m2/g for the sample from Sabga. The different SSAvalues were affected by the relative abundance of smectite and cristobalite (SiO2/Al2O3 = 2.2 and 6.5, respectively, from Bana and Sabga). The activated clays from Bana and Sabga displayed interesting physicochemical and textural properties and can be considered as promising adsorbents for the bleaching of vegetable oils.

Hydrolytic exchange was performed experimentally on four smectitic clays to evaluate the extent of clay alteration induced by this process and the associated ‘auto-transformation’ of H+ clays. Clay samples were Na-saturated and submitted to 10, 50 and 100 wetting-drying (WD) cycles and characterized after treatment using X-ray diffraction (XRD), infrared spectroscopy (FTIR) and cation exchange capacity analysis. Evidence for hydrolytic exchange was given by increasing amounts of exchangeable Mg2+ and precipitation of Na soluble salts for samples subjected to 100 WD cycles. Results indicated a decrease in the interlayer charge after 10 WD cycles but no further decrease was observed after 50 and 100 WD cycles. For one sample, XRD data indicated a decrease in the proportion of the smectite phase and a relative increase in the concentration of illite-smectite mixed layers also present in the sample. The results suggested that the reaction induces first a decrease in the layer charge and then a partial dissolution of some smectite layers.

Indurated volcanic soils (tepetates) of the Mexican Altiplano display thick columnar horizons, hard laminar horizons, and grey mottles at depth. X-ray diffraction (XRD) studies show a relative enrichment in cristobalite vs. halloysite in the indurated plates of the laminar horizons and in the clay fraction of the mottles. Transmission electron microscopy (TEM) and high-resolution TEM (HRTEM) studies of these two soil components have shown that they are composed of small tubes of halloysite in which numerous globular grains ∼1 μm in diameter are embedded. Based on the relative abundance of cristobalite in pedological features and on the spatial relations between successive mineral phases, we interpret the cristobalite as a transformation of halloysite with a transitional amorphous phase. In the globular grains, large platy 1:1 clay minerals undergo a progressive transformation into platy particles of opal-A and opal-C. These are in turn transformed into cristobalite without further major change in their shape and appearance, except for a higher electron density than opal and clay.

A unified system of projection of chemical composition, prepared initially for micas and chlorites, has been applied to minerals of the serpentine-kaolinite group. It has been shown that the chemical composition in the projection field is controlled by the formula, the unit of which is: (Si(2-x)Alx)O5(OH)4, where u+y+z=3, z=y-x. Using projection fields for different chemical systems it has been shown that among the most important end-members are kaolinite minerals, true serpentines, berthierine, brindleyite, amesite, cronstedtite, greenalite, nepouite and their analogues having different substitutions in the octahedral sheets.

X-ray diffraction (XRD), infra red (IR) spectroscopy, gloss goniophotometry and stylus profilometry were used to investigate the alignment of kaolinite applied as a thin coating on a polyester film substrate. The principles and applicability of the analytical methods are reviewed and discussed in the context of a kaolinite coating. X-ray diffraction and transmission IR were used to measure kaolinite misalignment and orientation distribution in the coating. Transmission IR measures the coating bulk; XRD data are surface biased, but contain contributions from the bulk. Attenuated total reflectance-IR (ATR-IR) provides a direct measure of kaolinite alignment within ~1 µm of the coating surface and also allows an assessment of surface smoothness. Gloss goniophotometry and contact profilometry measure surface microroughness and macroroughness, respectively, rather than kaolinite particle orientation. However, the properties of roughness and orientation are related. Bulk and surface texture are not necessarily correlated and a combined approach using both bulk and surface sensitive techniques is required for a full understanding of coating structure.

The intercalation complex of kaolinite and potassium acetate (KAc) was studied by HTXRD, IR spectroscopy and DTA-TG. The HTXRD patterns indicate that the 14.06 Å basal spacing of the complex contracts to 11.77 Å and 9.35 Å after heating at 60°C. The DTA-TG data indicate that water is present in these new complexes, the decomposition of which occurs between 290°C and 400°C. Modifications observed in the high-frequency region of the spectra obtained after heating suggest that K ions occupy the ditrigonal holes in the OH surface of the kaolinite layers, whereas water is probably located between the KAc layer and the OH surface of the kaolinite. This structural arrangement would favour the H-bonding between inner-surface OH groups and water and justifies the presence of new bands at lower frequencies. Electrostatic interactions between the keyed K ions and O of the inner OH groups would justify the modifications of the 3619 cm-1 OH-stretching band.

Aeolian sandstones of the Lower Permian Leman Formation (Rotliegend Group) provide the best gas reservoir in the southern North Sea, but permeability is greatly reduced by the presence of authigenic fibrous illites. New radiogenic (K/Ar) and stable (oxygen and hydrogen) isotope data are presented for fibrous illite cements (<0.1 µm), so that the absolute timing and controlling diagenetic factors for their formation can be more fully evaluated. Thus, the expected quality of gas reservoirs in the southern North Sea might be better predicted. Samples have been analysed from five wells in areas with contrasting structural evolution: the Sole Pit Basin, and the Indefatigable Shelf. The K/Ar ages of between 160 and 190 Ma have been obtained from the Indefatigable Shelf illites, and between 120 and 160 Ma for those from the Sole Pit Basin, reflecting different times of basin inversion. These K/Ar ages are interpreted by reference to burial/thermal models for each well. The temperature of illite precipitation falls between 88 and 140°C. Calculated pore-fluid compositions derived from oxygen and hydrogen isotopic analyses give values of ∼ + 1 to +9‰ (SMOW) δ18O and +1 to −50‰ (SMOW) δD. The illite δD values have probably been affected by isotopic exchange and fractionation with the surrounding gaseous hydrocarbon. The δ18O values reflect the degree to which evaporative concentration had affected Zechstein marine waters which subsequently invaded the Leman Sandstone. Comparisons between δ18O and δD values in clays and in formation water for the Leman Field suggest that oxygen isotope exchange might have taken place, and that the initial K+ and radiogenic 40Ar contents within illites may have been modified.

The fractal dimension values of several kaolins with different structural order and properties have been calculated from N2-adsorption isotherm data according to the Neimark method. All kaolins show a fractal regime in the same nitrogen relative pressure range, with fractal dimension values ranging between 2.38 and 2.57.

The correlation between fractal dimension and other kaolin characteristics (structural order of kaolinite, BET surface area, brightness and particle-size distribution) was determined. The correlation matrix shows that the fractal dimension (Ds) is highly correlated with the degree of structural order-disorder and is also moderately correlated with the particle-size distribution and brightness. No correlation was observed between BET and Ds, probably because the first is a measurement of the accessible surface while Ds represents the scaling properties of the area.

As Ds is a parameter easily calculated and related to the degree of surface heterogeneity, and well correlated with other kaolinite parameters, it can be used to estimate a set of kaolin technical properties for suitability of the kaolin in the paper industry.

On étudie les équilibres de distribution de deux éléments de transition divalents A,B, entre gels silicatés inorganiques de formule SiO2-(A,B)O-nH2O et solutions aqueuses A2+,B2+ (A.B = Mg, Mn, Ni, Co, Cu, Zn). On montre que l'enthalpie libre molaire standard d'échange de deux éléments A,B entre gel et solution est une fonction linéaire de l'enthalpie libre d'échange calculée en considérant un échange théorique entre hydroxyde et solution. Les relations obtenues permettent de prévoir le comportement d'autres éléments divalents.

Mineralogical and geochemical techniques have been used to determine the role of minerals in controlling the trace element composition of a set of clay-sized fractions from Albian siliciclastic rocks in NE Spain. These clay-sized fractions are composed of kaolinite and illite, minor quantities of quartz, and accessory heavy minerals. Kaolinite has a smaller crystal size than illite, accounting for its relative concentration in these fractions. The µm-sized heavy minerals are rutile, Fe-Ti- and Fe-oxides, zircon, pyrite, cassiterite, monazite and xenotime. Geochemical data indicate that most of the trace elements are relatively concentrated in clay-sized fractions, except for Zr, Hf, Y and HREE. Statistical treatment shows three different associations in the clay-sized fractions: (1) Rb, Cs and Ba with clay phyllosilicates, especially illite; (2) REE with Th, Y and P phases; and (3) Sc, Cr and V with Ti- and Nb oxides. Therefore, these data do not support the dominant REE control by clay mineralogy that other authors have reported.

Smectites were synthesised hydrothermally from zeolites in an Mg-rich brine at 300°C under a confining pressure of 30 MPa and characterized by XRD using the Greene-Kelley Li-saturation test and the K+-saturation/glycolation test. The synthetic smectites were found to be dioctahedral with only tetrahedral negative layer charge; the layer charge was also deduced to be low and they are classified as beidellites. The mechanism of formation includes H+ saturation of zeolites by the hydrolysis of Mg2+ under hydrothermal conditions, followed by decomposition of the zeolites and recrystallization to beidellites. These results show that solution chemistry is an important factor affecting stability of zeolites under hydrothermal conditions.

Mudrocks and sandstones from the Palaeocene of the central North Sea have been studied to assess the petrology, diagenesis and extent of any chemical interaction between the two lithologies. Authigenic and detrital minerals have been distinguished using a variety of electron microscope techniques. Small but significant quantities of authigenic minerals, which would not be detected by conventional petrographic tools, have been detected through the use of high-resolution electron beam techniques. Sandstone mineralogy has been quantified by point counting, and mudrock mineralogy semi-quantified by XRD. The detrital and authigenic mineralogy in the sandstone is almost identical to that found in the mudrock. The principal difference is in the relative proportions. Qualitative mass balance suggests that cross-formational flow has not been significant in either clay or quartz diagenesis.

Diagenetically modified muscovite grains occur as a frequent component of many Upper Palaeozoic and Mesozoic fluvial-deltaic sandstones and siltstones from Britain and the North Sea. Mineralogical, textural and chemical investigation of examples from the Great Limestone Cyclothem show that such grains consist simply of muscovite and kaolinite. No other sheet-silicate phases are involved. Diagenetic textures indicate that modified grains result from the displacive growth of kaolinite between opened cleavage sheets of detrital muscovite. Fabrics of this type should consequently be termed kaolinite-cemented. In contrast to similar sheet-silicate intergrowths reported from diagenetically altered biotite and chlorite, little or no alteration of muscovite is actually required to account for observed textures.

Kaolinite and synthetic γ-Al(OH)3 (gibbsite or hydrargillite) were reacted with phenylphosphonic, phenylphosphinic and 2-nitrophenol-4-arsonic acids. The products were studied by powder X-ray diffraction, transmission electron microscopy/selected area electron diffraction/ energy dispersive X-ray/Fourier transform infrared and simultaneous thermogravimetric/differential thermal analysis. The acids were not intercalated but, instead, easily destroyed the structure of the minerals. Lamellar Al phenylphosphonate and aluminium phenylphosphinate and phenylarsonate with polymeric linear-chain structures were formed from kaolinite. The reaction between gibbsite and the same acids yielded almost identical products. No evidence of formation of grafted kaolinite derivatives after the reaction with phenylphosphonic acid was found.

The radioactive contaminant plume in groundwater at the Karachai Lake site has been examined further. The source of pollution is the Karachai Lake which was used as a reservoir for liquid radioactive waste (LRW) from the Radiochemical Production Association “Mayak” (South Urals, Russia). Taking into account that colloid-facilitated transport of radionuclides can substantially increase the contaminant migration velocity, the composition and structure of colloid particles from the groundwater within the contaminant plume were studied. Sampling of groundwater was carried out in the observation well within the contaminant plume. Different fractions of colloid particles were extracted from the groundwater samples by sequential filtration through membranes with decreasing pore size. Chemical and mineralogical compositions of the colloid particles were determined by X-ray photoelectron spectroscopy in combination with ion etching of the particle surfaces. The host rocks were studied using characteristic samples from the surface outcrop nearest to the observation well. The analysis showed that the colloid particles consisted of an inorganic core with a discontinuous organic cover. The inorganic core was close in composition to the host rocks along the flow path with a predominance of layered hydrosilicates.

CP (Cetylpyridinium)-exchanged smectite was manufactured by the cationic exchange reaction of Na-smectite with CP. The adsorption behaviour shows a typical L-type isotherm representing continuous and stable adsorption in excess of twice the cation exchange capacity of CP. CP-smectite shows a strong interlayer (d001) expansion to 40.2 Å when an amount of CP equivalent to 140% of the CEC is exchanged into smectite. CP-smectite is characterized by strong alkalinity (pH 9.3), low swelling (4.5 ml/2 g), low viscosity (3.9 mPa s), and strong and fast flocculation. These characteristics are in striking contrast to Na-smectite except for the alkalinity. CP-smectite shows no signs of desorption of the organic species under varying pH conditions (pH 2–12). Desorption is slight even when washed three times with DH2O (distilled water). Pyrolysis of CP-smectite begins at 250°C and ends at 400°C. These stable and persistent characteristics and the relatively low price of CP point to the likely increased use of CP-smectite as an organoclay.

Isocitric acid oxidative decarboxylation was realized in the absence and in the presence of homoionic Na+-, Mn2+-, and Cu2+-montmorillonite. The catalytic activity of the clay depends upon the nature of the interlayer exchangeable cation. Isocitric acid is transformed into α-ketoglutaric acid under the action of the clay mineral saturated with Na+ cations which do not form a complex with the isocitrate anion. Nevertheless, the reaction rate is very much lower than in the presence of the enzymatic system (isocitrate dehydrogenase enzyme and nicotinamide adenine dinucleotide phosphate coenzyme). The reaction mechanism in the presence of clay is given showing the different steps of the transformation.