Laponite RD forms stable, coherent films which adhere strongly to glass slides. Such films are capable of supporting liquid drops allowing the direct measurement of contact angles for five liquids of which, two were apolar (0:-bromonaphthalene and diiodomethane) and three were polar (water, formamide, glycerol); surface tension components and parameters (γLw, γ⊕ and γ⊖) were determined by solving the Young equation. These determinations were made for homoionic samples saturated with Li, Na, K, Rb, Cs, Mg, Ca, Sr, Ba and NH4 as well as the natural material. Whereas the values of γLw (the apolar Lifshitz-van der Waals component) varied only within narrow limits (41-44 mJ/m2), the Lewis base parameter varied comparatively widely (24-41 mJ/m2). The Lewis acid parameter was small and relatively constant (1·3-3·0 mJ/m2). The variation of γ⊖ as a function of the exchangeable cation suggests that the divalent cations are shielded from the silicate surface by the water molecules of their sphere of hydration, whereas the monovalent cations are in direct contact with the oxygen atoms of the silicate surface. Furthermore, the divalent cations may screen the Lewis base sites to a greater degree than do the monovalent cations. Lithium behaves anomalously and this may indicate that it physically enters into the ditrigonal hole in the silicate layer.

A basic lead carbonate-montmorillonitec omplexw as prepared by treating a natural montmorillonite hydrothermally for 120 h at 250°C with lead powder, dry ice and lead nitrate solution. The product is a non-swelling material showing well-outlined, hexagonal, thin plates <1 µm in size; the symmetry is pseudo-orthorhombic, a = 5·141(7) Å, b = 9·005(5) Å, c = 17·420(4) Å, and Z = 2. The X-ray powder pattern is characterized by a 17·4 Å reflection and an integral series to the 14th order. The TG-DTA curves of this 17 Å-mineral showed one endotherm around 400°C accompanied by weight loss and two exthotherms at about 680 and 780°C By applying hightemperature X-ray diffractometry (XRD) and infrared (IR) spectroscopy, it was found that the endotherm is due to decomposition of carbonate hydroxide in the interlayer, while the two exthotherms are caused by crystallization of a hexagonal phase of PbAl2Si2O8 and by the conversion of this phase into lead feldspar, respectively. The crystal structure of the 17 Å-mineral was determined and refined as a 2:1 dioctahedral smectite interlayered with a hydrocerussite-like layer by a one-dimensional Fourier synthesis method.

The effect of temperature on the swelling of clay was studied by determining (1) the relation between the interlayer spacing, λ, and the swelling pressure,Π, at different values of the temperature, T, using the method of Viani et al. (1983) as modified by Wu et al. (1989); (2) the relation between λ and T at different values of Π; and (3) the relationship between Π and mw/mc, the mass ratio of water to clay, at different values of T using the method of Low (1980). The results showed that λ was essentially independent of T but that mw/mc decreased slightly with T at any value of Π. Such results are not consistent with electric double-layer theory. Therefore, it was concluded that the decrease in mw/mc with increasing T was due primarily to the thermal breakdown and consequent loss of water from the larger pores outside of the interlayer region.

Calcium-cadmium and calcium-zinc exchange equilibria were studied at 20°C and constant ionic strength (0·015) on four clay minerals, viz. montmorillonite, bentonite, illite and vermiculite. Vermiculite and, to a lesser extent, illite and bentonite showed the strongest affinity for Cd2+ or Zn2+ over Ca2+ ions, whereas on the Camp Berteau montmorillonite nearly nonpreferential exchange isotherms were observed. With this one exception, selectivity for the heavy metals was greatly enhanced in the trace Cd or Zn regions, suggesting the presence of specific adsorption sites in these clays. Generally, the adsorption increased with the polarizing power of the exchangeable cation. Thermodynamic equilibrium constants and standard free energy changes for the complete exchange of Ca-clay to Cd- or Zn-clay were calculated.

Amines are strongly adsorbed by the crystalline silica H4Si20O42·4H2O and are intercalated into the interlayer spaces. The adsorption of butyl-, hexyl-, octyl-, and decylamine from alcoholic solutions (ethanol, butanol…decanol) is competitive as both types of molecules, amines and alcohols, are adsorbed in the interlamellar space. The adsorption isotherms are presented as composite isotherms showing the specific reduced surface excess of amine, n°(n)/m, as a function of the molar fraction of amine in the equilibrium solution. These isotherms increase to a plateau-like section (n°(n)/m≈1·4 mmol/g) when the interlamellar adsorption is restricted to formation of monolayers of flat-lying molecules (in water, ethanol and butanol). In the presence of longer chain alcohols, the isotherms increase stepwise to a second "plateau" (at n1°(n)/m = 2·2-2·7 mmol/g) which corresponds to paraffin-type bilayers of amine and alcohol molecules. The composition of the adsorption phase is estimated from the specific reduced surface excess of amine on the basis of the interlamellar structure derived from basal spacing measurements.

It is well known that illite-smectite can form from smectite at elevated temperatures in natural and experimental systems. However, the conversion of smectite to illite-smectite is also found in some natural systems that have never been heated. The present experiments show that illite layers can form from smectite by chemical reaction at 35° and 60°C at high solution pH. The rate of this reaction is accelerated by wetting and drying.

The distribution of clay minerals from the N and S Atlantic Cretaceous deep-sea sediments is related to rifting, sea-floor spreading, sea-level variations and paleoceanography. Four main clay mineral suites were identified: two are inherited and indicative of ocean geodynamics, whereas the others result from transformation and authigenesis and are diagnostic of Cretaceous oceanic depositional environments. Illite and chlorite, together with interstratified illite-smectite and smectite occur above the sea-floor basalts and illustrate the contribution of volcanoclastic materials of basaltic origin to the sediments. Kaolinite, with variable amounts of illite, chlorite, smectite and interstratified minerals, indicates detrital inputs from continents near the platform margins. Kaolinite decreases upward in the series due to open marine environments and basin deepening. It may increase in volume during specific time intervals corresponding to periods of falling sea-level during which overall facies regression and erosion of the surrounding platforms occurred. Smectite is the most abundant clay mineral in the Cretaceous deep-sea sediments. Smectite-rich deposits correlate with periods of relatively low sedimentation rates. As paleoweathering profiles and basal deposits at the bottom of Cretaceous transgressive formations are mostly kaolinitic, smectite cannot have been inherited from the continents. Smectite is therefore believed to have formed in the ocean by transformation and recrystallization of detrital materials during early diagenesis. Because of the slow rate of silicate reactions, transformation of clay minerals requires a long residence time of the particles at the water/sediment interface; this explains the relationships between the observed increases in smectite with long-term sea-level rises that tend to starve the basinal settings of sedimentation. Palygorskite, along with dolomite, is relatively common in the N and S Atlantic Cretaceous sediments. It is not detrital because correlative shelf deposits are devoid of palygorskite. Palygorskite is diagnostic of Mg-rich environments and is indicative of the warm and hypersaline bottom waters of the Cretaceous Atlantic ocean.

The laser Raman microprobe spectrum of gibbsite displays four intense v (OH)- stretching bands at ~3365, 3435, 3525 and 3618 cm-1, bayerite shows three near 3425, 3545 and 3564 cm-1, nordstrandite has three near 3492, 3566 and 3623 cm-1, and doyleite one broad band centred at -3545 cm-1 with sometimes a prominent shoulder near 3615 cm-1. The four polymorphs also possess distinctly different Raman signatures of medium to strong bands in the region 100–1200 cm-1. These differences provide a non-destructive routine determinative procedure by direct microsampling of untreated crystals, fragments, and microcrystalline powders. Sample preparation is minimal. Excessive noise and non-quenchable fluorescence are the principle limitations of the technique.

Initial and de-intercalated (by washing with water from formamide molecules) kaolinite was investigated by X-ray and IR spectroscopic methods. As a result of de-intercalation by water washing, changes in structural characteristics and in some physical-chemical properties of kaolinites take place: (1) the content of low-defect phase (%ldp) evaluated by the expert system of Plançon & Zacharie (1990) decreases; (2) the degree of order of the structure as determined by the Hinckley index decreases; (3) the size of coherent scattering regions (CSR) determined by the method of fourth moments decrease; (4) the rate of repeated introduction of the formamide molecules to the interlayer increases. The cause of these changes are water molecules introduced into the kaolinite interlayer as a result of de-intercalation. These water molecules have IR absorption bands at 3646 (vas), 3550 (vs) and 1650 (vα) cm-1. The results obtained are discussed in relation to modern ideas on disorder models of kaolinite crystals.

The pillaring of a Laponite by alumina pillars, iron pillars and mixed Al-Fe pillars was obtained by a simple in situ method starting from AlCl3 and/or FeCl3 solutions with different molar ratio Fe/(Fe + Al), and from NaOH solution added simultaneously to the clay suspension. The Al13 pillars were evidenced by XRD and NMR spectra. The density and the charge of these pillars were calculated from the chemical analysis. The Fe pillars (in samples with Fe content >26%) are larger than Al13 pillars and slowly reducible by hydrogen temperature programmed reduction (H2TPR), but we do not have any information on their structure. There is also an excess of non-pillar Fe retained by the pillared clays probably as oxyhydroxides. The isomorphic substitution in the mixed (Al-Fe)13 pillars (in samples with an Fe content >26%) was evidenced by H2TPR results compared to the chemical analyses and by the interpretation of the 27A1 peaks in the NMR spectra.

The desorption of methanol (MeOH), propan-1-ol (n-PrOH), propan-2-ol (i-PrOH) and 2-methylpropan-2-ol (t-BuOH) from Na+-, Ca2+-, Al3+-, Cr3+- and Fe3+-exchanged montmorillonite has been studied using variable temperature infrared (IR) spectroscopy and thermogravimetric analysis (TGA). Alcohol-saturated trivalent cation (M3+) exchanged samples exhibit maxima in the derivative thermograms at 20 and 110°C (MeOH), 30 and 160°C (n-PrOH), 20 and 110°C (i-PrOH) and 20, 55 and 80°C (t-BuOH). Alcohol-saturated Na+ and Ca2+-exchanged montmorillonite samples exhibit maxima at higher temperatures in the i-PrOH (20 and 140°C) and t-BuOH (30, 90 and 110°C) desorption profiles but at the same temperatures for MeOH and n-PrOH. Mass spectroscopic analysis of the vapours desorbed from the alcohol-treated samples show that the low-temperature maxima in the alcohol desorption from the M3+-exchanged clays are due to unchanged alcohol, whilst those occurring at 80°C (t-BuOH), 110°C (i-PrOH) and 160°C (n-PrOH) are due, in the main, to alkene produced from the intramolecular dehydration of the respective alcohol. Changes in the IR spectra of the adsorbed alcohols occur at temperatures which are in accord with the mass spectral data. No mass spectral evidence was found for the formation of dialkylethers via the competing intermolecular process but dimerisation and oligomerisation of t-BuOH were observed.

Methylene blue (MB) and crystal violet (CV) have been found to be adsorbed in amounts greater than the cation exchange capacity (CEC) of clays (Hang & Brindley, 1970; Ghosal & Mukherjee, 1972; Venugopal & Nair, 1974).

In previous work (Rytwo et al., 1991), it was shown that CV adsorbs to montmorillonite up to 1·4 mmole dye/g clay. The amount of dye added in those experiments was up to 1·6 mM/g clay. Yet, when the added amount of CV and MB was 3·5 mM/g (Rytwo et al., unpublished), almost 1·6 (200% of the CEC) and 1·2 mM/g clay, respectively, were adsorbed. Margulies et al. (1988), who studied the adsorption of thioflavin T and MB to montmorillonite, showed that these dyes adsorb up to 1·4 and 1·2 mM dye/g clay, which corresponds to 175% and 150% of the CEC, respectively.

When studying surface free energies of clays in relation to clay composition, we calculated that in some instances the aggregate stability should be higher for Na- then for Ca-forms. This raised the question as to whether the results obtained with the surface free energy approach are reliable for estimation of soil aggregate stability. The aim of the present work was to measure the surface free energy components and attractive forces for a clay calculated from measurements of the contact angle of glycerol, diiodomethane and cis-decalin and to compare them with results of penetrometrical measurements.

Oxygen isotope analysis of clay minerals presents several practical difficulties. These include their very fine grain size, the presence of both hydroxyl and non-hydroxyl oxygen, adsorbed water and, where clays from oil reservoirs are concerned, the possibility of hydrocarbon contamination. To develop routines which would minimize these problems while leaving the isotope systematics of the clay undisturbed, a series of oxygen isotope analyses were made under different running conditions of the API Standard Illite–the Fithian illite.

Palygorskite has been widely reported as a clay phase in the Recent sediments of the northern Arabian Gulf (e.g. Aqrawi & Sadooni, 1988). It is usually thought to have originated from the sediments and soils of the Mesopotamian flood plains introduced by northwesterly (Shamal) winds (e.g. A1-Bakri et al., 1984). A1-Rawi et al. (1969) and Eswaran & Barzanji (1974) have detected palygorskite within Mesopotamian soils. This paper describes the occurrence of palygorskite in the Recent sediments of southern Mesopotamia and its possible origins will be discussed.