Photochemical isomerization of azobenzene intercalated in the hydrophobic, interlayer spaces of swelling fluor-tetrasilicic micas exchanged with dialkyldimethylammonium ions, with the alkyl chain length from 10 to 18, was investigated. Thin films of the organoammonium-mica-azobenzene intercalation compounds were obtained by depositing a suspension of the organoammonium-micas (prepared using a toluene/methanol solution of azobenzene) on quartz substrates. The intercalated azobenzene showed reversible photochromic reactions induced by UV and visible light irradiation. The fraction of the photochemically formed cis-isomer in the photostationary states decreased with a decrease in temperature. The observed change in the photochemical reactions is thought to reflect changes in the states of the dialkyldimethylammonium ions in the interlayer space of the swelling fluor-tetrasilicic mica.

A progressive decrease in cation exchange capcity (CEC) values was observed by treating Ca-montmorillonite with sulphuric acid solutions and this can be understood in terms of the layered structure of the clay. Elemental analysis showed that moderate activation occurred and only 25–30% of the octahedral cations were removed. At the same time the total surface area and the clay acidity increase. X-ray and FTIR data confirmed that acid activation affects both the octahedral and the tetrahedral sheets. The efficiency of acid-activated montmorillonite for the bleaching of cottonseed oil was investigated. The differences in bleaching efficiency appeared to be due to differences in the physical and chemical properties of the bleaching media. The oil acid value was not affected by the bleaching procedure but a slight shift in the absorption maximum of the bleached cottonseed oil was observed. Medium activation of the clay (treatment of Ca-montmorillonite with 4 N H2SO4) was the most effective in bleaching the cottonseed oil, resulting in the best colour index and the lowest peroxide value. A linear dependence of the bleaching efficiency on the clay surface area and acidity was observed. The role of the increased Bronsted acidity is also discussed.

The adsorption of DL-alanine at pH 4, 6 and 8 by a soil allophane has been determined. Two sets of experiments were carried out: (1) in which the allophane had been kept in a moist state throughout; and (2) in which the mineral had previously been dried at 50°C. In both instances, the adsorption isotherms showed three distinct regions as the concentration of alanine in solution was increased: (1) an initial, nearly linear, rise at low equilibrium concentrations; (2) a levelling off to a plateau at intermediate concentrations; and (3) a steep linear increase at high concentrations. For comparable concentrations of alanine in solution, adsorption decreased in the order pH 6 > pH 8 > pH 4. Irrespective of pH, however, more alanine was adsorbed by the ‘wet’ allophane than by its ‘dry’ counterpart. These observations are interpreted in terms of the morphology and aggregation of allophane unit particles together with the pH-dependent charge characteristics of allophane and alanine. The results are compared with published data on the adsorption of alanine by montmorillonite.

The adsorption of the silane coupling agents N-(2-amino-ethyl)-3-aminopropyl- trimethoxysilane (Z-6020), N-(2-(vinylbenzyl-amino)-ethyl)-3-amino-propyl-trimethoxysilane (Z-6032) and 3-glycidoxy-propyl-trimethoxysilane (Z-6040) onto the surface of kaolinite has been studied using the solvents water and ethanol. The adsorbed silanes were analysed using diffuse reflectance Fourier transform infrared (DRIFT) spectroscopy and FT-Raman spectroscopy. When the silane coupling agents are dissolved in water, silanol groups are formed. Raman spectra of aqueous solutions of the silanes show that condensation of the silanols into oligomers occurred. The peak at 1000 cm-1 assigned to Si–O–Si vibrations indicates that polymerization has occurred. A similar behaviour is observed when the silanes are dissolved in ethanol. The DRIFT spectra show that the silane coupling agents adsorb onto the surface of kaolinite. It is proposed that the oligomers are bonded to the kaolinite surface only by hydrogen bondings with no covalent bonds formed.

The use of disodium peroxodisulphate combined with a neutral buffer is a new method for the efficient removal of organic matter from clay-bearing sediments. The effects of this oxidation procedure on mineral structure were investigated by treatment of different standard clay minerals (kaolinite ‘china clay’, illite ‘Le Puy’, montmorillonite SWy-1). The materials were characterized by means of XRD, FTIR, SEM and TEM before and after leaching with disodium peroxodisulphate. Systematic experiments were conducted to determine the effects of leaching on the chemical and isotopic composition of oxygen, hydrogen and K-Ar in these samples. Effects on the physicochemical properties of the clays such as BET external surface area, cation exchange capacity (CEC) and expandability with ethylene glycol were also investigated. The results show that structure, chemical composition, oxygen and hydrogen isotope ratios, as well as the K-Ar system remain unaffected by leaching with disodium peroxodisulphate. The CEC and expandability remain unchanged, whereas changes in BET area can be attributed to mechanical dispersion by ultrasonic treatment.

Batch reactor experiments were performed at 35°C and 80°C to determine the effect of high molar KOH solutions on the mineralogy and solution chemistry of two different smectites. The Ceca smectite is a nearly pure montmorillonite, and the Ibeco clay has a significant component of 35% beidellitic charge. Each reactor was charged with 1 g of <2 mm fraction smectite and 80, 160, 240 ml of 0.1–4 M KOH solution. In these experiments, the changes in solution composition and mineralogy were monitored as a function of time.

In the experiments, at all temperatures and under all chemical conditions, the smectite appears to change in diffracting domain size, which decreases with time. This probably reflects a change in crystal shape. The structures then become more illite rich and the diffracting domain continues to decrease.

The hydrothermal reactivity of a smectite saturated with K was studied experimentally at 300°C and 100 bar in (Na,K) chloride solutions (Na/K = 0, 50 and 100, liquid/solid ratio = 10/1). X-ray diffraction, TEM and microprobe results show: (1) a partial to total dissolution of the initial smectite layers; and (2) the crystallization of newly-formed euhedral I-S. Random I-S is formed after 7 days, but an ordered mixed-layer I-S containing <30% expandable layers formed in the longest runs (112 days). The I-S is characterized by non-expandable layers of two distinct types: dehydrated smectite and illite. The Si content is lower in the I-S than in the initial smectite, thus creating a charge deficit, mostly compensated by the introduction of Na to the interlayer space, and yielding a silica release to the solution and subsequent crystallization of quartz and cristobalite.

A series of Mn-goethites was synthesized at highly alkaline conditions. The samples were aged for 15 days at a final [KOH] of 0.3 M. Products were washed free from non-goethite phases using 3 M H2SO4. The bulk mineralogy of the samples was determined by X-ray diffraction and verified on selected individual crystals by electron diffraction. The samples had a relatively low magnetic susceptibility (300≤MS≤400×10-9 m3/kg). As revealed by total acid dissolution, the Mn mole fraction XMn ranged from zero to 0.125. Five samples (XMn: 0.025, 0.050, 0.077, 0.099, 0.125) were selected to investigate the variability of the XMn value in single goethite needles (crystals) by analytical electron microscopy (AEM) using rastered and spot analyses. Linear regressions of both as a function of total Mn yielded unit slopes and zero intercepts, indicating that acid dissolution gave the same results as AEM. Spot AEM, however, revealed significant variation of Mn distribution within individual crystals which argues in favour of Mn zoning in goethite. Inhomogeneous transformation of ferrihydrite to goethite may partly explain the Mn zoning.

Ochre sediments from acid mine drainage in Cornwall have been investigated using X-ray diffraction, thermal methods, infrared spectroscopy, X-ray photoelectron spectroscopy, transmission electron microscopy and chemical methods in order to determine their mineralogical and chemical composition. Fresh sediments consist of ferrihydrite and goethite. Large fractions of these minerals are dissolved by the ammonium oxalate treatment reflecting their poorly crystalline structure. Fresh sediments contain large amounts of surface-adsorbed SO4 (up to 9.3%) which is readily desorbed by the PO4 treatment. Goethite is the only mineral present in relatively older sediments and the mineral is well crystallized with rod-shaped morphology. Environmental conditions, such as pH and SO4 content, are not favourable for the presence of schwertmannite at the site. Iron minerals appear to be precipitating around filamentous algae and the shape of algae is preserved in the Fe oxide matrix. The ubiquitous presence of algae in close association with Fe minerals indicate their possible role in the crystallization of Fe oxides.

The fine silt (2–5 μm) and fine clay (<0.1 μm) fractions from four acid soils developed from moraines of increasing age (80, 400, 3,000 and 6,500 years old) in Switzerland, were studied by X-ray diffraction and chemical analyses. The soil parent material is homogeneous at the four sites and the soils can be considered as forming a chronosequence of soil development leading to the formation of Podzols. Mineralogical evolution of silt-sized phyllosilicates and fine clay fractions follows different pathways according to their composition and the soil horizon in which they are located. Dioctahedral and trioctahedral minerals in the soil parent material were both weathered in the Bw and Bs horizons but the trioctahedral phase more strongly and faster than the dioctahedral one. Weathering products are mica-vermiculite mixed-layers, vermiculite and finally gibbsite and Fe oxy-hydroxides. Weathering of the trioctahedral fraction was faster in the eluvial A or E horizons than in the B horizons, being almost complete after 3,000 years of soil development. Appreciable weathering of the dioctahedral fraction occurs only in the eluvial horizons leading to the formation of mica-smectite mixed-layers and smectite. Although smectite has been reported in the E horizon of Podzols in different environments, the significant finding in this work is the presence of this mineral in soils developed from the same parent material. This supports the fact that smectite is the end- product of mica alteration in strongly leached and acidified E horizons of Podzols.

The finest fractions of Upper Jurassic shales from the North Sea and onshore Denmark contain 80–90% of an illite-smectite-vermiculite (I-S-V) mixed-layer mineral and, in addition a phase which has X-ray diffraction (XRD) peaks at 7.20–7.26 Å and 3.56–3.58 Å in air- dried and glycolated specimens. This phase may be a fine kaolinite with a small thickness of coherent scattering domains (CSDs) or alternatively a mixed-layer mineral which has kaolinite as the dominant component. For one sample from the Norwegian well 9/4-3, these alternatives are investigated using the multi-specimen method by which agreement between the experimental pattern and the pattern calculated for one and the same structure is obtained for each of several specimens saturated with different cations and with/without glycolation. It is demonstrated that the modelled XRD patterns for a kaolinite-illite-vermiculite (K-I-V) structure having 0.94 kaolinite, 0.03 illite and 0.03 vermiculite layers and random alternation fit the experimental patterns.

In order to determine the relative influence of palaeoenvironmental and diagenetic processes in clay assemblages, as well as their significance, both fine- and coarse-grained sediments from the Campo de Gibraltar flysch have been studied by means of X-ray diffraction, optical and electron microscopy, and chemical analysis. Diagenetic modifications appear to be lithologically controlled and mainly affect coarse-grained sediments, where Fe-chlorites, illite and kaolinite are the more characteristic authigenic clay minerals. The evolution of detrital assemblages, determined in fine-grained beds, indicates that, from Cretaceous to Eocene times, clay mineralogy, characterized by the opposite kaolinite+smectite and illite + I-S mixed-layer assemblages, was mainly controlled by sources, climate and transport processes. On the other hand, from the Oligocene, clay mineral assemblages, characterized either by the abundance of kaolinite, or by the illite+chlorite association, mainly reflect the petrology of source rocks, as a consequence of climatic cooling and the increasing tectonic activity, which impede the development of soils.

The deuteration technique was used to assign unknown infrared (IR) bands of Ge-bearing talcs. Procedures to achieve partial or complete H/D replacement in synthetic Ge-bearing (Mg, Ni and Co)-talcs have been investigated. From the spectral shift of IR absorption bands in the 4000–300 cm-1 region resulting from the H-D substitution, the IR bands of vibrations of Ge-bearing talcs could be identified and synthetic Ge-bearing talcs showed significantly different IR spectra from those for Si-talcs. After deuteration of synthetic Ge-bearing talcs, the unknown bands were attributed either to hydroxyl groups or to Ge–O vibrations of the clay skeleton, and the spectra were interpreted fully.

Diagenetic evolution of illite-smectite in shales corresponds more closely than in other rocks to the thermal history of a sedimentary basin. In bentonites, illitization can be significantly retarded by the diffusion of K+ (Altaner et al., 1984; Clauer et al., 1997), and in sandstones it can be related to a localized hot fluid flow (e.g. Whitney & Northrop, 1987). Thus, extracting the diagenetic ages of illite-smectite from shales remains an important opportunity for the verification of basin history models.