The adsorption of aniline (ANL) and p-chloroaniline (PCA) from 0·02 M methanol and chloroform solution on air-dried montmorillonite is determined by the conjunction of several factors: (i) basicity of the solute, (ii) complexing ability, Brönsted and Lewis acidity of the exchangeable cation, (iii) polarity and Lewis basicity of the solvent. The principal adsorption mechanisms, inferred from infrared data, are direct or indirect coordination and protonation of the adsorbate. They take place simultaneously and to a relative extent depending mainly on the exchange cation.

On Fe-, Al- and H(Al)-montmorillonite ANL and PCA give rise to type II complexes, characterised by an intense charge-transfer band in the infrared region and by the formation of radical cations, evidenced by ESR spectroscopy. This oxidation process occurs on heating in air, but with Fe3+ in vacuo also and even at ambient temperature in methanol solution. On Cu-montmorillonite ANL, contrary to PCA, does not give a type II complex; however, radical species are produced in air and in vacuo and their production is enhanced by heating.

The nature, crystallochemistry, organization and surface properties of soil clays derived from the most representative sedimentary formations of France are described, using qualitative and quantitative mineralogical methods and high resolution transmission microscopy (HRTEM). The main results show that soil clays differ significantly from reference clays. Even when 2:1 phyllosilicates are dominant, the clays always contain multimineral phases. The smectitic component is dioctahedral and of beidellite type. Soil clay organization is specific: all the clay particles have a short lateral extension and few layers (mean 5 layers, and even mono-layers occur). The superposition of such small particles leads to the formation of what are called “texturally interstratified minerals” which are dominant in soil clays. Exchange and surface properties (high ratio of external surface to total surface area), are related to clay organization.

A series of V-doped titania-pillared clay catalysts, characterized by ICP-AES chemical analysis, X-ray diffraction, BET surface area measurement, and ESR spectroscopy, have been tested in the selective catalytic reduction of NO by NH3. An ESR analysis shows that V dopant is anchored to the titania pillars. Vanadyl species with differing degrees of in-plane V-O π-covalent bonding are produced depending on the method of sample preparation. Polymeric V species appear as the V content is increased. Catalytic performance of these systems depends on the method of preparation and on the V content. The best catalyst, converting 90-100% NO in the temperature range 523-623 K, is obtained by exchange of pillared montmorillonite with vanadyl ions, at an extent of exchange below the level where significant amounts of polymeric V species appear. The co-pillared catalyst, containing vanadyl centres characterized by a higher degree of in-plane ncovalent bonding (according to ESR), is less selective than the exchanged samples.

Dissolution in HCl of hematite particles with different morphologies led to sigmoidal dissolution vs. time curves. The rate of dissolution was directly proportional to the sample surface area and independent of crystal morphology. Hematites produced by heating goethite at 600 or 800~ dissolved more rapidly per unit area than did hematites grown from solution. TEM showed that some platy crystals developed central holes after prolonged acid attack; the hole formation was attributed to enhanced dissolution at screw dislocations present on the (001) faces of the crystals. Except where particularly susceptible regions involving strained areas or dislocations were present, there appeared to be no preferential acid attack at any particular crystal face. The original morphology was usually maintained during the reaction.

Mössbauer spectroscopy obtained with the sample at low temperatures and subject to large magnetic fields is discussed in terms of its use in analysing the naturally occurring polymorphs of FeOOH and the common growth precursor, ferrihydrite. Experiments on well-characterized synthetic samples provided benchmark results. A relatively simple means of quantitative analysis was used, in which sextets of Voigtian-shaped lines were summed and least-squares fitted. The results are discussed in terms of the magnetic structures of each compound.

The K-Ar dates and oxygen isotope data of illite-to-mica mineral phases in Permian to Triassic sandstones from Germany and Libya have been compared to previously published results of similar minerals of Liassic ages taken from lithologically similar rocks in several sites in western Europe and northern Africa. The widespread Liassic age for the micaceous mineral phases can be related to abnormal heat pulses induced by pre-rifting conditions. The temperatures in most cases appeared to be in the 150–220°C range. Some of these hydrothermal activities were responsible for both gas generation and U and Pb-Zn concentrations.

An approach combining K-Ar isotope dates and oxygen isotope signatures provides a framework for the characterization of the clay separates used in isotopic investigations and for depicting any crystallization conditions. The trend in decreases in δ18O values relative to increases in K-Ar dates, while the size of the clay fractions in a single sample increases, is indicative of detrital contamination. Varied trends in the δ18O values at constant K-Ar dates for clay fractions with increase in size might be indicative of changes in the pore volume of the host rocks.

From equilibrium silica concentrations over imogolite and boehmite at 100–155°C, the heat and free energy of the reaction (HO)3Al2O3SiOH + H2O ⇌ 2AlOOH + Si(OH)4 have been obtained: ΔH°r (298·15 K)=38·6 ± 4·1, ΔG°r (298·15 K) = 26.8 ± 1·1 kJ mol−1, and hence the heat and free energy of formation of imogolite: ΔH°f (298·15 K) = −3189·6 ± 4·1, ΔG°f (298·15 K) = − 2926·7 ± 1·1 kJ mol−1 These results are consistent with observations indicating that imogolite, halloysite and gibbsite can co-exist in soils, but that imogolite is metastable relative to either halloysite or gibbsite in the long term. At temperatures above 25°C there is a widening range of silica concentrations in which imogolite is more stable than halloysite, although both are metastable relative to kaolinite.

XRD analysis and electron microscopy show that hexagonal platy halloysite is the main component of an altered tuff (Ueno tuff bed) in the Pliocene Seto group, Aichi Prefecture, Central Japan. In the natural state it shows a single basal peak at 10·1 Å, which collapses to 7·2 Å, by dehydration through a segregate-type interstratification. The (02,11) non-basal band consists of slightly separated peaks which indicates moderate ordering of the crystal structure. The b-dimension is 8·936–8·939 Å. The stability of the interlayer water is intermediate with respect to halloysites of different morphologies. Between 3·5 and 4% Fe2O3 is present in the deferrated sample and the calculated chemical formula can not explain the anomalously high CEC of 21·9 mEq/100 g. Because the curvature radius and b-dimension of halloysite increase with increase in Fe2O3 content, the platy morphology is ascribed to replacement of Al3+ by Fe3+ in the octahedral sheet. Based on the geological and chemical data, the hexagonal platy halloysite is considered to have been formed from volcanic glass after deposition in a freshwater lake, where conditions were oxidizing and weakly acidic.

Different montmorillonites (Otay, Chambers, Marnia, Camp Berteau, Moosburg, Greek White, Wyoming bentonite were deferrated with a dithionite/citrate solution; iron sulphide by-products were eliminated with an HCl washing and citrates with an H2O2 oxidation. The smaller CEC after deferration could not be assigned to either (i) the occurrence of a positive correlation between CEC and particle sizes smaller than 0.2 µm or (ii) to the mean charge density of these sub-fractions. All sub-fractions had a heterogeneous interlayer cation density distribution.

The preparation and characterization of Ti-pillared acid-activated clays (designated Ti PAACs) and conventional Ti-pillared clays (designated Ti PILCs) are described. Preliminary catalytic results show that these materials possess remarkably enhanced abilities to catalyse the dehydration of pentanol compared with their Al counterparts (in excess of 200% in the case of the PILCs and up to 82% for the PAACs). These activities approach those previously reported for non-pillared acid-activated clays.

Iran has significant deposits of high-purity natural zeolites. Many Iranian scholars conduct scientific research on porous materials, from natural and synthetic zeolites to metal organic framework materials. Iranian zeolite deposits and associated research are reviewed here. Various industrial applications of natural zeolites, from agriculture to animal husbandry to the construction industry and beyond are discussed here.

It has been known for some time that when a gel of montmorillonite is freeze-dried the residual clay retains the volume and shape of the gel, and forms a skeleton of low density and some rigidity. Because there is no apparent change in the gel structure during freeze-drying, the dry residues have been studied in the past in an effort to determine the structure of the gels. However, X-ray diffraction measurements have shown that, as a result of freeze-drying, the distance between the elementary layers of Na-montmorillonite drops from high spacings (>30 Å) to zero. The present investigation demonstrates that the main reduction in interlayer spacing takes place on freezing, with a further small collapse on drying. Na-montmorillonite gels, swollen oriented aggregates of Na-montmorillonite and Na-nontronite, and swollen single crystals of Li-vermiculite and butylammonium-vermiculite, all behave in the above manner.

Thin green clay layers and lenses in the lower part of the Lower Oligocene Kerkom Sand near Aardebrug, east of Louvain in Belgium, were found to consist of glauconitic illite. This mineral contains about equal amounts of iron and aluminium oxides (14%) and is therefore intermediate in chemical composition between most illites and glauconites.

Comparison with the results of five published investigations of similar green clays in France and the United States shows that the green clays, which all have an intermediate glauconite-illite composition, are formed, unlike pelletoidal glauconite, in a non-marine environment. It is assumed that they developed in a lagoonal or hypersaline-lacustrine environment, probably as a result of the alteration of detrital illite-montmorillonite clay.

It has been suggested that interlayer water in halloysite is due to the presence of hydrated cations that balance the negative layer charge produced by Al for Si substitution. To find evidence of 4-coordinate Al (Al(IV)), we investigated six halloysites and two kaolinites using ‘high-field’ and ‘medium-field’ solid-state 27Al MAS NMR spectroscopy. We found Al(IV) in both kaolinite and five halloysite samples, but the contents are all <1% and provide no basis for distinguishing between kaolinite and halloysite. Therefore, the presence of interlayer water in halloysite cannot be attributed to Al for Si substitution. There are, however, signals, tentatively assigned to A1(V), present in the kaolinite spectra but not in the halloysite spectra. The shapes of the low-frequency ‘tails’ of Al(VI) signals in medium-field NMR vary from sample to sample. We interpret this variation in terms of a ‘crystallinity index’. Disorder in kaolinite appears to be primarily the result of Al-vacancy displacements in the octahedral sheet. The NMR crystallinity indices correlate with those from IRS and DTA but not with those from XRD.

A new practical and precise method for determining soil aggregate stability is described. Four air-dry aggregate fractions (<0.25, 0.25–0.5, 0.5–1.0 and 1.0–2.0 mm) were added to thoroughly stirred water in a Mastersizer 2000 laser diffractometer. The suspension obtained was passed directly through the measuring system. The dynamics of median (equivalent diameter d50) particle-size distribution decrease (interpolated with a logarithmic function) was assumed to be the measure of soil aggregate stability. In order to show the applicability of the new method, the results obtained (for selected and diverse soils) were compared with those from the wet sieving standard method. The main conclusion is that the proposed method is convenient and can be successfully used for the estimation of soil aggregate stability. Moreover, it has wider application because standard sieving methods are restricted to aggregates >0.25 mm whereas, with the use of the laser diffraction method, smaller aggregates can be measured. The energy delivered to the aggregates in the process of aggregate disintegration is more reproducible in the method described here. The method also provides an opportunity to verify that the soil aggregates are completely destroyed (lack of the changes of the median value shows the end of soil aggregate disintegration).

New insights from the recent literature are summarized and new data presented concerning the formation, structure and morphology of halloysite. Halloysite formation by weathering always requires the presence of water. Where substantial drying occurs, kaolinite is formed instead. Halloysite formation is favoured by a low pH. The octahedral sheet is positively charged at pH < ∼8, whereas the tetrahedral sheet is negatively charged at pH > ∼2. The opposing sheet charge would facilitate interlayer uptake of H2O molecules. When halloysite intercalates certain polar organic molecules, additional (hkl) reflections appear in the X-ray diffraction pattern, suggesting layer re-arrangement which, however, is dissimilar to that in kaolinite. Associated oxides and oxyhydroxides of Fe and Mn may limit the growth of halloysite particles as does incorporation of Fe into the structure. Particles of different shape and Fe content may occur within a given sample of halloysite.

The REE contents in the clay-sized fractions of nineteen Cretaceous and Pliocene continental sediments, Portugal, were found to be correlated with kaolinite. No correlation is apparent between clay mineralogy and La/Lu or Eu/Sm ratios. The Eu anomaly is generally smaller (or even absent) in the clay-sized fraction than in the corresponding whole sediment, probably due to a greater ability of the clay minerals to accommodate Eu (as Eu2+) rather than the other REE released during weathering.

The Boom Clay Formation of early Oligocene age, which occurs underground in northern Belgium, has been studied intensively for decades as a potential host rock for the disposal of nuclear waste. The goal of the present study is to determine a reference composition for the Boom Clay using both literature methods and methods developed during this work. The study was carried out on 20 samples, representative of the lithological variability of the formation. The bulk-rock composition was obtained by X-ray diffraction using a combined full-pattern summation and singlepeak quantification method. Siliciclastics vary from 27 to 72 wt.%, clay minerals with 25–71 wt.% micas, 0–4 wt.% carbonates, 2–4 wt.% accessory minerals (mainly pyrite and anatase) and 0.5–3.5 wt.% organic matter. This bulk-rock composition was validated independently by majorelement chemical analysis. The detailed composition of the clay-sized fraction was determined by modelling of the oriented X-ray diffraction patterns, using a larger sigma star (σ*) value for discrete smectite than for the other clay minerals. The <2 μm clay mineralogy of the Boom Clay is qualitatively homogeneous; it contains 14–25 wt.% illite, 19–39 wt.% smectite, 19–42 wt.% randomly interstratified illite-smectite with about 65% illite layers, 5–12 wt.% kaolinite, 4–17 wt.% randomly interstratified kaolinite-smectite and 2–7 wt.% chloritic minerals (chlorite, “defective” chlorite and interstratified chlorite-smectite). All modelled clay mineral proportions were verified independently using major-element chemistry and cation exchange capacity measurements. Bulkrock and clay mineral analysis results were combined to obtain the overall detailed quantitative composition of the Boom Clay Formation.

A decade of research on clays that kill human pathogens, including antibiotic-resistant strains such as methicillin-resistant S. aureus (MRSA), has documented their common characteristics. Worldwide, ∼5% of clays tested to date are antibacterial when hydrated. Most antibacterial clays are from hydrothermally altered volcanics, where volcanogenic fluids produce minerals containing reduced metals. Ferruginous illite-smectite (I-S) is the most common clay mineral, although kaolins dominate some samples. Antibacterial clay mineral assemblages may contain other reduced Fe minerals (e.g. pyrite) that drive production of reactive oxygen species (H2O2, •OH, •O2−) and cause damage to cell membranes and intracellular proteins. Ion exchange can also cause loss of bacterial membrane-bound Ca2+, Mg2+ and PO43–.

Critically important is the role of clays in buffering the hydration water pH to conditions where Al and Fe are soluble. A nanometric particle size (<200 nm) is characteristic of antibacterial clays and may be a feature that promotes dissolution. Clay interlayers or the lumen of tubular clays may absorb reduced transition metals, protecting them from oxidation. When the clays are mixed with deionized water for medicinal applications, these metals are released and oxidized.

Different antibacterial clays exhibit different modes of action. The minerals may be a source of toxins, or by adsorption may deprive bacteria of essential nutrients. In the field, the pH and Eh (oxidation state) of the hydrated clay may help to identify potential antibacterial clays. If the pH is circum-neutral, toxic metals are not soluble. However, at pH < 5 or >9 many metals are soluble and the oxidation of transition metals increases the Eh of the suspension to >400 mV, leading to bacterial oxidation.

Understanding the antibacterial mechanism of natural clay may lead to design of new treatments for antibiotic-resistant bacteria, with potential applications in wound dressings, medical implants ( joint replacements, catheters), animal feed stocks, agricultural pathogens, and production of antibacterial building materials. This research exemplifies how ‘geomimicry’ (copying geochemical processes) may open new frontiers in science.

Late Cretaceous bentonitic clays in the Kelkit Valley region of Turkey are composed of an alternation of limestone lenses and silicified tuff nodule-bearing pyroclastic rocks and their alteration products. Quartz, feldspar, biotite, trace amounts of augite together with pumice and volcanic rock fragments comprise the volcanogenic components. Diagenetic minerals are represented by clay, calcite, opal-CT, zeoliteand dolomite. The clay fraction is dominated by smectite and lesser amounts of I-S, illite, chlorite and kaolinite. The d001 basal spacing of dioctahedral smectites ranges from 12.51 to 12.55Å in Na-smectites and 14.97 to 15.52 A˚in Ca-smectites. The CaO/Na2O ratio of smectites ranges from 0.15 to 19.50, and the interlayer Na and Ca contents are 0.22–0.30 in beidellitesand 0.02–0.09 while those in montmorillonites are 0.01–0.13 and 0.03–0.15, respectively. The data obtained indicate that bentonites formed in a marine environment by the alteration of volcanic ash of rhyodacitic/dacitic and intermediate/acidic composition.