Absorption and fluorescence spectroscopies were applied to study the adsorption of rhodamine 6G on several smectite-type clays in aqueous suspension. The dye can be adsorbed as the monomeric and the dimeric forms on both the external and the interlamellar surfaces of the clay. The presence of these species and their evolution with the stirring time of the sample and the relative dye/clay concentration depend on the nature of the smectite, the clay concentration and the particle size, factors that also affect the dispersion degree of the clay particles in water.

Heating experiments were carried out with ferrihydrite, in the presence of organics, to gain more insight into the intermediate formation of a ferrimagnetic cubic phase often observed in soils as the result of fire. Without an organic reductant, no intermediate cubic phase was formed when ferrihydrite was transformed into hematite, regardless of whether the ferrihydrite DTA curve showed one or two exothermic peaks. Addition of glucose or charcoal as reductant caused the initial formation of a cubic magnetite and/or magnetite/maghemite phase in samples heated above 300°C in both air and N2 atmospheres. Ferrihydrite reduction, as determined by increasing cubic unit-cell edge lengths between 0.832 and 0.840 nm, increased with reductant concentration and heating time, providing excess reductant remained. Following consumption of the reductant, FeII may be partially or completely reoxidized, forming maghemite and then hematite. The occurrence of maghemite, but not of magnetite, in soils where forest fires have occurred suggests that sufficient oxygen was available, while temperatures remained elevated, to oxidize magnetite to maghemite.

The interaction of aminotriazole (AMT) at pH 4 on Wyoming montmorillonite (mainly with Na ions) and Mg-vermiculite has been studied by X-ray diffraction and infrared spectroscopy. The AMT is adsorbed on montmorillonite in the cationic form by cation exchange. The amount of pesticide adsorbed was 71 mEq/100 g, which comprises ∼91% of the CEC of this sample (78.2 mEq/100 g). Saturation was reached in 24 h, giving rise to a complex with basal spacing 12.5 Å. Vermiculite adsorbs 167 mEq/100 g, almost 20% greater than the CEC (141 mEq/100 g), and the basal spacing was stabilized at 13.68 Å after five weeks of treatment with AMT. A part of the AMT is adsorbed in cationic form, displacing a great part of the exchangeable Mg2+ cations. The rest is adsorbed in molecular form by coordination to the Mg2+ cations which remain in the interlamellar space, removing a great amount of water, and remaining in the interlamellar space of vermiculite after washing with water, probably because of a steric hindrance from the AMT cations adsorbed.

Hydrogen-forms of <2 µm fractions of six bentonites of various Fe contents were prepared by H+→OH-→H+ ion exchange using resins. Potentiometric titration curves revealed that the number of strong acid sites varied and accounted for 60-95% of the total acidity in the freshly prepared H-forms. The number of strong acid sites decreased and that of the weak acid sites increased on ageing. The process of autotransformation in aqueous dispersion at 90~ was completed within four days. Layer-charge distributions of all samples were inhomogeneous with layer charges from 0.25-0.39 Eq/unit O10(OH)2. Oxalate pretreatment of the samples resulted in changes in the layer-charge distribution due to the removal of readily soluble phases which may have blocked exchange sites. After autotransformation, the alkylammonium exchange method revealed inhomogeneous charge density distributions; the fraction of layers of the highest charge decreased. Comparison of total CEC obtained from potentiometric curves and interlamellar CEC calculated from the mean layer charge confirmed attack of protons from particle edges. However, for several samples the structural attack may also occur from the interlayer space. Autotransformation of the Hsmectites decreased the mean layer charge. Protons probably attack the Mg(O,OH)6 octahedra preferentially during the autotransformation.

Soil clays contain a relatively large amount of disordered inorganic material. Chemical dissolution has been used for the removal of this material (Jackson, 1956; Hashimoto & Jackson, 1960; Follett et al, 1965 a,b; Wada & Greenland, 1970). On the other hand, Farmer et al. (1977) claimed that dissolution of allophane and imogolite with hot 5% Na2CO3 for periods of 2-100 h led to new phases which could be distinguished from the starting material by infrared spectroscopy. It is clear, therefore, that chemical dissolution can alter soil clays. This note suggests an electron microscopy specimen preparation technique to study the morphological changes. Collodion films containing densely arranged minute hollows are used for specimen supports.

Structural formulae and other crystallochemical parameters were used to study different species of dioctahedral micas in clay and coarse gravel fractions of horizons from a red soil (Ultic Haploxeralf) in southern Spain. Mineralogical analyses using X-ray powder diffraction, and measurements of the b0 parameter revealed dioctahedral micas, illite and paragonite. Structural formulae established from electron microprobe analysis and energy dispersive X-ray analysis showed the illites to be K mica related in elemental composition and structure to muscovite and phengite. The paragonites were found to be closer to ideal mica. Structural formulae for Na-K dioctahedral micas were obtained with crystallochemical characteristics intermediate between those of Na micas and K micas. The possibilty of these micas representing individual mineral phases or intergrowths of Na and K micas is discussed. In the soil profile, micas from the Bt horizon showed the largest crystallochemical changes induced by pedogenesis.

One of the most important properties of zeolitized volcaniclastic materials is the cation exchange capacity (CEC). Numerous techniques are available for measuring CEC and the methylene blue absorption (MBA) (Nevins & Weintritt, 1967) and the ammonium acetate saturation (AMAS) (Chapman, 1965) methods are two of those commonly used. The aim of this study was to compare the results obtained by the two methods when used with zeolite-rich materials.

A natural saponite was acid activated at room temperature or 90°C with different acid/clay ratios and the products were characterized by powder X-ray diffraction, infrared spectroscopy and thermogravimetry. The leaching of Mg from the octahedral sheets is enhanced by an increase in the acid/clay ratio and by an increase in temperature of activation. Textural properties are reported, and it appears that they are strongly correlated to the presence of a noncrystalline silica phase which is formed during the acid activation process. The desorption of cyclohexylamine indicates that for samples activated at 90°C the number of acid sites in the acidactivated saponites decreases following severe acid treatment. Infrared spectroscopy of adsorbed pyridine on samples after calcination at 500°C suggests that acid activation at 90°C produces a single type of Bronsted site but two types of Lewis sites whereas activation at room temperature results in only one type of Lewis site in addition to a Brønsted site. The two Lewis sites are suggested to originate from residual Al in the clay structure and to AI exsolved from the layers during activation. The dehydration of pentan-1-ol has been used as a further probe to measure acidity by monitoring the degree of conversion and selectivity for the different samples.

The reactivity of an Al-pillared interlayered clay (PILC) (AZA) and a mixed Fe/Al-PILC (FAZA), used as references by the Concerted European Action-Pillared Layered Structure (CEA-PLS), was investigated in the selective catalytic reduction (SCR) of NO by NH3 or propane, as either catalysts or as supports of Cu ions. Both AZA and FAZA, either with or without Cu were found to be inactive in the reduction of NO with propane and oxygen. This is different from the behaviour with alumina with or without Cu, because of the different surface acidity properties. Good NO conversions were observed for both PILCs using NH3. The best catalytic performances were shown by FAZA, but the activity of AZA was also remarkable. The addition of Cu ions to both AZA and FAZA leads to an improvment in the activity in NO conversion and a reduction in the side formation of N2O. The catalytic behaviour was found to depend on the method of Cu addition, the Cu loading and the nature of the PILC. With AZA the best results were obtained for a Cu content up to 2 wt%, while further increases in the amount of Cu resulted in a considerable decrease in the conversion of NO. With FAZA, on the other hand, a high activity was observed at up to 3% of Cu introduced by ion exchange. By comparison with other Cu containing catalysts, Cu-FAZA allows operation in a wider range of reaction temperatures due to the reduced rate of side ammonia combustion. The surface acidity properties of AZA and FAZA were also characterized to interpret the above effects.

Montmorillonites ion-exchanged with Li+, Na+, K+ Ca2+, Mg2+ and Ni2+ and acidic clay were used as catalysts for the polymerization of a cyclic siloxane monomer, 2,4,6,8- tetramethylcyclotetrasiloxane. Montmorillonites with Ni2+ and Mg2+ in the interlayer, and acidic clay exhibit a greater ability for siloxane polymerization in both yield and mean molecular weight of products than those containing Li+, Na+ and K+. The difference in catalytic ability of the ionexchanged montmorillonites is caused by the number of Brmasted acid sites due to the polarization of H2O. This was confirmed experimentally by FTIR analysis of pyridine-treated samples. Therefore, it may be possible to design a catalyst for controlling siloxane polymerization (i.e. mean molecular weight of product) by changing the number of Bronsted acid sites through exchange of the interlayer cations of montmorillonites.

Palygorskite and sepiolite occurrences and deposits are frequent in the Iberian Peninsula, mainly in the Tagus basin, in central Spain and Portugal (Galán & Castillo, 1984).

In Portugal, the first palygorskite occurrence was reported by Carvalho (1964) in the region of Ponte do Sor, Tagus basin, in Paleogene sediments. Later, Carvalho (1968) reported palygorskite occurrences in coarse detrital sediments that were occasionally carbonatic or hardened by silicification, and built up the Cenozoic base for the Tagus and Sado basins. Carvalho referred to such formations as the 'Attapulgite complex'. Overlying this attapulgite complex is the 'Montmorillonite complex', probably of Miocene age.

The interaction of the cationic hydroxo-bridged binuclear iron(III) complexes of the sevendentate ligands HPTP and HPTB with montmorillonite was studied. Both complexes can be introduced reversibly into the interlayer region of the smectite. The catalase active HPTP-complex preserves its activity in the smectite interlayers. The unstable peroxide adducts of both complexes can be introduced into montmorillonite interlayers from water/H2O2 at 273 K and can be stored there for months at 243 K. Adduct/montmorillonite compounds can also be prepared by direct reaction of H2O2 with the complexes already bound to montmorillonite. From IR spectra of the adduct/montmorillonite compounds it can be concluded that the adduct of the HPTP complex contains nitrate whereas the adduct of the HPTB complex does not. These results can help to decide whether structures of the adducts proposed in the literature are possible or not and may therefore open a new field of application of clay minerals in studies on unstable intermediates.

Clay minerals play an important role in the retention, transport and chemistry of organic micropollutants in soils. There has been considerable recent interest in modelling and designing modified clays as adsorbents and catalysts for the removal of contaminants from waste waters (McBride et al., 1977; Mortland et al., 1986; Boyd et al., 1988). Organo-clays have been used as chromatographic stationary phases over the past three decades. White (1957) and Barrer & Hampton (1957) used alkylammonium montmorillonites as stationary phases and determined the selective retention of aromatic hydrocarbons relative to paraffins, naphthalenes and xylenes. Until now only organo-clays have received attention as chromatographic stationary phases (McAtee & Robbins, 1980) while their pillared variants have been totally ignored.

The adsorption of the cationic dye acridine orange (AO) by Na-saponite and the colloidal properties of the aqueous suspension were investigated by visible spectroscopy and XRD. The organic cation is adsorbed by the mechanism of cation exchange. When small amounts of the dye are adsorbed, the system contains small tactoids and is peptized. At this stage the dye penetrates into the interlayer space and most of it undergoes metaehromasy due to interactions between the aromatic entity and the oxygen plane of the clay. When greater amounts of AO are adsorbed, the clay platelets flocculate to form book-house floes which, with excess AO, are transformed into card-house floes. At this stage metachromasy results from the aggregation of the dye in the interparticle space of the floes, in addition to the π interactions with the oxygen plane. In excess AO, the clay is gradually peptized. At this stage the dispersed clay platelets form small tactoids with monomeric AO in the interlayer space and at the same time adsorb dimerie and polymeric AO cationic species at the solidliquid interface.

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.