bluuebunny/crossref_metadata_2025 huggingface dataset:
Quantitative determination of goethite and hematite in kaolinitic soils by X-ray diffraction
Authors: Kämpf N. , Schwertmann N.
Published: December 2006

In the past, two factors have impeded the quantitative estimate of Fe-oxides in soils by X-ray diffraction. First, Fe-oxides are still quite often considered X-ray amorphous, although numerous results, e.g. a low ratio of oxalate- to dithionite-soluble Fe, have indicated the opposite. Second, even if crystalline, the cocentration of Fe-oxides in many soils is low, thereby complicating their identification by XRD. Recently, however, more sensitive methods such as Mössbauer spectroscopy and Differential-XRD (Schulze, 1981) have been introduced, which substantially reduce the lower limit of detection. Because these two methods are not generally available and, especially in the case of M&oum;ssbauer spectroscopy, are rather time consuming, ordinary XRD should be adapted for quantitative estimation of Fe-oxides.

Determination can be facilitated by using samples in which the Fe-oxides are concentrated by particle-size separation and a 5 M NaOH boiling treatment (Norrish & Taylor, 1961). The latter treatment is particularly suitable for kaolinitic soils as the Fe-oxides are unaffected―provided certain precautions are taken (Käimpf & Schwertmann, 1982a). This paper gives details of a procedure for the quantitative estimation of goethite (Gt) and hematite (Hm) by XRD.
Two examples of quantitative analysis by simulated X-ray powder diffraction patterns
Authors: Corbato C. E. , Tettenhorst R. T.
Published: December 2006

Quantitative estimates were made by visually matching computer-simulated with experimental X-ray powder diffractometer patterns for two samples. One was a natural mixture of dickite and nacrite in about equal proportions. The second sample contained mostly quartz with corundum and mullite in small (0.5–1%) amounts. Percentages deduced from pattern matching agreed to within ±10% of the weight fractions of the components determined by an alternative method of analysis.
Selective liquid adsorption on dodecylpyridinium clay by HPLC
Authors: Stul M.
Published: December 2006

Traditionally, adsorption from binary solutions is determined as the difference between the adsorbate concentration in the solution before and after contacting with the solid adsorbent e.g. hexadecylpyridinium-clay. this is essentially a static method. The bulk composition can be measured by means of a differential liquid interferometer (Dékány et al., 1978b) or by gas chromatography (Nikulitchev et al., 1979). The specific excess adsorption of the mixtures, n1°, is then calculated as (Kipling, 1965):

1

where n0 is the total amount of the liquid mixture referred to unit mass of the adsorbent (mmol/g adsorbent), xl,0 is the mole fraction of the ith component before adsorption, and xi is the mole fraction of the ith component in the equilibrium homogeneous liquid phase.
Mineralogical facies of a weathered serpentinized lherzolite from the Pyrenees, France
Authors: Fontanaud A. , Meunier A.
Published: December 2006

Weathering products of a serpentinized Iherzolite were investigated using optical microscopy, X-ray diffraction, infrared spectroscopy, and electron microprobe and wet-chemical analysis methods. The original mineral assemblage of the rock was chrysotile-enstatite-diopside-picotite-magnetite-calcite. Rock porosity governed the types of chemical microsystems from which the clay minerals were derived. These microsystems were grouped into three types. (1) Grain microcracks and grain boundaries. These were the earliest manifestations of weathering. Only pyroxenes were affected and transformed into talc + iron oxides. (2) Plasma zones in which the rock structure was preserved. The talc + oxide and chrysotile were both altered into a saponitic mineral. Picotite was oxidized to oxipicotite. (3) Fissure zones. In the argillized zones the rock was restructured. Saponite was altered to nontronite + magnesium silicate gel. Talc was also transformed to the same gel. Fissures were often filled with clay cutans and some were edged with iron oxides. Mineral facies in the different zones have been plotted in Si-R2-R3 coordinates.
Characterization of iron(II)-and iron(III)- exchanged montmorillonite and hectorite using the Mössbauer effect
Authors: Helsen J. A. , Goodman B. A.
Published: December 2006

At room temperature both Fe(III)-exchanged montmorillonite and Fe(III)-hectorite gave similar Mössbauer spectra, each consisting of a single doublet with parameters characteristic of ferric iron. At 77 K the Fe(III)-hectorite gave a spectrum similar to that observed at room temperature, but with the montmorillonite an additional distinct doublet, with relatively large values of both isomer shift and quadrupole splitting, was observed. The Fe(II)-exchanged samples behaved very differently at room temperature and 77 K. At 77 K well-defined doublets were produced; these had quadrupole splittings similar to those shown by the ion and appreciably greater than those observed for Fe(II) in the structural sites in layer-silicates. At room temperature, however, there was no absorption corresponding to ferrous ions in either of the specimens, because the recoil-free fraction was low as a result of the loose association between the ion and the mineral lattice.
Elements traces des argiles: des marqueurs
Authors: Mosser Christine
Published: December 2006

Resume

L'étude d'une vingtaine de cas montre que les caractéristiques principales du cortège d'éléments traces des roches éruptives et métamorphiques sont conservées par les fractions fines des produits d'altérations. On peut ainsi, à partir de l'ensemble des éléments traces contenus dans une fraction fine, identifier la famille pétrographique de la roche mère. La mémoire de la roche mère est partiellement conservée par la fraction fine après érosion des profils d'altération, et sédimentation des matériaux érodés dans des environnements divers. La conservation de la mémoire de la roche mère est cependant inversement proportionnelle à l'activité chimique du nouveau milieu de sédimentation. L'influence du milieu de sédimentation peut devenir prépondérante. Les exemples cités montrent que les éléments traces des argiles peuvent être interprétés, dans de nombreux cas, comme des marqueurs d'héritage: héritage direct d'une roche mère dans des conditions d'altération, héritage d'une histoire sédimentaire antérieure à des remaniements de dépôs; comme des marqueurs d'environnements sédimentologiques divers.
Organic reactions in a clay microenvironment
Authors: Ballantine J. A. , Purnell J. H. , Thomas J. M.
Published: December 2006

Although natural Na-bentonite has little catalytic activity, various cation-exchanged bentonites have proved to be effective catalysts for a wide variety of organic reactions. In the presence of these catalysts alkenes can be induced to add (a) water, to yield branched-chain symmetrical ethers; (b) alcohols, to give a variety of ethers; (c) thiols, to yield thio-ethers; (d) carboxylic acids, to give esters. The number of products obtained in each reaction depends on the ease of rearrangement of the carbocation intermediates. High yields are obtained where a single carbocation intermediate is formed, A variety of elimination reactions is also catalysed by these sheet silicates. Water is eliminated from alcohols to produce ethers, ammonia is eliminated from amines to make secondary amines, and hydrogen sulphide is eliminated from thiols to give dialkyl sulphides. In most cases the ion-exchanged bentonites react as acidic heterogeneous catalysts.
Catalysis by montmorillonites
Authors: Adams J. M. , Clapp T. V. , Clement D. E.
Published: December 2006

A preliminary set of ‘rules’ for acid-catalysis by ion-exchanged montmorillonites has been derived from the reaction of alkenes, alcohols and alicyclic acids over such catalysts. It has been shown that: 1. Cr(III) and Fe(III) are the most active interlayer cations. Although Al is also active, the exact procedures used for the ion-exchange and washing steps appear to be critical for giving catalysts of reproducible activity. 2. Below 100°C, the reactions proceed provided they involve tertiary or allylic carbocation intermediates, whereas at 150–180°C reactions involving primary and secondary carbocations are possible. 3. Reactions of carbocations with unsaturated hydrocarbons take place overwhelmingly in the interlayer region of the clay, where the hydrocarbon double bond can be effectively polarized. Reactions of carbocations with polar, oxygenated, species can take place on the surface of the clay particles as well as in the interlayer space. 4. When the acid-catalysed reactions are performed in the liquid phase and involve tertiary carbocations, the most suitable solvents are those which provide miscibility; 1,4-dioxan is especially good. However, when more acid conditions are required for the formation of primary and secondary carbocations a non-polar solvent is more efficacious.
Cadre géologique et minéralogie des argiles des Charentes, France
Authors: Dubreuilh J. , Marchadour P. , Thiry M.
Published: December 2006

Resume

Des kaolinites sont exploitées dans les sédiments du Tertiaire inférieur des Charentes, constitués d'argiles, de lignites, de sables noirs à gros bois et pyrite et de sables roux. Deux niveaux de kaolinite sont exploités: (i) des kaolinites ordonnées accompagnées de muscovite, (ii) des kaolinites désordonnées toujours accompagnées d'anatase. Ces deux niveaux correspondent à deux épisodes sédimentaires successifs, datés du Sparnacien et du Cuisien par la palynologie. Le premier épisode est vraisemblablement issu de la reprise d'altérations éablies sur le socle cristallin du Massif Central, alors que le second reprendrait des matériaux issus de l'altération des roches sédimentaires des bordures du bassin. Des kaolinites très bien ordonnées et de la gibbsite résultent de transformations géochimiques au sein des dépôts. Elles sont liées aux milieux acides des dépôts ligniteux et à l'oxydation des pyrites qui amènent la mobilisation de l'aluminium.
An iron-free volkonskoite
Authors: Khoury H. N. , Mackenzie R. C. , Russell J. D. , Tait J. M.
Published: December 2006

A green smectitic mineral from Jordan with 16% Cr2O3 (almost 22% on an ignited basis) has been shown by chemical, X-ray, electronoptical, electron microprobe, infrared and thermoanalytical evidence to be an iron-free volkonskoite of composition:

1·06 M+(Si7·39Al0·61)(Cr2·20Mg2·52)O20(OH)4.

The octahedral occupancy of 4·7, with only Mg2+ and Cr3+ in octahedral positions (in a ratio of 1·14), suggests that the mineral is intermediate between di- and trioctahedral—an inference supported by the uniformity of composition of individual particles (as revealed by the microprobe) and IR evidence, which indicates that it is predominantly dioctahedral but with certain trioctahedral characteristics. A volkonskoite sample from the type area in the USSR, examined for comparison, contained 23·5% Cr2O3 (about 29% on an ignited basis), but proved on electron microprobe examination to be a mixture of at least three species, one of which was aluminium-rich. IR and thermoanalytical characteristics are discussed in relation to the existence of tri-dioctahedral species.
A Mössbauer study of the effect of dithionite/citrate/bicarbonate treatment on a vermiculite, a smectite and a soil
Authors: Ericsson T. , Linares J. , Lotse E.
Published: December 2006

When describing clay minerals of natural origin one often has to take into account the possibility that they contain other phases, e.g. iron oxides and hydroxides which may form a ‘coating’ on the clay mineral itself or occur as physically inseparable ultra-fine particles. These iron oxyhydroxides are sometimes difficult to detect by XRD as a consequence of their very small ‘domain volumes’ (Kodama et al., 1977). The iron oxyhydroxides are normally removed chemically prior to detailed characterization of the clay mineral. Removal of iron oxyhydroxide coatings facilitates dispersion and subsequent particle-size fractionation of minerals and soils and also enhances the parallel orientation, and therefore the intensity, of basal X-ray reflections of layer-silicates.
Interpretation of the optical absorption spectrum of
Ni-substituted lizardites
Authors: Julg A. , Julg O.
Published: December 2006

The spectrum of Ni-substituted lizardite, (Mg,Ni)3Si2O5(OH)4, has been discussed by many authors, who have successively given contradictory interpretations concerning the symmetry of the Ni-sites. Lakshman & Reddy (1973) affirmed that in garnierites Ni is in a tetrahedral site. Faye (1974) rejected this conclusion and showed that Ni2+ occupies an octahedral site. However, the Ni … O distance of 2·01 Å which he deduced from the intensity of the crystal field is unacceptable. Recently, using a completely different approach to the interpretation of the spectrum, Cervelle & Maquet (1982) claimed that Ni2+ occupies a six-coordinated site of C3v symmetry, and concluded that the mean Ni … O distance is 2·06 Å.

The aim of this note is to show that it is possible to interpret the spectrum of Ni-lizardite as arising from a predominantly octahedral field with a weak C2v component which provokes a small increase in width of the absorption bands.
Distinction of tetrahedrally and octahedrally coordinated Al in phyllosilicates by NMR spectroscopy
Authors: Sanz J. , Serratosa J. M.
Published: December 2006

In recent years, the availability of high-field superconducting magnets complemented with mechanical spinning of the samples (magic-angle spinning technique) has resulted in a considerable improvement in resolution of NMR spectra and has widened the use of this technique in the structural analysis of solid samples. In particular, NMR spectroscopy can distinguish the different chemical environments of tetrahedrally coordinated silicon and also determine short-range order in the distribution of Si and Al in micas (Sanz et al., 1983) and zeolites (Fyfe et al., 1983; Klinowski et al., 1982).

For aluminium (I = 5/2), the existence of strong quadrupolar interactions means that, in general, only the m½↔m−½ transition is observed. However, the signal is broadened by second-order quadrupolar effects, dipolar interactions and chemical shift anisotropies.
Interactions of halloysites with amides: mineralogical factors affecting complex formation
Authors: Churchman G. J. , Theng B. K. G.
Published: December 2006

Complex formation between halloysites, from soil and geological sources, and a series of amides has been investigated. All the amides used can be intercalated to give single-layer complexes with basal spacings between 10·4 Å (for formamide) and 12·4 Å (for N,N-dimethylacetamide). When the interlayer space of halloysite has already been expanded by water, as is the case with fully hydrated samples, the rate and extent of intercalation depend more on the properties of the organic species than on the mineralogy of the clay. With partially and completely dehydrated halloysite, however, complex formation is influenced by the particle size, crystallinity, and iron content of the mineral. A large particle size, a high degree of crystallinity, and a low iron content are all conducive to complex formation. The iron content of halloysite also appears to affect particle shape. Low structural iron contents are associated with long tubular particles, intermediate contents with short and/or wide tubes, and high contents with spheroidal and other non-tubular forms. Halloysites containing high amounts of extractable (non-structural) iron generally show a low intercalating ability.
Mixed-layer illite-smectite in low-temperature diagenesis: data from the Miocene of the Carpathian Foredeep
Authors: Środoń J.
Published: December 2006

Bulk mineralogy, clay fraction mineralogy and layer ratio in interstratified illite-smectite were studied in three Upper Miocene profiles, up to 200 m deep and representing very low sedimentation rates (∼80 mm/103 yr) with environments of sedimentation ranging from hypersaline (gypsum deposits) to brackish. No correlation was found between mineralogy and depth, or between mineralogy and chemical environment of deposition, despite the use of precise identification techniques. It is concluded that smectites and interstratified illite-smectites are stable in marine sediments until the elevated temperatures of deep diagenesis are reached.
Etude du biopyribole formé par chauffage des vermiculites magnésiennes
Authors: Suquet H. , Mallard C. , Quarton M. , Dubernat J. , Pezerat H.
Published: December 2006

Les vermiculites magnésiennes chauffées durant plus de 24 h à une température de 700°C dans l'air, donnent une phase non gonflante qui est un biopyribole. Les diagrammes de diffraction X obtenus avec un monocristal montrent que ce matériau est constitué de deux phases: une enstatite en épitaxie sur le plan (010) d'un phyllosilicate. Le phyllosilicate a un empilement des feuillets semi-ordonné. Les rangées du plan (h0l) éant entièrement discrètes, la projection x0z a été étudiée par une analyse de Fourier classique à deux dimensions. Les autres rangéés du réseau réciproque sont plus ou moins diffuses dans la direction c*. Le désordre est creéé par une distribution aléatoire de trois translations entre les feuillets adjacents. Les relations structurales existant entre le phyllosilicate et l'enstatite expliquent l'absence de propriétés de gonflement de la phase phyllosilicate du biopyribole.
An IR cell for vacuum and high temperature
Authors: Lugli W.
Published: December 2006

Much interest has been shown in IR cells capable of maintaining one or more samples at constant temperature, constant water vapour or gas pressure, or under vacuum conditions (Farmer, 1974). This note describes a cell capable of maintaining a vacuum between 10-3 torr and 10-4 tort from room temperature to 1000°C whilst the spectrum is being recorded; such cells have been constructed previously but for less severe conditions.

The cell and associated vacuum system are shown schematically in Fig. 1. The vacuum in the cell body is produced by an Edwards rotary pump and a normal mercury diffusion pump. To obtain a vacuum of 10-3 to 10-4 torr, a liquid nitrogen trap and foreline trap are used. The trap is filled with activated alumina. The O-ring seals in the cell are made of Viton. The constant vacuum control is obtained with Pirani and Penning gauges.
Obtention de la fonction de modulation experimentale pour les gels de smectites contenant du fer
Authors: Rhaiem H. Ben , Pons C.H.
Published: December 2006

Lors de l'étude du gonflement des smectites par analyse de la diffusion des rayons X aux petits angles, Ponset al.(1981) et Ben Rhaiem (1983) ont obtenu des diagrammes de diffusion caractérisés dans le domaine étudié par des modulations plus ou moins prononcées de la courbe d'intensité.

L'analyse quantitative des courbes de diffusion, et en particulier de ces modulations, permet alors de remonter à une description de la structure du gel ou de la pâte et aux relations existant entre texture et structure (Ponset al., 1981; Ponset al., 1982). La méthode générale d'interprétation proposée par Ponset al.(1981) repose sur une comparaison entre intensité expérimentale et intensité théorique calculée à partir de modèles.
Controls on mineral authigenesis in Coal Measures sandstones of the East Midlands, UK
Authors: Hugget J. M.
Published: December 2006

Authigenic clay mineral formation in fluvial sandstones and one brackish sandstone from the lower and middle Coal Measures of the East Midlands has been studied using XRD, optical microscopy and a variety of electron optical techniques. The sandstones are quartz-rich with minor feldspar and mica. The clay minerals present are kaolinite, chlorite and illite; they form 10–15% by volume of most of the sandstones. Both detrital and authigenic illite and chlorite are present but the kaolinite is entirely authigenic. Kaolinite and illite authi-genesis has been important in all the sandstones but authigenic chlorite is only abundant in the phyllosilicate-rich Silkstone sandstone. The controlling factors in the diagenesis of the sandstones were primary composition, environment of deposition, bed thickness, pore-fluid migration and composition, pressure and temperature. These interacting factors have been of varying importance in time and space in the diagenesis of the sandstones. Authigenic clay morphology appears to have been controlled by time and environment of formation, pore-fluid chemistry and, possibly, parent minerals.
The nature, origin and distribution of authigenic clay minerals from Middle Jurassic Ravenscar and Brent Group sandstones
Authors: Kantorowicz J.
Published: December 2006

Middle Jurassic sandstones contain a variety of authigenic clay materials. The origin and distribution of these are related to the influence of several factors, principally depositional pore-fluid chemistry, sandbody geometry and the migration of aggressive fluids. Pore-lining illite, pore-lining chlorite and pore-filling vermiform kaolinite in the Ravenscar Group mutually exclude each other because of depositional pore-water chemistry; seawater in the case of the illite, anoxic freshwater in the case of chlorite and oxygenated freshwater in the case of the kaolinite. Blocky pore-filling dickite occurs ubiquitously within the large connected sandbodies. Its origin may be related to the migration of aggressive fluids and its distribution to depositional sandbody geometry. Mixed-layer chlorite-vermiculite also occurs, and is believed to have formed from chlorite during Recent weathering. Similar patterns occur in Ninian Field Brent Group sandstones, although the situation is more complicated (in these sandstones the kandite subgroup minerals are undifferentiated in this paper). Here too, pore-lining illite occurs in marine sandstones and pore-filling vermiform kandites in non-marine sandstones. However, vermiform kandites also occur in the marine sandstones, perhaps due to freshwater-table development following progradation. The more blocky kandites occur in large connected sandbodies. Finally, a second phase of illitization occurs, postdating blocky kandites, perhaps caused by alkaline formation waters. The occurrence of chlorite in the Broom Formation is anomalous and its possible origin is discussed.
Diagnetic history and reservoir quality of a Brent Sand sequence
Authors: Blackbourn G. A.
Published: December 2006

The Etive Formation of the Middle Jurassic Brent Group in part of the Northern North Sea comprises dominantly clean, fine- to medium-grained sands, deposited as part of a barrier-bar complex. The overlying Ness Formation was deposited on supra- or intertidal fiats, and comprises silty channel sands with silts, muds and thin coals. The sands of both Formations are mainly quartz-rich, with up to 12% by volume of feldspar, and variable proportions of clayey matrix. Early carbonate cementation preceded a phase of quartz overgrowth, which continued during burial. Later dissolution of unstable grains, dominantly feldspars, was followed by precipitation of pore-filling kaolinite and minor late-stage mineral phases. Better permeability of the Ness sands (up to 500 mD) relative to the Etive (mostly <10 mD) is mainly due to the effects of diagenesis on different lithofacies. Silty sands escaped intense quartz cementation and were thus more affected by acid groundwaters which improved permeability.
Patterns of diagenesis in the Sherwood Sandstone Group (Triassic), United Kingdom
Authors: Burley S. D.
Published: December 2006

The Triassic Sherwood Sandstone Group comprises a complex of continental red beds deposited by a major fluvial system flowing dominantly down a northerly inclined palaeoslope. Sedimentation took place in several distinct, tectonically active basins with varying maximum burial depths, ranging from shallow (<1 km) to deep (>3 km). Despite proximal to distal variations in stream type, a distinct suite of early diagenetic events can be recognized throughout all the depositional basins, which is related to the depositional environment. These events are best preserved in those basins with shallow burial histories, and show many similarities to the processes recorded from modern red beds of the Sonoran Desert, Baja California, although a more advanced grade of diagenesis has been reached in the Sherwood Sandstone. On the margins of the Irish Sea Basin in Cumbria, where burial was shallow, these early diagenetic textures are well preserved. The detrital grains underwent changes aimed at reaching equilibrium with the near-surface chemical environment. Unstable silicates were dissolved or replaced and the released ions were capable of precipitating authigenic phases, typically mixed-layer illite-smectite, K-feldspar, non-ferroan carbonates and hematite. Lateral variations in the early diagnetic assemblages reflect chemical and spatiotemporal changes ofinterbasin depositional and diagenetic environments. Deeply buried equivalents in the Irish Sea reached a maximum burial depth in excess of 3 km towards the end of the Mesozoic. Superimposed on the early diagenetic fabric are a series of depth-related changes. In the absence of early cements, compaction reduced porosity to low levels. Mixed-layer illite-smectites were converted to highly crystalline illites with low Fe and Mg contents. Early framework-preserving non-ferroan carbonates were extensively dissolved, generating widespread secondary porosity. Late pore-filling carbonate cements comprise ferroan dolomites and ankerites with compositions up to Ca(Ca0·02Mg0·43Fe0·53Mn0·02). Following late Mesozoic burial, inversion of the Triassic basins resulted in the re-exposure of basin margin sequences and shallow burial basins. Modern groundwaters are typically very dilute, with essentially neutral pH, and are capable of dissolving carbonate, sulphate and halite cements. In the Wessex Basin, however, the Triassic sandstones of the South Devon aquifer have been extensively modified by the percolation of post-inversion acidic groundwaters. These low-pH waters have resulted in thein situbreakdown of feldspar to produce abundant authigenic kandite, widespread dissolution of carbonate cements and removal of early-formed iron oxide cements. In contrast, the concealed, deeply buried eastern margin of the Wessex Basin exhibits a diagenetic evolution resultant of deep burial and has no development of authigenic kandite.
Interpretation of wireline log and core data from a mid-Jurassic sand/shale sequence
Authors: Peveraro R. C. A. , Russell K. J.
Published: December 2006

Interpretation of downhole wireline logs is generally a major source of information used to build up a picture of the quality and distribution of reservoir rocks. Logging tools respond to a number of variables and comparison of a suite of different logs is usually required to isolate and identify the response due to a single factor, e.g. porosity or clay content. A new tool, the litho-density tool (LDT), has been used along with conventional logging tools in a mid-Jurassic sand/shale sequence. The LDT simultaneously measures Pe (effective photoelectric cross-section) and ρa (apparent bulk density). Pe is a function of atomic number which in turn reflects lithology or mineral composition. By using cross-plots derived from the LDT and other logs, patterns of mineral abundance are indicated.
The influence of aluminium on iron oxides: X. properties of Al-substituted goethites
Authors: Schulze D. G. , Schwertmann U.
Published: December 2006

Fifty-seven goethites, synthesized by a variety of procedures and with Al substitutions of 0–33 mole%, were characterized by XRD, IR, DTA, TEM and chemical techniques. Most of the properties measured showed significant intercorrelations. Mole% Al substitution (measured chemically) did not explain all the relationships among variables, but the inclusion of Δa, defined as the observedadimension minus theadimension predicted by the Vegard rule, explained much of the variation not explained by Al substitution. OH stretching frequency, in particular, was better correlated with Δathan the Al substitution or other properties. The properties of the goethites could best be explained by a combination of Al substitution and structural defects, with Δabeing a measure of the defects. In general, the effect of structural defects was opposite to that of Al substitution. Increase in Al substitution led to a decrease in all three unit-cell dimensions and OH stretching frequency and to an increase in the distance between the two OH bending vibrations (δOH-γOH) and the temperature of dehydroxylation. Increase in structural defects, on the other hand, caused theadimension, Δa, and OH stretching frequency to increase andδOH-γOH and the average temperature of dehydroxylation to decrease. Crystal size tended to decrease with increases in both Al substitution and structural defects. Surface area was significantly correlated with the reciprocal of the mean crystal thickness in theadirection. Comparison of XRD and TEM data showed that many samples consisted of crystals with several coherently scattering domains. The nature of the defects, i.e. whether they occur primarily in the interdomain areas or whether they are also distributed throughout the coherently diffracting domains, could not be determined.
Mode d'empilement des feuillets dans la vermiculite sodique hydratee a une couche (phase a 11·85 Å)
Authors: de la Calle C. , Plançon A. , Pons C. H. , Dubernat J. , Suquet H. , Pezerat H.
Published: December 2006

Resume

Comme la plupart des vermiculites, l'hydrate à une couche de la vermiculite-Na (d001= 11·85 Å) présente une structure semi-ordonnée, avec des défauts d'empilement (glissements selon l'axeb). Le plan (h0l)* du réseau réciproque est entièrement discret, tandis que les rangées n'appartenant pas à ce plan sont plus ou moins diffuses dans la directionc*. La projectionx0zest obtenue par une classique analyse de Fourier bidimensionelle. Dans les plans (0kl)* et (1kl)*, certaines rangées semblent presque discrètes: ceci permet d'essayer de déterminer la translationselon l'axe 0yentre deux feuillets adjacents. Le calcul des intensités des diffusions le long des rangées des plans (0kl)* et (1kl)* conduit à ne retenir qu'un seul modèle. Le désordre résulte d'une distribution aléatoire de trois translations parallèles à l'axe Oy: l'une est nulle et les deux autres sont de +0·307bet −0·307b. Le principal intérêt de ce travail est de présenter une nouvelle méthode d'approche pour l'étude des structures semi-ordonnées.
Hydrothermal clay mineral formation in a biotite-granite in northern Switzerland
Authors: Peters Tj. , Hofmann B.
Published: December 2006

Clay minerals of several hydrothermally altered zones in a 1200-m biotite-granite core from a drillhole in northern Switzerland were studied microscopically, by XRD and by electron microprobe. The minerals principally affected by the hydrothermal alteration were plagioclase (An5-An20) and, to a lesser extent, biotite. Illite, regularly interstratified illite-smectite and dioctahedral chlorite-smectite, dioctahedral chlorite, trioctahedral chlorite and kaolinite were detected in the alteration products. Commonly, two or more clay minerals occurred together in pseudomorphs after plagioclase. The mineral chemistry of the clay minerals showed a predominance of the substitution KAl for Si and, to a lesser extent, MgSi for Al. Fluid-inclusion data and the absence of pure smectite and epidote indicated temperatures of ∼200°C for the fluid that caused this alteration.
L'‘halloysite’ blanche riche en fer de vate (vanuatu)—hypothese d'un edifice interstratifie halloysite-hisingerit
Authors: Quantin P. , Herbillon A. J. , Janot C. , Siefferman G.
Published: December 2006

Resume

L'argile blanche en provenance du sol ferrallitique dérivé de matériaux pyroclastiques de Vaté (Vanuatu) possède un rapport moléculaire SiO2/(Al2O3+ Fe2O3) proche de 2, est riche en fer (∼7% Fe2O3) et se présente sous forme de fines lamelles irrégulières et parfois froissées. Sous l'effet de tout traitement de déshydratation, l'espacement basal de cette argile passe progressivement de 10 Å vers 7 Å. Toutes ces caractéristiques permettraient son identification comme halloysite (10 Å) ferrifère hydratée. Cependant, les spectres de diffraction des rayons X de cette argile déshydratée puis déshydroxylée ne correspondent pas à ceux que l'on obtient pour une halloysite ‘normale’. Ils révèlent plutôt la présence d'un édifice interstratifié 1:1/2:1 où le minéral 2:1, présent à raison de 20% environ, est dioctaédrique. En outre, la CEC de ce matériau (∼44 mEq/100 g à pH 4) est anormalement élevée pour un minéral 1:1. Par spectroscopie Mössbauer, on établit que la quasi-totalité du fer présent dans cet échantillon doit être localisée en position octaédrique au sein d'un phyllosilicate. Comme ce fer est ferrique, son inclusion dans la couche octaédrique d'un minéral 1:1 ne pourrait justifier l'importante charge négative permanente que porte cette argile. En réalité, toutes les propriétés reconnues pour ce matériau justifient son identification comme minéral interstratififé de 80% environ d'halloysite et de 20% de smectite ferrifère. Certaines particularités des spectres d'infrarouge, notamment l'absence des bandes à 3560 et 820 cm−1caractéristiques des vibrations d'élongation et de déformation des hydroxyles de la nontronite, suggèrent que la smectite ferrifère inclue dans l'édifice interstratifié pourrait être une hisingérite dioctaédrique.
Las bentonitas sedimentarias de la formacion fardes, Granada, España
Authors: Sebastian Pardo E. , Aguayo F. Lopez , Huertas F. , Linares F.
Published: December 2006

La formación Fardes consiste en secuencias alternadas de turbiditas y hemipelagitas. Estos sedimentos han sido silicificados diagenéticamente y se presentan como estratos gruesos de color amarillo, que contienen jarosita y sideronatrita, inicialmente depositados en un medio reductor. Los niveles hemipelagíticos se pueden considerar por su composición quimica y mineralógica como bentonitas, compuestas principalmente de esmectitas, mica y cuarzo. En algunos casos se han encontrado asimismo, calcita, dolomita, halita y yeso. En la fracción <2 µm el mineral más abundante es la esmectita (48%) seguido por la palygorskita y la mica (28% y 32% respectivamente). La composición de la esmectita corresponde a los miembros ricos en Fe de la serie nontronita-beidellita; las micas son verdaderas moscovitas y la paligorskita tiene contenidos anormalmente altos de Fe y Al. Evidencias mineralógicas y geoquimicas indican que estas bentonitas son productos de alteración de rocas volcánicas, posiblemente, andesitas calcoalcalinas.
Re-examination of the kinetics of the thermal dehydroxylation of kaolinite
Authors: Criado J. M. , Ortega A. , Real C. , De Torres E. Torres
Published: December 2006

The results obtained from this study of kaolinite dehydroxylation explain why different investigators have ascribed both first-order kinetics and a diffusion mechanism to this reaction. The fact that activation energies reported by these workers agree well, in spite of the different kinetics assumed when performing the calculations, is also explained. From a comparison of the results obtained by isothermal and non-isothermal methods it is concluded that, for reacted fractions,α, <0·6, kaolinite dehydroxylation is controlled by a diffusion process. A reaction mechanism explaining this behaviour is proposed.
Characterization of X-ray amorphous material in a Scottish soil by selective chemical techniques
Authors: Smith B. F. L. , Mitchell B. D.
Published: December 2006

Mixed SiO2-Al2O3-Fe2O3 gel systems are a feature of many Scottish soils. They are usually associated with the surface of primary soil particles and consequently when present even in small amounts can have an effect on soil properties incommensurate with the proportion present. Currently, chemical dissolution methods provide the most satisfactory means of assessment. A range of chemical techniques, including dissolution by alkali, dithionite, acid oxalate and pyrophosphate, trimethylsilylation and fluoride exchange, have been used to examine the inorganic gel in a Scottish brown forest soil developed on glacial till derived from epidiorite. The reactivity of the gel, as determined by fluoride exchange, is similar to that reported for Japanese and New Zealand allophanic soils.
The use of combined thermal analysis to study crystallization, pore structure, catalytic activity and deactivation of synthetic zeolites
Authors: Gabelica Z. , Nagy J. B. , Derouane E. G. , Gilson J.-P.
Published: December 2006

Emphasis is placed on the advantages of combining simultaneous thermal analysis methods (TG-DTA-DTG) with other complementary physico-chemical techniques for investigating synthesis and various properties of zeolites belonging to the pentasil family. TG and DTA give quantitative information on the dehydration and decomposition of organic guest molecules that interact with intermediate phases obtained during hydrothermal transformation of amorphous aluminosilicate gels into crystalline zeolites. In particular, weight losses (TG) and heat effects (DTA) due to the oxidative decomposition of tetrapropylammonium ions occluded in an intermediate phase have been related to the amount of zeolite ZSM-5 present. As a result, very small particles of this zeolite, amorphous to X-rays, could be detected in the early stages of the crystallization process. Isothermal sorption of small hydrocarbon molecules (n-hexane, 3-methyl-pentane) is used to probe the intracrystalline pore volume of zeolite ZSM-5. The total hydrocarbon uptake (TG) and the shape of the corresponding DTA peak are sensitive to steric modifications of the ZSM-5 channel system by various chemicals, while the sorption rates are better correlated to the extent of zeolite surface poisoning by boron or carbon. TG-DTA data provide an easy means of describing the filling and packing ofn-hexane in ZSM-5 pore structure. Various steps characterizing isothermal competitive sorptions (nitrogen, ethylene, water) or catalytic conversions at high temperature (ethylene, methanol) over H-ZSM-5 are described. Finally, the progressive formation (removal) of carbonaceous residues resulting from these transformations are related to the actual rate of de-activation (re-activation) of a zeolitic material. In this respect, three different synthetic zeolites, namely mordenite, offretite and H-ZSM-5, which differ by their shape-selective properties and structure of their channel network, are investigated by TG.
Magnesia from seawater: a review
Authors: Bhatti A. S. , Dollimore D. , Dyer A.
Published: December 2006

The process developed in the UK to produce magnesium hydroxide from seawater is described, together with the heat treatment that the hydroxide receives to produce the active oxide. Some of the characteristics required of the dolomite used in the process are also discussed. Impurities introduced by the seawater are noted and the means by which they can be reduced explained.
Study of the water-bentonite system by vapour adsorption, immersion calorimetry and X-ray techniques: I. Micropore volumes and internal surface areas, following Dubinin's theory
Authors: Kraehenbuehl F. , Stoeckli H.F. , Brunner F. , Kahr G. , Mueller-Vonmoos M.
Published: December 2006

The adsorption and desorption of water, the layer spacing of the montmorillonite with increasing water content and the heat of immersion with water have been measured for a Na-bentonite and two Ca-bentonites. The bentonite-water system is treated in terms of a micropore-filling process. Uptake of water occurs in discrete stages as the montmorillonite structure expands and the internal surface is calculated from these discrete stages of water adsorption.
L'alteration directe de muscovites et de biotites en halloysite: mise en evidence par microscopie electronique a balayage
Authors: Esteoule-Choux J. , Blanchet C.
Published: December 2006

Resume

L'altération de biotites et de muscovites en halloysite a été mise en évidence par l'étude en MEB dans l'altération de roches granitiques et de micaschistes. Cette transformation débute par le développement d'un réseau losangique à la surface des feuillets de micas. La croissance par épitaxie de tubes d'halloysite est parfois accompagnée par celle de cristaux de goethite. Le MEB montre que l'halloysite se forme directement à partir du mica et qu'elle apparaît dans les tous premiers stades de l'altération, quelles que soient les conditions.
The dissolution of asbestos fibres in water
Authors: Gronow Janet R.
Published: December 2006

The interaction of chrysotile and crocidolite with water has been investigated in an attempt to identify the factors affecting the rate and the degree of dissolution of asbestos fibres within groundwater systems at landfill sites. Dissolution experiments were used to investigate rate laws and to obtain apparent activation energies for the dissolution of the two minerals. The activation energies related to transport-controlled processes, but as the overall dissolution occurred so slowly it was unlikely to be controlled by processes with such low activation energies. Congruent dissolution of both minerals tended to increase with temperature and time, suggesting that in the long-term environmental situation, congruent dissolution of these two asbestos minerals would occur. However these experiments show that, as the reaction was so slow, there is little likelihood of reduction of the asbestos pollution hazard by the complete dissolution of fibres on prolonged contact with natural waters.
Filtration of clay suspensions through sand
Authors: Ives K. J.
Published: December 2006

The filtration of suspensions containing clay and other particles in water is a common process in drinking water treatment. Such filtration processes are very efficient, producing clear water containing less than 1 mg/l from suspensions with particle concentrations of up to 100 mg/l. This filtration is not straining, but a process of collection of clay particles on the sand surfaces in the pores. The clays may range in size from sub-micron to ∼20 µm, and may be flocculated, and are retained in pores ∼200 µm in size within sand grains ∼500 µm in diameter. The collection process has three principal components (i) transport of clay particles across laminar water streamlines by diffusion, gravity and hydrodynamic forces, (ii) attachment by electrical or van der Waals' forces with hydrodynamic forces intervening, (iii) detachment by fluid shear or instabilities caused by arriving particles. Mathematical and physical models relate suspension concentration, quantity of deposit and permeability to depth in a filter, and time of operation. Fibre-optic endoscopes with CCTV enable video recordings to be made of the behaviour of clay particles in the filter pores, at magnifications up to 500 ×.
Adsorption-desorption of sotalol hydrochloride by Na-montmorillonite
Authors: Sánchez-Camazano M. , Sánchez-Martín M. J. , Vicente M. T. , Dominguez-Gil A.
Published: December 2006

The interaction of montmorillonite with sotalol hydrochloride (4-(1-hydroxy-N-isopropylaminoethyl) methane sulfanilide) was studied by means of adsorption isotherms, XRD and IR spectroscopy. The amount of sotalol adsorbed depended on pH, the maximum amount adsorbed (0·56 mEq g−1) being considerably less than the exchange capacity of the mineral (0·80 mEq g−1). XRD and IR data revealed that the sotalol is adsorbed into the interlayer space, forming a monolayer complex with a d001 spacing of 17·7 Å, and that the mechanisms involved are cation exchange and ion-dipole interactions. Experiments on the in vitro desorption of the drug from the sotalol-montmorillonite complex indicated that desorption is affected by pH, by the salt concentration of the electrolyte, and by the elimination rate of the desorbed organic cations.
Mineralogy of a hydrothermal sequence in a core from the Atlantis II Deep, Red Sea
Authors: Singer A. , Stoffers P.
Published: December 2006

The clay fractions from a 1191-cm long sediment core in the SW Basin of the Atlantis II Deep, Red Sea, were investigated by XRD, electron microscopy and chemical analysis. Talc dominates in the botton portion of the core, near the brine discharge vent. At 1183 cm depth, the clay consists of vermiculite/chlorite and chrysotile. These minerals are of hydrothermal origin and two possible formation pathways are proposed: (i) vermiculite/chlorite and chrysotile formed by the submarine alteration of previously deposited talc; (ii) vermiculite/chlorite and chrysotile authigenically precipitated as a result of changes in the chemical composition of the brine. At 1170 cm depth, a new depositional sequence results from the progressive alteration of swelling 2:1 minerals into vermiculite. At 1025 cm, Mg-rich clay minerals such as chlorite, chrysotile and talc again become prominent. The upper part of the core is characterized by a transition from non-expanding Mg-rich clay minerals to Fe-rich expanding clays, principally nontronite. Periodically, the content of well-crystallized oxides such as hematite in the layers increases. At 1025 cm, some of the Fe-oxides have a morphology similar to that of akaganéite. In the uppermost part of the core, iron oxides appear to consist of a poorly crystalline hydrothermal hematite. An attempt has been made to correlate the various mineralogical assemblages geochemically.
Analysis of illite-smectite interstratification
Authors: Corbató C. E. , Tettenhorst R. T.
Published: December 2006

A new approach to understanding illite-smectite interstratification is formulated which incorporates the concepts of interparticle diffraction and elementary illite particles. The analysis shows that nearest-neighbour ordering, non-nearest-neighbour ordering, ordering at the illite end of the composition scale, and the lack of ordering at the smectite end can be explained by expandable interfaces between elementary, i.e. two silicate layers, and larger illite particles. Ordering in I/S clays is significant only when the probability of occurrence of illite is ∼80%. New concepts proposed are an order parameter (ω) and an expansion parameter (β). Interparticle diffraction implies that I/S clays are unusual among all crystalline materials since their XRD size is equal to or larger than the size of their constituent physically separable particles.
Sorption of ethylene glycol monoethyl ether (EGME) on homoionic montmorillonites
Authors: Kellomäki A. , Nieminen P. , Ritamäki L.
Published: December 2006

Sorption isotherms of ethylene glycol monoethyl ether (EGME) on homoionic Na−, K−, Mg− and Ca-montmorillonites at 25°C were determined. The extent of sorption was found to depend on the exchangeable cations, being larger for the bivalent ionic forms. Uptake of EGME was compared with the retention value obtained by evacuation of the sample wetted with EGME and also interpreted from XRD data. The results indicate that the montmorillonite-EGME complex formed by sorption at the saturation vapour pressure is stable and less ambiguous than after wetting by EGME. Montmorillonites are not suitable reference materials for surface area measurements.
An unusually expandable low-charge vermiculite
Authors: Justo A. , Maqueda C. , Pérez-Rodríguez J. L. , Lagaly G.
Published: December 2006

A lamellar macroscopic Mg-vermiculite from Santa Olalla, Spain, which is accompanied by some talc and mica, shows a reversible expansion on glycolation due to the presence of layers with two different charges. The most probable origin of the vermiculite is by low-temperature hydrothermal transformation of phlogopite.
Decarboxylation catalytique de l'acide oxaloacetique en presence de montmorillonite
Authors: Siffert B. , Naidja A.
Published: December 2006

Resume

La décarboxylation de l'acide oxaloacétique en acide pyruvique a été étudiée en présence de montmorillonite saturée en cations différents et des mêmes cations à l'état libre (non incorporés). L'action catalytique dépend de la nature du cation, cést-à-dire de sa facilité à former des complexes avec l'acide oxaloacétique. Le réseau argileux intervient dans la catalyse essentiellement par les atomes d'aluminium (ou de fer) situés sur les bords des feuillets argileux. Il joue le rôle d'un métalloenzyme biologique. Le calcul des énergies d'activation pour les différents systèmes met bien en évidence l'activité catalytique de l'argile. En présence du phyllosilicate, la réaction a lieu avec un bon rendement jusqu'à une température de 60°C.