Mixed-layered phyllosilicates with composition intermediate between mica and chlorite were identified in very low-grade metaclastites from the Malàguide Complex (Betic Cordilleras, Spain), and studied by X-ray diffraction, and transmission and analytical electron microscopy. They occur both as small grains in the rock matrix, and associated with muscovitechlorite stacks. Transmission electron microscope observations revealed a transition from chlorite to ordered 1:1 interstratifications through complex 1:2 and 1:3 interstratifications. Analytical electron microscopy data indicate a composition slightly different from the sum of discrete trioctahedral chlorite and dioctahedral mica. The types of layer transitions suggest that mixed-layer formation included two main processes: (1) the replacement of a brucite sheet by a cation sheet in the chlorite structure; and (2) the precipitation of mica-like layers between the chlorite layers. The strongest diffraction lines in oriented X-ray patterns are: 12.60 Å (002), 7.98 Å (003), 4.82 Å (005) and 3.48 Å (007).

Commercial bentonite from the Kopernica deposit, Slovakia, is currently mined by the CERTECH Company, Poland, to produce materials intended for animal-care applications and other industrial purposes. The present study aimed to assess the mineralogical, petrographic and physicochemical characteristics of three bentonite varieties from Kopernica used by the company. The X-ray diffraction, optical microscopy, field emission scanning electron microscopy (FESEM), nuclear magnetic resonance, thermal analysis, infrared spectroscopy and chemical analyses showed that the main component of the rocks is montmorillonite with the average structural formula Ca0.31K0.08Na0.04(Al3.23Mg0.54Fe0.23)[(Si7.80Al0.20)O20](OH)4. In addition, opal-C/CT, biotite, potassium feldspar and plagioclase, quartz, clinoptilolite and kaolinite are present. Key information about the textural relationships between the mineral components identified was obtained from detailed thin-section petrography and FESEM studies. The rocks studied have fragmented, eutaxitic texture. They are composed of pumice fragments collapsed into lenticular masses (fiamme) which were strongly deformed and altered, though the shard structures were retained. The compressed glass shards were moulded around pyroclastic grains such as crystal fragments of quartz, biotite and zoned plagioclases, and clasts of volcanic rocks. Observations by FESEM showed that the axes of shards and the walls of the flattened vacuoles are outlined by the inward-growing microlites of silica (axiolitic texture), whilst the interiors of shards are altered to clay. Grain-size distribution, textural properties and microscope observations of grain-size fractions reveal that the Kopernica bentonite contains montmorillonite-opal aggregates difficult to disperse in water.

The effects of increasing nickel contamination of soil on the update of selected microelements by Brassica juncea L. in the presence of raw halloysite (RH) and halloysite modified by thermal treatment (calcination) at 650°C (MH) were investigated experimentally. Such treatment causes partial dehydroxylation and enhances mineral-adsorption properties towards cations. In a vegetative-pot experiment, four different levels of Ni contamination, i.e. 0 (control), 80, 160, 240 and 320 mg kg−1 were applied in the form of an analytical-grade NiSO4·7H2O solution mixed thoroughly with the soil. Among the minerals which were added to soil to alleviate the negative impact of Ni on plant biomass, MH had a particularly beneficial effect on the growth of B. juncea L. The amount of Ni, Zn, Cu, Mn, Pb and Cr in Indian mustard depended on the Ni dose and type of accompanying mineral structure. The average accumulation of trace elements in B. juncea L. grown in Ni-contaminated soil follow the decreasing order Mn > Zn > Cu > Ni > Pb > Cr.

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

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

Sandstones and shales from the southern flank of the Bilbao anticline in the Gordexola and Orozko valleys, northwestern Spain, have been subjected to a detailed sedimentological, mineralogical and geochemical study. They are composed of proximal frontdeltaic sandbars interbedded with silty-clayey sediments and correspond to a prograding sequence of a deltaic system. The clay mineral assemblages of doublets of sandstones and shales are composed mainly of illite, chlorite and illite-smectite mixed-layers R3 (ISII). The clay diagenesis consists of the transformation of smectite and I-S mixed-layers to illite, the precipitation of Fe-rich chlorite in the pore spaces, and the alteration of micas to chlorite. According to petrographic, mineralogical and geochemical analyses, chlorite is more abundant in sandstones than in shales in both the <2 µm and coarser fractions. The relative abundance of chlorite increases in the sandstones located at the top of coarsening upward sandbars. Furthermore, chlorite formation occurs preferentially in the coarser grained sansdstones previously cemented by ankerite. The geochemical and petrological investigations suggest that chlorite formed during burial diagenesis in a relatively closed system.

The clay-mineral fraction of samples from a bentonite deposit in the Zvolenská kotlina Basin (Slovakia), formed by the alteration of andesitic pyroclastics, was dominated by Fe-bearing montmorillonite of relatively low charge. The total Fe content of the samples ranged from 3.58 to 5.81 wt.% Fe. Variable-temperature Mössbauer spectroscopy revealed that structural Fe(III) in smectite accounts for 70–90% of the total Fe in the unfractionated samples. No structural Fe(II) was observed by Mössbauer spectroscopy, but a small amount was detected by wet chemical analysis. The remainder of the Fe is present in oxide and/or oxyhydroxide phases dominated by poorly ordered goethite and hematite. The hyperfine parameters of the Mössbauer spectra for the raw bentonite are consistent with structural Fe(III) in an aluminosilicate phase mixed with varying quantities of hematite, goethite and possibly maghemite. Except in the fine fraction of sample L28, the hematite failed to undergo the Morin transition, as shown by the negative values for quadrupole splitting at 298 K and 6 K.

Petrographic, X-ray diffraction, and microprobe analyses have been used to assess the significance of illite K-Ar ages from sandstones of two North Sea wells. Three closely spaced samples in one well from the upper Statfjord Formation yield similar ages (69-79 Ma) although the illites formed from different precursor minerals. Pore-filling illite in the upper Brent and the Upper Skagerrak Formations from a second well formed by replacing groundmass clays and other detrital minerals. The average layer charge and K+ content increase slightly with depth (0.69-0.80 K+) due to minor reaction and crystal growth during burial diagenesis. These K-Ar ages increase from 15 to 33 Ma within a 500 m depth interval. The K-Ar age vs. depth relationship for these samples corresponds to the burial rate during the middle Tertiary. In examples of extensive illitization of pore-filling clays in sandstones with little subsequent evolution of the clay minerals, the K-Ar ages indicate the age of diagenetic events.

In contrast, illitic minerals in shales from the Skagerrak Formation in the second well yield an age (108 Ma) that is much older than the clays in the sandstones, but is still younger than stratigraphic age. The K-Ar ages from illitic clay in shales reported in the literature can get younger, older, or remain essentially unchanged with increasing depth. These age vs. depth trends reflect the complex interplay of crystal growth and dissolution during diagenesis, as well as probable contamination by non-recrystallized detrital illites. The K-Ar ages of illitic clays, therefore, evolve in a different manner in shales than in sandstones.

α-amylase was immobilized on acid-activated montmorillonite K-10 via adsorption and covalent linkage. The immobilized enzymes were characterized by X-ray diffraction (XRD), surface area measurements, 27Al nuclear magnetic resonance (NMR) and scanning electron microscopy (SEM). Surface area measurements indicate pore blockage due to linking of the enzyme in the vicinity of the pore mouth. The XRD demonstrates intercalation of enzyme upon immobilization. The NMR studies indicate that, during adsorption, tetrahedral Al sites are involved, while covalent binding occurs exclusively on the octahedral Al sites. The SEM images depict the changed morphology of the clay surface due to immobilization. The efficiency of immobilized enzymes for starch hydrolysis was tested in a batch and a fixed-bed reactor and the performances were compared. The immobilized α-amylase showed a broad pH profile and improved stability characteristics in both reactor types when compared to the free enzyme. The effectiveness factor increased in the fixed-bed reactor, implying that diffusional restrictions to mass transfer operate in the heterogeneous reaction and the use of a fixed-bed reactor leads to a reduction in these diffusional resistances. In the continuous run, 100% initial activity was maintained for 72 h, and after 96 h, >80% activity was retained.

Upper Jurassic sandstones of the South Brae Field were deposited as a submarine fan complex. The earliest formed concretionary ferroan calcite cement passively encloses detrital feldspars which originally formed more than 10% of the rock. Later non-ferroan calcite at the concretion margins was precipitated from a more aggressive fluid. This fluid dissolved up to half of the feldspars and micas originally present, but little or no clay was precipitated. Aluminium must have been lost from the system.

A late dissolution event has enhanced porosity by up to 8%. Feldspar was again reduced in volume by about half, leaving only ∼2% in the rock today. Very minor amounts of fibrous illite and kaolinite (<1%) form the last diagenetic cement. Aluminium must have again been lost from the system.

As the Kimmeridge Clay Formation (KCF) encloses and interdigitates with the South Brae sandstones, a local source of organic acids is quite possible. These acid solutions may have increased the mobility of Al. The Al from the feldspars must have therefore been transported vertically into the KCF, or more probably transported laterally by compactional flows out of the basin (up to 10 km) during release of overpressured basinal water.

The aim of this research was to assess the potential application of the Late Cretaceous levels as raw material for the production of ceramic tiles. Mineralogical, chemical and grain size distribution studies were carried out on four clays sampled at different sites in the Tunisian Central Atlas. Clays are mainly composed of phyllosilicates, usually illite and kaolinite. Quartz, feldspars and dolomite were also detected.

Tiles were prepared by pressing clay bodies at 250 bar and then firing at different temperatures following industrial conditions as closely as possible. Thermal analysis showed the influence of mineralogical composition and grain size distribution on the material behaviour during firing. The physical properties of fired tiles were obtained from specific tests in accordance with international standards (ISO), i.e. the firing shrinkage, water absorption, apparent density and flexural strength. The development of physical properties indicates an optimal firing range between 1050–1150°C. Results demonstrate the potential of Late Cretaceous materials as raw materials for the production of ceramic tiles.

The dissolution of hectorite suspensions in M/20 CaCl2 has been studied under conditions of low acidity. The reaction was almost completed within 2 weeks but very slow changes continued. There was an initial preferential release of Mg which corresponded approximately to the number of Mg atoms exposed at the clay edges but thereafter Mg and Si were released into solution in nearly equimolar amounts until most of the clay was decomposed. The release of octahedral cations was equivalent to the amounts of H+ ions added. Some earlier views on the acid attack of 2:1 clays were supported. With increasing amounts of acid added, the Si released into solution as monosilicic acid become supersaturated before final precipitation as amorphous silica of high surface area.

The molar proportion of Si/Mg released into solution was less than that of the original sample yet there was no chemical or X-ray evidence of the development of significant siliceous ‘fringes’. The residues of the tetrahedral layer probably separate continually, thus maintaining the same kind of reaction surface throughout the reaction, without passing into solution or forming a stable sol. Acid attack in the presence of excess silicic acid did not result in any appreciable selective dissolution of octahedral layer.

The present paper shows the importance of Inverse Gas Chromatography (IGC) for the determination of the surface properties of bentonites. These properties are dispersive surface energy, acid-base properties, surface heterogeneity, sorption isotherms, BET surface areas and heat of sorption, using different probe molecules. IGC can contribute to the interpretation, prediction and optimization of the studied materials' properties. The paper focuses on two distinctive bentonite samples from Porto Santo Island, Madeira archipelago. In view of their potential value, achieved through their incorporation in products for dermopharmacy and dermocosmetics, particle size and particle surface properties are of fundamental importance.

The isomerization of limonene over natural the zeolite, clinoptilolite, was studied. The main products of limonene isomerization were terpinolene, α-terpinene, γ-terpinene and p-cymene. These products have numerous applications in the cosmetic, food and pharmaceutical industries. The main parameters affecting limonene isomerization were reaction time, temperature and catalyst content. These parameters varied within the following ranges: reaction time 15–1440 min; temperature 155–175°C; and catalyst content 5–15 wt.%. Terpinolene was obtained after reaction for 60 min at 175°C using 10 wt.% catalyst. p-Cymene was produced using similar conditions as for terpinolene except for a longer reaction time of 1440 min. The use of optimum experimental conditions allowed the greatest amounts of the desired products to be obtained in the shortest time.

The activity concentrations of natural radionuclides in peloids were studied to assess the radiologic hazard from 18 Turkish spas. The peloids are mainly used for therapeutic treatments, rheumatic diseases and aesthetic purposes. The concentrations of the natural radionuclides 226Ra, 232Th, 40K and 137Cs were determined with a gamma ray spectrometer using a HPGe detector. The average activity concentrations of 226Ra, 232Th, 40K, and 137Cs in the peloids studied were 110.69, 71.52, 576.48 and 0.447 Bq/kg, respectively. The radium equivalent activities in the peloid samples ranged from 63.3 to 766.77 Bq/kg. The absorbed dose rate (Dout) varied between 37.52 and 330.67 nGy/h and most of the observed spa doses are greater than the worldwide recommended values. The annual effective dose values range from 0.26 to 2.78 μSv/y. The annual gonadal dose equivalents of the samples vary from 224.07 to 2283.55 with a mean of 821.99 μSv/y.

An autochthonous origin for the bauxite deposits of the Eufaula district, south-eastern Alabama, appears to have received general acceptance but, compared with younger residual bauxites of the present day tropical regions of the world, the Eufaula deposits have a number of features that are difficult to reconcile with development in situ. In an attempt to resolve the enigma, a detailed study was undertaken of cores from three drill holes that intersected a complete succession through one of the Eufaula deposits. Although the results are not conclusive, it is believed that much of the observed phenomena can be explained on the basis of an essentially transported origin for the deposits.

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 ×.