The kieselguhrs or diatomaceous earths are composed essentially of more or less well crystallised silica, as well as a small quantity of alumina, iron oxide, and traces of other oxides. These earths are largely used as filtration aids; they can serve as supports for certain catalysts, and have also excellent calorifugic properties.

A study of different sorts of kieselguhrs used as supports for nickel and cobalt catalysts in the Fischer-Tropfsch synthesis has recently been carried out by Anderson et al. (1947). These authors find that a previous treatment of the raw kieselguhr by hot hydrochloric and nitric acids gives more active catalysts than those obtained using the same support untreated, and especially than those prepared from calcined kieselguhrs.

In the region of Illapel, Chile, dioritic and andesitic rocks of Cretaceous to Paleocene age from the Unidad San Lorenzo Formation have suffered strong alteration resulting in the formation of a kaolin-rich zone, which is mined in the La Vanguardia open pit near Combarbalá. Detailed mineralogical and chemical investigations of channel samples from this mine, involving a combination of optical microscopy, XRD, SEM-EDX, XRF and TEM, permitted recognition of a zone of silicification and a zone of advanced argillic alteration, both of which contain alunite s.s. and aluminium-phosphate-sulphate (APS) minerals of the woodhouseite group with subordinate amounts of gorceixite, florencite and goyazite. These minerals are found to have originated from infiltration of meteoric waters. The passage from silicification into advanced argillic alteration was associated with an increase in sulphate activity as manifested by the increase of SO42— at the expense of PO43— in the alunite s.s. and by an increase of the Au content from 0.01 to 0.03 mg/kg Au. This high sulphidation type of wallrock alteration may be roughly compared with the Nansatu type of White (1991).

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 layered double hydroxide (LDH) Al2Li(OH)6[NiCl4]1/2 was synthesized by anion exchange of Al2Li(OH)6(NO3) and the coordination structure of [NiCl4]2− in the interlayers was investigated. The LDH had a hexagonal cell with a = 5.06 and c = 23.06 Å. Since the basal spacing of one layer was 7.7 Å, the interlayer distance was calculated to be 2.9 Å and was too narrow for the usual tetrahedral NiCl4 structure. From extended X-ray absorption fine structure (EXAFS) measurements, the first neighbour Ni-Cl distances in the LDH were 2.10 Å which was compatible with four-fold coordination. Since the electron spin resonance (ESR) spectrum of the LDH showed no absorption, the [NiCl4]2− structure was considered to be square planar, rather than the usual tetrahedral structure in the interlayers of LDH.

High-gradient magnetic separation (HGMS) performed on the clay fraction (< 1 µm) of acid soils facilitates the separation and concentration of mineral fractions according to their Fe and Mg contents. As a result, smectitic layers formed by weathering of a chlorite were identified although they were not detected in the bulk sample. The concentration in the non-magnetic fraction of minerals with an intergrade vermiculite-chlorite behaviour enabled more accurate information to be obtained on these minerals.

The occurrence of sepiolite and palygorskite in soils, Eocene limestones and the Asmari dolomitic limestone of Iran has been described by many workers (Bentor et al., 1963; Martin Vivaldi & Robertson, 1971; Abtahi, 1977, 1980). No studies have been carried out on the genesis of these minerals in Iranian soils, however, and the purpose of this note is to describe some experimental conditions under Which sepiolite can form, and which also could apply to the genesis of the mineral in Iranian soils.