Identification of Na-smectite hydration by use of “humid cell” high voltage microscopy

Swelling of smectite clays is a property of fundamental importance for the use of such barrier materials in repositories for high level radioactive wastes and is readily observed macroscopically. The hydration process on a molecular scale, involving separation of adjacent smectite lamellae by penetrating water molecules, remains hypothetical but its detailed microscopic features have now been documented. A 3 MV electron microscope was used for the study, which comprised filling of Na-smectite in powder form in a closed cell that was penetrated by electron radiation in the microscope after exposing the clay to water and thereafter drying it.The study showed two practically important facts. Firstly, the wetting phase initially resulted in a thin hydrated “shell” of the dry aggregates. Micrographs taken after various periods of time demonstrated that the “shell” softened and expanded, thereby connecting clay aggregates that were initially separated. The inverse process took place in the drying phase, i.e. the very soft, relatively homogeneous clay gel was transformed to separate dense aggregates.Secondly, the expansion of the fully hydrated aggregates did not yield a homogeneous gel with uniform interparticle distance. Instead, the expansion of the aggregates was limited so that a stable condition was reached in which a small amount of the porewater was contained within the aggregates, while a major portion occupied larger inter-aggregate voids. This confirms the conclusion from various electron optical studies of smectites prepared by use of resin-embedding techniques, that it is necessary to distinguish between “internal” (i.e. interlamellar, also termed “interlayer”) and “external” water. Their ratio is a determinant of the percolation and diffusion properties in bulk.     

Formulation of muds for pelotherapy: effects of “maturation” by different mineral waters

Spa centres in northern Italy use clayey admixtures for the formulation of muds to be used in pelotherapy. The basic ingredient (“virgin” clay) is a dressed bentonitic geomaterial with mineralogical composition: smectite 60–70%, illite 5–10%, kaolinite 10–15%, quartz 5–10%, calcite 5–10% and feldspars 2–3%.The peloid muds are obtained by “maturation” of the virgin clay with mineral waters gushing out in situ which have different geochemistry: sulphureous, Ca-sulphate, Ca–Mg-sulphate and Br–I-salty (after the Italian regulation DPR 105/92). The maturation treatment is varying with respect to the mixing procedure and lasting time.Peculiar parameters have been tested to verify the effects of various maturation treatments, i.e., changes with respect to virgin clay.Formation of organic matter is due to the presence of microorganisms and algae in the maturation habitat. The <2 μm fraction is generally decreased due to clay particles agglomeration. Mineralogical changes are mainly concerning the degradation of clay minerals, as smectite and illite, and subordinately to the dissolution of calcite. Cation exchange capacity (CEC), soluble salts, water retention, swelling index, activity, consistency parameters (WL, WP and PI), thermal behaviour and cooling kinetics are influenced by the geochemistry of mineral waters used for the maturation treatments but with some opposite trends for Br–I-salty water, and for sulphureous and Ca-sulphate waters, respectively.Noteworthy was the influence of high-pH value of the virgin clay on the pH of peloid muds (in fact, the pH of the used mineral waters is ranging around the natural value). Furthermore, the temperature reached by the peloid muds after 20 min of application (calculated after an innovative mathematical model) is influenced by water retention. An increase in plasticity index and a slower cooling are considered to improve the quality of the obtained peloid muds for pelotherapy.The observed different cation exchange behaviour and soluble salt content could be discriminant for either dermatological masks or thermal body cataplasms.A need of regulation (standard procedures) is suggested to certificate the clay geomaterials suitable for pelotherapy and also for drugs formulation.     

Mineralogical transformations of calcareous rich clays with firing: A comparative study between calcite and dolomite rich clays from Algarve, Portugal

Mineralogical transformations during firing of two extremely calcareous clays, one calcite and other dolomite rich, and relatively poor in silica were studied. Original clays were mineralogical and chemically characterized with X-ray diffraction (XRD) and X-ray fluorescence (XRF). Firing of both clays was carried out in the temperature range 300–1100 °C under oxidizing conditions and the mineralogical transformations were investigated with XRD, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and scanning electron microscopy associated with energy dispersive X-ray spectroscopy (SEM-EDS).Important compositional differences in the neoformed phases were observed between calcite and dolomite rich clays. In the Ca-rich clay the assemblage gehlenite + wollastonite + larnite was observed. In the Mg(Ca)-rich clay the reaction products included akermanite, diopside, monticellite, forsterite, periclase and spinel.XRD and SEM-EDS showed the presence, in both clays, of a potassium–calcium sulfate in samples fired between 900 and 1100 °C.     

Behavior of kaolinite and illite-based clays as landfill barriers

The technical requirements for the landfill of municipal wastes in the European Union (EU) are given in the Council Directive 1999/31/EC. A geological barrier of at least 1 m thickness with a hydraulic conductivity (HC) of 1 · 10^− 9 m/s is required. Where the geological barrier does not naturally meet the above conditions, a geological barrier of at least 0.5 m thick must be artificially established. We studied at controlled conditions, the ability of some clays (kaolinite or illite based) to act as landfill barriers. Several Spanish ceramic clays were compacted in columns (0.5 m length) and characterized for mineralogical, physical–chemical and heavy metal ions adsorption properties after 10 months leaching experiments. Zn, Cd, Pb and Cr salts were dosed in the synthetic leachates in order to test their in-depth retention. The specific surface area decreased in the material located near the clay–leachate interface region (< 6 cm) due to biofilm formation around clay particles, but bulk mineralogical properties were not affected. Although all the clays fulfilled the HC requirements, the diffusion of anions (chloride) reached more than 30 cm in kaolinite–illite or pure illite clays. The presence of significant traces of smectite (< 5%) was critical in anion transport retardation. Heavy metal ions were generally retained in the first 10 cm but in high surface-area illitic clays, the anions and heavy metal ions transport was stopped at < 6 cm. The clay mineralogy and the presence of carbonates and soluble salts greatly influenced the behavior of the barrier materials. Carbonate dissolution and precipitation affected < 6 cm depth. Divalent cations of carbonates selectively occupied the exchangeable positions and inhibited the retention of Na⁺, NH₄⁺ and K⁺, in the leachates. Sulphate was reduced at a depth of 20–30 cm. This biogeochemical process contributed to cadmium retention, presumably precipitated as sulphide.     

The effect of kaolin properties on their behaviour in ceramic processing as illustrated by a range of kaolins from the Santa Cruz and Chubut Provinces, Patagonia (Argentina)

The Patagonian kaolins offer a wide set of origin of deposits, composition, mineral processing and ceramic properties, giving a rare opportunity for investigating the interdependence of mineralogy, chemical composition, particle size distribution, texture, and surface activity with their technological behaviour in sanitaryware and porcelain stoneware production. Plasticity is strictly dependent on surface activity, < 2 μm fraction and expandable clay minerals; slip rheology is affected by soluble salts and expandable clay minerals, but also by high specific surface or tubular halloysite. Kaolinite/halloysite play an opposite role versus smectite/interstratified I/S in slip casting and tile pressing: the former allow faster casting rates, while the latter improve powder flowability and mechanical strength. Kaolinite and quartz are beneficial for drying behaviour while high surface activity or expandable clay minerals increase significantly drying sensitivity. Firing behaviour is mainly affected by minor components supplying “fluxing” (i.e. iron, alkali and alkaline-earth) oxides. A great deal of technological parameters seem to be reasonably predicted by the surface activity of clays and especially the Methylene Blue index, which is the most reliable, simple and economic method to predict and control the ceramic response of kaolins and ball clays.     

Technological features of Renaissance pottery from Deruta (Umbria, Italy): An experimental study

This work is focused on the assessment of the basic technological features of the pottery production in Deruta in the Renaissance period. For this purpose, clay samples and two kinds of ceramic products (tiles and wares) dating back to the XVIth century were characterized using different analytical techniques: optical, cathodoluminescence and electron microscopy on thin sections, X-ray fluorescence and X-ray diffraction on the bulk powdered samples. Then two clays best representing the chemical composition of the ceramic products underwent laboratory experimental firing tests at different conditions following the procedure of firing applied in the XVIth century as reported in the ancient historical documents. The firing products underwent textural, chemical and mineralogical characterization by the same analytical techniques in order to be compared with the clays and the shards. Archaeometric investigation of the ceramic bodies led to the identification of two different clay raw materials, both of local provenance, for the tile and the ware production. Archaeometric investigation of the glazes showed some differences between the wares from different workshops. In this respect the typology and the quality of the glaze resulted to be much more effective than the texture and composition of the ceramic body in characterizing the wares from different coeval workshops. Results of the experimental tests evidenced the firing products result from a complex mix of physical and chemical variables strictly correlated to one another. Above all, the heating rate and the amount of calcite in the clay raw material are crucial driving forces of the kinetics of firing. Comparison between the original and the experimental ceramic products indicated ranges of biscuit firing temperature of 850–1050 °C and of 950–1050 °C for the tiles and the wares, respectively, and a low heating rate in both cases.     

The design and synthesis of a novel 1,8-naphthalimide PAMAM light-harvesting dendron with fluorescence “off-on” switching core

A novel polyamidoamine dendron core, peripherally functionalized with 1,8-naphthalimide fluorophores, was configured as a light harvesting antenna in which the system surface was labelled with blue emitting 4-allyloxy-1,8-naphthalimide “donor” dyes capable of both absorbing light and efficiently (96%) transferring the energy to a single, yellow-green emitting 4-N-methylpiperazinyl-1,8-naphthalimide “acceptor” dye. The 1,8-naphthalimide core was designed on the “fluorophore-spacer-receptor” format and was able to function as a fluorescence photoinduced electron transfer sensor. Two different photoinduced electron transfer effects were observed in the new antenna namely that from the receptor to the core fluorophore and that from the polyamidoamine backbone to the peripheral 1,8-naphthalimides. Althogh the core emission intensity of the system was enhanced > four times by reducing the pH from 10 to 2, the fluorescence enhancement of the system in acidic medium, excited within the periphery (λ_ex = 360 nm), was approximately twice that of the core fluorescence enhancement after direct excitation of the focal 1,8-naphthalimide (λ_ex = 420 nm), because of more efficient energy transfer. The observed “off-on” switching of the core fluorescence over a wid pH scale indicates that the novel light harvesting antenna would be able to act as a highly efficient fluorescent sensor.     

A novel “coral” carbon microprobe with and without N2 incorporation

“Coral”-type microstructure carbon films, with and without N₂ incorporation, were grown on sharpened tungsten microprobes by plasma enhanced chemical vapor deposition (PECVD) using H₂/CH₄/N₂ and H₂/CH₄ gas mixtures, respectively. The electrochemical behaviors of the coral-type carbon coated tungsten microprobe, characterized by various concentrations of ferrocyanide in a background of 0.1 M KCl, show excellent structural stability with similar microstructure before and after prolonged analysis without the need of surface pretreatment. The microprobes exhibit quasi-reversible kinetics with high signal-to-noise S/B ratio. The N₂ incorporated microprobe shows a slightly wider potential window, no surface adsorption of the analyte and higher sensitivity as compared to the sample without nitrogen incorporation. Furthermore, the wide potential window of  3 V is very good as compared to boron-doped diamond electrodes which are  3.5 V. This well behaved; broad electrochemical behavior and the simple fabrication method make the “coral” carbon film microprobe an excellent candidate for electrochemical sensing.     

Iron minerals and their influence on the optical properties of two Indian kaolins

Kaolin is mostly associated with minor quantities of ancillary minerals containing transition elements such as iron and titanium. These ions impart color to the white kaolin which adversely affects its application in paper and paint industries. Hence their removal is of prime importance in the optimum utilization of kaolin. The coloring effect as well as the mode of removal of these impurities depends on the “species” of the ion and/or the type of mineral. The present paper deals with the investigation on two Indian kaolins of different geological origin, one from Gujarat state at the western part of India and the other from Kerala State at the southern most part. Detailed physical, chemical and mineralogical characterization of the samples was carried out. The product clays after beneficiation by size classification, high gradient magnetic separation and chemical leaching were found to be of acceptable grade for paper industry with respect to optical properties and particle size. The impurity minerals were concentrated by different methods so that their identification was easier. Attempts were made to study the Fe species by correlating the XRD, chemical assay, DCB treatment and EPR spectral information of the clay samples before and after beneficiation. Iron stained anatase was found to be the major impurity in the Gujarat clay whereas iron was present as oxide/hydroxide in the Kerala sample. The beneficiated products from the Kerala clay were found to have better optical properties.     

Hydrothermal alteration of “La Serrata” bentonite (Almeria, Spain) by alkaline solutions

Bentonite and concrete are considered as backfilling and sealing materials in a deep geologic repository of high-level radioactive waste (HLRW). The pH of the pore waters leached during concrete degradation is >11 for a long period of time. Under these alkaline conditions, bentonite is susceptible to dissolution–precipitation reactions. The aim of this work is to study mineralogical changes in bentonite in contact with synthetic pore waters of cements. The temperature effect has been taken into account in order to consider the thermal impact of radioactive decay.The bentonite used comes from “La Serrata de Níjar” (Almería, Spain) and is mainly composed of montmorillonite. Bentonite was submitted to alkaline solutions at 35, 60 and 90 °C up to 365 days. Alkaline solutions were similar to the pore waters leached in the first stage of cement degradation.The zeolite crystallization and the increase of magnesium in a non-exchangeable form in the smectitic clay fraction are the main mineralogical changes detected in the bentonite. Both processes are enhanced with the duration time and temperature of reaction.     

Saudi Arabian clays for lead removal in wastewater

Three types of local clays–Tabuk, Baha, and Khaiber–were tested for their abilities to adsorb lead ions from wastewater. The effect of pH on the adsorption of lead ions was also investigated. The clays were treated with hydrochloric acid to activate adsorption sites within clay particles. Untreated Tabuk clay had the largest adsorption capacity, about 30 mg lead/g clay, in comparison with those of Baha and Khaiber clays. The smallest adsorption was observed with Khaiber clay, about 10 mg lead/g clay; this may be attributed to the prior existence of lead within the clay. The adsorption of the acid-activated clays was not enhanced compared to those of untreated clays. The Langmuir model described the experimental data for all untreated clays, while the Freundlich model described the experimental data of untreated Khaiber clay and treated Baha clay. The local clays tested in this study, especially Tabuk clay, may be utilized as cost-effective and efficient adsorbent materials for removing heavy metals from wastewater in Saudi Arabia.     

Moulding properties of a Nigerian silica–clay mixture for foundry use

The moulding properties of Igbokoda silica sand, bonded with Ijero–Ekiti clay, were investigated. American Foundrymen Society (AFS) standard cylindrical samples dimensioning Ø50 mm × 50 mm in height were prepared from various sand–clay ratios with 5% tempering water, by applying three ramming blows of 6.666 g each from a height of 50 mm as required for foundry sands. The samples were subjected to various physical and mechanical tests. These include permeability, green compression strength, and dry compression strength tests. Green shear strength, dry shear strength, field mould strength, shattered index and refractoriness tests were also carried out on the samples. Samples containing 23–32% clay were found to possess adequate permeability, good strength and refractoriness suitable for casting of both ferrous and non-ferrous alloys.     

Pharmaceutical applications of some spanish clays (sepiolite,palygorskite, bentonite): some preformulation studies

In this work, a pharmaceutical preformulation study of four Spanish clays (two sepiolites, one palygorskite and one bentonite) is presented, comparing the results obtained with those of three mineral products currently used in pharmaceutical technology. The results showed that the mineralogical and chemical purity of these clays is similar and even higher than that of the three commercial products. The microorganism content is inside the range required for non-sterile pharmaceutical forms. We also determined two parameters concerning the clays' suitability for use in tablet manufacture (colour and water content) and one indicating appropriateness as an antidiarrheic product (adsorption capacity of methylene blue). The clays are yellowish white in colour, although correction does not seem necessary; water content varies according to the structure of the clay and storage conditions. Adsorption capacity of methylene blue is affected by the amount of hydration water present, dehydration temperature and the type of interchangeable cation found in the clay.     

Adsorption and binding of the transgenic plant proteins, human serum albumin, β-glucuronidase, and Cry3Bb1, on montmorillonite and kaolinite: Microbial utilization and enzymatic activity of free and clay-bound proteins

Human serum albumin (HSA), β-glucuronidase (GUS), and the Cry3Bb1 protein from Bacillus thuringiensis subsp. kumamotoensis are expressed by genetically-modified plants. Commercial samples of these proteins adsorbed and bound rapidly on the clay minerals, kaolinite (K) and montmorillonite (M). Adsorption increased as the concentration of protein increased and then reached a plateau. The greatest amount of adsorption and binding occurred with the Cry3Bb1 protein, of which there was no desorption: 6.7 ±0.21 μg adsorbed and bound μg^− 1 of M; 2.1 ± 0.39 μg adsorbed and bound μg^− 1 of K. With GUS, 2.2 ± 0.29 μg adsorbed and 1.7 ±0.21 μg bound μg^− 1 of M; 1.5 ± 0.28 μg adsorbed and 1.0 ± 0.03 μg bound μg^− 1 of K. HSA was adsorbed and bound the least: 1.2 ±0.04 μg adsorbed and 0.8 ± 0.05 μg bound μg^− 1 of M; 0.4 ± 0.05 μg adsorbed and 0.4 ± 0.03 μg bound μg^− 1 of K. However, X-ray diffraction analyses indicated that only HSA intercalated M, and none of the proteins intercalated K, a nonswelling clay. When bound, the proteins were not utilized for growth by mixed cultures of soil microorganisms, whereas the cultures readily utilized the free (i.e., not adsorbed or bound) proteins as sources of carbon and energy. The enzymatic activity of GUS was significantly enhanced when bound on the clay minerals. These results indicated that recombinant proteins expressed by transgenic plants could persist and function in soil after release in root exudates and from decaying plant residues as the result of the protection provided against biodegradation by binding on clay minerals.     

Evaluation of different clay minerals as additives for soil water repellency alleviation

The objective of this study was to evaluate the effectiveness of kaolinite, illite, Na- and Ca-montmorillonite in alleviating water repellency for a simple model soil material of known composition before and after wetting and drying phases. Sand was rendered water repellent by adding 10 and 30 g kg^− 1 stearic acid followed by adding different amounts (1, 2 and 3 mass %) of respective clays. Treated and untreated control sand were wetted and exposed to prolonged drying phase at 50 °C to simulate the effects of wetting followed by drying under a hot spell. The persistence of water repellency was measured with the water drop penetration time (WDPT) test. During the wetting/drying cycle, the control samples (stearic acid treated sand) and clay treated sands behaved in a fashion typically observed in water repellent soils: they were wettable above and water repellent below a critical water content, with repellency persistence (WDPT) increasing with decreasing water content. Kaolinite and Na-montmorillonite were found to be the only clay minerals able to lower the persistence of repellency of the stearic acid sand. The difference between Ca- and Na-montmorillonite ability to alleviate water repellency is explained by the differences in inter-particle forces in the clay–exchangeable cation–water system. During the prolonged drying phase at 50 °C, the persistence of water repellency increased with the duration of heating at 50 °C, with the increase being greatest during the first 48 h in the majority of the samples. While kaolinite and Na-montmorillonite addition resulted in a reduction in the persistence of water repellency of the stearic acid sand, Ca-montmorillonite and illite addition increased the persistence of water repellency of the stearic acid sand. The net effect of clay mineral addition is dependent on the amount of Ca²⁺ ions occurring at the surface of clay minerals. Pools of available (exchangeable) calcium decrease in the order as follows: Ca-montmorillonite >> illite >> Na-montmorillonite ≈ kaolinite.     

Evaluation of geotechnical properties of bentonite from Lieskovec deposit, Slovakia

Chemical and mineralogical composition and geotechnical properties of Ca²⁺-bentonite samples from Lieskovec deposit, Slovakia, are reported. The main mineral is Fe-montmorillonite. Its content as obtained by the methylene blue adsorption method is relatively low, 28 to 49%; however, it is the dominant variable affecting geotechnical parameters of this bentonite. Rather low liquid limit values of 64–80% and water adsorption (Enslin test) data in a broad range of 123–606% were obtained. Permeability coefficients of the order of 10^− 11 m s^− 1 suggest the possible suitability of this bentonite for geosynthetic clay liners and other civil engineering applications.     

Electromagnetic determination of clay water content: role of the microporosity

The electromagnetic determination of clay water content requires a good understanding of the main factors that affect the relationship between the clay relative permittivity κ and the water content θ. The first part of this paper proposes a review of the different factors affecting it: (a) a significantly high imaginary part of the relative permittivity; (b) a frequency-dependent response; (c) a high content of bound water with a relative permittivity value lower than that of free water; (d) a geometrical effect associated with “platy” units that characterize the clay texture. The next sections focus on the c and d factors related to the microporosity of clayey geomaterials; both factors are studied with two theoretical tools: the Moment Method (MoM) and the Differential Effective Medium (DEM) theory.The calculations indicate that bound water effect and geometrical effect act as competing processes: when water is added in a dry clayey material, the geometrical effect contributes to increase the clay relative permittivity compared to media with isotropic particles; a significant amount of bound water generates a decrease in the clay bulk permittivity. Consequently, the results allow to identify two types of behaviour: (1) low surface area systems, typically kaolinite geomaterials, for which the geometrical effect is predominant, and (2) high surface area systems, typically smectite clays, for which a balance between the geometrical effect and the bound water effect is expected.Moreover, the MoM simulations suggest that the derivative ∂κ/∂θ is affected by the bound water content, but slightly depends on clay content. These numerical observations that may contribute to improve in situ water content monitoring should be validated by experimental investigations.     

Effects of sand addition on production of lightweight aggregates from Tunisian smectite-rich clayey rocks

Smectite-rich claystone–marlstone samples from 12 outcrops located in the Southern Atlas domain of Tunisia were investigated with regard to manufacture of lightweight aggregates (LWAs). The clayey materials mainly consist of smectite, kaolinite and illite, together with quartz, calcite, dolomite and feldspars as accessory components. 10–12 mm pellets were prepared from wet paste and initially heated to 600 °C, 700 °C or 800 °C (depending on the raw material) for at least 2 h in order to avoid any explosion of the aggregate. The pellets were then subjected to a quick firing process at 1180 °C. The addition of 15% of quartz sand (< 250 μm grain size) to the raw materials was found to improve some required pre-treatments and give better expansion properties to some of the aggregates. The addition of 1% used automobile oil to the clay and quartz sand mixtures caused the formation of more gas and a drop in bloating temperature. The obtained LWAs were characterized by physical properties such as apparent density, mechanical resistance, water absorption and expansion. The laboratory results were comparable to those of two commercial LWAs from France (Argidécor®) and Portugal (LECA®) and provide new openings for the utilization of Tunisian claystone in civil engineering work or in agricultural applications.     

Evaluation of Fiji phosphate rocks: Chemical and mineralogical properties of samples from the Lau group

The chemical and mineralogical characteristics of two major kinds of phosphate rock (PR) deposits identified in the Lau group, eastern Fiji, were investigated before and after acidulation and calcination. X-ray diffraction analyses of the Lau PRs showed the presence of Ca and Al rich phases of phosphate minerals. The oolitic material consisted of dominant amounts of fluorohydroxyapatite and only subordinate amounts of crandallite whilst the phosphatic clay consisted almost entirely of crandallite. Acidulation of the PRs caused a marked increase in water, citric and formic acid extractable-P. However the amounts extracted were almost 10–15 times less than that released by a reference North Carolina PR. Of the two types of PR found in Fiji, the apatite rich oolitic material released 8–10 times more extractable P than phosphatic clays following acidulation. Calcination of crandallite rich phosphatic clay at 800°C caused a small but significant increase in extractable P; but, the effect was less marked than that of acidulation, suggesting that the small amounts of apatite minerals present in the phosphatic clay have a greater influence following acidulation on available P than crandallite.     

Analysis of temperature effect on ceramic brick production from alluvial deposits, Tamilnadu, India

This study focuses on the thermal behaviour of alluvial clays in the production of ceramic brick industries, which are largely found on the bank of the Cauvery river, Tamilnadu, India. Clay bars were prepared which consisted of quartz, kaolinite, illite, chlorite, feldspars and iron oxides. The test samples were fired in the range of 700–1100 °C and were examined with chemical analysis, thermogravimetric–differential thermal analysis (TG–DTA), X-ray diffraction (XRD) and scanning electron microscopy (SEM). An increase in firing temperature resulted in dehydroxylation of clay minerals, persistence of quartz and formation of Ca-anaesthetic plagioclase. SEM images visualized the vitrification of the fired bricks, which increased the compressive strength of the fired bars. The bricks made with alluvial clays displayed less water absorption and higher compressive strength, indicating that they could be used in the brick industry. The results of this work assisted the industries to select more appropriate natural clay composition and firing dynamics for making the bricks.