Electrical measurements are used in various fields of geoscience and technology, e.g. gas/oil exploration or landslide-barrier monitoring. Although clays are amongst the most conducting geomaterials their electrical properties are not yet fully understood. For example, in a recent high-level-radioactive-waste repository large-scale test, a bentonite barrier was monitored geoelectrically. To facilitate interpretation of the results, the reasons for the observed differences in the electrical conductivity must be understood (e.g. changes in water content, temperature, salinity of pore water, etc.). To improve understanding of the electrical properties of clay minerals, in situ measurements must be combined with laboratory measurements. In situ measurements allow the characterization of the material in its natural state and laboratory measurements, for small sample amounts, allow the user to vary relevant parameters systematically such as water content, temperature, the salinity of the pore water, or even the cation population if swelling clay minerals are present. In situ measurements using different electrode distances, from m to cm range, proved that small-scale investigations are essential because of small-scale material heterogeneities. In the laboratory, all the relevant parameters mentioned above can be controlled more easily for small sample amounts. In the present study three different small-scale devices (SSM1–SSM3) were compared. The geometry factor, K, was determined both by calculation and by a calibration against solutions of different conductivity. Calculated and measured geometry factors were in good agreement. SSM1 and SSM2 — both with four pin-shaped electrodes — were found to be particularly applicable for in situ measurements. SSM2, with point contacts at the tips of the pins, was considered to be an improvement over SSM1 because the effects of both water content and temperature gradients (which are particularly relevant near the surface) were less pronounced using SSM2. SSM3, in which the contacts are placed at the bottom of a 4.5 mL trough, proved to be useful when systematically varying all of the parameters influencing the electrical properties in the laboratory.

Aflatoxins in contaminated corn do not degrade in corn fermentation solution (CFS) during biofuel production; rather, they are enriched in the co-product, dried distillers grain. Aflatoxin B1 (AfB1) is the most toxic form of all aflatoxins. Removing AfB1 from CFS is desirable to minimize its toxicity to animals. Smectites can adsorb AfB1 from aqueous solutions and, therefore, inactivate the toxin, but proteins in CFS inhibit the adsorption of AfB1 by smectites. The current study aimed to minimize the interference by CFS in adsorption of AfB1 on smectite by modifying a calcium-smectite (Ca-3MS) with a small nutritive organic compound, e.g. carnitine, choline, arginine, histidine, or tryptophan. The organo-smectites were characterized by X-ray diffraction (XRD) and Fourier-transform infrared (FTIR) spectroscopy, and adsorption of AfB1 in CFS by these composites was examined. Various degrees of intercalation of the organic nutrients into the smectites were observed with XRD and FTIR. After immersing the smectite and organo-smectites in the CFS, the d001 values of Ca-3MS expanded to ~1.82 nm due to protein interaction, but the organo-smectites were confined to ~1.39 nm, which indicated that the protein had limited access to the organo-smectite interlayers. The IR bands at ~1652, 1544, 1538, and 1454 cm–1 from the organo-smectites revealed, however, that complete protein inhibition was not achieved. The organo-smectites were capable of adsorbing AfB1 in simple aqueous solution with maximal adsorption capacity up to 0.55 mol kg–1. Significantly greater (p ≤ 0.05) AfB1 adsorption was achieved by choline- and carnitine-modified smectites compared with the original Ca-3MS in the presence of competing protein (pepsin) in simple aqueous solution. In real CFS, both AfB1 adsorption capacities (Qmax) and affinities (K) by all organo-smectites were greater (Qmax = up to 0.45 mol kg–1 and K = up to 0.165 μM–1) than those by Ca-3MS (Qmax = 0.22 mol kg–1 and K = 0.031 μM–1). The study suggested that using smectites modified with an organic nutritive compound could be an effective, economical, and safe strategy for removing mycotoxins, including aflatoxins, during biofuel production.

Two reference halloysites from New Zealand (Te Puke and Opotiki) were studied by X-ray diffraction under (1) various levels of relative humidity (RH) from 95 to 0% (dehydration), and (2) various temperatures increasing from 25 to 120°C (dehydration). They were also studied by differential thermal and thermogravimetric analyses at 40 and 0.2% RH. The impact of freeze drying along with the influence of cation saturation (Ca and K) on halloysite hydration were studied. The dehydration of the two halloysite samples upon decrease in RH started below 70% RH. However, the dehydration of Opotiki was still incomplete at ∼0% RH regardless of the saturation cation whereas Te Puke was completely dehydrated at ∼10% RH. For each sample, the decrease in RH and the increase in temperature induce similar dehydration behavior, but the dehydration processes of the Opotiki and Te Puke samples are different. The dehydration of Te Puke proceeds with one intermediate hydration state reacting as a separate phase due to the presence of ‘hole’ water molecules. The dehydration of the fully hydrated Opotiki halloysite gives a dehydrated phase and no 8.6 Å phase. The results suggest the presence of different types of water molecule, the ‘associated’ and the ‘hole’ water, controlling the dehydration behavior of halloysites. Freeze-dried halloysite samples are essentially dehydrated and the size of their coherent scattering domains is strongly reduced. Rehydration experiments performed after dehydration either at 95% RH or by immersing the sample in water for 3 months result in their partial rehydration. Calcium saturation promotes the rehydration process. The results suggest the presence of interlayer cations in the Opotiki sample, Ca ions being associated with the strongly held ‘hole’ water. As a result of this study, we assert that the (de)hydration behavior of halloysite is highly heterogeneous and cannot be generalized a priori.

A new model is proposed for analysis of the source clays used to create ceramics, based on geographic, petrographic, mineralogical, mineral-chemistry, and geochemical criteria. The development of this model became feasible after the discovery of a Pliocene volcanic clay horizon on NWAegina Island, Greece. The volcanic clay contains smectite, mixed-layer chlorite-smectite, biotite, and palygorskite and has greater feldspar content than the underlying Pliocene marls, which contain R0 mixed-layer illitesmectite, mica, dolomite, serpentine, talc and gypsum, and, in some places, palygorskite. The two units have distinct geochemical characteristics. In general the Pliocene volcanic clay is richer in SiO2, Al3O3, and Fe2O3 and poorer in Na2O, MgO, and P2O2 than the Pliocene marls. The Nb, Zr, Hf, Th, and rare earth element (REE) contents are also significantly greater in the Pliocene volcanic clay and comparable to those of the dacitic rocks of the island, reflecting the volcanic origin of the clay.

The proposed model was used to identify the source-clay materials that were used for the production of ceramics on the island of Aegina (Aeginetan Ware). All five criteria should be considered in any provenance study. The use of individual criteria on their own can lead to ambiguous conclusions. In the present study the geochemical criterion was particularly helpful. It provided robust evidence for the nature of the source clay. The Pliocene volcanic clay horizon and the underlying Pliocene marls are the candidate raw materials for Aeginetan Ware. Although the Pliocene marls have been invoked as raw materials for Greek Bronze Age (~3000–1100 BC) Aeginetan ceramics and are used as raw materials by modern Aeginetan ceramists, the geochemical characteristics of a large set of Bronze Age Greek Aeginetan sherds with fine and coarse fabrics coincide with those of the Pliocene volcanic clay. This comparative and cumulative evidence suggests that the Pliocene volcanic clay was the main source clay for ancient Aeginetan ceramics, regardless of the fabric (coarse or fine) and that admixture of different sources might not be necessary for fine-grained ceramics.

The surface modification of Zeolite 4A using cetyl trimethyl ammonium bromide (CTAB) as a modifier via an ultrasonic method was carried out and the surface physicochemical properties measured. Response surface methodology (RSM) was developed with CTAB concentration, handling time, and handling temperature as variables, to help predict the performance of the modified zeolite under particular conditions. The influence of organic-modified surface treatment and of the amount of modified zeolite on the water-absorption capability of starch-g-poly (acrylic acid) hydrogel composites was also assessed. The results showed that the channels and skeleton structure of zeolite 4A were unchanged after organic modification by CTAB and the surface modification was effective. The results suggest that organic-modified zeolite 4A has improved the water-absorption capability.

Evidence for the formation of maghemite from goethite due to a bushfire on acid sulfate soil at East Trinity, Australia, is presented. Oxidation of pyrite-bearing acid sulfate soils led to precipitation of goethite-impregnated leaf litter. During a major bushfire, goethite with a crystal size calculated from broadening of the 110 reflection of ∼9 nm was converted to microcrystalline maghemite (size 12 nm, 220 reflection) and hematite (17 nm, 104 reflection) in a matrix of partly combusted plant litter. Replication of this natural formation of maghemite from goethite was achieved in the laboratory by burning goethite-impregnated leaf litter.

The influence of dissolved species and particle morphology on the electrokinetic behavior and the initial yield stress values of Cuban lateritic aqueous suspensions was studied. The lateritic samples were mixtures of serpentine and goethite in different relative proportions. The addition of silicate and Mg ionic species, which are normally found in natural waters used in industrial processes, affected the electrokinetic and flow behavior of the lateritic suspensions. Specific adsorption of these species on particle surfaces was shown by a shift of the isoelectric point and the maximum of the initial yield stress to more acidic pH (Si ionic species adsorption) and more basic pH (Mg ionic species adsorption), when compared to suspensions containing only non-adsorbing electrolytes. The initial yield-stress values determined in samples consisting entirely of goethite varied from sample to sample. A detailed crystallochemical characterization revealed that these changes were associated with the axial ratio (i.e. ratio of particle length to width) of the mineral particles. Goethite samples with larger particle size (smaller number of particles for a given solid concentration) and greater axial ratios presented initial yield-stress values greater than those goethites with smaller particle size and lower axial ratio.

Heavy metals in the environment are a problem due to their toxicity and bioaccumulation. Adsorptive removal of heavy metals by clay minerals has garnered increasing attention due to the abundance, low cost, and exceptional physicochemical properties of the clays. The purpose of the present study was to investigate the utilization of two Turkish sepiolite samples, nodular sepiolite (NS) and industrial sepiolite (IS), as adsorbents in removing Ni2+ ions from aqueous solutions. The specific surface areas of NS and IS are 182.19 m2 g–1 and 63.78 m2 g–1, respectively. The effects of adsorbent dosage, initial pH, contact time, initial concentration, and temperature on the adsorption of Ni2+ ions onto the sepiolite samples were investigated using a batch method. The optimum adsorbent dosage was determined as 0.6 g/50 mL of adsorbent and the optimum pH value was 6.0, for both sepiolite samples. The adsorption process obeyed the Freundlich isotherm model (KF: 4.89–9.73 mg1–1/n L1/n g–1 for NS and 4.27–6.42 mg1–1/n L1/n g–1 for IS) and the pseudo-second order kinetics model (k2: 0.0049–0.0397 g mg–1 min–1 for NS and 0.0688–0.1195 g mg–1 min–1 for IS). The adsorption process was spontaneous and endothermic, and the randomness increased. The samples exhibited large adsorption capacities through three cycles of adsorption-desorption tests. The results revealed that the sepiolite samples are promising as cost-effective adsorbents for the removal of Ni2+ ions from aqueous solutions.

Titanium was introduced into the clay structure by cation exchange with polymeric Ti cations which were formed by partial hydrolysis of Ti alkoxide in HCl. X-ray diffraction, N2 adsorption-desorption, chemical analysis, thermogravimetric analysis, differential thermal analysis, temperature-programmed desorption of ammonia and temperature-programmed reduction were used to characterize the resulting Ti-pillared clays (Ti-PILCs). Titanium methoxide allows the synthesis of a solid with a large basal spacing (26 Å), a large surface area (360 m2/g), a significant amount of micropore surface area (90%), and notable acidity. Moreover, Ti-PILCs obtained from methoxide were found to be thermally stable up to 500°C. A correlation between the increase in acidity and the increases in both microporosity and Ti content was observed. The surface area, the micropore volume, the acidity and the d001 peak intensity all increased upon increasing the amount of Ti added to the preparation (up to ∼15 mmoles of Ti/g clay). The use of an aqueous suspension of 0.13 wt.% of clay yielded the best structural and textural properties in terms of subsequent use of the clay as a catalyst.

A novel method for the analysis of clay minerals using Fourier transform infrared spectroscopy is presented. Clay mineral suspensions are dried on a Si wafer substrate for transmission infrared (IR) analysis. Four natural Source Clays from the Source Clays Repository of The Clay Minerals Society, SWy-2, SAz-1, SHCa-1 and KGa-1b, as well as the synthetic hectorite, Laponite RD, were analyzed using the described method with signal to noise (s/n) ratios in excess of 100,000 for the strongly absorbing Si-O stretching frequency. Scanning electron microscopy (SEM) images show that the mineral films possess suitable uniformity and low surface roughness for transmission IR measurements that is confirmed by minimal deviations in the baseline of collected IR spectra. The IR spectra are generated and peak locations are compared to previously reported values, generated from KBr pellet and attenuated total reflectance methods.

River-dominated delta areas are primary sites of active biogeochemical cycling, with productivity enhanced by terrestrial inputs of nutrients. Particle aggregation in these areas primarily controls the deposition of suspended particles, yet factors that control particle aggregation and resulting sedimentation in these environments are poorly understood. This study was designed to investigate the role of microbial Fe(III) reduction and solution chemistry in aggregation of suspended particles in the Mississippi Delta. Three representative sites along the salinity gradient were selected and sediments were collected from the sediment-water interface. Based on quantitative mineralogical analyses 88–89 wt.% of all minerals in the sediments are clays, mainly smectite and illite. Consumption of ${\text{SO}}_4^{2-}$\$\end{document} and the formation of H2S and pyrite during microbial Fe(III) reduction of the non-sterile sediments by Shewanella putrefaciens CN32 in artificial pore water (APW) media suggest simultaneous sulfate and Fe(III) reduction activity. The pHPZNPC of the sediments was ⩽3.5 and their zeta potentials at the sediment-water interface pH (6.9–7.3) varied from −35 to −45 mV, suggesting that both edges and faces of clay particles have negative surface charge. Therefore, high concentrations of cations in pore water are expected to be a predominant factor in particle aggregation consistent with the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. Experiments on aggregation of different types of sediments in the same APW composition revealed that the sediment with low zeta potential had a high rate of aggregation. Similarly, addition of external Fe(II) (i.e. not derived from sediments) was normally found to enhance particle aggregation and deposition in all sediments, probably resulting from a decrease in surface potential of particles due to specific Fe(II) sorption. Scanning and transmission electron microscopy (SEM, TEM) images showed predominant face-to-face clay aggregation in native sediments and composite mixtures of biopolymer, bacteria, and clay minerals in the bioreduced sediments. However, a clear need remains for additional information on the conditions, if any, that favor the development of anoxia in deep- and bottom-water bodies supporting Fe(III) reduction and resulting in particle aggregation and sedimentation.

Halloysite nanotubes (HNTs) are hollow clay nanotubes in the nanometer size range, made up of double-layered aluminum silicate mineral layers. HNTs represent an extremely versatile, safe, and biocompatible nanomaterial, used in a wide range of applications in biomedicine and nanomedicine. For example, they are used as transporters for the controlled release of drugs or genes, in tissue engineering, in the isolation of stem cells and cancer cells, and in bioimaging. Consequently, the assessment of the biocompatibility of HNTs has acquired considerable importance. In recent years, HNT composites have attracted attention due to their improved biocompatibility, compared to HNTs, suggesting potential for applications in tissue engineering or as vehicles for drugs or genes. In this review, recent advances in the application of HNTs and HNT composites in biomedicine are discussed to provide a valuable guide to scientists in the design and development of viable, functional bio-devices for biomedical applications.

All’Umanesimo non si deve solo un nuovo interesse filologico verso i classici latini e greci, ma anche una rinnovata attenzione nei confronti della Bibbia. Tra quanti meditarono sul testo biblico e lo posero a fondamento del proprio agire si deve annoverare Ambrogio Traversari (1386–1439), monaco camaldolese e umanista. Attraverso l’esame di una sua lettera, indirizzata ai religiosi del proprio ordine a nome del pontefice Eugenio IV poco dopo essere stato elevato alla carica di abate generale, si metterà in luce come il Traversari, nell’esortarli alla vita monastica, fondi il suo operare tanto sulla letteratura patristica, quanto soprattutto sul ricorso alla Bibbia, rispetto alla quale tralascia l’allegoria medievale per essere invece attento a trarre dal dettato biblico un esempio morale per i propri confratelli.

The influence of clay preparation procedure on sorption and hydrolysis of carbaryl (1-naphthyl, A-methyl carbamate) by the reference smectite SWy-2 was examined. For research purposes, reference clays are sometimes used without purification, or more commonly, the <2 μm size fraction is obtained by gravity sedimentation or low-speed centrifugation. We determined that these common methods did not remove all the inorganic carbonate impurities present in SWy-2, and that these impurities caused alkaline conditions in aqueous clay suspensions leading to the alkaline hydrolysis of carbaryl to 1-naphthol. The hydrolytic activity of homoionic K-SWy-2 disappeared once carbonates were eliminated. Two methods were evaluated for preparing K-SWy-2 devoid of inorganic carbonates. In Method A, inorganic carbonates were first removed by incremental additions of a 0.5 M sodium acetate buffer (pH 5.0) until the clay suspension reached pH 6.8, followed by low-speed centrifugation to obtain the <2 μm size fraction; in Method B, the order of these steps was reversed. Carbaryl hydrolysis was used as a probe to determine the effectiveness of the two methods in terms of the removal of carbonate accessory minerals. Homoionic K-SWy-2 obtained by Methods A and B produced near neutral pH when suspended in water and hydrolysis of carbaryl in these suspensions was not evident. In this regard, both clay preparation methods were acceptable. However, there were procedural advantages with Method B, which is therefore recommended for the partial purification of reference clays, as detailed in this paper.

In order to extend the application of magadiite to optical fields (rather than the usual focus on adsorption, catalysis, ion exchange, etc.), a magadiite-CdS (Mag-CdS) composite was synthesized from Na-magadiite by ion exchange. Various techniques were used to characterize the composite. X-ray diffraction results indicated that the Mag-CdS composite retained the host magadiite structure in spite of decrease in the intensity of the X-ray diffraction peak of the host magadiite. The analytical results confirmed the formation of the Mag-CdS composite, along with the modification of the optical properties of CdS by the host magadiite.

The high fission yield and long half life of cesium and strontium make them the two most high-risk products from nuclear fission, so their separation from radioactive wastes is an important step in mitigating their harmful effects. Clinoptilolite, because of its thermal stability, high radiation resistance, and selectivity, was considered as the adsorbent for this purpose. In order to then separate the adsorbent-adsorbate complex from aqueous solution, the clinoptilolite was prepared as a magnetized composite with nanomagnetite. This magnetically modified zeolite enabled the efficient and quick separation of the adsorbent from solution using magnetic separation. The ability of this composite to remove Cs+ and Sr2+ from aqueous solutions was assessed and characterized using X-ray diffraction, X-ray fluorescence, Fourier-transform infrared spectroscopy, differential thermogravimetric analysis, and vibrating-sample magnetometry. Variables such as initial ion concentration, pH, contact time, and temperature in the sorption process were studied and optimized. The maximum adsorption capacities of the composite were 188.7 and 36.63 mg g-1 for Cs+ and Sr2+, respectively. Investigation of the kinetics revealed that the adsorption process onto the composite was quicker than in the case of the zeolite alone. The equilibrium data were analyzed using the Langmuir, Freundlich, and Dubinin-Radushkevich (D-R) isotherm models. The mean free energy of sorption (E) for both ions was in the range 8–16 kJ mol-1, confirming that an ion-exchange mechanism had occurred. Positive ΔH° and negative ΔG° values were indicative of the endothermic and spontaneous nature of the removal of Cs+ and Sr2+. The saturation magnetization of the composite was measured (17.46 Am2/kg), implying fast magnetic separation of the sample after adsorption. The results obtained revealed that the natural Iranian zeolite nanomagnetite composite was a good ion exchanger in the removal of Cs+ and Sr2+.