Clay minerals, such as layered double hydroxide (LDH) and montmorillonite (MMT), have attracted a great deal of attention for biological applications. Along with the rapid development of nanotechnology, public concern about the potential toxicity of nanoparticles is growing. In the present work, cytotoxicity of LDH and MMT was assessed in terms of inhibition of cell proliferation, generation of oxidative stress, and induction of inflammation response. Moreover, the biokinetics of LDH and MMT were evaluated; biokinetics provides information about in vivo absorption, distribution, and excretion kinetics. The results demonstrated that both LDH and MMT inhibited cell proliferation at relatively large concentrations and after long exposure time compared to other inorganic nanoparticles, although they generated reactive oxygen species (ROS). LDH induced pro-inflammatory cytokines in a size-dependent manner. Biokinetic study revealed that, after single-dose oral administration to mice, both LDH and MMT had extremely slow oral rates of absorption and did not accumulate in any specific organ. All the results suggest great potential of clay minerals for biological application at safe levels.

Bacteria play an important role in determining the properties and behavior of clay minerals in natural environments and such interactions have great potential for creating stable biofilms and carbon storage sites in soils, but our knowledge of these interactions are far from complete. The purpose of this study was to understand better the effects of bacteria-generated biofilms on clay interlayer expansion. Mixtures of a colloidal, 2-water hectorite clay and Pseudomonas syringae in a minimal media suspension evolve into a polysaccharide-rich biofilm aggregate in time-series experiments lasting up to 1 week. X-ray diffraction analysis reveals that upon aggregation, the clay undergoes an initial interlayer contraction. Short-duration experiments, up to 72 h, result in a decrease in the d001 value from 1.50 to 1.26 nm. The initial interlayer contraction is followed in long-duration (up to 1 week) experiments by an expansion of the d001 value of 1.84 nm. The expansion is probably a result of large, biofilm-produced, polymeric molecules being emplaced in the interlayer site. The resultant organo-clay could provide a possible storage medium for carbon in a microbial colony setting.

The Clay Minerals Society published a complete characterization scheme for its ‘Source Clays’ but not for its ‘Special Clays’. To address this issue, the specific surface areas (SSAs) of the 16 special clays from The Clay Minerals Society were determined using the Brunauer, Emmett and Teller (BET) method of adsorption of an inert gas. Two BET measurements were performed for each of the 16 special clays, and the average BET SSA of each of the special clays was determined. The BET SSA of cookeite is reported for the first time. In the present study, special clays from The Clay Minerals Society are classified under three groups based on their BET special surface area values as Group-I special clays, with BET values of 0.1–10 m2/g, Group-II special clays, with BET values of 10–100 m2/g, and Group-III special clays, with BET values >100 m2/g. Comparisons which proved interesting were the those involving the mixed-layer clays and the synthetic clays. The systematic approach employed in this paper will allow for better comparisons to be made between different clays and will provide a comprehensive database for future applications of such material (e.g. as catalyst carriers, as adsorbents in waste treatments, etc.).

As advances in technology have led to increased use of bentonites, more high-quality bentonite has been sought. The volume of high-quality bentonites available is shrinking and use of bentonite reserves containing impurities is inevitable. The aim of this study was to apply Box–Behnken experimental design and response surface methodology to model and optimize some operational parameters of a hydrocyclone to produce three groups of bentonite concentrates. The four significant operational parameters of hydrocyclones are feed solid ratio, inlet pressure, vortex diameter, and apex diameter, and these parameters were varied and the results evaluated using the Box–Behnken factorial design. In order to produce bentonite concentrates using a hydrocyclone, mathematical model equations were derived by computer simulation programming applying a least-squares method, using Minitab 15. Second-order response functions were produced for the swelling and to establish the quantity of smectite in the bentonite concentrates. Predicted values were found to be in good agreement with the experimental values (R2 values of between 0.829 and 0.999 for smectite and three different swelling groups for the bentonites). Although in natural states these bentonites are not suitable for industrial use, enhancements were obtained giving up to 81.45% smectite and by increasing swelling by 194% for the three bentonite groups. The swelling properties of the bentonites are improved by increasing the proportion of smectite content. The graphics were designed to relate swelling and smectite content according to the two-dimensional hydrocyclone factors, and each factor was evaluated in itself. The present study revealed that the Box–Behnken and response surface methodology can be applied efficiently to model the hydrocyclone for bentonite; the method is economical and provides the maximum amount of information in a short period of time and with the smallest numberof experiments.

Recently, studies on the use of polymer nanomaterial composites as pour-point depressants (PPD) have drawn much attention, but the crystallization properties and improved rheological performance of waxy crude oils using nanoclay-based composite PPDs have rarely been reported. In this paper, montmorillonite (Mnt) was first organically modified using octadecyltrimethylammonium chloride (C21H46NCl, or stearyltrimethylammonium chloride) in aqueous solution. Then, the organically modified Mnt (OMnt) material was dispersed into a polyoctadecylacrylate (POA) matrix to prepare a POA/OMnt composite PPD by melt blending. The composition, structure, and morphology of Mnt, OMnt, and the POA/OMnt composite PPDs were investigated. The results showed that the OMnt and POA were compatible and that the OMnt was exfoliated into several sheets in the POA matrix. Subsequently, the isothermal crystallization kinetics of the POA/OMnt composite PPDs showed that small amounts of OMnt had a dramatic impact on POA chain motion during crystallization and facilitated POA crystallization. After it was added to a waxy crude oil, the POA/OMnt composite PPDs produced better rheological properties and performance than identical concentrations of the neat POA. The POA/OMnt composite PPDs can act as wax nucleation sites for wax molecule precipitation and result in larger and more compact wax crystal flocs, which adversely affect the formation of a wax crystal network and, thus, favor the improvement of waxy crude oil rheology.

In some real and up-scale tests using high-level radioactive waste (HLRW), Mg accumulation was observed in smectites at the contact of heated Fe or Cu metal tubes. It is important to understand why Mg accumulated in order to model the long term performance of bentonites in HLRW systems. In some of these tests, an increased number of trioctahedral domains was measured in the smectites using X-ray diffraction (XRD) and infrared spectroscopy (IR). The trioctahedral domains either formed by the dissolution/precipitation of smectites or by the addition of Mg through a solid-state reaction similar to the Hofmann-Klemen effect. The Hofmann-Klemen effect is used in the Greene-Kelly test to distinguish montmorillonites from beidellites. Many studies have been carried out about Li-uptake by smectites, but Mg was rarely taken into account. The present study was, therefore, undertaken to compare the interactions of different bentonites with Li and Mg under various conditions. A significant CEC decrease was found for Li- and Mg-saturated bentonite samples after heating at 250°C under dry conditions. The extent of this CEC reduction depended on the octahedral to tetrahedral charge ratio and was smaller for Mg-saturated samples than Li-saturated samples. This finding proved that it is much more difficult for Mg to enter octahedral vacancies than Li, which probably can be explained by the larger hydration energy and/or slightly larger radius of Mg. The relationship between CEC reduction and the octahedral/tetrahedral charge ratio of both Li- and Mg-saturated samples, however, suggests a similar process. The Mg that can reside at the bottom of the pseudohexagonal holes would not explain this relationship. The important result with respect to understanding HLRW bentonite performance, on the other hand, is that Mg fixation only occurs under dry conditions and that Mg fixation acts as a sink for Mg and, hence, leads Mg to diffuse towards the heated metal surface.

Somen-alkyldiamines with thegeneral formulae H2N(CH2)nNH2 (n = 2–5) were intercalated into the layered silicic acid magadiite, from aqueous solution, causing an increase in the original interlayer distance of 1172 pm. The synthetic magadiite and all intercalated compounds were characterized by elemental analysis, infrared vibrational spectroscopy, X-ray diffractometry, 29Si nuclear magnetic resonance in the solid state, thermogravimetry, scanning electron microscopy, surface area and porosity. The intercalation was followed through a batch-wise method at 298±1 K and gave the maximum amounts 3.70, 2.80, 1.75 and 1.18 mmol g−1, for n varying from 2 to 5, respectively. The well characterized magadiite was calorimetrically titrated in a heterogeneous medium, to obtain the thermodynamic data of intercalation at the solid/liquid interface. Linear correlations were obtained for the number of moles intercalated (Nf), th einterlamellar distance (d) and the specific enthalpy (Δinth) values of the interactive process as a function of the number of C atoms of the aliphatic organic chains (nC) for n-alkyldiamine: Nf = (5.36±0.25) − (0.86±0.07)nC, d = (1406.6±1.9) + (20.9±0.5)nC and Δinth = (5.96±0.25) + (0.06±0.01)nC. The basic N guest atom/silanol acidic center interactions inside the host nanospace gallery gave exothermic enthalpies, positive entropies and negative Gibbs free energy values. This set of data suggests the spontaneity of these intercalation reactions.

The Boom Clay in northern Belgium has been studied intensively over recent decades as a potential host rock in the context of disposal of radioactive waste. One of the parameters of interest is the cation exchange capacity (CEC) as it is related to the sorption potential of radionuclides to the clay host rock. In the past, the CEC was determined using various methods on a limited number of samples, leading to significant variations. To constrain the CEC of the Boom Clay better, a sample set covering the entire stratigraphy was measured using the quick copper(II) triethylenetetramine method. Part of the sample set was also measured using the cobalt(III) hexamine method, as a quality control for the results of the former method. In addition, the exchangeable cation population of the Boom Clay was quantified systematically for the first time and these results were compared to the in situ pore-water chemistry, indicating a strong coupling between the pore-water composition and the exchangeable sites of clay minerals.

Freshwater has become increasingly scarce in many countries. To reduce the consumption of freshwater, the use of saline water resources in industry could provide an opportunity to meet the challenge of water-supply sustainability. However, the presence of electrolytes in saline water causes the coagulation of kaolinite, the colloid stability of which plays a key role in the processing of a number of minerals. Therefore, the dispersion of kaolinite in saline water was studied here. Electrophoretic mobility and colloid stability studies were conducted on a sodium hexametaphosphate-kaolinite system in the presence of NaCl, KCl, CaCl2, and MgCl2, the major electrolytes in saline water resources. The effect of each electrolyte on kaolinite dispersion was studied. Based on the studies of individual electrolytes, a method was developed to disperse kaolinite in 1:1 diluted synthetic seawater with distilled water, which may potentially reduce the consumption of freshwater by 50% when applied in industry.

This paper argues that being there, actually existing, is a notion that cannot be explicated by formal logicians, cannot be defined in terms of conscious perception, and cannot be satisfactorily explained using the theories of mathematics or natural science. So, must we turn to theology to make up for the deficiencies of the methods so far canvassed? The paper concludes by considering the Thomistic identification of God with existence itself, but argues that it would be a mistake to suppose that the mystery of actual existence is thereby dispelled.

The common observation that smaller particle-size fractions of sedimentary rocks yield younger K-Ar apparent ages than the larger particle-size fractions of the same stratigraphic age was analyzed with the aid of the 40Ar/40K ratio from 14 stratigraphically and regionally different sections. Estimation of the loss of radiogenic 40Ar from varied clay-rich size fractions was based on two models: a relationship between particle size and the 40Ar/40K ratio, and a theoretical diffusional loss from spherical particles. The differences between the two models and reconciliation of their results are discussed. For the smallest fractions (up to <0.5 μm), percent-wise losses of 40Ar from the spherical particles model increase from Upper Carboniferous and Permian (38±10%), to Late Triassic (47±10%), and to Miocene and Late Neogene (65±8%). This trend suggests that escape of 40Ar from the smaller particles in older sediments decreased or even stopped after deposition of the sedimentary sections.

The large 40Ar losses derived from small 40Ar/40K ratios in the younger Tertiary sediments, indicate that addition of K to the small fractions is, at least in part, responsible for the young K-Ar apparent ages in geologically different settings. In several 102–103 m thick sections, authigenic illite in the <0.1 to <2 μm fractions yields young K-Ar apparent ages resulting from simultaneous 40Ar production and release during clay authigenesis. In a production and loss model, a first-order escape-rate parameter (e) was estimated at 0.2 × 10−8 to 4 × 10−8 y−1, depending on the K-Ar apparent age of the size fractions and the stratigraphic age of the section. The limitations and uncertainties of the methods of evaluating diagenetic 40Ar losses from fine clay particles are discussed.

Quaternary marine terrace deposits consisting of gravels interbedded with thin sandy gravel layers have been subjected to subaerial weathering. Restricted to the sandy gravel layers, allophane gel either replaced bytownite sands to form a pseudomorph or coated the pebbles. The allophane has an average Al/Si atomic ratio of 1.5 with 45% H2O. The sandy gravels were originally rich in bytownite (av. An86) sands derived from underlying Tertiary basaltic lapilli tuff. The highly soluble and aluminous bytownite favored the formation of allophane. In the sandy gravel layers, pebbles coated with allophane gel were almost fresh whereas those in the gravel layers were highly weathered to form halloysite-rich clays. Allophane gels acted as a somewhat impermeable geochemical barrier impeding a mineral-water reaction in the bytownite-rich sandy gravel layers and thus significantly retarding pebble weathering, while prolonged weathering in the gravel layers resulted in the severe decomposition of pebbles. Bytownite protected the pebbles against weathering, implying that minor soluble minerals might be one of the factors in the natural variation of the weathering rates of rocks and sediments.

Purification of raw bentonites and organo-bentonite preparations is sometimes required for industrial use. Zeta (electrokinetic) potential (ζ), contact angle (wettability/hydrophobicity), and surface free energy (SFE) are important surface characteristics and vary significantly according to the applied surfactant concentration when preparing organo-bentonite. Changes in these characteristics determine the stability, behavior, and efficiency of organo-bentonites in various applications such as adsorption, composite materials, and drug-delivery systems. Knowing how much surfactant should be used to prepare organo-bentonite is, therefore, critical. The purpose of the present study was to determine the effect of concentration of the cationic surfactant cetyltrimethylammonium bromide (CTAB) adsorbed in organo-bentonite (prepared from two local and commercial raw bentonites with potential for use in adsorbent and composite materials) on the ζ potential, contact angle, and SFE profiles. The raw bentonites were purified using sedimentation and centrifugation techniques prior to preparation of the organo-bentonite. The purification results were evaluated in light of X-ray diffraction (XRD), cation exchange capacity (CEC), free swelling volume (FSV), X-ray fluorescence (XRF), and particle-size analysis data. Most of the gangue minerals (feldspar, calcite, clinoptilolite, opal, quartz, and mica) having particle size >5 μm were removed from the raw bentonites by using a one-stage sedimentation or a Falcon gravity separator (FGS). Higher yields (68.8% and 81.3% for two bentonites) were obtained with the FGS compared to sedimentation while purification levels were almost the same. ζ changed greatly from –35 mV (and –40 mV) toward 38 mV (and 40 mV) with increasing CTAB concentrations. Similar profiles were also obtained for wettability; maximum contact angles for organo-bentonites were measured as ~72–73o, while they were 12.65 and 14.1o for two purified and unmodified bentonites. SFEs were calculated using contact-angle data, and decreased to minimum values of 41.5–43.6 mJ/m2 from 78.6–78.2 mJ/m2 upon treatment of raw bentonites with CTAB. 100–130% CEC concentration was sufficient to prepare organo-bentonites with maximum hydrophobicity and positively charged surfaces.

MgO-clay nanocomposites were prepared from a synthetic smectite-type clay, TS, using three different non-ionic surfactants (Igepal CA-720, Brij 30 and Brij 56) and the resulting clay nanocomposites were impregnated with Ni for the methane reforming reaction with carbon dioxide to synthesis gas. A Ni/TS catalyst was also prepared for comparison. The prepared supports and catalysts were characterized by X-ray diffraction, X-ray fluorescence, thermogravimetric analysis and N2 adsorption/desorption isotherms. The thermal stability, pore structure and the surface area strongly influence the catalytic behavior of the catalysts. The methane conversions (at 700°C for 4 h) were 91, 95 and 97% for Ni/TSIGE, Ni/TSBR30 and Ni/TSBR56, respectively, indicating that the surface properties and the catalytic performance of the resulting solids slightly improved as the polyethylene oxide number of the surfactant increased. A reduced conversion (10%) and a rapid deactivation was observed in the Ni/TS catalyst, attributed to its Na content and low thermal stability, which led to sintering and coke deposition.

The early and sensitive detection of microbial contamination of kaolinite slurries is needed for timely treatment to prevent spoilage. The sensitivity, reproducibility, and time required by current methods, such as the dip-slide method, do not meet this challenge. A more sensitive, reproducible, and efficient method is required. The objective of the present study was to develop and validate such a method. The new method is based on the measured growth kinetics of indigenous kaolinite-slurry microorganisms. The microorganisms from kaolinite slurries with different contamination levels were eluted and quantified as colony-forming units (CFUs). Known quantities of E. coli (ATCC 11775) were inoculated into sterilized kaolinite slurries to relate kaolinite-slurry CFUs to true microbial concentrations. The inoculated slurries were subsequently incubated, re-extracted, and microbial concentrations quantified. The ratio of the known inoculated E. coli concentration to the measured concentration was expressed as the recovery efficiency coefficient. Indigenous microbial communities were serially diluted, incubated, and the growth kinetics measured and related to CFUs. Using the new method, greater optical densities (OD) and visible microbial growth were measured for greater dilutions of kaolinite slurries with large microbial-cell concentrations. Growth conditions were optimized to maximize the correlation between contamination level, microbial growth kinetics, and OD value. A Standard Bacterial Unit (SBU) scale with five levels of microbial contamination was designed for kaolinite slurries using the experimental results. The SBU scale was validated using a blind test of 50 unknown slurry samples with various contamination levels provided by the Imerys Company. The validation tests revealed that the new method using the SBU scale was more time efficient, sensitive, and reproducible than the dip-slide method.

Talc is an important industrial mineral with a broad range of applications. Particle size and crystal structure have a significant influence on the potential uses. The present study examined the influence of grinding and ultrasound treatment on talc from a new deposit, Gemerská Poloma, in Slovakia. The general knowledge that grinding produces progressive structural disorder leading to amorphization, whereas sonication has a negligible effect on the talc crystal structure, was confirmed by X-ray diffraction (XRD), infrared (IR) spectroscopy, and transmission electron microscopy (TEM). Partial reduction of particle size along with delamination was observed by XRD after sonication, low-angle laser light scattering (LALLS), scanning electron microscopy (SEM), and TEM. The specific surface area (SSA) increased slightly after prolonged sonication, but grinding initially caused a rapid increase in SSA followed by a drastic decrease after prolonged grinding time of up to 120 min which was attributed to the aggregation of amorphized talc. Sonication and grinding had different influences on the thermal behavior of the talc studied. Sonication decreased slightly the dehydroxylation temperature, whereas grinding added a significant mass loss at low temperature, arising from the dehydration of hydrated Mg cations released from the talc structure during amorphization. The initial high whiteness value of talc decreased slightly after grinding or sonication. Thermogravimetry was suggested as a useful tool to track and predict changes in the talc structure upon sonication and grinding.

Hydrotalcite-like layered double hydroxides (LDH), of the formulation M2Al(OH)6(CO3)0.5.H2O, where M = Mg, Zn, Co, Ni, have been prepared, the products characterized and their solubility products measured at ionic strengths of 0.0065 and 0.0128 M and at 25°C. Steady-state solubility was reached after 100 days. The solubility products have been formulated according to the following reaction: $M_2\text{Al}{\left(\text{OH}\right)}_{6}0.5{\text{CO}}_3\cdot {\text{H}}_2\text{O}+6{\text{H}}^{+}\to 2M^{2+}+{\text{Al}}^{3+}+0.5{\text{CO}}_3^{2-}+{\text{H}}_2\text{O}$ where

$K_{\text{SO}}=\frac{{\left[M^{2+}\right]}^2\left[{\text{Al}}^{3+}\right]{\left[{\text{CO}}_3^{2-}\right]}^{0.5}}{{\left[\text{H}\right]}^6}$

Average values of Kso for I = 0, estimated using the Davies equation, are 25.43, 20.80, 22.88 and 20.03 for Mg, Zn, Co and Ni, respectively. Model calculations reveal that the thermodynamic stability of the LDHs is greater than that of the corresponding divalent hydroxides for Zn, Co and Ni below a pH of ∼10, 9 and 8, respectively, and at least up to pH 12 for Mg.

Clay swelling, an important phenomenon in natural systems, can dramatically affect the properties of soils and sediments. Of particular interest in low-salinity, saturated systems are osmotic hydrates, forms of smectite in which the layer separation greatly exceeds the thickness of a single smectite layer due to the intercalation of water. In situ X-ray diffraction (XRD) studies have shown a strong link between ionic strength and average interlayer spacing in osmotic hydrates but also indicate the presence of structural disorder that has not been fully described. In the present study the structural state of expanded smectite in sodium chloride solutions was investigated by combining very low electron dose, high-resolution cryogenic-transmission electron microscopy observations with XRD experiments. Wyoming smectite (SWy-2) was embedded in vitreous ice to evaluate clay structure in aqua. Lattice-fringe images showed that smectite equilibrated in aqueous, low-ionic-strength solutions, exists as individual smectite layers, osmotic hydrates composed of parallel layers, as well as disordered layer conformations. No evidence was found here for edge-to-sheet attractions, but significant variability in interlayer spacing was observed. Whether this variation could be explained by a dependence of the magnitude of long-range cohesive (van der Waals) forces on the number of layers in a smectite particle was investigated here. Calculations of the Hamaker constant for layer-layer interactions showed that van der Waals forces may span at least five layers plus the intervening water and confirmed that forces vary with layer number. Drying of the disordered osmotic hydrates induced re-aggregation of the smectite to form particles that exhibited coherent scattering domains. Clay disaggregation and restacking may be considered as an example of oriented attachment, with the unusual distinction that it may be cycled repeatedly by changing solution conditions.