The negative effects of dye-contaminated wastewater on humans and the environment are well known, so the wastewater must be treated carefully before discharge into the environment. To overcome those impacts, the search for environmentally friendly and low-cost materials is essential, especially in developing countries The objective of the present study was to determine the feasibility of using bauxite from Malaysia as a new and efficient ceramic, hollow-fiber membrane for the degradation of reactive dyes in wastewater. A porous, hollow-fiber membrane was fabricated from bauxite (BHFM) using a phase-inversion technique, followed by sintering at various temperatures. The BHFM consisted of two types of voids, having either a finger-like or a sponge-like structure. As the sintering temperature was increased, the porosity of the BHFM decreased from 46.5 to 9.5%. The greatest mechanical strength of 308.1 MPa was achieved when the BHFM was loaded with 55 wt.% of bauxite and sintered at 1450°C. The remaining 45 wt.% consisted of solvent, polymer binder, and dispersant. The BHFM functioned well as a membrane for microfiltration and a support membrane for ultrafiltration. BHFM with loading of 45 wt.%, 50 wt.%, and 55 wt.% successfully eliminated 90%, 94%, and 98% of 10 ppm reactive dye (RB5) when sintered at the highest temperature.

K-Ar isotopic dating has been applied to alkali-rich nanometer-sized illite separates of bentonites since the late 1990s. In the present study, K-Ar and Rb-Sr isotopic analyses were based on mineralogical determinations and morphological observations of similarly nm-sized separates (<0.02, 0.02–0.05, and 0.05–0.1 μm) depleted in alkalis and recovered from Santonian (85.8–83.5 Ma) bentonites of the Campos Basin located offshore the southeastern Atlantic coast (Rio de Janeiro State, Brazil). On the basis of XRD analyses and geochemical/mineralogical simulations, the size fractions consist essentially of the smectite-rich end-member of the smectite-to-illite trend with no more than 9% authigenic illite layers. High K-Ar values from 42.6 ± 3.2 to 70.2 ± 2.1 Ma confirm the occurrence of detrital illite in one sample at least, the age data being meaningless. A second group of K-Ar values ranges from 15.5 ± 10.7 to 41.3 ± 10.8 Ma, while the smallest (<0.02 and 0.02–0.05 μm) fractions with <0.42% K2O lack detectable radiogenic 40Ar and yield analytically 0 Ma ages. Two samples including that with the detrital illite were leached with dilute acid and the Rb-Sr method was applied to the untreated, leachate, and residual fractions of the different separates. The combined isotopic data suggest that illitization started at ~44 ± 4 Ma when the bentonites were subjected to a temperature of ~60°C. The leachable Sr yielded 87Sr/86Sr ratios of 0.7106–0.7108, which is greater than those of seawater either during deposition or recently, and of the initial ashes. They do not correspond to the chemical signature of pore fluids, but more likely to removals from fragile edges of the illite-smectite layers probably impacted by the rough initial chemical treatment applied to empty the smectite interlayers. Illitization was either a side effect of a major contemporaneous smectitization or an independent process that occurred later, in the progressively buried bentonite beds. Of variable duration, it was probably dependent on burial-induced temperature increase in the bentonites, which monitored the fixation of K in the smectite layering with or without a changing fluid chemistry. On the basis of the combined K-Ar and Rb-Sr isotopic data, illitization lasted either until ~15 Ma or even 0 Ma for some of the finest size fractions.

Results from earlier laboratory and field experiments were interrogated for the possibilities of sequestration, or long-term accumulation, of carbon from excess greenhouse gases in the atmosphere. In the laboratory study, samples of three (top) soils dominated by kaolinite and illite (together), smectite, and allophane were examined for the adsorption and desorption of dissolved organic carbon (DOC). Adsorption and desorption of DOC were carried out on clay fractions extracted physically and after first native organic matter and then iron oxides were removed chemically. Labeled organic material was added to the soils to assess the priming effect of organic carbon (OC). In the field, changes in OC were measured in sandy soils that had been amended by additions of clay for between 3 and 17 years, both through incorporation of exogenous clay and delving of in situ clay. The laboratory experiments demonstrated that a portion of DOC was held strongly in all soils. The amount of DOC adsorbed depended on clay mineral types, including Fe oxides. Much adsorbed DOC was lost by desorption in water and a substantial amount of native OC was lost on priming with new OC. Addition of clay to soils led to increased OC. Therefore, addition of clay to soil may enhance net sequestration of C. Organic carbon close to mineral surfaces or within microaggregates is held most strongly. Carbon sequestration may occur in subsoils with unsaturated mineral surfaces. However, incorporation of carbon into macroaggregates from enhanced plant growth might be most effective in removing excess carbon from the atmosphere, albeit over the short-term.

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.

The dispersive behavior dynamics of clay determine soil characteristics such as permeability and aggregate stability, and, consequently, crop productivity. Soil dispersion is heavily influenced by the ionicity of clay–cation bonds and has been shown to be related to the net negative charge and pH of the system. Little work has been done, however, which considers these factors together, especially for K and Mg clays. The objective of the present study was to investigate the effect of changing pH on the dispersive behavior of Mg and K homoionic clays, in comparison to Ca and Na clays under equivalent pH conditions. The clay fractions used here were extracted from three soils and have distinctly different mineralogies. These clays were treated to become homoionic with regard to Na, K, Ca, and Mg. Excess salts were removed by dialysis and pH was adjusted to 3, 4, 5, 6, 7, 8, 9, 10, and 11 for all clays, except Mg (pH range 3–7). Clay dispersion-flocculation dynamics were investigated, and the net negative charge, pH, electrical conductivity (EC), and turbidity were measured. Mg has a similar but less flocculative effect than Ca, while K has a similar but less dispersive effect than Na, under similar pH conditions. The dispersive behavior of Na, K, Mg, and Ca homoionic clays was correlated well with the ionicity of clay–cation bonds at equivalent pH, with the degree of clay dispersion being explained by the pH, EC, ionicity, ζ-potential, and mean particle size of the clay–cation system. A predictive model for dispersion was developed with its applicability and limitations discussed.

Highly weathered soils of the humid tropics generally provide a poor mineral reserve of potassium (K), but evidence has been found which indicates that even in such soils non-exchangeable forms of K can be made plant available and this warrants further investigation. The objective of this study was, therefore, to determine the extent to which K can be released from poorly available reserves over a long period of time. The focus was on an Oxisol in southern Brazil cultivated for 32 years with a rotation of soybeans (Glycine max L.), maize (Zea mays L.), wheat (Triticum aestivum L.), and oats (Avena strigosa L.) with and without K fertilization. Mineral sources of K were identified by X-ray diffraction and by sequential chemical extraction from the clay fraction. The amounts of K-bearing mineral species and the amounts of total and plant-available K were quantified, then the effects of the long-term K-fertilization regime on these values were evaluated. The clay fraction was dominated by hematite, gibbsite, and phyllosilicates such as kaolinite. These minerals were unaffected by the K deprivation in the cropping systems, but in the clay fraction the absence of K fertilization for 32 years reduced the structural order of the 2:1 phyllosilicates associated with K reserves. This effect was most prominent in the root zone of the soil. Deprivation of K for more than three decades decreased the crystallinity of 2:1 phyllosilicates, which could be better evaluated from XRD patterns after the removal of kaolinite and Fe (oxyhydr)oxides. The K-free cultivation reduced the amounts of total soil K by increasing the depletion of K from pools that typically are poorly accessible to plants.

Most investigations into clay-mineral stability and new mineral formation within engineered barrier system (EBS) materials for geologic repositories of nuclear waste have focused on temperatures <100°C. In response to the United States Department of Energy’s interest in disposing of waste packages with higher thermal loads, higher temperature (200–300°C) and pressure (~150 bar), long-term (6-week to 6-month), hydrothermal experiments were conducted to evaluate the interaction of Opalinus Clay (wall rock) and Wyoming bentonite (clay buffer) with synthetic Opalinus Clay groundwater. Experiments were conducted in autoclaves using a flexible gold reaction cell with water:rock ratios between 6:1 and 9:1. Run products were characterized in terms of mineralogy and geochemistry. Montmorillonite remained stable at 200 and 300°C; traces of illite-smectite interstratified minerals were observed. Clay minerals in Opalinus Clay experienced significant changes at 300°C, including the formation of illite, illite-smectite, and chlorite-smectite. Montmorillonite illitization within the Wyoming bentonite EBS material was likely limited by the bulk chemistry of the system (i.e. low potassium) and newly formed illite was likely limited to the Opalinus Clay fragments, nucleating on pre-existing illite in the clay rock. Zeolite minerals with compositions between analcime and wairakite formed at 300°C along edges of Opalinus Clay fragments and within the bentonite matrix, but not at 200°C. Aqueous fluids remained undersaturated with respect to quartz in Opalinus Clay ± Wyoming bentonite 300°C experiments, and dissolution and re-precipitation of phases such as kaolinite, calcite, and smectite likely contributed to zeolite formation. These results can be applied to understanding zeolite formation, clay-mineral phase stability, and silica saturation within EBS materials of a high-temperature repository.

The chemical composition of the source magma along with the physiochemical conditions of the depositional environment are the main controlling factors in determining the behavior and mobility of trace elements and rare earth elements (REEs) during the transformation of volcanic ash to bentonite. The purpose of the present study was to determine the distribution pattern and mobility of trace elements and REEs in several bentonite deposits formed by diagenetic alteration of volcanic ash in shallow alkaline water in eastern Iran. Using geochemical and statistical data, the degree of weathering in the parent rocks and the distribution and mobility of trace elements and REEs during the alteration process at seven deposits (Chah-Taleb, Chah-Keshmir, Chah-Golestan, Chah-Pirouz, Gholeh-Gelia, Kharman-Sar, and Khal-Kooh) were studied. None of the parent rocks showed an advanced degree of depositional reworking and, therefore, their chemical composition is representative of the volcanic ash from which the bentonites were formed. In the chondrite-normalized REE patterns of both parent rocks and bentonites, the light rare earth elements (LREEs) were found to be enriched relative to the heavy rare earth elements (HREEs). The variation in δEu and δCe values suggested a high-temperature (<200°C), suboxic, aquatic environment in which the conversion of volcanic ash to bentonite occurred. In the bivariate correlation analysis, Si showed a strong inverse relationship with Al and LREEs, while large ion lithophile elements (LILEs), high field strength elements (HFSEs), HREEs, and LREEs displayed a positive correlation between the elements of their respective groups. The R2 values in the binary diagram of potential immobile elements against Al suggest a qualitative classification in which Ti, Gd, Ga, Pr, Tb, Nd, Sm, Ce, and Nb are considered immobile, and U, Dy, In, Sc, Hf, Zr, La, and Eu are considered to have had poor mobility during formation of the Eastern Iranian bentonite deposits.

Because they are so widespread, the use of saponites is significant in many industries. The modification of saponite-rich clay minerals is known to improve their existing characteristics and may provide new functional properties. The objective of the present paper was to characterize the effects of adding nanosized graphene-like molybdenum (Mo) and tungsten (W) sulfides on the textural and surface characteristics of composites based on native saponite and saponite pre-modified with nanoscale magnetite. The textural characteristics were investigated by the nitrogen adsorption-desorption method and scanning electron microscopy. The total acidity, Hammett Brönsted centers, and Quasi-Equilibrium Thermo Desorption (QE-TD) Lewis centers were characteristics used to probe the acid-base properties of the modified composites. In all cases, modification proved to have a significant effect on both the surface and textural properties of the clay matrix. Modification of the native saponite by graphene-like Mo and W sulfides resulted in a decrease in the specific surface area, except a slight increase in the surface area of the magnetite-containing saponite was observed. Analysis of the acid-base characteristics of native and magnetite-modified saponite (MMS) indicated the ability of modified MoS2 and WS2 additives to alter the acid-base state of the surface. The addition of graphene-like Mo and W sulfides increased the total acidity of native and MMS, with MoS2 modification being more promising because, in almost all the samples, saponite composite materials increased the number of both Brönsted and Lewis active centers compared with WS2, which was determined by the corresponding methods. The acid-base characteristics of the saponite-containing samples, which were studied in an aqueous medium by various methods, are in good correlation with each other, and are consistent with the sorption activity of cationic and anionic dyes.

Kaolins and clays are important raw materials for production of supplementary cementitious materials and geopolymer precursors through thermal activation by calcination beyond dehydroxylation (DHX). Both types of clay contain different polytypes and disordered structures of kaolinite but little is known about the impact of the layer stacking of dioctahedral 1:1 layer silicates on optimum thermal activation conditions and following reactivity with alkaline solutions. The objective of the present study was to improve understanding of the impact of layer stacking in dioctahedral 1:1 layer silicates on the thermal activation by investigating the atomic structure after dehydroxylation. Heating experiments by simultaneous thermal analysis (STA) followed by characterization of the dehydroxylated materials by nuclear magnetic resonance spectroscopy (NMR) and scanning electron microscopy (SEM) together with first-principles calculations were performed. Density functional theory (DFT) was utilized for correlation of geometry-optimized structures to thermodynamic stability. The resulting volumes of unit cells were compared with data from dilatometry studies. The local structure changes were correlated with experimental results of increasing DHX temperature in the following order: disordered kaolinite, kaolinite, and dickite, whereupon dickite showed two dehydroxylation steps. Intermediate structures were found that were thermodynamically stable and partially dehydroxylated to a degree of DHX of 75% for kaolinite, 25% for disordered kaolinite, and 50% for dickite. These thermodynamically stable, partially dehydroxylated intermediates contained AlV while metakaolinite and metadickite contained only AlIV with a strongly distorted coordination shell. These results indicate strongly the necessity for characterization of the structure of dioctahedral 1:1 layer silicates in kaolins and clays as a key parameter to predict optimized calcination conditions and resulting reactivity.

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.

Quantification of mineral assemblages in near-surface Earth materials is a challenge because of the often abundant and highly variable crystalline and chemical nature of discrete clay minerals. Further adding to this challenge is the occurrence of mixed-layer clay minerals, which is complicated because of the numerous possible combinations of clay layer types, as defined by their relative proportions and the ordering schemes. The problem of ensuring accurate quantification is important to understanding landscape evolution because mineral abundances have a large influence on ecosystem function. X-ray diffraction analysis of the variable cation-saturated clay fraction in soil and regolith from the Calhoun Critical Zone observatory near Clinton, South Carolina, USA, was coupled with modeling using NEWMOD2 to show that mixed-layer clays are often dominant components in the mineral assemblages. Deep samples in the profile (>6.5 m) contain mixed-layer kaolinite/smectite, kaolinite/illite-like, kaolinite-vermiculite, illite-like/biotite, and illite-like/vermiculite species (with ‘illite-like’ defined herein as Fe-oxidized 2:1 layer structure with a negative layer charge of ~0.75 per unit formula, i.e. weathered biotite). The 2:1 layers in the mixed-layer structures are proposed to serve as exchange sites for K+, which is known to cycle seasonally between plant biomass and subsurface weathering horizons. Forested landscapes have a greater number of 2:1 layer types than cultivated landscapes. Of two nearby cultivated sites, the one higher in landscape position has fewer 2:1 layer types. Bulk potassium concentrations for the forested and two cultivated sites show the greatest abundances in the surface forested site and lowest abundance in the surface upland cultivated site. These observations suggest that landscape use and landscape position are factors controlling the mixed-layer mineral assemblages in Kanhapludults typical of the S.E. United States Piedmont. These mixed-layer clays are key components of the proposed mechanism for K+ uplift concepts, whereby subsurface cation storage may occur in the interlayer sites (with increased negative 2:1 layer charge) during wetter reduced conditions of the winter season and as biomass decay releases cation nutrients. Cation release from the mixed-layer clays (by decreased 2:1 layer charge) occurs under drier oxidized conditions during the growing seasons as biota utilize cation nutrients. The types and abundances of mixed layers also reflect long-term geologic factors including dissolution/alteration of primary feldspar and biotite and the subsequent transformation and dissolution/precipitation reactions that operate within the soil horizons. Thus, the resulting mixed-layer clay mineral assemblages are often complex and heterogeneous at every depth within a profile and across landscapes. X-ray diffraction (XRD) assessment, using multiple cation saturation state and modeling, is essential for quantifying the clay mineral assemblage and pools for cation nutrients, such as potassium, in the critical zone.

Dioctahedral micas are composed of two tetrahedral sheets and one octahedral sheet to form TOT or 2:1 layers. These minerals are widespread and occur with structures differing by (1) the layer stacking mode (polytypes), (2) the location of vacancies among non-equivalent octahedral sites (polymorphs), and (3) the charge-compensating interlayer cation and isomorphic substitutions. The purpose of the present study was to assess the potential of parallel-illumination electron diffraction (ED) to determine the polytype/polymorph of individual crystals of finely divided dioctahedral micas and to image their morphology. ED patterns were calculated along several zone axes close to the c*- and c-axes using the kinematical approximation for trans- and cis-vacant varieties of the four common mica polytypes (1M, 2M1, 2M2, and 3T). When properly oriented, all ED patterns have similar geometry, but differ by their intensity distribution over hk reflections of the zero-order Laue zone. Differences are enhanced for ED patterns calculated along the [001] zone axis. Identification criteria were proposed for polytype/polymorph identification, based on the qualitative distribution of bright and weak reflections. A database of ED patterns calculated along other zone axes was provided in case the optimum [001] orientation could not be found. Various polytype/polymorphs may exhibit similar ED patterns depending on the zone axis considered.

Modification of the surfaces of montmorillonite (Mnt) by organic molecules is an effective method for improving their affinity toward non-aqueous substances, and has resulted in extensive industrial applications as rheological control agents, drilling fluids, and other functional materials used in applications ranging from environmental remediation to coatings. The present study reviewed recent progress in organo-modification of Mnt, and provides state-of-the-art insights into proposed modification mechanisms and the peculiar functionalities of the resulting organo-montmorillonite (OMnt). Several routes have been employed to modify Mnt, including ion exchange with organic ions, surface adsorption, and grafting of organics. Commonly used organic modifiers include cationic, anionic, zwitterionic, non-ionic, and polymeric species. Organo-modification is driven by multiple interactions: van der Waals forces, cation exchange, electrostatic interaction, hydrogen bonds, and ion–dipole interaction. OMnt, in general, exhibits synergistic and/or antagonistic effects when used in oil-based drilling fluids, environmental remediation, or layered silicate/polymer nanocomposites. The detailed mechanisms of non-ionic and zwitterionic modification of Mnt remain unclear. This literature survey suggests that future work should emphasize deeper understanding of interactions between the Mnt and the organic modifiers, and meanwhile expand the applications of OMnt into catalysis, drug carriers, and the biomedical field.

Swell-shrink clays are widely distributed in the Guangxi province of southern China in the form of expansive soils and lateritic clays. They have high particle dispersion, poor permeability, and significant swell-shrink properties. In recent decades, a series of problems closely related to the physical-mechanical properties of the swell-shrink clays have been encountered in various engineering projects. Mineral composition is a critical factor affecting the physical-mechanical properties of these clays. However, determining accurately their mineral compositions is difficult because the analytical methods available are expensive, time consuming, and have a high possibility of errors. Therefore, identifying a method suitable for quantitatively analyzing the mineral composition of the swell-shrink clays is necessary. In the current study several swell-shrink clays, including two expansive soils and four lateritic clays, from the Guangxi region were investigated. Qualitative analytical methods such as differential thermal analysis (DTA) and X-ray diffraction (XRD) were conducted to identify the mineral composition of the soils. The results indicated that the expansive soils were composed mainly of quartz (Qz), montmorillonite (Mnt), illite (Ilt), and kaolinite (Kln). The Baise specimen also contained a certain amount of calcite (Cal), while the lateritic clays primarily contained Kln and goethite (Gth) as well as lesser amounts of Qz and gibbsite (Gbs). On the basis of the aforementioned results, rough quantitative analyses of the mineral compositions were conducted using X-ray fluorescence (XRF) and the Bogue method. The results indicated that the lateritic clay samples from Wuming, Guilin, and Liuzhou contained 70–80% Kln, while the Laibin lateritic clay was 50% Kln. The lateritic clays contained ~10% Gth. The expansive soils were 30–40%, 25–30%, and 10–15% of Ilt, Qz, and Mnt, respectively. Finally, the relationships between the mineral compositions, zeta potentials, and free swelling ratios are discussed briefly. This investigation indicated that the zeta potential was mainly related to the type and content of clay minerals in the soil when neutral water was used as the free solution (pH = 7). The correlation between the swelling index and the zeta potential of the expansive soils was greater than that of the lateritic clays, which indicated that the swelling properties of expansive soils were more affected by the clay mineral composition than those of the lateritic clays. The results provide a systematic method for the qualitative and quantitative analysis of the mineral composition of swell-shrink clays and primary data for studying how mineral composition affects the physical properties of swell-shrink clays in the study area.

Ion-exchange modeling is one of the most widely used methods to predict ion adsorption data on clay minerals. The model parameters (e.g. number of adsorption sites and the cation adsorption capacity of each site) are optimized normally by curve fitting experimental data, which does not definitively identify the local environment of the adsorption sites. A new approach for constructing an ion-exchange model was pursued, whereby some of the parameters needed were obtained independently, resulting in fewer parameters being based on data-curve fitting. Specifically, a reversed modeling approach was taken in which the number of types of sites used by the model was based on a previous first-principles Density Functional Theory study, and the relative distribution of these sites was based on the clay’s chemical composition. To simplify the ion-exchange reactions involved, montmorillonite was Na-saturated to produce a well-controlled Na-montmorillonite (NaMnt) adsorbent. Ion adsorption data on NaMnt were collected from batch experiments over a wide range of pH, Cs+ concentrations, and in the presence of coexisting cations. Ion-exchange models were developed and optimized to predict these cation adsorption data on NaMnt. The maximum amount of adsorption of monovalent cations on NaMnt was obtained from the plateau of the adsorption envelope data at high pH. The remaining equilibrium constants (pK) were optimized by curve fitting the edges of the adsorption envelope data. The resultant three-site ion-exchange model was able to predict the retention of Li+, Na+, K+, and Cs+ very well as a function of pH. The model was then tested on adsorption envelopes of various combinations of these cations, and on Cs+ adsorption isotherms at three different pH values. The pK values were constant for all assays. The interlayer spacing of NaMnt was also analyzed to investigate its relation with cation adsorption strength. An X-ray diffraction study of the samples showed that the measured d001 values for these cations were consistent with their adsorption pK values. The Cs+ cation showed a strong ability to collapse the interlayer region of montmorillonite. In the presence of multiple competing cations, the broadening and presence of multiple d001 XRD peaks suggested that the cations in the interlayers may be segregated.

Çayırbağı magnesite is one of numerous magnesite deposits occurring throughout Turkey. In this deposit, sepiolite and newly found stevensite occur locally as two daughter minerals formed from magnesite. The sepiolite and stevensite show distinctive compositions and modes of formation compared to those described in the literature. The objective of the current study was to characterize these minerals by means of mineralogic, thermal, structural, geochemical, and textural analyses and to describe their mechanisms of formation. The geology, mineralogy, and geochemistry were examined by field work followed by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), differential thermal (DTA), and thermogravimetric (TG) analyses. Chemical analyses were performed by means of electron microprobe (EMPA), inductively coupled plasma-optical emission spectrometry (ICP-OES), and laser ablation inductively coupled plasma-mass spectrometry (LA-ICP-MS). The XRD analyses showed that the d110 of the sepiolite was at 12.64 Å and at 13 Å after air-drying and ethylene-glycol solvation, respectively. Identification of the sepiolite as sepiolite-13 Å was supported by FTIR and TG-DTA data. Chemical analyses showed an ideal composition with a structural formula of (Ca0.05K0.02)(Mg7.79Al0.10□0.11)Si12O30(OH)4. Stevensite displayed distinctive results for XRD, FTIR, and thermal characteristics. The structural formula of stevensite was: (Ca0.01Na0.20K0.04)(Mg1.90Al0.30Fe3+0.37Ti0.01□0.43)(Si3.93Al0.07)O10(OH)2, indicating a layer charge arising mainly from octahedral sheets. Field and SEM observations demonstrated that sepiolite was formed from magnesite by transformation via a dissolution–precipitation mechanism. Descending surface waters were responsible for this transformation. Thick magnesite veins were partly replaced whereas in thin veins sepiolite replaced the overall mass. Both surface waters with high Si, low Al and Fe activities, and pH values of 8–9.5 were responsible for sepiolite formation. Stevensite was formed similarly to sepiolite with respect to the mechanism and parent mineral under permanent groundwater; where both Si, Fe, Al activities and pH (>9.5) were high.

Alkaline solutions have significant effects on the mineral composition and on the microstructure of bentonite; in relevant geoenvironmental engineering applications, therefore, the properties of bentonite buffer materials must be taken into consideration in the presence of alkaline solutions. The objective of the present study was to determine the effect of alkaline conditions on the swelling of bentonite mixed with sand. Bentonite-sand mixtures were soaked in a NaOH solution and allowed to react over prescribed periods of 6, 12, and 24 months. Swelling deformation tests were conducted on the alkali-treated bentonite-sand mixtures; the swelling of the mixtures decreased significantly with increased reaction time. The fractal ec-σ relationship (ec is void ratio of bentonite, σ is vertical stress) was employed to express the swelling characteristics of the alkali-treated mixtures, wherein the swelling coefficient decreased as the bentonite content was reduced. Dissolution traces over the clay surfaces degraded the microstructural phase, thereby slightly increasing the fractal dimension. At higher dosages of bentonite, the swelling of bentonite-sand mixtures always followed a similar ec-σ relationship as that found for bentonite alone. On the contrary, in the mixtures with a small bentonite content that surpassed the designated threshold pressure, the void ratio of clay in the mixtures deviated from the ec-σ curve due to the appearance of the sand skeleton. The bentonite content for a particular bentonite-sand mixture at which deviation from the ec-σ curve began was ~50%. This deviation was almost negligible at 50% initial bentonite content in the bentonite-sand mixtures; after treatment with NaOH solution, however, a pronounced deviation in the ec-σ curve was observed which was caused mainly by the decrease in the bentonite percentage. Finally, the vertical pressure threshold was also estimated using the ec-σ relation for bentonite-sand mixtures with small bentonite contents over a range of various alkaline solution reaction times.

The problem to be solved is whether Al is a necessary component of Fe-Mg chlorites. Very unusual Al-depleted and Fe-enriched trioctahedral chlorites with the empirical formulae Na0.05Ca0.05(Fe2+3.01Mg2.01Ti0.14Fe3+0.04)Σ6.00[(Si3.53Fe3+0.41Al0.06)Σ4.00O10](OH)8·nH2O (Sample 1) and Na0.05Ca0.01(Fe2+3.26Mg1.97Fe3+0.75Mn0.01Ti0.01)Σ6.00[(Si3.16Fe3+0.75Al0.09)Σ4.00O10](OH)8 (Sample 2) have been discovered in Al-depleted dolomite carbonatites of the Kovdor complex of ultramafic, alkaline rocks and carbonatites, Kola Peninsula, Russia. The presence of substantial amounts of Ti in Sample 1 is another unusual feature of this mineral. In both samples, chlorites are intimately intergrown with cronstedtite-1T which is an indication of a low stability of chlorite structure in the absence of aluminum in the tetrahedral sheet. The crystal structure of chlorite in Sample 1 was solved by the Rietveld method. The mineral is triclinic (IIb-4-module), space group C-$1$, a = 5.4153(4), b = 9.3805(7), c = 14.5743(12) Å, α = 90.137(5)°, β = 96.928(5)°, γ = 90.043(6)°, V = 734.95(10) Å3, and Z = 2. A problem to be solved is how stable are Al-free chlorites belonging to the clinochlore–chamosite solid-solution series and whether their existence in natural mineral assemblages is possible. The results obtained indicate that even though Al-depleted chlorites belonging to the clinochlore–chamosite solid-solution series exist in Nature as metastable phases, these minerals are extremely rare and much less stable than Al-poor serpentines.

Injured bone tissues can be healed with bone grafts, but this procedure may cause intense pain to the patient. A slow and localized delivery of nonsteroidal anti-inflammatory drugs (NSAIDs) could help to reduce the pain without affecting bone regeneration. The objective of the present study was to use [Mg-Al]-layered double hydroxide (LDH) as a matrix for controlled release of sodium naproxen (NAP). This system could be applied in biomaterial formulations (such as bone grafts) to achieve a local delivery of naproxen. [Mg-Al]-LDH successfully incorporated up to 80% (w/w) of naproxen by the structural reconstruction route, with the [Mg-Al]-LDH interlayer space increasing by 0.55 nm, corresponding to the drug molecule size. The evaluation of the naproxen release kinetics showed that 40% of the drug was delivered over 48 h in aqueous medium (pH 7.4 ± 0.1), indicating the potential of [Mg-Al]-LDH/NAP for local release of naproxen at adequate concentrations. Kinetic modeling showed that the naproxen release process was closely related to the Higuchi model, which considers the drug release as a diffusional process based on Fick’s law. The chemical stability of NAP after the release tests was verified by 1H NMR. The [Mg-Al]-LDH/NAP also exhibited low cytotoxicity toward fibroblast cells (L929 cell line), without modifications in their morphology and adhesion capacity. These results describe a suitable approach for preparing efficient systems for local delivery of nonsteroidal anti-inflammatory drugs for biomedical applications.