The hydraulic conductivity of geosynthetic clay liners (GCLs) is not fully understood and certain gaps in knowledge are still present, such as the effect of coupled mechanical and chemical processes. The current study aimed to develop a simplified mathematical model to predict the hydraulic conductivity of GCLs, particularly regarding the coupled effects of mechanical and chemical processes. Based on Darcy's Law and Poiseuille’s Law, the method combines diffuse double layer (DDL) theory and fractal theory. External factors such as confining pressure and the concentration of the permeating solution, and inherent properties such as exchangeable cations, ionic radius, montmorillonite surface fractal dimension, the distance between two montmorillonite layers (m) after swelling at the exchangeable cation i (i denotes the primary exchangeable cations, such as Na+, Ca2+, K+, and Mg2+ in bentonite), density, and coefficient of viscosity of interlayer water between two montmorillonite layers, were considered. The proposed theoretical model gave relatively accurate predictions. A practical estimate of GCL hydraulic conductivity was also derived. The predictions were compared with experimental results and good qualitative agreement was found. From the experimental results, the proposed prediction model has a maximum deviation of ~1:10–10:1, and the empirical model has a mean deviation of ~1:15–15:1.

In spite of decades of research on the subject, the crystal structure of illite is still poorly understood. The purpose of this study was to address this problem by investigating the nature of the interlayer content in illite IMt-2 from Silver Hill, Montana, using analytical transmission electron microscopy (ATEM), thermogravimetry (TG), and X-ray powder diffraction (XRPD) analyses. The ATEM data, together with literature and TG results, yielded the formula K0.70a0.01(H2O)0.42 (Al1.53Fe2+0.06Fe3+0.19Mg0.28)Σ−2.06(Si3.44Al0.56)O10(OH)2 or, assuming the presence of H3O+, K0.69Na0.01(H3O)+0.28(Al1.47Fe2+0.06Fe3+0.19Mg0.28)Σ−1.99(Si3.40Al0.60)O10(OH)2. The first formula indicates surplus interlayer and octahedral species, whereas the second shows no excess. The XRPD data were refined by Rietveld techniques, down to an Rp factor of 10.48–13.8%. The mineral composition consists largely of illite-2M1, illite-1M, and minor quartz. Although the refinement accuracy is limited by the intrinsic poor quality diffraction of the illites, the partially refined model is consistent with the chemical composition; in particular, attempts to introduce octahedral cations in excess of 2 were fruitless. All the results support the simple structural model, by which the illite structure strictly corresponds to a dioctahedral mica with H3O+ replacing K. As a consequence, the crystalchemical formula of illites should be calculated on the basis of six tetrahedral plus octahedral cations.

Sedimentary zeolite occurrences are widespread in Central and Western Anatolia, Turkey. Erionite occurrences in Central Anatolia have significant health implications for inhabitants of the region. The widespread occurrences of zeolites are generally associated with volcano-sedimentary rocks and consist of low-temperature forms. The aim of the work was to define specifically the formation mechanism and chemical characteristics of these volcano-sedimentary deposits, and particularly, the stability conditions for erionite. The first step was to construct chemical potential diagrams and calculate thermodynamic data for erionite and Ca-saponite. Then, equilibrium activity diagrams were calculated for the zeolites and related minerals in the system of Ca-Na-K-Mg-Fe-Al-Si and H2O. Stability diagrams for log [aCa2+/(aH+)2] — log [aNa+/aH+] and log [aCa2+/(aH+)2] — log [aK+/aH+] for various saturation phase activities of Al3+ and SiO2 (aq) were plotted for sedimentary conditions. The coexisting phases and chemical characteristics of the each deposit were evaluated by examination of the activity diagrams. Deposits which do not include some of the common sedimentary zeolites, possibly have high Al3+ activity (equal to or greater than gibbsite saturation) or low SiO(aq) activity (less than quartz saturation) during formation. In addition, erionite was found to be very sensitive to the alkalinity of the system and is stable in only a limited range of thermochemical conditions.

Calcium-sodium exchange on Wyoming bentonite in methanol, ethanol and acetone-water systems were investigated at 0.03 N Cl and at room temperature. Calcium-sodium exchange isotherms were plotted at cosolvent concentrations ranging from 0 to 70% wt./wt. using Ca and Na ionic activities before and after correction for CaCl+ formation. In both cases and in all treatments, a greater selectivity of bentonite surfaces for Ca ions was observed. When compared to water, different trends were observed among and within cosolvents. These trends varied depending on whether or not CaCl+ formation was accounted for. Ignoring the formation of CaCl+, the preference of bentonite for Ca increased in methanolwater systems with increased percent methanol at low equivalent Ca fraction (<0.2). At higher Ca fractions, this preference matched that of water. In ethanol-water, no increased preference of the surface for Ca was observed. In acetone-water, increasing cosolvent concentration decreased the preference of the surface for Ca. The magnitude of this decrease was larger at low equivalent Ca fraction (<0.2). After correction for CaCl+, both in solution and on the surface, the preference of bentonite for Ca2+ was larger in methanol- and ethanol-water systems. In acetone-water, increased surface preference for Ca was only apparent at low acetone fractions (<50%). At higher acetone fractions, there was evidence of increased Na loading but no increase in Ca2+ selectivity. Clearly, ion-pair formation and its effects on Ca-Na exchange reactions cannot be ignored in mixtures of aqueous-organic solvents. After accounting for this effect, Ca-Na exchange in the studied solvents appears to be more of a surface- than a solution-controlled phenomenon that involves both electrostatic and specific solvent-surface types of interactions that have not been elucidated.

Stevensite-like sauconite, with the general composition: ${\text{Si}}_4\left({\text{Zn}}_{3-x}{\square }_x\right){\text{O}}_{10}{\left(\text{OH}\right)}_2{R}_{2x}^{+}$\$\end{document}, where □ is a vacant site, was synthesized. The objective was to study the possible migration of some cations (Li+ and Zn2+) within such trioctahedral smectites, under heating, following the so-called ‘Hofmann-Klemen’ (HK) effect. The initial gel was divided into five aliquots and placed in teflon-coated hydrothermal reactors with distilled water, and these were hydrothermally treated at 80, 100, 120, 150, and 200°C, respectively, over 30 days. X-ray diffraction (XRD) analysis confirmed that the samples synthesized were smectites. The number of vacant sites (x) per half unit cell (O10(OH)2) ranged from nearly 0 to 0.23 but no simple relationship was established between x and the temperature of synthesis. The samples were Li+- and Zn2+-saturated, and heated overnight at 300°C (HK treatment). Cation exchange capacity measurements were made by Fourier transform infrared spectroscopy (FTIR) on ${\text{NH}}_4^{+}$\$\end{document}-saturated samples. After LiHK treatment, the structural formula of samples could be expressed as: ${\text{Si}}_4{\text{Zn}}_{\left(3-x\right)}{\text{Li}}_x{\text{O}}_{10}{\left(\text{OH}\right)}_2{\text{NH}}_{4x}^{+}$\$\end{document}, while after ZnHK treatment, it could be expressed as: Si4Zn3O10(OH)2. Analysis by XRD and FTIR showed that the samples moved from a Zn-stevensite-like structure to Zn-talc-like structure after treatment with ZnHK. These results are interpreted asevidence that Zn2+ (and Li+) migrated into the previously vacant sites under HK treatment.

Three petrographically distinct styles of altered glasses in two hyaloclastites and one hyalotuff were studied. The texture and chemistry of these samples were investigated using electron probe microanalysis, scanning electron microscopy and transmission electron microscopy in order to understand better the mechanism by which alteration of sideromelane and formation of palagonite occurred in these samples. The results show that clay minerals (primarily smectites) are present in three different microenvironments: (1) coating the surfaces of glass and crystals or vesicle walls; (2) as a relatively heterogeneous, but well crystallized, replacement product (i.e. reddened smectite grain replacement or RSGR) of glass or; (3) as a relatively homogeneous, amorphous to poorly crystalline replacement product (i.e. palagonite). Both the grain size and composition of these smectite-like materials vary considerably.

Crystalline smectites occur in both hyaloclastites and have an intermediate composition between the two end-members nontronite and saponite. This composition could correspond to a mechanical intergrowth and/or an interstratification of two different smectites: one dioctahedral (i.e. nontronite) and one trioctahedral (i.e. saponite or stevensite) or simply to a true di-trioctahedral smectite. The coating smectite appears to have precipitated by a paragenetically-early, dissolution-precipitation mechanism prior to the formation of the RSGR. The high Ti content found in RSGR is attributable to an amorphous Ti-rich material which is intergrown with smectite and which behaves as a sink for immobile elements and those not included in smectite.

Palagonite from both hyaloclastites and hyalotuff is poorly to non-crystalline and more aluminous than the coating smectites. Palagonite from the hyalotuff has an Fe-rich montmorillonite-like composition. The TEM images show a 30–50 nm thick leached layer formed by selective (non-stoichiometric) dissolution that takes place in the fracture domain. The hydration and replacement of glass during the palgonitization process is accompanied by the loss of Fe, Mg and Ca with a concomitant gain of Al. Both palagonites (from hyaloclastites and hyalotuff) show smilar textural and chemical characteristics.

The production and industrial use of asbestos cement and other asbestos-containing materials have been restricted in most countries because of the potential detrimental effects on human health and the environment. Chrysotile is the most common form of asbestos and investigations into how to recycle this serpentine phyllosilicate mineral have attracted extensive attention. Chrysotile asbestos tailings can be transformed thermally, at high temperature, by in situ carbothermal reduction (CR). The CR method aims to maximize use of the chrysotile available and uses high temperatures and carbon to change the mineral form and structure of the chrysotile asbestos tailings. When chrysotile asbestos is employed as the raw material and coke (carbon) powder is used as the reducing agent for CR transformation, stable, high-temperature composites consisting of forsterite, stishovite, and silicon carbide are formed. Forsterite (Mg2SiO4) was the most abundant crystalline phase formed in samples heat treated below 1500ºC. At 1600ºC, forsterite was exhausted through decomposition and β-SiC formed by reduction of stishovite. A larger proportion of β-SiC was generated as the carbon content was increased. This research revealed that both temperature and carbon addition play key roles in the transformation of chrysotile asbestos tailings.

In X-ray diffraction (XRD) analysis, preparation of oriented clay specimens enhances their 00l reflections by arranging basal surfaces parallel to the specimen surface. In one-dimensional modeling of XRD intensities, degree of preferred orientation is one of the variable parameters and a user may choose different σ* values for different minerals. The usual assumption is, however, that the layers of all clay minerals that are present exhibit a similar degree of preferred orientation to that of the clay mineral flakes parallel to the basal plane. If the orientation of individual clay minerals is significantly different, and if this is not taken into account, the relative proportions of the constituent minerals cannot be modeled accurately. The actual or so-called ‘preferred’ orientation is a potentially large source of error in any attempt at quantitative XRD analysis because it cannot be assumed to be constant among different minerals and may also vary as a result of pretreatment. In the present study the influence of sample composition and sample pretreatment on the degree of preferred orientation was determined using the parameter σ*. A statistical parameter was calculated to determine and ensure the reproducibility of σ* measurements. The most important result was that, when mixed together, clay minerals influence each other in terms of the degree of preferred orientation. Among individual samples, the degree of preferred orientation can be different for each clay mineral. The power of sonication used in sample pretreatment of a pure kaolinite and a pure illite had no significant influence on the degree of preferred orientation. The changes in intensities upon variation of the tilting angle (χ) allowed for calculation of σ* of smectites in pure samples, in admixtures, and in samples treated in two different ways (air-dried and glycerol-intercalated), which is reported here for the first time. Smectites are very fine grained with flexible morphology which is believed to be the reason for their tendency to exhibit poor orientation (σ* = 22°); further research is required to establish whether this is a general feature of smectites. After glycerol treatment a soil smectite showed a slightly better orientation compared to the air-dried pattern. The results of the study illustrate the difficulty of predicting changes in preferred orientation of clay mineral admixtures, even if non-platy minerals such as clay-sized quartz are added. In general, σ* decreased when non-platy minerals were added, which is explained by changes in geometry of the specimen. Not all clay minerals, however, showed simultaneous changes in their orientation behavior.

Soil salinity is one of the most critical environmental stresses that affects crop productivity. In a context in which world demand for food is growing continuously, this problem requires urgent attention. Actions that go beyond traditional agricultural practices are needed. The objective of the current study was to develop a bioactive, economic, and sustainable compound that can increase the tolerance of cultivated plants in saline-stress situations by combining the hosting capacity of natural bentonite nanoclay (Bent) with a phytoactive osmoprotective compound, L-Proline (Pro). The Bent-Pro nanocomposite synthesis method, its final chemical structure, and in vitro bioactivity were addressed here. The results indicated that Bent can retain a maximum of 14.4% (w/w) of Pro. The (001) X-ray diffraction (XRD) peak of Bent shifted to smaller angles in the pattern of Bent-Pro, indicating that Pro has a monolayer arrangement between the Bent layers. The results of transmission electron microscopy (TEM) also supported this result. Pro was also retained on the edges or external surfaces of Bent, as indicated by thermogravimetric analysis (TGA) and scanning electron microscopy (SEM). In addition, Pro functional groups identified by Fourier-transform infrared (FTIR) spectroscopy indicated that it was present in its zwitterionic form. The role of Bent-Pro as a protector against plant saline stress was assayed using Arabidopsis thaliana (A. thaliana) as a model, demonstrating that it mitigates the detrimental effects of NaCl-mediated salt stress on seed germination and the leaf chlorophyll level, thus highlighting the relevance of this contribution and the versatility and broad applicability of clays.

The objective of this study was to determine whether smectites abiotically catalyze transformation of glucose under conditions relevant to soil organic matter (SOM) formation. Four smectites saturated with Na, Ca, Fe and Al were incubated under abiotic conditions with glucose solutions for 21 days at 37°C. After the incubations, soluble organic C recoveries ranged from 95 to 109.3%, relative to the amount of C added as glucose; however, glucose recoveries in the solutions ranged from 18.3 to 98.3%. The results indicate that a significant amount of the added glucose was abiotically transformed to soluble organic compounds other than glucose during the incubations. In general, glucose recoveries decreased with the acidic character of smectites: SWa-1 > Panther > Otay. Also, within clays, glucose recoveries decreased as the exchangeable cation became more acidic: Na > Ca > Al. Higher glucose recoveries were obtained for ‘Fe-rich’ smectites relative to ‘Fe-poor’ smectites, suggesting that Fe-oxyhydroxy coatings on smectite surfaces inhibit the transformation of glucose. High-pressure liquid chromatography analysis of the incubation solutions revealed small peaks for 5-(hydroxymethyl)-2-furaldehyde along with peaks for other unknown compounds. The results suggest that under conditions similar to those found in soils, smectites catalyze glucose dehydration to form furfural compounds. Polymerization of furfural compounds may be a major pathway leading to the formation of new humic materials in soils.

The elimination of Pb2+ and recovery of lead metal during the treatment of industrial sewage is an important research topic. Montmorillonite (Mnt) is a promising material in this regard. The purpose of the present study was to improve the Pb2+ adsorption ability of Na-containing Mnt (Na-Mnt) by pillaring titania (anatase) into its interlayer spaces using a sol-gel method. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The ratio of Ti to Mnt affected the crystal phase of titania-pillared Na-Mnt (Ti-Mnt), and changed the interlayer spacing of the (001) plane of Ti-Mnt and the growth of anatase. The Pb2+-adsorption capabilities of Ti-Mnt were tested using an aqueous solution of lead nitrate as a wastewater model. The Ti-Mnt prepared adsorbed >99.99% of the Pb2+; leached and activated Ti-Mnt adsorbed >95.7% of the Pb2+, indicating that Ti-Mnt could be recycled effectively. Furthermore, the Pb2+-adsorption capability of Ti- Mnt was related to the interlayer spacing of Mnt, the distribution of anatase particles pillared in Mnt, and the specific surface area, especially with respect to the relationship between the anatase particles and the interlayer spacing of the (001) plane.

Birnessite can be used as a precursor in the preparation of manganese oxides. Synthesis of pure birnessite is difficult because of a side reaction, which yields hausmannite. This study aimed to develop a modified oxidation-deprotonation reaction (ODPR) method to eliminate the formation of hausmannite, and to investigate the influence of alkalinity on the synthetic products. In contrast to the conventional synthesis of birnessite through oxygen or permanganate oxidation, the ODPR method can produce birnessite without any impurities, within 5 h, and in a reproducible fashion. The distinctive feature of the ODPR method is the bubbling of N2 gas into NaOH and Mn2+ solutions before mixing the NaOH with Mn2+, in order to keep oxygen away from each solution. As soon as white pyrochroite was formed, oxygen gas was forced in as an oxidant to initiate the oxidation reaction. A black suspension with a blue tint appeared after 5 h of reaction. These precipitates were collected and examined by X-ray diffraction (XRD), scanning electron microscopy (SEM), infrared (IR) and Raman spectroscopy. The average oxidation state of the Mn oxides was also determined. The results showed that pure birnessite with good crystallinity was formed. Oxidation of 1 M NaOH mixed with Mn2+ solution formed random-stacked birnessite. However, the oxidation of 4 M NaOH mixed with Mn2+ formed birnessite. Random-stacked birnessite can be transformed into birnessite by ageing suspensions at 313 to 373 K.

Pillared clays (PILCs) with magnetic properties have significant potential for application in industry and the environment, but relatively few studies of these types of materials have been carried out. The aim of the present work was to gain insight into the magnetic and structural properties of pillared clays by examining in detail the influence of the calcination temperature and the nature of different pillared clays on these properties.

Magnetic layered systems from different pillared clays were prepared and characterized. Firstly, Ti-, Al-, and Zr-pillared clays (Ti-PILCs, Al-PILCs, and Zr-PILCs, respectively) were produced at different calcination temperatures and then magnetic pillared clays (Ti-M-PILCs, Al-M-PILCs, and Zr-M-PILCs) were prepared at ambient temperature. The synthesis involves a reduction in aqueous solution of the original Fe-exchanged pillared clay using NaBH4. The structural properties of pillared clays and their magnetic forms were investigated using X-ray diffraction, N2 adsorption, cation exchange capacity determination, and X-ray fluorescence (XRF) measurements. The properties of the magnetic pillared clays were investigated by superconducting quantum interference devices and Mössbauer spectroscopy. An evaluation of the data obtained allowed an estimation of the pillared structure in one PILC-model before and after magnetization. The model was determined on the basis of a simple geometric model and experimental data leading to the calculation of a filling factor (FF) which contained information about the number of intercalated pillared layers and the unaffected layers. In the case of Ti precursors, the best calcination temperature was 400°C, which maintained the highest specific surface area and pore volume with magnetic parameters suitable for magnetic application. Similar experiments with Al- and Zr-pillars have been discussed. A correlation between the XRF data, porosity, FF calculation, and magnetic properties led to the conclusion that the sample Al-M-PILC previously calcined at 500°C was the most stable material after the magnetization process. The same examination in the case of Zr materials suggested that the most stable sample had been calcined at 300°C (sample Zr-M-PILC-300).

Extraction of meaningful information on the timing of fault activity from clay gouges using radiometric dating methods, such as those based on the K-Ar system, can be challenging. One of the factors complicating interpretation of the radiometric dating results is the presence of multiple K-bearing components in the gouge material. In the current study, an attempt was made to develop a new interpretative method for K-Ar and 40Ar-39Ar dating, capable of handling a three-component mixture. In addition, the mineral composition of clay gouges from the Tatra Mountains (Poland), which has not been investigated before, is reported. The mineral compositions of the bulk clay gouge material and separated size fractions were determined by X-ray diffractometry and Fourier-transform infrared spectroscopy. The gouge samples were composed of quartz, dioctahedral mica (as a discrete phase and as a component of mixed-layered illite-smectite), and chlorite, commonly with plagioclase and more rarely with K-feldspar, dioctahedral smectite, calcite, anatase, or trace kaolinite. One feldspar-free sample containing three mica polytypes (1Md, 1M, and 2M1) was chosen for dating with the 40Ar-39Ar method. The results of 40Ar-39Ar dating were interpreted using three concepts: Illite Age Analysis (IAA), a method based on the MODELAGE software, and a newly developed three-component concept. The age values obtained with IAA were −14 Ma ± 31 Ma and 180 ± 91 Ma for authigenic (1Md) and inherited (1M + 2M1) components, respectively. The MODELAGE-based approach returned –4 ± 40 Ma and 165 ± 62 Ma. The three-component approach returned age values of polytypes as follows: 1Md, 15 ± 37 Ma; 1M, 135 ± 57 Ma; 2M1, 121 ± 56 Ma based on the medians and the interquartile ranges of non-normal distributions of Monte Carlo-simulated age values. The results obtained indicated that the 1Md polytype was probably formed during the most recent stage of fault activity, while 1M and 2M1 polytypes are of equal age, roughly.

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.

A pseudomorphous aggregate after titanite composed of smectite, anatase and residual titanite of composition (Ca0.98,Mn0.02)(Ti0.65,Al0.35)[SiO4](O0.65,OH0.35), from a depth of 450 m in the Broken Hill South Mine, New South Wales, Australia, was investigated by electron microscopy and microanalysis to characterize the alteration products and the mobility of Ti. Examination of the pseudomorph showed randomly oriented anatase crystals dispersed throughout a matrix of beidellite, with 9% porosity. Around the periphery and along the (110) cleavage plane of titanite, alteration was most developed. The range of Ti mobility was found to be limited to ~500 nm, and the ratio between the average diameter of anatase crystals and the average distance between them is ≈1.3. This ratio is consistent with an alteration process in which Ti is conserved and the anatase crystals grow from the Ti available immediately around them. It is unlikely that Ti migrated beyond the titanite pseudomorph.

The present study considered the problem of halloysite nanoscroll synthesis by energy modeling of the formation of chrysotile and halloysite particles. The main aim of the study was to reveal an energy preference between scrolled and platy morphologies of the particles. Both hydrosilicates possess the ability to scroll spontaneously but relatively facile hydrothermal synthesis of the nanoscrolls is available only to the former, whereas halloysite forms mainly plates under the same conditions. This issue was investigated by a phenomenological energy model, taking into account: (1) strain energy due to the size difference between metal oxide and silica sheets; (2) surface-energy difference on the opposite sides of the layer; and (3) adhesion energy. Calculations showed that the halloysite layer had a significant scrolling potential due to the first energy component, but the surface-energy difference acted in the opposite direction and tried to unbend the layer. In contrast, these two actions were co-directional in chrysotile layers. In both cases, the formation of multi-layered plates became more energy favorable when the specific surface energy of the edges decreased. In the range 0.5–3 J/m2 for the specific surface energy, only halloysite layers showed an energy preference for platy particles over nanoscrolls, especially at small layer sizes. Certain processes, such as hydration, could reduce the corresponding specific surface energy value and, as a result, could stabilize the platy morphology of halloysite at the earliest stages of particle growth under hydrothermal conditions.