Argon physisorption at 87 K is the new standard for texture analysis of microporous media recommended by the International Union of Pure and Applied Chemistry (IUPAC). However, geoscientists routinely use nitrogen (77 K) and carbon dioxide (273 K), both molecules with permanent polarization and the preference to interact with specific surface sites. In this work, N2, CO2, and Ar physisorption isotherms were measured and classical physisorption theories applied to investigate the suitability of Ar physisorption for the porosity assessment of mudrocks, clays, and (non)-porous analogs.

N2 and Ar physisorption isotherms are qualitatively similar with the most significant discrepancies in the submonolayer range. Textural parameters reveal linear relations but parameter ratios vary randomly, independent of the sorbent class. While N2 and CO2 (mostly) underestimate micropore volumes, nitrogen BET areas are consistently larger than argon BET areas. Those differences are probably associated with differences in polarization. But its effect on molecular orientation, for example, is presumably masked by microporosity and a narrow spacing of specific surface sites.

Mesopore size distributions and Gurvich (total) pore volumes agree well for N2 and Ar indicating similar pore size and pore volume access. Combining both parameters proves effective in identifying saturation pressure offsets which pose the largest uncertainty factor in the present study. Ar-based micropore size distributions reveal three distinct classes of mudrocks differing in organic matter maturity, and its contribution to microporosity. Empirical αs plots corroborate this classification underlining the discrepancies in the micropore range of mudrocks. Comparative hysteresis loop analysis indicated cavitation as one dominant evaporation mechanism in mudrocks and clays effecting a sample-specific compartmentalization of their pore networks.

Conventional oil drilling fluids often fail under extreme (high-pressure high-temperature, HPHT) conditions, leading to wellbore instability and formation damage, causing substantial economic losses in the drilling industry. The objective of this study was to evaluate the performance of Claytone-ER, a novel rheological additive for oil-based drilling fluids (OBDF), compared with a conventional organoclay (OC). Claytone-ER improved the drilling fluid performance significantly, including enhancement of the emulsion stability by 3% (863 V to 891 V), mitigation of sagging behavior, and substantial improvement in key rheological parameters such as plastic viscosity (PV) by 26.5%, yield point (YP) by 98%, and apparent viscosity (AV) by 36.5%. Additionally, Claytone-ER enhanced gel strength (GS) and improved filtration properties, reducing filtrate volume by 8% (5.0 cm3 to 4.6 cm3) and filter cake thickness by 6% (2.60 mm to 2.45 mm). These results demonstrated the potential of Claytone-ER to enhance the stability and performance of OBDFs under extreme HPHT conditions, leading to improved drilling efficiency, reduced non-productive time, and cost savings for drilling operations. Furthermore, the enhanced rheological properties, sag resistance, and filtration control contribute to better wellbore stability and minimize the risk of formation damage, ensuring long-term well productivity. This study represents a significant advancement in drilling fluid technology, paving the way for safer and more efficient drilling operations in challenging HPHT environments. Future research will focus on field trials to validate the efficacy of Claytone-ER in real-world HPHT drilling scenarios.

This study focused on a detailed mineralogical and crystal-chemical analysis of Mg-smectites from four bentonite samples from Turkey. Mg-rich smectites, mainly associated with alkaline and evaporitic depositional conditions, are formed in environments such as salt lakes, brine springs, and sabkhas, as well as in hydrothermal systems, in some cases by transformation from other phyllosilicates. Saponite has also been documented on the surface of Mars. The systems that produce Mg-smectites are less common than those that produce dioctahedral Al-smectites and consequently Mg-rich smectites are less abundant than dioctahedral smectites. For this reason, information on nanoscale mineralogy and crystal chemistry of Mg-smectites is relatively lacking. In this study, X-ray diffraction, thermal analysis and electron microscopy were used to study Mg-smectites. The crystal chemistry of single crystals determined with analytical electron microscopy in transmission electron microscopy (AEM-TEM) revealed that all samples had notable variability in the composition of individual crystals, such that no point analysis resulted in ideal structural formulae for saponite, stevensite, sepiolite, or palygorskite. They contain SiO2 content greater than that corresponding to a Mg-smectite, even stevensite, and often are intermediate to Mg-smectites and the sepiolite-palygorskite series. Meanwhile, the number of octahedral cations is small for fibrous clay minerals. Neither the point analysis of smectitic particles nor the mean structural formula fit properly for Mg-smectites showing crystallochemistry complexity. The results of these point analyses, in which no contamination has been observed, suggest that these smectites have intermediate compositions between trioctahedral smectites and sepiolite-palygorskite, indicating nanometer-scale intergrowths of these minerals in Mg-rich clay deposits.

Thermally activated palygorskite and sepiolite clays are commonly used for the bleaching of edible oils and fats. However, their bleaching capacity can vary depending on physicochemical clay characteristics. The present study focused on the impact of thermally treated palygorskite and palygorskite-smectite clays on bleaching performance and showed a correlation between bleaching performance and the physicochemical characteristics of the clays. The mineralogical and chemical composition, along with certain physicochemical characteristics of thermally treated (heated at 300°C) palygorskite and palygorskite-smectite clays, were assessed for their effect on bleaching performance. The samples were collected from exploratory boreholes from four currently exploited clay deposits, namely Knidi, Pilori, Harami, and Velanida of the Upper Pliocene-Lower Pleistocene Ventzia Basin, west Macedonia, Greece. Palygorskite was formed diagenetically from smectite precursors of lateritic origin and deposited in a fluvial-palustrine environment. Clay minerals were characterized by X-ray diffraction (XRD), near-infrared spectroscopy (NIR), inductively coupled plasma optical emission spectrometry (ICP-OES) analysis, and gas porosimetry. The bleaching ability of the samples was evaluated by measuring the absorption of visible light through standard bleached rapeseed oil. Results revealed that the bleaching performance was superior in mixed palygorskite-smectite clays and was directly proportional to the palygorskite content and to both the apparent bulk density and external surface area of the clays. By contrast, bleaching ability was inversely proportional to the amount of non-clay minerals, but independent of the small variance in Al, Fe, and Mg contents of the clays or the octahedral composition of palygorskite. The presence of smectite in smaller amounts promoted to a small extent the efficiency of the palygorskite-rich clays from the Ventzia Basin.

The bauxite beneficiation process in the Amazon generates a significant amount of tailings, which were historically stored in large basins without a designated purpose. One of these materials is clay obtained from the bauxite washing process, which is rich in Al2O3 minerals, primarily gibbsite and kaolinite, and currently lacks practical applications. This study aimed to explore an application of this tailing in the production of low-temperature geopolymers, considering its material characteristics and availability. Geopolymer synthesis was conducted following a Doehlert-type experimental design to evaluate the properties of the raw materials. The tailing was characterized by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), thermogravimetry-differential scanning calorimetry (TG-DSC), X-ray fluorescence (XRF), and inductively coupled plasma optical emission spectroscopy (ICP-OES), whereas the geopolymers were characterized by XRD, FTIR, and mechanical compressive strength testing. The mineralogical composition of the bauxite tailings consists of 45% of low-ordered kaolinite, 34% of gibbsite, and 21% of other minerals. Compressive strength values of the geopolymer produced ranged from 8.99 to 41.89 MPa, a good value for the type of geopolymer produced. The best compressive strength results were obtained at a low Na/Al ratio (0.5–0.6) and low curing temperature, which favors the application of the material for the synthesis of geopolymer, contributing to lower energy consumption and lower CO2 emissions compared with usual geopolymers.

Cation exchange competition (CEC) is driven by water uptake during saturation of bentonite barriers surrounding canisters releasing heat from radioactive waste. CEC differences may be used to follow smectite degradation. The unanswered question is whether processes can be understood in more detail by studying a full set of 30 bentonite blocks of the Alternative Buffer Material (ABM) test series (ABM-5) after reaction in an underground laboratory operated in crystalline rock at temperatures of ~250°C, the highest reported temperature so far. In contrast to expectations, only a minor CEC decrease of, on average, 1.8 meq 100 g–1 was detected, although processes depending on high temperature were expected to alter the swelling properties of smectites that can be followed analytically by reducing bentonite CEC values. A critical role of initial water saturation and initially ~25% Na+/CEC on exchangers was identified by comparison with the first ABM-1 package where CEC decreased by on, average, 5.5 meq 100 g–1. ABM-1 was heated from the start whereas the packages ABM-2 and ABM-5 in this study were heated after water saturation. Exchangeable cations (EC) were distributed within the whole barrier in ABM-5 with (1) more pronounced horizontal EC gradients and (2) the absence of an exchangeable Na+ decrease. In all tests, a cation equilibration with the Äspö groundwater averaged over the whole packages of many different buffer materials was observed, showing, overall, a significant range in final composition after retrieval: Na+ (27–46%/CEC), Mg2+ (7–15%/CEC), and Ca2+ (45–100%/CEC). The groundwater for saturation, however, was locally variable in composition. Although excluded from the smectite interlayer (below or equal to 2 water layers), Cl– entered the barrier from groundwater, increased significantly in nearly all ABM-5 bentonite blocks, and was found to be mobile also in the less heated ABM-1 and ABM-2 test packages.

Saponite-like materials have a wide range of potential applications, especially in heterogeneous catalysis. Despite the simplicity of the synthesis, the mechanisms of the formation of saponite are not well understood yet. The aim of the present study was to investigate a possible correlation between the coordination of Al in the solid phase and in the solution. For this, samples were prepared by varying the initial OH:Si molar ratio from 0.18 to 2.14, leading to a pH in the supernatant after the hydrothermal treatment of 6.7 to 12.7, respectively. The characterization of the material was performed by combining nuclear magnetic resonance (NMR) and X-ray absorption near edge structure (XANES) spectroscopies, and good agreement was obtained between the two techniques. Between pH7 and pH10, 60–65% of aluminum was found to be in tetrahedral coordination, while this percentage increased above pH10 (up to 81%). These results correlated with the speciation of the aluminum in aqueous solution. Indeed, above pH10, all available aluminum was in the soluble form Al(OH)4–.

Layered double hydroxides intercalated with tungstate ions ([WO4]2–) are among the anionic clays with interesting applications due to the physicochemical properties of the element tungsten. Their transformation by calcination into the corresponding derived mixed metal oxides should modify their properties. In view of this, the aim of this study is to compare the light absorption behavior of tungstate intercalated Mg-Al layered double hydroxide (LDH) with that of its derived mixed metal oxide (MMO), as well as their electrical and dielectric properties. The LDH precursor was prepared successfully by the co-precipitation method at pH 10, while MMO was obtained by calcining LDH at 723 K. Subsequently, LDH and MMO were characterized by X-ray diffraction and analyzed by thermal gravimetric analysis/differential thermal analysis and Raman spectroscopy. The electrical response, modeled by an equivalent circuit, was found to be intimately dependent on the structures of LDH and MMO, while the light absorption behavior is mainly due to the presence of the distorted [WO4]2– and the tetragonal MgWO4 in LDH and MMO, respectively. In addition, MMO showed an improvement in the dielectric properties through the large decrease in the dielectric loss tangent and electrical conductivity. However, LDH exhibited greater absorption coefficients in the ultraviolet region with a lower optical energy gap compared with its derived MMO, resulting in energy gaps of 4.23 and 4.35 eV for LDH and MMO, respectively. Results revealed that calcining LDH to form MMO fails to improve light absorption, but does improve the dielectric behavior, which makes possible the use of LDH as a shielding material against UV light and MMO for energy storage applications.

Amongst the various strategies studied to reduce polluting agents in water, both from anthropogenic and natural sources, adsorption processes are among the most widespread techniques. Layered double hydroxides (LDH, anionic adsorbers) play a fundamental role in the treatment of industrial wastewater, which often contains both anionic and cationic species. The objectives of the present study were to synthesize a (Mg, Zn)Al-NO3 LDH, and a composite between the LDH and montmorillonite (Mnt, cationic exchanger), and to test their adsorption capacity for both cationic and anionic pollutants in two different samples of industrial wastewater. The compounds were characterized by means of inductively coupled plasma-atomic emission spectroscopy (ICP-AES), X-ray powder diffraction (XRPD), Fourier-transform infrared (FT-IR) spectroscopy, differential thermal analysis/thermogravimetry (DTA-TG), and transmission electron microscopy (TEM). Results of product yields and extraction performance provided evidence that the synthesized compounds were active in the removal of various kinds of pollutants from real wastewaters. The adsorption capacity, in the case of the removal of cations varied from ~85 to 100% and from ~92 to 100% when the LDH and the LDH-Mnt, respectively, were used. The 56–100% removal of anions was instead obtained for both the adsorbents.

This research tackles the challenge of enhancing the engineering properties of kaolinite-rich clay through innovative and sustainable treatment approaches. The main aim was to investigate the effects of nano-materials such as calcium carbonate and silica on the plasticity, strength, compressibility, and microstructural behavior of kaolin. The experimental process involved blending kaolin with varying concentrations (0.5–2% by dry weight) of calcium carbonate and silica. Standard laboratory tests, such as Atterberg limits, unconfined compressive strength (UCS), and one-dimensional consolidation tests, were performed to evaluate changes in plasticity, mechanical strength, and compressibility. Microstructural analyses using X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), and Brunauer-Emmett-Teller (BET) provided insights into the structural and surface modifications of the treated clay. The findings demonstrated a notable reduction in the plasticity index of kaolin as the nano-material content increased, with the optimal dosage identified at ~1% for both nano-materials. At this dosage, the UCS of the treated clay increased threefold, attributed to the formation of a nano-crystalline gel and improved particle interactions. Consolidation tests revealed a significant decrease in the compression index, while the hydraulic conductivity remained similar to that of untreated kaolin. Microstructural analysis confirmed the development of an aggregated-flocculated structure, enhanced pore connectivity, and increased surface area in the clay nano-composite. In summary, the incorporation of calcium carbonate and silica particles significantly enhanced the engineering characteristics of kaolinite-rich clay, highlighting their promise as sustainable alternatives for clay improvement. These results pave the way for broader applications of nano-materials in geotechnical engineering.

Sepiolite is considered a suitable substrate for Maya blue pigment. However, the interaction between sepiolite and indigo dye has not been fully understood. Previous studies have demonstrated that pre-treatment of sepiolite by heating or acid was useful in identifying the sepiolite–indigo interaction. The purpose of the present study was to prepare a series of hybrid sepiolite–indigo pigments after modifying the sepiolite using various alkali treatments (NaOH), then to evaluate their properties with respect to color, chemical resistance, and photostability. Samples were characterized using reflectance spectroscopy, X-ray diffraction, Fourier-transform infrared spectroscopy, Raman spectroscopy, transmission electron microscopy, and N2 adsorption-desorption. Under alkaline conditions, Si4+ and Mg2+ ions in sepiolite partially dissolved, disrupting the coordinated water associated with them. Mg2+ ions precipitated and blocked the structural channels of the sepiolite. The impact of the alkali treatment on the microporous structure and coordinated water of sepiolite significantly influenced the color properties and stability of the hybrid pigments. Proper alkaline treatment enhanced the greenish hue and chemical stability of the pigment, while severe treatments apparently compromised the structural integrity of the sepiolite, thus diminishing the quality of the hybrid pigment. Results from this study provide new insights into the color-causing and stabilizing mechanisms of sepiolite-based Maya blue pigment and also provide guidance for developing hybrid pigments based on clay minerals and organic dyes.