Mud shale is characterized by low strength and strong swelling, with rheological effects and deformation caused by drilling fluid and formation water. Establishing a rheological model to characterize the deformation characteristics is key to solving the problem of wellbore stability. The influence of moisture content on rock strength and creep mechanical properties were studied by means of water absorption, uniaxial compression, and creep tests. The tests showed that with the increase in moisture content, the elastic modulus and strength of hard brittle mud shale decreased. Further, under the same load, the instantaneous strain increased with increasing moisture content. Meanwhile, under various loading stresses, rock creep exhibited non-linear characteristics, which can be divided into three different creep stages: attenuated creep, stable creep, and accelerated creep. Starting with a non-linear viscous dashpot, and then introducing aging degradation and water-bearing weakening effects, based on the water-bearing creep characteristics of hard brittle shale as well as the modeling ideas of the classic component combination model, a new improved creep model based on the Nishihara model was established to describe the characteristics of the accelerated creep stage of hard brittle mud shale with various moisture contents. Subsequently, the Levenberg–Marquardt non-linear, least-squares method was adopted to invert the creep parameters. The results showed that the simulated creep curves achieved by employing the new creep model were consistent with the experimental results, thereby confirming the ability of the new non-linear creep model to provide a theoretical reference for the study of wellbore stability of hard brittle mud shale.

Clay minerals are common constituents of the Miocene Surma Group reservoir rocks in the Sylhet Trough, Bengal Basin, and may exert significant controls on reservoir quality. The relationship between diagenetic clay minerals and reservoir quality in the petroliferous Sylhet Trough is poorly understood, however. The current study was aimed at the origin and diagenetic pattern of clay minerals in interbedded sandstones and shales using thin-section petrography, scanning electron microscopy (SEM), and X-ray diffraction (XRD), and understanding their diagenetic effects on reservoir quality. The results showed that the clay mineral cements in sandstones comprise mainly chlorite, illite/illite-smectite, and minor smectite and kaolinite. In the early diagenetic stage, clay rims and growth of vermiform kaolinite occur and partly occlude the pore throats. Deep burial effects include pore-filling, pore-lining, and grain-coating authigenic clays (mainly chlorite and illite). Diagenetic clay minerals and mechanical clay infiltration showed a systematic distribution in sandstones lying in the vicinity of sequence and parasequence boundaries. In a lowstand systems tract (LST), clay minerals within the sandstones commonly include mechanically infiltrated smectitic clays that eventually evolved to grain-coating chlorite and/or illite during the meso-diagenesis stage. The presence of clays/clay minerals has no significant impact upon reservoir quality of sandstones. The Surma Group shales are enriched in illite with significant proportions of chlorite and kaolinite and are likely to be mainly detrital, with diagenetic changes of smectite to illite.

The incorporation of bentonites in aflatoxin-contaminated animal feeds to remedy aflatoxicosis has been tested widely in animal trials. Yet, a large variation in efficacy among samples has been observed which has been attributed to variations in the properties of the clay mineral adsorbents. The objectives of the current study were: (1) to evaluate the mineral and chemical composition of two selected bentonites to find minerals or elements which are potentially of concern; (2) to characterize the aflatoxin B1 (AfB1) adsorption (selectivity, capacity, reversibility, and interlayer accessibility) by the bentonites; and (3) to evaluate the safety and efficacy of selected clays as amendments of aflatoxin-contaminated feed for broiler chickens. The mineral, chemical, and exchange cation composition of the clays were analyzed, and they appeared to be safe for use in feed. The bentonites and their fractions showed that adsorption capacities range from 0.48 to 0.97 mol/kg. The interlayer spaces of both montmorillonites were accessible by AfB1, and the adsorption was irreversible. Three-day old broiler chickens were given clean and high-aflatoxin-concentration (1400 mg/kg) diets with and without the presence of the two bentonites. After three weeks the chickens were sacrificed and biomarkers were evaluated. The presence of aflatoxins reduced the body weight by 58% and resulted in a 25% mortality rate. Adding bentonites 1TX and 4TX increased the body weight of the chickens by 14 and 23%, respectively, but did not improve the mortality rates. The results suggested that selected bentonites could effectively sequester aflatoxins in vivo but did not eliminate the total toxicity present in highly contaminated poultry feed.

With fossil-fuel consumption at an all-time high, air pollution is becoming one of the most prominent problems of the 21st century. In addition to their devastating effects on the environment, sulfur-based pollutants are problematic for infrastructure by undermining the structural stability of various oxide-based surfaces found in clays and clay minerals. Calcite (CaCO3) and alumina (α-Al2O3) are two such mineral oxides with surfaces that are potentially susceptible to damage by sulfur-based adsorbates. Their surface interactions with a wide range of sulfur-based pollutants, however, have yet to be studied adequately at the atomistic level. This problem can be addressed by utilizing density functional theory (DFT) to provide molecular-level insights into the adsorption effects of H2S, SO2, SO3, H2SO3, and H2SO4 molecules on calcite and alumina surfaces. DFT can be used to compare different types of adsorption events and their corresponding changes in the geometry and coordination of the adsorbates, as well as delineate any possible mineral-surface reconstructions. The hypothesis driving this comparative study was that the mineral-oxide surface structure will dictate the surface adsorption reactivity, i.e. the flat carbonate unit in calcite will behave differently from the Al–O octahedra in alumina under both vacuum and hydrated surface conditions. The set of sulfur-based adsorbates tested here exhibited a wide range of interactions with alumina and fewer with calcite surfaces. Events such as hydrogen bonding, sulfate formation, atom abstraction, and the formation of surface water groups were more prevalent in alumina than calcite and were found to be dependent on the surface termination. The results of this work will prove instrumental in the design of clay and mineral-based materials resilient to sulfur-based pollutants for use in construction and infrastructure such as smart building coatings and antifouling desalination membranes, as DFT methods can garner the atomistic insights into mineral-surface reactivity necessary to unlock these transformative technologies.

Kaolin waste dumps contain a huge volume of material that cannot be commercialized due to the presence of variable amounts of iron minerals, which impart a yellowish color to the kaolin. Elimination of iron from kaolin using either a chemical or a biological method was the aim of this study. The chemical leaching of iron from kaolin was carried out using response surface methodology to optimize the reaction conditions. Time was found to be the most influential variable, although oxalic acid must be present to leach 32% of the iron. Biological leaching was also assayed for 14 days using a Bacillus strain. The results of bacterial leaching of iron from kaolin showed <1% iron elimination.

Methoxykaolinite is a very popular organo-modified kaolinite. Even though it has a number of interesting properties, this nanohybrid material is still underused in terms of practical applications. In the present study, methoxykaolinite was synthesized and used for the first time as an electrode modifier for Pb(II) determination in various aqueous media. X-ray powder diffractometry (XRD), 13C nuclear magnetic resonance (NMR), and Fourier-transform infrared (FTIR) spectroscopy were used as characterization tools to confirm the presence of grafted methoxy groups in the interlayer space of kaolinite. The electrochemical characterization of methoxykaolinite using the cationic probe Ru(NH3)63+ showed that the modified clay presents favorable interactions with cationic compounds. A methoxykaolinite-modified electrode was applied successfully to the quantification of Pb(II) in aqueous solution. At optimized experimental conditions, the calibration curve in the concentration range 0.025–0.3 μM showed excellent linearity (R2 > 0.99), a sensitivity of 3.36 μA μM–1, and a detection limit of 5.6 nM. This detection limit was 10 times lower than the minimum concentration of Pb(II) authorized in drinking water. The sensor was used also for the determination of Pb(II) in tap, river, and well water samples with only minor loss of sensitivity and recoveries (90±5% to 110±4%). Thanks to the excellent biocompatibility of kaolinite, the sensor was applied for Pb(II) detection in human urine. Recovery in the range 98±8% to 103±6% was obtained when three freshly collected urine samples were spiked with known amounts of Pb(II). These results showed the interesting potential of methoxykaolinite as an electrode modifier for trace-level detection of cations, even in biological samples.

Sub-surface clay samples are difficult to characterize using conventional methods so non-invasive Nuclear Magnetic Resonance (NMR) techniques were used to evaluate in a preserved state the pore structure, porosity, water mobility, and affinity of various clay systems. Within the CLAYWAT project launched by the NEA Clay Club, some of the most advanced NMR techniques were applied to samples from 11 clay-rich sedimentary formations (Boom Clay, Yper Clay (both Belgium); Callovo-Oxfordian shale, Upper Toarcian (both France); Opalinus Clay from two sites (Switzerland); Queenston Fm., Georgian Bay Fm., Blue Mountain Fm. (all Canada); Boda Clay (Hungary); and Wakkanai Fm. and Koetoi Fm. (Japan)). The degree of induration within this suite of samples varies substantially, resulting in a wide porosity range of 0.02–0.6. The key finding is the determination of pore-size distribution by NMR cryoporometry in the range of 2 nm–1 μm with the native fluid present in the pore space for most samples. The water volume in pore sizes of <2 nm could also be measured, thus providing a full description of the porosity system. A specific preparation by sample milling was applied to the preserved original cores minimizing disturbances to the samples in terms of water loss. The water content measured by NMR relaxation was comparable to values obtained by drying at 105°C. In general, the narrow T2 distributions indicate that water was diffusing throughout the pore network during the magnetization lifetime, implying that T2 distributions cannot be considered as proxies for the pore-size distributions. For the set of samples considered, the T1/T2 varied between 1.7 and 4.6, implying variable surface affinity. Finally, for most samples, a pore-shape factor of ~2.4, intermediate between a sheet (1) and a cylinder (4), was deduced.

Clay minerals in Gamalama volcanic soil have not yet been identified thoroughly. The soil is estimated to contain nanoscale natural clays, such as halloysite or imogolite. The occurrence of nanoclays in the soil will support the development of many applications in nanotechnologies from nature. The objective of the present study was to characterize soil samples from five different locations around the volcano at three different depths from the soil surface. A total of 50 g of dry soil sample was stirred slowly in 300 mL of distilled water. Stirring was stopped after the addition of 10 mL of 30% H2O2 and then allowed to stand for 24 h. The small floating particles with dimensions of <2 μm were separated from the mixture and collected using a centrifuge at 4000 rpm (1790×g) for 30 min. About 5 g of solid sample was obtained for further characterization. X-ray diffraction results showed the presence of halloysite, allophane, and kaolinite. Morphology analysis by scanning and transmission electron microscopy of some representative samples showed short tubes 10–20 nm in diameter and 50–100 nm long with the halloysite structure. Halloysite was found at 70 cm depth from the soil surface at almost all locations. The surface area determined by the surface area analyzer using the BET equation was as much as 112.51 m2/g. This surface area is thought to be the largest ever determined for a natural nanoclay, paving the way for future application as catalytic or photocatalytic-supporting materials.

In order to develop high-performance adsorbents to remove toxic methylene blue (MB) from wastewater, palygorskite (Plg) was utilized as a template to prepare palygorskite/carbon (Plg/C) composites by using a hydrothermal reaction in the presence of glucose. The porous Plg/C composites were then activated with ZnCl2. The effects of the dose of the activator and the activation temperature on the crystal structure, micro-morphology, specific surface area, and adsorption performance of the porous Plg/C composites were studied systematically here. X-ray diffraction (XRD) and scanning electron microscopy (SEM) results indicated that the crystal structure of Plg was destroyed during the activation process and irregular porous carbon was closely attached to the residual aluminosilicate skeleton. The activation was optimized at 400°C with a ZnCl2:Plg/C impregnation ratio of 2:1. The sample had a specific surface area of 1497.88 m2/g, together with a total pore volume and micropore volume of 1.0355 and 0.5464 cm3/g, respectively. The MB adsorption capacity was 381.04 mg/g. Such inexpensive, high-performance, porous Plg/C composites could find potential applications in wastewater treatment.

Montmorillonite (Mnt)-based solid acids have a wide range of applications in catalysis and adsorption of pollutants. For such solid acids, the acidic characteristic often plays a significant role in these applications. The objective of the current study was to examine the effects of H3PO4-activation and supporting WO3 on the textural structure and surface acidic properties of Mnt. The Mnt-based solid acid materials were prepared by H3PO4 treatment and an impregnation method with a solution of ammonium metatungstate (AMT) and were examined as catalysts in the dehydration of glycerol to acrolein. The catalysts were characterized by nitrogen adsorption-desorption, powder X-ray diffraction (XRD), Fourier-transform infrared (FTIR) spectroscopy, scanning electronic microscopy (SEM), X-ray photoelectron spectroscopy (XPS), diffuse reflectance ultraviolet-visible (DR UV-Vis) spectroscopy, temperature programmed desorption of NH3 (NH3-TPD), diffuse reflectance Fourier-transform infrared (DR FTIR) spectroscopy of adsorbed pyridine, and thermogravimetric (TG) analyses. The phosphoric acid treatment of Mnt created Brönsted and Lewis acid sites and led to increases in specific surface areas, porosity, and acidity. WO3 species influenced total acidity, acid strength, the numbers of Brönsted and Lewis acid sites, and catalytic performances. A high turnover frequency (TOF) value (31.2 h−1) based on a maximal 60.7% yield of acrolein was reached. The correlation of acrolein yield with acidic properties indicated that the cooperative role of Brönsted and Lewis acid sites was beneficial to the formation of acrolein and a little coke deposition (<3.3 wt.%). This work provides a new idea for the design of solid acid catalysts with cooperative Brönsted and Lewis acidity for the dehydration of glycerol.