Clay Minerals Research Articles

Creating Neoteric Inorganic-Organic Hybrid Functional Biocomposites By Fiber Welding

Natural fiber welding (NFW) is a process by which ionic liquids (ILs) are used to partially solvate and restructure biopolymer fibers. During NFW, the biopolymer fibers of adjacent cloth threads are intermingled, resulting in a highly nanoporous matrix surrounding a non-welded and structurally robust native thread core. Recent developments in this technique have led to the creation of all-biopolymer xerogel composites with pores of an ideal size regime (<20 nm) for growing and entrapping nanoscale materials, such as metal and semiconductor nanoparticles. However, larger nanoscale materials, such as traditional clay minerals, are too large (>100 nm in length and width) to include within the formed nanoporous matrix. These minerals are often used as fillers to enhance the properties of other polymeric materials, and their exclusion from NFW products is a significant limitation. Recent developments have shown that similar large additives can be entrapped in the welded matrix by first dispersing them in the welding solvent, though traditional clays (e.g., montmorillonite) are minimally soluble in typical welding IL. Fortunately, polyionic nanoclays (PINCs), an emergent class of synthetic and highly tailorable cationic clay minerals, are uniquely soluble in common NFW ILs. The present work aims to unite these two IL-based technologies by combining them into a suite of novel inorganic-organic hybrid functional composites. We will discuss the process for pre-treating NFW IL with PINCs to best aid their entrapment, then provide adequate characterization using microscopy, gas physisorption, and spectroscopic techniques to prove their inclusion within the NFW matrix. We will also demonstrate several basic applications of the hybrid cloth based on recent advances of PINC minerals, with a focus on selective dye sorption, fluorescence sensing, and catalysis.

Adsorption and oxidation of β-carotene by montmorillonite bleaching clays

The role that clay mineral acidity, specific surface area (SSA) and pore size distribution (PSD) have on the adsorption and oxidation of β-carotene by montmorillonite bleaching clays was investigated. Five commercially available clay minerals were studied, including three acid-activated montmorillonites (AACs) (K10, K30 and 22B), one aluminium-pillared montmorillonite (Al-PC) and an untreated montmorillonite (SWy-3). Each underwent physicochemical characterisation. X-ray diffraction and N2 gas sorption techniques provided structural and textural information. Titration with n-butylamine in the presence of Hammett and arylmethanol indicators characterised the concentration and strength of clay acid sites. The kinetics of β-carotene adsorption were then measured as a means of comparing their adsorptive power. The tendency of each clay to oxidise β-carotene to a variety of carotenoid-oxidation-products (COPs) was examined by analysing extracts of each clay with ultra-high-performance liquid-chromatography mass-spectrometry (UPLC-MS). The AACs adsorption and oxidation of β-carotene exceeded that of SWy-3 and Al-PC. This was attributed to a greater number of stronger acid sites, and a higher SSA. The clay PSD was also shown to play a significant role. 22B, which had a narrower PSD than K10 or K30, showed a lower tendency to adsorb β-carotene despite having the greatest number of strong acid sites. Lastly, the AACs had a greater oxidative power than SWy-3 or Al-PC and produced COPs in greater abundance than the other clays. They also produced more COPs of a higher oxidation state relative to β-carotene. These findings provide helpful information for the selection of efficient adsorbents for use in vegetable oil bleaching.

Water-salt transport modeling and sulfate erosion mechanisms in cultural heritage under microclimate

The microclimate of the environment influences the characteristics of salt erosion in historical cultural heritage, determining the pattern of salt weathering and the mechanism of salt-action. The study focuses on the influence of cultural heritage microclimate on salt weathering, and the study aims to understand the weathering mechanism by combining the theory of crystalline weathering with temperature and humidity variation. The study comprised immersing sandstone from the Yungang Grottoes, a World Heritage Site, in a sulfate salt solution and simulation of salt deterioration under on-site cyclic variable temperature and humidity conditions. The article designs the accumulation of salt crystallization at the sandstone surface under the effect of salt evaporation and visualizes the water-salt migration and crystallization process by ion chromatography (IC), microelectrode, and hyperspectral techniques. The corresponding types of sulfate deterioration under different weathering simulation conditions are investigated to probe the mechanism behind different weathering patterns. In the first part, we construct a water-salt migration test, combining hyperspectral techniques and microelectrodes to visualize the weathering patterns, compositional characteristics, and spatial and temporal changes of water-salt transport based on Fick's law to establish a mathematical model and simulate it in COMSOL multi-physics field simulation software. Subsequently, tests were carried out on sandstone with sulfate solution at variable temperatures and humidity levels to simulate the process of salt weathering. The results demonstrated that different salt solutions, such as Na2SO4 and MgSO4, lead to the dissolution of clay minerals. At the same time, crystallization disrupts the sandstone structure, causing degradation of its physico-mechanical properties after several weathering cycles, and there are significant differences in the salt crystallization patterns at different temperatures and after cycling at different humidities.

Behavior of Silver Species in Soil: Ag Nanoparticles vs. Ionic Ag.

Silver nanoparticles are one of the most commonly used forms of silver (Ag) in nanotechnology applications due to their antibacterial properties and electrical and thermal resistance. The increasing production and use of products containing nanoparticles has led to their release into and contamination of soil and water. This review summarizes the literature on the fate, behavior (adsorption/desorption, precipitation/oxidative dissolution, transformation), and transport/mobility of Ag forms in soils (Ag+ ions and Ag nanoparticles-AgNPs). The behavior of Ag+/AgNPs in soil is a complex process. It depends on many factors, including the characteristics of the Ag forms (ions, nanoparticle size, ligand type used for coating, surface charge, initial Ag concentration), the soil properties (organic matter and clay mineral content, textural properties, point of zero charge, cation exchange capacity, surface functional groups), and the solute properties (pH-Eh, ionic strength, cation type, oxygen content). The binding of Ag+ and AgNPs is significantly positively correlated with Al/Fe/Mn oxide and SOM content and depends on the surface charge of the minerals and CEC, which controls adsorption processes. Very important parameters to consider are the pH and Eh of the solution, which determine the durability of the ligands, the aggregation rate and the oxidation process of AgNPs, as well as the presence of sulfide and chloride and the Cl/Ag ratio, which determine the stability/mobility of Ag. Since AgNPs can be oxidized to Ag+ ions during their life cycle, it is necessary to consider the behavior of both forms of Ag in soils. Understanding the transport and behavior of Ag in soil is essential for the environmental risk assessment and management of wastes containing Ag.

Pedogenic evidence sheds light on the post-Roman pedo-sedimentological and human history of Tarsus, the Roman capital of CE 60, Cilicia, Mersin, Türkiye

The ancient city of Tarsus is underlying a sediment of 400 cm where the contemporary Tarsus grew. The diffusely stratified layers of the deposited sediment from the Kydnos (Tarsus) river overlying the Roman Road excavation site located in the heart of the modern city. The sediment is laden with technogenic materials. The profile of the stratigraphic layers represents a Pedocomplex (PDC) and its horizons are the Pedomembers (PDMs). All the PDMs were described and sampled for physical, chemical, mineralogical, micromorphological, and thermoluminescense analyses seeking pedogenic evidences. The origin of PDC materials is a fluvial and/or lagoon environment (archaeologically predicted date, about 60 CE, and they are calcareous, high in available P and some are high in total phosphorus contents). They have been partially modified by human activity in a settlement area, thus bringing some historical evidence suggesting that the site was part of the growing city after its abandonment. Thin sections show a vigorous biological degradation of the organic residues in the PDMs along with occasional evidence of soil-forming processes. The preliminary conclusions were extracted from the results obtained through the newly formed hydroxyapatite (Hap) determined by micromorphology, therefore proposing the new suffix π for the WRB soil naming system. Primary, high temperature and clay minerals together with TL analyses of the layers, were conducted to reveal the provenance and weathering phases of the horizons. The seeds recovered from an inhabited layer helped to interpret the food and medicinal habits of the local society and the contemporary presence of the lagoon.

The nexus of clay mineralogy and soil fertility under diverse parent materials in two distinct geomorphological settings

The nexus of clay mineralogy and soil fertility under diverse parent materials in two distinct geomorphological settings

The flotation deashing separation performance of high-ash fine coal-slime using humic acid depressant and insights to its depressant mechanism

Effective inhibition of clay minerals remains a challenge in the flotation separation of fine coal with high ash content. The quest for efficient, environmentally friendly, and cost-effective depressants to improve the flotation efficiency of fine coal-slime has become a focus of current research. Humic acid (HA), a macromolecular organic compound widely present in nature, is known for its non-toxic, low-cost, and biodegradable properties. In this study, the potential selective depressant HA was utilized to enhance the recovery of low-ash clean coal in the coal-kaolinite system. Adsorption and inhibition mechanisms were explored through contact angle measurements, X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM) methods. Flotation tests demonstrated that HA, at varying dosages, significantly increased combustible matter recovery while reducing ash recovery compared to conventional flotation. Optimal conditions, with an HA dosage of 750 g/t, resulted in a combustible matter recovery of 40.56 % and an ash content of 17.77 % in the clean coal. Contact angle measurements confirmed that high-dosage HA significantly reduces the coal surface hydrophobicity, resulting in a rapid decline in the recovery of combustible matter. It did not significantly alter the contact angle of kaolinite, however, across the entire range of HA dosages. Furthermore, XPS studies revealed that the reduction in hydrophobicity on the coal surface after HA adsorption is mainly attributed to the coverage of surface carbon–carbon/carbon-hydrogen groups (C–C/C–H) and the increased presence of carbonyl groups (C = O). Additionally, the study found that HA predominantly adsorbs on the Si-OH groups of kaolinite. Finally, AFM results showed that the primary mechanism underlying the altered heterocoagulation behavior between coal and kaolinite is HA’s effect on their interaction forces. The optimal flotation results achieved at the HA dosage of 750 g/t are primarily attributed to the consistent presence of repulsive forces during the approach process and weak adhesion forces during the retraction process between coal and kaolinite, thus reducing kaolinite coating on the coal surface. These findings provide a promising direction for utilizing HA to enhance flotation deashing of high-ash coal-slime.

Volcanic red soil in the tropical mountain region: landscape, parent materials, engineering characteristics, and its use on slope stability (case study: West Lampung, Sumatra, Indonesia)

ABSTRACT The characterization of tropical mountain volcanic red soil in the tropical mountain region, West Lampung area, Sumatra, Indonesia concerning the landslide disaster has been carried out. The research methods used in this research are remote sensing methods, field geological mapping, petrographic analysis (thin section analysis), soil geotechnical analysis, soil geochemical analysis, slope stability analysis, and statistical analysis. The findings indicated that the study area’s volcanic red soil is distinguished by rolling hills with a V-shaped valley, a moderate to severe incline, and an elevation ranging from 850 to 1150 m above sea level. The soil is volcanic residual soil which resulted in wet tropics and from tuff layer and tuffaceous breccias in the felsic composition of the hydrothermal alteration environment. The soil of the study area has a reddish-brown color, and loose characteristic, and belongs to the type of very loose to solid high plasticity uniform inorganic sandy clayey silt. Based on saturated soil slope stability analysis, volcanic red soil has a stable to unstable category if forming a slope. The intrinsic factor that affects the stability of the slope is the percentage of clay content, electrical sensitivity, plasticity index, degree of saturation, and percentage of clay mineral content.

Micro-Topographic Controls on Rare Earth Element Accumulation and Fractionation in Weathering Profiles: Case Study of Ion-Adsorption Rare Earth Element Deposit in Hedi, Zhejiang Province, China

Ion-adsorption rare earth element (REE) deposits are a major source of REEs and are found mainly in China. The formation of such deposits is affected by a combination of endogenic and exogenic factors. This study investigated the effect of micro-topography on the REE distribution in four weathering profiles at different topographic sites on a knoll in Hedi, Zhejiang Province, China. The weathering profile and REE accumulation are both most developed at mid-slope positions of the knoll. The intensity of chemical weathering decreases in the order of mid-slope &gt; base &gt; summit. As weathering progressed, REE enrichment initially increased but later decreased, with a progressive increase in light/heavy REE fractionation. REE fractionation is more pronounced on the north-facing slope than on the south-facing slope. Weathering degrees and clay mineral characteristics are key factors influencing the varying REE distributions on the knoll. Water leaching and the evolution of clay minerals towards higher maturity reduce REE adsorption capacity. Clay minerals also play a significant role in REE fractionation; the abundance of these minerals and the presence of illite enable the retention of more HREEs with minimal desorption. Taking into account water content, it is inferred that hydrological conditions, modulated by the micro-topography, strongly affect the depth and extent of REE accumulation, as well as fractionation.

Acid-etched halloysite and Co-Ni-B composites for high-performance supercapacitor application

The rational design and optimization of electrode materials can effectively enhance the electrochemical performance of supercapacitors. In this work, by utilizing the microemulsion method to combine the nanoflake-structured Co-Ni-B material with the highly porous hollow tubular structure of acid-etched halloysite (eHal), the stable and porous Co-Ni-B@eHal composites have been successfully synthesized. Simultaneously, the bimetallic composition in Co-Ni-B can offer a wealth of redox reactions, while the eHal tubes provide support and facilitate the ionic transport channels. The optimal electrode exhibits a high specific capacitance of 1534 F g−1 at a current density of 0.5 A g−1 and maintains 99.67 % of its initial specific capacitance at a current density of 20 A g−1, demonstrating excellent rate performance. Furthermore, it shows remarkable cyclic stability, retaining a specific capacitance of approximately 100 % after 60,000 cycles at a current density of 5 A g−1. The assembled Co-Ni-B@eHal-based asymmetric supercapacitor operates at a working voltage of 1.5 V and achieves a maximum energy density of 105.73 W h kg−1 at a power density of 375 W kg−1. These findings offer new insights into the development of bimetallic boride-based nanostructures and clay minerals in the field of electrochemical energy storage.

Amelioration of Potassium Humate as Ligand Exchanger for Adsorbed P Fractions and their Relationships with Chemical Properties of an Indonesian Andisol

Andisols are specifically characterized by a very high P adsorption capacity owing to their acidic reaction and dominance of variable-charged clay minerals. This crop cultivation problem can be overcome by potassium humate amelioration intended to exchange the adsorbed soil P fractions into the more available (labile) forms. This study aims to evaluate the effects of potassium humate application at 0, 20, 40, and 60 kg ha-1 on the dynamics of P fractions and their relationships with the chemical properties of an Indonesian Andisol. Using the Tiessen and Moir procedure, PH2O, PNaHCO3-Pi-Po, PNaOH-Pi-Po, and PHCl fractions were obtained in topsoil (0–30 cm) and subsoil (30–60 cm) samples 16 weeks after the treatment. The organic soil P (PPo) fractions tended to increase and were attributed positively to total P and negatively to base saturation (BS) at the topsoil, whilst the subsoil PPo fractions tended to increase with the decreasing soil BS. At 60 kg ha-1, the potassium humate application effectively decreased PPo and increased PPi fractions in the subsoil. The results also revealed that humic acid component of potassium humate was an effective organic ligand exchanger for the adsorbed PPo fractions that simultaneously altered soil anion-cation equilibrium in the studied Andisol. As an implication, soil P availability was increasing.

Long-lasting and efficient peroxydisulfate-based groundwater remediation driven by the slowly released Fe(II) from natural chlorite

The rapid depletion of peroxydisulfate (PDS) and the competitive inactivation of reactive species by excessive Fe restrict the oxidation duration and performance of iron (Fe)-based catalysts activated PDS for in situ chemical oxidation (ISCO). Here, natural chlorite, one of the Fe-rich clay minerals, is used as activator to enhance the performance and efficiency of PDS-based ISCO. It was found that acidification of contaminated groundwater drives the slowly release of aqueous Fe(II) from chlorite and serving as the source of multiple reactive species including hydroxyl radical (•OH), sulfate radical (SO4•−), and Fe(IV). Benefitting from the controlled release of Fe(II), the scavenging of oxidative species by Fe(II) is notably alleviated, leading to the oxidant utilization efficiency of chlorite/PDS improved by 24–95 % compared to the Fe(II)/PDS and ZVI/PDS, and the costs of oxidants reduced by over 50 %. Long-term experiments indicate that PDS is relatively persistent and slowly consumed by chlorite, hence the oxidative ability for pollution control remains for over one month. This work not only proposes an effective, low-cost and promising alternative process for groundwater remediation, but also demonstrates the significance of slowly released Fe(II) in breaking the trade-off between peroxide activation rate and peroxide utilization efficiency in ISCO.

Molecular Hydrophobicity Signature in Charged Bidimensional Clay Materials.

The unraveling of the hydrophobicity/hydrophilicity molecular signature of nanometric bidimensional confined systems represents a challenging task with repercussions in environmental transport processes. Swelling clay minerals represent an ideal model system, as hydrophobicity can be modified during material synthesis by substituting hydroxyls by fluorine in the structure, without additional surface treatment. This following work presents a combined approach, integrating experimental inelastic neutron scattering spectroscopy and ab initio molecular dynamics simulations, with the objective of advancing our understanding of the role of surface hydroxylation/fluorination and the extent of confinement on water properties. From computed structures, the analysis of molecular hydrophobicity/hydrophilicity signature was investigated in detail through water-cation-surface interactions. The results elucidate the influence of fluorination on interlayer species, thereby tracing the impact of the surface on the diminished number of water molecules in such a sample. It is notable that the strong cation-water interaction can overcome the disruptive influence of fluorine, thereby maintaining comparable water hydration shells around cations and resulting in an almost identical bidimensional confinement geometry for both hydroxylated and fluorinated specimens. The analysis of the hydrogen-bond network revealed a significant reorganization of the water molecules due to fluorination. Our results suggest that a quantitative molecular signature of hydrophobicity/hydrophilicity can be derived from the analysis of the formation of cavities in the confined fluid. This new finding represents a robust approach for generalizing the hydrophobicity/hydrophilicity character for a wide variety of bidimensional systems while proposing a framework for the design of new materials with controlled water properties.

Soils of Tundra and Sub-Tundra Larch Open Woodland of Tit-Ary Island (Delta of the Lena): Genesis, Properties, and Distribution Trends

Physico-chemical properties and vertical distribution patterns of clay minerals were studied in the permafrost affected soils from the tundra and sub-tundra larch open woodland of Tit-Ary island. That unique complex is located in the delta of the Lena river, Republic of Sakha (Yakutia). Despite the small size of the island and the fact that permafrost is close to the surface, several variants of pedogenesis determine the soil diversity in this area. The soils are characterized by various degrees of gleyic and stagnic properties due to sandy or loamy texture and location in the landscapes (top of the hills as well as steep or gentle slope). Mineral association is the same in the studied profiles characterized by the predominance of two components – chlorite and illite. Iron hydroxide–lepidocrocite occurred on the boundary of permanently frozen ground in the profile within pronounced spodic features as well as smectitic clay indentified in the both horizon of this permafrost affected soil can be attributed as a result of modern pedogenesis.

Short wavelength infrared (SWIR) spectral and geochemical characteristics of white micas in the Xiaonangou gold deposit, East Qinling: As a hyperspectral tool in exploration

The Xiaoqinling-Xiong’ershan region, a prominent component of the East Qinling Belt, is renowned worldwide for its molybdenum and gold ore fields. Moreover, with gold reserves of at least 1300 tons, it is also China’s major gold mining province, second only to Jiaodong. Seated in eastern center of the Xiong’ershan area, the Xiaonangou gold deposit has an estimated gold reserve of over 60 tons and is characterized by disseminated gold in altered rocks. Based on detailed petrographic investigation, coupled with an analysis of crosscutting relationships, there are three stages of hydrothermal alteration and mineralization: pre-ore K-feldspar + quartz (stage Ⅰ), ore quartz + ankerite + disseminated pyrite + polymetallic sulfide (stage Ⅱ), and post-ore quartz + carbonate (stage Ⅲ). As revealed by a systematic analysis of short wavelength infrared (SWIR) spectroscopy, four main types of alteration minerals exist, including white micas, clay minerals, chlorite, and carbonate minerals. In the ore body, white micas mainly developed in stage Ⅱ, and slightly occurred in stage Ⅰ. The clay minerals and chlorite usually developed in the banded alteration zones outside the orebody. Most of the carbonate minerals, including calcite and dolomite, mainly developed in stage Ⅲ, but the ankerite was associated with disseminated pyrite, quartz and polymetallic sulfides in stage Ⅱ. Of these, white micas were recognized as the most abundant hydrothermal alteration minerals, which were observed to be widely distributed within alteration zones in the Xiaonangou gold deposit. The SWIR parameters and its spatial variation of white mica indicate that the Al-OH absorption positions (Pos2200) exhibit a drifting tendency towards longer (>2205 nm) wavelengths in the ore body vicinity. Additionally, there is a discernible increase in illite crystallinity (IC values) in the same region. The temperature, redox, and pH conditions for associated fluids can be reflected through characterization of these parameters. Furthermore, it demonstrates that the ore-proximal zones are situated in a relatively oxidized, alkaline, and high-temperature environment in the Xiaonangou gold deposit. According to the electron probe microanalysis (EPMA) results, two distinct end members exist in white mica: a Si-poor, Al-rich muscovite and an Al-poor, Si-, Fe-, and Mg-rich phengite. The Si, ivAl, viAl, Mg, Fe, and Ti elements exhibit a linear correlation with the wavelength of Pos2200, demonstrating that the shift in wavelength of white mica is predominantly controlled by Tschermak substitution (ivSivi(Mg，Fe) ↔ivAlviAl). The application of spatial variation in the SWIR spectral parameters along with geochemical properties of white mica facilitates the effective guidance of mineral exploration. In comparison to other deposits, it can be concluded that the longer (>2205 nm) wavelength of the Pos2200 along with the higher IC values (>1.4) of white mica are applicable as valid vectors towards gold mineralization in the Xiaonangou gold deposit.

Controlling factors of fluid mobility in the tuff reservoirs of the Huoshiling formation, Dehui fault depression, southeastern Songliao Basin: insights from micro-nano pore structures

This study addresses the unclear understanding of the primary factors controlling fluid mobility in the tuff reservoirs of the Huoshiling Formation from the Dehui Fault Depression, southeastern Songliao Basin. Through physical property analysis, X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), thin section (TS), pressure-controlled porosimetry (PCP), rate-controlled porosimetry (RCP), and nuclear magnetic resonance experiments (NMR) on ten tuff samples, we conducted a comprehensive and in-depth exploration of the influencing factors that control the mobility of reservoir fluids. The results indicate: 1) The primary mineral types in the tuff reservoirs are quartz, feldspar, and clay minerals, with porosity predominantly characterized by dissolution pores and intergranular pores; 2) Based on the morphology of PCP intrusion curves, the tuff samples from the study area can be categorized into three types, with reservoir quality progressively deteriorating from Type I to Type III; 3) Compared to the movable fluids saturation (MFS), movable fluids porosity (MFP) is more suitable for characterizing fluid mobility. The mobility of fluids is influenced by various factors such as mineral composition, physical property, pore-throat connectivity, pore type and heterogeneity. MFS and MFP show a positive correlation with permeability, the content of quartz and feldspar, median pore-throat radius (R50), average throat radius (ATR), average pore-throat radius ratio (APT), T2 cutoff value (T2-C), average throat radius (RT), sorting coefficient (SC), and intergranular pore dominate space (Inter-DS), while a negative correlation with the content of calcite and clay minerals, average pore-throat radius ratio, and the fractal dimension from NMR (DNMR). This study elucidates the influencing factors of fluid mobility in tuff reservoirs, which has important reference significance for the scientific development of this type of gas reservoir.

Clay Mineralogy and Solution Chemistry of Waterlogged Saline Soil Undergone Subsurface Drainage: Study from North-Western India-Western India

Clay Mineralogy and Solution Chemistry of Waterlogged Saline Soil Undergone Subsurface Drainage: Study from North-Western India-Western India

Distribution of trace elements and rare earth elements in coal from the Bhalukasba Surni coal block, Rajmahal coalfield, Eastern India

AbstractExploration of secondary resources for isolation of valuable constituents, such as rare earth elements (REEs) and trace elements (TEs), is of importance owing to the need to identify new domestic sources and reduce reliance on imports. The present study systematically discusses the distribution of REEs and TEs in core samples from the coal block of Bhalukasba Surni {(B1(125 m)-B9 (409 m)} located in Rajmahal coalfield, Jharkhand, India, which has not been investigated previously for its geochemistry. The studied coal samples were found to be enriched in TEs whose abundances were in the order of Mn &gt; Mo &gt; Zr &gt; Ni &gt; Cr &gt; V &gt; Cu &gt; Zn &gt; Pb, and REEs (La, Ce, Pr, Nd, Sm, Eu, Gd, Dy, Er, Tm, Yb, Lu) along with Sc and Y. The average concentration of REEs with yttrium (ΣREY) on an ash basis was 528 ppm, which is significantly higher than the world average for coal ash (435 ppm). Of the samples investigated, B3 (182–184 m) and B8 (396–399 m) demonstrated relatively higher concentrations of potentially economic elements, with B3 containing a higher proportion of middle to heavy REEs Gd, Dy, Ho and Er, and B8 showing relative enrichment in Nd and Y. On dry whole coal basis, B6 (275–278 m) showed a considerably higher concentration of Ge (55 ppm) than other samples, whereas the concentration of Zr varied in the range of 90–160 ppm in the whole coal block. X-ray diffraction studies revealed the presence of quartz, keatite, hematite, zircon, anatase and orthoclase in the coal ash samples prepared at 815 °C. REEs exhibited prominent positive correlation with Al2O3 (0.4 &lt; r &gt; 0.9) which is supportive of their residence in primary clay minerals such as kaolinite and illite-smectite. Additionally, a positive correlation of REEs with P2O5 (0.4 &lt; r &gt; 0.9) suggests their association with phosphate minerals (such as monazite, xenotime, apatite). Positive correlation with TiO2 (r &gt; 0.7) corroborates the possible association of REEs with anatase. The morphology of the coal ash samples viewed in SEM showed the presence of Al2O3 and SiO2 enriched irregular-sponge particles likely derived from partly-fused clay minerals, which accounted for the lower extent of REE encapsulation. The Bhalukasba Surni coal block is potentially of economic importance due to its enrichment in Ge, Zr, and the REEs.

A mechanistic model for the complex conductivity of clay materials. I. Theory

Summary Clay materials are ubiquitous in the Earth's continental and oceanic crusts. They are characterized by a large specific surface area, and, in contact with water, they have remarkable adsorption, catalytic and containment properties. Clay materials also exhibit a high electrical conductivity response associated with their large surface. However, sedimentary clay minerals have a complex microstructure and electrochemistry that are not fully understood and make the quantitative petrophysical interpretation of geoelectrical measurements difficult. In this study, we have developed a new mechanistic model to better understand and predict the complex conductivity of clay materials from their microstructure and electrical double layer properties. For the conductive component, our model considers ion electromigration in bulk water, clay electrical diffuse layer, and interlayer space, if any. Concerning polarisation, it takes into account ion back-diffusion in the Stern layer and in the interlayer space, if any, and also Maxwell-Wagner effect. Water and clay surface conductivities, formation factor, cementation exponent and sample electrically connected porosity can be extracted from the comparison of the model to experimental data. This study is a step forward to better understand and quantify the complex conductivity of clays observed during electrical and electromagnetic measurements, from laboratory to geological formation scales.

Deciphering Whether Illite, a Natural Clay Mineral, Alleviates Cadmium Stress in Glycine max Plants via Modulation of Phytohormones and Endogenous Antioxidant Defense System

Globally, cadmium (Cd) stress dramatically reduces agricultural yield. Illite, a natural clay mineral, is a low-cost, environmentally acceptable, new promising method of reducing the heavy metal (HM) stress of cereal crops. In research statistics, there is little research on stress tolerance behavior of Illite (IL) on an experimental soybean plant. In the present study, we took IL and examined it for tolerance to Cd, as well as for other plant-growth-promoting (PGP) characteristics in Glycine max (soybean). The results showed that applying clay minerals in different concentrations enhanced the level of SA (defense hormone) and reduced the level of ABA (stress hormone). Cd 1 mM significantly reduces plant growth by altering their morphological characteristics. However, the application of IL significantly enhanced the seedling characteristics, such as root length (RL), 29.6%, shoot length (SL), 14.5%, shoot fresh biomass (SFW), 10.8%, and root fresh biomass (RFB), 6.4%, in comparison with the negative control group. Interestingly, IL 1% also enhanced the chlorophyll content (C.C), 15.5%, and relative water content (RWC), 12.5%, in all treated plants. Moreover, it resulted in an increase in the amount of superoxide dismutase (SOD), phenolics, and flavonoids in soybean plants, while lowering the levels of peroxidase (POD) and H2O2. Furthermore, compared to control plants, soybean plants treated with the Illite exhibited increased Si absorption and lower Cd levels, according to inductively coupled plasma mass spectrometry (ICP-MS). Thus, the IL can operate as an environmentally beneficial biofertilizer and sustainable approach under Cd stress by promoting plant development by activating signaling events.