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Concentrating simple organic molecules, such as amino acids, in the adsorbed phase could have been an early step in prebiotic evolution towards more complex bio-macromolecules on the early Earth. Smectite clay minerals represent potential selective sorbents for prebiotic molecules because of their negative structural charge and high surface area. This study evaluated the adsorption behavior of amino acids to montmorillonite, a well-characterized smectite, at varying pH and fluid compositions. At both pH 5 and 7 in a sodium chloride fluid, amino acids with basic sidechains (L-arginine and L-lysine), which are primarily cationic under these conditions, were selectively adsorbed to montmorillonite with Langmuir constants much greater than amino acids that were predominantly zwitterionic or anionic in solution. On average, the Langmuir constants for the cationic amino acids were 30 (pH 5) and 50 (pH 7) times greater than the constants for zwitterionic amino acids and 120 (pH 5) and 80 (pH 7) times greater than the constants for L-glutamic acid. Under the same pH conditions in a magnesium chloride solution, the adsorption of L-arginine and L-lysine was substantially inhibited with Langmuir constants ∼ 10 times smaller. These observations suggest that cation exchange is the dominant adsorption mechanism for amino acids on montmorillonite. X-ray diffraction and infrared spectroscopy indicate that L-arginine and L-lysine enter the smectite interlayer where the protonated amino sidechain has the strongest interactions with the mineral surface, further supporting adsorption driven primarily through electrostatic interactions. Therefore, smectites on the early Earth may have selectively concentrated cationic amino acids, providing a potential template for the polymerization of α-amine linked peptides. [ABSTRACT FROM AUTHOR]

Smectites are reactive minerals that are present in surface environments. Most of the smectite dissolution kinetics reported in the literature are related to Al-rich smectites, whereas Fe(III)-rich smectites, which are commonly found in soils, have not been well studied. In this study, the impact of structural Fe(III) in smectites on the dissolution kinetics is determined under acidic conditions. The dissolution kinetics of three pure Fe(III)-rich smectites with different crystal chemistries (Si 7.16 Fe3+ 0.84)(Fe3+ 3.46 Mg 0.54)O 20 (OH) 4 Na 1.38 , (Si 6.86 Fe3+ 1.14)(Fe3+ 4)O 20 (OH) 4 Na 1.14 , and (Si 7.34 Fe3+ 0.66)(Fe3+ 4)O 20 (OH) 4 Na 0.66 are investigated at 25 °C using flow-through experiments at pH values between 1.8 and 5.5. The measured dissolution rates are compared with published rates for Al-rich smectites. The concentrations of dissolved Si, Fe and Mg are measured as a function of time, and the retrieved residual solids are analyzed via infrared spectroscopy and transmission electron microscopy. The steady-state dissolution rates of the synthetic smectites, calculated from the amount of Si release (R Si), decrease with increasing pH. A comparison of the dissolution rates as a function of pH does not allow us to observe major effects of the crystal chemistry among the synthetic smectites, demonstrating the need to develop another approach. However, the dissolution rates calculated for synthetic Fe(III)-rich smectites are systematically greater than those of Al-rich smectites. The measured dissolution rates decrease as the aqueous system approaches equilibrium. Different behaviors are observed for Fe(III)-rich (i.e., > 4 Fe(III)/O 20 (OH) 4) and Al-rich smectites as the R Si = f(ΔG) functions differ, with Fe(III)-rich smectites exhibiting greater instability than Al-rich smectites. Under the most acidic conditions investigated (pH 1.8 and 2), the crystal chemistry and mineralogy of the smectite changed during dissolution, with a relatively greater loss of tetrahedral Fe than of octahedral Fe and the formation of amorphous silica phases. These results show that the amount and location of structural Fe(III) in smectites impact the stability of the minerals. This suggests that the dissolution rate of smectites as a function of the ionic activity product classically used to describe reactive transport should consider the effects of the crystal chemistry, in particular, the amount of structural Fe(III), which is rather high, especially in soil smectites. [ABSTRACT FROM AUTHOR]

Clay minerals have great potentials in pinpointing sediment provenance for large depositional systems. However, source identification using clay minerals for small floodplain lakes is not well known. Situated in the North China Plain, the Dongping Lake receives sediments from both the Yellow River and the Dawen River, thereby representing an ideal site for testing the utility of this method. Here we use clay minerals in conjunction with the Bayesian end-member modeling analysis (BEMMA) to quantify the riverine contribution to modern sediments in the Dongping Lake. Results showed that modern sediments of the Dongping Lake are characterized by four primary clay minerals: illite, smectite, kaolinite, and chlorite, with average contents of 60.53%, 11.37%, 12.70%, and 15.40%, respectively. Clay minerals in modern sediments of the Dongping Lake are mainly delivered by the Yellow River, accounting for approximately 58.99–72.33%; whereas those originating from the Dawen River only account for 27.67–41.01%. It is also found that clay mineral from these rivers have a marked spatial variability. For example, source materials from the Yellow River are widely distributed across the lake, while those from the Dawen River only occur at the estuary of the river and slightly spread out in all directions under the action of water flow. [ABSTRACT FROM AUTHOR]

Iron(II)-bearing trioctahedral smectites (saponites) form during anoxic alteration of basaltic rock. They are predicted to have been widespread on the early Earth and are observed in the oceanic subsurface today. Smectite structures, including the occupancy of sites in the octahedral sheet, affect iron redox behavior but the rates and products of trioctahedral smectite oxidation have been largely unexplored to date. In this study we synthesized two Fe(II)-bearing trioctahedral smectites, one moderate (22 wt% Fe) and one high (27 wt% Fe) in iron content. We then examined the rate, extent, and products of their oxidation by dissolved oxygen, nitrite, and hydrogen peroxide. Dissolved oxygen caused partial oxidation of Fe(II) in the smectites with 14 to 43% of Fe(II) unoxidized after 20 to 30 days of exposure. The rate and extent of oxidation correlated with the dissolved oxygen concentration and the Fe(II) content of the clay. The incomplete oxidation in these experiments is consistent with the mixed-valent trioctahedral smectites observed in oxidized natural samples but contrasts with the complete reoxidation by oxygen shown by chemically- or microbially-reduced dioctahedral smectites. Oxidation of structural Fe(II) by 5 mmol L−1 nitrite was negligible for the moderate-iron smectite and yielded only ∼17% oxidation after 54 days of reaction for the high-iron smectite. Hydrogen peroxide caused rapid and near-complete oxidation of both clays. Powder X-ray diffraction, variable-temperature Mössbauer spectroscopy, and extended X-ray absorption fine structure spectroscopy together detected no crystalline or short-range-ordered secondary phases and show that oxidized iron remained in the trioctahedral smectite structure. The recalcitrant Fe(II) pool in oxidized trioctahedral smectites exists in less distorted sites than Fe(II) in the initial clays. Its unreactive nature at prolonged reaction times indicates an elevated redox potential generated by the local coordination environment. Slower oxidation rates create a larger recalcitrant Fe(II) pool, suggesting kinetic competition between oxidation and a process involved in redox stabilization, such as electron exchange between octahedral iron sites or deprotonation of hydroxyl groups in the structure. The resistance to complete oxidation of trioctahedral ferrous smectites and their full retention of iron demonstrates that transitions from anoxic to oxic conditions generate mixed-valence smectites rather than a mixture of new phases. Identifying the diagenetic products of mixed-valent trioctahedral smectites may provide an indicator in the rock record of past redox cycling. Substantial portions of structural Fe(II) in trioctahedral smectites display slow abiotic oxidation kinetics and represent potential electron donors for both microaerophilic iron oxidizing and nitrate-reducing, iron-oxidizing microorganisms in altered mafic rocks and related settings. [ABSTRACT FROM AUTHOR]

Amorphous calcium carbonate (ACC) is known as a precursor to crystalline calcium carbonate polymorphs (CaCO 3) in various natural and synthetic systems. While ACC has been shown to form by heterogeneous nucleation in biological systems, it is less obvious whether it plays any role in inorganic settings where carbonate minerals grow on pre-existing surfaces. Tight assemblies of calcium carbonate (CaCO 3) phases and clay minerals occur in rock-forming quantities in marlstones, are abundant in Earth's critical zone, in the sediments of aqueous environments, and in the atmosphere as aerosol particles. Previous studies suggested that the co-occurrence of clay and carbonate minerals (especially smectite and calcite) results from the heterogeneous nucleation of CaCO 3 on the surface of smectite. In order to understand the role of ACC in the heterogeneous nucleation of carbonate minerals and the effects of common silicate mineral surfaces on the stability of ACC, we synthesized ACC both in the presence and absence of smectite, kaolinite, and quartz, monitored the pH of the solution during the experiments, and studied the precipitated phases with various transmission electron microscopy techniques. Since Mg2+ and (PO 4 3−) ions are known to prolong the lifetime of ACC and are important components in natural aqueous environments, we tested their effects on ACC transformation in both homogeneous and heterogeneous systems. In all studied systems ACC was the first condensed carbonate phase. The presence of smectite in the solution reduced the lifetime of ACC and led to the rapid formation of calcite. We suggest that the main factor driving the transition was the enhanced growth of ACC particles on the surfaces of smectite flakes. On the other hand, the presence of kaolinite and quartz slightly increased ACC stability; ACC typically rimmed the silicate particles and transformed slower than separated, individual ACC particles. When Mg2+ was present in the solution, ACC stability significantly increased and led to the formation of aragonite instead of calcite in both homogeneous and heterogeneous systems. The presence of (PO 4)3− ions caused only a minor delay in ACC transformation and the crystalline product was calcite, irrespective of the presence of silicate minerals. These observations suggest that smectite minerals play important roles in the formation of carbonate minerals by providing a suitable surface for the rapid growth and coalescence of ACC particles, leading to larger particle sizes which, in turn, result in the conversion of ACC into calcite. [ABSTRACT FROM AUTHOR]

Clay minerals are ceramics materials that are involved in a wide range of economic uses. But, their structure and composition are modified by heating and, consequently, compromise their final applications. The actual temperatures at which changes occur vary greatly from one group to another group and even for different specimens within a given group. The aim of this research has been to evaluate the thermal behaviour of a set of design swelling micas, Na-Mica- n (M n) and compare them with a set of natural smectites. All samples were heated in the range 200 °C to 1000 °C; afterwards, they were rehydrated thorough water suspension (0.4% wt). The results have shown that swelling micas have better property of hydration/dehydration than natural clay minerals and those with higher layer charge exhibited higher rehydration ability and dehydration temperature. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • Smectites doped with Ni(II), Cu(I) or Ag(I) show a remarkable styrene uptake. • The d-block metals induced high selectivity for π-electron-rich styrene molecules. • DFT supported higher affinity of the beidellite mineral towards styrene. • Trends in adsorption energies explained different efficiencies of the adsorbents. • Desorption of styrene in time was not observed suggesting strong bonding. Two natural smectite minerals (montmorillonite and beidellite) differing in structural charge location were impregnated with varying amounts of transition metals: Ni(II), Cu(I) or Ag(I). The modification aimed to increase the affinity of the minerals towards styrene vapors. The structure, texture, chemical composition and surface chemistry of the materials were studied by XRD, FTIR, Raman, N 2 adsorption/desorption, XRF and XPS. The experiments examined the influence of the starting smectite and the type of introduced metal on styrene adsorption efficiency. The styrene uptake mechanisms were investigated through solid state analysis and supported by DFT calculations. The study demonstrated that the small content of introduced metals (<2% wt.) substantially increased styrene uptake (∼200–350% wt.) surpassing values reported for surfactant-intercalated smectites (∼40–80% wt.) and activated carbons (∼30% wt.). This enhancement was attributed to the π-complexation between dispersed d-block metals and π-electron-rich styrene molecules, subsequently leading to polystyrene formation. The DFT calculations were consistent with experimental findings, indicating a higher affinity of the raw beidellite towards styrene than the raw montmorillonite connected to the charge location. Moreover, the observed trends in calculated adsorption energies and lengths of weak hydrogen bonds allowed to explain a significant adsorption increase observed for the Ni- and Cu-impregnated montmorillonite-based materials. [ABSTRACT FROM AUTHOR]

• The curing temperature does not induce significant physicochemical or structural changes on metakaolin based geopolymer. • The argillite based geopolymers display a decrease in pH values and an increase of the amorphous content when cured at 80°C. • 29Si, 27Al and 1H MAS-NMR evidenced the formation of different networks under the effect of temperature due the dissolution of Argillite's associated minerals. This study investigates how the curing temperature can enhance the reactivity of poorly reactive aluminosilicate source for geopolymer synthesis using a structural approach. The studied geopolymers are based on different aluminosilicate sources, a metakaolin and argillite, under varying curing temperatures (20 and 80°C). The impact of curing temperature on the reactivity of the two aluminosilicate sources and on the resulting consolidated materials was highlighted using pH value measurements, X-ray diffraction (XRD), and MAS-NMR for silicon (29Si), aluminum (27Al), and hydrogen (1H) nucleus. Metakaolin-based samples exhibited stable pH values, unvaried amorphous content, and structural consistency whatever the curing temperature. In contrast, argillite-based samples showed a significant drop in pH values (from 13 to 12) and a rise of amorphous content when cured at 80°C, indicating a reactivity change with temperatures. This was corroborated with MAS-NMR analysis, that highlighted a dissolution of the associated minerals such as illite and smectite. It was evidenced the presence of the geopolymer phase Q4(2Al) and Q4(3Al), in addition to two other networks based on silicon (Q4(1Al) and Q4(0Al)), and on aluminum Q4(4Al). The 1H MAS-NMR corroborated this finding by an increase of the bounded water (the band at 4.8 ppm) in the geopolymer network. All these data underline how temperature influences the reactivity of geopolymer materials, especially argillite-based samples by enhancing the dissolution of associated minerals (illite muscovite and smectite). [ABSTRACT FROM AUTHOR]

Protein therapeutics hold immense promise for treating a wide array of diseases. However, their efficacy is often compromised by rapid degradation and clearance. The synthetic smectite clay Laponite emerges as a promising candidate for their sustained delivery. Despite its unique properties allow to load and release proteins mitigating burst release and extending their effects, precise control over Laponite-protein interactions remains challenging since it depends on a complex interplay of factors whose implication is not fully understood yet. The aim of this review article is to shed light on this issue, providing a comprehensive discussion of the factors influencing protein loading and release, including the physicochemical properties of the nanoclay and proteins, pH, dispersion buffer, clay/protein concentration and Laponite degradation. Furthermore, we thoroughly revise the array of bioactive proteins that have been delivered from formulations containing the nanoclay, highlighting Laponite-polymer nanocomposite hydrogels, a promising avenue currently under extensive investigation. [Display omitted] [ABSTRACT FROM AUTHOR]

In diagenetic solutions, ammonium may be incorporated into smectites as an exchangeable cation and become fixed within the interlayer space of illites and other white micas. To study the potential impact of NH 4 + on the smectite-to-illite transformation reaction, a series of hydrothermal experiments were carried out at 100, 150 and 200 °C, spanning reaction duration from 15 to 90 days, and two NH 4 + concentrations (0.1 and 0.2 M). The solids resulting from these alteration experiments were characterized using X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), and transmission and analytical electron microscopy (TEM and AEM). The XRD analysis revealed that, under the specified experimental conditions, smectite incorporates NH 4 + in the structure, leading to the formation of non-swelling layers, resulting in partial transformation to illite layers and producing packets of disordered illite/smectite (I/S). In addition, a minor XRD peak at ∼10 Å suggests the formation of discrete illite crystals. The FTIR spectra demonstrated the uptake of NH 4 +, with deformation bands observed at 1400 and 1430 cm−1, corresponding to exchangeable NH 4 + in smectite and fixed NH 4 + in high-charge layers, respectively. TEM analysis revealed that smectite particles exhibited wavy stacks comprising a few layers with abundant defects and lateral discontinuities. The interlayer spacing in these particles ranged from 12 to 15 Å and became thinner and more plate-like with increasing temperature and time. Moreover, they contained inclusions of 10–10.3 Å layers, either as discrete layers or in packets of several layers, indicating the formation of disordered mixed-layer illite-smectite. Lateral transitions from 12 to 15 Å to 10 Å layers were frequently observed and interpreted as reaction fronts due to local rearrangement. At 150 and 200 °C, isolated packets of 10 Å layers were identified as discrete illite crystals that precipitated directly from solution. Analysis of the chemical composition of individual particles revealed an increase in octahedral charge (MgVI for AlVI substitution) in smectite particles, followed by increase in tetrahedral charge in I/S particles. Interlayer NH 4 + played a stabilizing role in the high-charge layers and favored the smectite-to-illite conversion process. • Smectite transforms into illite under alkaline (NH 4 +) hydrothermal solutions by NH 4 + adsorption at the interlayer spaces. • Dissolution and NH 4 + fixation convert smectite to illite, increasing AlIV and MgVI, and forming disordered I/S structures. • The process is further enhanced with higher temperature, prolonged reaction times, and increased NH 4 + concentration. [ABSTRACT FROM AUTHOR]

Water is a ubiquitous adsorbate relevant for many natural systems and engineering applications. Water adsorption behavior on clays, sediments, soils, and related geomaterials was studied for over a century and fueled a continuous discussion on the meaning of water sorption as a measure of mineral surface area (MSA). Despite this, MSA quantification using nitrogen established itself as the most widely accepted approach despite the relevance of water for a wide spectrum of in-situ environmental conditions. Many attempts at water-based MSA measurements are reported in dispersed literature. To date, interlaboratory comparison of MSA has been hampered by disparate methodologies for conducting measurements using both water and nitrogen adsorbates. Water and nitrogen-based MSA both using the BET equation for a variety of minerals and mineral matrices relevant for earth, environmental, and clay science was compiled in this contribution. The historical development of water-based MSA determination is also reviewed. The overlay of multitude of factors including mineralogy, interlayer spaces, organic matter, structural water, electrostatic interactions, microstructure, sample preparation and measurement conditions, influencing both nitrogen and water-based MSA quantities are discussed and general guidance is provided on the interpretation of complex MSA datasets. • Superimposed effects influence mineral surface area quantification • N2 and H2O mineral surface area quantification methods are both biased and can be complementary • Basic research is needed to retrieve accurate mineral surface area quantities from complex matrices [ABSTRACT FROM AUTHOR]

This work focuses on the study of the trace elements allocation in smectites throughout the statistical analysis of geochemical data corresponding to a very wide group of pure or almost bentonite samples. Data of trace elements contents corresponding to both analysed samples and bibliographic references were treated with different statistical analysis such as Partial Least Squares Discriminant Analysis (PLS-DA), Wilcoxon-Mann-Whitney rank sum test (WMW test). A clear relationship between trace elements and smectite crystallochemistry was evidenced from the PLS-DA results because the contents in certain the trace element separated the dioctahedral smectites from the trioctahedral smectites. In addition, the WMW test indicated that dioctahedral smectites preferentially accumulate Er, Eu, Gd, Sm, Tb, Nd, Ga, Dy, Ho, Tm, Be, Y, Yb, La, Pb, Ce, Lu, Pr, Hf, Bi, Zr, Zn, Nb, In, Th, Ta, Sn, and Ge, while trioctahedral smectites preferentially accumulate As. Complementary analysis by X-Ray Micro-Fluorescence and a study after homoionization were done to help to discuss these results. According to these results, the presence of these elements as interlayer cations or their adsorption at layer edges has been excluded. In addition, external factors such as impurities and the geological origin of bentonites have been discussed and ruled out as influencing factors that could invalidate the obtained results. An evaluation of atomic parameters for trace elements indicates that As, with an effective cationic radius of 33.5 pm for coordination number CN = 4, can be allocated in tetrahedral positions, whereas the remaining elements can occupy octahedral positions. • Trace elements are associated with the crystallochemistry of smectites. • Dioctahedral smectites preferentially accumulate 28 trace elements. • Trioctahedral smectites preferentially accumulate As. • As could occupy tetrahedral positions. • The rest of trace elements could occupy octahedral positions. [ABSTRACT FROM AUTHOR]

• Mudstone top-seals such as silty-shales possess a wide range of grain sizes and so have complex heterogeneity of pore structure. • The combination of two fluid invasion methods allow a full range of pore body and pore throat diameter representation. • Shale mineralogy strongly influence the pore system and exposed surface area. Fine-grained lithologies above CCS reservoirs cannot automatically be assumed to be mineralogically stable, or high quality top-seals to highly pressured CO 2 as saline aquifer have previously contained hydrostatically pressured water. We have investigated the mineralogy, pore systems and surface area characteristics of the Lower Cretaceous Rodby Shale, the caprock to the Captain Sandstone at the UK's planned Acorn/Goldeneye CCS site. Rodby Shale core was logged and analysed by XRD, light microscopy, and SEM. Grain size was measured using laser particle size analysis. Mercury intrusion porosimetry and nitrogen adsorption analysis were used to characterise the pore network. The Rodby is smectite-rich and contains abundant calcite as well as quartz silt with small quantities of chlorite and plagioclase. Calcite was sourced from benthic microfossils, locally recrystallised to create a pore-filling cement. The mean pore throat and pore body diameter are about 17 nm putting the Rodby in the mesopore range and suggesting a predominance of slit-like pores. There are three lithofacies in the Rodby Shale: (i) high surface area clay-rich shale, (ii) low surface area calcite-rich shale, (iii) intermediate surface area quartz-rich. if the second lithotype encountered CO 2 , then the resulting calcite dissolution would lead to increasing surface area of the remaining shale. The Rodby Shale has good potential to be an effective barrier for CO 2 escape, based on assessments of diffusion rate and post-breakthrough advection rate as well as stability and sealing assessments. [ABSTRACT FROM AUTHOR]

Both natural and anthropogenically-generated hydrogen gas occurs in sedimentary rocks and geotechnical barriers. Due to high-pressure conditions, a significant portion of H 2 can be physisorbed in available micropores of clay minerals, which have been proven to control the gas adsorption properties of rocks. This study investigates H 2 adsorption on clay minerals naturally occurring in rocks, by combining the high-pressure H 2 experiments with sample characterization analyzed using low-pressure adsorption of N 2 and CO 2 , and structural analysis using X-ray diffraction. We found that H 2 adsorption depends strongly on the mineral texture, which is not related directly to its structure. Most of H 2 is adsorbed in the micropores accessible to CO 2. H 2 intercalates in the smectitic interlayers with a basal spacing larger than 10.8 Å. The density of adsorbed H 2 is about double that of free H 2 gas under given pressure and temperature, effectively increasing the gas storage capacity of rocks. • High-pressure H 2 adsorption was studied using pure illites and smectites. • H 2 intercalates in the smectitic interlayers with a basal spacing larger than 10.8 Å. • The majority of H 2 adsorption sites in smectites might be located in interlayers. • The adsorbed H 2 density does not depend on the cation form of the clay mineral. • H 2 adsorption depends on the mineral texture (e.g., crystallite planar dimensions). [ABSTRACT FROM AUTHOR]

Analyses of clay minerals within the Early Cretaceous Weald Basin, Southeast England reveal kaolinite, illite and chlorite as the main detrital clay minerals while glauconite and smectite are subordinates. A kaolinite-rich assemblage which characterized the sand-dominated Ashdown and Tunbridge Wells Sand formations and an illite-dominated assemblage associated mostly with the Wadhurst Clay and Weald Clay formations are recognized. Kaolinite was enriched in the Ashdown and Tunbridge Wells Sand formations during warm and humid climate with high precipitation that encouraged chemical weathering and leaching, while cold and dry conditions favoured the concentration of illite in the Wadhurst Clay and Weald Clay formations. Rainfall patterns associated with warm climate were drastically reduced during the drier climatic conditions. Most clay minerals are detrital in origin, with chlorite being more prominent than previously recognized. Contrary to previous studies and assumptions, this study revealed that authigenic clay minerals are present in the Hastings Beds, with vermiform and mica-replacive kaolinite being the most common, consistent with humid depositional environments. Isolated authigenic illite is also present, along with a chloritized grain, providing evidence for mesodiagenesis. The absence of dickite and occurrence of kaolinite, suggest that authigenic illite formed in relatively shallow burial conditions, indicating a maximum burial depth of 2500 m–3000 m, about 1000 m deeper than previous estimates of 1500 m–2000 m. Authigenic clay minerals are absent in the Weald Clay Formation possibly because of hindered flow of meteoric water and limited growth space for authigenic minerals. This study is significant in: 1) reinforcing multiple methods to facilitate a robust and balanced knowledge of formation and transformation of clay minerals; 2) investigating detrital and authigenic clay mineral assemblages when assessing the palaeoenvironments of sedimentary basins. [ABSTRACT FROM AUTHOR]

Humic substances (HS) are frequently incorporated into soils to improve soil health and nutrient availability. However, existing literature presents discrepancies regarding the soil-HS interactions and their impact on orthophosphate (inorganic phosphorus (IP)) adsorption, specifically, concerning the influence of soil clay mineralogy on these interactions. This study aims to investigate whether the impact of soluble humic acid (HA) on IP adsorption in semi-arid Mediterranean soils is contingent upon their clay mineralogy. This was tested by constructing IP- adsorption isotherms in the presence and absence of HA of four illite/smectite (I/S) or kaolinitic dominated soils. The results revealed that the addition of HA increased IP adsorption to I/S soils by up to 80%, yet IP did not affect HA adsorption to these soils. This suggests that while HA and IP are adsorbed onto different sites on the I/S clay, HA adsorption probably increases the number of adsorption sites accessible for IP. In contrast, IP and HA adsorption onto the kaolinitic soil was fully competitive: IP reduced HA adsorption and vice versa. It is suggested that new adsorption sites for IP resulted from the HA interactions with the I/S clay planar surfaces. In addition, HA moieties containing cationic (ionized) nitrogen, could possibly interact with clays to increase the number of platelets per tactoid. Unlike I/S clays, kaolinite that possesses low degree of isomorphic substitution, low net negative charge, and high degree of platelets stacking, does not tend to such interactions with HA. Instead, HA will be adsorbed mostly onto the clay edges, competing with IP on adsorption sites. • Humic acid (HA) – inorganic P (IP) adsorption to kaolinitic soil is competitive. • Dissolved HA increases IP adsorption to illite/smectite (I/S) soils by 5 to 72%. • HA increases IP adsorption through interactions with negatively charged clay surfaces. • HA increases the IP-buffering capacity of the I/S soils by up to 60%. [ABSTRACT FROM AUTHOR]

Detrital smectite is a ubiquitous clay mineral in marine sediments and has a variable total Fe, Al, and Mg composition depending on the source, i.e., bedrock or unconsolidated sedimentary strata, the smectite is derived from. Analyses of elemental composition of smectite minerals in marine sediments can help to differentiate the smectite sources and, thus, sediment provenance, with potentially far-reaching paleo-environmental implications. In this study, we investigated the smectite compositions of modern-latest Holocene seafloor surface sediments deposited offshore from the Amundsen Sea drainage sector, where the West Antarctic Ice Sheet is currently unstable and losing mass due to ocean-forced melting, to detect and understand the variabilities of their elemental composition and geographical distribution. The smectite composition in continental rise sediments was compared to that of potential source areas on the Amundsen Sea continental shelf and in the sub-Antarctic South Pacific basin. Furthermore, we analyzed the smectite composition of sediments in continental rise cores deposited during the last glacial and last interglacial periods to reconstruct source variations over glacial-interglacial cycles. In particular, high contents of Al–Fe-rich smectite indicate that the glacial sediments had been supplied from the coastal region around Pine Island Bay by the cross-shelf advance of the West Antarctic Ice Sheet during the last glacial period. This clearly contrasts with the smectite minerals in rise sediments deposited during the present and the last interglacial periods that are composed of two distinct smectite types (Mg-rich and Al-rich, respectively), indicating their supply from multiple sources. During interglacials, Mg-rich smectite is probably transported by Circumpolar Deep Water from the sub-Antarctic South Pacific basin to the continental rise, while Al-rich smectite is supplied as part of ice rafted debris and by marine currents from the coasts around the Amundsen Sea embayment. Our research demonstrates that analysis of the elemental composition of smectite minerals on the Amundsen Sea continental margin provides a valuable tool to trace variations in sources for detrital sediment components and their pathways throughout glacial-interglacial cycles. • Various types of smectite appeared in the continental margin sediments in the Amundsen Sea. • Elemental composition of smectite can differentiate sediment sources and their pathways during glacial-interglacial cycles. • New mineralogical proxy to trace the sediment provenance using smectite composition has been suggested. [ABSTRACT FROM AUTHOR]

• Adsorption of binary cations may behave distinctly when containing NH 4 +; • Impacts on cation adsorption follow as charge density > charge location > confinement; • Charge density vs. other factor greatly alters NH 4 + selectivity and recovery & uptake; • Co-ions affect cation selectivity and further regulate NH 4 + uptake and recovery; • Beidellite is only for NH 4 + recovery while montmorillonite is also for NH 4 + uptake. Ammonium (NH 4 +) salts have been extensively applied as nitrogen fertilizers that are essential for plant growth, while also cause a number of environmental problems. NH 4 + uptake by plants and recovery proceed mainly through cation exchange, where clay minerals play a central role. Herein, selective adsorption and release of NH 4 + at smectites/water interfaces are addressed using molecular dynamics simulations. Adsorption behaviors of cations are nearly unperturbed by co-ions, except NH 4 + at montmorillonite surface (0.75 e∙uc-1), and distinct from metal ions, inner-sphere NH 4 + seems non-competitive. Cation adsorption (amount and stability) is affected by charge density > charge location > confinement. Charge location and density reverse NH 4 + vs. K+ adsorption, while NH 4 + above the center of ditrigonal cavities has superior stability and emerges at high charge densities. Charge density rather than location and confinement greatly alters cation selectivity, and montmorillonite with low charge densities is strongly NH 4 +-selective favoring NH 4 + recovery while with high charge densities strongly K+-selective favoring NH 4 + uptake. Impacts of co-ions onto cation adsorption (promoting/inhibiting) are predicted under different conditions that further regulate NH 4 + management; e.g., for montmorillonite (0.75 e∙uc-1), Ca2+/NH 4 + facilitates NH 4 + recovery while K+/NH 4 + facilitates NH 4 + uptake. Impacts of co-ions are altered by charge density > confinement > charge location, and become magnified by stronger confinement and especially at higher charge densities. Montmorillonite is potential for both NH 4 + uptake and recovery depending on magnitude of charge densities and identification of co-ions, while beidellite is applicable only for NH 4 + recovery owing to superior adsorption stability. The comprehensive study for selective adsorption and release of NH 4 + at clay minerals/water interfaces is critical to understand NH 4 + uptake and recovery, and also facilitates development of NH 4 + scavengers. [ABSTRACT FROM AUTHOR]

Terrestrial silicate weathering records from the tectonically active Tibetan Plateau are crucial to explore the interactions among climate change, tectonic uplift and chemical weathering during the Cenozoic. However, the complex sedimentary facies changes and frequent occurrence of coarse lithologies related to intense tectonic uplift of the Tibetan Plateau have largely limited the reliability of bulk chemical weathering indexes to reveal the silicate weathering history. Here, we present detailed records of clay minerals and geochemical compositions from clay-sized (< 2 μm) sediments collected from the well-dated Huaitoutala section (ca. 15.3–1.8 Ma) in the NE Qaidam Basin to reconstruct the chemical weathering history of the NE Tibetan Plateau during the late Cenozoic. The relatively high (illite–smectite mixed layers + smectite)/(chlorite + illite) ratio indicates a strong silicate weathering intensity from 15.3 to 12.6. Ma, while a continuous decrease in this ratio since 12.6 Ma reflects a long-term decreasing intensity of silicate weathering. By comparing the clay mineral records with the climatic reconstruction and the tectonic events in the NE Tibetan Plateau, the results reveal that middle Miocene global cooling-related drying exerted a significant influence on the decreasing weathering intensity since ca. 12.6 Ma. Furthermore, the late Cenozoic episodic and persistent uplift of the NE Tibetan Plateau may have exerted an additional influence on the long-term decrease in weathering intensity. Specifically, the dramatic fluctuation in the silicate weathering intensity during ∼11–9.6 Ma is mainly due to uplift-induced provenance changes. Moreover, the fluctuating increase in the silicate weathering intensity during ∼8–5 Ma may have been caused by intensified East Asian summer monsoon precipitation. Our study suggests that both climate change and tectonic deformation controlled the chemical weathering intensity in the NE Tibetan Plateau during the late Cenozoic. • Detailed 15.3–1.8 Ma clay minerals records from the northeastern Qaidam Basin. • Long-term continuous weakening of silicate weathering intensity since 12.6 Ma. • Global cooling-related drying mainly caused weakening of silicate weathering. • Uplift-induced provenance change influenced weathering proxy during 11–9.6 Ma. • Increase in silicate weathering intensity during ∼8–5 Ma caused by monsoon rainfall. [ABSTRACT FROM AUTHOR]

Selected layered clay minerals of smectite group with different chemical composition (e.g. synthetic hectorite, synthetic smectite and natural smectite) were modified by rare earth cations such as Er3+ and a stochiometric mixture of Er3+/Yb3+. Raw and modified smectites were systematically heated up to temperatures ensuring their dehydration (400 °C), dehydroxylation (800 °C) and formation of new high temperature phases (1200 °C). The products of heating were investigated by terahertz-time domain spectroscopy to follow changes of their dielectric properties in the far-infrared region. The frequency-dependent refractive index of raw and modified clays was determined in the range of 0.2–3.8 THz (6.6–126.5 cm−1). The heating at 800 °C and above resulted in increase frequency dependent index of refraction and decrease absorption coefficient in comparison to the raw clays. The ion-exchanged smectites by rare earth cations further decreased the absorption coefficient of the samples heated at 1200 °C. Raw natural smectite sample revealed a low frequency band at 0.86 THz, already reported in the literature, which shifted to 0.67 THz after sample modification by rare earth cations. Heating of modified JP to 1200 °C resolved a new absorption band at ∼3.40 THz in the ceramic phase produced from raw natural smectite. • Cation exchange reaction was used for modification of clays by selected rare earth elements. • Effect of sample heating up to 400, 800 and 1200 °C was studied. • Terahertz time domain spectroscopy was used to study the refractive index dispersion. • The frequency dependence of absorption in THz region resolved new typical absorption bands. • The high temperature treatment can be used for synthesis of new ceramic phosphor materials. [ABSTRACT FROM AUTHOR]

The processes controlling aridity/humidity variations in mid-latitude Asia dust source regions on orbital timescales are unclear. Both insolation and polar ice sheets can affect the climate at mid-latitudes, but determining their individual contributions is challenging. Here we present a compilation of paleoclimate data (the content of smectite and aeolian sand, and the proportion of the hydraulic component) from sites in the Hexi Corridor and Alxa Plateau, located at the junction of the regions influenced by the mid-latitude East Asian Monsoon (EAM) and the Westerlies. Our objectives were to determine the links between aridity/humidity variations in this region and Earth orbital forcing and changes in high-latitude ice sheets. We found that the aridity/humidity variations in the Hexi Corridor and Alxa Plateau were paced mainly by the long eccentricity cycle (∼400 ka), facilitating roughly coherent beat in changes of the mass accumulation rate (MAR) and the excursions of thick/coarse loess layers L1, L5, L9, L15 and L24 on the Chinese Loess Plateau. Additionally, spectral analysis of the paleoclimate data revealed that the expression of the Mid-Pleistocene transition (MPT) was spatially variable. A transition between the dominant periodicities in the western Hexi Corridor and Alxa Plateau occurred at ∼0.9 Ma, but in the eastern Alxa Plateau this transition occurred at ∼0.7 Ma. Our data compilation also demonstrates an interval of wet climate in the Hexi Corridor and Alxa Plateau after ∼0.34 Ma, which is consistent with paleoclimate records from loess deposits in Westerlies-dominated Central Asia. We attribute this to insolation forcing via complex internal feedbacks in the Southern Ocean, involving the enhancement of the Atlantic deep-water circulation, and the interplay between Indian Monsoon and the Westerlies. Overall, our findings highlight the importance of the Earth orbital control of aridity/humidity cycles on the boundary of the EAM and the Westerlies in mid-latitude Asia. • Fluctuations of aridity in the Hexi Corridor and Alxa Plateau are dominantly paced by long eccentricity periodicity. • A clear shift of dominant periodicity at ∼0.9 Ma in western Hexi Corridor and Alxa Plateau • A phase of wetting after ∼0.34 Ma in Hexi Corridor and Alxa Plateau is linked to orbital forcing. [ABSTRACT FROM AUTHOR]

Mars once possessed liquid water on its surface. In investigations of aqueous conditions on early Mars, the Mars Science Laboratory rover Curiosity has provided mineralogical and geochemical data from lacustrine sediments of Gale Crater, site of a former lake. Recently, the top-down method for quantitative reconstruction of the chemical parameters of ancient pore water, based on exchangeable cation compositions in smectite and secondary minerals, was developed and applied to the Yellowknife Bay sediments in Gale Crater. Here we report the application of this method to lacustrine sediment from the Quela drill site in Gale Crater, in the Karasburg member of the Murray formation. The results show that the final pore water to interact with the sediments had the following chemistry: pH = 3.6–5.6, Eh > 0.22 V, molality of Na ({Na}) = 0.14–2.2 mol/kg, {K} = 0.0080–0.31 mol/kg, {Ca} = 0.021–0.21 mol/kg, {Mg} < 0.14 mol/kg, {Fe(II)} < 0.063 mol/kg, {Cl} = 0.096–2.6 mol/kg and {SO 4 } = 0.048–0.33 mol/kg. At two adjacent drill sites (Marimba and Sebina), the comparable mineral assemblages and smectite interlayer compositions imply that they have water chemistry similar to that of the Quela sediment. The inferred pore water was undersaturated with respect to halite by an order of magnitude, although the sediment contains halite. This suggests that the final water in the Quela sediment disappeared by freezing and sublimation rather than evaporation. One interpretation of the high Na and Cl concentrations of the final pore water at Quela is that the sediment was deposited in an arid climate at around 3.5 Ga. The high salinity of the final pore water at Quela relative to that at Yellowknife Bay suggests that climate may have shifted from semi-arid when the Yellowknife Bay formation was deposited to arid when the Karasburg member was deposited. Alternatively, the high salinity at Quela suggests that the post-depositional fluids at 2–3 Ga was enriched in Na. In contrast to low Na in the post-depositional fluids in the underlying Yellowknife Bay, the high salinity of the post-depositional fluids of the Quela suggests different origin and/or timing of the re-wetting events between these two sites. The acidic pH and high Eh suggest that the Quela sediment was intensively affected by oxidizing and acidic post-depositional fluids. The pH of the final pore water would not have allowed the preservation of Ca and Mg carbonates under attainable CO 2 partial pressures, which is consistent with the scenario of carbonate dissolution by acidic post-depositional fluids on Mars. [ABSTRACT FROM AUTHOR]

Carbonaceous chondrites contain both soluble and insoluble organic materials (SOM and IOM) which may have been produced in different environments via different processes or share possible genetic relationships. The SOM may have been produced from IOM during hydrothermal episodes on asteroids, and vice versa. The potential role played by the mineral matrix during these episodes (clay minerals of variable crystallinity) remains to be constrained. Here, we exposed a mixture of formaldehyde and glycolaldehyde with ammonia-bearing liquid water together with Fe-rich smectitic minerals to hydrothermal conditions mimicking asteroidal conditions. We used both amorphous gel of smectite or crystalline smectites in order to understand the influence of the crystallinity on the evolution of OM. The organo-mineral experimental residues were characterized at a multiple length scales using X-ray diffraction and microscopy/spectroscopic tools. Results evidence that some IOM polymerizes/condenses in the absence of Fe-rich smectites. Yet, the presence of Fe-rich smectites inhibits this production of IOM. Indeed, the interactions between the SOM and clay surfaces (interlayers or edges) reduce the concentration of SOM available for polymerization/condensation reactions, a necessary step for the production of IOM. In addition, the presence of OM disorganizes the crystallization of the Fe-rich amorphous silicates, leading to smaller crystal sized particles exhibiting a lower permanent charge. This might suggests that the smectite permanent charge distribution may help better constraining the origin and evolution of chondritic clay minerals. Altogether, the present study sheds new light on the organo-mineral interactions having occurred during hydrothermal episodes onto/within chondritic asteroids. Indeed, IOM formation from OM-rich aqueous fluids does not occur during the alteration of amorphous silicates. This would mean that IOM is either produced within pockets free of clay minerals or initially accreted as IOM-rich grain. Last, about ∼50 wt% of the initial C could not be removed from the clay minerals at the end of the experiments using classical solvent extraction protocols, demonstrating that a high fraction of the SOM in carbonaceous chondrites may have been overlooked. [ABSTRACT FROM AUTHOR]

Pearl River sediments have been reported to have changed greatly in composition due to the impact of human activities on erosion and landscapes in southern China since 2500 years BP. Here, sediments from four cores (PRD-1, PRD-3, PRD-6 and PRD-7) from the Pearl River Delta (PRD) were collected for high-density clay mineral analyses to determine the vertical variations in clay mineral compositions since the middle Holocene. The results showed that the clay mineral compositions of these four cores remained constant. In the PRD, the clay mineral assemblage dominantly consists of illite and kaolinite (averaging more than 85%), with smaller amounts of chlorite (averaging 10%) and scarce smectite (averaging 1%). The stable clay mineral assemblages in the PRD confirm that the clay mineral compositions of the sediments continuously supplied by the Pearl River have not changed. However, the smectite percentage in core PRD-7 increased by 7% downward from a depth of 12.4 m, which was correlated with the weathering of local volcanic materials and sediment transport in the east of the Pearl River under the influence of the Guangdong coastal current in winter. The stable clay mineral compositions in the core sediments indicate that the Pearl River sediments have accumulated naturally in the PRD instead of under the influence of human activities, which would have altered the compositions of the core sediments. [ABSTRACT FROM AUTHOR]

[Display omitted] Clay adsorption is a critical process responsible for the mobilization and cycling of potassium (K) on Earth's surface. Recent studies emphasized the potential of using stable K isotopes (δ41K) to understand chemical weathering. However, the direction, degree, and mechanism of K isotopic fractionation linked to clay K uptake during chemical weathering remain poorly constrained. This work investigated the mechanism of K adsorption on clays (kaolinite and smectite) and the isotopic fractionation in three experimental sets with K-containing solutions. The time-series experiments revealed that the adsorption and isotope equilibria were attained after less than 12-hour reaction. Potassium adsorption rate slowed down and its isotopic fractionation approached the steady-state during 15-day reaction. The pH-dependent experiments demonstrated that the percentage of clay K adsorption and the isotopic composition of adsorbed K (and aqueous K) display negative linear correlations. Net isotopic fractionation between adsorbed and aqueous phases (Δ41K ad-aq) remained near-constant (0.6–0.8‰), regardless of variations in pH ranging from 4 to 10. The concentration-control experiments demonstrated that the percentage of K adsorption decreased with increasing KCl concentrations from 0.005 to 20 mM. The δ41K values of aqueous K reached the minimum of −0.53‰ after 92.7% K adsorbed (initial KCl of 0.005 mM). Potassium adsorption was substantially suppressed as ionic strength (fixed by Na+) increased from 0.001 to 0.5 M without apparent Δ41K ad-aq variations. The K K -edge XANES demonstrated that primary K incorporated in clay lattice and surface KCl derived from sorbed K+ and Cl− synchro-dehydration can be identified after drying of clays. These features indicate that adsorbed K+ was bounded onto clays as outer-sphere complexes, which can be replaced with excess Na+ at high ionic strength. Based on experimental results, we cannot distinguish specific mineralogy regulation on K isotopic fractionation. In sum, isotopically heavy K is preferentially sorbed on clay minerals. The results confirm an equilibrium fractionation path independent of reaction time, pH, ionic strength, and initial KCl concentration. Observed K isotopic fractionation is best fitted by an equilibrium isotopic fractionation law with a fractionation factor α ad-aq of 1.00075. We highlight the opposite direction of K isotopic fractionation in clay adsorption and structural incorporation during chemical weathering, and their comparative contributions should be considered for future field investigations. [ABSTRACT FROM AUTHOR]

The most effective approach to mitigating the environmental impact of cement production is through the utilisation of pozzolanic materials to prepare blended cement. Calcined kaolinitic clays are one of the most promising materials to be used as supplementary cementitious materials (SCM) due to their final performances. However, there are locations where kaolinitic rocks are not available. This work presents the study of two dioctahedral smectite standards from the Clay Minerals Society (CMS), SWy-3 and SAu-1, to be used as references. After thermal activation optimisation, their pozzolanic performances are compared with those of low-grade kaolinitic clay. On the one hand, raw SWy-3 has an amorphous content of ∼80 wt%, considered montmorillonite, with quartz and feldspars. The optimum calcination temperature was 800ºC, at which the smectite is fully dehydroxylated (as determined by thermal analysis) but not completely amorphized (as shown by powder diffraction). After calcination (800ºC), with a median particle size by volume (D v,50) of ∼11 μm, ∼480 J/g were released at 7 days in the R3 test. On the other hand, SAu-1 has a higher amount of amorphous content, ∼96 wt%, which includes interstratified illite/smectite. The optimum calcination temperature was found to be 750ºC. This sample (D v,50 ∼10 μm) gave 452 J/g at 7 days in the R3 test. The optimised active smectites gave a pozzolanic activity comparable to clay with 30–35 % kaolinite, as determined, for the first time, by the R3 test. This work has established descriptors for the activation of natural smectites/bentonites and reference values for the resulting smectite-based SCMs. • Two reference smectites were activated at 750–800ºC with competitive pozzolanic performances. • R3 test gave the pozzolanic activities of optimally-calcined smectites to be used as references. • The calcination temperature should not cause total amorphization of the montmorillonite phase. • The presence of Al(V) species in the calcined montmorillonite is desirable but not required. • The strengths for PC-Mnt blends are similar to those from low-grade calcined kaolinitic clays. [ABSTRACT FROM AUTHOR]

Developing approaches to determine the modes of transport and weathering of mafic detrital minerals in natural sedimentary environments is critical to our understanding of sediment production, dispersal and provenance, as well as carbon capture under natural and enhanced weathering regimes. We integrated the characterisation of morphological and surface textures with the surface composition of recent detrital clinopyroxene grains concentrated in a sandy coastal area from the western North Island of New Zealand and a rocky shore area of Santa Maria Island in the Azores Archipelago. Using the compactness shape descriptor, 341 grains were subdivided into elongated, elongated angular, euhedral, angular and subangular groups, with each group further characterised using morphological and microtextural indicators of abrasion, breakage and dissolution/chemical weathering. In both studied environments, the clinopyroxenes are dominated by elongated to angular shapes with flat cleavage surfaces and conchoidal fractures. This is consistent with dominant subaqueous transport by rivers and longshore currents for New Zealand, and dominant wave action with limited sediment supply by rivers along the rocky shore of Santa Maria. More abundant subabraded and abraded shapes with bulbous and elongated depression microtextures are observed in New Zealand, which indicates additional effects by aeolian transport that are not seen in Santa Maria. Consistent with semi-quantitative EDS spot analyses that document fresh clinopyroxenes surfaces, chemical weathering textures are very rare to absent. In Santa Maria, sampling of recent beach sand was complemented by ∼125 kyr-old palaeobeach clinopyroxenes, but these yielded similar textural results without evidence for chemical weathering. However, the surface of these older clinopyroxenes includes small adhering smectite (typically <50 μm in width and a few μm in thickness) interpreted to reflect incipient cementation with buffering of acidic fluids by more reactive lithic fragments in the deposits. The lack of chemical weathering but pervasive evidence for mechanical breakage of clinopyroxenes indicate that, at the sand size, these minerals break faster than they dissolve due to frequent subaqueous and/or aeolian reworking in the studied high-energy environments and temperate climatic conditions. [ABSTRACT FROM AUTHOR]

A series of laboratory experiments are conducted to simulate the acidification and subsequent recovery of a sand aquifer exploited by in situ recovery (ISR) mining. A sulfuric acid solution (pH 2) is first injected into a column packed with sand from the Zoovch Ovoo uranium roll front deposit (Mongolia). Solutions representative of local groundwater or enriched in cations (Na+, Mg2+) are then circulated through the column to simulate the inflow of aquifer water. pH and major ion concentrations (Na+, Cl−, SO 4 2 − , Ca2+, Mg2+, K+) measured at the column outlet reproduce the overall evolution of porewater chemistry observed in the field. The presence of minor quantities of swelling clay minerals (≈6 wt% smectite) is shown to exert an important influence on the behavior of inorganic cations, particularly H+, via ion-exchange reactions. Numerical models that consider ion-exchange on smectite as the sole solid-solution interaction are able to reproduce variations in pH and cation concentrations in the column experiments. This highlights the importance of clay minerals in controlling H+ mobility and demonstrates that sand from the studied aquifer can be described to a first order as an ion-exchanger. The present study confirms the key role of clay minerals in controlling water chemistry in acidic environments through ion-exchange processes. In a context of managing the long-term environmental footprint of industrial and mining activities (ISR, acid mine drainage...), this work will bring insights for modeling choices and identification of key parameters to help operators to define their production and/or remediation strategies. • Laboratory column experiments can reproduce field observations at a mining site. • Ion-exchange reactions control the evolution of pH in an acidified sandy aquifer. • Swelling clay minerals, even at low concentrations, control the porewater chemistry. • A multi-site ion-exchange model can reproduce the behavior of H+ and major cations. [ABSTRACT FROM AUTHOR]

Clays have been extensively utilized in various fields due to their remarkable adsorption properties. In pharmaceutical and medical applications, they serve as potential excipients in pills. Emerging research demonstrated their effectiveness as vehicles for controlling drug release. Little has been elucidated, however, regarding the optimal clay characteristics for such applications. Therefore, this study aimed to investigate the influence of clay pores volume on the adsorption of isoniazid (INH), a key drug in tuberculosis treatments worldwide. To achieve this, seven clays were investigated to examine the impact of pores volume on the adsorption and release of INH. Chemical characterization of the clays was conducted using X-ray fluorescence (XRF) and Infrared vibrational spectroscopy (IR), while their mineralogical composition was determined through X-ray diffraction (XRD) and their pore volume by BET method via N 2 adsorption/desorption isotherms. Additionally, the interaction between clay and INH was evaluated using FT-IR, XRD, and Thermogravimetric Analysis (TGA). Kinetic adsorption studies were performed to determine the time to reach the equilibrium saturation of the clay by the drug, which was found to be around three hours for all clays. By comparing the pore volume of the studied clays, it became apparent that the clay with an optimal pore volume of approximately 0.100 cm3/g exhibited superior adsorption/retention compared to those with lower or higher volumes. Furthermore, in vitro INH release curves were obtained mimicking release conditions in the intestine (pH 7.4) for a duration of 5 h. It was clearly shown that the release of INH from the clays depend on the pore volume. Our results provided valuable insights into the optimal clay characteristics which would enhance the adsorption and release of INH. • Clays successfully release isoniazid, a drug used for tuberculosis. • Clays pore volume has a crucial role in drug adsorption and release. • An optimum pore volume guarantees a higher adsorption capacity. • An optimum pore volume guarantees a higher drug release performance. [ABSTRACT FROM AUTHOR]

• Dissolution of calcite, plagioclase and K-feldspar caused major elemental loss (to solutions) of Na, K and Ca in the BTG. • Weathering patterns were linked to seasonal hydrological changes affected by both reservoir filling and groundwater system. • More evidence for surface illitization of smectite in natural alkaline environments was provided. Alkaline environments are common in arid and semi-arid regions in northwestern China and have preserved quantities of rock heritages along the Silk Road. In contrast to the frequently reported weathering mechanism of stone heritages in acidic conditions, mineral weathering mechanism (especially the transformation mechanism of smectite) in natural alkaline environments still remains to be evaluated. To deepen the understanding of weathering in such an environment, research idea from critical zone science was applied to investigate the element transport and mineral transformation from protolith (interbedded sandstone and conglomerate) to regolith in a world cultural heritage, Bingling Temple Grottoes (BTG), in northwestern China. From geochemical and mineralogical characterizations on boreholes, excavated profiles, fractures and cliff surface, we found that dissolution of calcite, plagioclase (anorthite, albite) and K-feldspar (orthoclase) caused major elemental loss of Na, K and Ca (to aqueous solution) in the BTG, and elements of Mg and Fe mostly retained in solid materials. Characterizations on the cliff surface demonstrated higher extents of element depletion and mineral weathering and lower ultrasonic P -wave velocities in sandstone than in conglomerate, and in the bottom sandstone layers (located in the capillary zone and exposure to rain scouring) than in upper sandstone layers (located in the cave and free of precipitation). The transformation of smectite from protolith to regolith follows the sequential reactions: dehydrated smectie → bihydrated smectite → randomly interstratified illite/smectite → illite. Such transformation pathway is favored by alkaline pH and wetting–drying cycles frequently occurred at the BTG. Typical weathering patterns such as clay swelling damage, efflorescence, salt precipitation, etc., are highly-linked to seasonal changes in the hydrological process influenced by both reservoir construction and groundwater system. Our study provides more evidence for the illitization of smectite in natural alkaline environments and highlights the hydrological impacts on weathering patterns of rock grottoes. [ABSTRACT FROM AUTHOR]

In this research work, AlIII substituted by MgII and ZnII atoms in smectites (Sm) of the formula [Na 0.7 Mg 2.5- x Zn x Li 0.3 Si 4 O 10 (OH) 2 ] were synthesized. Its structural and intrinsically highly photoluminescent (PL) properties were reported. The complex distributions of MgII and ZnII atoms were observed in both octahedral and tetrahedral sites in the synthesized Sm (as evident with XRD, XPS, and ESR studies). The visible white light emission was observed when excited with UV light (250 nm). The observed strong photoluminescence (PL) was attributed to the electronic transition from oxygen vacancy to acceptor atoms induced by isomorphous substitution in both tetrahedral and octahedral sites (Mg Al ′ , Mg Si ′ ′ , Zn Al ′ , Zn Si ′ ′). With introduction of ZnII atom, there was an increase in Mg Al ′ and Mg Si ′ ′ defects energy levels that resulted in bathochromic shifts in V O ∙ ∙ → Mg Al ′ ′ , V O ∙ ∙ → Mg Si ′ ′ and V O ∙ ∙ → V O emission lines. Moreover, two additional emission lines in blue and red-light regions were observed due to two new Zn Al ′ , Zn Si ′ ′ defect centers that led to V O ∙ ∙ → Zn Al ′ and V O ∙ ∙ → Zn Si ′ ′ electronic transitions. [Display omitted] • Intrinsically luminescent, ZnII substituted trioctahedral smectite (Sm) synthesis by simple hydrothermal method. • White colour emission in synthesized Sm with UV (λ = 250 nm) light irradiation. • Defect-induced electronic transition leads to broad emission in the visible region. • Bathochromic shift and red light emission with ZnII substitutions. [ABSTRACT FROM AUTHOR]

Hybridized zinc silicate adsorbent (Zn–Si/(I/S)) with excellent adsorption property was synthesized by hydrothermal-roasting process based on Illite/Smectite (I/S) clay. The morphological structures and elemental compositions of adsorbents were analyzed by various characterization techniques, and the Zn–Si/(I/S) adsorbent had a 2-D film-like structure. In addition, the average pore size was obviously increased. The Zn–Si/(I/S) adsorbent had a good adsorption performance for cationic dyes and antibiotics, and the adsorption process was influenced by the structure, pore size, type and surface groups of the pollutants. The results of adsorption isotherm, kinetic and thermodynamic model fitting showed that: i) the adsorption performance depended on the pore size and surface charge rather than the specific surface area, ii) the proposed second-order kinetic model and Freundlich isotherm model fitted the adsorption process of RhB better, iii) the thermodynamic analysis proved that the adsorption process proceeded spontaneously by heat absorption. In summary, the adsorption mechanism was controlled by electrostatic attraction, chemical conjugation, ion exchange, hydrogen bonding interactions and pore adsorption. Graphical abstract image shows that hybridized zinc silicate adsorbent (Zn–Si/(I/S)) with excellent adsorption property was synthesized by hydrothermal-roasting process based on Illite/Smectite (I/S) clay, and the adsorption mechanism was controlled by electrostatic attraction, chemical conjugation, ion exchange, hydrogen bonding interactions and pore adsorption. [Display omitted] • Hybridized zinc silicate adsorbent (Zn–Si/(I/S)) was synthesized based on Illite/Smectite (I/S) clay. • Zn–Si/(I/S) adsorbent have good absorption abilities to cationic dyes and antibiotics. • The removal efficiency and adsorption capacity to RhB were 93.0% and 35.4 mg g−1 within 50 min. • Zn–Si/(I/S) adsorbent have stable adsorption ability to RhB after 4 cycles. [ABSTRACT FROM AUTHOR]

This study focuses on compositional diversity and origin of green clays within the Late Cretaceous volcaniclastic horizons (green boles) in Deccan volcanics based on petrographical, mineralogical and geochemical investigation on outcrop samples. Green boles, showing either sharp or gradational contacts with the underlying basalt, were comprised of three different green clays: type 1 dark green void-filling clay, type 2 light green clay formed by the alteration of volcanic lithic and vitric grains, and type 3 light green clay pellet formed by the alteration of fine-grained vitric materials. FTIR and XRD data indicated 10 Å (celadonite type) and 15 Å (smectite) as dominant clay constituents. The type 1 clay showed higher oct. Fe total (∼1.03 a.p.f.u.), Mg (∼0.62 a.p.f.u.) and lower oct. Al (∼0.34 a.p.f.u.) compared to types 2 and 3. Type 2 green clay showed two subtypes. Interlayer cations in type 2A and 2B averaged 0.86 and 0.72 a.p.f.u., respectively. The high K 2 O and interlayer cation of type 1 and 2A clays confirmed celadonite. Type 2B and 3 green clays, variably mixed with smectite and quartz, belonged to interlayer cation deficient mica category. The association of type 1 celadonite with Fe, Mg-smectite and Ca-zeolite indicated its formation from pore fluid with changing chemistry. The alteration of volcanic lithic and vitric fragments under weakly reducing conditions with steady supply of relevant cations formed type 2 and 3 green clays. The study of green clays in bole beds is crucial for understanding the wide compositional diversity of potassic clay associated with continental flood basalts. • Three varieties of K and Fe-rich green clays interlayered with Cretaceous basaltic flows. • Celadonite is the dominant clay in the bole beds along with smectite. • Celadonite shows wide spectrum of chemical composition. • Depositional redox condition affects the chemical composition of celadonite • Potassium content of celadonite derives from K-rich volcanic glasses. [ABSTRACT FROM AUTHOR]

[Display omitted] • I/S significantly boosted the degradation rate of lignin during composting. • Adding I/S in composting enhanced the content of HS by 7.21%. • The abundances of CAZymes genes were analyzed by metagenomics technology. • RDA showed temperature effectively regulated abundances of AA2, AA10, GH1 and GH10. The purpose of this study was to analyze the effects of illite/smectite clay (I/S) on lignocellulosic degradation and humification process via metagenomics analysis during cattle manure composting. The test group (TG) with 10% I/S and the reference group (RG) were established. The results indicated that the addition of I/S made the degradation rate of cellulose, hemicellulose and lignin in TG (1.56%, 29.01%, 19.95%) was higher than that in RG (1.16%, 17.24%, 13.14%). Compared with RG, the abundance values of AA2, AA10, GH1 and GH10 in TG increased by 15.18%, 29.28%, 31.08%, 21.65%, respectively. Meanwhile, humic substance (HS) content was increased by 3.49% and 7.16% during RG and TG composting. Furthermore, the microbial community in TG changed, in which the relative abundance of Actinobacteria increased and Proteobacteria decreased. Redundancy analysis (RDA) showed that the temperature was positively correlated with the abundance of AA2, AA10, GH1 and GH10, whereas the organic matter content was negatively correlated. Overall, adding I/S to the composting could stimulate microbial activity, promote the degradation of lignocellulose and humification process. [ABSTRACT FROM AUTHOR]

Fluid-rock interactions in hydrothermal systems at or near mid-oceanic ridges (MOR) play a major role in determining the composition of the oceanic crust and seawater. To quantify the processes that govern cation exchange in these environments we have experimentally studied the isotopic evolution of δ26/24Mg in the fluid phase during seawater-basalt interaction at 250 and 290 °C. Mass balance constraints indicate that isotopically heavy Mg was preferentially incorporated into non-exchangeable (octahedral) sites in secondary clay minerals such as saponite (Mg-rich smectite), leaving residual fluids enriched in light Mg isotopes. The magnitude of fractionation observed during smectite precipitation in our experiments (ε Smectite - Liquid 26 / 24 ) ranged from 0.35 ‰ to 0.42 ‰. This observation, which contrasts with the preferential uptake of light Mg isotopes into biogenic and inorganic marine carbonates, highlights the potential utility of Mg isotopes as tracers of the precipitation dynamics of authigenic Mg-silicate and Mg-carbonate phases. Furthermore, although Mg isotopic fractionation is often masked by the almost complete removal of Mg in high temperature marine hydrothermal systems, our experiments demonstrate that it does become significant at lower temperatures where Mg removal by clay formation is incomplete. Under such conditions, this fractionation will create isotopically light fluids due to smectite precipitation, thus potentially represents an important component of the marine Mg isotope inventory. [ABSTRACT FROM AUTHOR]

Many technologies exist to treat medication residues however their implementation in different types of treatment processes for wastewater and water intended for human consumption is balanced against their cost-effectiveness and faces technical difficulties. The contribution of a set of natural industrial minerals commonly used in filtration to the elimination of ciprofloxacin was evaluated. This amphoteric antibiotic is also widely found in hospital effluents. The best adsorption rates found in a non-competitive environment were obtained for MONADOR montmorillonite. This natural, inert, readily available mineral is known for its high crystallinity, its high cation exchange capacity (CEC) and its very high specific surface area. By taking into account the size and volume of the ciprofloxacin molecule, the principal component analysis clearly shows that the CEC is a determining factor in the elimination of this molecule and that the microporosity of activated carbon is not involved in this process. Adsorption in tap water, the innovative element of this study, shows that MONADOR <20 μm bentonite shows a mean CIP adsorption rate of 184 ± 6 mg/g, and can therefore compete with activated carbon. This work constitutes the first stage in the qualification of low-cost industrial minerals for environmental protection in its broadest sense. Unlabelled Image • Extraction of ciprofloxacin from tap water • Solubility Equation of ciprofloxacin between 6 and 40 °C • Adsorption capacity of the main industrial adsorbents of the ciprofloxacin • Determinant factor in adsorption of ciprofloxacin • Proposal and preparation of the suitable bentonite for ciprofloxacin adsorption [ABSTRACT FROM AUTHOR]

Diagenetic smectite dehydration and smectite-to-illite transition in clay-rich sediments can contribute to the generation of overpressure in sedimentary basins, because of the release of water associated with these mineralogical reactions. However, the challenge of deciphering the contribution of smectite dehydration and illitisation to fluid pressure amongst other mechanisms generating overpressure requires the different mechanisms at play to be jointly considered. Here, we developed a coupled chemical and thermo-hydro-mechanical code, named SURP, to calculate the overpressure generation in a sedimentary pile because of sediment compaction during its burial, temperature increase, water flow and because of the release of water by clay dehydration and illitisation. For this purpose, a revised thermodynamic model describing smectite dehydration by a solid solution approach was considered, together with the different thermo-hydro-mechanical processes occurring in sedimentary basins. The SURP code was applied to the case study of an overpressured passive margin in the Niger Delta, composed of thick shale layers in a sedimentary pile. In this geological scenario, smectite dehydration was simulated and could explain 10–30% (20–50 bar) of the present day overpressure in the main reservoirs, in addition to compaction disequilibrium. • Coupled model to decipher the influence of smectite dehydration on overpressures. • SURP code for chemical and thermo-hydro-mechanical coupling during sediment burial. • Use of a thermodynamic model to describe smectite dehydration by a solid solution approach. • In the Niger Delta, 10–30% of the overpressure by smectite dehydration, in addition to compaction disequilibrium. [ABSTRACT FROM AUTHOR]

Slip on clay fault planes at shallow depths in the seismogenic zone could be controlled by their rheology as well as their frictional properties; however, the rheological nature of clay faults is still an open question. Investigating the rheological properties of clay minerals is essential for understanding and modeling shallow earthquake faulting. Here, we perform dynamic viscoelasticity measurements on three clay minerals, namely kaolinite, illite, and smectite, wetted with water using a custom-made high pressure, high temperature rheometer. Our results confirm that the rheological properties resulting from the microstructure of clay minerals depend on the oscillation frequency, oscillation amplitude, temperature, and amount of water contained. In addition, the rheological properties vary systematically with the type of clay mineral. This suggests that the viscoelastic behavior of earthquake faults varies with the type of clay minerals present. • Dynamic viscoelasticity measurements are performed on clay minerals under high temperature and high pressure. • Dynamic viscoelasticity of clay minerals depends on oscillation frequency, oscillation amplitude, temperature and the type of mineral. [ABSTRACT FROM AUTHOR]

This study aims to employ an integrated depositional and sequence stratigraphic approach to assess the control of diagenesis on reservoir porosity of a hybrid-energy delta system. The study focuses on examining the outcropped Upper Cambrian-Lower Ordovician Barik Formation representing a highstand system tract of a hybrid-energy delta in the Haushi-Huqf region of Central Oman, which is equivalent to the subsurface gas reservoirs within the Interior Oman Salt Basins. The petrographic, mineralogical, and geochemical assessments revealed that the Barik Formation primarily consists of moderately to very well-sorted coarse-grained siltstones to fine-grained sandstones, with a composition mainly comprisingfeldspathic- and subfeldspathic arenite and the reservoir porosity is controlled by various degrees of diagenetic processes. Eodiagenetic alterations comprise mechanically infiltrated clays and kaolinitization of silicate grains, including detrital feldspars, micas, and mud matrix. The mechanically infiltrated clays (e.g., smectite) were introduced into the sandstones by the percolation of muddy waters under the control of tidal pumps. Although these clays may affect reservoir porosity during eodiagenesis, they positively preserve reservoir porosity during deep burial (mesodiagenesis) by inhibiting cementation by feldspar and quartz overgrowths. Kaolitization of silicate detrital grains was facilitated by the influx of meteoric waters into the sandstones as the delta progrades during the highstand system tract. During progressive burial and lack of extensive eodiagenetic cement, compaction continued and reduced reservoir porosity. Illitization and chloritization of the mechanically infiltrated smectitic clays took place; however, they limited the cementation by quartz and feldspar overgrowths. The quartz and feldspar overgrowths on detrital grains with discontinued smectitic clay coats supported the detrital grains from further compaction and, thus, helped in reservoir porosity preservation. Moreover, extensive feldspar dissolution and kaolinitization has occured during mesodiagenesis and enhanced the reservoir porosity. Subordinate amounts of calcite, dolomite, and gypsum cement have a minor reduction in the reservoir porosity of the Barik Formation. Hence, it can be concluded that, on the one hand, lack of eodiagenetic cementation favored intense reservoir porosity reduction due to compaction. Nevertheless, on the other hand, the mechanically infiltrated clays during the eodiagenetic stage helped preserve the reservoir porosity by hindering the formation of quartz and feldspar overgrowths during the mesodiagenetic stage. This study may serve as an analog model for a similar hybrid-energy delta sandstone reservoirs to better understand the type, and spatial and temporal of diagenetic alterations and their role in controlling the reservoir quality in deeply buried sandstone reservoirs. • Eodiagenetic alterations in a hybrid energy delta system are linked to depositional facies and sequence stratigraphy. • Mesodiagenetic alterations in a hybrid energy delta system is controlled by eodiagenetic alterations. • Porosity deterioration and enhancement can be predicted within depositional facies and sequence stratigraphy. [ABSTRACT FROM AUTHOR]

The non-aqueous extraction (NAE) is an alternative to the commercial water-based extraction technology used to liberate bitumen from oil sands. Although the impact of kaolinite, illite, chlorite, illite-smectite and montmorillonite on NAE process has been previously studied, the effect of different types of smectites has not been fully understood yet. In this work, mixtures of bitumen with bentonites dominated by saponite, hectorite, nontronite, beidellite and montmorillonite were reacted for several days and then washed with solvent (cyclohexane) to remove bitumen from the bentonites. The main goal was to better understand the impact of different smectites properties (specific surface area, pore structure characteristics, particle size, crystallite thickness, swelling ability, cation exchange capacity, layer charge and crystal-chemistry of smectites) on NAE process. The results showed that the porosity, particle size and swelling ability were the key parameters affecting the solvent-based bitumen recovery under the studied conditions. Samples with larger initial total pore volume and smaller particle size displayed reduced solvent bitumen extractability. The particle size of studied samples was affected primarily by swelling of smectites during the solvent bitumen extraction experiments. Smectites were swelling in water but not in cyclohexane. Swelling of smectite caused splitting of larger clay particles into many smaller particles. As a consequence, the efficiency of solvent bitumen extraction was significantly lower for fine grained samples, consisting of thin delaminated smectite particles, in which the bitumen was distributed among small-sized clay particles. • Porosity, particle size and swelling were key parameters affecting solvent bitumen extraction. • Samples with larger total pore volume retained more organics after solvent bitumen extraction. • Solvent bitumen recovery decreased with smaller particle size of studied samples. • Fine delaminated smectite platelets originated due to swelling reduced solvent bitumen recovery. [ABSTRACT FROM AUTHOR]

Quartz cement is an essential authigenic mineral in the tight sandstones of the Shaximiao Formation in the Sichuan Basin, China. Accurately identifying its sources and investigating its impact on reservoir quality is important for understanding diagenetic fluid evolution and pore development in these reservoirs. To address this, we conducted a systematic analysis of the silicon sources in quartz cement employing mineralogical, fluid inclusion, and geochemical data. Quartz cement is characterized by two phases of quartz overgrowth and pore-filling authigenic quartz. Homogenization temperatures of fluid inclusions range from 60 to 150 °C, indicating that quartz cementation occurred from the early diagenetic phase (B stage) to the late mesodiagenetic phase. During the early diagenetic stage, volcanic material was dissolved by meteoric water, resulting in the formation of the earliest quartz cement and smectite. At temperatures of approximately 70–100 °C, smectite illitization, accompanied by K-feldspar consumption and SiO 2 precipitation. In the mesodiagenetic stage (temperature approximately 100–130 °C), organic acids led to the dissolution of minerals like feldspar and laumontite, releasing SiO 2. In the deep burial stage, clastic quartz grains experienced dissolution due to high stress, providing a limited source of SiO 2. Smectite alteration and the dissolution of aluminosilicate minerals represent the primary sources of silicon for quartz cementation, while contributions from volcanic material hydrolysis and pressure solution are relatively minor. The presence of chlorite films inhibits the development of quartz overgrowths, and the limited precipitation of authigenic quartz within the primary porosity has a minimal impact on reservoir quality. Consequently, sandstones rich in chlorite films represent a favorable lithology for the development of high-quality reservoirs. • The precipitation of quartz cement was a prolonged and complex diagenetic process. • The illitization of smectite and dissolution of aluminosilicate minerals provide a significant supply for quartz cementation. • The hydrolysis of volcanic materials and pressure dissolution provide limited sources for the formation of quartz cement. • Chlorite films inhibit quartz overgrowths, and authigenic quartz has little effect on reservoir quality. [ABSTRACT FROM AUTHOR]

The structural hydroxyl hydrogen (H)-isotope compositions of clay minerals are frequently used as tracers of alteration or change in paleoenvironmental and material science studies. Dissolution pre-treatments are commonly used to remove cements and H-bearing impurities prior to isotopic analysis. These pre-treatments commonly include reactions respectively with: HCl or acetic-acetate buffer, H 2 O 2 or NaClO, and a Na-dithionite-Na-citrate-bicarbonate (DCB) solution in order to remove carbonates, organic matter, and iron (oxy)hydroxides. However, there has been inconsistent data regarding to what extent the structural hydroxyl H-isotope composition of a clay mineral is altered during exposure to these chemical pre-treatments. This study examined the "most extreme" impacts of each pre-treatment on the structural H-isotope composition of reference nontronite, montmorillonite, saponite, and kaolinite samples obtained from the Clay Minerals Society Source Clay Repository. All chemical reagents were isotopically labeled to a δ 2H value ≈ +200 or +570‰, to sharply contrast the average clay starting material δ 2H value ≈ –120‰. H-isotope compositions were measured before and after pre-treatments by High Temperature Elemental Conversion (TCEA) coupled with an Isotope Ratio Mass Spectrometer (IRMS). TCEA-IRMS measurements were done on potassium (K)-exchanged samples pre-dried under active vacuum at 220 °C to mitigate isotopic contamination by adsorbed water vapor. The results showed that only the H-isotope composition of kaolinite was unaffected by all pre-treatments. NaClO and DCB treatments affected the H-isotope compositions of saponite and nontronite, respectively, with the remaining pre-treatments not causing measurable changes for these two clay minerals. The HCl and H 2 O 2 pre-treatments caused massive alteration to the H-isotope compositions for montmorillonite and are considered unadvisable for use with this clay mineral, with respect to H-isotope analysis. The study confirms the possibility of altering the H-isotope composition of clays when using common selective dissolution procedures. The choice of applied pre-treatments before H-isotope measurements for clay-bearing materials should be based on the specific properties and mineralogy of the investigated samples and the amount and type of impurities they contain. • H-isotope composition of kaolinite is not altered by chemical pre-treatments. • Bleach and DCB treatments change H-isotope composition of saponite and nontronite, respectively. • H-isotope composition of montmorillonite can be drastically changed by reactions with H 2 O 2 and HCl. • The choice of pre-treatments before H-isotope measurements should be based on the mineralogy of the material. [ABSTRACT FROM AUTHOR]

Thermal treatment of clay minerals is used to produce building materials like supplementary cementitious materials (SCM). New, environmentally friendly binders, that are alkali activated materials (AAM) or geopolymers can be produced with calcined clay minerals, too. Four typical reactions occur during thermal treatment of clay minerals, namely dehydration, dehydroxylation, breakdown of structure, and recrystallization of high temperature phases. Heating to temperatures below the breakdown of structure makes rehydration and rehydroxylation of the clay minerals possible, ass observed in ancient bricks and pottery. As swellable clay minerals or mixtures of different clay minerals come into focus as precursors for geopolymers or as SCM, it is important to pay attention to rehydroxylation in this context as well. This work studied the rehydration and rehydroxylation of three different homoionic (Na+, Ca2+, Mg2+) exchanged trans- and cis-vacant dioctahedral smectites at equal relative humidity (75% r.H.) at different temperatures (22, 40, and 60 °C) after calcination at 700 °C. Simultaneous thermal analysis was used to determine the amount of H 2 O uptake (after 4, 24, 48, 72, and 168 h) due to rehydroxylation. Rehydroxylation between 8.7% for a Na+ exchanged sample and up to 37.3% for a predominantly Mg2+ exchanged sample took place within 7 d. The process of rehydroxylation could be further verified by X-ray diffraction, these measurements should be part of future studies. The α-free isoconvertional approach resulted in E a of rehydroxylation in the range 32–90 kJ/mol for Ca2+ exchanged samples. • Rehydroxylation of smectites takes place at ambient conditions. • Degree of rehydroxylation increased with time and temperature. • Ca2+ and Mg2+ exchanged samples showed larger values for rehydroxylation than Na+ exchanged ones. • Activation energies of rehydroxylation in the range 32–90 kJ/mol for Ca2+ exchanged samples. [ABSTRACT FROM AUTHOR]

Red-coloured clay-rich beds (bole beds) occur at flow breaks in parts of the Deccan volcanic province (DVP). These boles in the Deccan province retain paleoenvironmental information that prevailed at the K-T boundary, including the timing of the Deccan eruption synchronous with the K-T mass extinction. This contribution assesses the origin of clays in various red boles, selected based on their field appearances, physical properties, and relation with bounding units. The saprolitic red bole, fragile red bole and grey bole capping red bole have kaolinite and smectite clay with broad 001 peaks (FWHM>0.62°). The selective dissolution of grey bole reveals the highest Al o , Si o and Fe o /Fe d (>3) characteristics of short-range ordered alumino-silicates and oxyhydroxide. Both red and grey boles show relative enrichment in immobile elements, indicating leaching within the incipient stage of weathering (saprolite equivalent). Clays from these boles show Fe Fe and Al Al segregated domains in the octahedral sheet, features characteristic of short-range ordered clay, indicative of a pedogenesis. Smectite in these boles shows Fe > 0.3 apfu with trans vacant (tv) nature, suggesting oxidizing conditions at low temperatures. The STEM-EDS of clay FIB section reveal smectite laths with multiple chemistries in each sample, indicating re-equilibrating conditions in a closed system due to fluctuating wet and dry seasons. Contrary to the above two red boles, indurated-structure less and indurated-laminated red boles have glass shards with yellowish rinds and smectite clay (FWHM<0.5°), indicating palagonitization. The cation occurrence probability in the smectite octahedral sheets of later boles has values characteristic of randomly distributed cations, suggesting a relatively higher temperature of interacting solution. We envisage two processes of clay formation in red boles: a) pedogenesis and b) palagonitization of basalt flow top and/or mafic volcanoclastic deposits. • Palagonitization due to hot fluids resulted in celadonite and homogeneous smectite clays. • Pedogenic weathering resulted poorly crystalline, chemically heterogeneous short-range-ordered clays. • Elemental leaching during pedogenesis suggest incipient stage of weathering under fluctuating climate. [ABSTRACT FROM AUTHOR]

An analysis of clay minerals in core samples around the megasplay fault of the Nankai Trough, Japan, recovered during the Integrated Ocean Drilling Program Nankai Trough Seismogenic Zone Experiment reveals a local progression of the smectite-to-illite conversion (S–I) reaction in the slip zone, possibly associated with local thermogenesis caused by seismic slip on the fault. Our semiquantitative X-ray diffraction analysis demonstrates that the illite content in mixed-layer illite/smectite is ∼15% higher in the gouge than in the host sediments. The thermal history of the fault, constrained in a previous study, requires a reduction of the apparent activation energy by 20–30% compared with the literature value to explain the observed illitization. The Shirako Fault in the Miura–Boso accretionary complex, which is thought to have been activated in a tectonic setting similar to that of the megasplay fault of the Nankai Trough, also shows a 20–30% reduction in the apparent activation energy. These results suggest that the kinetic barrier of the smectite–illite reaction is lowered as a result of mechanochemical processes in seismogenic fault zones. • Local progression of clay-mineral reactions in fault zones was assessed kinetically. • The reactions can be reproduced by lower activation energy than in the static state. • The kinetic barrier may be mechanochemically lowered owing to fault activity. [ABSTRACT FROM AUTHOR]

Deformation bands in porous volcaniclastics are little studied structural heterogeneities despite their relevance for constraining the modalities of deformation development and related fluid-rock interactions in volcanic areas. We document a dense network of normal-sense Deformation Bands (Normal-sense Compactional Shear Bands (NCSBs) affecting upper Pliocene felsic glassy tuffites in Milos, Greece. NCSBs probably formed between 300 and 500 m of burial depth, in response to NE-SW directed extension which is related to volcanic rift development in the area. They accommodate mm-to m-shear-offsets, trend either N105 ± 10° or N070 ± 10°, and show mutual cross-cutting relations. The NCSB fault rock is made of ultracataclasite in which the cataclastic mechanisms have affected both the mineral fraction and the volcanic glass. Minerals are fractured along their cleavages whereas pumices are interestingly fractured along their vesicles. The development of chemical alteration (dissolution and cementation) essentially into the ultracataclasite is expressed through glass-hosted corrosion gulfs and smectites filling the intergranular porosity. These observations support that NCSBs preferentially retained water, have been the seat of greater fluid flow, and are the locus of ongoing phyllosilicate self-sealing in the vadose zone. A significant decrease (up to one order of magnitude) in porosity is measured within the studied NCSBs. • We document Normal-sense Compactional Shear Bands (NCSBs) in porous volcaniclastics. • Pumice vesicles are zones of mechanical weakness promoting cataclasis development. • Glass alteration is expressed by corrosion embayments and smectites neoformation. • This study details hydraulic self-sealing of NCSBs in the vadose zone. [ABSTRACT FROM AUTHOR]

The presence of organic ligands may exacerbate the mobility of contaminants by stabilizing them in the aqueous phase and reducing their retention on the solid phases, representing an additional environmental hazard. We investigated the impact of EDTA, citrate and phthalate on the adsorption of four different radionuclides (RN = 137Cs, 85Sr, 152Eu and 233U) by a well-characterized smectite clay and evaluated the capability of sorption modeling to incorporate the impact of these organic ligands. We analyzed the effect of ligand concentration (from 1·10−6 to 1·10−3 M) on RN retention at two different pH values (approximately 5 and 9) to contemplate the occurrence of different adsorption mechanisms in clays (cation exchange or surface complexation) as well as the RN and organic speciation. The results suggested that phthalate had a minimal effect on the retention of the studied RNs, while EDTA and citrate significantly decreased the adsorption of Eu, Sr and U, even making it drop to zero in some cases. The simulation outcomes demonstrated that, in most cases, the variation in the distribution coefficient (K d) as a function of the organic concentration could be accurately replicated with the available thermodynamic data, but few relevant discrepancies were identified. The importance of the possible competitive effects of trace ions in the equilibrium water (notably Ca) for the overall assessment of the role of organic matter on RN retention was highlighted. [Display omitted] • Phthalate has a negligible effect on the adsorption of all the studied radionuclides. • EDTA and CIT may significantly compromise the adsorption of Eu and U. • Ca is very important on the overall role of EDTA on radionuclide retention. • Organic ligand adsorption on the clay under acidic pH cannot be ruled out. • The role of CIT on U retention by the clay is underestimated by calculations. [ABSTRACT FROM AUTHOR]

Magnesium silicate hydrate (MSH) is a low-crystalline material of recent interest in the fields of geoengineering, low-temperature geochemistry, and planetary science. Despite the potential importance of the phase in a wide range of research areas, methods for identifying MSH in natural samples are limited because of its low crystallinity and variable chemical composition. The use of Mg-XANES spectroscopy for identifying MSH and Mg-bearing clay minerals were examined in this study. The spectra of various MSHs synthesized under different conditions were systematically compared against the spectra of various other natural and synthetic clay mineral species (montmorillonite, Fe-montmorillonite, saponite, Fe-saponite, stevensite, talc, antigorite, chrysotile, and chlorite). The spectra for all the mineral species were similar, regardless of composition and crystallinity. Quantitative comparison of the spectral similarities revealed that species with the same structure had similar spectra, such that 2:1 dioctahedral smectites (montmorillonite), 2:1 trioctahedral smectites (saponite and stevensite), 2:1 trioctahedral talcs, and 1:1 trioctahedral serpentines all have unique Mg-XANES spectra. The spectra of six freshly prepared MSHs with Mg/Si ratios of 0.7–1.3 and synthesized under different pH conditions (pH = 10 or 12) were comparable. Two freshly prepared Fe-containing MSHs showed very similar Mg-XANES spectra to those of the MSHs. Spectral analysis revealed that the spectra of the freshly prepared MSHs could not be reconstructed by combining the spectra of the other Mg-bearing clay minerals, indicating that the coordination environment of Mg in freshly prepared MSH is unique and common regardless of the material's composition and reaction pH. The spectra of two MSHs (Mg/Si ratio, 0.8–1.3) aged for 12 months were slightly different from those of the freshly prepared MSHs due to partial transformation of the MSH to trioctahedral clay minerals. In summary, Mg-XANES spectroscopy can be used to identify MSHs and certain other clay minerals due to their unique spectra. • Mg XANES spectra of Mg bearing clay minerals and magnesium silicate hydrate were compared. • Clay minerals with similar structure show comparable Mg XANES regardless of the origins. • Freshly prepared MSH show comparable Mg XANES regardless of compositions and solution conditions. • Mg XANES of MSH is unique among other Mg bearing clay minerals. [ABSTRACT FROM AUTHOR]

Quinacridone, a red pigment, was hybridized with a synthetic hectorite by a mechanochemical reaction. Though quinacridone was not photoluminescent, the products were photoluminescent and the photoluminescence quantum yield was 0.89 when the dye loading was 0.00009 g dye/g clay. The product was dispersed in water to give stable suspensions with varied viscosities depending on the concentration of the hybrids. The photoluminescence of the aqueous suspension was quenched by Cr3+, Co2+, Cu2+, Fe2+, Ni2+ and Pb2+ as described by linear Stern-Volmer plots at the concentration of 1–600 ppm. Among the tested metal ions, Cr3+ gave the most efficient quenching (the K SV value of 0.0125). The quenching of the photoluminescence of the quinacridone-synthetic hectorite hybrid was applicable to detect Cu2+ and Cr3+ at ppb level. [Display omitted] • Hybridization of quinacridone and smectites was achieved by a solvent-free mechanochemical reaction. • The hybrid of quinacridone and synthetic hectorite was luminescent (Photoluminescence quantum yield was 0.89). • Thanks to swelling characteristic of the smectite, the hybrid was dispersible in water as a stable colloidal suspension. • Luminescence of the aqueous suspension was quenched by Cu2+ at a low concentration of 1.5 ppb. [ABSTRACT FROM AUTHOR]

Swelling capacity of smectite was studied over decades regarding its application as barrier in disposal of nuclear wastes in geological repositories as well as the induced volume change potential in soils according to moisture. In order to improve our knowledge in the swelling capacity of smectite, a miniaturized oedometer was developed to combine swelling pressure measurement with wide angle X-ray scattering (WAXS) characterization in real time during hydration of smectite. This coupled set up allowed studying hydration of smectite up to saturation under confined condions and linking crystalline swelling to pressure at various densities. The modeling of the WAXS patterns gave also quantitative information about the relative proportion of the different interlayer water types at saturation. In situ and operando data were acquired for homo-ionic Na+- and Ca2+-exchanged smectite at two different densities (1.5 and 1.8 g/cm3). The results showed that the swelling pressure rise was correlated to a sequence of water layer type with the transition from 0W to interstratification of 2W/3W layers, depending on the density. The cation valency controlled the rate of hydration with faster hydration in the case of divalent exchanged smectite. At saturation, with increasing density, the amount of 3W layers decreased to the gain of 1W and 0W layers. Results also confirmed that at saturation and a density of 1.8 g/cm3, the interlayer porosity represented the total one. Finally, this development provided opportunity to improve our knowledge in the swelling mechanism of compacted swelling clay materials upon hydration. • Miniaturized oedometer was developed to study in real time smectite hydration. • Combined acquisitions of WAXS patterns and swelling pressure was achieved in operando. • The smectite hydration state is relied to the development of swelling pressure. • A sequence of interlayer water types controlled the swelling pressure development. [ABSTRACT FROM AUTHOR]