Smectite Clay Research Articles

Effects of inhibitor KCl on hydration swelling and softening of a smectite-poor mudstone

The swelling and softening of mudstones caused by water often lead to serious geological disasters. In petroleum exploration and development, the hydration expansion of mudstone can also lead to serious wellbore instability hazards. The swelling of smectite clays is the main reason for this hydration expansion in mudstones. It is generally recognized that illite and illite–smectite mixed layer clays are both poor swellable and has a low effect on rock strength of smectite-poor mudstone. Furthermore, weakening law and degree of smectite-poor mudstone in water is not clear. This study conducted swelling tests and rock mechanics experiments on a smectite-poor mudstone from the Sichuan basin. The results show that both water content and swelling capacity tend to remain steady after soaking the samples for 24 h. The mudstone water content reached 5.36%, and the swelling rate was 2% after soaking in water for 72 h, and the rock had a lower unconfined compressive strength (UCS) value of 1.41 MPa. Adding KCl inhibited these processes, and elevated KCl concentrations drastically reduced the mudstone water content and swelling rate. Compared to water, the water content and swelling rate of mudstone soaked in a 6% KCl solution both decreased by 50%. The UCS and the elastic modulus also increased for a half-dry mudstone, although the inhibitor was important. At elevated KCl inhibitor concentrations, the UCS and elastic modulus of the hydrated mudstone were lower than those of the dry mudstone. The findings of this study can help for better understanding of the application of KCl inhibitor in water-based fluid for drilling engineering.

The geology, mineralogy, petrography, and geochemistry of the Miocene Dursunbey coal within fluvio-lacustrine deposits, Balıkesir (Western Turkey)

The Dursunbey coalfield, a typical example of coalfields in the western Anatolia, hosts a mineable coal seam (about 9.0-m coal thickness) with altered tuff layers within early Miocene fluvio-lacustrine sequences. The aim of this study is to identify peat-accumulation conditions and factors controlling the mineralogy and geochemistry of this seam. The standard coal features and petrographical, mineralogical, and elemental compositions display changes throughout the seam. Ash yields display decreasing trends towards to the upper parts of seam, while total C contents and gross calorific values are increasing. Furthermore, the coal-facies patterns evidence changes of depositional conditions and vegetation in the palaeomires. During initial stages of peat accumulation, the contribution of herbaceous peat-forming plants were more common and palaeomires were open to detrital inputs, whereas woody peat-forming were becoming predominant, and the water table was stable and high, which caused development of anoxic conditions, during late stages. Therefore, the content of detrital minerals, such as quartz and clay minerals (illite, smectite, and chlorite) increases in the lower parts of seam, while that of pyrite increases in the upper parts. In addition, the SEM-EDX data show that matrices of clay mineral aggregates are illitic in composition in the lower parts of seam, while those of smectite prevalence are more common below and above altered tuff layers. Interestingly, authigenic rhomboid K-feldspar grains are observed within smectite clay aggregates in the samples from the upper parts of seam. Framboidal pyrite grains and clusters were also commonly identified from these samples as well. This data shows that synchronous volcanic inputs were altered within a hydrologically closed system under slight acidic to neutral conditions during late syngenetic stages.The enriched elements, such as Cr, Ni, Cs, and V, display moderate to strong positive correlations with ash yields while Al2O3, and K2O indicate an aluminosilicate affinity (clay mineral and feldspar). Considering the presence of metamorphic and ophiolitic rocks in the basement and the adjacent areas, clastic inputs into the palaeomire seems to be controlling aluminosilicate-affiliated elements. Additionally, the SEM-EDX analyses denoted that Ni and As are associated with pyrite. The Ni and As-bearing epigenetic pyrite infillings are mostly identified in coal samples below altered tuff layers; hence, As and Ni enrichments are controlled by precipitation of leached pore waters from altered tuff layers. Nevertheless, As- and Ni-bearing syngenetic pyrite grains and clusters are related with the development of anoxic conditions within palaeomires. This could also favour a Mo and U enrichment, which is another testimony for synchronous volcanic inputs altered under anoxic conditions. Overall, high detrital-input ratios from adjacent areas during initial stages of peat-accumulation in the study area controlled by enrichments of aluminosilicate affiliated elements, whereas during late stages of peat-accumulation, the development of a hydrologically closed system and redox conditions within the palaeomire caused As, Ni, Mo, and U enrichments and the formation of smectite and authigenic K-feldspars.

Molecular mechanisms of per- and polyfluoroalkyl substances on a modified clay: a combined experimental and molecular simulation study

Repeated application of aqueous film-forming foams (AFFF) in designated firefighting training areas has caused severe groundwater contamination by per- and polyfluoroalkyl substances (PFASs). Many research efforts are currently engaged for the effective removal of these chemicals from environmental waters. In this study, we demonstrate that modified clay produced by intercalating quaternary ammonium cations in the exchangeable interlayer sites of smectite clay can effectively remove PFAS pollutants in real groundwater via strong adsorption. The performance of the modified clay (with removal efficiencies 95~99%) is superior to those of granular activated carbon or hard-wood biochar and comparable to an ion exchange resin. Removal efficiency is not impacted by potential organic co-contaminants (e.g., diesel, BTEX, TCE, and 1,4 dioxane) or water chemistry (Ca2+ and Na+) at environmentally relevant concentrations. Furthermore, piecewise isotherms are identified to represent the uptake of PFASs by the modified clay. Based on molecular dynamics simulations, the anionic PFASs first occupy the highly polarized bare interlayer edge sites leading to a linear isotherm and then the interlayer surface sites resulting in a Langmuir isotherm. The ionic interactions between the cationic intercalant (N+) and the terminal oxygen atoms of carboxylate or sulfonate groups of PFASs play a dominant role in adsorption, and the lateral interaction in particular fluorophilic attraction among PFASs accelerate the adsorption. The strength of these interactions is quantified using Density Functional Theory calculations. Simulation results match reasonably well with the experimentally determined basal spacing and Fourier transform infrared spectroscopy of the modified clay loaded with PFASs. Overall, the combined experimental and molecular simulation studies elucidate the adsorption mechanism of PFASs on the modified clay and provide critical information to guide the use of modified clays for PFAS water treatment in the field.

Effect of organo-smectite clays on the mechanical properties and thermal stability of EVA nanocomposites

Ethylene vinyl acetate (EVA) nanocomposites containing hydrophobic organo-clays were prepared by a solution blending method to investigate the role of organic modifiers stabilized in the interlayer space of host clays on the thermal stability and mechanical strength of EVA. The smectite clays such as Mt. (Na-montmorillonite), Mica (Na‑fluorine mica), and Ht (Na-hectorite) were used as the host with different particle sizes, but hydrophobically modified by intercalating the long chained alkylammonium surfactants like cetyltrimethylammonium (CTA) bromide, and dimethyldistearylammonium (DMDSA) bromide to form organo-clays. Thus, prepared organo-clays were dispersed homogeneously in a toluene solution of EVA, and then the toluene was evaporated to obtain the organo-clay/EVA nanocomposites. According to the powder XRD analyses for all the nanocomposites, the CTA-clays were better exfoliated and dispersed in EVA matrix than the DMDSA-ones. Among three CTA-clay/EVA nanocomposites, the CTA-Mica/EVA one was determined to be the best in terms of thermal stability compared to the other two nanocomposites, CTA-Mt/EVA and CTA-Ht/EVA. The thermal stability of the CTA-Mica/EVA nanocomposite was significantly improved by ~38 °C, compared to that of the pristine EVA. Upon increasing the CTA-Mica loading concentration up to 12 wt% in EVA matrix, the Young's modulus and tensile strength of the EVA nanocomposites were increased up to 54% in maximum. It is, therefore, suggested that the CTA-Mica is a potential nanofiller for enhancing the thermal stability and mechanical properties of EVA.

Smectite clay waste as an additive for Portland cement

This study aims at investigating the possibility of using smectite clay waste, generated during the oil bleaching process as an additive for Portland cement. The smectite clay waste consists of montmorillonite, quartz, anorthite, calcium sulfate, and amorphous phase. For the regeneration of this waste, the extraction with hexane and thermal method were chosen. The results showed that the extraction of smectite clay waste with hexane significantly increased the pozzolanic activity of this waste; however, the extracted additive prolonged the induction period of Portland cement hydration, slowing down initial cement hydration, and reduced the compressive strength of Portland cement samples.The thermal activation method achieves the best results by calcining smectite clay waste at 600 °C. The calcined additive indicated the strong pozzolanic activity. However, this phenomenon is associated with the formation of the amorphous phase by activating the smectite clay with the sulfuric acid rather than the degradation of the clay minerals during the combustion. The calcined smectite clay waste (CSCW) accelerates the hydration of calcium silicates in the second period of the exothermic reaction. The results of the investigation showed that in samples with the CSCW additive proceed the intense pozzolanic reaction, which can be clearly identified after 28 days of hydration. Up to 15 wt% of the Portland cement can be replaced by the smectite clay waste additive calcined at 600 °C without reducing the compressive strength of Portland cement samples.

Assessment of soil response to exchangeable sodium percentage by consistence and water retention properties

The use of low-quality water for irrigation is expected to keep increasing worldwide, which increases the risk of soil degradation. The response of soil to irrigation waters with excessive sodium depends on the soil clay behavior. Soil physical properties that can distinguish smectitic soils from non-smectitic soils could identify soils that are sensitive to exchangeable sodium. This study explores the use of Atterberg limits, coefficient of linear extensibility (COLE) and soil water retention as possible properties to determine if a soil is sensitive to exchangeable sodium. Soils used were synthetic soils prepared from mixtures of silt and clay minerals, and six natural soils. Atterberg limits, COLE and soil water retention was measured at ESP values of 0, 50 and 100% on these soils. Multiple linear regression functions were developed to predict soil liquid limit, plasticity index, COLE, and soil water retention at −336 cm H2O. The liquid limit, and COLE increased as the amount of sodium-saturated smectite increased in the synthetic soils. The liquid limit, COLE and water retention at matric potentials greater than −336 cm of H2O increased on smectite clay dominant soils when elevated ESP was combined with low salinity. The liquid limit increased from 49 to 67 on average and −336 H2O water content increased from 38 to 70% on average between 0 and 100% ESP treatments on the four smectitic soils. On a kaolinitic soil liquid limit decreased from 56.1 to 51.8 and −336 H2O water content increased from 33.7 to 35.9% between the ESP 0 and 100% treatment. Liquid limit increased from 188 to 679 and COLE increased from 0.47 to 1.19 mm mm−1 between calcium smectite (fullers earth) and sodium smectite (Wyoming bentonite), whereas liquid limit decreased from 56 to 39 and COLE decreased from 0.195 to 0.104 mm mm−1 between calcium and sodium saturated kaolinite. Plasticity index increased by 75% between the ESP 0 and ESP 100 treatments on the smectitic soils, whereas there was a 260% increase in plasticity index between fullers earth and bentonite. The root mean squared error that liquid limit could be predicted with was 3.3 plastic limit was 2.4, COLE was 0.036 mm mm−1, and 1/3rd bar water content was 2.2 × 10−3 g g−1. Smectitic soils had increases in soil swelling related properties, whereas non-smectitic clay soils had no changes in swelling related properties from ESP. Liquid limit and water retention at water potentials of −1/10th and −1/3rd bar were the properties that best distinguished soils that respond to ESP from soils that do not respond to ESP. Soil consistence properties and water retention can determine soils that contain smectite clay which is the clay mineral that is most sensitive to soil ESP.

Characterization of a highly heterogeneous flysch deposit and excavation implications: case study from Auckland, New Zealand

Engineering geological characteristics of the rapidly growing Auckland urban area are of increasing interest due to ongoing and planned tunnels and excavations. Auckland is mainly underlain by Miocene-age East Coast Bays Formation (ECBF), a highly heterogeneous flysch deposit, and is also affected by lava flows from the Late Quaternary Auckland Volcanic Field (AVF). Therefore, excavations in the region can encounter highly variable rock mass. Here, the geological strength index (GSI) and rock mass rating (RMR) were applied to outcrop in coastal cliff exposures located on Auckland’s North Shore, to evaluate the engineering geological properties of the ECBF. Samples were also extracted for laboratory analysis of elastic wave velocities, intact strength parameters and thin section analysis of microtexture. Specific issues identified include lenses of the heavily zeolitized Parnell Volcaniclastic Conglomerate, and marked strength contrasts within the weaker ECBF siltstone and sandstone. The ECBF sandstone, where uncemented, is much weaker and is highly permeable, while the presence of smectite clay may be problematic for tunnelling if it disaggregates, forming a ‘sticky spoil’. The presence of larger-scale defects has been problematic for tunnelling, including the presence of low shear strength clay seams along ECBF bedding planes, and bedding planes intersecting tunnel crowns.

The effect of montmorillonite functionalization on the performance of glucose biosensors based on composite montmorillonite/PAN nanofibers

Herein, composite electrospun nanofibers (NFs) based on polyacrylonitrile (PAN) and smectite clay, montmorillonite (Mt) were employed as matrices for the development of amperometric glucose biosensors. Clays are established as suitable immobilization platforms for biocatalysts and allow functionalization through intercalation with organic molecules. The present study was focused on utilization of functional Mt in biosensing by incorporation in nanocomposite NFs and cross-linking of model enzyme, glucose oxidase (GOx).The initial clay mineral utilized was industrial type Mt (K10) and a comparison between simple PAN and composite nanofibers PAN/Mt K10 as biosensing matrices was performed. Further on, the study focused on modification of Mt with dioctadecyl dimethyl ammonium chloride (DDAC), an ammonium salt with extended alkyl chain and methylene blue (MB) as a redox mediator. The functionalization of Mt with each molecule was assessed by infrared spectroscopy (FTIR), correlated with the morphology of the nanocomposite NFs, visualized by scanning electron microscopy (SEM) and with the efficiency in amperometric glucose detection.Ultimately, both incorporation and functionalization of Mt improved the performance of the constructed biosensors, increasing the linearity, which extended up to 15 ˟ 10−3 M within two linear ranges (1.0 ˟ 10−5 - 2.45 ˟ 10−3 M and 2.45 ˟ 10−3 -15 ˟ 10−3 M) and improving the sensitivity up to 52 and 25 mAM−1cm−2, respectively. The detection limits were also lowered from 4.2 to 2.4 μM and the operational stability was enhanced up to 85% as a result of incorporation of DDAC-Mt.

Swelling properties and lime stabilization of N'Gaous expansive marls, NE Algeria

The interaction of marly soils and buildings in the town of N'Gaous has led to the appearance of deformations and disturbances that have affected many constructions due to the swelling of the underlying soil. In addition, when these soils are used as construction material, embankments, they are extremely problematic. In this article, three sets of samples, from three different locations, were sampled. Their average carbonate content varies from 14% to 33%.The mineralogical and microsctructural characteristics of these soils are studied by X-ray diffraction (XRD), TG/DTA and SEM analysis. These are mainly smectite clays containing kaolinite and other minor constituents. They all have similar structure, laminar texture with an arrangement of clay particles oriented parallel to the bedding and pores of varying size. These soils are very plastic and have a plasticity index ranging from 41.5 to 54.3%. It was found that the swelling pressure before any treatment ranged from 2.3 to 2.7 bars, after treatment the swelling pressure becomes stable with 5% lime, this behavior has a link with the formation of a cementitious phase of calcium silicate hydrate (CSH) type, as revealed by XRD, ATD/TG and analysis and SEM. In terms of results, it was found that the addition of quicklime has clearly reduced the swelling of the tested samples. It was also found that the presence of carbonates with the above mentioned contents in the studied samples (<50%) does not affect negatively the lime treatment of these soils. However, it promotes the stabilization of swelling, which gives encouraging results.

Antimicrobial release from cleaning poultices for the conservation and disinfection of stone surfaces

Poultices, predominantly based on clays or silica powders, are commonly used by restorers for cleaning operations and disinfection of stone surfaces. However, operators often use poultices without paying particular attention to kinetics of release of the used antimicrobial agent from different types of supporting material. Cleaning procedures with poultices generally require fast and nearly complete release of the active agent. In this paper, releases of a commonly used antimicrobial ammonium salt (i.e. N-alkyl-N-benzyl-N,N-dimethylammonium chloride, shortly known as benzalkonium chloride, BAC) from poultices based on a sepiolite clay (Sep) or on a silica fume (SiO2), are studied by different techniques (WAXD, TGA, FT-IR, UV–Vis). Cation release from these poultices in aqueous media has been compared with those observed from intercalated compounds with a smectite clay (montmorillonite, Mt). Our results show that, for cleaning and disinfecting operations that require fast ammonium salt release, silica-based poultices would be preferred.

The interweaving roles of mineral and microbiome in shaping the antibacterial activity of archaeological medicinal clays

Ethnopharmacological relevanceMedicinal Earths (MEs), natural aluminosilicate-based substances (largely kaolinite and montmorillonite), have been part of the European pharmacopoeia for well over two millennia; they were used generically as antidotes to ‘poison’. Aim of the studyTo test the antibacterial activity of three Lemnian and three Silesian Earths, medicinal earths in the collection of the Pharmacy Museum of the University of Basel, dating to 16th-18th century and following the methodology outlined in the graphical abstract. To compare them with natural clays of the same composition (reference clays) and synthetic clays (natural clays spiked with elements such as B, Al, Ti and Fe); to assess the parameters which drive antibacterial activity, when present, in each group of samples. Materials and methodsa total of 31 samples are investigated chemically (ICP-MS), mineralogically (both bulk (XRD) and at the nano-sized level (TEM-EDAX)); their organic load (bacterial and fungal) is DNA-sequenced; their bioactivity (MIC60) is tested against Gram-positive, S. aureus and Gram-negative, P. aeruginosa. ResultsReference smectites and kaolinites show no antibacterial activity against the above pathogens. However, the same clays when spiked with B or Al (but not with Ti or Fe) do show antibacterial activity. Of the six MEs, only two are antibacterial against both pathogens. Following DNA sequencing of the bioactive MEs, we show the presence within of a fungal component, Talaromyces sp, a fungus of the family of Trichocomaceae (order Eurotiales), historically associated with Penicillium. Talaromyces is a known producer of the exometabolite bioxanthracene B, and in an earlier publication we have already identified a closely related member of the bioxanthracene group, in association with one of the LE samples examined here. By linking fungus to its exometabolite we suggest that this fungal load may be the key parameter driving antibacterial activity of the MEs. ConclusionsAntibacterial activity in kaolinite and smectite clays can arise either from spiking natural clays with elements like B and Al, or from an organic (fungal) load found only within some archaeological earths. It cannot be assumed, a priori, that this organic load was acquired randomly and as a result of long-term storage in museum collections. This is because, at least in the case of medicinal Lemnian Earth, there is historical evidence to suggest that the addition of a fungal component may have been deliberate.

Mineralogical and geochemical characteristics of Belevi clay deposits at Denizli, SW Turkey: industrial raw material potential

The present article addresses the potential usability of the Belevi clay from the Denizli region as a raw material in different ceramic applications and industrial products by investigating their mineralogical (X-ray diffraction), chemical (X-ray fluorescence), thermal (differential thermal analyzer-thermogravimetry), physical, firing, and geotechnical characteristics. For this context, cylindrical samples have been prepared and fired from 700 to 1200 °C; the mineralogical transformations during the firing process were obtained by X-ray diffraction. After that, linear firing shrinkage, bulk density (BD), water absorption (WA), unconfined compression strength (UCS), and ultrasonic pulse velocity (Vp) values of all of the samples were measured. In mineralogical point of view, samples were considered smectitic clays (56%) and rarely chlorite, illite, and kaolinite. In addition, calcite, quartz, feldspar, and dolomite minerals are observed in small quantities. Chemically, the major oxides of Belevi clay consist of SiO2, Al2O3, and Fe2O3 and characterized by higher CaO contents. The studied samples are generally composed of fine particles (clayey-silty). The plasticity indices (PI) are determined with a high value as 19%; this suggests that the studied clays are highly plastic raw materials. Samples with the particle size < 2 μm are abundant in clay deposits (∼ 20%), which is suitable for the ceramic applications. The presence of silt fraction in Belevi clay material can be eliminated by crushing and sieving. The main transformations during firing processes of the samples were determined at 900 °C together with the appearance of new crystalline phases especially anorthite, diopside, gehlenite, and hematite. An increase in the firing shrinkage and bulk density values with decrease in water absorption values is determined at 1000 °C and above. UCS and Vp values are also started to increase significantly from 900 °C due to mineralogical transformation. Technical tests show that Belevi clays are suitable in manufacturing of porous structural ceramic products such as brick and tiles, and also in pottery production.

Enhancement in selective adsorption and removal efficiency of natural clay by intercalation of Zr-pillars into its layered nanostructure

In this study, the adsorptive removal efficiency of locally available smectite clay (Montmorillonite, MMT) is enhanced with intercalation of tetrameric Zr polyoxocations into its layered structure and their subsequent pillarization into Zr pillared interlayered clay (Zr-PILC). The enhancement in adsorption capacity was studied with removal of four pharmaceuticals and personal care products (PPCPs) namely Amoxicillin (AMOX), Imipramine (IMP), Paracetamol (PCM), and Diclofenac-sodium (DIF-S). After modification, the adsorption capacity of clay increased 238–2078% for various PPCPs. The maximum adsorption capacity of Zr-PILC for these PPCPs varies as DIF-S > IMP ≫ PCM > AMOX. The uptake of the selected PPCPs is fast and almost 75–80% of adsorption capacity is achieved within 15 min. The post-intercalation changes in clay were investigated with various surface and structural analysis techniques. The results confirm an increase in the surface area, microporosity, and acidic sites (lewis acid) which improved and regulates Zr-PILC interactions with electron-rich PPCPs molecules. The kinetics of adsorption was explained with the pseudo-second-order model whereas; the mechanism of adsorption was explained in view of the intra-particle diffusion model. The adsorption of AMOX was explained with the Langmuir model, while adsorption of IMP, PCM, and DIF-S followed Redlich Peterson model. The reuse of Zr-PILC was evaluated up to three successive adsorption-desorption cycles, where the results indicated that the efficiency of regeneration is subject to PPCP adsorbed.

The formation of •OH with Fe-bearing smectite clays and low-molecular-weight thiols: Implication of As(III) removal

Low-molecular-weight thiols (LMWTs) are widely occurring in waters and soils, which can act as electron shuttles in biogeochemical cycles. It is interesting to study the interactions between LMWTs and clay minerals, which would produce free radicals on clay surfaces and influence As(III) transformation. Batch experiments and spectroscopic analysis in combined with computational modeling were conducted with three Fe-bearing clay minerals (Na–NAu-1, Na–NAu-2 and Na-SAz-2) and four LMWTs (l-cysteine, cysteamine, homocysteine, and glutathione) to investigate the reaction mechanisms of LMWTs with Fe-bearing clay minerals and influences of clay types and LMWT structures on the interactions. The results showed that Fe-bearing clay minerals can improve 2.4–3.7 times of •OH formation in 96-h LMWTs oxidation. Quenching experiments confirmed surface-Fenton-like reactions were the main pathways of •OH formation in the presence of Fe-bearing smectite clay minerals. The most possible hypothesis is that structural Fe (III) can accept electrons from LMWTs through proton-coupled transfer from –SH functional group, which was supported by FTIR, XRD and Mössbauer spectroscopies. The results of DFT calculations suggested that clay surfaces could accelerate RS• formation and stabilize the radicals. The addition of Na–NAu-2 in the cystein solution could increase As(III) oxidation to As(V) from 16.3% to 42.0%. The results imply that in-situ •OH formation in the presence of LMWTs and smectite clays may be an important geochemical process for the transformation of environmental contaminants.

Smectitic clays enriched with ferric ions for the rapid removal of anionic dyes in aqueous media

AbstractSodium smectite clays were enriched with ferric ions (Argel-Fe and Volclay-Fe) to convert the surface charge of the clays from negative to positive and to use the clays in the discolouration of a synthetic effluent composed of seven anionic dyes (mixed from tartrazine, Brilliant Blue FCF and amaranth). The iron content increased from 5.99% to 11.02% for Argel-Fe and from 5.39% to 10.54% for Volclay-Fe. The efficiency of the discolouration of the anion dye mixture was evaluated by measuring the absorbance of the mixture at 562 nm, where the band with the greatest intensity was found. The contact time required for the system to reach equilibrium was ~5 min for both adsorbents. The kinetic adsorption data supported a pseudo-second-order kinetic model. The experimental data support the dual-site Langmuir–Freundlich isotherm model. The maximum adsorption capacities were 88.68 mg g–1for Argel-Fe and 392.21 mg g–1for Volclay-Fe. The enrichment of clays with Fe(III) added functionality to the clays and generated adsorbents with rapid adsorption abilities and high discolouration capacities.

The role of clay surfaces in the heterogeneous nucleation of calcite: Molecular dynamics simulations of cluster formation and attachment

In many environments calcium carbonate minerals precipitate in the presence of clay minerals, and observations suggest that clays, particularly smectites, facilitate carbonate formation. In order to understand the interactions between clay surfaces and carbonate-precipitating solutions, we built model aqueous solutions of various compositions (containing Ca2+, Mg2+ and CO32– ions) between layers of clay minerals (montmorillonite and kaolinite), and performed extensive molecular dynamics simulations. The results were compared with simulations for bulk solutions. Contrary to intuition, ionic clusters formed preferentially in the interlayer solution (instead of on the clay surface). The clusters grew both by the association of individual ions and aggregation, and were adsorbed to the clay surfaces with distinctly different efficiencies in the various systems. Montmorillonite was found to be more efficient than kaolinite in capturing clusters from solution. However, the efficiency of anchoring ionic clusters to the clay surfaces strongly depended on the Na+ concentration of the solution, since Na+ appeared to strongly attach to the surface and thereby block it from clusters in the solution. Montmorillonite (and probably other smectite clays as well) may thus have an important role in certain, primarily freshwater, systems in the localization of ionic clusters on its surface, thereby promoting the nucleation and templated growth of crystalline calcium‑magnesium carbonate minerals.

New insights into fluid-rock interaction mechanisms at mud volcanoes: Implications for fluid origin and mud provenance at Bahar and Zenbil (Azerbaijan)

Understanding the fluid-rock interactions occurring in terrestrial mud volcanoes is a premise for elucidating the (bio)geochemical processes involved in the release of aqueous fluids, mud and gases to the Earth's surface and atmosphere. For the first time, fluid and mud ejecta from the mud volcanoes at Bahar and Zenbil, located in eastern Azerbaijan and in the shallow coastal water of the South Caspian, were collected and analyzed for their mineralogical, textural and chemical composition. The expelled aqueous fluids have a Na-Cl-(HCO3) composition and are generated by the mixing of evaporitic Caspian seawater and ancient, low- to high-salinity, sedimentary pore water at temperatures of 32 ± 3 °C and 42 ± 5 °C for the mud volcanoes at Bahar and Zenbil, consistent with mud chambers to be situated in the Pliocene sediments at 2–3 km depth. These aqueous fluids are strongly enriched in major solutes, like Na, Cl, HCO3, B, Br, NH4 and DOC, as well as in some trace elements (As, Ba, Cu, Fe, Li, Sr and Zn), with concentrations up to 220 times that of the current Caspian seawater. This chemical concentration is caused mainly by a combination of (i) strong surface evaporation, ion exchange and adsorption-desorption involving smectite clays, redox-driven reactions and carbonate mineral precipitation at relatively shallow depths (not deeper than 4 km) as well as (ii) thermal breakdown of organic matter and methane production in deeply buried (4 to 7 km depth) organic-rich strata. Biogenic processes are only of minor importance. The mud is sourced from all horizons the mud volcanoes are cross-cutting, partly altered by diagenetic processes. Alteration is comprised of illitization of smectite during burial diagenesis (120 to 150 °C), replacements of feldspar by kaolinite and smectite, weathering of sulfide minerals, Fe-(oxy)hydroxide formation, as well as oxidation of methane and organic matter in the near sub-surface environments at low temperature (<40 °C). Our results indicate that fluid-mud mixtures expelled from mud volcanoes of the South Caspian basin can influence the chemistry of local surface and ground water as well as of (sub-)surface sediments.

Controlled delivery of tetracycline hydrochloride intercalated into smectite clay using polyurethane nanofibrous membrane for wound healing application

This study reports application of electrospinning for controlled drug delivery by using polyurethane monolithic nanofibrous web. The endeavor of this study was to explore the effects on release, antimicrobial activity, and morphological behavior of drug–nanoclay intercalates vis-à-vis direct drug inclusion in the form of nanofibrous structures. Antibiotic drug, tetracycline hydrochloride was incorporated into montmorillonite clay interlayer spacing and then embedded into the synthetic polymeric nanofibrous structures. In vitro release study was conducted to assess the release characteristics. Disk diffusion experiment was organized to observe antimicrobial activities and finally human dermal fibroblast cells were grown on the nanofibrous web to address morphological behavior. The results showed that the nanoclay performed as a better way in the form of sustained drug release carrier. The produced electrospun nanofibrous webs could provide broad spectrum antibacterial activities beneficial for topical applications. The fibroblast cell growth on the nanofibrous web caused proliferation to result a mesh like structure which would certainly have a positive effect on wound healing.

Multi-element modeling of heavy metals competitive removal from aqueous solution by raw and activated clay from the Aleg formation (Southern Tunisia)

The present study has been carried out for potential use of a raw clay from Gabes district (southern Tunisia) in wastewater treatment. A representative clay sample was collected from the outcropping feature of the Aidoudi area to the west of Gabes city; it followed a simple treatment to enhance its physicochemical properties. Adsorption experiments were performed by using a simple batch technique in single- and multi-element solution (Pb2+, Cd2+, Cu2+ and Zn2+). The obtained results were fitted to different adsorption models, including extended and modified Langmuir, extended Freundlich and modified Redlich–Peterson. Our results indicated that the collected clay sample is mainly a smectite with high amounts of silica, alumina and iron. Adsorptive removal of single elements revealed encouraging efficiencies for most of the studied metals, reaching nearly 100%. Our results also indicated that lead removal reached 26.78 mg/g and 45.94 mg/g for natural and activated clay samples, respectively. Competitive adsorption showed strong dependence on the initial concentration and the metal properties, with preferential removal of lead that reached 41.71 mg/g in binary systems. In most of the mixed systems, metal removal substantially decreased in the presence of competing ions. It showed preferential removal of lead over other metals, regardless of the studied mixture. Further, the use of smectitic clay from southern Tunisia showed a good potential for metal ions removal in single and multi-element systems from aqueous solutions. Thus, it could be turned out to a viable material for the treatment of metal loaded waters.

Colombian clays binary mixtures: physical changes due to thermal treatments

Usually, smectite clays, which are used for catalytic purposes, are subjected to chemical and thermochemical treatments to enhance their surface features. This research aims to analyze textural and structural features of the physical mixtures of two Colombian smectite clays at room temperature and after the treatment at 600°C, 800°C, and 1000°C. The physical mixtures of two Colombian clays were characterized by X-ray techniques, thermal analysis, and BET surface area to evaluate physical changes resulting from the three thermal treatments. The results showed the appearance of microstructural changes in basal spacing and other crystals minerals because of the loss of carbonates and alkaline oxides in the clays. Additionally, a dramatic reduction in surface area features was evidenced by the temperature increase. Simultaneously, an increase in the pore size was also observed because of the increase of the temperature treatment. The results reveal that the physical mixture is not an appropriate solution to enhance the textural properties of the Colombian clays for sorption or catalytic purposes.