Pure Montmorillonite Research Articles

Engineering binary-network structured montmorillonite/silica composite aerogels with improved mechanical strength as water-resistant thermal insulators

Developing clay-based aerogel composites with integrated high strength, low thermal conductivity, and hydrophobicity remains a great challenge. Here, binary-network structured montmorillonite/silica composite aerogels (CSACs) with improved mechanical strength were engineered via the in-situ growth of silica networks in the montmorillonite aerogel scaffolds. Tunable density (0.065–0.149 cm3/g) and porosity (92.3–96.2%) can be achieved by different silica sol volumes (silica network content). The filled silica networks endow aerogels with a complete transition from hydrophilicity to hydrophobicity, showing high water contact angles of >130° and extremely low water absorption of 9.9%. CSACs show enhanced stress transfer and load-bearing capacity, with 2.6 and 4.4 times increased compressive modulus and strength compared to pure montmorillonite aerogel scaffolds. Moreover, a noteworthy reduction in thermal conductivity (0.041 to 0.034 W/(m∙K)), the decreased maximum thermal decomposition rates (dw/dt), increased temperature at the maximum decomposition rates (Tmax), and residues confirm the improved thermal insulation and thermal stability of CSACs, respectively. This research provides new insights into the design of efficient thermal insulation materials for diverse energy-saving scenarios that require excellent combined properties.

Importance of clay-H2 interactions for large-scale underground hydrogen storage

Underground hydrogen storage is considered an option for large-scale green hydrogen storage. Among different geological storage types, depleted oil/gas fields and saline aquifers stand out. In these cases, hydrogen will be prevented from leaking back to the surface by a tight caprock seal. It is therefore essential to understand hydrogen interactions with shale-type caprocks. To this end, natural pure montmorillonite clay was exposed to hydrogen gas at different pressures (0–50 bar) and temperatures (77, 195, 303 K) to acquire data on its adsorption capacity related to UHS and caprock saturation. Montmorillonite was chosen because of its large specific surface area enabling quantification of the adsorption process. Hydrogen adsorption was successfully fitted with a Langmuir isotherm model and yielded small partition coefficients indicating that hydrogen does not preferentially adsorb to the clay surface. Adsorption on montmorillonite goes back to weak physisorption as inferred from minor negative changes in the enthalpy of reaction (−790 J/mol), derived from an Excel Solver approach to the van't Hoff equation. Based on own as well as literature values, adsorption capacities, which were originally reported as mol/kg or wt%, are recast as hydrogen volume adsorbed per specific surface area (μL/m2). The acquired range is surprisingly narrow, with values ranging from 3 to 6 μL/m2, and indicates the normalised volume of hydrogen that can be expected to remain in the shale-type caprock after injected hydrogen migrated upwards through the porous reservoir. This ‘residual’ caprock saturation with hydrogen can be further restrained by considering the geothermal gradient and its effect on the molar volume of hydrogen. The experimental results presented here recommend injecting hydrogen deeper rather than shallower as pressure and temperature work in favour of increased storage volumes and decreased hydrogen loss through clay adsorption in the caprock.

Acid Treated Montmorillonite—Eco-Friendly Clay as Catalyst in Carvone Isomerization to Carvacrol

Acid-treated montmorillonites (MMT) were used as catalysts of carvone isomerization to carvacrol. Mineral acids—sulfuric, hydrochloric, nitric acids and organic acids (acetic and chloroacetic)—were used for the acid treatment. Prepared materials were characterized by available characterization methods, namely XRD, EA, TPD, TPO, UV-Vis, laser light scattering and nitrogen physisorption. The structure of montmorillonite remained intact after treatment. However, TPD proved the increase of acidity of acid-treated materials comparing pure montmorillonite. All materials were tested in the isomerization of carvone, producing carvacrol as the desired product. The initial reaction rate increased using the materials in the row MMT-COOH < MMT-HNO3 < MMT-ClCOOH < MMT-H2SO4 < MMT-HCl, which is in accordance with the pKa of acids used for the treatment. The number of weak acid sites strongly influenced the selectivity to carvacrol. The optimal solvent for the reaction was toluene. Total conversion of carvone and the selectivity to carvacrol 95.5% was achieved within 24 h under 80 °C, with toluene as solvent and montmorillonite treated by chloroacetic acid as catalyst. The catalyst may be reused after calcination with only a low loss of activity.

Building the bridge between U(VI) and Ca-bentonite – Influence of concentration, ionic strength, pH, clay composition and competing ions

In the context of a high-level nuclear waste disposal, the retention of U(VI) on non-pre-treated Ca-bentonite as potential technical barrier is studied. The objective of this study is to reveal the retention behaviour of U(VI) under extreme geochemical conditions, such as hyperalkaline pH range as well as high salinity at the same time, and taking into account other relevant parameters. This should lead to a better understanding of necessary safety precautions for avoiding a release of U(VI) in the environment. Batch experiments were conducted to determine the influence of the initial U(VI) concentration, salinity, pH value, clay composition and the presence of other elements (Ca(II), I−, Cs(I), Eu(III)). After the sorption experiments, the remaining U(VI) concentration in solution was determined via mass spectrometry with inductively coupled plasma. U(VI) can be immobilised from 10% to 100% under all investigated conditions. Precipitation plays a role in the U(VI) retention but only at higher concentrations (≥10−5 mol L−1). The retention is reversible especially with decreasing pH (<10.5) as the aquo complex Ca2UO2(CO3)3(aq) is formed. Ca(II) strongly enhances the U(VI) adsorption onto Ca-bentonite in the hyperalkaline pH range, probably due to the formation of Ca(II)-bridges. The best retention could be observed on natural bentonite compared to pure montmorillonite and altered bentonite. From a waste cocktail containing important elements of the repository inventory (Cs(I), Eu(III), U(VI) and iodide), only Eu(III) as homologous element to trivalent actinoids competes with U(VI) for binding sites, especially at low metal concentrations, but also facilitates the precipitation at higher concentrations.

Enhanced Storage Stability of Different Polymer Modified Asphalt Binders through Nano-montmorillonite Modification.

The storage stability concern, caused by phase separation for the density difference between polymers and asphalt fractions, has limited the widespread application of polymer modified asphalt (PMA). Therefore, this study aims to improve the storage concern of PMA by incorporating nano-montmorillonite. To this end, different nano-montmorillonites were incorporated to three PMAs modified with three typical asphalt modifiers, i.e., crumb rubber (CRM), styrene–butadiene-rubber (SBR) and styrene–butadiene-styrene (SBS). A series of laboratory tests were performed to evaluate the storage stability and rheological properties of PMA binders with nano-montmorillonite. As a consequence, the incorporation of nano-montmorillonite exhibited a remarkable effect on enhancing the storage stability of the CRM modified binder, but limited positive effects for the SBR and SBS modified binders. The layered nano-montmorillonite transformed to intercalated or exfoliated structures after interaction with asphalt fractions, providing superior storage stability. Among selected nano-montmorillonites, the pure montmorillonite with Hydroxyl organic ammonium performed the best on enhancing storage stability of PMA. This paper suggests that nano-montmorillonite is a promising modifier to alleviate the storage stability concern for asphalt with polymer modifiers.

Suppression Effects of Hydroxy Acid Modified Montmorillonite Powders on Methane Explosions

In this paper, montmorillonite inhibitors modified with polyhydroxy functional groups by gluconic acid (GA) were successfully prepared. The particle size distribution, composition, surface functional groups, and pyrolysis characteristics of the pure montmorillonite powders (Mt) and the gluconic acid modified powders (G-Mt) were analyzed by using a laser particle analyzer, X-ray diffraction (XRD), Fourier transform infrared (FTIR) and thermogravimetry–differential scanning calorimetry (TG-DSC), respectively. The suppression effect of Mt and G-Mt on the 9.5% methane–air premixed gas was tested in a 20 L spherical explosion device and a 5 L pipeline experimental system. The results show that G-Mt displays a much better suppression property than that of Mt. The optimal explosion suppression effect concentration of Mt or G-Mt powders is about 0.25 g·L−1. In this concentration, for G-Mt, the maximum explosion pressure declined by 26.7%, the maximum rate of pressure rise declined by 74.63%, and the time for the flame front to reach the top of the pipe was delayed by 242.5%. On the basis of the experimental data, the better suppression effect of G-Mt than Mt might be attributed to the presence of more hydroxyl groups on the surface.

Characterization of Nanoformulations from Montmorillonite clay for the decontamination of zearalenonein cereals using X-ray Diffraction Technique

Montmorillonite clay due to its abundance and environmental friendliness has several industrial applications among which are the adsorption of mycotoxins in foods and feed. The mycotoxin; zearalenone (ZEA) is oestrogenic and has been implicated in hormonal and reproductive issues for both man and animals. Thus, nanoformulations from Montmorillonite clay and Cymbopogoncitratus (lemongrass) extracts were developed for the reduction of the toxin in millet. The various formulations include: Montmorillonite clay to which extract of Cymbopogoncitratus(lemon grass essential oil)has been incorporated (Mont-LGEO), Montmorillonite clay mixed with C. citratus(lemon grass)powder (Mont-LGP) and Montmorillonite clay washed with NaCl (Mont-Na). Pure Montmorillonite clay (Mont) and C. citratus (lemon grass) powder (LGP) served as the controls for the treatment. Each of these compositions were applied to millet samples at a concentration of 8 % and 12% and stored for 4 weeks. XRD patterns for compositions containing Montmorillonite clay revealed major peaks at 2-Theta value of 20.06° representing Montmorillonite and 26.56° and 68.53°representing quartz. The level of ZEA in all treated samples was quantified after 4 weeks using the Liquid Chromatography tandem mass spectrophotometer LC-MS/MS. All the compositions were effective in the decontamination of zearalenone. Furthermore, C. citratus powder was the most effective in the decontamination of zearalenone in the cereal after 4 weeks.

Modification of Asphalt Rubber with Nanoclay towards Enhanced Storage Stability.

Asphalt rubber (AR), which is prepared by blending crumb rubber and bitumen, provides various advantages, including superior rutting resistance, lower road-tire noise and longer service life. However, contractors have expressed concerns regarding its poor storage stability, which in turn limits its wider application. This study aims to address the storage stability concern by incorporating nano-montmorillonite (nanoclay). Three types of nanoclay were dispersed into hot AR binder by high shear blending. The rheological properties of nanoclay-crumb rubber modifier (CRM)-modified bitumen were evaluated through Superpave performance grade (PG) tests and the storage stability was characterized by measuring the difference in softening points or complex moduli at the top and bottom portions of binders after lab-simulated storage. X-ray diffraction (XRD) evaluation was conducted to observe the variation of nanoclay layer gap distance for mechanism investigation. It was found that all selected nanoclays had insignificant effects on workability, rutting and fatigue properties. The layered nanoclay transformed to intercalated or exfoliated structures after interaction with bitumen fractions, providing superior storage stability. Among the three selected nanoclays, pure montmorillonite with Na+ inorganic group, which has an intermediate hydrophilic property and middle layer gap, showed the most obvious effect on enhancing the storage stability of AR.

Redistribution of Cs 137 introduced into montmorillonite in association with organic matter coming from biomass composting

The adsorption and later bioavailability of 137Cs from the system humic acid (HA)/humic acid like compounds (HALC) and montmorillonite was investigated. The setup of the experiments should approach as much as possible natural conditions when 137Cs is introduced into soil with HALC from decomposed biomass. The significant differences were found in the trials containing various HA/HALC and also pure montmorillonite. The 137Cs was more available when it reached soil in association with HALC originated from compost than when it was adsorbed on stable humic acids. Moreover, the long term interaction of 137Cs with HALC led to decrease of 137Cs adsorbed on montmorillonite and increase of its bioavailable fraction. UV–Vis spectrometry and infrared spectroscopy showed the clear difference between HA, fresh HALC and old HALC which could partially explain the different results.

Swelling Pressure in Systems with Na-Montmorillonite and Neutral Surfaces: A Molecular Dynamics Study

In the present work, we used molecular dynamics simulations to evaluate the distance between montmorillonite layers, and between montmorillonite and a neutral surface for a range of applied pressures as in an oedometer-like setup. The neutral surface was represented by a layer of pyrophyllite. Due to explicit water in the simulation, the resulting osmotic pressure and basal distance relationship differs from that of DLVO theory for both interlayer types. In agreement with experiment, basal distances change abruptly between hydration states at certain pressures. Within a given hydration state, the basal distances were found to vary with applied pressure also seen experimentally. For the pressure range in the study, we found that water adjacent to neutral surfaces has interlayer character. The hydration state of the interlayer between montmorillonite and the neutral surface was found to be either the same or one water layer less compared to the pure montmorillonite interlayer. Water densities in this region...

Adsorption capacity of multiple DNA sources to clay minerals and environmental soil matrices less than previously estimated

The cultivation and consumption of transgenic crops continues to be a widely debated topic, as the potential ecological impacts are not fully understood. In particular, because antibiotic resistance genes (ARGs) have historically been used as selectable markers in the genetic engineering of transgenic crops, it is important to determine if the genetic constructs found in decomposing transgenic crops persist long enough in the environment and if they can be transferred horizontally to indigenous microorganisms. In the present study, we address the question of persistence. Others have also estimated the DNA adsorption capacity of various clays, but have done so by manipulating the surface charge and size of particles tested which may overestimate sorption and underestimate the DNA available for horizontal transfer. In the present study, isotherms were generated using model Calf Thymus DNA and transgenic maize DNA without surface modification. Montmorillonite, kaolinite, and 3 soil mixtures with varying clay content were used in this study. The adsorption capacity of pure montmorillonite and kaolinite minerals was found to be one to two orders of magnitude less than previously estimated likely due to the distribution of clay particle sizes and heteroionic particle surface charge. However, it appears that a substantial amount of DNA is still able to adsorb onto these matrices (up to 200 mg DNA per gram of clay) suggesting the potential availability of free transgenic DNA in the environment may still be significant. Future studies should be conducted to determine the fate of these genes in agricultural soils.

Cysteine-montmorillonite composites for heavy metal cation complexation: A combined experimental and theoretical study

Green composites based on montmorillonite (Mt) and cysteine, were prepared for heavy metal removal. A comparison between the adsorption properties of the resulting hybrid inorganic-organic materials and the pure montmorillonite was carried out for the following heavy metal cations Cd2+, Hg2+, Pb2+, Co2+ and Zn2+. It appears that the adsorption capacity is higher on the composite. Moreover, in release experiments, the heavy metal cations are more strongly retained by the hybrid material. Interactions between the hybrid clay mineral and the inorganic hosts were studied by spectroscopic methods such as solid-state NMR (Nuclear Magnetic Resonance) and FTIR (Fourier Transform Infrared). The experimental data were in agreement with the theoretical periodic DFT (Density Functional Theory) calculations where a molecular picture of the adsorption complex is proposed.

Effects of OH− activity and temperature on the dissolution rate of compacted montmorillonite under highly alkaline conditions

AbstractThe highly alkaline environment induced by cementitious materials in a deep geological disposal system of high-level radioactive waste is likely to alter montmorillonite, the main constituent of bentonite buffer materials. Over long time periods, the alteration may cause the physical and/or chemical barrier functions of the buffer materials to deteriorate. In order to evaluate the long-term alteration behaviour, the dissolution rate, RA (kgm−3 s−1), of compacted pure montmorillonite (Kunipia-F) was investigated experimentally under conditions of hydroxide ion concentration of 0.10—1.0 mol dm−3 at temperatures of 50—90°C. The dissolution rate data, including those from a previous study at 130°C, were formulated as a function of the activity of hydroxide ions, aOH− (mol dm−3), and temperature, T (K), and expressed as RA = 104.5·(aOH−)1.3·e−55000/RT by multiple regression analysis, where R is the gas constant. The dissolution rate of montmorillonite was greater in the compacted montmorillonite than in the compacted sand-bentonite mixtures. The difference can be explained by considering the decrease in aOH− in the mixtures accompanied by dissolution of accessory minerals such as quartz and chalcedony. The dissolution rate model developed for pure montmorillonite is expected to be applied to bentonite mixtures if quantification of the decrease in aOH− is achieved somehow.

Estudo da incorporação de argilas montmorilonitas em cimentos asfálticos de petróleo

A utilização de nanotecnologia em pavimentos asfálticos é uma revolução, pois esta permite construir pavimentos mais resistentes à deformação, à trinca por fadiga, à trinca por temperatura e à ação da água.Nesse contexto uma alternativa é o uso da nanoargila. Sua incorporação ao cimento asfáltico de petróleo (CAP) proporciona melhoria nas propriedades físicas e reológicas e nas propriedades mecânicas das misturas asfálticas. Para o desenvolvimento deste trabalho utilizou-se o método da dosagem SUPERPAVE para a análise do comportamento das misturas asfálticas utilizando o CAP 50/70 modificado com as seguintes adições: Argila Montmorilonita organofílica (OMMT) e a Argila Montmorilonita pura (MMT). Foram analisados os efeitos dos modificadores por meio de ensaios mecânicos de Resistência à Tração por Compressão Diametral e Módulo de Resiliência, sendo todas as amostras submetidas ao processo de compactação por amassamento. Os resultados indicaram que as adições das argilas OMMT e MMT as misturas asfálticas promoveram aumento no valor do Módulo de Resiliência e da Resistência à Tração quando comparados ao ligante asfáltico sem modificador.

The Use of Epoxy Silanes on Montmorillonite: An Effective Way to Improve Thermal and Rheological Properties of PLA/MMT Nanocomposites Obtained via “In Situ” Polymerization

Polylactic acid (PLA) nanocomposites were prepared via “in situ” ring opening polymerization (ROP) of lactide using a montmorillonite, Cloisite 15A, employed after surface treatment with 3‐Glycidoxypropyltrimethoxysilane. The dispersion of the nanoparticles was checked using Wide Angle X‐Ray Scattering (WAXS) and Transmission Electron Microscopy (TEM); both the effects of different amounts of montmorillonite and silane were measured on molecular weights and on thermal and rheological properties, using Size Exclusion Chromatography (SEC), Differential Scanning Calorimetry (DSC), thermogravimetric analyses (TGA), and rheological analyses. It was found that even very low amounts (0.1% w/w) of nanoparticles greatly affect nanocomposites properties. Unmodified montmorillonite tends to decrease molecular weights, deactivating the catalytic system used for ROP of lactide, but when epoxy silane is present molecular weights increase. Melt crystallization temperatures increase with modified nanoparticles, which enhance crystallization process. TGA analyses show that when pure montmorillonite is present, nanocomposites have lower thermal stability with respect to standard PLA; when silane is used thermal stability can get much higher than standard PLA as silane content increases. The rheological behaviour of nanocomposites shows that melt viscosity is far higher than that of standard PLA at low shear rates and also a marked shear thinning behaviour can be achieved.

Thermal Activation of a Pure Montmorillonite Clay and Its Reactivity in Cementitious Systems

Clay minerals are potential candidates as raw materials for new supplementary cementitious materials (SCMs) that can partly replace Portland cement and thereby significantly reduce CO2 emissions associated with cement production. We present the characterization of the complex, disordered structure of a pure montmorillonite clay heated at various temperatures (110–1100 °C), by solid-state 27Al and 29Si MAS NMR methods. The SiO4 tetrahedra and AlO6 octahedral sites become progressively more distorted, exhibit a significant degree of disorder upon dehydroxylation (600–800 °C), and do not lead to the formation of any metastable phase. At high temperatures (1000–1100 °C), the layer structure of the clay breaks down, forming stable crystalline phases. The chemical reactivity, measured as the degree of dissolution/precipitation in an alkaline solution, is found to be proportional to the degree of disorder/dehydroxylation. The maximum reactivity as a function of the heating temperature is achieved at 800 °C prior to the formation of inert, condensed Q4-type phases in the material. At maximum reactivity the calcium silicate hydrate (C-S-H) phase contains silicate chains with the highest aluminum incorporation, leading to blended cements containing a C-S-H phase with longer chain lengths. Most importantly, by exploiting the differential spin–lattice relaxation behavior of the 29Si spins, evidence of multiple sites and components in both the naturally occurring and heated montmorillonite is being reported for the first time.

Interaction of methane hydrate complexes with smectites: Experimental results compared to molecular models

Molecular simulations were performed to determine the structure and behavior of methane hydrate complexes in the interlayer of Na-rich montmorillonite and beidellite smectite. Molecular dynamics (MD) simulations used NPT ensembles in a 4 × 4 × 1 supercell comprised of montmorillonite or beidellite with methane hydrate complexes in the interlayer. The simulations presented here are in agreement with experimental data that show a significantly expanded interlayer (Guggenheim and Koster van Groos 2003; Koster van Groos and Guggenheim 2009). The smectite 2:1 layer forms part of the coordination sphere enclosing methane molecules; the MD results show that water molecules close to the siloxane surface form mixed cages that enclose methane molecules between basal oxygen atoms of the silicate rings and water molecules from the hydrogen bonding network. However, the higher tetrahedral charge did not favor the formation of methane hydrate components in the interlayer. Thus, methane hydrate complexes can be formed in pure montmorillonite more easily than in beidellite. Clay minerals obtained from marine localities with associated methane seeps and with variable Na, K, Ca, and Mg interlayer compositions were used to examine how swelling capacity affects the crystallization of smectite-methane-hydrate complexes. Results show that the formation of these complexes depends on the swelling capacity in the smectite. In samples with limited swelling properties, methane hydrate is formed in the pore spaces between particles and on the external surface of clays.

Kaolin/montmorillonite mixtures behaviour on oedometric path and microstructural variations

The aim of this study is to understand and to characterise the influence of the montmorillonite fraction on the behaviour of several mixtures of kaolin and montmorillinite, ranging from pure kaolinite to pure montmorillonite. We show that beyond 35% in weight, montmorillonite is responsible for the global behaviour of the mixture. At the global level, the influence of montmorillonite becomes apparent through the fact that one-dimensional compressibility path, in the (logσ′v-e) plane, loses its linearity. At the local level, MIP results show that the compressibility, for any of the studied mixtures, results in variations in inter-aggregate porosity. The qualitative analysis of SEM images explains the macroscopic behaviour, showing that the more flexible particles of montmorillonite form a structured network surrounding the kaolinite particles. When the percentage of montmorillonite exceeds 35%, the role of this phase becomes major, imposing in particular the particles orientation mechanisms.

Adsorption Removal of Fluoride from Aqueous Solution by Hydroxy-Iron Pillared Montmorillonite

Hydroxy-iron pillared montmorillonite (Fe-Mont) was prepared and characterized, and the fluoride adsorption capacity of Fe-Mont was investigated. Compared to pure montmorillonite (Mont), the interlayer spacing, specific surface area (SSA), surface fractal dimension and isoelectric point (IEP) of Fe-Mont increased. At pH 4.5, the Langmuir adsorption capacity (qmax) for fluoride of Mont and Fe-Mont was 4.23 and 6.92 mg/g, respectively. The adsorption data for fluoride by Fe-Mont could be fitted by Langmuir model (R2 =0.986) and also by Freundlich isotherm (R2 =0.948), and indicating that the monolayer and multilayer adsorption behaviors are simultaneously involved in the fluoride adsorption processes of Fe-Mont.

Evaluation of sorption-desorption processes for metalaxyl in natural and artificial soils

The main process controlling soil-pesticide interaction is the sorption-desorption as influenced by active soil surfaces. The sorption phenomena can influence translocation, volatility, persistence and bioactivity of a pesticide in soil. The present investigation was conducted on natural and artificial soils in order to enumerate the effect of soil components such as montmorillonite and ferrihydrite on the sorption behaviour of the fungicide metalaxyl and if sorption-desorption of the chiral pesticide affects the enantiomeric ratio. The sorption-desorption characteristics of metalaxyl were investigated by batch equilibration technique in a natural soil, two artificial soils, and in pure montmorillonite and ferrihydrite. After extraction, pesticide residues were analyzed by conventional and chiral chromatography using tandem mass spectrometry. A KdSorp (2.3–6.5) suggests low level sorption of metalaxyl with an appreciable risk of run-off and leaching. Thus, metalaxyl poses a threat to surface and ground water contamination. Furthermore, desorption tests revealed a hysteretic effect (H ≤ 0.8) in natural and artificial soils. Significant amount of metalaxyl was found tightly bound to the adsorbents without desorbing readily after desorption cycle. Desorption of 22–56% of the total amount of the retained metalaxyl was determined. This study reveals that an artificial soil derived from different soil constituents can be used to assess their influence on sorption/desorption processes. The present investigation showed that both montmorillonite and ferrihydrite play a significant role in the sorption of metalaxyl. The sorption doesn't influence the enantiomeric ratio of racemic metalaxyl.