Hydrous Montmorillonite Research Articles

A CSS surface based THM bounding constitutive model for volumetric behavior of bentonite

Development of the constitutive model for bentonite under coupled thermo-hydro-mechanical (THM) condition is of great significance for the construction and safety assessment of deep geological disposal repositories for high-level radioactive waste (HLW). In this work, a new temperature-suction-mean net stress (T-s-p) space with the conception of critical saturated state (CSS) surface was defined to represent the actual stress state of bentonite under coupled THM condition. Then, based on the CSS surface, a THM constitutive model was proposed for describing the volumetric behavior of compacted bentonite. Under the THM model framework, two bounding surfaces were proposed to describe the elastoplastic volume changes induced by mechanical response of skeleton and hydration of montmorillonite, respectively. The model responses upon some typical THM paths were simulated and discussed to reveal the performance of the proposed constitutive model for bentonite. Finally, the proposed model was validated by simulating by several volume change tests carried out on different bentonites. The results confirmed that the proposed model shows more advantages in describing the THM volumetric behavior.

Experimental Study on Permeability and Gas Production Characteristics of Montmorillonite Hydrate Sediments Considering the Effective Stress and Gas Slippage Effect

Summary Gas permeability in hydrate reservoirs is the decisive parameter in determining the gas production efficiency and gas production of hydrate. In the South China Sea (SCS), the gas flow in tight natural gas hydrate (NGH) silty clay reservoirs is significantly affected by the gas slippage effect and the effective stress (ES) of overlying rock. To improve the effectiveness of hydrate exploitation, it is necessary to understand the influence of gas slippage in hydrate reservoirs on the permeability evolution law. For this paper, the gas permeability characteristics and methane production of hydrate montmorillonite sediments were studied at different pore pressures and ESs. Experimental data revealed that the gas permeability of montmorillonite samples before methane hydrate (MH) formation is seriously affected by the Klinkenberg effect. The gas permeability of montmorillonite sediments before hydrate formation is generally smaller than that after hydrate formation, and the gas slippage effect in the sediments after hydrate formation is weaker than that before hydrate formation. With the change in ES, the intrinsic permeability of sediment has a power law relationship with the simple ES. The ES law coefficient n was determined using the response surface method to eliminate the influence of gas slip on gas permeability. As pore pressure decreases and MH decomposes, montmorillonite swelling seriously affects gas permeability. However, the gas slippage effect has a good compensation effect on the permeability of montmorillonite sediments after MH decomposition under low pore pressure. The multistage depressurization-producing process of MH in montmorillonite sediments is mainly 3 MPa depressurization-producing stage and 2 MPa depressurization-producing stage. In this paper, the influence mechanism of gas slippage effect of hydrate reservoir is studied, which is conducive to improving the prediction accuracy of gas content in the process of hydrate exploitation and exploring the best pressure reduction method to increase the gas production of hydrate in the process of exploitation.

Preparation and Application of New Polyhydroxy Ammonium Shale Hydration Inhibitor

Wellbore instability caused by the hydration of shale formations during drilling is a major problem in drilling engineering. In this paper, the shale inhibition performance of polyhydroxy-alkanolamine was evaluated using an anti-swelling test, linear swelling test, wash-durable test and montmorillonite hydration and dispersion experiment. Additionally, the shale inhibition mechanism of polyhydroxy-alkanolamine was studied via Fourier transform infrared spectroscopy (FTIR), particle size, zeta potential, thermogravimetric analysis (TGA) and scanning electron microscopy (SEM). The results show that the use of polyhydroxy-alkanolamine (EGP-2) could result in a relatively lower linear swelling rate of montmorillonite, and the linear swelling rate of 0.3% EGP-2 is 26.98%, which is stronger than that of 4% KCl. The anti-swelling rate of 0.3% EGP-2 is 43.54%, and the shrinkage–swelling rate of 0.3% EGP-2 is 34.62%. The study on the inhibition mechanism revealed that EGP-2 can permeate and adsorb on the surface of montmorillonite. The rolling recovery rate of easily hydrated shale was as high as 79.36%, which greatly reduces the dispersion ability of water to easily hydrated shale. The results of this study can be used to maintain the stability of a wellbore, which is conducive to related research.

Influence of montmorillonite hydration and delamination on coal flotation

Influence of montmorillonite hydration and delamination on coal flotation

Near-IR study of the impact of alkyl-ammonium and -phosphonium cations on the hydration of montmorillonite

Organo-montmorillonites (O-Mts) are attractive inorganic-organic hybrid materials used in numerous industrial applications. In this work the adsorption of water onto montmorillonite saturated with the alkylammonium and alkylphosphonium cations tetramethyl-(Me4-N/P), tetrabutyl-(Bu4-N/P) and tetraoctyl-(Oc4-N/P) was studied. The effect of the organic cation size and particularly of the central atom of the organic cation head-group (N vs P) was followed at different relative humidities (RH). The samples were characterized using carbon analysis, N2 adsorption, X-ray powder diffraction analysis (XRPD), and infrared spectroscopy (IR) in the middle-IR (MIR) and near-IR (NIR) regions. Gravimetric analysis and NIR spectroscopy were used to monitor the hydration of the O-Mts. A gradual shift of the combination band of water molecules, (ν+δ)H2O, to lower wavenumbers on increasing the amount of adsorbed water indicated an increase in the number of H2O molecules involved in stronger hydrogen bonds. A shift of the 2νCH3 band to higher wavenumber with increasing RH, observed for Me4-N/P-Mts and Bu4-N-Mt, provided evidence that water molecules interacted directly with the methyl groups of the Me4-N/P and Bu4-N cations. Gravimetric analysis confirmed that at each RH the content of adsorbed water decreased in the direction Me4-N/P-Mts ⟹ Bu4-N/P-Mts ⟹ Oc4-N/P-Mts due to the increasing hydrophobicity of the organic cations. The area of the (ν+δ)H2O band, reflecting the degree of O-Mt hydration, confirmed the results obtained by gravimetry, i.e. the content of adsorbed water decreased as the size of the organic cation increased. The results of the NIR spectroscopy as well as gravimetric analysis showed a higher hydrophobicity of O-Mts saturated with alkylphosphonium cations compared to their alkylammonium counterparts. The obtained results showed that NIR spectroscopy is a very useful method for the characterization of organo-montmorillonite hydration.

Synthesis of alkali-activated uncalcined Pisha sandstone cement composites

This work reports the utilization of natural Pisha sandstone (PS) as a new precursor to manufacture a novel alkali-activated cement. The rheological properties, compressive strength, drying shrinkage, hydration properties, CO2 emission and energy consumption of the alkali-activated uncalcined Pisha sandstone cement composites (AUPC) were investigated. AUPC mortar containing 1.0 wt% of sodium hexametaphosphate and 0.2 wt% of ligneous calcium sulfonate as plasticizers showed similar rheological properties to those of ordinary Portland cement (OPC) mortar. The compressive strength of AUPC could reach 52.7 MPa after curing at 80 °C for 12 h. The increase of activator concentration (up to 4 mol/L) and the extending of curing time (up to 12 h) significantly increased the hydration of feldspar, montmorillonite and blended slag in AUPC. This resulted in the formation of more low Al/Si ratio aluminosilicate gels, calcium silicate hydrate (C-S-H) gels, and calcium alumina silicate hydrate (C-A-S-H) gels. When the concentration of NaOH and the curing time exceeded 4 mol/L and 12 h respectively, the porosity of AUPC increased, thereby lowering the compressive strength. The 90-day drying shrinkage of the AUPC with 4 mol/L NaOH activator increased from 1.68 to 3.04 mm/m when the water-to-binder ratio increased from 0.25 to 0.45. The total CO2 emissions and energy consumption for producing AUPC were estimated to be much lower than producing OPC.

Molecular Dynamics Simulation of Clay Hydration Inhibition of Deep Shale

In the process of the exploitation of deep oil and gas resources, shale wellbore stability control faces great challenges under complex temperature and pressure conditions. It is difficult to reflect the micro mechanism and process of the action of inorganic salt on shale hydration with the traditional experimental evaluation technology on the macro effect of restraining shale hydration. Aiming at the characteristics of clay minerals of deep shale, the molecular dynamics models of four typical cations (K+, NH4+, Cs+ and Ca2+) inhibiting the hydration of clay minerals have been established by the use of the molecular dynamics simulation method. Moreover, the micro dynamics mechanism of typical inorganic cations inhibiting the hydration of clay minerals has been systematically evaluated, as has the law of cation hydration inhibition performance in response to temperature, pressure and ion type. The research indicates that the cations can promote the contraction of interlayer spacing, compress fluid intrusion channels, reduce the intrusion ability of water molecules, increase the negative charge balance ability and reduce the interlayer electrostatic repulsion force. With the increase in temperature, the inhibition of the cations on montmorillonite hydration is weakened, while the effect of pressure is opposite. Through the molecular dynamics simulation under different temperatures and pressures, we can systematically understand the microcosmic dynamics mechanism of restraining the hydration of clay in deep shale and provide theoretical guidance for the microcosmic control of clay hydration.

Study of a Polyamine Inhibitor Used for Shale Water-Based Drilling Fluid.

Here, we report a water-soluble shale inhibitor for inhibiting shale hydrate formation. The copolymer denoted as thermogravimetric analysis (TGA) was synthesized via triethanolamine, two maleic anhydrides, and glacial acetic acid. The infrared (IR) and gas chromatography (GC) results indicated that TGA is a low molecular weight polymer inhibitor (IR) and is the most commonly used method to identify compounds and molecular structures qualitatively. It is mainly used to study the molecular structure of organic substances and conduct qualitative and quantitative analyses of organic compounds. The main function of GC is for polymer molecular weight analysis. With the aid of shale rolling recovery experiments, particle size distribution experiments, triaxial stress experiment methods, bentonite slurry rate inhibition experiments, and thermogravimetric experiments to evaluate TGA inhibition characteristics, the inhibition effect of TGA is better than that of the traditional inorganic salt inhibitor KCl, polymer amine inhibitor UHIB, and organic cationic shale inhibitor NW-1. When the mass fraction is 0.2%, the cutting recovery rate increases from 18.3 to 94.1%. The compressive strength of the shale core after adding 1% TGA inhibitor is 177.9 MPa, which is close to the original core compressive strength of 186.5. The wet sodium montmorillonite crystal layer spacing after treatment with 0.5%, 1.5%, and 3% TGA aqueous solution is 1.38, 1.35, and 1.35 nm, respectively, and the sodium montmorillonite crystal layer spacing after diesel treatment is 1.34 nm, indicating that the inhibitory effect of TGA on sodium montmorillonite is equivalent to that of diesel and that TGA can effectively inhibit the hydration and dispersion of sodium montmorillonite. At the same time, the crystal layer spacing and the weight loss rate of sodium montmorillonite modified by TGA inhibitors did not change significantly after adsorption of deionized water, which proved that TGA inhibitors could be adsorbed in the crystal layer space of sodium montmorillonite to inhibit hydration and dispersion of sodium montmorillonite. Field test results show that TGA can significantly improve the inhibition performance of the field drilling fluid, and the effect is better than the strong conventional inhibition water-based drilling fluid system, which solves the problems of wellbore instability and considerable friction in horizontal shale sections and provides a new idea and method for efficient shale gas drilling.

Molecular Simulation of the Hydration of Montmorillonite under High-temperature and Highpressure

The hydration expansion of clay minerals in shale is an important factor affecting the sidewall stability of shale gas well. The montmorillonite is the main constituent of clay minerals, and its hydration mechanism is very important to solve the problem of borehole wall instability in shale gas well. In order to further explore the hydration mechanism of the montmorillonite under high temperature and high pressure, molecular simulation software was used to study the inter-layer spacing, inter-layer material movement, ionic hydration properties and mechanical parameters of the montmorillonite under different temperature and pressure conditions from a microscopic perspective. The results show that when the temperature increases and the pressure decreases, the inter-layer spacing of montmorillonite augments, and relatively the temperature has a great influence on the inter-layer spacing, which ranges from 1.823-2.042 nm. The diffusion rate of inter-layer water molecules and sodium ions increases with the increase of temperature and decreases with the increase of pressure. The hydration coordination number of sodium ion is large at low temperature and high pressure, and the coordination number varies from 2.35 to 4.35. When the temperature goes up, the volume modulus, shear modulus and elastic modulus of montmorillonite crystal goes down and poisson's ratio increases, while the effect of pressure on the mechanical parameters of montmorillonite crystal is the opposite. It can be seen that the research results of this paper have important theoretical guiding significance for the research of shale formation hydration mechanism under high temperature and high pressure formation environment.

Water Trapping Dynamics in Carbohydrate-Populated Smectite Interlayer Nanopores

Smectite-type clays play a critical role in the trapping of fluids within soil and atmospheric nanoparticles. The hydrodynamics of cation-saturated smectite nanopores are well documented. However, little is known about the influence of small organic compounds. Here we investigate the effects of carbohydrates (glucose and cellobiose), representing an important class of organic compounds, on the hydration and nanopore structures of montmorillonite, a prototypical smectite. To achieve the same amount of adsorbed water, higher relative humidity was required in the presence of the adsorbed carbohydrates than with the clay alone. The decrease in the characteristic micropore water adsorption with the clay–carbohydrate aggregates implied that water adsorption was constrained within the clay nanopore regions. The presence of carbohydrates promoted water retention as a function of gradual decrease in moisture content. Moisture-dependent X-ray diffraction patterns determined that, relative to the mineral alone, grea...

Momentum transfer in hypervelocity cratering of meteorites and meteorite analogs: Implications for orbital evolution and kinetic impact deflection of asteroids

Kinetic impact is regarded as an effective way to divert an asteroid on a collision course with the Earth. However, asteroids show a wide diversity in their mineralogy, porosity, and water content. Asteroids range in composition from primitive undifferentiated objects to differentiated objects. Among the undifferentiated asteroids they range from more reflective, carbon-poor bodies to darker, carbonaceous bodies. Porosities of asteroids range from 0 to >50%, with most >20%, and some asteroids exhibit a 0.7 µm water feature in their reflection spectra. Mineralogy, porosity and hydration are each expected to influence the momentum transferred in hypervelocity collisions. We conducted a series of measurements of the post-impact momentum, which is characterized by a factor β, the ratio of the total linear momentum acquired by the target to the momentum of the impactor. We measured β for anhydrous meteorites, which sample their asteroidal parent bodies, spanning a wide range of porosities: including 7 samples of the CV3 carbonaceous chondrite Northwest Africa (NWA) 4502 (2.1% porosity), 7 samples of the ordinary chondrite NWA 869 (6.4% porosity), 4 samples of the ordinary chondrite Saratov (15.6% porosity), and, to extend our measurements to higher porosity than is found among meteorites, 2 samples of terrestrial pumice (80% porosity). We also measured β for hydrous meteorite analog targets: including 2 samples of terrestrial serpentine (17.9% porosity) and 4 samples of terrestrial montmorillonite (51.5% porosity), the two clay minerals that dominate the composition of the hydrous CI carbonaceous chondrite meteorites, as well as 4 samples of hydrous meteorite analog material prepared by powdering and hydrating an anhydrous carbonaceous chondrite. We found that for both the anhydrous and the hydrous samples β decreased with increasing porosity, consistent with hydrocode modeling. However, the β values we measured for the ∼5 km/s impacts onto these anhydrous samples, with β = 3.55 for NWA 4502, 2.69 for NWA 869, 2.10 for Saratov, and 2.15 for pumice, are larger than results from hydrocode modeling for 10 km/s impacts into relatively strong, porous rock targets. The β values for the moderate porosity (17.9%) hydrous serpentine targets (β = 4.70), the highly porous (51.55%) hydrous montmorillonite targets (β = 2.79), and the moderately porous CI-analog targets (β = 2.99) are each significantly larger than the β value for anhydrous targets of comparable porosities. This is likely due to jetting of water vapor, which could significantly affect the deflection of hydrous asteroids and icy comets in natural or human-induced collisions.

Molecular dynamics simulation of strength weakening mechanism of deep shale

Due to the dissimilarities in the hydration characteristics and degree of clay minerals, the wellbore instability and sloughing of deep shale is more sudden and destructive than that of the shallow shale. Previous works mainly consider the effects of temperature and pressure condition on the wellbore instability of deep shale at macroscopic scale, and ignore the microscopic mechanism of strength weakening during hydration and the evolution characteristics of montmorillonite(MMT) hydration under different isomorphic substitutions, temperature and pressure conditions. By considering the characteristics of clay minerals and drilling fluids in deep shales, the molecular dynamics simulations of MMT hydration in deep shale under different isomorphic substitutions, water content, temperature and pressure conditions were carried out to analyze the distribution and conduction evolution characteristics of water molecules and cations, and the response characteristics of crystal elastic parameters during the hydration process. The results indicate that: (1) As the water content increases, the interlayer spacing increases, but it is less sensitive to the temperature and pressure. Moreover, with the increase of water content, water molecules and ions are accelerated to intrude into crystal layer, and the hydration effects are enhanced and the weakening effects on rock strength are increased as well. (2) Both temperature and pressure have significant influences on the hydration characteristics of MMT, but the influential trends are opposite. Increasing temperature promotes the invasion of water molecules and sodium ions into the crystal layer so as to enhance the hydration, the weakening effect on rock strength becomes more remarkable. On the contrary, with the increase of pressure, the diffusion coefficient of water molecules and sodium ions to interlayer decreases which inhibits the weakening effect of clay hydration. (3) The differences of hydration characteristics of MMT with typical isomorphic substitutions are significant. The hydration ability of sodium ion in Fe-substituted MMT was weaker and the diffusion coefficient of water molecules was larger, so that water molecules more easily invade into the crystal layer, and the strength weakening is more significant than that of the Mg-substituted MMT system. Furthermore, the weakening effect is more significant under high temperature and low pressure conditions. The microscopic dynamic mechanism of clay hydration in deep shale can be throughly understood through molecular dynamics simulation, which provides an innovative research approach for the quantitative evaluation of drilling fluid hydration inhibition and microscopic control of clay hydration in deep shale.

Effect of montmorillonite content and sodium chloride solution on the residual swelling pressure of an expansive clay

Expansive clays may continue to swell even after obtaining fully saturated condition due to the continuing montmorillonite hydration process. Expansive clays in this case, if confined, will generate swelling pressure, which is termed as residual swelling pressure in this study. The residual swelling pressure poses significant impact on the long-term safety and stability of adjacent geotechnical infrastructure. Despite its significance, currently, there are very limited studies on the residual swelling pressure. In this paper, the influence of (1) the montmorillonite content and (2) sodium chloride (NaCl) concentration in the pore water on the residual swelling pressure of a compacted expansive clay was evaluated using constant-volume swelling tests. Scanning electron microscopy analyses were applied to investigate the influence of NaCl solution on the microstructure of the compacted expansive clay. Tests results showed that the residual swelling pressure increases with montmorillonite content and dry density of specimen and decreases with an increase in the NaCl concentration. The NaCl in the pore water used for compacting the clay influences the particle orientation and arrangement. High NaCl concentrated solution contributes to soil structures with higher integrity that exhibit lower residual swelling pressure. An equation is developed to interpret and predict the residual swelling pressure of expansive soils considering their montmorillonite content and dry density. The proposed equation is verified using experimental data determined in this study as well as data obtained from the literature.

Estimating mineral abundances of clay and gypsum mixtures using radiative transfer models applied to visible-near infrared reflectance spectra

Quantitative mineral abundances of lab derived clay–gypsum mixtures were estimated using a revised Hapke VIS-NIR and Shkuratov radiative transfer model. Montmorillonite–gypsum mixtures were used to test the effectiveness of the model in distinguishing between subtle differences in minor absorption features that are diagnostic of mineralogy in the presence of strong H2O absorptions that are not always diagnostic of distinct phases or mineral abundance. The optical constants (k-values) for both endmembers were determined from bi-directional reflectance spectra measured in RELAB as well as on an ASD FieldSpec3 in a controlled laboratory setting. Multiple size fractions were measured in order to derive a single k-value from optimization of the optical path length in the radiative transfer models. It is shown that with careful experimental conditions, optical constants can be accurately determined from powdered samples using a field spectrometer, consistent with previous studies. Variability in the montmorillonite hydration level increased the uncertainties in the derived k-values, but estimated modal abundances for the mixtures were still within 5% of the measured values. Results suggest that the Hapke model works well in distinguishing between hydrated phases that have overlapping H2O absorptions and it is able to detect gypsum and montmorillonite in these simple mixtures where they are present at levels of ∼10%. Care must be taken however to derive k-values from a sample with appropriate H2O content relative to the modeled spectra. These initial results are promising for the potential quantitative analysis of orbital remote sensing data of hydrated minerals, including more complex clay and sulfate assemblages such as mudstones examined by the Curiosity rover in Gale crater.

Study on hydration of montmorillonite in aqueous solutions

Using a parameter representing the degree of hydration of particles in a liquid called hydration index I, which we derived based on Einstein’s viscosity equation, we evaluated the degree of hydration of fine montmorillonite particles in different aqueous solutions by measuring the viscosities of the montmorillonite dispersions and plotting relative viscosity against volume fraction of dry montmorillonite particles in the dispersions. We investigated the effects on the hydration of montmorillonite in aqueous solutions of (1) the type and (2) the concentration of electrolytes in the solutions and (3) pH. For the same concentration of electrolytes, the hydration index I of montmorillonite was found to increase in the order of Na+ > K+ for monovalent cations and Mg2+ > Ca2+ for divalent cations, and to decrease with increasing valence of cations in the order of Na+ > Ca2+ > Al3+. For both Na+ and Ca2+, the hydration index I first increased with increasing concentration of electrolytes and then decreased after a certain concentration. The hydration index I increased with increasing pH.

Synthesis of a Biglucoside and Its Application as Montmorillonite Hydration Inhibitor

A biglucoside (BG) was synthesized with glucose and epichlorohydrin as raw materials. The inhibition of BG against montmorillonite swelling was investigated by various methods including montmorillonite linear expansion test, mud ball immersing test, thermogravimetric analysis, and scanning electron microscopy. The results show that the BG has good inhibition ability to the hydration swelling and dispersion of montmorillonite. Under the same condition, the linear expansion ratio of montmorillonite in BG solution is much lower than that of MEG. The particle distribution measurement, thermogravimetric analysis, FT-IR, and scanning electron microscopy results all prove the efficient inhibition of BG.

Experimental study on slime water flocculation sediment based on the montmorillonite hydration expansion inhibition

Through the montmorillonite settlement experiment in the clear water and electrolyte solution, the influence of slime water settling character was studied in clear water and different electrolyte solution, the montmorillonite’s hydration expansion effectively restrained was verified, the process method to wash coal with the electrolyte was put forward, and the results indicate that the solution of 10 g/L KCl is optimal inhibitor on the montmorillonite in the tested three kinds of electrolyte solution. With the contrast test in clear water and electrolyte solution, two reagent adding way can be selected in KCl solution: one way is to add PAM separately, the effectively sedimentation can be made with simply 0.1% anion; the other way is the coordination with polymeric aluminum and PAM, the anionic of PAM and polymeric aluminum are 0.02% and 0.5% respectively. However, in clear water, the polymeric aluminum must be joined together with the anionic PAM, and the amount of the PAM reaches 0.5%, which is 25 times as great as that in KCL solution. The field work with raw coal further verifies the above conclusions further.

Combined Salt and Temperature Impact on Montmorillonite Hydration

AbstractBentonite is to be used as a sealing material for long-term storage of radioactive waste. During permafrost periods the buffer may freeze, causing the following: montmorillonite dehydration, ice formation, and pressure build-up that may fracture the surrounding rock. No previous study has been done on freezing of bentonite in saline water. Using small and wide angle X-ray scattering, the present study aimed to increase understanding of the combined impact of salt and temperature on the hydration (swelling) of Wyoming montmorillonite. The basal spacing of the Na-montmorillonite was very dependent on the water content, while this was not the case for the Ca-montmorillonite (after reaching 19 Å). The basal spacing of the free-swelling Na-montmorillonite (34–280 Å) was estimated successfully using simple calculations. During freezing of Na-montmorillonite in NaCl solution, both ice and hydrohalite formed (at -50 and -100ºC). At starting concentrations ≥ 1.5 M the basal spacing was not affected by freezing. During freezing of Ca-montmorillonite in CaCl2 solution, ice formed; antarcticite formed only sporadically. The basal spacing of the Ca-montmorillonite at high NaCl concentrations (>1 M) was greater at -50 and -100ºC (18 Å) than at 20ºC (16 Å). The opposite was observed at low concentrations. This change was attributed to small amounts of salts introduced into the montmorillonite interlayer, hence changing the interlayer water properties. The montmorillonite hydration was also temperature dependent; decreasing temperature increased the hydration (as long as no ice was formed) and increasing the temperature decreased the hydration. This was attributed to the temperature impact on the entropy of the hydration reaction. This observation was also reproduced in an experiment up to 90ºC. A small amount of salt in the groundwater was noted to reduce significantly the potential problem of ice formation in bentonite sealings.

Electron microscopic observation of montmorillonite swelled by water with the aid of hydrophilic ionic liquid

The morphology and structure of hydrous montmorillonite in different swelling condition have been observed with the aid of hydrophilic ionic liquid (IL; 1-Butyl-3-methylimidazolium Tetrafluoroborate) using electron microscope. The observation mechanism of hydrous montmorillonite with layer structure using IL was revealed by swelling behavior as measured by X-ray diffraction (XRD) and transmission electron microscopy (TEM) with selected area electron diffraction pattern (SAED). The morphology of hydrous montmorillonite containing a large amount of water was also successfully observed by field emission electron microscope (FE-SEM). In addition, the inductively coupled plasma (ICP) and thermogravimetric – differential thermal analysis (TG-DTA) results showed the ion-exchange behavior of hydrous montmorillonite during the IL treatment. The technique allowed the exact morphology to be observed of hydrated materials with layer structure in civil engineering, cosmetics, medical and agricultural fields.

Molecular dynamics simulation study of benzene adsorption to montmorillonite: Influence of the hydration status

Clay minerals are ubiquitous in soil and sediments and they have been considered as important geosorbents for organic contaminants. However, the adsorption capacity of clay minerals strongly depends on their hydration status. In this work, the adsorptive characteristics of benzene on a set of hydrated montmorillonites which contain different counterions (Na+, K+, Cs+) and water content were studied using classical molecular dynamics (MD) simulations. On the outer surface of unhydrated montmorillonites the adsorption energy of benzene decreases in the order: Na–montmorillonite (−0.46eV)>K–montmorillonite (−0.39eV)>Cs–montmorillonite (−0.36eV). After hydration benzene molecule will be gradually expelled away from the siloxane surface by water molecules and be adsorbed at the water–vacuum interface. Within the interlayer space of unhydrated montmorillonite benzene molecule can only lay flat on the siloxane surface, and a large positive adsorption energy is obtained due to the energy consumption which is needed to expand the interlayers. Hydration causes the expansion of montmorillonite interlayers, which then can help the adsorption of benzene to the interlayer spaces. As a result, the adsorption energy gradually evolves from large positive to negative as the water content increases to monolayer arrangement, and after that the adsorption energy remains negative. Hydration also significantly influences the interaction between counterions and benzene molecule, and benzene can bind closer to the counterbalance cation with weaker hydration capacity. Compared to the hydrated counterions, the hydrated siloxane surface is more likely to be the adsorption sites for benzene molecule. The above findings indicate that the hydration of montmorillonite has versatile effects on the adsorption of organic contaminants.