Na-saturated Montmorillonite Research Articles

The Effect of Humidity on the Mass and Unit Cell Volume of Montmorillonite near Room Temperature

Phase equilibria between montmorillonite (Swy-2 from Wyoming, USA) and H2O vapor phase were established by using the humidity buffer technique at 0.1 MPa and room temperature (23 ± 0.5°C). The Relative Humidity (RH; equivalent to the activity of H2O) levels of the system were defined between 6.5% and 97.4% by using six different salt-saturated aqueous solutions. There was no direct physical contact between Swy-2 sample and the buffer solution to prevent any metal ion exchanges between them. The reaction time at each humidity buffer was 10 days, after which the mass of the sample was determined and X-ray powder diffraction spectrum was collected. The experiments were carried out in two directions: one is adsorption (i.e., from low to high RH), and the other is desorption (i.e., from high to low RH), and the equilibrium of the system was demonstrated by the adsorption-desorption reversal experiments in terms of both mass change and crystal parameters (d-001 spacing and unit cell volume). When compared our data with those from previous study for Na-saturated montmorillonite, either synthetic or natural, the Na replacement in the crystal structure favored the retention of water, but only under RH higher than about 62%.

Ion-Exchange Modeling of Divalent Cation Adsorption on SWy-3 Montmorillonite

AbstractIon-exchange modeling is used widely to describe and predict ion-adsorption data on clay minerals. Although the model parameters are usually optimized by curve fitting experimental data, this approach does not confirm the identity of the adsorption sites. The purpose of the present study was to extend to divalent cations a previous study on the retention of monovalent cations on Na-saturated montmorillonite (NaMnt) which optimized some of the model parameters using density functional theory (DFT) simulations. The adsorption strength of divalent cations increased in the order Mg2+ < Cd2+ < Ca2+ < Sr2+ < Ba2+. After adding adsorption of metal hydroxide species (MOH+), the three-site ion-exchange model was able to describe adsorption data over a wide pH range (pH 1–10) on NaMnt. X-ray diffraction (XRD) analyses were conducted to investigate the interlayer dimension of clay samples under various conditions. The cation retention strengths of divalent cations did not correlate with interlayer dimensions. The XRD analyses of the Mnt showed a d001 value of 19.6 Å when saturated with alkaline earth cations, 22.1 Å with Cd2+, 15.6 Å with Na+, and 15.2 Å with H+. In the case of Na+, the 15.6 Å peak decreased gradually and disappeared, and new peaks at 22.1 and 19.6 Å appeared when the percentages of Mg2+ and Ba2+ adsorbed increased on NaMnt. The peak shifted from 22.1 to 20.3 and 19.6 Å when the pH increased for all cations except Cd2+, which stayed constant at 22.1 Å. The coexistence of multiple d001 peaks in the XRD patterns suggested that the interlayer cations were segregated, and that the interlayer ion–ion interactions among different types of ions were minimized.

Structural effect of imidazolium-type ionic liquid adsorption to montmorillonite

The adsorption of 1-alkyl-3-methylimidazolium-type ionic liquids (ITILs) coupled with different counteranions (Tf2N−, PF6−, BF4−, and Cl−) with variational cation alkyl chain lengths (n = 2, 4, 6, and 8) to montmorillonite was investigated to explore the structural effect of ITILs on their adsorption. A series of montmorillonite with different cation exchange capacities (CECs) and possessing a set of homoionic K- and Cs-exchanged interlayer cations were also examined to assess the influence of montmorillonite structure and characteristics. The adsorption of ITILs to Na-saturated montmorillonite (Na-MAz) was counteranion-independent but increased with the increase in the alkyl chain length of the imidazolium cation. X-ray diffraction results indicated that ITIL cations with different alkyl chains lay flat between the montmorillonite interlayers with different contact angles. The uptake of ITILs by Na-MAz increased with the increase in the solution pH and decrease in ionic strength. Na-MAz exhibited greater adsorption than K- and Cs-saturated MAz due to the larger hydrated radii of Na+ than those of K+ and Cs+. The uptake of ITILs to Na-MZj (CEC = 64 mmol/100 g) was almost half compared with that of Na-MAz (CEC = 117 mmol/100 g). Consequently, this work demonstrated that the ITIL adsorption to montmorillonite was dependent on the structures of both adsorbate and adsorbent.

Removal of chromate from aqueous solutions by dendrimers-clay nanocomposites

Nanocomposites of phosphorus-based dendrimers and montmorillonite were prepared and examined using X-ray diffraction, thermal analysis, solid-state nuclear magnetic resonance, and high-resolution transmission electron microscope. The adsorption of chromate by the nanocomposites and the basic clay was studied in the temperature range 298–318 K. For the latter purpose, the kinetics was followed and adsorption isotherms were plotted. The results showed that intercalated nanocomposites (GC1-AT) were formed with the first generation of cationic dendrimers. The use of the second generation of cationic dendrimers resulted in the formation of a mixture of exfoliated and intercalated nanocomposites (GC2-AT). For both dendrimers, adsorption was by cation exchange. The kinetics of the adsorption of chromate on both nanocomposites and Na-saturated montmorillonite (Na-AT) followed the pseudo-second-order equation and the rate constants varied in 0.08–0.19 g/mmol s−1. The rate-limiting steps were discussed on the basis of the results of the external mass transfer and the internal diffusion models. The experimental isotherms fitted will the model of Temkin, and chromate adsorption was an endothermic process and occurred spontaneously (−13 < ΔG° < −6 kJ/mol). The maximum uptake amounts of chromate were in the range 23–38 mg/g. It was shown that as a result of the adsorption of chromate by Na-AT, the adjacent environment of the tetrahedral sheet cation (Si4+) changed. For GC1-AT, the closest environment of the phosphorus atoms of the confined dendrimers was modified, and the interlayer expanded. In the case of GC2-AT, both environments of Si4+ and the inner phosphorus atom of the dendrimers became shielded and the interlayer shrunk.

Influence of mineralogical and morphological properties on the cation exchange behavior of dioctahedral smectites

Structure and morphology determine the smectites properties. Thereby, edge sites play a key role for the reactivity and colloidal behavior of the smectite. Even so, the edge surface area represents only 1–3% of the total surface area its contribution is up to 10% of the cation exchange capacity (CEC). Na-saturated dioctahedral smectites <0.2 μm were characterized in detail with respect to their structure (layer charge, octahedral cation distribution, iron content, and layer charge distribution within tetrahedral and octahedral sheets). Furthermore, reduced charge montmorillonite (RCM) of these materials were studied. Particle dimension was estimated from argon adsorption, calculation of specific surface area and direct observation of single layers by atomic force microscopy (AFM), which also revealed morphology and particle size distribution of single layer. CEC was measured both for Na-saturated samples and RCM using the Cu-trien method over a pH range of 4–9. The Wyoming smectite with a mean layer diameter of 277 nm and a low layer charge of 0.26 eq/f.u. differs strongly from the others smectites with a mean layer diameter of about 100 nm and layer charges between 0.30 and 0.37 eq/f.u. Furthermore, the layer stacking is much higher for the Wyoming smectite in powder and RCM. Accordingly the edge properties differ between the four smectites. Based on calculation of edge site density and CEC measurements, we showed that the RCM can be used to study the edge site reactivity of the montmorillonites. The increase of CEC above their pHPZC,edge is equal for Na-saturated montmorillonite and RCM. The present study highlights the diversity in structure and morphology and resulting edge properties of four smectites.

Study on the effect of modified clay on the properties of high density polyethylene and Vietnamese starch blend

This study focuses on the preparation of organoclay by intercalating the new kind of modifying agent, monoglyceride (M-Gly), into the Vietnamese Na-saturated montmorillonite (Na-MMT) layers. The modification of clay was conducted in using internal thermo Hakee mixer with high shear rate which gave the obviously expansion of the layer galleries of clay, in having the dspacing more than 60Å showed by X-ray diffraction (XRD). The Low density polyethylene (LDPE)/thermal plastic starch (TPS) blend has been studied to prepare the green nanocomposite material in using the montmorillonite clay as the reinforced phase. The mixtures of LDPE/TPS/ montmorillonite nanocomposites have been elaborated by melting method at 1600C in 5 minutes. The nanocomposite morphology was investigated by X-Ray Diffraction (XRD) and Transmission Electronic Microscopy (TEM), and the results have shown the good dispersion of clay in the matrix polymer blend. As result, the thermal and mechanical properties of material are also enhanced when the claywas added. By mechanical testing machine showed tensile strength and modules of the mixture increased and good result in 3%wt of organoclay, which have shown interface adhesion between components so good in mixture

Mechanism of rhodamine 6G molecular aggregation in montmorillonite colloid

Abstract Stopped-flow mixing device and visible absorption spectroscopy were used for the analysis of dye rhodamine 6G (R6G) molecular aggregation in the colloids based on Na-saturated montmorillonite. Two stages of the reaction were identified: The first stage was very short and taking only several seconds, involving the adsorption of R6G cations and their initial aggregation on the surface of colloid particles. The initially formed J-aggregates exhibited similar spectral properties as monomeric form of R6G. In the second stage, initially formed aggregates converted to sandwich-type H-aggregates absorbing light at significantly lower wavelengths and adsorbed monomers. The aggregate rearrangement took several hours. Monomers, with the spectral properties identical to R6G solution, were also identified as a component in complex spectra using principal component analysis (PCA) and multivariate curve resolution (MCR). Partial bleaching of the dye was also proven. Reaction kinetics of the rearrangement of the aggregates followed the model considering a complex mechanism of the molecular aggregation. Data fits using stretched-exponential function led to the determination of rate constants, which had been in the range 10−3−4×10−3s−1.

CO2 Sorption to Subsingle Hydration Layer Montmorillonite Clay Studied by Excess Sorption and Neutron Diffraction Measurements

Geologic storage of CO(2) requires that the caprock sealing the storage rock is highly impermeable to CO(2). Swelling clays, which are important components of caprocks, may interact with CO(2) leading to volume change and potentially impacting the seal quality. The interactions of supercritical (sc) CO(2) with Na saturated montmorillonite clay containing a subsingle layer of water in the interlayer region have been studied by sorption and neutron diffraction techniques. The excess sorption isotherms show maxima at bulk CO(2) densities of ≈ 0.15 g/cm(3), followed by an approximately linear decrease of excess sorption to zero and negative values with increasing CO(2) bulk density. Neutron diffraction experiments on the same clay sample measured interlayer spacing and composition. The results show that limited amounts of CO(2) are sorbed into the interlayer region, leading to depression of the interlayer peak intensity and an increase of the d(001) spacing by ca. 0.5 Å. The density of CO(2) in the clay pores is relatively stable over a wide range of CO(2) pressures at a given temperature, indicating the formation of a clay-CO(2) phase. At the excess sorption maximum, increasing CO(2) sorption with decreasing temperature is observed while the high-pressure sorption properties exhibit weak temperature dependence.

Influence of the ionic strength and solid/solution ratio on Ca(II)-for-Na+ exchange on montmorillonite. Part 1: Chemical measurements, thermodynamic modeling and potential implications for trace elements geochemistry

Na/Ca ion-exchange isotherms were performed on a Na-saturated montmorillonite for different constant normalities of the aqueous chloride solution and at two solid/solution ratios. The experimental data suggest that the affinity of Na(+) for the solid increases with total normality and m/V ratio and that a significant proportion of CaCl(+) is also sorbed. A thermodynamic modeling procedure with one sorption site and three sorbed cations (Na(+), Ca(2+) and CaCl(+)) was applied to interpret the data. We show that by accounting for the activities of aqueous species, the experimental data obtained at different total normalities for a given solid/solution ratio can be fitted using a unique set of selectivity coefficient values. However, when the m/V ratio is decreased from 25 to 2.5 g/L, an increase in the log Kc(Na(+)/Ca(2+)) of up to 0.4 ± 0.05 was required to interpret the data with a constant log Kc(Na(+)/CaCl(+)) value. The same behavior concerning the increase in the log Kc(Na(+)/Ca(2+)) with a m/V ratio decrease was observed when using a multi-site model taking into account the specific sorption of H(+). The results clearly indicate that the Na(+)/Ca(2+) selectivity coefficients strongly depend on the solid/solution ratio but are independent of the exchanger composition and the total normality of the solution. Such findings provide possible pitfalls when using selectivity coefficients obtained in diluted suspension to assess the sorption in compacted clayrocks and allow a better prediction of the sorption of trace elements in competition with major cations.

Adsorption of phosphate on hydroxyaluminum- and hydroxyiron-montmorillonite complexes

One hydroxyaluminum-montmorillonite complex (HyAl-Mt), two hydroxyiron-montmorillonite complexes (HyFe-Mts) with different iron contents, and three hydroxyiron/aluminum-montmorillonite complexes (HyFeAl-Mts) with various Fe:Al molar ratios were synthesized. Behavior and kinetics of phosphate (P) sorption on selected Mt-complexes mentioned above were investigated under acidic conditions. The results indicated that the intercalations of polymeric HyFe and/or HyAl ions in interlayers of Na-saturated montmorillonite (Na-Mt) caused significant changes in surface properties of the Na-Mt, such as cation exchange capacity, specific surface area, pH at zero point of charge. In pH range tested (3.0–6.5), P adsorption on the Mt-complexes decreased with increasing pH, whereas the effect became weaker with increasing Fe contents in the Mt-complexes. The adsorption capacities of the HyFeAl-Mts were greater than those of the HyAl-Mt and HyFe-Mt, which could be attributed to decreasing crystallinity of Fe and Al oxides in the HyFeAl-Mts. The equilibrium adsorption of P on the Mt-complexes could be well described using the Langmuir isotherm, and the kinetics of P adsorption could be well described by both the pseudo-second-order and Elovich models. An increase in Fe contents in the Mt-complexes could enhance the initial kinetic rate of P adsorption, as suggested by the Elovich models. It is inferred that a great number of Fe-related active sorption sites have been located on the outer surfaces of the HyFe-Mt, as indicated by extremely high α value in the Elovich model. Previous studies focusing mainly on P sorption on HyAl-Mt complexes might have underestimated the contributions of Mt-complexes to P retention in acidic soils high in Fe contents.

Sorption of sodium dodecylbenzene sulfonate by montmorillonite

Sorption of linear alkylbenzene sulfonates by soils and sediments is an important process that may affect their fate, transport, toxicity and their application in remediation of contaminated soil and groundwater. In this study, batch experiments were conducted to elucidate the sorption of a widely used anionic surfactant, sodium dodecylbenzene sulfonate (SDBS), by montmorillonite. It was observed that: (i) SDBS was sorbed significantly by montmorillonite saturated with Ca 2+, but little by Na-saturated montmorillonite; (ii) the amount of SDBS sorbed by Ca 2+–montmorillonite was enhanced by NaCl; and (iii) no significant intercalation of SDBS into Ca 2+–montmorillonite was observed by X-ray diffraction (XRD) analysis. These results indicate that the removal of SDBS by Ca 2+–montmorillonite was primarily attributed to the precipitation between DBS − and Ca 2+ in solution which was released from montmorillonite via cation exchange. These results will help us to understand the sorption behavior and environmental effects of anionic surfactants.

The effect of iron concentration, hindered settling, saturating cation and aggregate density of clays on the size distribution determined by gravitation X‐ray sedimentometry

SummaryX‐ray sedimentation is potentially attractive for estimating the particle‐size distribution of soil, but has been thought to overestimate clay fractions because of the iron they contain. We have examined X‐ray sedimentation for estimating the particle‐size distribution of fully dispersed and of aggregated clay. We obtained good agreement between the pipette and X‐ray sedimentation methods using two different kaolinite samples with a small iron concentration. We also studied montmorillonite saturated with Li, Na, K, Mg or Ca to investigate possible effects of hindered settling. For the Ca montmorillonite, we obtained good agreement between X‐ray sedimentation and the pipette method at concentrations up to 40 g l−1. We also found that X‐ray sedimentation could be used at concentrations less than those recommended by the manufacturer. Hindered settling was observed at concentrations &gt; 20 g l−1 for Li‐ and Na‐saturated montmorillonite. Our data suggest that conducting experiments at different mass concentrations is a sensitive test to detect such problems. Finally we used a fractal model to investigate the possible errors that might result from the size dependence of aggregate density and show that the error caused by assuming a single value for particle density of solids is small.

An Experimentally Derived Kinetic Model for Smectite-to-Illite Conversion and Its Use as a Geothermometer

AbstractThe smectite-to-illite conversion during shale diagenesis has recently been used to constrain the estimate of a basin's thermal history. We have systematically investigated the kinetics for the conversion of a Na-saturated montmorillonite (SWy-1) to a mixed-layer smectite/illite as a function of KCl concentration (from 0.1 to 3 moles/liter) over a temperature range of 250° to 325°C at 500 bars in cold-seal pressure vessels using gold capsules. The results show that the conversion rate can be described by a simple empirical rate equation-dS/dt = A · exp(-Ea/RT) · [K+] · S2where S = fraction of smectite layers in the I/S, t = time in seconds, A = frequency factor = 8.08 × 10-4 sec-1, exp = exponential function, Ea = activation Energy = 28 kcal/mole, R = gas constant, 1.987 cal/deg-mole, T = temperature (degree Kelvin), [K+] = K+ concentration in molarity (M) in the fluid.The results also show that Ca2+ in solutions barely affects the illitization rate, whereas Mg2+ significantly retards the rate. The retardation, however, is not as severe as previously reported. Na+ ion can significantly retard the rate only if the concentration is high.We found that by assuming a range 0.0026-0.0052 moles/liter (100-200 ppm) of K+, concentrations similar to the value typically reported in oil field brines, the present kinetic model can reasonably predict the extent of the smectite-to-illite conversion for a number of basins from various depths and age. This narrow range of potassium concentrations, therefore, is used to model the smectite-to-illite conversion in shale when the actual chemical information of pore fluid is not available.The kinetic equation has been tested using field data from a large variety of geologic settings worldwide (i.e., the Gulf of Mexico, Vienna Basin, Salton Trough Geothermal Area, East Taiwan Basin, Huasna Basin, etc). The results show that the equation reasonably predicts the extent of the reaction within our knowledge of the variables involved, such as burial history, thermal gradients, and potassium concentration.

Polynuclear hydroxyaluminum-montmorillonite complexes: Formation of 18.8 Å and 28 Å pillared structures

Polynuclear hydroxyaluminum-montmorillonite complexe were prepared by treating Na-saturated montmorillonite with partially neutralized solutions of Al-containing monomer and polynuclear hydroxyaluminum species. The polynuclear hydroxyaluminum cations were preferably adsorbed by montmorillonite over monomer Al. The maximum quality of the polynuclear hydroxyaluminum adsorbed was ≈400 meq Al/100 g of montmorillonite and was independent of OH/Al molar ratios of hydroxyaluminum solutions. Three types of complexes were characterized by X-ray diffraction analysis; 18.8 Å phase, 28 Å phase and an intermediate phase. Initial conditions for drying suspensions containing complexes were found to be determining factors for the type of solid complex formed. Extremely dry conditions favored the formation of the 18.8 Å phase, whereas ambient conditions produced the intermediate phase. On aging, these phases were gradually transformed to the 28 Å phase. Upon heating at 700°C the 18.8 Å phase was converted to the 28 Å phase. The calculated average chemical composition of the polynuclear hydroxyaluminum cations adsorbed in montmorillonite layers was [Al(OH) 0.56+ 2.44] n. The quantity of the maximum adsorption, ≈400 meq, was only a quarter of the quantity of the interlayer cations required to form a chlorite structure which has a layer thickness of 14.2 Å. In spite of low amounts of hydroxy-Al adsorbed, the observed large basal spacings indicated that the complexes found in the present investigation must have pillared structures. From X-ray data, the height of the pillars was found to be ≈9.2 Å. This and chemical data suggested that the Johansson's model molecule [Al 13O 4(OH) 24(H 2O) 12] 7+, was most suitabl e for the pillar. If this is the case, then one molecule occupied an area of 12–13 montmorillonite unit cells at every layer in the 18.8 Å phase, whereas two cations occupied the corresponding area at every second layer in the 28 Å phase. Therefore, a transformation from the 18.8 Å phase to the 28 Å phase could be explained by the migration of the cations from an interlayer space of the 18.8 Å phase to one layer above or below.

The isothermal compressibility of water mixed with Na-saturated montmorillonite

The isothermal compressibility of water mixed with Na-saturated montmorillonite was measured in mixtures containing from 1.2 to 5.0 g of water per gram of montmorillonite. The isobaric expansibility of the water in some of these mixtures was also measured. It was found that the interparticle water was less compressible but more expansible than pure bulk water. Reasons were given for ascribing these differences to the influence of the surfaces of the montmorillonite particles.

Displacement of acid—base equilibria in clay suspensions as calculated from double layer theory

The effects of the clay-water interface on the acid-base equilibria of weakly basic compounds have been calculated from electrical double-layer theory. Negatively charged clays, such as montmorillonite, interact coulombically with the cationic form of the base so that the acid-base equilibrium is displaced. The degree of displacement of the reaction, as manifested in the shift of the effective p K from the solution p K value, was calculated as a function of pH (and ionic strength), clay interparticle separation distance (i.e., suspension concentration), surface charge density, and dielectric constant of the medium. The results of the calculations are compared to the experimental results obtained by allowing tetracycline, a weakly basic antibiotic, to interact with a Na-saturated montmorillonite suspension. The agreement between theory and experiment is remarkable considering the limitations of double-layer theory when used to model a montmorillonite clay suspension. The calculations show clearly that the degree of displacement of the reaction BH + = B + H + is very sensitive to the level of background salt, only mildly sensitive to the concentration of clay and surface charge density, and not at all dependent on the dielectric constant of the medium.

Interlayer Spacings of Expanded Clay Minerals at Various Swelling Pressures: An X-Ray Diffraction Technique for Direct Determination

An X-ray diffraction technique for determining interlayer spacings of expanded clay minerals at various swelling pressures has been developed. A swollen clay sample that has been equilibrated with an electrolyte solution is placed in a holder containing a porous ceramic plate, collection well, and drain outlet. The holder with sample is placed in a diffractometer mounted environmental chamber and then X-rayed at various applied air pressures. Brief results are given to demonstrate the applicability of the technique. These results show that a very stable average diffraction spacing of 45A persisted during the drying of a previously swollen Na-saturated montmorillonite until the air pressure exceeded 7.6 bars. With contraction the average diffraction spacings decreased from 45A to 19A in a quantized fashion without the appearance of intermediate spacings.

Shear Strength of Montmorillonite and Kaolinite Related to Interparticle Forces

AbstractShear strength of saturated, remolded clay mineral samples was measured in an attempt to relate strength to forces acting between clay particles. The fine fractions of the clays, purified when necessary, were consolidated to different void ratios and subjected to quick, translatory shear in a direct shear device. Relative values for shear strength were obtained in this way. Interparticle forces in the clays were altered and the effect on shear strength was observed.For a high-swelling, Na-saturated montmorillonite, strength at constant void ratio decreased with increasing salt concentration. To explain the decrease in strength with decrease in force of repulsion between particles a model is suggested where strength results from the force of repulsion resisting displacement of particles in the shear plane. Addition of small amounts of dispersing and of soil-conditioning chemicals had little effect on shear strength.Calcium montmorillonite had a lower strength than sodium montmorillonite when compared at the same void ratios. This is related to the lower surface area of interaction and lower repulsion found with divalent ions.Water content at the liquid limit showed the same dependence upon interparticle forces in the montmorillonite clays as did shear strength.In kaolinite, interparticle forces of attraction result in a structure or particle arrangement which has the major influence on shear strength. A clay at low pH which was flocculated in a network, edge-to-face structure owing to presence of positive edge-charge had higher strength than a dispersed clay, but a clay flocculated by electrolyte which produced a lamellar, face-to-face structure had a lower strength.