Na-montmorillonite Clay Research Articles

Contaminant Barrier Material Textural Response to Interaction with Aqueous Polymers

An experimental investigation of the use of polymers dissolved in aqueous solutions to enhance the resistance of clay-based barrier materials to freeze-thaw action and desiccation was performed. The polymers considered included a nonionic polysaccharide (guar gum) and a cationic polyacrylamide (PAM). Concentrations ranging from 0.25 to 8.00 g/L were used and mixed with three barrier materials, namely, 100% Na-montmorillonite clay, a mixture of 70% sand, 30% clay, and a mixture of 90% sand, 10% clay (by weight). Freeze-thaw and desiccation tests were used to investigate material durability. The effects of freeze-thaw action on the materials were assessed in terms of crack measurements, while the drying rates as well as crack measurements were used to assess the influence of desiccation. The extent to which crack formation was mitigated by polymer amendment varied according to polymer type, mode of crack initiation, and clay fraction. In particular, unmodified mixtures of 70% sand and 30% clay exposed to desiccation stress resulted in crack area density values as high as 11.9% while modification with guar or PAM reduced this to 2.7 and 3.4%, respectively, as revealed by analysis of the computed tomography-generated images. Increases or reductions in performance are attributed to polymer–clay interactions and relative hydration between clay and polymer phases.

Electrical Properties of Sand–Clay Mixtures Containing Trichloroethylene and Ethanol

A series of laboratory experiments that measured electrical properties and permeability was performed on carefully characterized sand–clay mixtures. Different mixtures and configurations of quartz sand and 10% Na-montmorillonite clay were investigated using solutions of NaCl, [Formula: see text], and deionized water. A sample containing 10% dispersed clay was also studied using fluids containing 20- and [Formula: see text] trichloroethylene (TCE). Each sample’s electrical properties after fluid saturation were measured at frequencies between [Formula: see text] and [Formula: see text] by using the four-electrode method with Ag–AgCl inner electrodes at room temperature and [Formula: see text] confining pressure, which corresponds to a soil depth of [Formula: see text]. Our results show that adding TCE had a small effect on electrical resistivity: resistivity was greater at higher concentrations of TCE. The influence of TCE on electrical properties was most prominent in plots of loss tangent as a function of frequency. These plots showed that loss-tangent peaks occurred at [Formula: see text] and that peak and peak frequency were smaller at higher concentrations of TCE. Additional experiments were performed on a sample that contained a distinct clay layer parallel to the current flow. The electrical properties of the sample were measured as it was saturated with deionized water and [Formula: see text] solutions, and as an ethanol–water mixture (80:20) was flowed through the sample. Resistivity increased by about a factor of 4 as the ethanol mixture replaced the water solution. Nondestructive x-ray imaging of the sample at various stages of dewatering indicated a decrease in the thickness of the clay layer as more pore volumes of ethanol–water were flowed. Our results show that electrical measurements are useful tools for characterizing porous rocks and soils and that it is feasible to remotely detect the presence and follow the transport of contaminants such as TCE in the subsurface.

Kinetics and thermodynamics studies of copper exchange on Na–montmorillonite clay mineral

The kinetics of Cu ion exchange on Na–montmorillonite clay has been investigated at 20, 30, and 40 °C in water, methanol, and ethanol. The reaction is endothermic in nature. Solvent effects on the reaction rate have been discussed. The thermodynamic activation parameters were calculated and discussed in terms of solvation effects. A multiple reaction rate order equation was used to describe the adsorption process. Lower rates and higher activation energies ( E a ) were observed in aqueous solution than in either of the alcohols. The E a values ranged from 20.88 kJ mol −1 in water to 9.20 kJ mol −1 in ethanol, while at 20 °C the rate constant ( k) varied from 0.111 ppm −1 s −1 in water to 0.205 ppm −1 s −1 in ethanol. The main factor influencing the rate of the adsorption process is the mobility of the adsorbed Cu cations, which is apparently larger in alcohols than in water, due to the difference in the molar activation energy of the solvent. The determined isokinetic temperature indicates that the reaction is enthalpy-controlled, where the interaction between solvent and clay surface plays an important role. A reaction mechanism that describes the solvent effect on the rate of Cu ion exchange is proposed.

Electro-chemo-mechanical couplings in saturated porous media: elastic–plastic behaviour of heteroionic expansive clays

Chemically active saturated clays containing several cations are considered in a two-phase framework. The solid phase contains the negatively charged clay particles, absorbed water and ions. The fluid phase, or pore water, contains free water and ions. Electroneutrality is ensured in both phases, which gives rise to electrical fields. Water and ions can transfer between the two phases. In addition, a part of free water diffuses through the porous medium. A global understanding of all phenomena, deformation, transfer, diffusion and electroneutrality, is provided. Emphasis is laid on the electro-chemo-mechanical constitutive equations in an elastic–plastic setting. Elastic chemo-mechanical coupling is introduced through a potential, in such a way that the tangent elastic stiffness is symmetric. Material parameters needed to estimate the coupling are calibrated from specific experiments available in the recent literature. The elastic–plastic behaviour aims at reproducing qualitatively and quantitatively typical experimental phenomena observed on natural clays during chemical and mixed chemo-mechanical loadings, including chemical consolidation and swelling already described in Int. J. Solids Structures (39 (10), 2773–2806) in the simpler context of Na-Montmorillonite clays. Crucially, the successive exposure of a clay to pore solutions with chemical content dominated by a cation already present in the clay or quasi-absent leads to dramatically different volume changes, in agreement with experimental data.

Chemo-mechanical coupling in saturated porous media: elastic–plastic behaviour of homoionic expansive clays

Chemically active saturated homoionic clays are considered in a two-phase framework. The solid phase contains the clay particles, absorbed water and salt. The fluid phase, or pore water, contains free water and salt. Water, and possibly salt, can transfer between the two phases. In addition free water may diffuse through the porous medium. A global understanding of the phenomena involved, namely deformation, transfer and diffusion, is proposed. Emphasis is laid on the chemo-mechanical constitutive equations in an elastic–plastic setting. Elastic chemo-mechanical coupling is introduced through a potential, in such a way that the tangent poro-elasticity matrix remains symmetric. Material parameters needed to quantify the coupling are calibrated from specific experiments available in the recent literature. The elasto-plastic behaviour aims at reproducing qualitatively and quantitatively the typical experimental responses observed on almost pure Na-Montmorillonite clays during chemical and mixed chemo-mechanical loadings. Increase of the salinity of pore water at a constant confinement stress leads to a volume decrease, so-called chemical consolidation. Subsequent exposure to a distilled water solution produces swelling: however, the latter is smaller than the chemical consolidation so that the chemical loading cycle results in a net contractancy, the amount of which increases with the confinement. In fact, plastic yielding takes place at low salinities of pore water, and when it stops, chemical preconsolidation is generated. Natural clays which contain cations of different species are considered in a companion paper, Gajo et al. [Int. J. Solids Struct., this issue], as they require to account for electro-chemo-mechanical couplings. � 2002 Published by Elsevier Science Ltd.

Natural Ground Water Colloids From the USGS J-13 Well in Nye County, NV: a Study Using SAXS and TEM

We report results from ultra small angle x-ray scattering (USAXS) and transmission electron microscopy (TEM) of dilute silicate colloids that occur naturally in groundwater from the USGS J-13 well, located near the Yucca Mountain Site in Nevada. We also examined a separate sample of this groundwater that had been treated by heating to 90 degrees C in contact with crushed Topopah Spring Tuff from the Yucca Mountain. The USAXS measurements were done at the UNICAT undulator beamline at the Advanced Photon Source at the Argonne National Laboratory. Power-law plots (scattering intensity verses momentum transfer) were fitted to the USAXS data. Colloids in the untreated J-13 groundwater were shown to have a fractal dimension of nearly 3, whereas colloids in the treated groundwater (“EJ-13”) have a dimensionality of approximately 2.4 over a length scale of approximately 3 to 300 nm. Similar power-law plots with dimension 3 characterized concurrent SAXS measurements from aqueous suspensions of Na-montmorillonite and NIST Brick Clay (NBS-67). We attribute these results to the sheet silicate layered structure of the clay colloids present in J-13 well water, montmorillonite, and “brick clay” systems. The differences between EJ-13 and as-received J-13 are perhaps owing to exchange of calcium for sodium with the tuff. Radionuclide incorporation into, adsorption onto, or ion exchange with existing groundwater colloids may promote colloidal transport of radionuclides in groundwater. Such radionuclide-bearing colloids could thereby increase the concentrations of actinides in groundwater and enhance migration into human-accessible aquifers. Our results demonstrate the first application of USAXS to study the physical nature of such groundwater colloids, and represent perhaps one of the most dilute systems ever studied by small angle scatering.

Na-montmorillonite clay as thermal energy storage material

Sodium montmorillonite (Na-M) was investigated as an energy storage material. The study was conducted through the adsorption isotherms, infrared (IR) spectroscopic and differential thermal analysis (DTA). The clay systems were subjected to different preheating temperature, 125, 160, and 200°C, before subjecting the clay to the adsorption process carried out. The adsorptive capacities of Na-M ranged between 0.12 and 0.48g H2O/g of dry clay, depending on the preheating conditions of the clay. The stored energy of Na-M 781 cal/g when the clay preheated to 200°C, at which the clay has lost all the water molecules that could be evaporated, and become, therefore, able to adsorb the maximum amount of water vapor allowed. Na-M, when appropriately set, could be considered as an energy storage material.

ADSORPTION OF NONIONIC AND ANIONIC POLYMERS ON γ-ALUMINA AND NA-MONTMORILLONITE AND THEIR MIXTURES

Adsorption isotherms of nonionic polyvinylpyrrolidone (PVP) and anionic ionized polyacrylic acid (PAA) polymers on single Na-montmorillonite clay and γ-alumina adsorbents in 0.01M NaCl and pH 5.6 are reported and compared to results obtained with aqueous adsorbent mixtures. Microeiectrophoretic behaviours of adsorbents are also observed. It can be shown that antagonistic effects due to interactions between oppositely charged adsorbent surfaces largely limit the nonionic PVP adsorption.

A Kinetic Study of the Copper Exchange Reaction on a Sodium-Montmorillonite Clay Mineral in Acetonitrile and Dimethylformamide

The kinetics of Cu2+exchange on a Na-montmorillonite clay mineral were investigated at three temperatures, in acetonitrile (AcN) and dimethylformamide (DMF) solvents. The solvent effects on the reaction rate were discussed. The thermodynamic activation parameters were calculated and discussed in terms of the solvation effects.

Scanning force microscopy and polymerization studies on cast thin films of hectorite and montmorillonite

Thin films of the smectite clays Na+ exchanged montmorillonite, Ca2+ exchanged montmorillonite, Na2+ and Cu2+ exchanged hectorite, Cu2+ exchanged sintered hectorite, and Cu2+ and Na2+ exchanged hectorite exposed to benzene, aniline, and thiophene were studied using the techniques of scanning force microscopy (SFM), electron spin resonance (ESR), and x-ray diffraction. The microstructure of the two montmorillonite clays was markedly different, with the Ca-montmorillonite exhibiting a sturdy, close packed array of crystallites of average dimension 0.4 μm. The Na-montmorillonite clays consisted of smaller (0.1 μm), more poorly defined crystallites with an overall cauliflowerlike appearance. The pure Na-hectorite and Cu-hectorite clays exhibited large flat regions composed on interlocking platelets. Heat sintering as well as exposure to benzene resulted in measurable shifts in the platelets perpendicular to the surface for the Cu-hectorite. It is proposed that in the sintered case these shifts are due to interlayer water loss accompanied by Cu reactions, while in the benzene case interlayer benzene polymerization causes inhomogeneous vertical expansion of the clay. Exposure of Cu-hectorite films to both aniline and thiophene results in large-scale polymerization of these monomers. The microstructure of both of these polymers is similar to that observed in electrochemically prepared films on Pt substrates. Na-hectorite samples did not exhibit surface polymerization upon thiophene, aniline, or benzene exposure.

Solvent Effect on the Kinetics of the Exchange of Copper Ions on Na–Montmorillonite

The specific rate coefficients of adsorption of Cu2+on Na–montmorillonite clay in dimethyl sulfoxide (DMSO) and acetone solvents are determined at 20, 30, and 40°C. The reaction is endothermic in nature. It was found that theEvalues range from 3.66 kJ mol−1in acetone to 13.54 kJ mol−1in DMSO, while at 20°C, the rate constantkvaries from 3.34 (ppm)1−nper second in DMSO to 16.07 (ppm)1−nper second in acetone. The data have been analyzed to obtain activation parameters ΔG*, ΔH*, and ΔS* for reaction in corresponding mixtures. A reaction mechanism which describes the copper ion exchange reaction is proposed.

Sorption of Humic Materials onto Inorganic Surfaces for the Mitigation of Facilitated Pollutant Transport Processes

The transport of hydrophobic organic pollutants in groundwaters is facilitated by sorption of these chemicals onto natural organics and transport with these materials. One strategy to mitigate pollutant transport through clay liners and slurry walls is to reduce the transport of the natural organics by enhancing their sorption onto the containment barrier materials. A controlled experimental study of the adsorption of humic acid onto typical inorganic constituents of soils was performed using two types of model solid phases: 1) pure solids (washed Na-montmorillonite clay, amorphous ferrihydrite, and amorphous aluminosilicate gel) and 2) binary combined phases (Na-montmorillonite coated with ferrihydrite or aluminosilicate gel). The combined phases were synthesized for a range of metal to clay mineral ratios. Adsorption tests were conducted to investigate the relative sorption affinity of these solid phases for humic acid. Addition of a ferrihydrite coating was found to increased the sorption of humic acid onto montmorillonite clay.

Adsorption of non-ionic surfactants on activated carbon and mineral clay

A series of non-ionic surfactants of nonyl-phenol ethoxylates, with n = 4−23;0 ethylene oxide groups and dinonyl-phenol ethoxylate were studied in dilute aqueous solution. Their removal efficiencies and mechanisms by adsorption on powdered and granular activated carbon and on Na-montmorillonite clay were investigated. The powdered activated carbon proved to be the most efficient with 94–100% non-ionic surfactants removal by addition of 40–80 mg activated carbon. Various models of adsorption isotherms such as Langmuir, BET and S-type were used to determine Q 4, the limiting adsorption capacity. The relationships between Q o and parameters affecting the adsorption of non-ionic surfactants such as n, HLB and CMC were determined. The cross-sectional area σ 0 occupied by surfactant molecules on the adsorbent was calculated. Adsorption has been proven to be a potential advanced physicochemical treatment method for the effective removal of non-ionic surfactants present in effluents intended for reuse.

Interparticle Potential Energies in Na-Montmorillonite Clay Suspensions

AbstractThe small angle X-ray scattering data obtained in an earlier investigation of a series of Na-montmorillonite clay samples containing varying concentrations of sodium metaphosphate have been used to calculate the potential energy φ(x) of the interaction between two isolated parallel clay platelets separated by a distance x. All φ(x) curves have the form expected for Na-montmorillonite. In each curve there is a potential well for a platelet separation approximately equal to the most probable separation distance determined in the earlier study. Because the depth of the potential well is of the order of 0·01 eV for all samples, the attractive forces are relatively weak. While the calculated φ(x) functions are not highly accurate, in future investigations precautions can be taken to increase the reliability of the computed potential energy functions. This preliminary study suggests that determination of φ(x) from small angle X-ray scattering data can be a useful method for quantitative study of interparticle forces in Na-montmorillonite clays.

Effect of Steam on Permeabilities of Water-Sensitive Formations

Abstract Steam permeability measurements have been made in the laboratory on several samples of natural reservoir materials. The steam temperatures and pressures were selected to simulate conditions which might exist in a reservoir during the injection of steam. For each sample tested, the experimental permeability to superheated steam was comparable to that measured with air and no evidence of plugging was detected. Some samples were exposed to water at various temperatures and plugging was found to occur in materials which contained significant quantities of montmorillonite clay. Temperature had little effect on the degree of plugging between 75 and 325 F. The measured permeabilities tended to increase slightly with temperature, but the changes were small compared with the initial loss of permeability on wetting. Sequential permeability measurements were made on two samples using air, water, steam, water and air, in that order. Both samples were water-sensitive and plugged extensively after the initial injection of water. Upon exposure to superheated steam, the samples dehydrated and their permeabilities to superheated steam were comparable to those initially measured with air. The remaining measurements with water and air confirmed that the water plugging was reversible and that the samples were not seriously damaged during the tests. INTRODUCTION The swelling of water-sensitive clays during water floods has long been recognized as a potential source of reservoir damage. The recent extensive application of steam injection and stimulation has compounded this problem since both hot water and steam (as well as fresh water at reservoir temperatures) are, at some time, in contact with the producing zone adjacent to the bore of a steam injection well. The purpose of this paper is to present data which compare the sensitivity of some natural sedimentary rock samples to water at various temperatures, and to superheated steam. Some properties of montmorillonite clay are briefly reviewed, and comparisons are drawn between empirical data and the predicted behavior of the montmorillonite known to be present in the samples. PROPERTIES OF MONTMORILLONITE CLAY Water initially adsorbs on dry Na-montmorillonite clay in discrete layers in the interlaminar space between clay platelets. The platelet spacing, which is 9.6 A (angstroms) for a dehydrated clay, has been observed to expand in discrete steps to 12.4, 15.5, 18.4 and 21.4 A spacings, indicating the formation of four discrete layers of regularly oriented water molecules.1 The first two layers are easily formed by hydrating a dry sample to equilibrium in an atmosphere with carefully controlled humidity. The formation of the higher layers is more difficult. The usual X-ray diffraction patterns of the more highly hydrated samples indicate a gradual increase in the average spacing between 15.5 and 19.2 A, followed by a discontinuous expansion to 31 A when the weight ratio of water to dry clay is between 0.5 and 1.2.2 Platelet expansion above 31 A proceeds monotonically as the moisture is increased and no regular arrangement of the platelets is observed. Water-sensitivity in sedimentary rocks is usually associated with Na-montmorillonite clay when it is in the noncrystalline state. Mering3 found that the average lattice spacing of sodium montmorillonite hydrated at 68 F and 70 per cent relative humidity was 15.5 A, and that the spacing. at 92 per cent humidity was 16.5 A. The water adsorbed at the higher humidity has the same free energy as liquid water at 65.6 F. Kolaian and Low4 used a tensiometer to measure the thermodynamic properties of water in diffuse suspensions of montmorillonite clays relative to pure water. They observed that water in suspensions as dilute as 6 per cent clay became partially oriented when left undisturbed. The bonding associated with this orientation was not extensive because the free energy difference between the water in suspension and pure water was only a few millicalories per mole. They also found that the measured free energy difference decreased rapidly with temperature and became negligible above 100 F. This evidence indicates that montmorillonites contained in sedimentary rocks would dehydrate to a crystalline structure when exposed to superheated steam, and that the rock permeability measured with steam would be equivalent to that measured with air.