Behavior Of Montmorillonite Research Articles

Effect of Polyethylene Oxide on the Rheological Behavior of Bentonite Suspensions

The effect of Polyethylene Oxide (PEO) with a molecular weight 10000g/mol on the rheological behavior of bentonite suspension was examined in terms of viscosity, yield stress and viscoelastic modulus (G’ and G’’); characteristic of complex behaviour of montmorillonite in water. A Physica MCR301 rheometer has been used to measure the rheological properties of samples (6% bentonite) as well as bentonite-PEO mixtures at different concentrations of PEO (0.18%, 0.25%, 0.5% and 1%). The polyethylene oxide adsorbs onto clay particles, which changes their basic characteristics depending on the amount of PEO adsorbed.

Influence of dielectric constant of pore fluids on double-layer swelling: a validation study

The clay platelets are negatively charged, and hence, the behavior of clays is physicochemical in nature. The clay–pore liquid interaction depends upon pore medium chemistry, which is a function of many factors. Dielectric constant of the pore medium is one such important factor. The clay swelling is considered to be explained by the Gouy–Chapman theory of diffuse double layer. This paper intends to study the effect of dielectric constant of the pore fluid on the equilibrium sediment volume in light of diffuse double-layer equation of the Gouy–Chapman theory. It has been illustrated that the Gouy–Chapman theory cannot explain the equilibrium sediment volume behavior of montmorillonite and kaolinite clay minerals satisfactorily. It is also brought out that the equilibrium sediment volume behavior of these two clay minerals is quite opposite to each other.

Effect of mechanical and electro-chemical contacts on the particle orientation of clay minerals during swelling and sedimentation: A DEM simulation

The importance and quality of particle orientation on the performance of clay has been well-documented experimentally. This paper aims to quantitatively evaluate clayey mineral reorientation during swelling/sedimentation according to the balance of mechanical contacts and electrochemical forces. A DEM code has been developed and the behavior of montmorillonite, kaolinite and illite, each having different pore fluid characteristics, has been simulated as for platy-shaped particles. Nonlinear contact law was considered for the induced net force as it relates to the mechanical contacts, Van der Waals attractive force, and diffuse double-layer (DDL) repulsive force. Good compatibility was observed between the DEM simulation and DDL theory. The results showed that the particle weight, magnitude of the repulsive force, and number of DDL contacts were effective parameters controlling particle reorientation. At a low swelling pressure, the particles rotated easily such that an edge-to-face fabric was created and the potential for overlap between particles as well as the mechanical contacts increased. The number of the mechanical contacts versus the time of sedimentation was not linear, but bell-shaped. Kaolinite ranked higher on the DDL repulsive contact list; however, it had a higher deposition rate due to its higher particle weight and lower repulsion force.

Swelling Capacity of Montmorillonite in the Presence of Electrolytic Ions

The aim of this study was to investigate the effect of inorganic cations (Na+, Ca2+, Ba2+, Fe3+, Al3+) with different valence and concentration on the swelling behaviors of montmorillonite. Na-montmorillonite, obtained from China, was chosen as experimental objective. It was first characterized through the measurements of swelling capacity and zeta potential. Then, swelling properties of Na-montmorillonite influenced by cation concentration, valence, and hydration analyzed were studied. The results showed that the swelling capacity was much inhibited by cations of higher concentrations, higher valences, or weaker hydration. This work also verified the conclusion that the decreased degree of potential is more significant caused by cations of higher valence.

Effect of SiO2 particles on dispersion of montmorillonite (MMT) in polyimide nanocomposite during thermal imidization

In this research, the effect of SiO2 particles on the dispersion behavior of montmorillonite (MMT) in polyimide(4-APS/BTDA)/SiO2–MMT nanocomposite film(where 4-APS is 4-aminophenyl sulfone and BTDA is 3,3′,4,4′-benzophenonetetracarboxylic dianhydride), and the changes in the molecular structure and morphology of the polymer matrix during thermal imidization were characterized by means of temporal analyses. For this purpose, the X-ray diffraction (XRD) patterns of PI/MMT and PI/SiO2–MMT nanocomposite films prepared at different heating steps under ambient atmosphere were studied. The MMT d-spacing in the polymer matrix was determined using Bragg’s equation. The XRD results showed that modified organophilic MMT (OMMT) is initially exfoliated in the poly(amic acid) for both nanocomposite films. The results showed that, with increasing temperature and duration of thermal imidization, the peak of the MMT layers moved to slightly higher angle and also the peak intensity increased concurrently for both nanocomposite films. Comparison of the temporal XRD patterns of PI/MMT and PI/SiO2–MMT nanocomposite films revealed that the increase in the peak intensity as well as the displacement of the peak position of MMT layers were less for the latter film. Indeed, the obtained results indicated that, in the presence of SiO2 particles, there was more dispersion of MMT layers in the polymer matrix. The morphology of all the specimens was investigated by atomic force microscopy. The obtained results showed that presence of SiO2 particles can cause the surface of nanocomposite film to become smoother. The temporal ultraviolet–visible spectra of both nanocomposite films showed a bathochromic shift with increase of the thermal treatment temperature and duration.

An investigation on the sorption behaviour of montmorillonite for selected organochlorine pesticides from water

The sorption behaviour of montmorillonite towards organochlorine pesticides (OCPs) from aqueous solutions is reported. After preliminary investigation of the sorption capability of clay for selected OCPs, aldrin was used as a model compound for further experiments. The batch sorption experiments were carried out as functions of contact time, pH of the solution, initial aldrin concentration and dosage of the montmorillonite. After traditional liquid–liquid extraction, the determination of OCPs was carried out by gas chromatography coupled with a μ-electron capture detector (GC-μECD). The results indicated that sorption of aldrin followed the second-order kinetic model and that the equilibrium time depended on the initial aldrin concentration. The film diffusion was found to be a main sorption rate control mechanism. The removal was explained according to the electrostatic bonding mechanism. The Freundlich isotherm model better represented the sorption data than the Langmuir model. The montmorillonite was also used efficiently for the removal of OCPs from fortified tap and surface (lake) water samples.

Alteration and dissolution of Na-montmorillonite in simulated groundwaters

ABSTRACTThis study aims at gaining a better understanding of the behaviour of montmorillonite in contact with different ground waters; alteration of montmorillonite and possible formation of secondary minerals. Batch experiments were conducted with purified Swy-2 montmorillonite in simulated fresh (I=0.05 M, pH 8) and saline (I=0.1 M, pH 11) waters at 25 and 60ºC in anaerobic (Ar(g)) conditions. The concentrations of Al, Fe; Mg and Si were analysed from ultra-filtered solution samples with HR-ICP-MS (High Resolution Inductively Coupled Plasma Mass Spectrometry). The amount of released Si depended strongly on the experimental conditions. The Si concentrations at 60oC in the saline and fresh waters showed a difference greater than an order of magnitude. The initial purified montmorillonite and the solid materials from experiments were analysed with XRD. The analysis indicated that the nature of smectite did not change, but the experimental conditions, more or less, modified the structure of montmorillonite, e.g., in fresh waters the XRD spectra showed peaks typical of mixed layer minerals, which can refer to the presence of either randomly ordered illite/smectite or randomly ordered collapsed smectite/ hydrated smectite layers. The dissolution of montmorillonite was studied also by modelling with TOUGHREACT. The experimental and modelled results were compared revealing a need to develop the model e.g. in respect of the evolution of pH.

Freezing and thawing of montmorillonite — A time-resolved synchrotron X-ray diffraction study

The evolution of phases over time during freezing and thawing of unconfined Na- and Ca-montmorillonites (Wyoming, MX-80) was studied with time-resolved synchrotron X-ray diffraction. The clay samples were: (i) powder equilibrated to ambient atmosphere and (ii) pastes of 30 mass% montmorillonite in pure water. The phases were characterised in-situ using a stream of nitrogen gas for temperature control. The behaviour of montmorillonite during freezing and thawing is important in final repositories for spent nuclear fuel that are using bentonite as a buffer material. The Na-montmorillonite equilibrated to ambient atmosphere (one-layer hydrate) was unaffected by freezing down to − 50 °C. The Ca-montmorillonite equilibrated to ambient atmosphere (two-layer hydrate) showed a minor decrease in basal spacing (0.11 Å) by freezing down to − 50 °C. The magnitude of the decrease in basal spacing was high compared to the thermal contraction of the similar minerals muscovite and pyrophyllite and some dehydration of the clay was likely to be involved. Wet Na-montmorillonite in pure water was highly affected by freezing causing the osmotic phase to collapse during ice formation to 19 Å (three-layer hydrate) and later to a mixture of two and three-layer hydrates (− 15 °C) and at lower temperatures to two-layer hydrate (16 Å, − 50 °C). The Ca-montmorillonite in pure water was present as a 19 Å three-layer hydrate at + 20 °C and expanded upon cooling, producing two partly overlapping 001 reflections corresponding to three and four-layer hydrates prior to the ice formation. A mean d-value of the 002 peaks of the four-layer hydrate was determined to be 10.8 Å, which corresponded to a basal spacing of 21.6 Å. To our knowledge this is the first time a distinct four-layer-water hydrate is reported for Ca-montmorillonite in pure water. After the ice formation started, the montmorillonite was dehydrated to three-layer hydrate and at − 15 °C to a mixture of two and three-layer hydrates. At − 50 °C only two-layer hydrate was present. The ice formation and the dehydration of the montmorillonite occurred simultaneously. The effects of freezing on the montmorillonite were shown to be reversible during the thawing. The two dimensional diffraction rings gave information on the ice texture. The highly dispersed Na-montmorillonite (high surface area) in pure water facilitated the nucleation of the ice crystals and gave rise to uniformly sized crystals, while the Ca-montmorillonite (not dispersed, lower surface area) gave rise to non-uniformly sized ice crystals.

Interaction of metal ions with montmorillonite and vermiculite

The behaviour of montmorillonite and vermiculite toward adsorption of Cd2+, Pb2+, Zn2+, Mn2+, Cu2+ and Zn2+ was compared. In general, the uptake of metal ions on both clay minerals decreased with decreasing of pH and in the presence of ligands forming stable complexes. Metal ion retention on montmorillonite was less affected by the competition of sodium ions at high ionic strengths with respect to vermiculite. On the other hand, the total capacity of vermiculite with respect to the investigated metal ions was found to be much higher than that of montmorillonite, whereas the order of affinity of the metal ions for the two clay minerals was similar, i.e.: Pb2+=Cd2+<Cu2+<Zn2+<Mn2+<Ni2+ for montmorillonite and Pb2+<Cu2+<Cd2+<Zn2+<Ni2+<Mn2+ for vermiculite.The similarities and differences between the two clay minerals were also investigated by principal component analysis and hierarchical cluster analysis.The results of this study may be used to predict the uptake efficiency of these adsorbents in view of their application for the removal of metal ions from contaminated effluents. The choice of vermiculite or montmorillonite for the uptake of metal ions or other elements will depend on the composition of the effluent to be treated.

Characterization of Montmorillonite Saturated with Various Cations

Emanation thermal analysis (ETA) supplemented by thermogravimetry (TG and DTG) and evolved gas analysis (water) were used for the characterization of the thermal behavior of montmorillonite samples saturated with lithium, sodium, magnesium and aluminum cations. The ETA revealed microstructure changes that occur during the gradual heating of the clay. These changes are associated with the dehydration, dehydroxylation and formation of an amorphous meta-montmorillonite phase, and its subsequent annealing and recrystallization. On the basis of the ETA results it was demonstrated that exchangeable metallic cations have a great effect on the thermal behavior of montmorillonite.

Thermal analysis of montmorillonite-aminotriazole interactions

In the present investigation, DTA and TG techniques were used to study the thermal behaviour of montmorillonite treated with solutions of the pesticide aminotriazole (AMT), in nitrogen flow. These techniques have been complemented by mass spectrometry of the evolved gases (EGA-MS).

Nature and Behavior of Montmorillonite in an Acid Inland Marine Shale from East Central Saskatchewan

AbstractThe mineralogy and chemistry of an acid clayey Cretaceous marine shale outcropping near Arborfield in east central Saskatchewan were studied. pH values as low as 3.6 and levels of exchangeable Aluminum of up to 28 cmol(+).kg−1 were recorded in this material. Clay separates of the shale were monomineralic, consisting of highly crystalline smectite (montmorillonite) with an average composition: M+0.71 (Si7.74Al0.26) (Al3.44Fe3+ 0.12Mg0.45)O20(OH)4 Ion activity product values, calculated from saturation extract composition data, indicated that the montmorillonite is stable despite the intense acidity of the shale. The high pH values (up to 8.5) which were observed in the upper soil horizons overlying the shale are due to the incorporation, by glacial action, of calcareous till into the shale. This till was apparently the source of the mica, kaolinite, and quartz present along with the montmorillonite in clays isolated from the upper horizons. The implications of the findings to the genesis and chemical characteristics of Saskatchewan soils are discussed.

Effects of Permanent Charge on the Electrical Double‐Layer Properties of Clays and Oxides

AbstractTwo complimentary models which describe the surface chemistry of, respectively, clay minerals and oxides submersed in an aqueous solution are presented. Both models incorporate isomorphous‐substitution charge, specific adsorption of counter ions at the inner Helmholtz plane, and a diffuse double layer outside the outer Helmholtz plane. In addition, one of the models allows for adsorption of potential‐determining ions at the surface plane, which is located inward of the inner Helmholtz plane. General algorithms to solve surface chemistry models are given and methods to determine the associated empirical parameters are discussed. With the model which includes adsorption of potential‐determining ions, it is shown that isomorphous substitution may be of great importance to the adsorption properties of oxides. Based on published data for NaCl/Al2O3 and KCl/SiO2, computations are made which show that changes in the charge density of the potential‐determining ions adsorbed at the surface plane tend to be equal in magnitude but opposite in sign to changes in the isomorphous‐substitution charge density (σo). However, this cancellation is not perfect, and especially for KCl/SiO2 systems, the counter‐ion exchange capacity and its pH dependency and the zeta potential are strongly dependent on σo. The dependence on σo is particularly strong in the region where σo is small (−0.04 &lt; σo &lt; 0.02 C/m2). This implies that small amounts of isomorphous substitution may have a dramatic effect on the physico‐chemical properties of oxides. The ion‐adsorption behavior of montmorillonite cannot be explained with our generalized model for oxide surfaces. Thus, our calculations confirm the long‐standing view that the basal planes of clay minerals do not adsorb H+ and OH‐ as potential‐determining ions.