Showing papers in "Clays and Clay Minerals in 2004"
TL;DR: In this paper, four simulant tank waste (STW) solutions, which are high in NaOH (1.4 and 2.8 mol/kg), NaNO3 (3.7 mol/ kg), NaAlO2 (0.125 and 0.25 mol/g), were prepared and reacted with reference kaolinite KGa-1 and Kga-2 at 50 and 80°C for up to 2 months.
Abstract: Caustic nuclear wastes have leaked from tanks at the US Department of Energy’s Hanford site in Washington State (USA) causing hundreds of thousands of gallons of waste fluids to migrate into the underlying sediments. In this study, four simulant tank waste (STW) solutions, which are high in NaOH (1.4 and 2.8 mol/kg), NaNO3 (3.7 mol/kg) and NaAlO2 (0.125 and 0.25 mol/kg), were prepared and reacted with reference kaolinite KGa-1 and KGa-2 at 50 and 80°C for up to 2 months. The structure and morphology of the resulting products were characterized using X-ray diffraction, scanning electron microscopy, and Fourier transform infrared spectroscopy. The products were also examined for cation exchange and Cs+ sorption as a function of ionic strength and types of cations in the background solutions. Cancrinite and sodalite were the only new minerals observed in all of the conditions tested in this experiment. Two major chemical processes were involved in the reactions: dissolution of kaolinite and precipitation of cancrinite and sodalite. Increasing NaOH concentration and temperature, and decreasing NaAlO2 concentration increased the transformation rate. Both cancrinite and sodalite appeared stable thermodynamically under the experimental conditions. The newly formed feldspathoids were vulnerable to acid attack and pronounced dissolution occurred at pH below 5.5. Cancrinite and sodalite can incorporate NaNO3 ion pairs in their cages or channels. Sodium in cancrinite and sodalite was readily exchangeable by K+, but less easily by Cs+ or Ca2+. The feldspathoid products sorb nearly an order of magnitude more Cs+ than the unaltered kaolinite. The Cs adsorption is reduced by competing cations in the background solutions. At low ionic strength (0.01 M NaNO3 or 0.005 M Ca(NO3)2), Ca2+ was more competitive than Na+. When the concentration of the background solution was increased 10 times, Na+ was more competitive than Ca2+.
139 citations
TL;DR: In this article, the micropore characteristics of four soil samples, with different particle-size distributions, and four natural silicate clay minerals were investigated to characterize the microstructure of the soils and clays.
Abstract: Limited information is available on microporosity in soils. A study was undertaken to investigate the micropore characteristics of four soil samples, with different particle-size distributions, and four natural silicate clay minerals. Specific surface area and the differential micropore-size distribution were taken into account to characterize the microstructure of the soils and clays. The micropore-size distributions showed a maximum contribution to the total microporosity by pores having an effective pore radius of ∼20 A, thus indicating that that category of pore contributes more than others to the total microporosity of the system. For both soils and clays a good exponential correlation was found between the maximum contribution to the microporosity and their specific surface area. A linear relationship was also found between the microporosity of the soils and their clay content. It has been concluded that the micropore system formed by 20 A pores is mainly located in the clay fraction of the soil, and contributes significantly to defining some of the most notable physicochemical properties of soils and clays.
117 citations
TL;DR: In this paper, the ordering conformation of surfactant molecules in intercalated montmorillonite prepared at various concentrations was investigated by C-13 MAS NMR, which demonstrates the coexistence of ordered and disordered chain conformations.
Abstract: The ordering conformation of surfactant molecules in intercalated montmorillonite prepared at various concentrations was investigated by C-13 MAS NMR. The C-13 MAS NMR study demonstrates the coexistence of ordered and disordered chain conformations. Two main resonance peaks are associated with the backbone alkyl chains: the resonance at 33 ppm corresponds to the ordered conformation (all-trans), and the resonance at 30 ppm corresponds to the disordered conformation (mixture of trans and gauche). Deconvolution of C-13 MAS NMR spectra indicates that the ordering conformation of surfactant molecules within the gallery of montmorillonite depends very much on their orientation and packing density. When amine chains are oriented parallel to the silicate layers, the amount of all-trans conformer decreases with the increase of amine concentration. However, the amount of all-trans conformer increases with the increase of amine concentration when amine chains radiate from the silicate layers. Furthermore, C-13 MAS NMR spectra show that the intercalated surfactant molecules in the clay minerals never attained the complete liquidlike or solidlike behavior.
98 citations
TL;DR: In this article, the authors used the multi-specimen method developed by Drits et al. and Sakharov et al., and showed that all samples contain a physical mixture of an unusually (?) illitic (~65 %I) randomly interstratified I-Exp (Illite-Expandable MLM) and of a discrete smectite, in addition to discrete illite, kaolinite and chlorite.
Abstract: A clay-rich Callovo-Oxfordian sedimentary formation was selected in the eastern Paris Basin (MHM site) to host an underground laboratory dedicated to the assessment of nuclear waste disposal feasibility in deep geological formations. As described initially, this formation shows a mineralogical transition from an illite-smectite (I-S) mixed-layered mineral (MLM), which is essentially smectitic and randomly interstratified (R=0) in the top part of the series to a more illitic, ordered (R≥1) I-S in its deeper part. This description has been challenged by using the multi-specimen method developed by Drits et al. (1997a) and Sakharov et al. (1999). It is shown that all samples contain a physical mixture of an unusually (?) illitic (~65 %I) randomly interstratified I-Exp (Illite-Expandable MLM) and of a discrete smectite, in addition to discrete illite, kaolinite and chlorite. Structural parameters of the different clay phases vary little throughout the series. According to the proposed model, the mineralogical transition corresponds to the disappearance of smectite with increasing burial depth. Comparison with clay minerals from formations of similar age (Oxfordian-Toarcian) throughout the Paris basin shows that the clay mineralogy in the deeper part of the series originates from a smectite-to-illite transition resulting from a low-temperature burial diagenesis. The anomalous lack of evolution of clay minerals in the upper part of the series is thought to be related to specific interactions between organic matter and clay minerals.
97 citations
TL;DR: In this article, a set of replicate hydraulic conductivity tests were conducted using 100 mM KCl and 20 and 40 mM CaCl2 solutions to evaluate how changes in hydraulic conductivities are related to changes in the exchange complex and physical properties (water content and free swell) of prehydrated and non-prehydrated bentonite used for geosynthetic clay liners.
Abstract: Sets of replicate hydraulic conductivity tests were conducted using 100 mM KCl and 20 and 40 mM CaCl2 solutions to evaluate how changes in hydraulic conductivity are related to changes in the exchange complex and physical properties (water content and free swell) of prehydrated and non-prehydrated bentonite used for geosynthetic clay liners (GCLs). Essentially no change in hydraulic conductivity and water content (or void ratio) occurred during tests with the 100 mM KCl solution even though K+ was replacing Na+ on the exchange complex. In contrast, for the CaCl2 solutions (20 mM and 40 mM), the hydraulic conductivity increased and the free swell and water content decreased as exchange of Ca2+ for Na+ occurred. Faster changes in hydraulic conductivity and the exchange complex occurred in the tests with the 40 mM CaCl2 solution and the non-prehydrated bentonite ( i.e. the hydraulic conductivity changed more rapidly when exchange occurred more rapidly). Even though exchange of Ca2+ for Na+ was essentially complete at the end of testing, the hydraulic conductivity obtained with the 20 mM CaCl2 solution was less and the water content greater than obtained with the 40 mM CaCl2 solution (2.6 × 10−8 cm/s vs. 6.7 × 10−8 cm/s, 122% vs. 111%, and 3.2 vs. 2.9). Similarly, the prehydrated bentonite had lower hydraulic conductivity (1.9 × 10−8 cm/s vs. 6.7 × 10−8 cm/s) and greater water content (167% vs. 111%) than the non-prehydrated bentonite at the end of testing, even though Ca-for-Na exchange was essentially complete.
93 citations
TL;DR: In this paper, a special sample-preparation technique was used to eliminate the contribution of molecular water and the OH-stretching regions of the spectra were decomposed and curve-fitted, and the individual OH-straining bands were assigned to all the possible types of OH-bonded cation pairs that involve Al, Mg and Fe.
Abstract: Dioctahedral smectite samples of a wide range of compositions (beidellites, montmorillonites, nontronites, Fe-rich montmorillonites and Al-rich nontronites) were studied by infrared (IR) spectroscopy. A special sample-preparation technique was used to eliminate the contribution of molecular water. The OH-stretching regions of the spectra were decomposed and curve-fitted, and the individual OH-stretching bands were assigned to all the possible types of OH-bonded cation pairs that involve Al, Mg and Fe. The integrated optical densities of the OH bands were assumed to be proportional to the contents of the specific types of OH-linked cation pairs with the absorption coefficients being the same for all individual OH bands. Good agreement between the samples' octahedral cation compositions calculated from the IR data and those given by crystal-chemical formulae was obtained for a representative collection of samples in terms of a unique set of individual OH-band positions that vary within narrow wavenumber intervals. This has allowed us to minimize the ambiguity in spectra decomposition caused by the poor resolution of smectite spectra and confirmed the validity of the resulting band identification. The bands associated with specific OH-bonded cation pairs in the spectra of smectites are, on the whole, shifted to greater wavenumbers with respect to the corresponding bands in micas. In addition to OH bands that refer to the smectite structure, AlOHAl and AlOHFe bands of the pyrophyllite structural fragments were identified. The band-position variation ranges overlap in a few cases (AlOHFe and MgOHMg; AlOHAl of smectite and AlOHFe of pyrophyllite-like component). Unambiguous interpretation of the OH-stretching vibrations was found to be possible only for smectite samples with known chemical compositions, so that IR data cannot be used for quantitative determination of octahedral cation composition of mixtures of dioctahedral 2:1 phyllosilicates. In the case of the studied monomineral smectites with known chemical compositions, IR data provided information on the short- range order/disorder in the distribution of octahedral cations along cation-OH-cation directions. This information can be employed, in conjunction with the data of other spectroscopic and diffraction techniques, in the analysis of short-range octahedral cation distribution. Key Words—Cation Distribution, Dioctahedral Smectite, IR Spectroscopy, OH-stretching Vibrations, Short-range Order/Disorder.
93 citations
TL;DR: In this article, the dehydration and rehydration processes of the clay mineral palygorskite (PFl-1) were studied by textural analysis, thermogravimetric analysis connected with mass spectrometry (TGA-MS), and 29Si and 1H solid-state NMR techniques.
Abstract: The dehydration and rehydration processes of the clay mineral palygorskite (PFl-1) were studied by textural analysis, thermogravimetric analysis connected with mass spectrometry (TGA-MS), and 29Si and 1H solid-state NMR techniques. The TGA-MS results clearlyreveal weight losses at maxima of 70°C, 190°C, 430°C and 860°C. PFl-1 is characterized by a micropore area of 93 m2/g, corresponding to a micropore volume of 47 mm3/g. These values are also obtained for the sample heated up to 200°C for 20 h. Further heating at 300°C produces a collapse of the structure, as shown by the almost complete loss of microporosity. The 29Si NMR spectra of palygorskite show two main resonances at −92.0 and −97.5 ppm, attributed to one of the two pairs of equivalent Si nuclei in the basal plane. A minor resonance at −84.3 ppm is attributed to Q2(Si-OH) Si nuclei. The resonance at −92.0 ppm is assigned to the central Si position, while the resonance at −97.5 ppm is assigned to the edge Si sites. It is confirmed bysolid-state 29Si and 1H NMR that nearly complete rehydration is achieved by exposing palygorskite samples that have been partially dehydrated at 150°C and 300°C, to D2O or water vapor at room temperature. When the rehydration is accomplished with D2O, the atoms are disordered across all the protons sites.
87 citations
TL;DR: In this article, X-ray absorption fine structure (XAFS) and electron paramagnetic resonance (EPR) spectroscopic experiments on copper (II) sorbed on smectite clays using suspension pH and ionic strength as variables.
Abstract: Due to the importance of clay minerals in metal sorption, many studies have attempted to derive mechanistic models that describe adsorption processes. These models often include several different types of adsorption sites, including permanent charge sites and silanol and aluminol functional groups on the edges of clay minerals. To provide a basis for development of adsorption models it is critical that molecular-level studies be done to characterize sorption processes. In this study we conducted X-ray absorption fine structure (XAFS) and electron paramagnetic resonance (EPR) spectroscopic experiments on copper (II) sorbed on smectite clays using suspension pH and ionic strength as variables. At low ionic strength, results suggest that Cu is sorbing in the interlayers and maintains its hydration sphere. At high ionic strength, Cu atoms are excluded from the interlayer and sorb primarily on the silanol and aluminol functional groups of the montmorillonite or beidellite structures. Interpretation of the XAFS and EPR spectroscopy results provides evidence that multinuclear complexes are forming. Fitting of extended X-ray absorption fine structure spectra revealed that the Cu-Cu atoms in the multinuclear complexes are 2.65 A apart, and have coordination numbers near one. This structural information suggests that small Cu dimers are sorbing on the surface. These complexes are consistent with observed sorption on mica and amorphous silicon dioxide, yet are inconsistent with previous spectroscopic results for Cu sorption on montmorillonite. The results reported in this paper provide mechanistic data that will be valuable for modeling surface interactions of Cu with clay minerals, and predicting the geochemical cycling of Cu in the environment.
85 citations
TL;DR: In this article, the thermal stability of quaternary alkyl ammonium-modified layered silicates was investigated using mass spectrometry and thermal and electrochemical analysis, N,N-dimethyl-N,N, N-dioctadecyl quaternaries modified montmorillonite and fluorinated synthetic mica were found to degrade primarily through elimination and nucleophilic attack by these anions.
Abstract: Bromide-containing impurities were found to decrease the thermal stability of quaternary alkyl ammonium-modified layered silicates. Improved purification procedures completely removed bromide and led to a 20°C to >100°C increase in organic modified layered silicate thermal stability. Using mass spectrometry and thermal and electrochemical analysis, N,N-dimethyl-N,N-dioctadecyl quaternary ammonium-modified montmorillonite and fluorinated synthetic mica were found to degrade primarily through elimination and nucleophilic attack by these anions. The nature of residual bromides was identified and quantified, and the efficiency of removing these anions was found to be solvent dependent; sequential extraction, first ethanol then tetrahydrofuran, gave the best results. This exhaustive extraction method represents a viable alternative to the use of expensive, more thermally stable oniumion treatments for layered silicates.
79 citations
TL;DR: In this article, an O2 oxidation and freeze-dry procedure has been used to synthesize birnessite through the oxidation of Mn2+ in alkali media, where the effects of O2 flow rate, the fluxion velocity of reaction suspension, the reaction temperature, pretreatment the reaction solutions with N2, and the hydration conditions on the purity of Birnessite, the crystallinity, the ion-exchange properties, and phase transformation of intermediate phases were examined.
Abstract: An O2 oxidation and freeze-dry procedure has been used to synthesize birnessite through the oxidation of Mn2+ in alkali media. The effects of O2 flow rate, the fluxion velocity of reaction suspension, the reaction temperature, pretreatment the reaction solutions with N2, and the hydration conditions on the purity of birnessite, the crystallinity, the ion-exchange properties, and the phase transformation of intermediate phases were examined. Buserite with a 1 nm basal spacing, produced after the oxidation, is transformed to 0.7 nm Na birnessite by complete freeze drying. Increasing the fluxion velocity of the reaction suspension and the O2 flow rate facilitated oxidation of Mn(OH)2. Prephase I (a phase related to hausmannite, γ-Mn3O4 (Luo and Suib, 1997; Luo et al., 1998), and feitknechtite (β-MnOOH) were formed as intermediates during the synthesis. Mechanical stirring was used to change the fluxion velocity of the reactive suspension. When the speed of stirring and the O2 flow rate were raised to 250 rpm and 3.0 L/min, respectively, or 450 rpm and 2.0 L/min, respectively, birnessite was the only phase in the final product. Irrespective of temperature in other reactions, pure birnessite was synthesized as long as the temperature during the initial mixing of the reaction solutions was maintained below 10°C. Increasing the reaction temperature led to a larger crystal size, better crystallinity and lower surface area. The pretreatment of solutions with N2 or O2 had little effect on the synthesis; synthesized birnessites had the same purity (100%) as, and similar crystallinity to, that of the no-pretreatment control. Dehydration of the buserite by freeze drying and heating at 60°C did not affect the production of birnessite; however, the latter caused partial loss of ion-exchange capacity with Mg2+. The pathways of the birnessite formation in this study might be:
Mn(OH)2 existed in an X-ray amorphous state, not in the form of ‘pyrochroite’, during the synthesis. The adopted conditions for synthesis of pure birnessite were NaOH to Mn molar ratio of 13.7, O2 flow rate of 2 L/min and oxidation for 5 h during vigorous stirring at 450 rpm at room temperature. The birnessite synthesized had a hexagonal platy morphology with good crystallinity, an average composition of Na0.25MnO2.07.0.66H2O, and a surface area of 38 m2/g.
76 citations
TL;DR: In this paper, the isotope dilution technique using Na and Cs as index cations was used to determine the cation exchange capacity (CEC) of illite du Puy as a function of background electrolyte composition.
Abstract: The isotope dilution technique using Na and Cs as index cations was used to determine the cation exchange capacity (CEC) of illite du Puy as a function of background electrolyte composition. The work showed, in accord with previous studies, that the CEC values were in the order Cs-CEC > Na-CEC. Sodium is commonly chosen as the index cation in CEC determinations using the isotope dilution method. The experimentally measured Na-CEC values for Na-illite increased from ∼75 to ∼200 meq kg−1 for NaClO4 concentrations in the range 5.6 × 10−4 to 1.25 × 10−2 M. Cesium CEC determinations showed a much less pronounced trend over a CsNO3 concentration range from 10−3 to 10−2 M. A reference Cs-CEC value of 225 meq kg−1 was chosen. Careful chemical analyses of the supernatant solutions revealed that Ca and Mg at the (sub)umolar level were present in all the determinations, despite the extensive conditioning procedures used. Competition between (Ca + Mg) and Na for the exchange sites was put forward as an explanation for the variation of Na-CEC values. This hypothesis was confirmed in a series of single (45Ca) and double (45Ca plus 22Na) labeling experiments. Calcium-sodium selectivity coefficients (
$(_{{\rm{Na}}}^{{\rm{Ca}}}{{\rm{K}}_{\rm{c}}})$
) were calculated from the experimental data for NaClO4 concentrations from 5.6 × 10−4 to 0.1 M and exhibited a variation from 1.6 to 14.3. A two-site cation exchange model was developed with site capacities and $_{{\rm{Na}}}^{{\rm{Ca}}}{{\rm{K}}_{\rm{c}}}$
values for each site: planar site capacity =180 meq kg−1, $_{{\rm{Na}}}^{{\rm{Ca}}}{\rm{K}}_{\rm{c}}^{{\rm{PS}}} = 2$
; type II site capacity = 45 meq kg−1, $_{{\rm{Na}}}^{{\rm{Ca}}}{\rm{K}}_{\rm{c}}^{{\rm{II}}} = 80$
. The model was able to predict the Na and Ca occupancies in the Na-CEC experiments over the whole range of NaClO4 concentrations. It is recommended that Cs should be used instead of Na as the index cation for determining the CEC of illite.
TL;DR: Palygorskite in Miocene mudstones, palustrine limestones and calcretes from the Esquivias locality (Madrid Basin, Spain) has been analyzed by X-ray diffraction, infrared spectroscopy, scanning and analytical electron microscopy to determine its characteristics and chemical composition as mentioned in this paper.
Abstract: Palygorskite in Miocene mudstones, palustrine limestones and calcretes from the Esquivias
locality (Madrid Basin, Spain) has been analyzed by X-ray diffraction, infrared spectroscopy, scanning
electron microscopy, transmission electron microscopy and analytical electron microscopy to determine its
characteristics and chemical composition. Other palygorskites from the literature are used as references.
The mean structural formula obtained from the analysis of isolated particles is
(Si7.87ALO.13)O20(Al1.04Fe3+
0.20Mg3.11&0.65)(OH)2(OH2)4(Ca0.02K0.05Na0.08). This palygorskite has the
largest Mg content reported in the literature, and it seems that, chemically, it fills the ‘compositional
gap’ existing between sepiolite and palygorskite. Infrared spectroscopy reveals the absence of trioctahedral
Mg and therefore the possibility of the existence of magnesic clusters in the ribbons is discounted. An
homogeneous distribution of the octahedral cations (Al, Fe3+ and Mg) along the ribbons is proposed.
TL;DR: In this paper, the illite-smectite (I-S) mixed-layer mineral series during alteration of felsic vitric materials in volcaniclastic sediments through two drill holes (IT-2 and IT-8) near the Kakkonda active geothermal system, Japan, were examined by optical microscopy, scanning and transmission electron microscopy (SEM and TEM), electron microprobe analysis, X-ray diffraction (XRD), and oxygen isotope analysis.
Abstract: Crystallization processes of the illite-smectite (I-S) mixed-layer mineral series during alteration of felsic vitric materials in volcaniclastic sediments through two drill holes (IT-2 and IT-8) near the Kakkonda active geothermal system, Japan, were examined by optical microscopy, scanning and transmission electron microscopy (SEM and TEM), electron microprobe analysis, X-ray diffraction (XRD), and oxygen isotope analysis. Temperatures measured through the drill holes increased nearly linearly with depth up to 317°C at the bottom (1700 m) of IT-8. Homogenization temperature measurements of fluid inclusions indicated that the alteration occurred at temperatures similar to the present temperatures. In selected volcaniclastic rocks, excluding andesitic rocks and black shales, clay minerals occurred as glass replacements and pore fillings as seen under SEM and optical microscopy, and exhibited predominantly euhedral hexagonal and elongated forms under TEM, implying that they precipitated in situ through hydrolytic reactions of glass and fluid. Based on XRD examination, I-S minerals showed a sigmoidal variation in illite layer percentage in the range of ∼150 to 220°C and R0 I-S minerals with intermediate %I between 20 and 40% rarely occurred (where R is the Reichweite parameter). The chemical composition also showed a specific variation with depth. Intermediate clays including smectite and I-S minerals are enriched in Al compared to those reported previously from hydrothermal alteration of almost equivalent parent rocks. The oxygen isotope data indicated that the reacting solution was percolating groundwater in the shallow levels and with fossil seawater in the deeper levels. Furthermore, calculating the fluid/rock (W/R) ratio from the isotope variations revealed that the alteration occurred at a nearly constant W/R ratio condition irrespective of %I. Consequently, the observed specific variations in structure and chemical composition of I-S minerals reflect the compositional variations of fluid participating in the crystallization at given temperatures under the conditions of a given original rock and constant W/R ratio. High pH and Na-rich solutions generated by progressive hydrolytic reactions between felsic glass and groundwater favored the precipitation of Al-rich smectite up to ∼150°C and was followed by precipitation of an aluminous R1 I-S mineral with few intermediate R0 I-S minerals at higher temperatures. The crystallization obeys Ostwald’s step rule behavior of smectite illitization processes under a high geothermal gradient.
TL;DR: In this paper, the authors synthesize two continuous series of ferrihydrites with between 2 and 6-7 peaks at room temperature in two different ways: (1) by varying the rate of hydrolysis of an Fe(NO3)3 solution (HR series); and (2) by oxidizing an FeCl2 solution containing up to 73 mmol Si/L (Si series).
Abstract: Ferrihydrite is a poorly crystalline Fe oxide of which 2-(XRD)line and 6-line varieties are commonly used in experiments, although species with intermediate numbers of peaks have been found in nature. To simulate nature, we synthesized two continuous series of ferrihydrites with between 2 and 6–7 peaks at room temperature in two different ways: (1) by varying the rate of hydrolysis of an Fe(NO3)3 solution (HR series); and (2) by oxidizing an FeCl2 solution containing up to 73 mmol Si/L (Si series), both at pH 7. Mossbauer spectra at 4.2 K showed that the ferrihydrites of the HR series had a constant magnetic hyperfine field (Bhf) at 4.2 K of 48.8 T whereas Bhf in the Si series dropped from 49.4 to 46.7 T as the Si content of the ferrihydrites increased from 0 to 74.7 g/kg of Si. Temperature scans between 4 and 170 K illustrate that the magnetic order breaks down at a temperature which is lower the higher the hydrolysis rate and the Si concentration in the ferrihydrite.
TL;DR: In this article, a new method has been developed for quantifying smectite abundance by sorbing polyvinylpyrrolidone (PVP) on smectites dispersed in aqueous solution.
Abstract: A new method has been developed for quantifying smectite abundance by sorbing polyvinylpyrrolidone (PVP) on smectite particles dispersed in aqueous solution. The sorption density of PVP-55K on a wide range of smectites, illites and kaolinites is ∼0.99 mg/m2, which corresponds to ∼0.72 g of PVP-55K per gram of montmorillonite. Polyvinylpyrrolidone sorption on smectites is independent of layer charge and solution pH. PVP sorption on SiO2, Fe2O3 and ZnO normalized to the BET surface area is similar to the sorption densities on smectites. γ-Al2O3, amorphous Al(OH)3 and gibbsite have no PVP sorption over a wide range of pH, and sorption of PVP by organics is minimal. The insensitivity of PVP sorption densities to mineral layer charge, solution pH and mineral surface charge indicates that PVP sorption is not localized at charged sites, but is controlled by more broadly distributed sorption mechanisms such as Van der Waals’ interactions and/or hydrogen bonding. Smectites have very large surface areas when dispersed as single unit-cell-thick particles (∼725 m2/g) and usually dominate the total surface areas of natural samples in which smectites are present. In this case, smectite abundance is directly proportional to PVP sorption. In some cases, however, the accurate quantification of smectite abundance by PVP sorption may require minor corrections for PVP uptake by other phases, principally illite and kaolinite. Quantitative XRD can be combined with PVP uptake measurements to uniquely determine the smectite concentration in such samples.
TL;DR: In this article, X-ray diffraction analyses of samples from three profiles of partially weathered gneisses have revealed that kaolinite becomes more abundant than halloysite with increasing intensity of the decomposition processes.
Abstract: Halloysite and kaolinite occur in gneissic weathering profiles developed under a temperate climate in the Leucogia area of NE Greece. X-ray diffraction analyses of samples from three profiles of partially weathered gneisses have revealed that kaolinite becomes more abundant than halloysite with increasing intensity of the decomposition processes. To resolve the genetic relationship between halloysite and kaolinite, microtextures were examined by scanning electron microscopy using polished thin-sections and freshly exposed fracture surfaces, and their chemical compositions were determined using an analytical scanning electron microscope fitted with energy dispersive and wavelength dispersive spectrometers. Different morphological forms of halloysite and kaolinite were detected within the same rock mass. In the earliest stage of weathering, spheroidal aggregates consisting of microcrystalline halloysite are formed on the plagioclase surface. With progressive weathering, spheroidal halloysite converts to tubular halloysite. As weathering advances, tubular halloysite converts to platy halloysite, which in turn converts to kaolinite. Halloysite and kaolinite may coexist in the upper parts of the profiles. Electron microprobe analyses of spheroidal, tubular and platy halloysite and kaolinite show that the chemical composition of the various forms indicate a progressive Fe enrichment and Al depletion with advancing kaolinization, from VIFe0.08VIAl3.70 a.p.f.u. in spheroidal halloysite through VIFe0.29VIAl3.50in platy halloysite to VIFe0.53VIAl3.32 in newly formed kaolinite. Final-stage, book-type kaolinite approaches its ideal chemical composition (VIFe0.04VIAl3.95). The mineralogy and composition of the kaolin minerals and the development of the various morphological forms of halloysite and kaolinite in different parts of the profiles are attributed to the chemistry of the ambient solutions. However, other physical and microenvironmental conditions (e.g. time and space available) also seem to have strong influence on the precipitation processes producing the morphological variations.
TL;DR: In this paper, two soil sequences in northern Italy (Val di Fiemme and Val Genova) along an elevational gradient ranging from moderate (950 m a.s.l.) to high alpine (2440 m a sl.) climate zones were investigated with respect to element losses and development of clay minerals.
Abstract: Two soil sequences in northern Italy (Val di Fiemme and Val Genova) along an elevational gradient ranging from moderate (950 m a.s.l.) to high alpine (2440 m a.s.l.) climate zones were investigated with respect to element losses (Ca, Mg, K, Na, Fe, Al, Si, Mn) and development of clay minerals. Soils formed on paleo-rhyolitic parent material in Val di Fiemme and on tonalitic-granodioritic morainic material in Val Genova. All the soils have a similar age (∼12,000 y) and have been classified as Podzols. The soils are very acid and the pH values tend to increase with decreasing altitude. Podzolization processes were most intense in the range of the subalpine forest up to the timberline (1400–1900 m above sea-level (a.s.l.)). Element leaching was greatest in this range and weathering rates decrease with both higher and lower altitudes. Due to the different lithologies and precipitations between the two valleys, the total amount of chemical weathering was slightly different, although the same trends with altitude could be observed. Imogolite-type materials (ITM) are generally of minor importance. Greater concentrations of ITM were observed in the Bhs or Bs horizons of the Episkeleti-Entic Podzols at the lower altitudes. Iron eluviation was similar in all Podzols while larger amounts of eluviated Al were detected in Val Genova. The pattern of smectite distribution along the climosequences had similarities to the trend of cation losses. The largest amount of low-charge expandable minerals seems to exist in the range of the subalpine forest up to the timberline. The development of clay minerals with a smaller layer charge was more advanced in Podzols on rhyolitic material where smectite could be detected in the Bhs and Bs horizon. Parent material influenced chemical weathering in the soils along the two climosequences and essentially determined the degree of weathering and the formation of clay minerals.
TL;DR: In this article, X-ray diffraction, infrared spectroscopy (FTIR), cation exchange capacity (CEC) and permanent and variable charges analyses were used, and the data showed that clay minerals varied according to soil horizon and topographic position of the soil.
Abstract: Clay minerals from soils of a red-black soil complex developed from basaltic parent material in Sardinia are formed along a short toposequence (200 m). At the foot of the sequence, a clay-rich, black Vertisol forms, whereas at the summit, the soil is a dark reddish-brown Inceptisol. X-ray diffraction, infrared spectroscopy (FTIR), cation exchange capacity (CEC) and permanent and variable charges analyses were used, and the data show that clay minerals varied according to soil horizon and topographic position of the soil. Clay minerals in the Inceptisol are dominated by kaolinite and mixed-layer kaolinite-smectite (K-S, K:S >0.5), whereas the Vertisol contains smectites and K-S with K:S proportions <0.5. In the Vertisol, the proportion of kaolinitic layers in the K-S increases from the C horizon (K:S ∼0.35-0.40) to the Ap horizon (K:S ∼0.40-0.45). This soil clay-mineral distribution, in relation to topography, is similar to that reported for other (kaolinitic) red-black (smectitic) soil associations in subtropical and tropical areas. The sequence forms by downward drainage on summits and slopes, and buildup of ions in 'lows' produces smectites. Fourier transform infrared spectra indicate that two types of smectite are formed in the C horizon of the Vertisol; one is more ferric (Fe-beidellite, nontronite), the other more aluminous. Mineralogical evolution in the soil profile (from C to Ap horizon) shows a decreasing proportion of ferric smectite layers (compared to the more aluminous smectite layers). This would indicate that ferric smectite layers are preferentially transformed (or dissolved) to give kaolinite layers, with Fe precipitating as oxides and/or oxy-hydroxides or retained partly in kaolinite layers. Because the surface properties of clay minerals are related to mineralogy, the CEC (33-41 cmol kg -1 ) in the brown Inceptisol is ∼50% pH-dependent charge while in the Vertisol up to ∼75% of the CEC (48-61 cmol kg -1 ) comes from accessible permanent charges.
TL;DR: A 2 m thick brecciated zone containing magnesian minerals is present at the contact of tectonites and cumulates as mentioned in this paper, which includes serpentine and gabbro relics.
Abstract: A 2 m thick brecciated zone containing magnesian minerals is present at the contact of tectonites and cumulates. Tectonites below this zone comprise serpentinized orthopyroxenite and serpentinite. An alteration zone with vein-type bedding comprises four different levels; from bottom to top they are: (1) green-brown serpentinite with dolomite (0.9 m), (2) light greenish-white dolomite with serpentine (0.5 m), (3) white dolomite with sepiolite (0.4 m), and (4) greenish-white dolomite with smectite-chlorite (0.2 m). The first level has a mineral association of serpentine + dolomite ± calcite ± aragonite, the second level consists of dolomite + serpentine ± calcite or dolomite + magnesite + serpentine, the third level comprises dolomite + sepiolite, and the fourth level is made up of dolomite + chlorite + smectite + serpentine. Dolomite, the main mineral of the alteration zone, occurs as coarse crystals (microsparitic-sparitic) in fractures and as small crystals (microsparitic-micritic) in the matrix, which includes serpentine and gabbro relics. Sepiolite developed at the edges and surfaces of dolomite and as fibrous forms in voids. Cumulate rocks above this zone comprise uralitic gabbros. The occurrences of magnesian minerals developed in three stages: the first stage was the serpentinization of olivine; the second stage was the dissolution of serpentine by groundwater and/or meteoric water containing carbon dioxide; and the last stage was the synthesis of neoformed minerals.
TL;DR: In this article, the Gibbs free energy of green rusts has been investigated and a linear relationship is obtained between the Gibbs energy of formation of GR, normalized to one Fe atom, and the electronegativity ϰ of the interlayer anion, as: μo/n = −76.5
Abstract: Fe(II)–Fe(III) green rust identified in soil as a natural mineral is responsible for the blue-green color of gley horizons, and exerts the main control on Fe dynamics. A previous EXAFS study of the structure of the mineral confirmed that the mineral belongs to the group of green rusts (GR), but showed that there is a partial substitution of Fe(II) by Mg(II), which leads to the general formula of the mineral: ${[{\rm{Fe}}_{1 - x}^{2 + }{\rm{Fe}}_x^{3 + }{\rm{M}}{{\rm{g}}_y}{({\rm{OH}})_{2 + 2y}}]^{x + }}{[x{\rm{O}}{{\rm{H}}^ - } \cdot m{{\rm{H}}_2}{\rm{O}}]^{x - }}$
. The regular binary solid-solution model proposed previously must be extended to ternary, with provision for incorporation of Mg in the mineral. Assuming ideal substitution between Mg(II) and Fe(II), the chemical potential of any Fe(II)-Fe(III)-Mg(II) hydroxy-hydroxide is obtained as: ${\rm{\mu }} = {X_1}{\rm{\mu }}_{\rm{1}}^{\rm{o}} + {X_2}{\rm{\mu }}_{\rm{2}}^{\rm{o}} + {X_3}{\rm{\mu }}_{\rm{3}}^{\rm{o}} + {\rm{R}}T[{X_1}{\rm{ln}}{X_1} + {X_2}{\rm{ln}}{X_2} + {X_3}{\rm{ln}}{X_3}] + {A_{12}}{X_2}(1 - {X_2})$
. All experimental data show that the mole ratio X2 = Fe(III)/[Fetotal + Mg] is constrained (1) structurally and (2) geochemically. Structurally, Fe(III) ions cannot neighbor each other, which leads to the inequality ${X_2}\leqslant {\raise0.5ex\hbox{$\scriptstyle 1$}\kern-0.1em/\kern-0.15em\lower0.25ex\hbox{$\scriptstyle 3$}}.$
Geochemically, Fe(III) cannot be too remote from each other for GR to form as Fe(OH)2 and Mg(OH)2 are very soluble, so ${X_2}\geqslant {\raise0.5ex\hbox{$\scriptstyle 1$}\kern-0.1em/\kern-0.15em\lower0.25ex\hbox{$\scriptstyle 4$}}$
. A linear relationship is obtained between the Gibbs free energy of formation of GR, normalized to one Fe atom, and the electronegativity ϰ of the interlayer anion, as: μo/n = −76.887ϰ — 491.5206 (r2 = 0.9985, N = 4), from which the chemical potential of the mineral fougerite μ is obtained in the limiting case X3 = 0, and knowing ${\rm{\mu }}_{\rm{1}}^{\rm{o}} = - 489.8$
kJmol−1 for Fe(OH)2, and ${\rm{\mu }}_{\rm{3}}^{\rm{o}} = - 832.16$
kJmol−1 for Mg(OH)2, the two unknown thermodynamic parameters of the solid-solution model are determined as ${\rm{\mu }}_{\rm{2}}^{\rm{o}} = + 119.18\;{\rm{kJmo}}{{\rm{l}}^{ - 1}}$
for Fe(OH)3 (virtual), and A12 = −1456.28 kJmol−1 (non-ideality parameter). From Mossbauer in situ measurements and our model, the chemical composition of the GR mineral is constrained into a narrow range and the soil solutions-mineral equilibria computed. Soil solutions appear to be largely overstaurated with respect to the two forms observed.
TL;DR: In this paper, the 3R1 and 3R2 polytypes of hydrotalcites (HT) have distinctly different X-ray powder diffraction (XRPD) patterns.
Abstract: DIFFaX simulations show that the 3R1 and 3R2 polytypes of hydrotalcites (HT) have distinctly different X-ray powder diffraction (XRPD) patterns. The HT samples obtained by coprecipitation as well as those subjected to a subsequent hydrothermal treatment exhibit non-uniform broadening of lines in their XRPD patterns as well as anomalous variation in the intensities of the basal reflections. The reflections appearing in the mid-20 region (30-50°; 3-1.8 A ) are excessively broadened and do not correspond to either of the 3R polytypes. This broadening is shown to be due to a stacking of layers randomly rotated about the c crystallographic axis by n A 120° (n = 1,2). The intensities of the basal reflections vary due to the departure of the layer composition from the nominal value, essentially due to an increase in the intercalated water content. Copyright © 2004, The Clay Minerals Society.
TL;DR: In this paper, the effect of a saline environment on illitization in volcanoclastic rocks is examined in deep boreholes in the East Slovak Basin, and it is concluded that illite-smectite (I-S) expandability is always less in the salt-bearing bentonites (SBB) than in salt-free bentonite (SFB) for a given depth interval.
Abstract: The effect of a saline environment on illitization in volcanoclastic rocks is examined in deep boreholes in the East Slovak Basin. Based on X-ray diffraction analysis, it is concluded that illite-smectite (I–S) expandability is always less in the salt-bearing bentonites (SBB) than in the salt-free bentonites (SFB) for a given depth interval. These two lithologies can be distinguished easily by water-leachate chemistry. Within the depth interval 2100–2500 m, the expandability in SBB varies within the range 25–10% expandable with R1 and R3 ordering in SBB and 68–35% expandable with R0 ordering in SFB. In two shallow SBB samples the expandability is close to that of SFB, suggesting that salinity alone does not enhance the illitization; but salinity may enhance it when combined with higher burial temperature. Vitrinite reflectance and Tmax of RockEval pyrolysis measured in adjacent shales confirm that the increased illitization in SBB is not due to heating and/or erosion. The model of burial and thermal history calibrated by organic maturity suggests that the same thermal history produces two different expandabilities in the two lithologies (SBB and SFB). Particle thickness measurements and K-Ar data were used to deduce the crystal growth mechanism of illitization in SBB. Whereas surface-controlled growth is typical for SFB, simultaneous nucleation and growth played a more important role in the case of SBB. The effect of a salty environment on the illitization is not yet fully understood and may have severe consequences for the utilization of bentonites as engineering barriers in radioactive waste disposal sites if salt formations used as host rocks are taken into account.
TL;DR: In this paper, the properties of a weathering profile derived from serpentinite were studied using classical pedological methods (Munsell soil colors, particle-size distribution, density, cation exchange capacity, exchangeable bases, among others) and inductively coupled plasma-atomic emission spectroscopy (ICP-AES) results.
Abstract: Bulk mineralogical and chemical properties of a weathering profile derived from serpentinite were studied using classical pedological methods (Munsell soil colors, particle-size distribution, density, cation exchange capacity, exchangeable bases, among others) and inductively coupled plasma-atomic emission spectroscopy (ICP-AES) results. Bulk clay fractions were characterized using X-ray diffraction, thermal analysis, electron microprobe, Mossbauer and infrared spectroscopies. Bulk geochemical mass-balance calculated from ICP-AES results shows leaching of both Mg and Si which reflects the early weathering of serpentine minerals. As a consequence, newly formed clay minerals are enriched with the least mobile elements, i.e. Fe and Al, producing dioctahedral smectites. These dioctahedral smectites are complex, heterogeneous and consist mainly of two populations. One population is an Fe-rich montmorillonite with little or no tetrahedral charge and Fe3+ as the dominant octahedral cation whereas the second population exhibits tetrahedral charge. Both populations occur as interstratified layers in the lower horizon of the weathering profile but show increasing segregation into well-defined end-members towards the surface horizons. Considering total Al and Fe contents, these clays differentiate into two chemical composition domains, Fe-rich clays in the lower profile and Al-rich clays towards the surface horizons.
TL;DR: In this paper, the adsorption of polyvinyl alcohol (PVA) on montmorillonites saturated with calcium (Ca-Mt) and sodium (Na)-Mt as a function of the pH value and PVA concentration in aqueous solution was studied.
Abstract: The adsorption of poly(vinyl alcohol) (PVA) on montmorillonites saturated with calcium (Ca-Mt) and sodium (Na-Mt) as a function of the pH value and PVA concentration in aqueous solution was studied. Owing to the binding effect of the bivalent cation, the adsorption of PVA on Ca-Mt decreases as the pH of the suspension increases, whereas adsorption on Na-Mt is unaffected by the suspension pH. The adsorption maximum of PVA (pH 6) on Ca-Mt was 151.2 mg of PVA g−1 of clay, which is considerably lower than that on Na-Mt (496.2 mg g−1). These adsorption data coincide with the basal spacings obtained for the clays: 1.72 and 2.26 nm for Ca-Mt and Na-Mt, respectively. Sodium permits a greater separation between the clay laminae than calcium, but in both clays the presence of the polymer gives rise to a material in which PVA is intercalated between the laminae and is also adsorbed on the external surface. Adsorption is a slow process and is irreversible in both clays.
TL;DR: In this paper, the texture and chemistry of altered glasses in two hyaloclastites and one hyalotuff were studied using electron probe microanalysis, scanning electron microscopy and transmission electron microscope.
Abstract: Three petrographically distinct styles of altered glasses in two hyaloclastites and one hyalotuff were studied. The texture and chemistry of these samples were investigated using electron probe microanalysis, scanning electron microscopy and transmission electron microscopy in order to understand better the mechanism by which alteration of sideromelane and formation of palagonite occurred in these samples. The results show that clay minerals (primarily smectites) are present in three different microenvironments: (1) coating the surfaces of glass and crystals or vesicle walls; (2) as a relatively heterogeneous, but well crystallized, replacement product (i.e. reddened smectite grain replacement or RSGR) of glass or; (3) as a relatively homogeneous, amorphous to poorly crystalline replacement product (i.e. palagonite). Both the grain size and composition of these smectite-like materials vary considerably. Crystalline smectites occur in both hyaloclastites and have an intermediate composition between the two end-members nontronite and saponite. This composition could correspond to a mechanical intergrowth and/or an interstratification of two different smectites: one dioctahedral (i.e. nontronite) and one trioctahedral (i.e. saponite or stevensite) or simply to a true di-trioctahedral smectite. The coating smectite appears to have precipitated by a paragenetically-early, dissolution-precipitation mechanism prior to the formation of the RSGR. The high Ti content found in RSGR is attributable to an amorphous Ti-rich material which is intergrown with smectite and which behaves as a sink for immobile elements and those not included in smectite. Palagonite from both hyaloclastites and hyalotuff is poorly to non-crystalline and more aluminous than the coating smectites. Palagonite from the hyalotuff has an Fe-rich montmorillonite-like composition. The TEM images show a 30–50 nm thick leached layer formed by selective (non-stoichiometric) dissolution that takes place in the fracture domain. The hydration and replacement of glass during the palgonitization process is accompanied by the loss of Fe, Mg and Ca with a concomitant gain of Al. Both palagonites (from hyaloclastites and hyalotuff) show smilar textural and chemical characteristics.
TL;DR: The Eocene Huber Formation, exposed in the CFI Hall mine south of Irwinton, in Wilkinson County, Georgia, displays colored zones that are a consequence of an oxidative weathering front as discussed by the authors.
Abstract: The Eocene Huber Formation, exposed in the CFI Hall mine south of Irwinton, in Wilkinson County, Georgia, displays colored zones that are a consequence of an oxidative weathering front. These zones vary from very light gray (gray) to pinkish white (pink) to very pale yellow (cream) (Munsell N8, 5YR 8/2 and 2.5Y 8/2, respectively) with increasing degree of oxidation. A representative sample from each zone was collected and analyzed for its chemical, crystallographic and Raman spectroscopic properties. The comparison of these genetically related samples allowed for a quantitatively accurate assessment of anatase’s contribution to the total TiO2 content. All samples contain ∼1.5 wt.% TiO2. Progressing from gray to pink to cream, anatase contents range from half to nearly all the TiO2. The a lattice parameter for anatase is constant in all three kaolins (3.7916 A), suggesting a constant 4.6 mol.% isomorphous substitution of Fe for Ti. Phase characterization and mass-balance considerations of the gray, pink and cream kaolins indicate that ilmenite and pyrite are precursor Ti- and Fe-bearing phases in the gray kaolin that undergo oxidation. Pseudorutile is a proposed intermediate phase resulting from the anodic corrosion of ilmenite. Hematite, goethite and anatase are the dominant end-products via dissolution-precipitation from the reactants pyrite and pseudorutile. The removal of Fe sulfides and organic matter and addition of hematite and goethite causes kaolin colors to change from gray to pink. Oxygen diffusing from groundwater in permeable overlying and underlying formations facilitates a process that probably involves aerobic and anaerobic bacteria that utilize Fe from pyrite, hematite and goethite. We postulate that the end result is the mobilization of Fe by siderophores and a kaolin color change from pink to cream.
TL;DR: In this article, an organically modified bentonite to ethanol-water solutions was determined to approximate the effects of organo sorption-induced swelling, and measured coefficients of permeability for the BODMA bentonite decreased from ∼1 × 10−7m s−1 for pure water to ∼8 × 10 − 10−10m s − 1 for pure ethanol.
Abstract: Permeability is often the limiting factor in clay-based barrier systems designed to attenuate miscible or immiscible contaminant transport. One critical aspect of barrier design is prediction of the effects of permeant conditions on physicochemical properties (e.g swelling) of the clay component and thus, ultimately, the permeability of the barrier. To this end, the permeability of an organically modified bentonite to ethanol-water solutions was determined to approximate the effects of organo sorption-induced swelling. The bentonite was modified with a substituted alkylammonium cation: benzyloctadecyl-dimethylammonium (BODMA). Powder X-ray diffraction (XRD) measurements were used to measure interlayer expansion and to estimate aggregate particle densities at any given ethanol concentration. Permeability measurements were conducted on samples under confining overburden stresses of 43 kPa (∼2.5 m of saturated soil) using a hydraulic gradient of ∼300. Sample thickness was continuously monitored during measurements of volumetric flow so that sample strain, void ratio and porosity could be calculated from changes in sample pore volumes. For calculations of porosity and void ratio, the swelling solid volume, determined from XRD, was assumed to include the sorbed layer (crystalline water/ethanol), the thickness of which is not normally considered in engineering applications. Exposure of the BODMA bentonite to increasing ethanol concentrations increased the swell volume of the clay. Measured coefficients of permeability for the BODMA bentonite decreased from ∼1 × 10−7m s−1 for pure water to ∼8 × 10−10m s−1 for pure ethanol. Exposure of the organo clay to ethanol-water solutions containing 0.2 M NaCl increased the effect of ethanol on clay swelling and permeability. Probable consequences of the effects of sorption-induced swelling on permeability and the performance of organo clay-based permeable reactive barriers are discussed.
TL;DR: In this paper, a collection of green earths belonging to traditional artists' pigments was examined in terms of mineralogy and provenance, including green micas (glauconite or celadonite), chlorite, or smectite as pigmenting agents.
Abstract: A collection of green earths belonging to traditional artists’ pigments was examined in terms of mineralogy and provenance. The studied specimens included both mineralogical reference compounds and selected commercially available artists’ pigments, and contained green micas (glauconite or celadonite), chlorite, or smectite as pigmenting agents. The samples were examined by X-ray diffraction, Mossbauer spectroscopy, infrared (IR) spectroscopy, ultraviolet-visible (UV-Vis)-near-IR diffuse-reflectance spectroscopy and voltammetry of microparticles. Particular attention was paid to the Kadaň green earth, mined until the 20th century in the West Bohemia deposit. The Greene-Kelly charge-reduction test, detailed description of non-basal diffraction patterns and characteristic vibrations in the mid-IR spectra were used to classify the major pigmenting agent of the Kadaň green earth as ferruginous smectite with separately diffracting saponite-like clusters. The smectite contains ∼15% Fe, mainly in the trivalent form, a detectable fraction of Fe in tetrahedral sites, and it is accompanied by a significant amount of Ti-bearing relict minerals due to its volcanogenic origin. On the contrary, in green micas (glauconite and celadonite) the Ti content is much smaller. Diffuse reflectance spectroscopy was found suitable for distinguishing Fe as a constituent of free Fe oxides from Fe in the clay structure. It was also found to be useful for discriminating between green micas and smectites.
TL;DR: In this paper, the influence of smectite properties on the complex electrical conductivity spectra of hydrated smectitic clays was examined using X-ray diffraction.
Abstract: Electrical conductivity is an important soil property related to salinity, and is often used for delineating other soil properties. The purpose of this study was to examine the influence of smectite properties on the complex electrical conductivity spectra of hydrated smectitic clays. Four smectites were saturated with Ca, Mg, Na or K and equilibrated at four relative humidities ranging from 56 to 99%. X-ray diffraction was used to determine fractions of the various smectite layer hydrates (0 to 4 layers of interlayer water molecules) in each sample. A vector network analyzer was used to determine the real component of the complex electrical conductivity spectra (σ') for frequencies (f) ranging from 300 kHz to 3 GHz. Values of the dc electrical conductivity (σ 0 ), the frequency where the slope changes in the spectra (f r ), and the slope at the high-frequency end of the spectra (n) were determined by fitting σ' to σ'(f) = σ 0 (1 + f/f r ) n . Both σ 0 and f r increased with the total amount of water, the amount of interlayer water, and, for saturating cations in the order K < Mg < Ca < Na. The opposite trends were observed for n. The values of these parameters were influenced by the type of smectite, but the trends were not consistent for the effect of layer charge. The results indicate that interlayer water in smectites contributes to the electrical conductivity of hydrated smectites, and that polarization of water by local electrical fields has a substantial influence on the complex electrical conductivity spectra of smectites. The accuracy of salinity estimates for soils and sediments that are based on conductivity measurements may be adversely affected unless the effects of hydrated clays on electrical conductivity are considered.
TL;DR: In this paper, X-ray diffraction with a position-sensitive detector (XRD-PSD) was used to make a time-resolved study of the dynamics of deposition and dehydration of Na-montmorillonite crystallites on flat substrates from deionized water suspensions.
Abstract: X-ray diffraction with a position-sensitive detector (XRD-PSD) was used to make a time-resolved study of the dynamics of deposition and dehydration of Na-montmorillonite crystallites on flat substrates from deionized water suspensions. The static PSD geometry and simultaneous counting procedure allowed the acquisition of high-resolution data on the dynamics of interlayer and interparticle arrangements during dehydration. Three experimental datasets of Na-smectite dehydration are presented, each one representing different initial sample states (suspension, slurry and re-wetted thin film). The computer program NEWMOD was used to simulate one of the three datasets (dehydration of a smectite suspension) and thus obtain the apparent changes in relative proportions of different 00l values as smectite crystallites formed and dehydrated. Two types of diffracting domains formed: water-dispersed ‘packets’ of 1–2 smectite layers gaining long-range order in the c axis direction as water was lost to evaporation, and smectite layers deposited as hydrated crystallites with variable interlayer water contents. The experimental patterns show the rapid step-wise transition of Na-montmorillonite layers from d values of ∼55 to 18.5, 15.4 and 12.5 A, with variations that depended upon how the hydrated smectite sample was prepared. The simulations show that there was a wide range of d values whose frequency distribution changed as dehydration proceeded and that transient d values occurred between the peaks observed experimentally. The data obtained in this study illustrate that XRD-PSD instruments have great potential in providing detailed data on the rapid kinetics of interlayer reorganization.