Showing papers in "Clays and Clay Minerals in 2005"
TL;DR: In this article, the thermal stability of surfactant-modified montmorillonites was analyzed using differential thermal analysis (DTA), thermogravimetric measurement (TG) and differential scanning calorimetry (DSC).
Abstract: The thermal stability of surfactant-modified clay plays a key role in the synthesis and processing of organoclay based nanocomposites. Differential thermal analysis (DTA), thermogravimetric measurement (TG) and differential scanning calorimetry (DSC) were used in this study to characterize the thermal stability of hexadecyltrimethylammonium bromide (HDTMAB) modified montmorillonites prepared at different surfactant concentrations. DSC shows that the molecular environment of the surfactant within the montmorillonite galleries is unique from that in the bulk state. The endothermic peak at 70-100 oC in the DTA curves of the modified montmorillonites is attributed to both the surfactant phase transformation and the loss of free and interlayer water. With an increase of surfactant packing density, the amount of water residing in the modified montmorillonite decreases gradually, reflecting the improvement of the hydrophobic property for organoclay. However, the increase of the surfactant packing density within the galleries leads to the decrease of the thermal stability of the organoclays.
With an increase of initial surfactant concentration for the preparation of organoclays, the surfactant packing density increases gradually to a "saturated" state. It was found that the cationic surfactant was introduced into the montmorillonite interlayer not only by cation exchange but also by physical adsorption.
192 citations
TL;DR: In this paper, the authors present an updated fabric map on the pH-ionic concentration space, which takes into account all experimental results, and is structured around a critical pH level and a threshold ionic concentration beyond which van der Waals attraction prevails.
Abstract: The behavior of fine-grained mineral systems is dependent on pore-fluid characteristics. The systematic analysis of previously published studies supports the development of a fabric map in the pH and ionic concentration space as a working hypothesis. This conceptual study is complemented with an extensive battery of tests where surface charge and particle interactions are controlled through pore-fluid characteristics. The macro-scale tests include sedimentation, viscosity and liquid limit, and involve a wide range of solid volume fractions (suspension to sediment) and strain levels. Experimental results permit the development of an updated fabric map on the pH-ionic concentration space which takes into consideration all experimental results. The fabric map is structured around a critical pH level and a threshold ionic concentration beyond which van der Waals attraction prevails.
178 citations
TL;DR: In this article, a conceptual model for smectite destabilization is proposed, which involves first the release of protons from the structure, MeFe3+OH groups being deprotonated preferentially and metal Fe acting as proton acceptor.
Abstract: Interaction between metal Fe and a variety of natural and synthetic smectite samples with contrasting crystal chemistry was studied by scanning electron microscopy and X-ray diffraction from experiments conducted at 80°C. These experiments demonstrate an important reactivity contrast as a function of smectite crystal chemistry. An XRD method involving the use of an internal standard allowed quantification of the relative proportion of smectite destabilized as a function of initial pH conditions as well as of smectite structural parameters. In mildly acidic to neutral pH conditions, a significant proportion of metal Fe is corroded to form magnetite without smectite destabilization. Under basic pH conditions, smectite and metal Fe are partly destabilized to form magnetite and newly-formed 1:1 phyllosilicate phases (odinite and crondstedtite). More specifically, systematic destabilization of both metal Fe and smectite is observed for dioctahedral smectites while trioctahedral smectites are essentially unaffected under similar experimental conditions. In addition, smectite reactivity is enhanced with increasing Fe3+ content and with the presence of Na+ cations in smectite interlayers. A conceptual model for smectite destabilization is proposed. This model involves first the release of protons from smectite structure, MeFe3+OH groups being deprotonated preferentially and metal Fe acting as proton acceptor. Corrosion of metal Fe results from its interaction with these protons. The Fe2+ cations resulting from this corrosion process sorb on the edges of smectite particles to induce the reduction of structural Fe3+ and migrate into smectite interlayers to compensate for the increased layer-charge deficit. Interlayer Fe2+ cations subsequently migrate to the octahedral sheet of smectite because of the extremely large layer-charge deficit. At low temperature, this migration is favored by the reaction time and by the absence of protons within the ditrigonal cavity. Smectite destabilization results from the inability of the tetrahedral sheets to accommodate the larger dimensions of the newly formed trioctahedral domains resulting from the migration of Fe2+ cations.
114 citations
TL;DR: In this article, the Hofmann-Klemen effect on the charge reduction of homoionic swelling clay minerals upon heating is reviewed. But the authors focus on the changes of various mineral properties connected with charge reduction, including the loss of swelling and the decrease in the cation exchange capacity.
Abstract: Layer charge reduction of selected homoionic swelling clay minerals upon heating is reviewed. This phenomenon is known for Li+-montmorillonites as the Hofmann-Klemen effect. Aspects covered in the review include: mechanism of the charge reduction caused by the irreversible migration of small cations into the mineral layers; final sites of the fixed cations in the octahedral and/or tetrahedral sheets, as deduced on the basis of structural and spectroscopic data obtained in several studies; effects of octahedral and tetrahedral components of the layer charge; properties of the exchangeable cations; and the chemistry and structure of the mineral on charge reduction. Current knowledge has been summarized on the changes of various mineral properties connected with charge reduction, including the loss of swelling and the decrease in the cation exchange capacity, the most important change upon cation fixation. Also discussed are the preparation, properties, and advantages of uses of series of reduced-charge montmorillonites (RCMs) in research; interactions of RCMs with alkylammonium cations and organic cationic dyes, with some examples on the interactions with organic polymers and other organic compounds. Properties of organo-complexes and composite materials prepared from RCMs are also included in this review.
89 citations
TL;DR: In this paper, an atomic model of pyrophyllite interlayer was constructed using steered molecular dynamics simulations and external forces were applied to individual atoms to study the response of the model to applied forces.
Abstract: Pyrophyllite is the precursor to other smectite-group minerals which exhibit swelling. The mineral structure of pyrophyllite can lead to other minerals in the smectite group, including montmorillonite, through appropriate isomorphous substitutions. In this work, an atomic model of the pyrophyllite interlayer was constructed. The response of the interlayer was evaluated using steered molecular dynamics simulations. In steered molecular dynamics, external forces were applied to individual atoms to study the response of the model to applied forces. In this work, forces are applied to the surface clay atoms to evaluate the displacement vs. applied stress in the interlayer between clay layers. This paper describes the construction of the model, the simulation procedure, and the results of the simulations which show that under the applied loading, deformation occurs mainly in the interlayer. The clay layers show relatively little deformation. The results show that the relationship between applied stress and displacement of the interlayer is linear. The stress-deformation relationship for the interlayer is presented.
86 citations
TL;DR: In this paper, the authors used transmission electron microscopy (TEM) to demonstrate the biological formation of a hollow spherical halloysite-like mineral in freshwater systems, referred to hereafter as bio-halloysite.
Abstract: Transmission electron microscopy (TEM) has been used to demonstrate the biological formation of a hollow spherical halloysite-like mineral in freshwater systems. The interaction between clays and microbes was investigated in microbial films from laboratory cultures derived from natural sediments. Optical and electron microscopic observations of cultured microbes revealed that thin clay films covered areas of the bacterial cell wall. X-ray diffraction of the thin films after 2 y of ageing showed a 7.13 A d spacing, consistent with a 7 A halloysite-like phase [Al2Si2O5(OH)4 H2O]. Fourier transform infrared analysis of the thin film exhibited the characteristic adsorption bands for O−H (3651 cm−1), C−H and C−N (2925, 1454 and 1420 cm−1, respectively), suggesting that the phase was closely associated with adhesive organics. Observation by TEM of the thin films revealed that spherical, hollow, halloysite-like material formed on both coccus- and bacillus-type bacterial cells. Electron diffraction analysis of this material showed 2.9, 2.5, 2.2 and 1.5 A d spacings. The present investigation strongly suggests that the thin film wall of the spherical halloysite-like material was associated with bacteria as a bio-organic product. This material, referred to hereafter as bio-halloysite, is further evidence for the microbially-mediated formation of clay minerals. The identity of the bacteria responsible for bio-halloysite formation is unknown, but is tentatively assigned to sulfate-reducing bacteria on the basis of morphology and the presence of reducing conditions in the microcosm at the end of the experiments.
80 citations
TL;DR: In this paper, the influence of clay preparation procedure on sorption and hydrolysis of carbaryl (1-naphthyl, A-methyl carbamate) by the reference smectite SWy-2 was examined.
Abstract: The influence of clay preparation procedure on sorption and hydrolysis of carbaryl (1-naphthyl, A-methyl carbamate) by the reference smectite SWy-2 was examined. For research purposes, reference clays are sometimes used without purification, or more commonly, the <2 pm size fraction is obtained by gravity sedimentation or low-speed centrifugation. We determined that these common methods did not remove all the inorganic carbonate impurities present in SWy-2, and that these impurities caused alkaline conditions in aqueous clay suspensions leading to the alkaline hydrolysis of carbaryl to 1-naphthol. The hydrolytic activity of homoionic K-SWy-2 disappeared once carbonates were eliminated. Two methods were evaluated for preparing K-SWy-2 devoid of inorganic carbonates. In Method A, inorganic carbonates were first removed by incremental additions of a 0.5 M sodium acetate buffer (pH 5.0) until the clay suspension reached pH 6.8, followed by low-speed centrifugation to obtain the <2 μm size fraction; in Method B, the order of these steps was reversed. Carbaryl hydrolysis was used as a probe to determine the effectiveness of the two methods in terms of the removal of carbonate accessory minerals. Homoionic K-SWy-2 obtained by Methods A and B produced near neutral pH when suspended in water and hydrolysis of carbaryl in these suspensions was not evident. In this regard, both clay preparation methods were acceptable. However, there were procedural advantages with Method B, which is therefore recommended for the partial purification of reference clays, as detailed in this paper.
72 citations
TL;DR: In this paper, a borate-pillared double hydroxide (LDH) with boric acid was formulated as [Mg065Al035(OH)2][B3O5]035065H2O and an interlayer spacing of 107 nm Infrared and 11B magic angle spinning nuclear magnetic resonance data are consistent with the presence of polymeric triborate anions in the interlayer galleries so that the material can be formulated as
Abstract: Reaction of a Mg-Al carbonate layered double hydroxide (LDH) with boric acid leads to a borate-pillared LDH with the stoichiometry [Mg065Al035(OH)2][B3O5]035065H2O and an interlayer spacing of 107 nm Infrared and 11B magic angle spinning nuclear magnetic resonance data are consistent with the presence of polymeric triborate anions of the type [B3O4(OH)2]nn- in the interlayer galleries so that the material can be formulated as [Mg065Al035(OH)2][B3O4(OH)2]035030H2O The flame-retardant properties of the borate-pillared material and the carbonate precursor in composites with ethylene vinyl acetate copolymer were compared Introduction of the borate anion leads to a significant enhancement in smoke suppression during combustion without compromising the flammability of the material This is related to the synergistic effect between the host layers of the LDH and the borate anions uniformly distributed in the interlayer region
71 citations
TL;DR: In this paper, the edge surface area (ESA) was used to calculate the dissolution rate for montmorillonite under alkaline conditions, and the results indicated that dissolution occurred at edge surfaces.
Abstract: Montmorillonite dissolution under highly alkaline conditions (pH = 133; I = 03 M) was investigated by bulk dissolution methods and in situ atomic force microscopy (AFM) In bulk dissolution experiments, initial SiO 2 concentrations were high, and a steady state was reached after 136 h The dissolution rates derived from the edge surface area (ESA) at the steady-state condition at 30, 50 and 70°C were 339 × 10 −12 , 175 × 10 −11 and 581 × 10 −11 mol/m 2 s, respectively The AFM observations were conducted under three conditions: (Run I) short-term in situ batch dissolution at RT; (Run II) long-term in situ flow-through dissolution at RT; and (Run III) long-term batch dissolution at 50°C The observed reductions in montmorillonite particle volume for Runs I and II were due primarily to edge-surface dissolution The ESA-based dissolution rate for Run I (10 −9 mol/m 2 s) was three orders of magnitude faster than that for Run II (10 −12 mol/m 2 s) The rate obtained for Run II corresponded to the rate at the steady-state conditions in the bulk dissolution experiments A small number of etch pits developed in Run III slightly increased the ESA of montmorillonite since most of the montmorillonite particles were separated into monolayers lacking three-dimensional periodicity The ESA-based dissolution rate for Run III was 226 × 10 −11 mol/m 2 s Dissolution rates based on long-term AFM observations could be directly compared with steady-state rates obtained from bulk dissolution experiments The AFM observations indicated that dissolution occurred at edge surfaces; therefore, the ESA should be used to calculate the dissolution rate for montmorillonite under alkaline conditions Dissolution rates of individual particles with different morphologies estimated by AFM were similar to rates estimated from bulk dissolution experiments
67 citations
TL;DR: For most clay chemists, including this reviewer, vibrational spectroscopy is a means to an end, but it is an extremely powerful means as discussed by the authors, which can give information about how equivalent units within the material are interacting with each other, information that is difficult to obtain in any other way.
Abstract: This wide-ranging, well produced and inexpensive volume belongs on the work shelf of every research group involved in the study of clays or layered double hydroxides. The list of authors is a roll-call of the most prominent workers in the field, and, while not offering a comprehensive survey, the diverse contributions provide snapshots of the variety of techniques currently being employed in this area, and how these may be brought to bear on a wide range of problems of interest to all workers in the area, not just spectroscopists.
This reviewer has long held that the vibrational spectroscopy of layered materials is a rich source of detailed information, some of it unobtainable in any other way, and deserves a place second only to X-ray diffraction. This volume may help persuade more researchers that without at least routine collection of infrared spectra, the characterization of layered materials is seriously incomplete. And if this involves a walk over to the Chemistry Building, so much the better for all concerned.
For most clay chemists, including this reviewer, vibrational spectroscopy is a means to an end, but it is an extremely powerful means. Through the operation of selection rules, the number of distinct observable modes gives information about local symmetry. Frequency (more precisely, frequency2 × effective mass) relates directly to the stiffness of a bond, and thus, indirectly, to its strength. From this, it immediately follows that in favorable cases the vibrational spectrum can give information about the number and nature of subtly different sites. Finally, in favorable cases the separation of frequencies can give information about how equivalent units within the material are interacting with each other, information that is extremely difficult to obtain in any other way. While these broad general themes are not, on the whole, spelt out explicitly, their …
63 citations
TL;DR: In this article, five bentonites originating from different environments were selected for the present study: hydrothermal alteration of obsidian perlite glass inside the volcanoes themselves (Providencia and Tribia deposits), alteration of pyroclastic flows in a marine shallow water to lagoonal lacustrine environment (Ibourhardayn deposit), ash falls in marine or lacustine systems (Moulay Rachid and Melg el Ouidan (formerly Camp Berteau) deposits), and mixed-layer beidellite-montmorillonite
Abstract: The Gourougou volcanic massif (northeastern Morocco) is actively prospected for bentonite deposits. Five bentonites originating from different environments were selected for the present study: hydrothermal alteration of obsidian perlite glass inside the volcanoes themselves (Providencia and Tribia deposits); alteration of pyroclastic flows in a marine shallow water to lagoonal lacustrine environment (Ibourhardayn deposit); ash falls in marine or lacustrine systems (Moulay Rachid and Melg el Ouidan (formerly Camp Berteau) deposits). All of these bentonites were probably formed from volcanic glass originating from a rhyolitic magma at different stages of differentiation as shown by slight variations of REE and incompatible element abundances. The crystal-chemical characteristics of the smectite vary according to alteration conditions: beidellite predominates in hydrothermal systems, whereas montmorillonite predominates in lagoonal and lacustrine environments, and mixed-layer beidellite-montmorillonite in the sea-water-altered pyroclastic flows. All these dioctahedral smectites exhibit a heterogeneous distribution of charge as shown by the presence of partially expandable (1 EG) or non- expandable (0 EG) layers in the K-saturation state. The proportion of the collapsed or partially expandable layers is not related to the average layer charge or to the cation exchange capacity. This militates for an overall heterogeneous charge distribution. Compared to other natural or experimental alteration systems of similar rhyolitic glass, the formation of beidellite or montmorillonite appears to be controlled by the amounts of Mg in the system.
TL;DR: Most detrital ilmenite grains in sandstones of the Chaswood Formation are completely altered to pseudorutile, leucoxene and rutile as discussed by the authors.
Abstract: Most detrital ilmenite grains in sandstones of the Chaswood Formation are completely altered to pseudorutile, leucoxene and rutile The textural, chemical and mineralogical changes involved in alteration were tracked using electron microprobe analyses, backscattered electron images, and elemental maps Ilmenite grains (Ti/(Ti+Fe) ≈ 048) alter patchily to pseudorutile (Ti/(Ti+Fe) 05–07) with volume loss, forming a porous structure and this process continues with the development of leucoxene (Ti/(Ti+Fe) 07–09) Within the pseudorutile and leucoxene, stubby prismatic rutile crystals have been precipitated Si and A1 occur in the altered ilmenite, either (1) inherited from original quartz and muscovite inclusions in the parent crystal or (2) as kaolinite altered from muscovite inclusions or precipitated in the pore space, under pedogenic or early diagenetic conditions Distribution of alteration phases has been related to facies and diagenetic variations With increasing amounts of leaching in different types of paleosols, there was increasing alteration of pseudorutile to leucoxene In light gray mudstones and interbedded sandstones with diagenetic kaolinite that formed beneath the water table from percolating meteoric water, most leucoxene was converted to rutile Burial diagenesis (to vitrinite reflectance values >04%) also promoted the change from leucoxene to rutile The alteration of ilmenite is an important source of Fe for diagenetic minerals in the Chaswood Formation and correlative offshore deltaic and marine facies of the Scotian basin
TL;DR: In this article, the authors show that the use of saturation protocols using both liquid ethylene glycol and liquid glycol vapor yields useful additional information about the distribution of charges in clay minerals.
Abstract: The study of the transformation of smectite to illite, chlorite or vermiculite via interstratified clay minerals needs precise qualitative and quantitative determinations of the different layers in the mixed- layer clays and is generally based on X-ray diffraction (XRD) patterns after specific treatments of the clay samples. Saturation with K or Mg followed by ethylene glycol (EG) solvation are classical methods used to identify high-charge smectite and vermiculite. These procedures have been applied to two experimental clays, one composed of smectite layers and the second, a mixture of vermiculite and smectite layers. Different methods of glycolation (EG vapor or liquid EG) produce significant differences in the XRD patterns. Comparison with literature data indicates that K-saturated, high-charge smectite (~0.8 < total charge <1/unit-cell) and Mg-vermiculite (whatever its charge) do not expand in ethylene glycol vapor (d values ~14y15 A E ). Expansion to 17 A E in liquid ethylene glycol occurs for Mg-vermiculite with a total charge of <~1.2/unit-cell and for K-saturated, high-charge smectite, when the tetrahedral charge is <~0.7/unit-cell. This study shows that: (1) procedures of glycolation need to be standardized; (2) the use of saturation protocols using both liquid ethylene glycol and ethylene glycol vapor yields useful additional information about the distribution of charges in clay minerals.
TL;DR: In this article, the authors compared the effects of trihydroxamate siderophores desferrioxamine-B (DFO-B), desferrizoxamines-D1 (D FO-D 1 ), desferrixamine-D2, desferriaoxamine -D1, desiderrioxamines -D2 and desferrousoxamines E (DDF-E) on Pb and Cd adsorption to kaolinite at pH 4.5 to 9.
Abstract: Siderophores are low molecular weight organic ligands synthesized by aerobic microorganisms to acquire Fe. In addition to Fe(III), siderophores may complex other metals such as Pb and Cd. This study compared the effects of the trihydroxamate siderophores desferrioxamine-B (DFO-B), desferrioxamine-D1 (DFO-D1), desferrioxamine-E (DFO-E), and the monohydroxamate siderophore-like ligand acetohydroxamic acid (aHA) on Pb and Cd (except for DFO-E) adsorption to kaolinite (KGa-1b) at pH 4.5 to 9, in 0.1 M NaClO4, at 22°C, in the dark. At pH >6, all of the studied ligands decreased Pb adsorption to kaolinite: aHA by 5–40% and DFO-B, DFO-D1 and DFO-E by 30–75%; the greater effects were at higher pH. The studied ligands decreased Cd adsorption to kaolinite at pH >8: aHA by 5–20% and the trihydroxamates by as much as 80%. We also observed enhancement of Pb adsorption in the presence of DFO-B at pH ≈5–6.0, probably due to adsorption of the doubly positively charged H3Pb (DFO-B)2+ complex, although spectroscopic evidence is needed.
TL;DR: In this article, the authors characterized structural modifications induced by the presence of such ion pairs, and more especially those related to smectite hydration properties, from the modeling of experimental X-ray diffraction (XRD) profiles.
Abstract: Montmorillonite was equilibrated with high normality Cl− solutions to assess the possible presence of MeCl+ ion pairs in smectite interlayers suggested by chemical modeling of cation exchange experimental studies. Structural modifications induced by the presence of such ion pairs, and more especially those related to smectite hydration properties, were characterized from the modeling of experimental X-ray diffraction (XRD) profiles. As compared to those obtained from samples prepared at low ionic strength, XRD patterns from samples equilibrated in high ionic strength CaCl2 solutions exhibited a small positional shift of 00l basal reflections indicating a greater layer thickness. The rationality of basal reflection positions is also improved and the width of these reflections is decreased. These qualitative modifications are related to the existence of a more homogeneous hydration state with the sole presence at 40% relative humidity (RH) of bi-hydrated smectite layers (2W layers) in high ionic strength samples. By contrast, layers with contrasting hydration states coexist in samples prepared at low ionic strength. The stability of this homogeneous 2W hydration state is also extended towards low RH values in the sample prepared at high ionic strength. In addition, the intensity distribution is modified in samples prepared at high ionic strength as compared to those obtained at low ionic strength. In particular the relative intensity of the 002 reflection is strongly enhanced in the former samples. This modification arises from an increased electron density in the interlayer mid-plane of 2W layers which is best explained by the presence of cation-chloride ion pairs replacing the divalent cations occupying this structural position in low ionic strength samples. The increased amounts of interlayer species (ion pairs and H2O molecules), which are confirmed by nearinfrared diffuse reflectance spectroscopy results, and the larger size of CaCl+ pairs as compared to Ca2+ cations lead to a more stable layer thickness, probably as a result of decreased layer corrugation. Consistent results were obtained for Sr and Mg cations.
TL;DR: In this paper, a series of mixed-layer illite-smectite (I-S) minerals from a drill hole near the Kakkonda geothermal field, one-dimensional structure analysis by X-ray diffraction was performed using Ca-saturated specimens at both air-dried and ethylene glycol solvated states.
Abstract: For a series of mixed-layer illite-smectite (I-S) minerals from a drill hole near the Kakkonda geothermal field, one-dimensional structure analysis by X-ray diffraction (XRD) was performed using Ca-saturated specimens at both air-dried and ethylene glycol solvated states. The expandability characteristics of component layers were also examined by means of alkylammonium exchange and Li-saturation. The K content in illite layer was almost constant at 1.5-1.7/O20(OH)4 in the I-S series from 3% to 85% of I-layer content (% I). The layer charge of smectite layer varied slightly within the ranges of R1 I-S samples showed complicated expandability with alkylammonium exchange. The XRD patterns of dodecylammonium exchanged I-S samples can be interpreted by random interstratification of several types of sub-units such as layer-doublets, layer-triplets and layer-quarutets present in the crystallites. This interpretation is consistent with the variation in the occurrence probabilities of layer-multiplets calculated from the junction probabilities and the proportions of layers. Because the interpretation indicates that I-S is a stack of various types of the sub-units, the smectite illitization can be described by a systematic change in the type and proportion of the sub-units constituting crystallites.
TL;DR: In this paper, the authors show that stacking faults arising from a mixture of 3R and 2H(1) motifs, while having the same enthalpy as that of the ordered crystal, nevertheless contribute to thermodynamic stability by enhancing disorder.
Abstract: Carbonate-intercalated layered double hydroxides of Co(II) and Ni(II) with Fe(III) and Al(III) were precipitated under different conditions(pH = 8-12; T = 25-80 degrees C). All the samples are replete with stacking faults which are not eliminated by post-precipitation hydrothermal treatment (80-180 degrees C, 18 h). DIFFaX simulations show that the layer stacking sequence of the disordered samples can be generated by a mixture of motifs corresponding to the 3R(1) and 2H(1)polytypes. These specific sequences are selected in preference to others because of the need for hydrogen bonding between the intercalated carbonates and hydroxide sheets. Thermodynamic considerations show that faulted crystals have greater stability than ordered crystals. Stacking faults arising from a mixture of 3R(1) and 2H(1) motifs, while having the same enthalpy as that of the ordered crystal, nevertheless contribute to thermodynamic stability by enhancing disorder.
TL;DR: In this paper, Fe-rich kaolinites were synthesized at 225°C in distilled water from gels with different Fe/Al ratios and with Si/(Al + Fe) = 2.4Fe0.
Abstract: Fe-rich kaolinites were synthesized at 225°C in distilled water from gels with different Fe/Al ratios (0.15, 0.25, 0.35) and with Si/(Al + Fe) = 2. X-ray diffraction patterns of the reaction products showed that kaolinite was the only long-range crystalline phase synthesized. Analytical electron microscopy analyses of individual particles and Fourier transform infrared spectra indicated that Fe3+ was isomorphously incorporated into the kaolinite octahedral sheet and that tetrahedral substitution did not occur. The Fe content hosted in the synthetic kaolinites was similar to that incorporated into its corresponding starting gel. The highest Fe content in the particles reached 30 mol.% of the octahedral occupancy. Increases in the b parameter are proportional to increases in Fe for Al substitution. The extent of isomorphic substitution of Al by Fe is the highest ever reported for both natural and synthetic samples. At the nano-scale, there is no evidence of discontinuity in the solid-solution between the Si2Al2O7 and Si2Al1.4Fe0.6O7 end-members, such as short-range disorder or clustering of Fe and Al in domains.
TL;DR: In this paper, the weathering process of volcanic glass to allophane was investigated based on the NMR spectra of size-fractionated soil samples of four Japanese volcanic glasses and two (Al and Si-rich) allophanes.
Abstract: To clarify the weathering process of volcanic glass to allophane, solid-state 29 Si and 27 Al magic angle spinning (MAS) nuclear magnetic resonance (NMR) signals of four Japanese volcanic glasses and two (Al- and Si-rich) allophanes were assigned. The volcanic glasses showed a broad 29 Si NMR signal between −80 and −120 ppm with the peak centered at ~−104 ppm, indicating that they were rich in Si–O–Si bridging structure (silica gel-like polymer Si). Aluminum was present in tetrahedral form in the four volcanic glass samples. In both Al- and Si-rich allophanes, octahedral Al (3 ppm by 27 Al NMR) and imogolite-like Si ( Q 3 3 VI Al, −78 ppm by 29 Si NMR) were the major components. In a Si-rich allophane, NMR signals centered at around −85 ppm for 29 Si and 55 ppm for 27 Al were also observed, although it is possible that those signals were derived from impurities. Impurities could have originated from the soils and/or been unexpectedly synthesized during the purification procedures, e.g. during hot 2% Na 2 CO 3 treatments. Based on the NMR spectra of size-fractionated soil samples, the weathering process of volcanic glass to allophane was proposed as follows: (1) dissolution of Al from volcanic glass accompanied by the transformation of IV Al to VI Al; (2) formation of a gibbsite-like sheet resulting from the hydrolysis of the dissolved Al; (3) dissolution of silica gel-like polymer Si in volcanic glass resulting in the formation of monosilicic acid; and (4) formation of Si(OH)(O VI Al) 3 structure ( Q 3 3 VI Al) as a result of the reaction between the gibbsite-like sheet and the monosilicic acid. These formation reactions of allophane could occur in solution as well as on the surface of volcanic glass.
TL;DR: In this paper, the transformation process between palygorskite and smectite was studied by examining the morphological and structural relationships between these two minerals in an assemblage from the Meigs Member of the Hawthorne Formation, southern Georgia.
Abstract: The transformation process between palygorskite and smectite was studied by examining the morphological and structural relationships between these two minerals in an assemblage from the Meigs Member of the Hawthorne Formation, southern Georgia. Studied samples were related to an alteration horizon with a tan clay unit above and a blue clay unit below. Atomic force microscopy (AFM) and transmission electron microscopy (TEM) were used to study the mechanism of transformation. From AFM data, both clay units contain euhedral palygorskite fibers. Many fibers are found as parallel intergrowths joined along the [010] direction to form ‘raft-like’ bundles. Degraded fibers, which are common in the tan clay, have a distinctly segmented morphology, suggesting a dissolution texture. Many of the altered palygorskite fibers in the tan clay exhibit an oriented overgrowth of another mineral phase, presumably smectite, displaying a platy morphology. This latter mineral forms along the length of the palygorskite crystals with an interface parallel to {010} of the palygorskite. The resulting grain structures have an elongate ‘wing-like’ morphology. Imaging by TEM of tan clay material shows smectite lattice-fringe lines intergrown with 2:1 layer ribbon modules (polysomes) of the palygorskite. These features indicate an epitaxial overgrowth of smectite on palygorskite and illustrate the structural relationship between platy overgrowths on fibers observed in AFM data. The epitaxial relationship is described as {010} [001] palygorskite ‖ {010} [001] smectite. Energy dispersive spectroscopy indicates that the smectite is ferrian montmorillonite. Polysomes of palygorskite fibers involved in these textures commonly vary and polysome widths are consistent with double tetrahedral chains (10.4 A), triple tetrahedral chains (14.8 A), quadruple tetrahedral chains (21.7 A) and quintuple tetrahedral chains (24.5 A). The transformation of palygorskite to smectite and the resulting intergrowths will cause variations in bulk physical properties of palygorskite-rich clays. The observation of this transformation in natural samples suggests that this transformation mechanism may be responsible for the lower abundance of palygorskite in Mesozoic and older sediments.
TL;DR: In this paper, a combined experimental and theoretical study of uranyl complexes that form on the interlayer siloxane surfaces of montmorillonite was performed, showing that uranyl ions form outer-sphere surface complexes with the [O=U=O] 2+ axis tilted at an angle of ~45° to the surface normal.
Abstract: We report a combined experimental and theoretical study of uranyl complexes that form on the interlayer siloxane surfaces of montmorillonite. We also consider the effect of isomorphic substitution on surface complexation since our montmorillonite sample contains charge sites in both the octahedral and tetrahedral sheets. Results are given for the two-layer hydrate with a layer spacing of 14.58 A. Polarized-dependent X-ray absorption fine structure spectra are nearly invariant with the incident angle, indicating that the uranyl ions are oriented neither perpendicular nor parallel to the basal plane of montmorillonite. The equilibrated geometry from Monte Carlo simulations suggests that uranyl ions form outer-sphere surface complexes with the [O=U=O] 2+ axis tilted at an angle of ~45° to the surface normal.
TL;DR: In this article, the authors employed spent cetyltrimethylammonium bromide (CTMAB)-bentonite and Cetyl pyridinium chloride (CPC) to prepare porous clay heterostructures (PCHs).
Abstract: Model spent cetyltrimethylammonium bromide (CTMAB)-bentonite, and cetyl pyridinium chloride (CPC)-bentonite used for sorbing p -nitrophenol (PNP) from wastewater, as well as virgin CTMAB-bentonite and CPC-bentonite, were employed as the starting materials to prepare porous clay heterostructures (PCHs). The BET surface areas and total pore volumes of the PCHs based on these spent and virgin organobentonites (PNP-CTMAB-PCH, CTMAB-PCH, PNP-CPC-PCH and CPC-PCH) are 661.5 m2/g and 0.25 cm3/g, 690.4 m2/g and 0.27 cm3/g, 506.3 m2/g and 0.30 cm3/g, and 525.4 m2/g and 0.30 cm3/g, respectively. These values approximate those of activated carbon (AC), at 731.4 m2/g and 0.23 cm3/g, and are much larger than those of bentonite and CTMAB-bentonite, at 60.9 m2/g and 0.12 cm3/g, and 3.7 m2/g and 0.0055 m2/g, respectively. The PCHs have slightly higher adsorption capacities for benzene and CCl4 than AC at higher relative pressures despite their comparatively lower benzene and CCl4 adsorption capacity at lower relative pressures. The existence of PNP in organobentonites also enhances the volatile organic compounds (VOCs) adsorption capacity of PCHs at lower adsorbate concentrations, although some adsorption capacity is lost at higher concentrations. The hydrophobicity order of the adsorbents is: CTMAB-bentonite > AC > PCHs > bentonite. The micro- to mesoporous pore sizes, superior VOC adsorption properties, thermal stability to 750°C and hydrophobicity and negligible influences of PNP on PCHs make spent PNP-containing organobentonites ideal starting materials for synthesis of PCHs and especially attractive adsorbents for VOC sorption control.
TL;DR: In this paper, the authors used X-ray diffraction, scanning electron microscopy (SEM), TEM and Fourier transform infrared spectroscopy (FTI) to study green grains in pelagic calcareous sediments recovered at a water depth of 3000 m near the Costa Rica margin.
Abstract: Millimetric to centimetric green grains widespread in pelagic calcareous sediments recovered at a water depth of3000 m near the Costa Rica margin were studied by X-ray diffraction, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Fourier transform infrared spectroscopy. Samples were collected, during the Ticoflux II expedition, from the upper bioturbated part of four sedimentary cores (0.13–3.75 m below seafloor). The sediments are calcareous and siliceous nanofossil oozes (coccoliths, diatoms, radiolarians, etc.). Green grains show generally a concentric zoning with a green rim in which smectite largely predominates over pyrite and a black core in which pyrite is prevalent. Observations by SEM indicate that this zoning results from a progressive inward alteration and replacement of the accumulations of pyrites by smectites. The high-resolution TEM observations of the smectite-pyrite interfaces suggest that the replacement of pyrites by smectite occurs through a dissolution-precipitation process with the formation of a gel. The pyrite matrix is composed of a huge number of very small (0.5–22 µm) pyrite octahedra, a typical texture resulting from the pyritization of organic material in early diagenetic environments. The accurate mineralogical and crystal chemical characterization of the smectites indicate that they are Fe3+-montmorillonites (Fe3+-rich smectite with a dominant octahedral charge, rarely recorded in the literature). The formation of such Fe3+-montmorillonites forming green grains could be explained by two successive diagenetic redox stages: (1) reducing stage: early pyritization of the organic matter by microbial reduction within reducing micro-environments; (2) oxidizing stage: Fe3+-montmorillonite crystallized in space liberated after dissolution of pyrite connected with the rebalancing of the redox conditions of the micro-environments with the oxidizing surrounding sediments.
TL;DR: In this article, the potential influence of Fe-cycle bacteria on Fe cycling during post-depositional clay-weathering alteration was examined in open-pit, subsurface mine samples from kaolin lenses and smectite formations collected from sites in central Georgia.
Abstract: Dark Fe oxides and sulfides are major discoloring impurities in mined commercial white kaolin clay. In order to evaluate the potential influence of Fe-cycle bacteria on Fe cycling during post-depositional clay-weathering alteration, Fe(III)-reducing and/or Fe(II)-oxidizing microorganisms were examined in open-pit, subsurface mine samples from kaolin lenses and smectite formations collected from sites in central Georgia. Samples of varying age were examined, including late Eocene smectite overburden, hard kaolin of Middle Eocene age, soft gray kaolin from the late Paleocene, and soft tan kaolin of late Cretaceous age. These clays contained 0.06–5.33% organic carbon, which included various potential organic electron donors for bacterial metabolism: formate (1.1–30.6 mmol/kg), acetate (0–40.5 mmol/kg), lactate (0–12.1 mmol/kg), pyruvate (0.4–78 mmol/kg), oxalate (0–141.7 mmol/kg), and citrate (0–1.4 mmol/kg). All clay samples studied had small concentrations of ‘bio-available’ Fe(III) (0.5 M HCl-extractable Fe, 0.5–2.8 mmol/kg) compared to total Fe (HF-extractable, 25–171.9 mmol/kg). The highest Fe(III)/[Fe(II)+Fe(III)] ratio and the lowest organic carbon content were in kaolin samples in which Fe(III) reduction was determined to be the dominant terminal electron accepting process by hydrogen analysis. All clay samples showed greater numbers of Fe(II)-oxidizing bacteria (22–22,000 cells/g) than Fe(III)-reducing bacteria (3–410 cells/g) as determined by MPN analysis. The Fe(III)-reducing activity in clays could be stimulated with the addition of 1 mM of the Fe(III) chelator, nitrilotriacetic acid. The addition of nitrate stimulated anaerobic Fe(II) oxidation. These results suggest that anaerobic bacteria involved in both oxidation and reduction of Fe exist in these subsurface clay formations, and might have had an influence on post-depositional weathering reactions.
TL;DR: It is suggested that the increase in net negative charge caused by microbial Fe(III) reduction significantly promoted clay flocculation by increasing the electrochemical attraction in the smectite suspensions.
Abstract: This study was undertaken to investigate the changes in flocculation properties of Fe-rich smectite (nontronite, NAu-1) suspensions, including settling velocity, aggregate size and floc architecture associated with microbial Fe(III)-reduction in the smectite structure. The dissimilatory Fe-reducing bacterium Shewanella oneidensis MR-1 was incubated with lactate as the electron donor and structural Fe(III) as the sole electron acceptor for 3, 12, 24 and 48 h in an anaerobic chamber. Two controls were prepared; the first was identical to the experimental treatments except that heat-killed cells were used (non-reduced control), and the second control was the same as the first except that the incubation was carried out in an aerobic environment. The extent of Fe(III) reduction for the 48 h incubation was observed to reach up to 18%. Neither the non-reduced control nor the aerobically inoculated sample showed Fe(III) reduction. Compared with the non-reduced control, there was a 2.7 μm increase in mean aggregate size and a 30-fold increase in average settling velocity in the bioreduced smectite suspensions as measured using a Micromeritics Sedigraph®. The aerobically inoculated smectite showed a similar aggregate-size distribution to that of the non-reduced control. Significant changes in physical properties of smectite suspensions induced by microbial Fe(III) reduction were measured directly using transmission electron microscopy. The floc architecture of bioreduced smectite revealed less open structures compared to those of a non-reduced control. The aspect ratio (thickness/length) of individual smectite particle increased from 0.11 for the non-reduced control to 0.18 on average for the bioreduced smectite suspensions. The effects of pH on the clay flocculation were minimal in this study because the value of pH remained nearly constant at pH = 7.0–7.3 before and after the experiments. We therefore suggest that the increase in net negative charge caused by microbial Fe(III) reduction significantly promoted clay flocculation by increasing the electrochemical attraction in the smectite suspensions.
TL;DR: In this paper, the authors used high-resolution transmission electron microscopy (HRTEM) to obtain one-dimensional structure images of mixed-layer illite-smectite (I-S) minerals normal to [hk0].
Abstract: Smectite illitization was investigated in felsic volcaniclastic rocks from a drill core near the Kakkonda active geothermal system, Japan, using high resolution transmission electron microscopy (HRTEM) that provided one-dimensional structure images of mixed-layer illite-smectite (I-S) minerals normal to [hk0]. Simulated images of a rectorite-like structure revealed that smectite can be distinguished from illite in mixed-layer I-S by HRTEM if the basal spacing of smectite is larger than that of illite. The larger basal spacing of smectite, 1.3 nm under HRTEM, was obtained by intercalation of dodecylammonium ions into smectitic interlayers. In simulated and observed images normal to [hk0], tetrahedral (T) and octahedral (O) cation-layers are imaged as dark lines, an illitic interlayer a bright line, and a smectitic interlayer a dark line sandwiched by two bright lines. Samples are from 435 m (5% I; R0), 635 m (35% I; R0), 656 m (62% I; R1), and 756 m (85% I; R3) depths where % I is the percent of illite layers in a sample and R is the Reichweite parameter. Sample 435 consisted mostly of smectite, and illite layers occurred, though small in amount, as M1 units (module of type 1, defined as one consisting of two polar T-O-T silicate layers with one central illitic interlayer and two, half smectitic interlayers at the outermost surface; the number corresponds to that of central illitic interlayers). M1 units were dominant and isolated or consecutive smectite layers of > two were present in sample 635. Sample 656 consisted mostly of packets of M1 units of 1 to 5 containing M2 to M5 units occasionally. Isolated or consecutive smectite layers of > two were not present in 656. Illite layers occurred almost as M1 units in samples 435, 635 and 656, and the number of M1 units increased with increase in % I. Sample 756 was characterized by the presence of M2 to M10 units accompanied by smectitic interlayers at the external surface and the absence of M1 units and isolated smectite layers. HRTEM data strongly suggest that illitization in a hydrothermal system occurs by precipitation of M1 units for mixed-layer I-S minerals up to 60% I. This does not require the presence of precursor smectite. Illitization of I-S minerals with more than 60% I proceeds by precipitation of various types of Mn(n≥2) units. Illite occurs only as Mn(n≥1) units throughout illitization.
TL;DR: In this paper, the authors used X-ray diffraction, Fourier transform infrared spectroscopy, the Brunauer, Emmett and Teller method and thermogravimetric analysis to determine the heat of dissolution of synthetic goethite.
Abstract: High-temperature oxide-melt solution calorimetry and acid-solution calorimetry were used to determine the heat of dissolution of synthetic goethite with particle sizes in the range 2–75 nm and measured surface areas of 30–273 m2/g (27–240 × 103 m2/mol). Sample characterization was performed using X-ray diffraction, Fourier transform infrared spectroscopy, the Brunauer, Emmett and Teller method and thermogravimetric analysis. Water content (structural plus excess water) was determined from weight loss after firing at 1100°C. Calorimetric data were corrected for excess water assuming this loosely adsorbed water has the same energetics as bulk liquid water. The enthalpy of formation was calculated from calorimetric data using enthalpies of formation of hematite and liquid water as reference phases for high-temperature oxide-melt calorimetry and using enthalpy of formation of lepidocrocite for acid-solution calorimetry. The enthalpy of formation of goethite can vary by 15–20 kJ/mol as a function of surface area. The plot of calorimetric data vs. surface area gives a surface enthalpy of 0.60±0.10 J/m2 and enthalpy of formation of goethite (with nominal composition FeOOH and surface area = 0) of −561.5±1.5 kJ/mol. This surface enthalpy of goethite, which is lower than values reported previously, clarifies previous inconsistencies between goethite-hematite equilibrium thermodynamics and observations in natural systems.
TL;DR: In this article, the authors used X-ray diffraction, N2 adsorption-desorption, chemical analysis, thermogravimetric analysis, differential thermal analysis, temperatureprogrammed desorption of ammonia and temperature-programmed reduction were used to characterize the resulting Fe-pillared clays.
Abstract: Iron-pillared clays (Fe-PILCs) were synthesized from hydrolyzed FeCl3 solutions added to NaOH solutions using different synthesis conditions X-ray diffraction, N2 adsorption-desorption, chemical analysis, thermogravimetric analysis, differential thermal analysis, temperature-programmed desorption of ammonia and temperature-programmed reduction were used to characterize the resulting Fe-pillared clays (Fe-PILCs) A higher degree of pillaring was obtained when the Fe content was adjusted to 60 mmoles of Fe/g of clay It was observed that higher values of this ratio led to worse acidity and textural characteristics, a consequence of the probable formation of Fe oxides that could not only deposit on the surface but also block the pores formed during the pillaring process Likewise, it was found that the amount of Fe that can be introduced depended on the OH/Fe ratios Total surface and micropore area decreased and Fe content increased with increasing pillaring solution concentrations Finally, all pillared samples prepared here were thermally stable at temperatures up to 400°C
TL;DR: The Plio-Pleistocene deposits of the Olduvai Basin in northern Tanzania consist of a sequence of lacustrine and fluvial sediments, the formation of which is related to an interaction of volcanic material or detrital clays with saline alkaline lake water and groundwater as mentioned in this paper.
Abstract: The Plio-Pleistocene deposits of the Olduvai Basin in northern Tanzania consist of a sequence of lacustrine and fluvial sediments. They contain various amounts of zeolite minerals, the formation of which is related to an interaction of volcanic material or detrital clays with saline alkaline lake water and groundwater. Petrographic characteristics of zeolite occurrences provide information about their conditions of formation. They were studied for all four main stratigraphical units that are recognized at Olduvai (Beds I to IV), sampled in the southeastern part of the basin. In the lake-margin deposits of Bed I and the lower part of Bed II, chabazite is the dominant zeolite mineral accompanied by phillipsite and minor amounts of erionite and clinoptilolite. Chabazite commonly occurs as part of altered volcanic rock fragments, characterized by partial or complete dissolution of volcanic glass and the formation of chabazite inside vesicles, following the development of thin smectite coatings. It also formed within the sediment matrix, requiring extended periods of impregnation of the deposits by saline alkaline solutions. Chabazite also occurs extensively as coatings and infillings of pores, developed during periods of subaerial exposure which were characterized by high groundwater levels. Phillipsite formed at a later stage, from more evolved solutions, with higher K/Na ratios than during chabazite formation. The fluvial deposits of Bed IV, Bed III and the upper part of Bed II have a high analcime content. They also contain various amounts of chabazite, phillipsite and natrolite. All zeolite minerals mainly occur in pores. The predominance of analcime indicates a higher salinity and alkalinity than during the preceding period with sedimentation and diagenesis in a lake margin environment. Early development of zeolite occurrences, shortly after the deposits became exposed during breaks in sedimentation, is recorded for some intervals, where zeolites are covered by illuvial clay coatings or by sparitic carbonate cement. In most intervals, however, zeolites mainly formed at a later stage.
TL;DR: In this article, the crystal chemistry of Ti-rich three octahedral tetrahedral micas of plutonic origin was investigated by combining electron microprobe analysis, single crystal X-ray diffraction, Mossbauer spectroscopy and Xray photoelectron spectroscopic analysis.
Abstract: The crystal chemistry of Ti-rich trioctahedral micas of plutonic origin, cropping out at Black Hill (South Australia) has been investigated by combining electron microprobe analysis, single crystal X-ray diffraction, Mossbauer spectroscopy and X-ray photoelectron spectroscopy Chemical analyses have shown the samples taken to be quite homogeneous and Ti-rich (TiO2 ≈ 7 wt%) Mossbauer investigation yielded Fe2+/Fe3+ ≈ 30 X-ray photoelectron spectroscopy analysis seems to suggest the occurrence of three Ti species: octahedral Tr4+(60%), octahedral Ti3+(26%), and tetrahedral Ti4+(14%) The analyzed sample belongs to the 1M polytype and the relevant crystal data from structure analysis are: a = 5347(1) A, b = 9261(2) A, c = 10195(2) A, β = 10029°(1) Anisotropic structure refinement was performed in space group C2/m, and converged at R = 262, Rw = 280 Structural details (the c cell parameter, the off-center shift of the M2 cation towards 04, the bond-length distortions of the cis-M2 octahedron, the interlayer sheet thickness, the projection of K−O4 distance along c*, the difference outer- inner) support the occurrence of the Ti-oxy substitution (VIR2+ + 2(OH)− ⇌ Ti4+ + 202− + H2) in the sample Analysis of structural distortions as a function of the Ti content revealed that the positions of the oxygens 03 and 04 are displaced in opposite senses along [100] This produces an enlargement of the M1 site with respect to the M2 site and a shortening of the interlayer distance This trend seems to be in common with other Ti-rich 1M micas of plutonic origin