Twenty two samples were studied to investigate the nature and evolution mechanism of mixed-layer kaolinite-smectite (K-S). We examined the <2 µm or <0.2 µm fraction of K-S formed by hydrothermal and hypergenic alteration of volcanic material. The samples are from three localities: 20 specimens from a Tortonian clay deposit in Almería, Spain; one specimen from weathered Eocene volcanic ash from the Yucatan Peninsula, Mexico; and one sample from a weathered Jurassic bentonite from Northamptonshire, England. The samples were studied using chemical analysis, X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). The XRD patterns of the oriented, glycolated mounts were modeled using NEWMOD and the proportion of smectite and kaolinite layers was determined, ranging between 0 and 80% kaolinite. The analysis of the OH-stretching region of the FTIR spectra at different temperatures (180–550°C) showed the progressive dehydroxylation of kaolinite domains and, perhaps, of smectite domains, but no detailed information could be obtained about the sequential OH loss in different cation environments. The abundance and short-range ordering of the octahedral cations were studied using the OH-bending bands. The chemical and FTIR-estimated octahedral cation abundances were broadly similar. Aluminum showed a tendency to mix with Fe and Mg rather than to form AlAl pairs. Al-for-Mg substitution accompanying kaolinization was evident from the increase in AlAl pairs and decrease in AlMg pairs. Iron is retained in the structure. No other octahedral cation rearrangement was observed. The intensity of the 750 cm−1 band, assigned to translational vibrations of external OH groups in a kaolinitic environment, was quantified and modeled in relation to kaolinite layer proportion. The chemical data show that there are residual interlayer cations in kaolinite domains, which, in accordance with the model mentioned above, disturb external OH-translation vibrations. These results indicate the persistence of certain chemical and structural smectite features in kaolinite domains and thus support a smectite kaolinization process via a solid-state transformation. This confirms previous XRD, thermal, chemical and NMR analyses of the same sample set.

The reactivity of colloidal particles is regulated by their surface properties. These properties affect the wettability, flocculation-dispersion characteristics, ion exchange, sorption capacities and transport of inorganic colloids. Most studies have focused on hydrophilic, charged-particle surfaces, often ignoring the alterations in surface properties produced by the adsorption of natural organic matter, surfactants and other compounds. Adsorption of these substances can potentially render a surface substantially more hydrophobic. Nevertheless, comparatively little is known about changes in surface properties and reactivity of minerals upon sorption of hydrophobic organic compounds. In this study, the properties of four minerals (kaolinite, pyrophyllite, montmorillonite and Min-U-Sil®) and two inorganic materials (X-ray amorphous Al hydroxide and X-ray amorphous Si oxide) were compared before and after treatment with the common silylating agent, trimethylchlorosilane (TMCS). The samples were characterized by measurements of total carbon, cation exchange capacity (CEC), particle size, specific surface area (SSA), electrophoretic mobility, contact angle, particle aggregation, and by X-ray diffraction and diffuse reflectance infrared spectroscopy. For the layer silicates, surface coverage was limited to ∼2% trimethyl silane (TMSi). TMSi covered 7.5% of the Min-U-Sil® surface and 33% of the X-ray amorphous Si oxide. Treatment did not affect the structure of the minerals but reduced the CEC, SSA and electrophoretic mobilities. Water contact angles increased to between 18 and 114° with treatment. While the apolar characteristic of the surfaces decreased minimally with treatment, the Lewis acid/base properties were substantially reduced and interfacial free energy shifted from positive to negative values indicating a more hydrophobic surface character. For all the samples except kaolinite, these changes affected the stability of the colloids in suspension depending upon solution pH. Although the grafting of TMSi altered colloidal mineral surface properties and increased their hydrophobicity, these changes were not sufficient to predict colloid aggregation behavior.

Clays and their composites have been widely used for secondary containment walls for underground storage tanks and landfills. The pore-size changes occurring in the clay have a profound effect on its permeability. This study presents a new method for evaluating the use of an atomic force microscope (AFM) for studying wet clay in a non-aqueous state in order to determine the pore-size of clay at various water contents, a type of study typically performed by the more expensive environmental scanning electronic microscope. The method consists of mounting a sponge saturated with water under the sample in order to prevent drying by the heat generated by the AFM electronics. The micro-scale AFM image results show that the clay-particle separations reduce linearly as the water content increases. This change in pore-size is postulated to be attributed to the reduction in the size of the diffuse double layer and more extensive hydrogen bonds between clay particles and bipolar water molecules. The AFM was not able to produce nano-scale images due to excessive adhesion between the cantilever arm and the wet clay sample.

The effects of pH and ionic strength on the rheological behavior of aqueous suspensions of both crude and purified Wyoming bentonite and natural interstratified illite-smectite from Tunisia were investigated. Flow tests were performed on the four clay suspensions at a 10% clay concentration at different pH values. They showed that the rheological properties were highly sensitive to pH and the nature of the clay. The evolution of the yield stress as a function of pH is characterized by the presence of maxima and minima attributed to changes in the mode of association of the particles. The effect of pH on the behavior of clay suspended in NaCl solutions was also studied. The results show that the presence of NaCl has very little effect on the pH and yield stress values of the four materials.

The objective of this study was to determine whether smectites abiotically catalyze transformation of glucose under conditions relevant to soil organic matter (SOM) formation. Four smectites saturated with Na, Ca, Fe and Al were incubated under abiotic conditions with glucose solutions for 21 days at 37°C. After the incubations, soluble organic C recoveries ranged from 95 to 109.3%, relative to the amount of C added as glucose; however, glucose recoveries in the solutions ranged from 18.3 to 98.3%. The results indicate that a significant amount of the added glucose was abiotically transformed to soluble organic compounds other than glucose during the incubations. In general, glucose recoveries decreased with the acidic character of smectites: SWa-1 > Panther > Otay. Also, within clays, glucose recoveries decreased as the exchangeable cation became more acidic: Na > Ca > Al. Higher glucose recoveries were obtained for ‘Fe-rich’ smectites relative to ‘Fe-poor’ smectites, suggesting that Fe-oxyhydroxy coatings on smectite surfaces inhibit the transformation of glucose. High-pressure liquid chromatography analysis of the incubation solutions revealed small peaks for 5-(hydroxymethyl)-2-furaldehyde along with peaks for other unknown compounds. The results suggest that under conditions similar to those found in soils, smectites catalyze glucose dehydration to form furfural compounds. Polymerization of furfural compounds may be a major pathway leading to the formation of new humic materials in soils.

Various secondary phases formed during alteration/dissolution of HLW (high-level nuclear waste) borosilicate glass represent a significant retention potential for radionuclides including divalent actinides. The trioctahedral smectite, hectorite, Na0.7[Li0.7Mg5.3Si8O20(OH)4], is one of the secondary phases identified within the alteration layer of corroded HLW glass. Numerous studies have clearly shown that many radionuclides are associated with clay minerals and the migration of radionuclides is strongly reduced by complexation. Due to the structural complexity and chemical variability of smectites, sorption of radionuclides involves several sorption mechanisms: (1) adsorption via inner-sphere and outer-sphere complexation; (2) cation exchange in the interlayer; and (3) incorporation into the smectite structure. Up to now, it was not known whether trivalent actinides such as Cm(III) and Am(III) become incorporated into the crystal structure of clay minerals like hectorite. We have used a new method, developed by Carrado et al. (1997b), to synthesize a Eu- and a Cm-containing hectorite, utilizing Cm(III) and chemically homologous Eu(III) coprecipitated with Mg(OH)2 as a precursor. X-ray diffraction, Fourier transform infrared spectroscopy and atomic force microscopy identified the reaction products unambiguously as hectorite. The sorption mechanisms of Eu associated with the synthesized hectorite were investigated by time-resolved laser fluorescence spectroscopy (TRLFS). An unhydrated Eu species (fluorescence lifetime 930 µs) and a partly hydrated Eu species (fluorescence lifetime 381 µs) could be identified. The unhydrated Eu species can be interpreted as incorporating Eu(III) into the hectorite structure or a remaining X-ray amorphous silica phase. The spectra of Eu hectorite and the Eu silica complexation are too similar to permit differentiation between these species, but dialysis experiments demonstrated the close association of the unhydrated Eu species with the crystalline hectorite phase. Time-resolved laser fluorescence spectroscopy (TRLFS) measurements identified the same incorporated Eu species as long as the Eu hectorite was stable under acidic conditions. The stability of the Eu hectorite could be shown by the dialysis experiment over a time period of 160 h. Between 160 und 500 h, hectorite became unstable and a new silica phase was detected. In addition, TRLFS measurements of the Cm-containing hectorite confirmed the incorporation of actinides in the smectite structure. The Cm-hectorite and Cm-silica species can be differentiated unambiguously by TRLFS. In order to differentiate between coprecipitated and surface-sorbed Eu species, batch sorption studies were performed with synthetic Eu-free hectorite. For the surface-sorbed Eu species, a fluorescence lifetime of 284 µs (3.1 H2O molecules) was found, which clearly differs from the coprecipitated species with a fluorescence lifetime of 930 µs. The different lifetimes indicate a different chemical environment. Based on all observations it seems to be very likely that trace amounts of Cm/Eu occupy a distorted octahedral site in the hectorite.

Alumina-pillared montmorillonite clays (Al-PILC), prepared under ultrasonic (US) agitation and normal stirring (S) methods, have been used as a host material to encapsulate Co phthalocyanine (CoPc) complex. The amount of Co varies from 0.27 to 1.48 wt.% in the samples, depending on the input concentration of Co. Powder X-ray diffraction and other characterization techniques reveal that the structure of Al-PILC remains intact after the incorporation of the complex into the pores through a pyridine solution of the complex by ultrasonic agitation. A substantial decrease in the BET surface area and total pore volume of Al-PILC points to the occupation of the CoPc moieties within the porous structure of the pillared clay. This is further supported by the observation of a band at 1489 cm−1 in the Fourier transform infrared (FTIR) spectra of the encapsulated samples. The FTIR and diffuse reflectance ultraviolet-visible (DRUV-Vis) spectral results indicate that the encapsulated CoPc complex in the clay matrix undergoes distortion in order to accommodate itself within the pores of the Al-PILC. The encapsulated samples prepared by ultrasonification show better dispersion of the complex than the samples prepared under normal stirring conditions. Compared to the ‘neat’ complex, the encapsulated samples (CoPc in Al-PILC) exhibit greater turnover in the test reaction of the oxidation of benzyl alcohol to benzaldehyde with tertbutyl hydroperoxide as the oxidant at 373 K. The method of preparation and consequent site isolation of CoPc in Al-PILC influence the catalytic activity.

Specific surface area measurements of The Clay Minerals Society source clays were made by the Brunauer, Emmett and Teller (BET) method of adsorption of nitrogen gas. Two replicate measurements of specific surface area were performed for each source clay. All pair values were within 3%, which is very good agreement for this type of measurement.

Shewanella putrefaciens CN32 reduces Fe(III) within two illites which have different properties: the Fithian bulk fraction and the <0.2 µm fraction of Muloorina. The Fithian illite contained 4.6% (w/w) total Fe, 81% of which was Fe(III). It was dominated by illite with some jarosite (∼32% of the total Fe(III)) and goethite (11% of the total Fe(III)). The Muloorina illite was pure and contained 9.2% Fe, 93% of which was Fe(III). Illite suspensions were buffered at pH 7 and were inoculated with CN32 cells with lactate as the electron donor. Select treatments included anthraquinone-2,6-disulfonate (AQDS) as an electron shuttle. Bioproduction of Fe(II) was determined by ferrozine analysis. The unreduced and bioreduced solids were characterized by Mössbauer spectroscopy, X-ray diffraction and transmission electron microscopy. The extent of Fe(III) reduction in the bulk Fithian illite was enhanced by the presence of AQDS (73%) with complete reduction of jarosite and goethite and partial reduction of illite. Mössbauer spectroscopy and chemical extraction determined that 21–25% of illite-associated Fe(III) was bioreduced. The extent of bioreduction was less in the absence of AQDS (63%) and only jarosite was completely reduced with partial reduction of goethite and illite. The XRD and TEM data revealed no significant illite dissolution or biogenic minerals, suggesting that illite was reduced in the solid state and biogenic Fe(II) from jarosite and goethite was either released to aqueous solution or adsorbed onto residual solid surfaces. In contrast, only 1% of the structural Fe(III) in Muloorina illite was bioreduced. The difference in the extent and rate of bioreduction between the two illites was probably due to the difference in layer charge and the total structural Fe content between the Fithian illite (0.56 per formula) and Muloorina illite (0.87). There may be other factors contributing to the observed differences, such as expandability, surface area and the arrangements of Fe in the octahedral sheets. The results of this study have important implications for predicting microbe-induced physical and chemical changes of clay minerals in soils and sediments.

Dioctahedral smectite was prepared hydrothermally from dickite [Al2Si2O5(OH)4] as a starting material by autoclaving in a closed stainless steel vessel with variable temperature, pressure, time and pH conditions. Highly crystalline smectite can be obtained at 290°C under a pressure of 69 bar for 48 h. The pH of the solution was an important factor and should be maintained at 10 to 11 for the successful formation of smectite. Characterization by X-ray powder diffraction, scanning electron microscopy, infrared spectroscopy, thermogravimetric analysis, differential thermal analysis and the Greene-Kelly test showed that the smectite synthesized was Na-beidellite, mostly because of the heat treatment of the starting material and the stoichiometric batch composition.

Under closed geochemical conditions, the weathering of a serpentinite rock composed of serpentine (70–85%) and magnesian chlorite (10–15%) associated with magnetite and chromite leads to the complete replacement of serpentine and chlorite by 2:1 layer silicates and produces new Fe oxides. The serpentine minerals crystallize under different habits issued from the serpentinization processes: mesh and hourglass pseudomorphic textures were formed from olivine, and thin-bladed pseudomorphic textures from pyroxene and amphibole crystals. Serpentine veins crosscut the whole rock with locally non-pseudomorphic interpenetrating and interlocking serpentines.

Specific weathering microsystem habits with specific clay mineral crystallizations originate from these different habits: a poorly aluminous saponite in thin-bladed textures, two Fe-rich montmorillonites in mesh and hourglass (MH) textures, and in veins (V) which differentiate on Al, Mg and Fe contents. Magnesian chlorites, isolated from serpentine by hand-picking under a stereomicroscope, are found to weather to trioctahedral vermiculite. Magnetite and chromite extracted from the bulk samples are replaced by newly formed Fe oxides, maghemite, goethite and hematite, which give way to specific Fe accumulation habits in the regolith zone of the weathering profile.

The Weches Formation of the Claiborne Group (Eocene) in northeast Texas consists of clayey sandstones and mudrocks, both with variable proportions of dark green to brown clay peloids deposited in a marginal to open marine setting on the Gulf Coast margin. The composition of the dark green peloids, from two localities, has been investigated using X-ray diffraction, back-scattered electron microscopy with X-ray analysis, electron energy-loss spectroscopy (EELS), Mössbauer spectroscopy, chemical analysis and Fourier transform infrared spectroscopy. These peloids were previously described on the basis of their color as glauconite (Yancey and Davidoff, 1994); our results, however, show that the dark green indurated pellets are predominantly composed of mixed-layer clays with a high proportion of Fe-rich 7 Å serpentine layers coexisting with a mixed-layer phase containing glauconite, nontronite and vermiculite layers, in addition to discrete illite and kaolinte. Analyses by EELS of single particles with a chemical composition consistent with them being the Fe-rich clay indicate that the Fe is >95% ferric, while Mössbauer analyses of the bulk magnetically separated fraction for the same samples indicates a ferric iron content of ∼60–70%, despite the variable relative proportions of expandable and 7 Å layers. Taking into account that there is a significant amount of 2:1 layers containing ferric Fe, we interpret these data as indicating that the Fe in the 7 Å layers has a significant amount of Fe2+ even taking into account the high ferric Fe ratio from the EELS analysis when the coexisting 2:1 layers are considered. Thus, these 1:1 layers are closer to berthierine in composition than to odinite. The vermiculite layers in the Texas clay may indicate partial ‘verdinization’ of expandable 2:1 clay. A possible reaction is smectite → vermiculite → berthierine-like phase. We estimate a temperature of 20°C for the seawater in which the Texas clay formed, the lower end of the range for modern occurrences of odinite.

Burial-induced and hydrothermal-related illitization in bentonites and in sandstones can be modeled on the basis of isotopic studies of fundamental particles separated from mixed-layer illitesmectite. The model envisages different reaction rates and durations relative to the varied impacts of temperature, considering that the water:rock ratio also has an influence. The different pathways for illitization are suggested on the basis of the K-Ar, Rb-Sr and δ18O compositions of previously studied materials.

New information is provided on why fundamental particles separated from mixed-layer illite-smectite in shales yield K-Ar age data that are systematically greater than the ages of the fundamental particles from associated bentonites and/or sandstones, and greater than the reported stratigraphic ages. The study of pure authigenic, recent to present-day smectite from Pacific sediments shows that (1) those collected from active hydrothermal vents have 40Ar/36Ar ratios identical to that of the atmosphere, and (2) those of mud sediments have 40Ar/36Ar ratios above the atmospheric value, indicating addition of 40Ar not generated in situ by radioactive decay. A preliminary but detailed analysis of the noble-gas (Ar, Xe, Kr) contents of authigenic smectite-rich size fractions from Pacific deep-sea red clays suggests trapping of these gases by smectite. Therefore, the results point to the fact that fundamental particles can incorporate excess 40Ar into their structure when nucleating in restricted to closed systems, such as shales. This excess 40Ar, which represents radiogenic 40Ar released from nearby altered silicates, might be temporarily adsorbed at the surface of the rock pore spaces and is therefore available for incorporation in nucleating and growing particles.