We used high-resolution X-ray texture goniometry to quantify changes in the mm-scale orientation of phyllosilicate minerals in a suite of Paleogene mudstones from the Podhale Basin in southern Poland. The sample set covers an estimated range of burial depths between 2.4 and 7.0 km, corresponding to a temperature range of 60–160°C. Although mechanical compaction has reduced porosities to ∼10% in the shallowest samples, the phyllosilicate fabric is only modestly aligned. Coarser-grained (>10 µm) detrital chlorite and mica appear to be more strongly aligned with (001) parallel to bedding, suggesting their deposition as single grains rather than as isotropic flocs or aggregates. From 2.4 to 4.6 km, R0 illite-smectite with 40–50% illite layers changes to R1 illite-smectite with 70–80%) illite layers. At the same time kaolinite is lost and diagenetic chlorite is formed. The mineralogical changes are accompanied by a strong increase in the alignment of illite-smectite, chlorite, and detrital illite, parallel to bedding and normal to the presumed principal effective stress. We propose that the development of a more aligned I-S fabric results from the dissolution of smectite and the growth of illite with (001) normal to the maximum effective stress. Water released by illitization may act as a lubricant for the rotation of all platy minerals into nanoporosity transiently formed by the illitization reaction. At greater depths and temperatures, further illitization is inhibited through the exhaustion of K-feldspar. After the cessation of illitization, a further 2.4 km of burial only results in a small increase in phyllosilicate alignment. At such small values for porosity and pore size, increasing stress does not substantially reorient phyllosilicates in the absence of mineralogical change.

High resolution imaging by transmission electron microscopy has revealed a mechanism for the weathering of intermediate microcline in a humid, temperate climate. Dissolution of the feldspar begins at the boundary of twinned and untwinned domains and produces circular holes which enlarge to form negative crystals. Amorphous, ring-shaped structures develop, about 25 Å in diameter, within the larger holes. These rings, in turn, crystallize to an arcuate phase having a 10-Å basal spacing and then to crinkled sheets of illite or dehydrated montmorillonite. The 10-Å layer silicate shows an irregular stacking sequence, including 10-,-20-, and 30-Å sequences. Included plagioclase crystals show a similar mechanism of weathering and, moreover, are more intensely weathered.

The adsorption of Ni(II) and Cu(II) on to the clay minerMs kaolinite, chlorite, and illite has been investigated. The quantity of Ni(II) at pH 6 and Cu(II) at pH 5 adsorbed has been found to vary in the manner chlorite > illite > kaolinite. Examination of the mode of bonding of the metal ions to the clay minerals using X-ray photoelectron spectroscopy (XPS) has been carried out. Comparison of the binding energies for metal ions in octahedral sites in selected minerals (reference minerals) and in simple nickel and copper containing compounds with values for Ni(II) and Cu(II) adsorbed on chlorite indicate that nickel(II) is probably bound as the aquo ion while copper(II) may be adsorbed as Cu(OH)+.

Low-temperature FTIR spectroscopy was used to characterize the v(OH) region of kaolin-group minerals including well ordered to poorly ordered kaolins from Georgia, Brazil, and England, along with samples of discrete dickite and nacrite. Low-temperature FTIR spectra were useful in resolving dickite- and nacrite-like features present in the spectra of kaolins when cooled to <30 K. These features were not resolved at room temperature and only partially resolved at liquid N2 temperature (77 K). The room-temperature and low-temperature positions of the ν(OH) bands of kaolinite, dickite, and nacrite were linearly correlated with the interatomic OH⋯O distances and this relationship served as the basis for polytype/disorder identification. Dickite or dickite-like disorder was found in high Hinckley-Index kaolinite from Keokuk, Iowa, and from Cornwall, England. Dickite- and nacrite-like features were observed in both high- and low-Hinckley-index kaolinite and the amounts of these stacking sequences generally increased with decreasing Hinckley Index.

The absorption of biologically important purines, pyrimidines, and nucleosides by Li-, Na-, Mg-, and Ca-montmorillonite has been studied in aqueous solutions over a range of pH values 2–12. The initial organic concentrations were about 1 m.molar. The ratio clay to organic compounds was such that only up to 25 per cent of the exchange capacity could be saturated by organic cations, but, depending on conditions, up to 100 per cent of the available organic material was absorbed. Of the nineteen compounds studied, only thymine, uracil, and their nucleosides were not absorbed under the experimental conditions. Absorption occurs primarily as a cation exchange reaction under acid conditions and varies with the basicity of the compounds, their aromatic or non-aromatic character, and the possible extent of their van der Waals interaction with the silicate layers. Nucleosides generally are less strongly absorbed than their purines or pyrimidines because their non-planar structure permits less van der Waals interaction; their absorption is influenced by the differences in swelling behavior of montmorillonite with mono- and divalent cations.

Ordered illite/smectite (I/S) and illite in a pelitic rock from a prograde metamorphic sequence in North Wales were observed by transmission electron microscopy. The dominant phyllosilicate noted was diagenetic-metamorphic illite, occurring as subparallel packets of layers, each about a few hundred Ångstroms thick. It exhibited two-layer polytypism (presumably 2M1) and numerous strain features and had a composition of (K1.21Na0.12)(Al3.36Fe0.31Mg0.33)(Si6.28Al1.72)O20(OH)4.

I/S occurred as thick packets of wavy layers having 10-Å subperiodicity and sharp differences in contrast in successive lattice fringes. All stages in a replacement series were noted, from one or two layers of smectite within illite, through thin packets of I/S, to thick packets that contained inherited deformation textures of diagenetic-metamorphic illite. Deformed illite was replaced by I/S more commonly than was undeformed illite. The I/S replacing undeformed original illite had significantly greater order, primarily of R1 type (ISISIS…), than that replacing deformed illite. R> 1 I/S occurred as small crystallites and contained relatively less smectite than the ordered I/S, Single smectite layers were spaced within several illite layers, forming curved packets of layers. IISIIS… (R2) and IIISIIIS… (R3) ordering were present locally, as was discrete smectite. Analytical electron microscopic analyses indicated that the I/S, (K0.46Na0.43)(Al3.75Fe0.06Mg0.19)(Si6.26Al1.74)O20(OH)4, was rectorite-like in composition and had smaller (Mg + Fe) contents and greater Al/Si ratios than the coexisting illite, which was also anomalous in terms of general crystal-chemical relationships between coexisting illite and I/S in burial diagenesis environments. The I/S appears to have formed by replacement of diagenetic-metamorphic illite, presumably at very low temperatures under hydrous conditions via dissolution and crystallization.

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 Å d spacing, consistent with a 7 Å 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 Å 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.

Palygorskite and sepiolite show a high sorption capacity for organic molecules. Adsorption of 2 organic cations, methylene blue (MB) and crystal violet (CV), by palygorskite and sepiolite were examined. The maximum sorption of MB and CV far exceeded the cation exchange capacity (CEC) of these minerals. This shows that, besides the contribution of free negative sorption sites (P-), the sites satisfied with sorption of single cations (PXi0) and neutral sorption sites (N) on clay surfaces may contribute to the sorption of organic cations. The number of neutral sites was determined by examining the sorption of 2 neutral organic molecules, triton-X 100 (TX100) and 15 crown ether 5 (15C5), and by application of the Langmuir isotherm.

To determine the contribution of different sites, an adsorption model that applies the Gouy-Chapman equation and takes into account the formation of different clay-organic complexes in a closed system was employed. Application of this model to sorption data provided the calculation of binding coefficients for neutral sites, as well as the surface potential of the minerals at different sorbate concentrations.

At sorption maxima, for both palygorskite and sepiolite, the contribution of neutral sites for sorption of organic cations was the highest, followed by the PXi0 sites in case of CV sorption, while in sorption of MB the contribution of P- sites was the second highest. The Fourier transform infrared (FTIR) patterns of clay-organic cation complexes compared with pure clays confirm that the sorption of organic cations is by silanol groups located at the edge of fibrous crystals, which account for neutral sorption sites.

The factors. (1) possible violations of Darcy’s law. (2) electrokinetic coupling. (3) high viscosity. (4) tortuous flow paths, an. (5) unequal pore sizes have been suggested as possible explanations for the differences between hydraulic flow rates in liquid-saturated clays and sands. The effects of these factors on hydraulic flow rates through saturated clays were investigated.

Hydraulic flow rates, electrical conductivities, and streaming potentials were measured on natural, sodium, and calcium samples of kaolinite, illite and Boston blue clay. Data were taken after increments of one-dimensional consolidation and rebound over the pressure range from one-sixteenth to 256 atm.

The influences of electrokinetic coupling on the hydraulic flow rates were calculated from irreversible thermodynamic relationships together with the hydraulic and electrical data. The other factors were studied by examining the extent to which each factor explains the discrepancies between measured flow rates and those predicted from Darcy’s law and the Kozeny-Carman equation.

The results show that. (1) the possible violations of Darcy’s law and electrokinetic coupling are insignificant. (2) high viscosity and/or tortuous flow paths fail completely to account for the discrepancies between measured and predicted flow rates in clays, an. (3) unequal pore sizes can explain all the discrepancies.

The three-dimensional order shown by the two-layer hydrates of Na- and Ca-vermiculite, prepared from Mg-vermiculite from Llano, Texas, has enabled clear, two-dimensional Fourier projections of their interlayer structures to be obtained. Structure factor calculations were made in space group C2 and with unit-cell dimensions of a = 5.358 Å, b = 9.232 Å, and ß = 96.82°; for Na-vermiculite C = 14.96 Å and for Ca-vermiculite c = 15.00 Å. In Na-vermiculite the interlayer cations are octahedrally coordinated to water molecules with the sodium-water polyhedra only located between the triads of oxygen atoms forming bases to tetrahedra in adjacent silicate layers. In Ca-vermiculite the interlayer cations are in both octahedral and 8-fold (distorted cubic) coordination with water molecules. The octahedrally coordinated Ca ions are between the bases of tetrahedra in adjacent silicate layers, but the 8-fold coordinated Ca ions are between the ditrigonal cavities. In both Na- and Ca-vermiculite some water molecules are drawn from planar networks appreciably towards the ditrigonal cavities. The three-dimensional order observed for these vermiculites contrasts with the stacking disorder reported for Mg-vermiculite from Llano. The distinct crystallographic behavior of Na+, Ca2+, and Mg2+ in the hydration layers of Llano vermiculite probably depends on cation sizes and field strengths, together with the need to achieve local charge balance near the sites of tetrahedral Al-for-Si substitution.

Nine synthetic Na-saponites with charge densities varying between 0.33 and 1.0 have been prepared. Their swelling properties and structural organization in water, ethylene glycol and glycerol show discontinuities in the physico-chemical behaviour of these samples. The layer charge densities caused changes in swelling properties and structural organization of the minerals. These changes also depended upon the nature of the solvation liquid and the interlayer cation involved.

Electron diffraction patterns of the Ba-saponites showed no abnormal diffusion making honeycomblike patterns between Bragg reflections.

The results indicate criteria for estimating the layer charge of tetrahedrally substituted trioctahedral 2/1 phyllosilicates.

There is no upper limit until x = 1 for the layer charge x which is specific to the smectite-group. Consequently, the changes in the swelling properties observed when x = 0.5-0.6 and x = 0.8-0.9 come from the modifications of the interlayer structure, which are mainly a function of cation-liquid and silicate layer-liquid interactions. Consequently, there is an overlap between the saponite and the vermi-culite mineral groups.

Phase and morphological changes during thermolysis of Mg4Al2(OH)12CO3·nH2O and Zn6Al2(OH)16CO3·nH2O layered double hydroxides (LDH) and their nanocomposites with poly(styrene sulfonate) (PSS) are studied by X-ray powder diffraction (XRD), scanning and transmission electron micrography (SEM and TEM) and thermal analyses. Mg4Al2(OH)12CO3·nH2O and Mg2Al(OH)6[CH2CH(C6H4SO3)]·3H2O show comparable thermal stabilities: the layered structure is lost above 300 °C with the nucleation of the MgO phase at approximately 400 °C and the MgAl2O4 phase at approximately 800 °C Zn3Al(OH)8[CH2CH(C6H4SO3)]·nH2O undergoes complete oxidative pyrolysis of the polyanion by 500 °C. Crystalline oxide products are obtained at a temperature approximately 300 °C lower than that of thermolysis of Zn6Al2(OH)16CO3·nH2O. The SEM and TEM images show that the thermolysis of LDH carbonates produces dense aggregates containing microcrystalline particles, whereas Mg2Al(OH)6[CH2CH(C6H4SO3)]·3H2O forms a macroporous solid.

Structural Fe3+ in kaolinites and dickites covering a broad range of disorder was investigated using electron paramagnetic resonance (EPR) spectroscopy at both the X and Q-band frequencies. A procedure based on a numerical diagonalization of the spin Hamiltonian was used to accurately determine the second and fourth-order fine-structure parameters. A least-squares fitting method was also developed to model the EPR spectra of Fe3+ ions in disordered local environments, including multimodal site-to-site distributions. Satisfactory fits between calculated and observed X and Q-band spectra were obtained regardless of the stacking order of the samples.

In well-ordered kaolinite, Fe3+ ions are equally substituted in sites of axial symmetry (Fe(II)sites, namely Fe(II)a and Fe(II)b) which were determined to be the two non-equivalent Al1 and Al2 sites of the kaolinite structure. In dickite, Fe3+ ions were also found to be equally substituted for Al3+ in the two non-equivalent Al sites of the dickite structure. In poorly ordered kaolinites, the distribution of the fine-structure parameters indicates that Fe3+ ions are distributed between Fe(II) sites and other sites with the symmetry of the dickite sites.

Hence, when stacking disorder prevails over local perturbations of the structure, the near isotropic resonance owing to Fe3+ ions in rhombically distorted sites (Fe(I) sites) is a diagnostic feature for the occurrence of C-layers in the kaolinite structure, where C refers to a specific distribution of vacant octahedral sites in successive layers.

Chromium(VI) in the environment is of particular concern because it is toxic to both plants and animals, even at low concentrations. As a redox-sensitive element, the fate and toxicity of chromium is controlled by soil reduction-oxidation (redox) reactions. In-situ remediation of chromium combines reduction of Cr(VI) to Cr(III) and immobilization of chromium on mineral surfaces. In this study, Fe-rich smectite, montmorillonite, illite, vermiculite, and kaolinite were examined to determine reactivity in sorption-reduction of Cr(VI). The clays were compared to forms that were reduced by sodium dithionite. Clays containing Fe(II) efficiently removed soluble Cr(VI) from solution. Chromium K-edge X-ray absorption near edge structure (XANES) suggested that clays containing Fe(II) reduced Cr(VI) to Cr(III), immobilizing Cr at the clay/water interface. Adsorption of Cr(VI) by the Fe(II)-containing clay was a prerequisite for the coupled sorption-reduction reaction. Sodium dithionite added directly to aqueous suspensions of non-reduced clays reduced Cr(VI) to Cr(III), but did not immobilize Cr on clay surfaces. The capacity of clays to reduce Cr(VI) is correlated with the ferrous iron content of the clays. For dithionite-reduced smectite, the exchangeable cation influenced the sorption reaction, and thus it also influenced the coupled sorption-reduction reaction of Cr(VI). The pH of the aqueous system affected both the amount of Cr(VI) reduced to Cr(III) and the partition of Cr(III) between aqueous and adsorbed species. A plot of pH vs. amount (adsorption envelope) adsorbed for the coupled sorption-reduction reaction of Cr by reduced smectite exhibited a similar pattern to that of typical anion-sorption.

The binding of tris-bipyridyl metal complexes of the type M(bp)32+ (M = Fe2+, Cu2+, Ru2+) to hectorite surfaces is shown to occur by two mechanisms. (1) replacement of Na+ ions in the native mineral by cation exchange up to its cation exchange capacity and (2) intersalation of excess salt beyond the exchange capacity. In the cation exchange mechanism, the binding of metal complex is strongly favored over Na+. The intersalation reactions are dependent on the nature of the counter-anion: SO42-, Br- > CIO4−, Cl−. The homoionic M(bp)32+-hectorites, which exhibit rational 18 Å X-ray reflections, have been characterized with regard to their BET surface areas, water adsorption isotherms, types of water present, selected reactions in the intercalated state, and orientation of the complex ions in the interlayer regions. Mixed Fe(bp)32+, Na+-hectorites have also been examined and the results suggest segregation of the two ions between interlayers or within interlayers. Solid state intersalated phases have been isolated with 18 Å and 29.5 Å spacings. In general, surface areas of the intersalated phases are low, but the 18 Å phase derived from [Fe(bp)3]SO4 adsorption shows a high surface area, which even exceeds the surface area of homoionic Fe(bp)32+-hectorite.

The effect of Fe oxidation state on the specific surface area, Sm, of nontronite was studied using the <2-µm, Na+-saturated fraction of the SWa-1 and Garfield nontronite reference clays. The reduction of structural Fe3+ in the octahedral sheet of the nontronite decreased Sm as measured by the adsorption of 2-ethoxyethanol (ethylene glycol-monoethyl ether, EGME). The swellability in water of the nontronite also decreased during reduction. The amount of nonexchangeable Na+, on the other hand, increased with increasing Fe2+ content and was highly correlated with EGME adsorption (r = -.985). The relationship between Sm and Fe2+ was attributed to the collapse of partially or fully expanded layers to unexpanded layers.

Redox cycles are common in nature and likely have a profound effect on the behavior of soils and sediments. This study examined a key component of redox cycles in smectites, namely, the reoxidation process, which has received little attention compared to the reduction process. Unaltered (oxidized) and reoxidized ferruginous smectites (nontronites) were compared using infrared and Mössbauer spectroscopies, and thermal gravimetric analysis. The infrared and thermal gravimetric data revealed that the structural OH content of reduced-reoxidized clay is about 15 to 20% less than in the original (oxidized) sample, indicating that the structure remains partially dehydroxylated even after reoxidation. Mössbaner spectra of reoxidized samples consisted of larger quadrupole splitting for Fe(III) doublets than in the unaltered samples, suggesting that the environment of Fe(III) is more distorted after the reduction-reoxidation treatment.

The different types of iron oxide phases associated with the surfaces of two suites of kaolins from Georgia, U.S.A., and from the Southwest Peninsula of England, have been identified using electron spin resonance (ESR) spectroscopy combined with magnetic-filtration, thermal, and chemical treatments. It has been shown that the English kaolins are coated with a lepidocrocitelike phase, which is readily removed by de Endredy's method of deferrification, while the Georgia kaolins are coated with a hematite- or goethitelike phase, which is not removed by this treatment. Throughout the course of this study, the effects of the various physical and chemical treatments on the brightness values of the kaolins were examined.

Many soils developed from volcanic rocks in southern Brazil exhibit spontaneous magnetization caused by the presence of fine-grained maghemite (γ-Fe2O3), but few attempts were made to quantify or characterize this important soil component. To that end, clays were separated from freely drained soils derived from acid (≥63% SiO2), intermediate (54–62% SiO2), and basic (≤53% SiO2) igneous rocks produced by the Paraná flood volcanism. The sample set included soils with a wide range of pedogenic development on different landscape positions. The Fe oxide mineralogy of these samples was examined by using a combination of selective dissolution, magnetic susceptibility, and X-ray diffraction (XRD) techniques. Hematite and maghemite were the primary Fe oxides in mature soils (Oxisols, Ultisols, and Alfisols) developed from basic rocks; whereas goethite was dominant in all other soils, especially those formed from acid-intermediate rocks. The association of maghemite with basic rock materials suggests that it was primarily formed by oxidation of lithogenic magnetite. A strong, positive correlation (R2 = 0.89) was obtained between mass specific magnetic susceptibility (χ) of the clay fractions and maghemite contents estimated by XRD. Either method could be used for quantitative analyses, but χ was more sensitive than XRD at low maghemite concentrations (<2 wt. %). The clay-sized maghem-ites were superparamagnetic with an estimated value for the mass specific magnetic susceptibility (χlf) value of 91,000 × 10−8 m3 kg−1 and frequency dependent variations of 10–15%. The maghemites also had low unit cell constants, which, if attributed entirely to replacement of Fe by Al, would correlate with Al substitutions in the range of 5–16 mole %. Selective dissolution of the soil maghemites was achieved by treatment of Fe oxide concentrates with 1.8 M H2SO4 at 75°C for 2 h.

While studying the retention of additives used in tertiary recovery of petroleum (waterflooding) on minerals present in a rock reservoir, an investigation has been undertaken into the adsorption mechanism of Polyacrylamides on to clays. The adsorption of amides and Polyacrylamides takes place exclusively on the external surfaces of the clay particles. The organic molecules are protonated on the surface and adsorbed by ionic forces. There is a linear relationship between the adsorption ratio and the polarizing power of the exchangeable cations of the clay mineral. The adsorption isotherms and the thermal analyses reveal the existence of two adsorption mechanisms: (i) a strong, irreversible adsorption, which corresponds to the formation of a monolayer of chemisorbed molecules, (ii) a more important adsorption of molecules retained by hydrogen bonding, which can be eliminated by heating at low temperature. The retention ratio in the irreversible process, which is practically identical both for acetamide and Polyacrylamide, is low (3 mg/g). It depends on the external cation exchange capacity (CEC) of the mineral and increases with the surface area. The Polyacrylamide adsorption depends on the physico-chemical characteristics of the macromolecule, more particularly on the CONH2/COO−ratio, which determines the extent of the carbon chain, and the molecular weight. The accessibility of the organic macromolecule to the clay particle is controlled by the preceding factors. The quantity of Polyacrylamide irreversibly adsorbed by clay minerals is important in the context of the use of the polymer on a petroleum field. It may be reduced to a minimum by working at low concentrations with a weakly hydrolyzed Polyacrylamide solution.