The changes in amount and location of layer charge during diagenetic alteration have been investigated for smectites and smectite layers of illite/smectite interstratified minerals (I/S) by X-ray powder diffraction analysis with various expansion behavior tests: 1) ethylene glycol (EG) solvation (XRD); 2) K-saturation and EG solvation; 3) Li-saturation, heating at 250 °C and glycerol or EG solvation (Greene-Kelly test); and 4) alkylammonium saturation. In the course of low-temperature diagenesis but before the onset of illitization, mean layer charge of smectites continuously increases from approximately 0.56 to 0.73 per O20(OH)4 with increasing depth, and tetrahedral charge also increases continuously from approximately 0.21 to 0.38 per O20(OH)4 (beidellitization). The continuous increase in tetrahedral charge without change in peak intensity and shape suggests that the solid-state Al for Si substitution mechanism appears to predominate within beidellitization. After illitization, the content of the beidellitic layers continuously decreases, while the mean layer charge of expandable layers and the content of illite layers in I/S increase. This suggests that the conversion of a beidellitic layer to an illitic layer preferably occurs during early illitization. Thus, before illitization, beidellite-like layers are formed from precursor smectite, and during the early stage of illitization, the high charged beidellitic layers are probably consumed to form illite layers.

The crystal structure of a natural, ordered IIb-4 triclinic clinochlore has been refined in space group C1̄ from 4282 unique X-ray intensity measurements of which 3833 are greater than 3 times the statistical counting error (3σ). Unit cell parameters are a = 5.3262(6) Å; b = 9.226(1) Å; c = 14.334(3) Å; α = 90.56(2)°; β = 97.47(2)°; and γ = 89.979(9)°, which represents the greatest deviation from mono-clinic symmetry yet recorded for a triclinic chlorite. The final weighted R is 0.059 for reflections with I > 3σ and 0.064 for all reflections. The chemical formula is (Mg0.966Fe0.034)MI(Mg0.962Fe0.038)M22(Si2.96Al1.04)O10 (OH)2(Mg0.996Fe0.004)M32(Al0.841FeIII0.102Cr0.004Ti0.004)M4(OH)6, which is consistent with electron microprobe (EMP), wet chemical analyses, Mössbauer spectroscopy and X-ray structure refinement. The high degree of ordering of the divalent versus trivalent octahedral cations in the interlayer is noteworthy, with FeIII and Al in M4 and virtually no Fe in M3. In the 2:1 layer, M1 and M2 each contain similar amounts of Fe. The 2 tetrahedral sites have nearly identical mean oxygen distances and volumes, and thus show no evidence of long-range cation ordering.

Micaceous layer silicate clay minerals are attractive materials for applications involving non-linear optics because of their low cost and ability to form well ordered, platy aggregates, but such applications require precise knowledge of the dielectric behavior of the clay. The purpose of the present study was to use Terahertz time-domain spectroscopy (THz-TDS) to determine the dielectric properties of certain cleavable layered clay minerals, including muscovite, vermiculite, phlogopite, and biotite. The samples were characterized by X-ray diffraction and Fourier transform infrared spectroscopy as well as chemical analysis by Energy dispersive X-ray spectroscopy. The THz frequency window investigated was the far-infrared region of 3.3 to ∼40.0 cm−1 corresponding to 0.1 and 1.2 THz, respectively. The samples were selected so that the hydrated form of the interlayer cation, e.g. Mg2+ present in the interlayer gallery of vermiculite, could be compared to species such as phlogopite, biotite, and muscovite with the dehydrated form of interlayer cations such as K+ or Na+. The frequency-dependent complex index of refraction of these natural materials was determined to vary between 2.50 and 2.80. The presence of water in the interlayer space of vermiculite was reflected in the detection of increased values of the absorption index in comparison with the muscovite, phlogopite, and biotite.

Cu montmorillonite heated with or without potassium halide was studied by IR and ESR spectroscopy, supplemented by XRD measurements, microprobe and chemical analyses. It appears that on heating Cu montmorillonite, most of the Cu ions migrate into hexagonal cavities and eventually, when dehydroxylation occurs, into octahedral vacancies. Some Cu ions may penetrate into octahedral vacancies before dehydroxylation. In the presence of potassium halide, deprotonation facilitates penetration of Cu into octahedral vacancies. The presence within the layers of non-exchangeable Cu ions that are inaccessible to water does not necessarily cause the perturbation of OH bending vibrations conventionally attributed to migration of small cations into the structure. Such perturbation was only observed when the basal spacing was reduced to ~9.5Å.

Soils developed on Pleistocene andesitic lava flows and fluvial detritus in the Atlantic coastal plain of Costa Rica display a clay mineral assemblage that includes 10 Å and 7 Å halloysite and lesser amounts of kaolinite and dioctahedral vermiculite. Other secondary minerals include gibbsite, goethite, hematite, maghemite, allophane and amorphous Al hydroxides. Active floodplain soils are dominated by 10 Å halloysite and contain less allophane, while soil clays from Pleistocene terraces consist of a mixture of 10 Å and 7 Å halloysite as well as less dioctahedral vermiculite, kaolinite, and amorphous Al hydroxides. Residual soils formed on Pleistocene lava flows are dominated by 7 Å halloysite with less abundant kaolinite, dioctahedral vermiculite, 10 Å halloysite and amorphous Al hydroxides. This sequence suggests transformations of 10 Å halloysite to 7 Å halloysite and allophane to amorphous Al hydroxides with time. The presence of 10 Å halloysite in Pleistocene terrace soils implies slow reaction rates or metastability.

Quantitative X-ray diffraction (QXRD) analysis indicates a decrease in the amount of plagioclase feldspar from 34 wt.% in the 1–2 year floodplain to 0–1.6% in terrace and residual soils. Plagioclase weathering is paralleled by the formation of dioctahedral clay, allophane and Al hydroxides. Analysis by QXRD also indicates that crystalline minerals comprise 70–95% of the soil fraction, implying 5–30% X-ray-amorphous material. These data are verified by selective extraction using ammonium oxalate, which indicates 8–30% amorphous material. Chemical analysis of the extractant by inductively coupled plasmaatomic emission spectrometry indicates that allophane (Al:Si ratios of 0.92–3.82) occurs in floodplain and some terrace soils while amorphous Al hydroxides appear to coexist with allophane in Pleistocene terrace and residual soils with Al:Si ratios of 6.53–8.53. Retention of Mg to a greater extent than Na, Ca and K suggests Mg incorporation into hydroxide sheets in dioctahedral vermiculite as well as substitution into hydroxides.

The behavior of mineral mixtures can be significantly different from the behavior of the individual components of the mixture due to differences between the mechanical and chemical properties of the individual minerals, and their ensuing effects on interparticle interactions and fabric formation. This study examines mixtures of kaolinite and calcium carbonate at different mass fractions using sedimentation, viscosity, and liquid-limit tests. These macroscale tests represent a wide range of solid-volume fractions and strain levels, with emphasis on high water-content conditions to magnify the effects of electrical forces. The results demonstrate that interparticle interactions depend on mineral surface-fluid effects, particle geometry, relative particle size, and solids content. With small solids contents, the kaolinite/calcium carbonate mixture behavior is a function of electrostatic interactions between oppositely charged mineral particles that promote flocculation; however, with large solids contents, the specific surface area of the minerals is the controlling factor. These results are relevant to many natural soil environments and to the possible development of engineered mineral mixtures for industrial applications.

The long-term impermeability of clay barriers in waste disposal facilities and hydraulic structures is of critical importance to environmental, agricultural, and industrial concerns. Changes in the oxidation state of Fe in the constituent clays of compacted clay barriers may degrade the hydraulic conductivity of these structures because other properties related to hydraulic conductivity, such as swelling, gel microstructure, and particle size, are greatly altered by the oxidation state. Two Na-saturated smectites (SWa-1 and API 25) were reduced by sodium dithionite (Na2S2O4), both in suspension and in situ after consolidation, to examine the effects of structural Fe reduction on hydraulic conductivity. Results indicated that the hydraulic conductivity depended on both the oxidation state and the consolidation history of the clay. The hydraulic conductivity of clay reduced in suspension before consolidation was lower than that of oxidized clay. Initially reduced smectite, thus, may be compactable to a less-permeable material with higher bulk density. But reduction of smectite in situ after consolidation increased the hydraulic conductivity and its variability. The oxidized state of clay liners should, therefore, be preserved.

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 Å. 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.

The Kimmeridgian-Volgian(-Ryazanian) clay stone is the principal oil source rock in the troughs of the North Sea. Randomly (R0) ordered mixed-layer illite/smectite (I/S) appears to have transformed to R1-(IS) or R3-(ISII) ordered simultaneously with oil generation. The proportion of illite layers in I/S increased to 95% during diagenesis in these claystones. Exceptions are three samples of I/S of probably bentonitic origin; these have apparently changed during diagenesis to R0-ordered I/S containing 40-50% illite layers. Fine fractions of the claystones dominated by I/S were analyzed by 27Al and 29Si magic-angle spinning (MAS)-nuclear magnetic resonance (NMR) spectroscopy, 57Fe Mössbauer spectroscopy, and X-ray powder diffraction (XRD), and for total chemical composition. Si/Al ratios determined from MAS-NMR agree closely with those calculated from total chemical analysis; however, tetrahedral and octahedral Al occupancies were most accurately determined by NMR. An increase in the percentage of illite layers and in the ordering of the I/S was accompanied by fixation of K+ and NH4+ in the I/S, by tetrahedral Al-for-Si substitution, and by octahedral Al-for-(Mg + Fe) substitution, resulting both in an increase of charge in the 2:1 layers and in a migration of charge from octahedral to tetrahedral sheets. The I/S of probably bentonitic origin had a larger tetrahedral and a smaller octahedral charge than expected from its content of illite layers. MAS-NMR showed a significantly higher content of tetrahedral Al (most likely in smectitic sites) than expected from the percentage of illite layers calculated from XRD. Correspondingly, XRD of K+-saturated and glycolated specimens showed that several smectite layers possessed a significant charge. A constant b-dimension of the I/S and the presence of a significant charge in the smectite layers suggest that a transformation of smectite to illite layers in the I/S by tetrahedral Al-for-Si substitution followed by interlayer cation fixation and interlayer contraction is the most probable genesis for the I/S investigated.

A method for extracting Ni and other metals from lateritic ores by means of shock heating has been investigated. Shock heating releases some of the metal from its goethitic host. Even though the transformation of pure goethite to hematite is known to occur via intermediate hydroxylated phases, the effect of other metals such as Ni substituting for Fe in goethites on this thermal transformation to hematite is unknown. The purpose of this study was to fill this gap, with the hope that the results will lead to more energy-efficient extraction methods and/or a better understanding of Fe geochemistry in thermally activated soils. X-ray diffraction, transmission electron microscopy with EDS, and thermal analysis were used to investigate mineralogical changes in nickeliferous goethites from five oxide-type lateritic nickel ore deposits that had been subjected to shock heating at temperatures in the range 220–800°C. Acicular, nano-sized goethite was the main constituent of the samples with minor to trace amounts of quartz, talc, kaolinite, chromite, maghemite, and Mn oxides. Goethite was partially dehydroxylated to OH-hematite at 340–400°C and had completely altered to well ordered hematite at 800°C. The OH-hematite was characterized by broad XRD peaks for reflections associated with the Fe sublattice. The goethite unit-cell a and b lengths remained almost constant with increasing preheating temperature up to 300°C, while the size of the c axis dimension contracted. The neoformed hematite crystals were larger than the precursor goethite crystals due to development, by sintering and surface diffusion, of regularly ordered hematite domains. The increase (1.5–2.6 fold) in surface area with increasing heating temperature (up to 340–400°C) reflected the development of slit-shaped micropores (∼300°C), which further developed into elliptically shaped micropores (∼400°C) in OH-hematite. With increased heating temperature, well ordered hematite formed with only a few micropores remaining. Such results may contribute to the development of more efficient procedures for extracting Ni from lateritic nickel ores, as the rate of dissolution of goethite in acid in ‘heap and pressure’ leach facilities will be enhanced by the increases in surface area and microporosity. The results may also provide valuable information on the probable effects of natural heating on pedogenic Fe oxides.

The results of X-ray diffraction, DTA, i.r. spectroscopy, and chemical tests are presented for some chlorites typical of the Flagstaff Hill area. The area is notable for the large variety of chlorite types occurring in considerable quantities. Chlorite, in this area, is found as veins, as pseudomorphs, and as individual crystals. Textures vary from massive, fine-grained aggregates to books which are more than 20 mm in width. Crystals more than 5 mm in size occur in parallel groupings at rock interfaces. Judging from 45 chlorite samples studied, sheridanite is most abundant; clinochlore and ripidolite are common. Penninite and its Cr-chlorite equivalent are less abundant. The parent rock is an irregularly shaped ultramafic body surrounded by low-grade schists and located very close to a granodiorite stock. The original ultramafic rocks have been highly altered by metamorphism and metosomatism into assemblages comprised mainly of serpentine, talc, hornblende, and chlorite with relics of olivine, pyroxene, and other less abundant original minerals. Much of the exposed rock is essentially monomineralic, mostly consisting of various polytypes of serpentine. Preliminary investigation indicates that the area merits much more study because of the opportunity for readily observing the various chlorite types and determining their genesis, alteration sequences and weathering characteristics. The area, being easily accessible, could also serve as an adequate source for samples to be used as reference standards.

Halloysite and kaolinite coexist in anorthosite weathering profiles in the Sancheong district, Korea. X-ray diffraction (XRD) analysis on a transect of partially weathered anorthosites reveals an increasing amount of kaolinite development with weathering age. Microtextures were examined by scanning electron microscopy (SEM) of thin sections and raw samples in an attempt to resolve the genetic relation between halloysite and kaolinite. In the earliest stage of weathering, halloysite ellipsoids and short tubes form on the plagioclase surfaces. The successive formation of new grains from the early grains results in globular aggregates where halloysite grains are partially interconnected. With the further progress of weathering, the halloysite grains coalesce from the inner part of the aggregate outward, and convert into stacked kaolinite plates. Continuous addition of halloysite grains on existing plates and their subsequent conversion into plates form long vermicular kaolinite. Solid-state transformation is suggested as a major conversion mechanism. Concurrently with its successive transformation into kaolinite, halloysite also continuously precipitates, giving rise to overgrowths on vermicular kaolinite. Halloysite forms as a kinetically favored metastable precursor and is subsequently transformed into thermodynamically stable kaolinite. Halloysite and kaolinite coexist temporarily in the weathering profile far from equilibrium.

Bulk mineralogical and chemical properties of a weathering profile derived from serpentinite were studied using classical pedological methods (Munsell soil colors, particle-size distribution, density, cation exchange capacity, exchangeable bases, among others) and inductively coupled plasma-atomic emission spectroscopy (ICP-AES) results. Bulk clay fractions were characterized using X-ray diffraction, thermal analysis, electron microprobe, Mössbauer and infrared spectroscopies. Bulk geochemical mass-balance calculated from ICP-AES results shows leaching of both Mg and Si which reflects the early weathering of serpentine minerals. As a consequence, newly formed clay minerals are enriched with the least mobile elements, i.e. Fe and Al, producing dioctahedral smectites. These dioctahedral smectites are complex, heterogeneous and consist mainly of two populations. One population is an Fe-rich montmorillonite with little or no tetrahedral charge and Fe3+ as the dominant octahedral cation whereas the second population exhibits tetrahedral charge. Both populations occur as interstratified layers in the lower horizon of the weathering profile but show increasing segregation into well-defined end-members towards the surface horizons. Considering total Al and Fe contents, these clays differentiate into two chemical composition domains, Fe-rich clays in the lower profile and Al-rich clays towards the surface horizons.

The interaction of water with synthetically prepared goethite (α-FeOOH) and amorphous hyd-rated ferric oxide surfaces was studied using i.r. absorption and water vapor adsorption measurements. I.R. results show that the last traces of physically adsorbed water are removed from the amorphous material by outgassing at 25°C. In contrast, goethite retains approximately a monolayer of physically adsorbed water with similar outgassing. This monolayer of water on goethite, which is presumably hydrogen-bonded at least in part with structural hydroxyls, is readily exchangeable with D2O.

Integral entropies of adsorption were evaluated from water vapor adsorption isotherms at 15, 25 and 35°C and compared with values for mobile and immobile layers calculated through application of statistical mechanics (McCafferty and Zettlemoyer, 1970). Entropy values for both the first physically adsorbed monolayer of water on the amorphous material and the second monolayer on goethite were about the same as or greater than those calculated for an immobile layer, indicating strong hydrogen bonding of water by both surfaces. The larger deviation between the entropy values for goethite and those calculated for the immobile layer may be associated with changes in the structure of the first as well as the second physically adsorbed water layers. Surface areas, calculated using the BET method, were 320 and 32 m2 g-1 for the amorphous material and goethite respectively. Since the unit surface activity is probably about the same for the two materials, it follows that as the amorphous material crystallizes to form goethite, there would be a reduction in total surface activity in proportion to the reduction in surface area.

The adsorption of poly(vinyl alcohol) (PVA) on montmorillonites saturated with calcium (Ca-Mt) and sodium (Na-Mt) as a function of the pH value and PVA concentration in aqueous solution was studied. Owing to the binding effect of the bivalent cation, the adsorption of PVA on Ca-Mt decreases as the pH of the suspension increases, whereas adsorption on Na-Mt is unaffected by the suspension pH. The adsorption maximum of PVA (pH 6) on Ca-Mt was 151.2 mg of PVA g−1 of clay, which is considerably lower than that on Na-Mt (496.2 mg g−1). These adsorption data coincide with the basal spacings obtained for the clays: 1.72 and 2.26 nm for Ca-Mt and Na-Mt, respectively. Sodium permits a greater separation between the clay laminae than calcium, but in both clays the presence of the polymer gives rise to a material in which PVA is intercalated between the laminae and is also adsorbed on the external surface. Adsorption is a slow process and is irreversible in both clays.

A new technique utilizing Raman microscopy and Fourier transform infrared (FTIR) microsacopy is described. This technique uses thin films of oriented clay aggregates on glass slides suitable also for X-ray diffraction (XRD). Raman microscopy proved the most useful technique providing both better resolution of the OH-stretching bands and greater spectral resolution. Kaolinites from Washington County, Georgia, with varying defect structures involving layer stacking were intercalated with formamide and additional Raman bands were observed at 3610 and 3627 cm−1. A concomitant decrease in the inner-surface OH band intensities at 3695 and 3685 cm−1 occurred. These bands are attributed to the inner-surface OH hydrogen bonded to the formamide molecule through the C=O group. The 3627 cm−1 band is sharp with a half width of 7.5 cm−1 and comprises 11% of the total normalized band area. When two additional OH bands are observed at 3610 and 3627 cm−1 two C=O bands at 1674 and 1658 cm−1 are observed also. The two additional Raman inner-surface OH bands were not observed in the IR spectra. However, a band of low intensity was observed at 3590 cm−1. Models for the intercalation of formamide in kaolinites are proposed.

Inverse gas chromatography (IGC) at zero surface coverage was used for determining the surface characteristics of a slate sample. Previously this sample had been characterized by means of X-ray diffraction (XRD), chemical analysis, infrared (IR) spectroscopy and nitrogen adsorption. Quartz, muscovite and chlorite were the minerals foming the slate. A well-defined mesoporous structure with pores of 15 Å of interlayer distance was observed. Chemical analysis and IR spectroscopy corroborated the X-ray results. The surface characteristics of the slate were defined in relation to nonspecific and specific interactions with organic molecules. In accordance with the nonspecific interactions, the London component (γSD) of the surface free energy gave an estimation of the surface energy of the slate sample. The obtained values for γSD were 140.0, 124.8, 108.2 and 96.8 mN m-1 at 100, 110, 120 and 130 °C, respectively. These values were characteristic of an inorganic sample of high surface energy. The values of the thermodynamic variables—differential heat of adsorption, free energy and entropy of adsorption—were in accordance with these results. At the same time, specific interactions were characterized by the ηπ parameter and the acid-base (KA, KB) indices. The positive value of ηπ (0.09 kJ mol-1) indicated the presence of Lewis acidic sites on the slate surface. The value of KA (acid index) of 1.17 was higher than the value of KB (base index) of 0.37; this result confirmed the acidic nature of the studied slate's surface.

The assignments of OH-bending bands in the infrared (IR) spectra of dioctahedral smectites (montmorillonites, ferruginous smectites, and nontronites) have been revisited using a cation mass-valence sum (CM-VS) approach to quantify octahedral cation occupancy. The CM-VS approach enabled prediction of OH-bending band positions (in wavenumbers) related to OH-sharing octahedral cation pairs that had valence sums of 4 and 5, and cation masses associated with Fe(II) and Mg. Application of rules for the relationship enabled determination of the location of OH-sharing octahedral cation pairs containing Mg and Fe(II) for which previous assignments have been considered controversial, e.g. Fe(III)Mg-OH and MgMg-OH, or for which assignments have been missing due to lack of spectroscopic evidence, e.g. AlFe(II)-OH, Fe(III)Fe(II)-OH, Fe(II)Mg-OH, and Fe(II)Fe(II)-OH. Examples of these bands from several natural ferruginous smectites and nontronites are discussed. Quantification of IR spectra was used to develop a better understanding of the octahedral cation occupancy of this important class of Fe(III)-enriched smectites. While Fe(II) contents may be somewhat overestimated by the IR technique, those for four of the six ferruginous smectites studied here agree well with data from Mössbauer spectroscopy.

The mechanism by which the anionic polymers interact with platelets of 2:1 clay minerals is not fully understood. The objective of the present study was to evaluate the effect of the electric field associated with the basal and edge surfaces of the clay minerals on the adsorption of anionic polymers. Two negatively charged polymers, PAM90 and ACC86, of the same molecular weig ht (2 × 105 g mol−1) but with different degrees of hydrolysis (90 and 20%, respectively), were used. The effect of pH (6, 10), NaCl concentration (0, 10 mmolC L−1) and clay particle size on PAM90 adsorption by pyrophyllite and the effect of NaCl concentration on the adsorption of these polymers by Na-montmorillonite in aqueous suspensions were studied. Adsorption of PAM90 on pyrophyllite was greater at pH 6 than at pH 10 and greater in 10 mmol L−1 NaCl than in distilled water. Adsorption of PAM90 on pyrophyllite increased with decreasing particle size. On pyrophyllite the high-charge-density PAM90 was adsorbed to a greater extent than the low-charge-density ACC86; by contrast, ACC86 adsorption was greater than that of PAM90 on Na-montmorillonite. These results were attributed to the repulsive forces which develop between the negatively charged extended-chain polymer and the extended negative electric field associated with the basal surfaces, around the Na-montmorillonite platelets. The results may suggest that the edge surfaces play a major role in PAM adsorption.