The environmental conditions and reaction paths of shallow-water glauconitization (<500 m water depth, ~15°C) close to the sediment-seawater interface are generally considered to be well understood. In contrast, the key factors controlling deep-sea glauconite formation are still poorly constrained. In the present study, green grains formed in the recent deep-sea environment of the ODP Site 959, Ivory Coast-Ghana Marginal Ridge, (~2100 m water depth, 3-6°C) were investigated by X-ray diffraction and electron microscopic methods in order to determine the rate and mechanism of glauconitization.

Green clay authigenesis at Hole 959C occurred mainly in the tests of calcareous foraminifera which provided post-depositional conditions ideal for glauconitization. Within this organic-rich microenvironment, Fe-smectite developed <10 ky after deposition of the sediments by precipitation from precursor gels containing Fe, Mg, Al, and silica. This gel formation was supported by microbial activity and cation supply from the interstitial solution by diffusion. At a later stage of early marine diagenesis (900 ky), the Fe-smectites reacted to form mixed-layer glauconite-smectite. Further down (~2500 ky), almost pure glauconite with no compositional gaps between the Fe-smectite and glauconite end members formed. This burial-related Fe-smectite-to-glauconite reaction indicates that the glauconitization process was controlled mainly by the chemistry of the interstitial solutions. The composition of the interstitial solution depends heavily on micro-environmental changes related to early diagenetic oxidation of biodegradable (marine) organic matter, microbial sulfate reduction, silicate mineral alteration, carbonate dissolution, and Fe redox reactions. The availability of Fe is suggested as the probable limiting factor for glauconitization, explaining the various states of green-grain maturity within the samples, and this cation may be the most important rate-determining element.

The rate of glauconite formation at ODP Site 959 is given by %GlSed = 22.6·log(ageSed) + 1.6 (R2 = 0.97) where %GlSed is the state of glauconitization in the sediment and ageSed is the sediment age (in ky). This glauconitization rate depends mainly on continuous cation supply (in particular Fe) and is about five times less than that in shallow-shelf regions, suggesting significantly slower reaction at the lower temperature of deep-sea environments.

Clay minerals in the upper 50 cm of sediment that surround the Cu- and Ni-rich manganese nodules in the North Equatorial Pacific form two fractions: terrigenous (mostly eolian) illite, chlorite, and kaolinite, and authigenic smectite. Smectite increases with depth in box cores from 26 to 39% and from 53 to 66% in the easternmost and westernmost areas respectively, and with distance seaward from the Americas from 26 to 53% in surface deposits. The change in the amount of smectite relative to other clay minerals is due to dilution by terrigenous debris; smectite probably forms at a uniform rate over much of the North Pacific deep-sea floor. The δO18 value for the smectite is +29.6‰ which suggests that it formed authigenically at a temperature characteristic of the deep-sea floor. The smectite is an Fe-rich montmorillonite that probably forms by the low-temperature chemical combination of Fe hydroxides and silica. Silica is derived from dissolution of biogenic debris, and the Fe hydroxide is from volcanic activity at the East Pacific Rise, 4000 to 5000 km to the east. Al in the authigenic montmorillonite may be derived from the dissolution of large amounts of biogenic silica or from river-derived Al that is adsorbed on Fe-Mn hydroxides in the oceans. The Fe-montmorillonite contains relatively abundant Cu, Zn, and Mn and is of possible economic importance as a source of these and other metals.

Montmorillonites, with the general composition where x = ξ = 0.2–0.6, x = y+z, and y≪z, vary widely in composition and structure. The commonly used classification into five montmorillonite and two beidellite groups for the solid-solution sequence does not allow an unambiguous classification with respect to structural features and the resulting properties.

The smectite structure reveals five features that allow an unambiguous description of a sample: (1) identification as either a dioctahedral or a trioctahedral smectite; (2) layer charge; (3) charge distribution between tetrahedral and octahedral sheets; (4) cation distribution within the octahedral sheet; and (5) Fe content. In addition, the nature of interlayer cations should be given as they influence certain properties of montmorillonites. Analytical methods are now available to measure and determine these structural features. Therefore, a precise classification for montmorillonites requires determination of layer charge and exchangeable cations, analysis of chemical composition, and thermal analysis (to determine the octahedral structure), in addition to X-ray diffraction analysis.

A comprehensive classification of montmorillonites based on these parameters is proposed. Ninety-six structural variations (expressed by systematic names) theoretically exist within the montmorillonite-beidellite series. Descriptive names can be used to elucidate the macroscopic properties of the montmorillonite samples in question.

A modified version of the Bertaut-Warren-Averbach (BWA) technique (Bertaut 1949, 1950; Warren and Averbach 1950) has been developed to measure coherent scattering domain (CSD) sizes and strains in minerals by analysis of X-ray diffraction (XRD) data. This method is used to measure CSD thickness distributions for calculated and experimental XRD patterns of illites and illite-smectites (I-S). The method almost exactly recovers CSD thickness distributions for calculated illite XRD patterns. Natural I-S samples contain swelling layers that lead to nonperiodic structures in the c* direction and to XRD peaks that are broadened and made asymmetric by mixed layering. Therefore, these peaks cannot be analyzed by the BWA method. These difficulties are overcome by K-saturation and heating prior to X-ray analysis in order to form 10-Å periodic structures. BWA analysis yields the thickness distribution of mixed-layer crystals (coherently diffracting stacks of fundamental illite particles). For most I-S samples, CSD thickness distributions can be approximated by lognormal functions. Mixed-layer crystal mean thickness and expandability then can be used to calculate fundamental illite particle mean thickness. Analyses of the dehydrated, K-saturated samples indicate that basal XRD reflections are broadened by symmetrical strain that may be related to local variations in smectite interlayers caused by dehydration, and that the standard deviation of the strain increases regularly with expandability. The 001 and 002 reflections are affected only slightly by this strain and therefore are suited for CSD thickness analysis. Mean mixed-layer crystal thicknesses for dehydrated I-S measured by the BWA method are very close to those measured by an integral peak width method.

A new, well-ordered, thermally robust ethylene glycol intercalate of kaolinite was formed by refluxing the dimethyl sulfoxide intercalate of kaolinite (Kao-DMSO) with dry ethylene glycol (EG). This new phase (Kao-EG 9.4 Å) which is characterized by a d001 of 9.4 Å is distinct from a previously reported ethylene glycol intercalated phase of kaolinite (Kao-EG 10.8 Å) which has a d001 of 10.8 Å. The characterization of these two phases was studied by XRD, NMR, FTIR, and TGA/DSC. It was found that the concentration of water in the ethylene glycol reaction media played a crucial role in governing which of the phases predominated. Water favored Kao-EG 10.8 Å formation, while anhydrous conditions favored the formation of Kao-EG 9.4 Å. It is hypothesized that Kao-EG 9.4 Å is a grafted phase resulting from the product of the condensation reaction between an aluminol group on the interlamenar surface of kaolinite and the alcohol group of ethylene glycol. Ethylene glycol units would be attached to the interlamellar surface of kaolinite via Al-O-C bonds. The Kao-EG 9.4 Å phase was found to be resistant to both thermal decomposition up to 330°C and also, once formed, in the absence of interlamellar water molecules, to decomposition by hydrolysis in refluxing water.

The electrochemical properties of kaolinite before and after modification with chlorodimethyl-octadecylsilane have been studied by electrophoretic mobility, surface charge titration, and extrapolated yield stress measurements as a function of pH and ionic strength. A heteropolar model of kaolinite, which views the particles as having a pH-independent permanent negative charge on the basal planes and a pH-dependent charge on the edges, has been used to model the data. The zeta potential and surface charge titration experimental data have been used simultaneously to calculate acid and ion complexation equilibrium constants using a surface complex model of the oxide-solution interface. The experimental data were modeled following subtraction of the basal plane constant negative charge, describing only the edge electrical double layer properties. Extrapolated yield stress measurements along with the electrochemical data were used to determine the edge isoelectric points for both the unmodified and modified kaolinite and were found to occur at pH values of 5.25 and 6.75, respectively. Acidity and ion complexation constants were calculated for both sets of data before and after surface modification. The acidity constants, pKa1 = 5.0 and pKa2 = 6.0, calculated for unmodified kaolinite, correlate closely with acidity constants determined by oxide studies for acidic sites on alumina and silica, respectively, and were, therefore, assigned to pH-dependent specific chemical surface hydroxyl groups on the edges of kaolinite. The parameters calculated for the modified kaolinite indicate that the silane has reacted with these pH-dependent hydroxyl groups causing both a change in their acidity and a concomitant decrease in their ionization capacity. Infrared data show that the long chain hydrocarbon silane is held by strong bonding to the kaolinite surface as it remains attached after washing with cyclohexane, heating, and dispersion in an aqueous environment.

Nanomorphological structure of well-crystallized Georgia and poorly crystallized North Queensland kaolinite particles have been compared using field emission scanning electron microscopy (SEM) and atomic force microscopy (AFM). In general, there is good agreement in information from the 2 very different imaging techniques. AFM gives more detailed information on step and ledge dimensions, microvalleys and crystallographic orientation of irregularities on basal planes and edges of the crystallites. There are major differences in nanomorphology and surface structure between the 2 kaolin samples with the Georgia kaolin showing 200–500-nm, relatively flat basal planes with some cascade-like step growth 50–100 nm wide. The edges, apparently flat and right-angled in SEM images, appear beveled in AFM images due to artifacts from the aspect ratio of the AFM tip. The North Queensland kaolinite has much more complex surface structure with anhedral crystallites attached to larger particles, high density of steps and nm-scale irregularities (often crystallographically directed). The additional step edge site contribution from the attached crystallites is estimated as a minimum of 6%, giving a total edge contribution above 30% of the kaolinite total surface area. These structures will generate a substantial pH-dependent charge across the surfaces of the North Queensland kaolinite platelets. An idealized, uniform, pH-independent, negatively charged basal plane cannot be assumed from these structures. There is also some evidence, from both SEM and AFM images, of curvature in the thinner, poorly ordered structures of the North Queensland kaolinite particles.

Hydrotalcite-like compounds, described by the formula [Zn1-xAlx(OH)2][(CO3)x/2 · nH2O], were prepared by coprecipitation methods at 80°C and characterized by bulk chemical analysis, X-ray powder diffraction (XRD), nuclear magnetic resonance (NMR), and scanning-transmission electron microscopy (STEM). An x value of 0.33 was previously assumed to be an upper limit, but recently, Al-rich hydrotalcite-like compounds have been prepared with x as large as 0.44 by hydrothermal synthesis. In the Zn-Al system, Al-rich hydrotalcite was synthesized at normal pressure by coprecipitation. Zn-Al hydrotalcite-like compounds were obtained in the range of x = 0.3 to 0.4. An Al-rich hydrotalcite-like compound with x = 0.44 was formed in mixtures containing large amounts of a poorly crystalline Zn-Al phase. A continuous contraction of the hydrotalcite-like structure occurred as x increased, both the a and c lattice parameters decreasing for x values as large as 0.44. This study illustrates the advantages of using quantitative analytical electron microscopy with high spatial resolution to complement conventional (and bulk) characterization techniques for correlating structural and compositional characteristics of finely divided materials.

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.

Chloride-, sulfate-, and perchlorate-exchanged forms of hydrotalcite have been prepared and their layer spacings determined after equilibration in hydrous atmospheres and after heat-treatments up to the temperature of decomposition in the range 300–400°C. The initial carbonate form of hydrotalcite and also brucite, for purposes of comparison, have been similarly studied. Only chloride-hydrotalcite and brucite exhibit a single phase stable to the decomposition temperature. The other anionic forms exhibit various phases with different layer spacings which are interpreted in terms of the size, orientation, and stability of the anions and, in some cases, the presence of additional water. A regularly interstratified form of sulfate-hydrotalcite (layer spacing = 19.80 Å) is obtained at room temperature and relative humidity <50%; at higher humidities, a fully hydrated phase is obtained, and at 50°C a collapsed form is obtained. In the preparation of perchlorate-hydrotalcite, an interstratified phase (layer spacing = 17.0 Å) was recognized with alternating carbonate and Perchlorate layers, although the evidence is less certain.

A method using Li saturation and heating to 250°C to differentiate montmorillonite from beidellite and nontronite has been developed. The test utilizes three washings with 3 M LiCl and two washings with 0.01 M LiCl in 90% methanol to prevent dispersion. An 'infinitely thick’ sample (6–8 mg/cm2) on a glass slide is used to avoid the effects of the reaction of a thin clay film with sodium of the slide when it is heated at 250°C. Solvation with glycerol rather than ethylene glycol is used, because all of the Li smectites studied expanded to some extent in ethylene glycol after the heating. The smectites included several montmorillonites, a nontronite, and saponites. The presence of interstratified montmorillonite and beidellite layers was clearly shown by the test for several smectite samples, including the so-called beidellites from Beidell, Colorado, and Chen-yuan, Taiwan, and several soil clays. The test thereby provides more mineralogical information than the often-used arbitrary dividing point between montmorillonite and beidellite at 50% tetrahedral charge. Heating the Li-saturated clays at 250°C caused substitution of 35 to 125 meq/100 g of nonexchangeable Li. These amounts exceeded the changes in cation-exchange capacity plus Li by 4 to 21 meq/100 g, except for the end-member beidellite from the Black Jack mine, Idaho. Fusion with LiNO3 at 300°C could not be used to differentiate between smectites instead of washing with LiCl solution and heating to 250°C, because fused montmorillonite subsequently expanded to 18 Å with glycerol. Large increases in nonexchangeable Li were caused by the fusion of smectites, a vermiculite, and two partially expanded micas.

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 di-trigonal 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.

The conversion of lepidocrocite (-γFeOOH) to its more stable polymorph, goethite (αFeOOH) was followed by observing changes in crystal morphology, oxalate solubility, surface area and X-ray diffraction. In conjunction, kinetics were measured as functions of surface area, temperature, alkalinity and seeding with goethite crystals.

The results suggest that the transformation is not topochemical, but proceeds through the solution phase. The main steps governing the rate of transformation are, (1) the dissolution of lepidocrocite, and (2) the formation of goethite nuclei and subsequent growth. Either of these processes can be rate-determining under appropriate conditions.

Phenol (benzenol) oxidation by three synthetic manganese oxides (buserite, manganite, and feitknechtite) has been studied in aerated, aqueous, acidified suspensions. The rate of reaction was pH dependent. Oxidation was greatly enhanced below pH 4, when diphenoquinone and p-benzoquinone were identified as the first products. Initial reaction rate was correlated with standard reduction potential (E°) of the oxides following the order: feitknechtite > manganite > buserite. A more gradual process of phenol oxidation after the initial reaction was influenced by electrochemical properties of the solution. High soluble manganese activity and increase in pH adversely affected reaction rates. Thus, the reactivity of the oxides was related to their stability and possibly the ability to readsorb Mn(II), following the order: buserite > manganite > feitknechtite. The results indicate that thermodynamic and electrochemical data for oxides and phenols are useful in predicting under which conditions phenols can be oxidized by a given system.

The present work shows the results of X-ray diffraction (XRD), Fourier transform infrared (FTIR), and thermal analysis of untreated (RMnt) and acid-treated red mud (RMa), a bauxite ore-processing waste, exchanged with Pb2+, Cd2+, and Zn2+ cations. These studies were performed in order to investigate the changes in the sorbent structure caused by the exchange with metals of different ionic radii.

The XRD pattern of RMnt, analyzed according to the Rietveld method, showed a mixture of eight different phases. However, just three phases made up 78 wt.% of the RMnt: cancrinite (33 wt.%), hematite (29 wt.%), and sodalite (16 wt.%). X-ray diffraction patterns of RMnt exchanged with Pb2+ and Cd2+ cations revealed two additional phases, namely hydrocerussite [Pb3(CO3)2(OH)2 (10 wt.%))] and octavite [CdCO3 (8 wt.%)].

These two phases probably originated from the carbonate precipitation processes which were due to the decarbonation of cancrinite. Hydrocerussite and octavite were not found in the case of acid-treated red mud samples.

In the FTIR spectra, the introduction of cations caused a distinct shift to higher wavenumbers in the peak at ∼1100 cm−1, which is attributed to the asymmetric stretch of Si-O-Al. This effect may be associated with the Pb2+, Cd2+, and Zn2+ adsorbed by the red muds which caused a deformation of the initial structure.

Thermal analysis data of the red mud samples were obtained by thermogravimetric/differential thermogravimetric analysis, and these methods were employed to evaluate the desorption behavior of water and to clarify the thermal stability of the chemical phases of the different red mud samples. The loss of metal-bound water in the red mud samples was found to depend on the size of non-framework cations and water loss consistently followed the order: Zn2+>Cd2+>Pb2+.

In any clay deposit, the nature of the mineral assemblage and the composition of individual clay minerals can change radically in a few em. Consequently, any given locality can contain many subtly different types of clay minerals. Results from different laboratories on ostensibly the same clay material may not always be comparable because the samples may indeed not contain an assembly of identical clay minerals. Such confusion slows the understanding of this important group of minerals. Several attempts were made to provide investigators with reasonably constant clay materials, the first being that of the American Petroleum Institute Project 49 (Kerr, 1949). The Clay Minerals Society Source Clays project proposed to provide investigators with gently homogenized clay materials, carefully collected and processed under the supervision of clay specialists. The collection would include metric ton amounts to ensure a long-lasting collection. The program began in 1972, with the introduction of the materials described in this paper. Later the program expanded to include the Special Clays. These samples are materials not amenable to homogenization, or they are available in very small amounts.

Large-pore La-Al-pillared montmorillonite was prepared by reacting montmorillonite with hydrothermally treated mixtures of aluminum chlorohydrate and lanthanum chloride. The large-pore La-Al-pillared montmorillonite is characterized by basal spacings of about 26 Å, surface areas of 300–500 mVg, and pore volumes in the range 0.2–0.3 cm2/g. Large-pore pillared montmorillonite products were obtained from solutions refluxed for >72 hr or treated in autoclaves at 120°–160°C for 12–96 hr. The most favorable pillaring solution for the production of large-pore La-Al-pillared montmorillonite had an OH/Al ratio of 2.5, a La:Al ratio of 1:5, and was 2.5 M with respect to Al. The elemental composition of large pore La-Al-pillared montmorillonite is similar to that of a conventional Al-pillared montmorillonite that has a basal spacing of about 19 Å. The 26-Å spacing is believed to be associated with the formation of large polymeric La-bearing Al-cations upon hydrothermal treatment of the solutions.

The effect of acid type and concentration on the reaction rate and products of dissolution of hectorite in inorganic acids was investigated. The dissolution of hectorite in hydrochloric (HCl), nitric (HNO3) and sulphuric (H2SO4) acids was characterized using quantitative chemical analysis, infrared (IR) and multinuclear MAS NMR spectroscopies. The rate of dissolution increased with acid concentration and decreased in the order HCl ≥ HNO3 = H2SO4 at the same molar concentration. No differences were found in the reaction products of hectorite treated with the three acids. The rate of Li dissolution was slightly greater than that of Mg at lesser acid concentrations (0.25 M), indicating that protons preferentially attack Li octahedra. The gradual changes in the Si-O IR bands reflects the extent of hectorite dissolution. The analysis of 29Si MAS NMR spectra relative peak intensities with dissolution time and acid concentration provided direct dissolution rates for tetrahedral (Q3) Si. After acid dissolution, most Si was bound in a three dimensional framework site (Q4), but a substantial part also occurred in the Si(OSi)3OH (Q31OH) and Si(OSi)2(OH)2 (Q220H) environments. These three sites probably occur in a hydrous amorphous silica phase. Both AlJV and AlVt rapidly disappeared from 27Al MAS NMR spectra of the dissolution products with acid treatment. The changes in IR and MAS NMR spectra of hectorite due to acid dissolution are similar to those of montmorillonite.

The resolution of the infrared spectra of structural OH in kaolin-group minerals increases with decreasing temperature. Poorly crystalline kaolinite gives typical infrared spectra, which suggest the existence of kaolinite-, dickite-, and nacrite-like configurations. The relative amount dickite- and nacrite-like configurations compared with kaolinite-like configurations increases with decreasing crystallinity. Low-temperature infrared spectroscopy is a more sensitive means of estimating the degree of order of poorly crystalline kaolinite than is X-ray powder diffraction.

The destruction of the crystal structure of kaolinite caused by mechanical forces was investigated by X-ray diffraction, thermal analysis, infrared spectroscopy, and specific surface area determination. Attention was also directed to the change of thermal reactions of milled kaolinite. Grinding experiments for 5 min, 10 min, and 1, 2, 4, 6, and 10 h were carried out in an AGO I planetary mill. After 1 h of grinding, the crystalline order of kaolin is destroyed; but the amorphization continues in the course of prolonged grinding. Grinding for 1 h produces a favorable state for forming mullite-type crystals after heating even at 1000°C.