The crystal structure of bannisterite, a modulated, mica-like mineral species, of general composition Ca0.5(K,Na)0.5(Mn,Fe,Mg,Zn)10(Si,Al)16O38(OH)8·nH2O, has been solved and refined for specimens from Franklin Furnace, New Jersey (FF), and Broken Hill, Australia (BH). The crystals are mono-clinic in space group A2/a, with (for FF) a = 22.265(1) Å, b = 16.368(1) Å, c = 24.668(2) Å, β = 94.285(5)°; and (for BH) a = 22.286(1) Å, b = 16.386(1) Å, c = 24.575(2) Å, β = 94.355(7)°; Z = 8. Refinement with anisotropic thermal factors reached Rw = 0.034 (FF) and 0.039 (BH). Like stilpnomelane and ganophyllite, bannisterite has a modified 2:1 trioctahedral layer structure in which some of the tetrahedra are inverted towards the interlayer region and linked to inverted tetrahedra in the opposite layer. The octahedral sheet is strongly corrugated along b. The tetrahedral sheet consists of 5-, 6-, and 7-fold rings, and bond distance calculations indicate that Al is concentrated into two of the four inverted tetrahedra. The interlayer Ca, K, and H2O species are highly disordered, as indicated by anomalously large temperature factors and partial occupancies. Localized differences in the Al/Si arrangements in the inverted tetrahedra induce disorder among the interlayer cations.

Hydrotalcites of high aluminum content have been synthesized from aluminate liquors of varying composition and activated magnesia obtained by calcination of hydroxide or hydroxycarbonate precursors. Lattice parameter measurements and chemical analyses of 21 synthetic hydrotalcites show that the aluminum substitution $$\left( {\rm{X = \frac{{Al}}{{Al + Mg}}}} \right)$$ for most of the products is about 0.35, which is at the maximum experimentally-observed limit of solid solubility. Pillared hydrotalcites were also prepared by molybdate, Chromate, and silicate anion replacement. A maximum distance of 10.4 Å between the brucite-like layers was observed for the Mo7O246− intercalated material.

The clay-polysaccharide interaction is of practical importance in the formation and stabilization of soil aggregates. This study examined the adsorption of three synthetic polysaccharides (PSS) and one soil PSS on Silver Hill illite. The adsorption of PSS was influenced by both the adsorbed cations on the adsorbents and the charge characteristics of the polymers. The adsorbed cations formed different surface complexes with the clay surfaces, with varying ability to screen the surface negative charge and thereby influenced the adsorption of charged polymers. Na-illite adsorbed substantially higher amounts of the cationic PSS, but lower amounts of the anionic PSS, than hydroxy-Al illite. The adsorption of the nonionic PSS was, however, little influenced by those adsorbed cations. The adsorption of the soil PSS resembled that of anionic PSS. However, it yielded linear adsorption isotherms due to the heterogeneous nature of the soil PSS. The adsorption of the three synthetic PSS on Na-illite was in the general order: cationic > nonionic > anionic, confirming that electrostatic forces played a role in the adsorption of charged polymers. pH and ionic strength influenced the adsorption of the charged PSS, because of their influences on the charge characteristics of both the polymer and the clay, and on polymer conformation. This study indicates that surface charge properties of both clays and organic polymers and the presence of polyvalent cations in the system are important factors influencing the complexation between soil clays and organic constituents.

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.

Bentonite- and sepiolite-supported copper catalysts have been prepared either by adsorption of Cu(II) from aqueous solutions of copper nitrate at pH ~4.5 or by adsorption of a [Cu(NH3)4]2+ complex from an ammonia solution of CuSO4 at pH ~9.5. The structure and composition of the calcined preparations have been studied by X-ray diffraction, chemical analysis, and energy dispersive X-rays. Textural characteristics have derived from the analysis of the adsorption-desorption isotherms of N2. All catalysts have been tested for the dehydrogenation of methanol to methyl formate. For this reaction, bentonite-based catalysts were found to have very little activity, which indicates that copper located in the inter-lamellar spaces is inaccessible to methanol molecules. On the contrary, copper-sepiolite catalysts showed a very high specific activity even for those catalysts with a very low copper content. The chemical state of copper in the catalysts on-stream has been revealed by X-ray photoelectron spectroscopy and X-ray-induced Auger techniques. In most of the catalysts Cu+ is the dominant copper species.

Selected Brazilian Oxisols were sampled and submitted to high-gradient magnetic separation (HGMS) to study the iron oxide-clay mineral associations. The soils, derived from four different parent materials, have mineralogy dominated mostly by hematite, goethite, and kaolinite. Gibbsite appears in most soil samples. The high-gradient magnetic separation showed good separation for some soils, as indicated by color differentiation and iron oxide segregation between magnetic and nonmagnetic fractions. Soils that showed a somewhat low surface area for the iron oxides associated with high phosphate adsorption were poorly separated by HGMS. This suggests a strong interaction between kaolinite and iron oxides, which would indicate a low estimation of their surface areas obtained by the difference method using BET-N2 data. A relative concentration of anatase and rutile in the magnetic portion of some of the samples was attributed to the presence of Fe, either as coatings on the crystals or within the structure of these two minerals.

Expandable fluorine micas were synthesized using talc and Na2SiF6 at 800°C for 2 hours in air, nitrogen, argon, and under vacuum. Gaseous SiF4, generated from Na2SiF6, and the resultant amorphous sodium silicofluoride formed during the reaction between talc and Na2SiF6 below 900°C are taking active part in the formation of expandable micas because the intensity of the 12.5 Å reflection of expandable micas decreases as the gas flow increases in the furnace. Expandable micas seem to be formed by the transformation from talc taking place without the entire disruption of the original atomic arrangement. This takes place with the loss of one Mg2+ from an octahedral site and by the intercalation of every two Na+ into the interlayer site of talc. Infrared absorption and thermal analyses show that expandable micas include a small amount of OH− in their structures.

High-resolution solid-state, fluorine-19, magic-angle spinning-nuclear magnetic resonance spectroscopy (MAS-NMR) was used to study natural and synthetic fluorinated 2:1 layer silicates of known composition. This technique enabled us to determine directly the coordination of structural fluorine and it was found to be sensitive to both the chemical nature of the octahedral elements (Al, Mg, Li) and the type of octahedral sheet (di- or trioctahedral). The observed chemical shifts at −132, −152, −176 and −182 ppm (relative to CFC13) were assigned to different environments of fluorine. The results were then used to characterize synthetic 2:1 layer silicates with unknown octahedral composition.

Boron adsorption at constant ionic strength [0.09 ± 0.01 moles/liter of KClO4 or Ca(ClO4)2] on 0.2−2 μm clay fraction of pretreated kaolinite was modeled using both phenomenological equations and surface complexation reactions. Phenomenological equations were expressed as linear relationships between the distribution coefficient and adsorption density or equilibrium concentration. The normalized form of the isotherms allowed the distribution coefficient to be predicted over a wide range of adsorption densities or equilibrium concentrations and pH. The Langmuir isotherm revealed a weak two-part linear trend supported by a similar behavior of the van Bemmelen-Freundlich isotherm. Potential adsorption mechanisms were assessed from these isotherms. The bases for the inner-sphere (surface coordination) and outer-sphere (ion-pair) surface reactions were postulated, and equations were developed and incorporated into the generalized triple-layer surface-complexation model [TL(g)-SCM]. Boron adsorption was best modeled using the inner-sphere complexes. The results confirm that the generalized triple-layer surface-complexation model can provide information regarding plausible reactions at the substrate/aqueous interface. Intrinsic constants for postulated surface reactions were derived as fitting parameters over a range of pH and initial boron concentrations.

The reactions between montmorillonite and carbonates and hydroxides of Na, K and Li were studied at 550°C as a function of salt content and time. The reactions were found to be rapid with a half-time of 20–30 minutes. Good agreement was obtained between theoretical and experimental stoichiometric values for the clay-carbonate reaction. The 001 and 02,11 reflections of the products of the clay-salt reactions diminished in intensity and/or disappeared at and above the stoichiometric concentrations of the reactants.

Parallel-oriented and exceptionally long (> 10 μm) tubes of halloysite occur in the pallid zone of a deeply-weathered lateritic profile on granite in southwest Australia.

Transmission electron microscopy and selected-area electron diffraction of ultrathin sections showed that kaolinite plates within pseudomorphs of mica crystals had fractured at irregular intervals along the a crystallographic axis to produce laths elongated along the b axis. The laths near the edges of the pseudomorphs were less constrained by the pseudomorph and had rolled to produce halloysite tubes. The tubes varied in diameter and degree of roundness. Some tubes were polyhedral rather than cylindrical in cross section. The length and number of planar faces in a tube and the angle between faces varied, exhibiting no consistent pattern.

Tubes in dispersed clay samples showed two types of twinning. In the first type, tubes and associated laths were joined together side by side. In the second type, single tubes bifurcated into two individual tubes. It is proposed that the first type of twinning occurred by folding of adjacent laths that remained joined together while the second type occurred due to exfoliation of a thick lath followed by folding of the exfoliated lath fragments into tubes.

Analytical electron microscopy showed that the chemical compositions of halloysite tubes, laths, and kaolinite plates were similar with the average cation exchange capacity of single tubes being small (4.5 meq/100 g) but higher than values for laths (2.8 meq/100 g) and plates (1.9 meq/100 g).

A new chemical, Peldri II, is evaluated as a compound for drying soft clay materials. Peldri II, a fluorocarbon (1,1-difluorotetrachloroethane), is a solid at room temperature and is a liquid above 25°C. Clay gels are embedded in Peldri II by immersing them in the liquid and allowing it to solidify. Once solidified, Peldri II will sublime, with or without vacuum, to a dry specimen, probably without introducing surface tension. Wyoming montmorillonite saturated in 10−3 M NaCl and 1 M CaCl2 solutions has been examined to compare preservation of its initial structure after Peldri II, critical point, and freeze drying techniques. Transmission electron microscopy of ultrathin sections, scanning electron microscopy, and mercury intrusion porosimetry techniques were used. No differences were detected between Peldri II and critical point drying methods. Peldri II appears to be a significant improvement as an alternative drying agent for clay materials in studies of their structural properties. It is also very convenient for drying large numbers of samples.