bluuebunny/crossref_metadata_2025_split huggingface dataset:
Unifying Features Relating to the 3D Structures of some Intercalates of Kaolinite
Authors: Adams J. M. 
Published: August 2006

AbstractThe recent determination of the three-dimensional crystal structure of a dickite:formamide intercalate allows insight into the clay:organic bonding schemes of amides and other small organic molecule intercalates of the kaolin minerals. It is demonstrated that the observed basal spacings of intercalates with these molecules are consistent with hydrogen bonding schemes in which, if possible, triple hydrogen bonds from the clay hydroxyls to 0=C< are formed. Variations in basal spacing within a series of amides can be explained by considering the maximization of hydrogen bonding while avoiding close van der Waals contacts.
The Effect of Grinding on the Structure and Behavior of Bentonites
Authors: Mingelgrin U. , Kliger L. , Gal M. , Saltzman S. 
Published: August 2006

AbstractThe structure and behavior of homoionic bentonites was markedly affected by a grinding procedure often applied to clays. The main changes observed on clay powders were the breakage of weakly bound large aggregates, the reduction in the tactoids’ thickness by delamination, the reduction in the plates’ area, and the formation of colloidal matter. The tendency of clays to form secondary aggregates in aqueous suspensions is probably due to the exposure of active broken edges following grinding.The mild mechanical stress applied increased both the rate and the amounts of parathion sorbed by clays from an apolar solvent. The effect of grinding on parathion adsorption in aqueous clay suspensions seems to be a rate effect.
Ion Exchange and Intersalation Reactions of Hectorite with Tris-Bipyridyl Metal Complexes
Authors: Traynor Mary Frances , Mortland M. M. , Pinnavaia T. J. 
Published: August 2006

AbstractThe 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 Influence of Aluminum on Iron Oxides. Part I. The Influence of Al on Fe Oxide Formation from the Fe(II) System
Authors: Taylor R. M. , Schwertmann U. 
Published: August 2006

AbstractThe influence of Al on the products formed by aerial oxidation at pH 5.5-7 and 20°C of Fe(II) chloride, sulfate and carbonate solutions, was examined. In all cases Al at levels Al/Al + Fe = 0.09−0.30 inhibited the formation of y phases (lepidocrocite and maghemite) in favor of goethite under conditions where, in the absence of Al, these y phases formed. The influence of Al in these laboratory studies was supported by field observations.At higher levels of Al, ferrihydrite formation was favored. This effect of Al was seen to be the result of a slowing down in the hydrolysis/oxidation rate of the Fe(II) system.The presence of Al not only changed the direction of mineral formation, but also caused the formation of Al substitued goethites which resembled in particle size and morphology the natural aluminiferous goethite extracted from a soil.
Effects of Micro-Sized Mixtures of Kaolin Minerals on Properties of Kaolinites
Authors: Keller W. D. , Haenni R. P. 
Published: August 2006

Abstract“Kaolinites” from classic, large deposits of kaolin are shown commonly in scanning electron micrographs to be mixtures, at least in part, in microdimensions, of kaolin-mineral polymorphs.Artificial mixtures of selected kaolin polymorphs simulating the natural mixtures, also micrographed, show crystallinities intermediate between the crystallinities of the end members in X-ray powder diffractograms. Thus, apparent crystallinity interpreted from diffractograms of a kaolin specimen may be a product of kaolin-mineral mixture in microdimensions as well as from ordering in the crystals. Evaluation of the crystallinity of a kaolin from powder diffraction may be suspect if independent means, such as SEM, are not used to assess the monomineralic character of that kaolin specimen.Analogous to the apparent crystallinity of a “kaolinite” being the product of a mixture, so may other widely ranging properties of “kaolinite” be products of kaolin-mineral mixtures in microdimensions. These properties include DTA, IR, chemical composition, free energies of formation, and industrial applications.Specifications for a monomineralic, nearly ideal kaolinite are considered—the Keokuk geode variety possesses desired crystallographic and chemical properties.
The Release of Aluminum from Aluminosilicate Minerals. I. Kinetics
Authors: Cabrera F. , Talibudeen O. 
Published: August 2006

AbstractThe rates of release of Al by M NH4NO3 (pH 3) from minerals saturated with Al ions at pH 3 suggest that Al ions migrated from the surface layers and the matrix cores of kaolinite, montmorillonite, illite, and biotite, but only from the matrix core of muscovite mica. From the 0.25–0.5 μm kaolinite and montmorillonite, part of the ‘surface’ Al is released ‘instantaneously’ and the rest by first order kinetics, but the coarse 1.5–2.5 μm kaolinite has only the former component. From illite and biotite, ‘surface’ Al is released by ‘bulk diffusion’ kinetics suggesting the existence of disturbed peripheral layers of finite thickness. The diffusion coefficients, Dm, for the matrix core follow the trend: mica ≃ biotite > illite > montmorillonite > kaolinite.Based on models proposed in previous work, the ionic composition of the ‘surface’ Al is calculated. This shows that (1) this composition varies according to the mineral from 3 to 100% Al3+, the remainder being in the hydrolyzed form, and (2) the apparent hydrolysis constants are different for each mineral and significantly different from those of Al ions in solution.
Adsorption of Uranium from Solutions by Montmorillonite; Compositions and Properties of Uranyl Montmorillonites
Authors: Tsunashima A. , Brindley G. W. , Bastovanov Marija 
Published: August 2006

AbstractWyoming montmorillonite, <2-µm particle size, saturated with Na, K, Mg, Ca, and Ba ions, was reacted with uranyl nitrate solutions in the concentration range 1–300 ppm uranium. With constant amounts of clay and solution volume, the adsorption isotherms of uranyl ions on the clay followed Langmuir-type curves with increasing concentration of uranium. The maximum adsorption derived from linear Langmuir plots corresponds to the exchange capacity of the clay. Experiments with solutions of constant volume and constant ionicity, but with variable proportions of uranyl and other cations, showed that uranyl ions were strongly preferred by the clay to Na+ and K+, but less strongly than Mg2+, Ca2+, and Ba2+.Chemical analyses of uranyl montmorillonites prepared with nitrate solutions, 0.05 M and pH ≃ 2.0, gave interlayer cations (UO2)0,094H0,12. Addition of NaOH to the uranyl nitrate solution to increase the pH to 4.0 gave a montmorillonite with interlayer cations (UO2)0,083Na0,12H0,04. A fully exchanged uranyl montmorillonite was prepared with 0.05 M uranyl acetate solution, pH ∼ 4.0, followed by further treatment with 1.25 × 10−5 M solution, pH ∼ 4.5. The resulting interlayer composition was (UO2)0,19(H2O)1.15 which corresponds with the hexahydrate ion, [(UO2)−6H2O]. X-ray powder diffraction and thermal data are recorded for the fully exchanged uranyl montmorillonite.
Potassium- and Ammonium-Treated Montmorillonites. II. Calculation of Characteristic Layer Charges
Authors: Machajdík Daniel , Číčel Blahoslav 
Published: August 2006

AbstractThe formation of an interstratified structure in dioctahedral smectite was assumed to be influenced by (1) the overall layer charge density and its distribution in the structure, (2) the solvation energy of the cation, and (3) the nature of the solvation agent. By holding factors (2) and (3) constant it was possible to calculate the average local charge densities $\overline {{\rm{QA}}}$, $\overline {{\rm{QC}}} $, and $\overline {{\rm{QE}}} $ which are necessary for formation of 10-, 14-, and 16.8-Å mixed-layer phases in potassium-treated and ethylene glycol (EG) saturated smectites. The values of $\overline {{\rm{QA}}} $, $\overline {{\rm{QC}}} $, and $\overline {{\rm{QE}}} $ were 1.99, 1.2, and 0.56 esu/unit cell, respectively. Ammonium-treated smectites saturated with EG gave corresponding mean local charge densities of 2.7, 1.6, and 0.72 esu/unit cell. Calculations were made under the limiting condition QA > QC > QE > 0.For K-smectites saturated with EG, Qtot = 1.99pA + 1.2pC + 0.56pE, where Qtot is the total charge (esu/unit cell), and pA, pC, and pE are probability coefficients for 10-, 14-, and 16.8-Å phases in the interstratified structure. The above equation calculated with the aid of least squares and without the limiting condition yields
$${{\rm{Q}}_{{\rm{tot}}}} = {\rm{2}}{\rm{.05pA + 1}}{\rm{.29pC + 0}}{\rm{.33pE}}{\rm{.}}$$
There is a good agreement between values obtained for K-smectites and those for mica, vermiculite, and montmorillonite layer charges for which the above unit-structure distances are typical.
Adsorption of Ethylene Glycol on Amine-Substituted Montmorillonites
Authors: Burba John L. , McAtee James L. 
Published: August 2006

AbstractTo determine the reason why the adsorption of ethylene glycol on organo-smectites does not result in an expansion along the c-axis of the clays, smectites containing relatively small organo-ammonium ions (lauryl-, benzyl-, dibenzyl-, and dicyclohexylammonium), larger organic cations (dimethylbenzyloctadeyl- and methylbenzyldioctadecylammonium), and the heterocyclic organo-ammonium ion 1,4a-dimethyl-7-isopropyl-1,2,3,4,4a,9,10,10a-octahydro-1-phenanthrenemethylammonium and the corresponding ethoxylated compound were exposed to ethylene glycol vapor for up to several months and examined by X-ray powder diffraction (XRD), surface area, and thermogravimetric methods. Weight loss data showed that all samples adsorbed ethylene glycol. XRD data for oriented samples indicated that lauryl-, benzyl-, dicyclohexyl-, and ethoxylated heterocyclic ammonium clays expanded by one layer of ethylene glycol and that methylbenzyldioctadecylammonium smectite expanded by two layers. Dibenzyl-, dimethylbenzyloctadecyl-, and heterocyclic smectites did not expand because the clay oriented in such a manner as to leave free clay surface between the organo-ammonium cations.
Redetermination of the Lepidolite-2M1 Structure
Authors: Swanson Teresa H. , Bailey S. W. 
Published: August 2006

AbstractThe structure of a lepidolite-2M1 from Biskupice, Czechoslovakia, has been redetermined. Violations of systematic extinctions and of monoclinic equivalences plus the results of a second harmonic generation test indicate that the true symmetry most likely is C1̄. The deviation of the data set from C2/c symmetry, however, proved to be too small to permit a statistically significant refinement in C1̄. Refinement in C2/c symmetry indicated no ordering of tetrahedral cations but ordering of octahedral cations so that M(1) = Li0.93R2+0.06Fe3+0.01 and M(2) = Al0.58Li0.35□0.07. The tetrahedra are elongated to form trigonal pyramids with a rotation angle of 6.2°. The anomalous orientation of the thermal ellipsoid for the F,OH anion plus the large equivalent isotropic B value of 2.58 for F,OH and of 1.74 for the interlayer K cation, whose position is partly restricted in C2/c symmetry, suggest a lower symmetry than C2/c.The compositions of this sample and of a second lepidolite-2M1 from Western Australia fall outside the stability field of lepidolite-2M1 in the synthetic system. Structural control of the stacking sequence is discounted on the basis of the structural similarity of the lepidolite unit layers. Crystallization parameters are considered more important than composition or the structure of the unit layer in determining the stability and occurrence of different layer-stacking sequences in lepidolite.
Dissolution Kinetics of Phlogopite. I. Closed System
Authors: Lin Feng-Chih , Clemency Charles V. 
Published: August 2006

AbstractDry ground phlogopite was placed in deionized water saturated with CO2 at room temperature and pressure. The bulk solution was buffered between a pH of 5 and 6 which is close to the pH of natural weathering systems. The conditions simulated a closed system. After 1010 hr, 2.0% of the total K, 0.95% of the Mg, 0.54% of the Si, and 0.74% of the F had been released, indicating that the dissolution was incongruent. Most of the K was released within 3 min, apparently by a rapid surface exchange with hydrogen ion. One-third of the cation-exchange capacity of this phlogopite arises from cations released from the outer surfaces, while two-thirds arises from the release of more deeply seated cations. All cations exhibited decreasing release with time, the slowest being Si. The rate-controlling “factor” in the later stages is related to the release of Si. It is difficult to distinguish linear from parabolic kinetics in the later stages because of the slow rate of dissolution; however, linear kinetics is most likely. If linear kinetics is applicable, the dissolution rate of Si was 3.8 × 10−17 mole/cm2/sec. Conclusions may be affected by the length of the experimental run.
Chemical Characteristics and Origin of Ordovician K-Bentonites along the Cincinnati Arch
Authors: Huff Warren D. , Türkmenoglu Asuman Günal 
Published: August 2006

AbstractK-bentonites of the Middle Ordovician High Bridge Group along the Cincinnati arch are characterized by interstratified illite/smectite (I/S) clays with rectorite-type ordering. Approximately 20% of the layers are expandable. They are structurally similar to I/S formed at temperatures exceeding 100°C during burial diagenesis, however stratigraphic evidence and a color alteration index of < 1.5 for conodonts in associated carbonates reveals they have never been deeply buried or subjected to temperatures greater than 80°C.Whole-rock samples of K-bentonites contain ∼8% K2O and ∼4% MgO, whereas the <0.1-µm size fraction contains 6–7% K2O and 5% MgO. By comparison with a hypothetical parent ash, these values represent a net gain of K and Mg and a net loss of Si, Fe, Ca, and Na during post-depositional alteration. K-fixation is accounted for by a layer charge imbalance arising primarily out of octahedral substitution of Mg+2 for Al+3, indicating that the interstratification evolved from a montmorillonite precursor. The chemical characteristics of I/S layers in K-bentonites developed early during the alteration of volcanic ash to montmorillonite. Relatively high contents of K and Mg probably reflect both seawater and parent material composition at the time of formation. The composition and ordered stacking in K-bentonites was determined by the composition of the original smectite rather than by the pressure-temperature conditions of burial diagenesis.
Experiments on the Hydrothermal Formation of Calcium Zeolites
Authors: Wirsching Ulrike 
Published: August 2006

AbstractThe crystallization of calcium zeolites was carried out in an open hydrothermal system at 100°–250°C, using reactants that in nature are known to alter to calcium zeolites and 0.1 N CaCl2, 0.01 N CaCl2, and 0.01 N CaCl2 + 0.01 N NaOH (1:1) solutions. The following calcium zeolites were identified by X-ray powder diffraction:
Rhyolitic glass: heulandite, phillipsite, epistilbite, wairakite;Basaltic glass: phillipsite, scolecite, wairakite, levynite;Nepheline: thomsonite, wairakite, gismondine;Oligoclase: heulandite, phillipsite, wairakite.Factors that influenced the type of zeolite formed were: Si/Al ratio of the starting material, calcium/alkali ratio of the starting material, calcium activity of the reacting solution, presence of an open alteration system, and temperature. The Si/Al ratio of the starting material was of special importance in that zeolites formed with Si/Al ratios similar to or smaller than that of the parent material. The calcium/alkali ratio of the starting material also influenced the kind of the early alteration products in the open system. As alteration progressed, the importance of the starting material decreased. The importance of the calcium activity of the reacting solution and the influence of the open system increased as alteration proceeded. Because of mass transfer during alteration in the open system, the calcium content of the minerals formed increased, while their Si/Al ratio decreased. Temperature was especially effective during prolonged alteration, in that the higher the alteration temperature the smaller was the H2O content of the alteration product. Initially, H2O-rich zeolites formed transitorily at higher temperatures.
Geochemistry and Mineralogy of an Unusual Diabase Saprolite Near Columbia, South Carolina
Authors: Gardner L. R. , Kheoruenromne I. , Chen H. S. 
Published: August 2006

AbstractEmpirical reaction progress diagrams showing the trends of major element oxide concentrations (in g/cm3) as functions of bulk density for a diabase saprolite reveal discontinuities in the trends of Al2O3, MgO, H2O+, and nonextractable Fe2O3. The discontinuities coincide with discontinuities in the trends of (1) the kaolinite-smectite 001 peak-intensity ratio, (2) the smectite 002-001 peak intensity ratio, and (3) the smectite basal spacing as functions of bulk density. The discontinuities are apparently related to redox conditions in the weathering profile because they occur at a depth where siderite veins first appear in the saprolite. Oxidizing conditions in the upper part of the profile appear to have favored the formation of Ferich smectite over kaolinite, whereas reducing conditions deeper in the profile favored the formation of kaolinite over Al-rich smectite. These results indicate that where geochemical conditions favor retention of Fe over Al, smectites can form in preference to kaolinite or gibbsite even under conditions of strong leaching.
Boron Adsorption by Clay Minerals Using a Phenomenological Equation
Authors: Keren R. , Mezuman U. 
Published: August 2006

AbstractBoron adsorption by Ca forms of montmorillonite, illite, and kaolinite was determined as a function of pH and boron concentration in solution. Data from batch experiments were compared with results computed for each clay according to fitted adsorption coefficients (maximum boron adsorption and affinity constants related to the binding energy). The agreement between calculated values and experimental results indicates that a phenomenological equation can be used to predict boron adsorption on clays as a function of both of these variables. For the solution-to-clay ratios examined, the water content does not affect the boron-surface interaction as expressed by the above adsorption parameters. Because the affinity of clays for B(OH)4− is much stronger than for B(OH)3 , the adsorption maximum was obtained only under alkaline conditions at approximately pH 9.0 to 9.7. It is suggested that the pH of maximum adsorption is a function of the ratios of affinity coefficients of the three species B(OH)3, B(OH)4−, and OH− competing for the same adsorption sites. The adsorption coefficients indicate that in some cases the difference in the amount of adsorbed boron between montmorillonite and kaolinite could be either small or large, depending on the circumstances. The main factor that would affect this difference is the total amount of boron in the suspension. Estimated value of the adsorption maximum was 2.94, 11.8 and 15.1 µmole/g for Ca-kaolinite, Ca-montmorillonite, and Ca-illite, respectively.
Mössbauer Studies of Palygorskite and Some Aspects of Palygorskite Mineralogy
Authors: Heller-Kallai L. , Rozenson I. 
Published: August 2006

AbstractFe3+ ions in palygorskite occupy sites at the edges and in the interior of the alumino-silicate chains. The Mössbauer parameters of the doublets associated with Fe3+ ions in edge sites indicate that the sites have a regular 6 coordination. Fe3+ ions in the interior of the chains occupy M(1) sites in three of the samples examined and M(2) sites in the fourth. Fe3+ ions in edge positions of palygorskite become 5-coordinated when water is lost on heating. They maintain this coordination on dehydroxylation, probably by cross-linking of the chains. The temperatures at which changes occur in the X-ray powder diffraction patterns and the Mössbauer and infrared (IR) spectra differ from sample to sample. The intermediate stages observed also vary, either due to different reaction paths or to different stabilities of the intermediate phases. The deduced distribution of cations in the octahedral sheets is in good qualitative agreement with the observed IR hydroxyl absorptions.
Adsorption of Alkylphosphoric Acid on Kaolinite and Smectite in an Organic Medium (Decane)
Authors: Siffert B. , Trescol J. J. 
Published: August 2006

AbstractDi-ethyl 2-hexylphosphoric acid (di-2 EHPA) was chemisorbed on kaolinite and smectite in decane solution. The resultant isotherms were of the Langmuir type and made possible the determination of limiting adsorption values of 12 mg/g and 23.8 mg/g on H+-kaolinite and H+-montmorillonite, respectively. The acidic phosphoric group of the di-2 EHPA molecule reacted in the anionic form (RO)2PO2− with the surface cations of the clay structures. Theoretical calculations, based on structural considerations, are in agreement with the experimental data and show that adsorption took place at the rate of one alkylphosphate anion per surface cation if the phyllosilicate was dioctahedral (e.g., montmorillonite and kaolinite). If the phyllosilicate was trioctahedral (e.g., hectorite), adsorption took place at the rate of two di-2 EHPA molecules for three surface cations. Spectroscopic investigations performed with visible, ultraviolet, and infrared radiation confirmed the formation of salts or surface complexes.
Kinetic Model of Zeolite Paragenesis in Tuffaceous Sediments
Authors: Dibble W. E. , Tiller W. A. 
Published: August 2006

AbstractThe sequence of mineral reactions involving zeolites and other authigenic phases in tuffaceous sedimentary rocks can be explained by growth- and dissolution-reaction kinetics. Kinetic factors may determine the specific authigenic phases which form and the temporal and spatial constraints on the solution composition during irreversible dissolution and growth reactions in glass-bearing rocks. The glass phase generates a high level of supersaturation with respect to a variety of aluminosilicates in the pore fluid. The sequence of assemblages formed during a series of metastable reactions resembles an Ostwald step sequence. Metastable reactions occur because formation of less stable phases such as gels, clays, and disordered zeolites may lower the total free energy of the glass-bearing system faster than the growth of the stable assemblage including ordered feldspars, quartz, and micas. Eventually, after a series of steps, the most stable silicate assemblage for the bulk composition, temperature, and pressure may form. However, the formation of intermediate metastable phases can delay the attainment of equilibrium by as much as tens of millions of years.