bluuebunny/crossref_metadata_2025_split huggingface dataset:
Condensation of Olefins on Clays. Gas-Solid Systems. Part II: Spectroscopic Methods
Authors: Choren Eduardo , Moronta Alexander , Arteaga Arnedo , Sánchez Jorge 
Published: August 2006

AbstractThe adsorption of olefins at 25 °C in gas- or vapor-solid systems on 4 clays dried at 120 °C was studied by infrared spectroscopy. Products of condensation have the spectra of paraffinic oligomers. Paraffins are adsorbed onto the same structural surface hydroxyls that adsorb olefins, confirming the physical unspecific character of this adsorption. These hydroxyls do not participate in the condensation reaction. The reappearance of these hydroxyl bands after evacuation suggests that product molecules are not adsorbed onto the surface but remain on it because of its low vapor pressure. The reversible adsorption sites participate in feeding the condensation sites. Double-bond isomerization of olefins was not observed, at room temperature, on clays, alumina and silicas dried at 120 °C. When the gas-phase is evacuated or swept with inert gas, reaction does not proceed with a new monomer. Paraffins are only physically adsorbed.
Adsorption of 137Cs on Montmorillonite and Illite: Effect of Charge Compensating Cation, Ionic Strength, Concentration of Cs, K and Fulvic Acid
Authors: Staunton Siobhán , Roubaud Muriel 
Published: August 2006

AbstractA thorough understanding of the capacity of clay minerals to adsorb radiocesium is essential in order to predict the fate of this pollutant in the environment and to interpret routine measurements, such as desorbability. We have investigated the adsorption of radiocesium onto 2 contrasting reference clay minerals in dilute suspensions after a 2-h contact period. The results have been expressed as the distribution coefficient, Kd, or the selectivity coefficient, Kc. The adsorption properties have been studied with respect to various parameters: nature of the charge compensating cation, ionic strength, concentration of Cs, concentration of K and concentration of a soil-extracted fulvic acid.A Freundlich isotherm has been found to fit experimental data well for levels of adsorbed cesium in the range 10−7 to 1 mol kg−1. Evidence of surface heterogeneity is discussed, but it was not possible to deduce the exchange capacities of the groups of exchange sites with differing affinities for Cs, which are thought to exist in illites. The concentration dependence of adsorption upon montmorillonite is postulated to arise from a modification of the exchange complex with increasing presence of Cs, rather than from heterogeneity of exchange sites. Increasing ionic strength caused a decrease in the relative affinity for a trace amount of cesium on both minerals, although mass action led to a fall in Kd. This is thought to indicate a high covalent interaction between Cs and the clay surface.Potassium caused a smaller decrease in adsorption than stable Cs, which suggests that neither K nor NH4 plays a decisive role in the immobilization of radiocesium by clay minerals. There was a small decrease in adsorption upon addition of soil organic matter, which may contribute to the poor fixation capacity observed for some soils with a high organic matter content.
Properties of Goethite and Jarosite Precipitated from Acidic Groundwater, Dalarna, Sweden
Authors: Herbert Roger B. 
Published: August 2006

AbstractThis study characterizes various chemical and mineralogical properties of goethite and jarosite from a mine drainage environment using chemical extraction techniques, X-ray diffractometry (XRD), 57Fe Mössbauer spectroscopy and scanning electron microscopy (SEM). Goethite and jarosite precipitates were collected from leachate-contaminated soils and from groundwater samples that were stored for up to 3 y. The results indicate that the soil goethites have primarily microcrystalline morphologies with moderately large mean crystallite dimensions (MCD110 ∼ 40 nm), and are superparamagnetic at room temperature and magnetically ordered at 77 K. The substitution of Al for Fe in the goethites is less than 0.03 mol/mol, and there is consequently no measured contraction in the goethite unit cell volume. The jarosite unit cell dimensions, Mössbauer parameters and chemical compositions indicate that the precipitates are primarily well-crystallized K-Na-H3O solid solutions, although the presence of poorly crystalline H3O-rich jarosite is also identified in one sample.
Origin and Classification of Coastal Plain Kaolins, Southeastern USA, and the Role of Groundwater and Microbial Action
Authors: Hurst Vernon J. , Pickering Sam M. 
Published: August 2006

AbstractAlong the inner Coastal Plain, kaolinite-metahalloysite-rich, neritic muds of Cretaceous-Eocene age have undergone intense postdepositional alteration in the recharge area of the regional groundwater system. Weathering processes have had the following profound effects on the original sediments: 1) strong compositional and textural modification of both clay and non-clay minerals; 2) whitening of the originally darker sediments by partial removal of organic matter, Fe and Mn; and 3) recrystallization of kaolinite and metahalloysite, most conspicuous where there are coarse stacks and vermiforms. Where the combination of initial sediment composition and alteration intensity was most favorable, these changes have produced important deposits of commercial quality, which now sustain the world's largest kaolin production district. The earliest change was partial sequestration of iron as sulfide and concurrent destruction of some organic matter, mediated by sulfate-reducing bacteria. Subsequent weathering resulted in gradual leaching of alkalies, alkaline earths, iron and silica, and attendant nucleation and growth of minerals compatible with the compositional changes. The existence of several closely spaced erosional unconformities, separated by neritic sediments, is proof that weathering conditions commonly changed at a given site, in response to changes in thickness or lithology of the overlying rocks. Dsyoxic → ← oxic reversals modified both the rate and kind of alteration. (“Dysoxic” refers to molecular oxygen concentration too low to be toxic to anaerobes or cause abiotic oxidation; less extreme than “anoxic”.) Kaolins were produced partly by slower dysoxic weathering in saturated groundwater zones but mainly by more rapid oxic weathering in unsaturated zones, where bauxites also locally formed. Gradual transformation of some sediments to kaolin rarely began and ended in the same epoch. At several places most of the kaolinization (see “Definitions”) took place during Recent time, tens of millions of years after deposition of the sediments. Since the kaolins resulted from postdepositional alteration rather than sedimentary processes, they are better referred to as “Coastal Plain” rather than “sedimentary” kaolins.
Refinement of an Amesite-2H1 Polytype from Postmasburg, South Africa
Authors: Zheng Hong , Bailey Sturges W. 
Published: August 2006

AbstractThe crystal structure of amesite-2H1 from the Postmasburg Mn ores of South Africa has been refined to R = 4.7% using Siemens P4 rotating-anode MoKα X-ray data and SHELXL-93 software. Partial ordering of tetrahedral Si,Al and especially of octahedral Mg,Al has reduced the ideal P63cm symmetry to triclinic P1 (refined as C1). Tetrahedral rotation of 15° moves the basal oxygens toward the octahedral cations in the same layer but away from the OH H-donors of the next layers. The ordering pattern of AlIV and AlVI is unique in that the locus of Al-rich sites consists of 2 intersecting sets of zigzag lines parallel to X2 and X3, plus 2 Al-rich octahedra in layer 2 instead of the usual 1 site.
Interaction of Vermiculite with Aliphatic Amides (Formamide, Acetamide and Propionamide): Formation and Study of Interstratified Phases in the Transformation of Mg- to NH4-Vermiculite
Authors: Ruiz-Conde Antonio , Ruiz-Amil Antonio , Perez-Rodriguez Jose L. , Sanchez-Soto Pedro J. , Aragon de la Cruz Francisco 
Published: August 2006

AbstractThe Mg-vermiculite from Santa Olalla has been treated with aliphatic amides—formamide (FM), acetamide (AM) and propionamide (PM)—in aqueous solution. These treatments produce the transformation towards NH4-vermiculite and interstratified NH4-vermiculite-Mg-vermiculite phases. The NH4-vermiculite, Mg-vermiculite and interstratified (mixed-layer) phases have been identified from basal X-ray diffraction (XRD) interval peaks between 10.3 Å and 14.4 Å, and confirmed by direct Fourier transform method, as well as by atomic absorption spectrometry (AAS), infrared (IR) spectroscopy and thermal analysis.According to their NH4-vermiculite/Mg-vermiculite probability coefficients ratio (PA/PB), and PAA, these interstratified phases can be divided into 3 categories: 1) If the PA/PB ratio is ≥ 7/3 and PAA ≥ 0.7, there are interstratified phases with a strong tendency toward segregation (case of FM, AM and PM). 2) If the PA/PB ratio is between 5/5 and 6/4, with PAA in the range 0.45–0.6, there are nearly regular alternating and random interstratified phases (case of AM and PM). 3) If the PA/PB ratio is ≤ 5/5 and PAA ≤ 0.45, there are interstratified phases with a strong tendency toward alternation (case of PM).Experimental evidence reported in the present work indicates that the mechanism of interaction of Mg-vermiculite with FM, AM and PM in an aqueous medium takes place by ion exchange of NH4 between the layers. The hydrolysis of these aliphatic amides leads to the liberation of NH4+ into the medium. It has been found that the NH4+ sorption depends on the physico-chemical characteristics of the particular aliphatic amide, and the transformation of Mg-vermiculite to interstratified and/or NH4-vermiculite phases depends on the amide concentration. These treatments allow one to control the formation of interstratified and NH4-vermiculite phases.
Sorption of Atrazine by Al- and Ca-Saturated Smectite
Authors: Sawhney B. L. , Singh S. S. 
Published: August 2006

AbstractBecause of the large surface area and common occurrence of smectites in the clay fractions, they are important in sorption/desorption reactions of organic pollutants entering soils and sediments. Results of sorption and desorption of atrazine by Al- and Ca-saturated smectite reported here showed that Al-saturated smectite sorbed much higher amounts of atrazine than Ca-saturated smectite. Al-saturated smectite sorbed 3820 mg kg−1as compared to 1902 mg kg−1by the Ca-saturated smectite during 5 consecutive sorptions from 10 ppm atrazine solution. Sorption isotherms over 2–10 ppm atrazine concentration range were nonlinear in all cases. Freundich coefficients,Kf, obtained from the sorption isotherms were much higher for Al- than Ca-saturated smectite;Kfvaried from 405 to 3035 for Al-saturated and 100 to 306 for Ca-saturated. The pH values of Al- and Ca-saturated smectites were 3–4 units higher than the pKa(1.68) of atrazine, which suggests that atrazine was sorbed as neutral molecules. Stronger H-bonding between the more polarized H2O associated with the trivalent Al ion than the divalent Ca ion is likely responsible for the greater sorption by Al-smectite.
The Chemical Composition of Serpentine/Chlorite in the Tuscaloosa Formation, United States Gulf Coast: EDX vs. XRD Determinations, Implications for Mineralogic Reactions and the Origin of Anatase
Authors: Ryan P. C. , Reynolds R. C. 
Published: August 2006

AbstractThe chemical composition of mixed-layer serpentine/chlorite (Sp/Ch) in Tuscaloosa Formation sandstone was analyzed by energy dispersive X-ray spectroscopy (EDX) in the scanning electron miscroscope (SEM) and by X-ray diffraction (XRD). EDX results indicate little depth-controlled variation in composition, whereas XRD results suggest distinct decreases in octahedral Fe and tetrahedral Al. XRD-determined compositions appear to be erroneous and actually reflect progressive changes in Sp/Ch unit-cell dimensions caused by polytype transformations of Ibb layers to Iaa layers in a mixed-layer Ibb/Iaa polytype. The relative lack of variation in Sp/Ch composition, especially when compared to other studies of chlorite minerals over similar temperature ranges, is attributed to a reaction mechanism whereby mineralogic transformations (serpentine layers to chlorite layers and Ibb layers to Iaa layers) occur on a layer-by-layer basis within coherent crystallites, rather than by dissolution-precipitation crystal growth.The lack of titanium in chlorite minerals is attributed to high levels of octahedral Al3+ that prohibit inclusion of the highly charged Ti4+ in the octahedral sheet. Anatase (TiO2) in the Tuscaloosa Formation apparently formed when Ti was liberated during crystallization of Sp/Ch following the breakdown of a Ti-bearing precursor (detrital ultramafic clasts and/or odinite). Odinite, an Fe-rich 7-Å phyllosilicate that forms in some shallow marine sands, apparently existed as a short-lived, poorly crystallized intermediary between dissolution of the ultramafic clasts and formation of Sp/Ch.
Phosphates in Some Missouri Refractory Clays
Authors: Hall Robert B. , Foord Eugene E. , Keller David J. , Keller Walter D. 
Published: August 2006

AbstractThis paper describes in detail phosphate minerals occurring in refractory clays of Missouri and their effect on the refractory degree of the clays. The minerals identified include carbonate-fluorapatite (francolite), crandallite, goyazite, wavellite, variscite and strengite. It is emphasized that these phosphates occur only in local isolated concentrations, and not generally in Missouri refractory clays.The Missouri fireclay region comprises 2 districts, northern and southern, separated by the Missouri River. In this region, clay constitutes a major part of the Lower Pennsylvanian Cheltenham Formation. The original Cheltenham mud was an argillic residue derived from leaching and dissolution of pre-Pennsylvanian carbonates. The mud accumulated on a karstic erosion surface truncating the pre-Cheltenham rocks. Fireclays of the northern district consist mainly of poorly ordered kaolinite, with variable but minor amounts of illite, chlorite and fine-grained detrital quartz. Clays of the southern district were subjected to extreme leaching that produced well-ordered kaolinite flint clays. Local desilication formed pockets of diaspore, or more commonly, kaolinite, with oolite-like nubs or burls of diaspore (“burley” clay).The phosphate-bearing materials have been studied by X-ray diffraction (XRD), scanning electron microscopy-energy dispersive spectral analysis (SEM-EDS) and chemical analysis. Calcian goyazite was identified in a sample of diaspore, and francolite in a sample of flint clay. A veinlet of wavellite occurs in flint clay at one locality, and a veinlet of variscite-strengite at another locality.The Missouri flint-clay-hosted francolite could not have formed in the same manner as marine francolite. The evidence suggests that the Cheltenham francolite precipitated from ion complexes in pore water, nearly simultaneously with crystallization of kaolinite flint clay from an alumina-silica gel. Calcian goyazite is an early diagenetic addition to its diaspore host. The wavellite and variscite-strengite veinlets are secondary, precipitated from ion complexes in ground water percolating along cracks in the flint clay. The flint clay host of the variscite-strengite veinlet contains strontian crandallite. All of the phosphates contain significant amounts of strontium. The source of P, Ca and Sr was the marine carbonates. Dissolution of these carbonates produced the argillic residue that became the primordial Cheltenham paludal mud, which ultimately altered to fireclay.Preliminary firing tests show that the presence of phosphates lowers fusion temperature. However, it is not clear whether poor refractoriness is due to the presence of phosphates, per se, or to Ca, Sr and other alkaline elements present in the phosphates.
Experimental Study on the Formation of Zeolites from Obsidian by Interaction with NaOH and KOH Solutions at 150 and 200 °C
Authors: Kawano Motoharu , Tomita Katsutoshi 
Published: August 2006

AbstractExperimental alteration of obsidian was performed in 0.001 to 0.5 N NaOH and KOH solutions at 150 and 200 °C for 1 to 30 d. The products were examined by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy dispersive X-ray analysis (EDX). Changes in chemical composition and pH value of solutions during the reactions were also measured. As the pH of reacting solutions was increased, smectite, phillipsite and rhodesite crystallized progressively in NaOH solutions, while smectite, merlinoite and sanidine grew successively in KOH solutions. In addition, a small amount of less-soluble, poorly ordered boehmite was present as products of all the experiments. Smectite mainly appeared at slightly high pH, Si/Al and Na/K conditions, whereas rhodesite should be produced in extremely high pH, Na/K and Si/Al conditions. Sanidine was also formed in conditions of very high pH and Si/Al and very low Na/K. In intermediate conditions of pH and Si/Al, crystallization of phillipsite was stimulated in solutions of Na/K > 10, while formation of merlinoite was favored in conditions of Na/K < 1.
Textural Transition and Genetic Relationship between Precursor Stevensite and Sepiolite in Lacustrine Sediments (Jbel Rhassoul, Morocco)
Authors: Chahi Azeddine , Fritz Bertrand , Duplay Joelle , Weber Francis , Lucas Jacques 
Published: August 2006

AbstractIn the Tertiary lacustrine sediments of the Jbel Rhassoul (Morocco), stevensite and sepiolite, confined to the dolomitic facies, are commonly mixed at lower parts of the so-called “Formation Intermédiaire”. Transmission electron microscopy (TEM) observations reveal a relation between these 2 magnesian clay minerals. One can observe the different transition steps, from the initial folded layers of stevensite to the fibers emerging from the layers, and finally to the complete replacement of stevensite by sepiolite. That transition can also be observed by scanning electron microscopy (SEM), where the fibers seem to grow at the expense of stevensite. Thermodynamic calculations have been applied to provide geochemical conditions for the formation of sepiolite after stevensite. Early deposition of the “Formation Intermédiaire” occurred under climatic conditions varying between dry and wet. During dry periods, the relative silica enrichment and the pH decrease in the lake water should destabilize stevensite, leading to the formation of sepiolite. Subsequently, a perennial wet climate would lead to the formation of pure stevensite without any trace of sepiolite.
Crystallographic Controls on the Alteration of Microcline Perthites from the Spruce Pine District, North Carolina
Authors: Sheets Julia M. , Tettenhorst Rodney T. 
Published: August 2006

AbstractAltered perthites from a weathered pegmatite in the Spruce Pine District, North Carolina, were characterized by electron microprobe as a K-rich microcline host with lesser Na-rich plagioclase having a lamellar morphology. Light-optical and transmission electron microscopy (TEM) show microtextural elements such as phase boundaries, holes and microfractures that could serve as potential nucleation sites for alteration to clay minerals.The host microcline contains albite and pericline twinning textures that vary in character; the amount of each twinning type and/or the size of twin individuals changes on a μm scale. Plagioclase ranges from large lamellar vein and film albite (visible in the light microscope) to cryptoperthite whose size ranges from μm to perhaps 100 Å. The smallest-scale albite appears to be a late-stage phase of exsolution in which lamellae have nucleated heterogeneously on albite-twin composition planes in the microcline.Alteration is concentrated in vein and film albite, especially along grain boundaries with microcline. Powder X-ray diffraction (XRD) patterns of intensely altered pegmatite show halloysite. Holes, microfractures, vein albite/host microcline boundaries and microcline/halloysite boundaries trend parallel to the traces of (010) and {110}, suggesting that these directions are pathways along which fluids migrate. Cleavage and microfractures occur along, and holes are bounded by, these directions. Holes are associated with dislocations and the latter are observed at feldspar/clay boundaries. Twin domains and cryptoperthitic albite are less susceptible to alteration than coarse lamellar albite and regions containing negative crystals and microfractures. However, microtextures in some areas containing halloysite suggest that once fluids penetrate the crystal, alteration may proceed preferentially in more strongly twinned regions.
Quantitative Phase Analysis of Bidi-Koum Bauxites (Guinea)
Authors: Feret Frank , Authier-Martin Monique , Sajó István 
Published: August 2006

AbstractFifty-two Bidi-Koum bauxites from Guinea, Africa, of diversified chemical composition were characterized for their mineral composition. First, 14 element oxide concentrations were determined by X-ray fluorescence (XRF) using a fusion sample preparation technique. Loss of Mass (LOM) and organic carbon (OC) concentrations were also determined. The initial X-ray diffraction (XRD) phase quantification was carried out employing XDB software. This software allows for full interpretation of a sample diffractogram and helps generate initial concentrations of identified minerals based on a standardless approach. In the stage that followed, the mass balance procedure on the XDB software helped refine the final phase composition. Then, gibbsitic Al2O3 concentrations obtained by wet chemistry for all samples and kaolinitic SiO2 concentrations obtained for selected samples were compared with the concentrations obtained using the XDB software. Phases that were quantified are: gibbsite, boehmite, kaolinite, wavellite, goethite, hematite, quartz, anatase, rutile and illite. Phase concentrations were obtained for illite from K2O and for wavellite from P2O5 concentrations. The alumina substitution in the goethite lattice was also estimated.
Analytical Electron Microscopic Study of the Noncrystalline Products Formed at Early Weathering Stages of Volcanic Glass
Authors: Kawano Motoharu , Tomita Katsutoshi , Shinohara Yasushi 
Published: August 2006

AbstractFormation processes of weathering products of pumice collected from a rhyolitic pyroclastic flow deposit were investigated by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy dispersive X-ray analysis (EDX). SEM clearly showed the presence of some weathering products adhering to the surface of pumice. XRD showed that the products were composed mainly of noncrystalline materials with a relatively small amount of halloysite (10 Å). TEM and EDX revealed texture transformation sequences from the earliest weathering product to a final product of halloysite as follows: 1) precipitation of very thin flaky or film-like noncrystalline Al-hydroxide; 2) transformation into irregularly aggregated Al-Fe-Si-rich fibrous material; 3) morphological changes to rounded aggregates; 4) development of halloysite-like curled domains with successive decrease in Fe content; and 5) further development of curled domains in rounded aggregates. These materials must be metastable phases at early reaction stages with kinetics limiting formation of the stable equilibrium phase of kaolinite.