bluuebunny/crossref_metadata_2025 huggingface dataset:
Pentachlorophenol Sorption by Organo-Clays
Authors: Boyd Stephen A. , Shaobai Sun , Lee Jiunn-Fwu , Mortland Max M.
Published: August 2006

Several clay organic complexes were prepared by placing organic cations on the exchange sites of smectite clays and studied as sorbents for pentachlorophenol (PCP). The organic cations used ranged from very hydrophobic in nature (e.g., dioctadecyldimethyl+ (DODMA+)- and hexadecyltrimethyl+ (HDTMA+)-ammonium) to those having minimal hydrophobic properties, such as tetramethylammonium+ (TMA+). In general, the more hydrophobic the cation on the smectite the greater the uptake of PCP from water. For the very hydrophobic clays (DODMA+- and HDTMA+-smectite) the uptake of PCP was via non-polar interactions between the alkyl (e.g., -C18) groups on the organic cation and PCP. In a mechanistic sense, this interaction appeared to be similar to a partitioning process between water and the organic phase of the clay-organic complex. The organic phases of DODMA+-smectite were about 10 times more effective than the organic matter of natural sediments for removing PCP from water. For those organo-clays containing small organic cations (e.g., TMA+), the organic phase consisted of separate small organic moieties, such as the methyl group. This phase did not act as an effective partitioning medium despite a significant carbon content, and very little PCP was taken up. Results from this study suggest the possibility of treating soils and subsurface materials with large hydrophobic organic cations to enhance the sorptive properties of these natural materials.
Sodic Clay-Zeolite Assemblage in Basalt at Boron, California
Authors: Wise William S. , Kleck Wallace D.
Published: August 2006

An assemblage of clay minerals, Na-zeolites, Fe- and Sb-sulfides, and borates occurs in cavities in the basalt flow that underlies the main borax ore body exposed by the U.S. Borax open pit at Boron, Kern County, California. Analcime and saponite are widespread in cavities and fractures near the top of the basalt. Part of the basalt recently exposed, although restricted in distribution, contains a much more diverse assemblage of diagenetic minerals. Although only a few different minerals occur in each cavity, the composite order of deposition is: ferroan saponite, pyrrhotite, saponite, phillipsite, gmelinite, clinop-tilolite, herschelite, analcime, greigite, rhodochrosite, searlesite, borax, calcite, and colemanite. In some cavities early-formed zeolites appear to have dissolved as later ones crystallized.

Microprobe analyses of the zeolites yielded the following compositions: phillipsite, Na4.28K0.08(Al4.36-Si11.64O32)·xH2O (Si/Al = 2.67); gmelinite, Na6.64K0.10(Al6.80Si17.22O48· xH2O (Si/Al = 2.53); herschelite, Na2.96K0.24(Al3.21Si8.79O24)· xH2O (Si/Al = 2.75); clinoptilolite, Na6.48K0.56(Al7.15Si28.77O72) · xH2O (Si/Al = 4.02); analcime, Na14.02K0.09(Al13.33Si34.44O96)· xH2O (Si/Al = 2.58).

These zeolites formed by reactions between the basalt and evolving fluids, which were controlled by the development of an overlying, Na-borate lake. The wide distribution of saponite, analcime, and searlesite suggests that these minerals formed by the diagenetic reaction between basaltic glass and Na- borate water. The localized occurrence of the complex mineral assemblage, including some of the saponitic clay and the zeolites, phillipsite, gmelinite, and clinoptilolite, formed through a different process, perhaps deuteric or hydrothermal alteration of the basalt, before the lake developed. Because these zeolites are extraordinarily rich in Na, cation exchange may have taken place as the pore fluids became increasingly Na rich. In the latest stages of mineral growth, each of these zeolites was apparently partially dissolved and epitaxially overgrown by a second generation crystal, phillipsite on phillipsite, herschelite on gmelinite, and sodian heulandite on clinoptilolite.
Authigenic Kaolinite and Dickite Associated with Metal Sulfides—Probable Indicators of a Regional Thermal Event
Authors: Keller W. D.
Published: August 2006

Authigenic, well-crystallized kaolinite and dickite occur within sulfide mineral deposits (mine-size to hand-specimen size occurrences) of the Mississippi Valley type in Arkansas, Kansas, Missouri, Iowa, Wisconsin, Illinois, and Indiana. Fluid inclusions in these rocks indicate temperatures of formation as high as 140°C. These authigenic kaolin-group minerals are probable geologic indicators of a regional thermal event. Such elevated temperatures are probably the result of heated waters derived from deeply buried sedimentary or tectonic basins, of passage of the region over a hot spot, or of an episode of thinning of the crustal plate in the mid-continent region.
Influence of Silicon and Phosphorus on Structural and Magnetic Properties of Synthetic Goethite and Related Oxides
Authors: Quin Thomas G. , Long Gary J. , Benson Christopher G. , Mann Stephen , Williams Robert J. P.
Published: August 2006

A series of synthetic goethites containing varying amounts of Si and P dopants were characterized by X-ray powder diffraction, electron diffraction, microbeam electron diffraction, and Mössbauer spectroscopy. Very low level incorporation produced materials having structural and spectral properties similar to those of poorly crystalline synthetic or natural goethite. At higher incorporation levels, mixtures of noncrystalline materials were obtained which exhibited Mössbauer spectra typical of noncrystalline materials mixed with a superparamagnetic component. Microbeam electron diffraction indicated that these mixtures contained poorly crystalline goethite, poorly crystalline ferrihydrite, and a noncrystalline component. If the material was prepared with no aging of the alkaline Fe3+ solution before the addition of Na2HPO4 or Na2SiO3, materials were obtained containing little if any superparamagnetic component. If the alkaline Fe3+ solution was aged for 48 hr before the addition, goethite nuclei formed and apparently promoted the precipitation of a superparamagnetic phase. The Mössbauer-effect hyperfme parameters and the saturation internal-hyperfine field obtained at 4.2 K were typical of those of goethite; however, the Mössbauer spectra indicated that the ordering temperature, as reflected in the relaxation rate and/or the blocking temperature, decreased with increasing incorporation of Si and P. The complete loss of crystallinity indicates that Si and P did not substitute for Fe, but rather adsorbed on crystal-growth sites, thereby preventing uniform crystal growth.
Verification of the Triclinic Crystal Structure of Kaolinite
Authors: Young R. A. , Hewat A. W.
Published: August 2006

On the basis of neutron diffraction studies, the two inner-hydroxyl ions in highly ordered kaolinite were recently shown to be differently oriented. One of the inner-hydroxyl ions points generally toward a hole in the octahedral sheet and the other toward a hole in the tetrahedral sheet. These orientations and the locations of the other atoms in the primitive triclinic unit cell have now been determined for a sample of Keokuk kaolinite with improved precision compared with that reported earlier. Rietveld structure refinement was carried out for the entire crystal structure simultaneously (99 atom positional and 17 other parameters) with each of two newly collected sets of high-resolution neutron powder diffraction data. The different orientations of the inner-hydroxyl ions are the most marked evidence that the unit cell is not C centered. The positions of the inner-surface hydrogen atoms provide further evidence in that all differ from a C-centered relationship by six to eight estimated standard deviations in their y coordinates. The cell is, therefore, not centered. The space group is P1.
Components of Surface Free Energy of Some Clay Minerals
Authors: Jańczuk Broniseaw , Białopiotrowicz Tomasz
Published: August 2006

The wetting contact angle was measured for water drops settled on the surface of pressed discs of kaolinite, alumina, bentonite, marble, montmorillonite, and quartzite immersed in hexane, octane, dodecane, cis-decalin, and air. Minimum and maximum values of the contact angle were obtained for the given systems of solid-water drop-hydrocarbon, depending on the manner of disc preparation. Using both minimum (θmin) and maximum (θmax) values of the contact angle, values of the dispersion component (γsd) of surface free energy of these solids were calculated from the equation which was derived on the basis of an equilibrium state of the system solid-water drop-hycrocarbon for two different hydrocarbons. The values of γsd for kaolinite, alumina, bentonite, marble, montmorillonite, and quartzite obtained from θmin are 83.5, 98.1, 98.9, 80.2, 95.9, and 89.7 mJ/m2, and from θmax are 73.1, 85.0, 84.4, 75.8, 85.5, and 75.5 mJ/m2. These values for marble and quartzite are similar to those in the literature (marble = 67.7 mJ/m2; quartzite = 71.3 and 76.0 mJ/m2). The values of the dispersion components of surface free energy for marble and quartzite covered with a water film (γsfd) were found to be: 41.8, 36.9; 49.2, 42.5; 49.6, 42.2; 40.2, 38.1; 48.1, 42.8; and 44.9, 38.0 mJ/m2, respectively. Values of γsfd for kaolinite, bentonite, and montmorillonite agreed well with those obtained from hydrocarbon adsorption isotherms determined by differential thermal analysis (35.5, 36.5, and 37.4 mJ/m2).

Using values of γsfd and contact angles measured in the system solid-water drop-air, the nondispersion component of the surface free energy of solids with adsorbed water film (γsfn) was calculated from the modified Young equation. The values of γsfn for kaolinite and quartzite are as follows: 55.8, 69.0; 85.6, 94.0; 52.1, 75.0; 64.7, 68.9; 54.9,71.3; and 59.2,74.4 mJ/m2. The values of the nondispersion components determined for kaolinite, bentonite, and montmorillonite agreed well with those obtained by differential thermal analysis (67.6, 78.3, and 65.5 mJ/m2, respectively). Further, based on the assumption that the adsorbed water film decreased the surface free energy of these solids by the value of the work of spreading wetting, the nondispersion component (γsn) of the surface free energy of the solids was calculated to be: 86.9,129.6; 169.5, 187.7; 67.1, 144.8; 117.5, 129.3; 83.0, 135.7 and 100.2, 143.4 mJ/m2. These calculated values of the nondispersion component of marble and quartzite surface free energy agree with those obtained from adsorption isotherms determined by chromatographic and differential thermal analysis (marble = 103.8, 106.4; quartzite = 112, 115, 153.6 mJ/m2).
Weathering of Chlorite and Vermiculite in Ultramafic Rocks of Cabo Ortegal, Northwestern Spain
Authors: Buurman P. , Meijer E. L. , van Wijck J. H.
Published: August 2006

Chloritic veins in serpentinite and their weathering products were analyzed by X-ray powder diffraction (XRD) and X-ray fluorescence spectrometry (XRF). Chlorite formed during the Hercynian-age orogenesis had apparently been partly transformed to high-charge vermiculite during subsequent metamorphism of the rocks. The idealized structural formulae for these minerals are (Al1.9Fe3+0.2Fe2+0.4Mg9.2Cr0.2)(Si5.8Al2.2)O20(OH)16 and X1.3(Fe3+0.7Fe2+0.1Mg5.2Ni0.1)(Si5.8Al2.2)O20(OH)4, respectively. This transformation appears to have taken place by the removal of the hydroxy-interlayer from the chlorite without major effect on the rest of the structure. It is not clear whether other hydroxy-interlayered vermiculites containing less tetrahedral aluminum were intermediate weathering products or inherited minerals. The ultimate weathering product of chlorite and vermiculites was a Fe3+-rich smectite, which probably formed by precipitation from solution.
Electron Transfer Processes Between Hydroquinone and Hausmannite (Mn3O4)
Authors: Kung K.-H. , McBride M. B.
Published: August 2006

A kinetic study of the oxidation of hydroquinone by aqueous suspensions of hausmannite at pH 6 was conducted using an on-line analysis system. Electron transfer between hydroquinone and the oxide was monitored by ultraviolet and electron spin resonance spectroscopy to measure the loss of hydroquinone and the appearance of oxidation products. Although hydroquinone oxidized on the surface of the oxide and the oxide surface was altered after the reduction, hydroquinone and its oxidation products did not adsorb strongly on the surface. At a high concentration of hydroquinone, p-benzosemiquinone free radicals persisted in aqueous solution and were oxidized by dissolved O2. Calculations based on the thermodynamic stabilities of the oxide and the organic species involved show that the formation of p-benzosemiquinone radical by Mn reduction is feasible. The presence of the radicals indicates that the oxidation of hydroquinone by the oxide proceeded by a one-electron transfer process. At high organic/ oxide ratios, an increase in the amount of hausmannite dissolved with increasing hydroquinone concentration suggests that the reduction of the oxide by the organic was not limited to the surface layer of the oxide. At a high concentration of hydroquinone, polymers were detected in solution, suggesting that radical-mediated reactions played a role in the polymerization process. A reaction scheme is proposed to explain the effect of the Mn oxide to hydroquinone ratio on the consumption of O2 and the appearance of quinone, p-benzosemiquinone, and polymers in solution.
Chromate Adsorption by Kaolinite
Authors: Zachara J. M. , Cowan C. E. , Schmidt R. L. , Ainsworth C. C.
Published: August 2006

Chromate (CrO42−) adsorption was investigated on kaolinite (0.2–2 μm) saturated with NaClO4 over a range of pH. Adsorption increased with decreasing pH because of protonation of chromate and/or variable charge sites on kaolinite. Chemical pretreatment to remove noncrystalline and crystalline oxide contaminants affected the magnitude of CrO42− adsorption, but not the pH range over which CrO42− adsorbed. Chromate adsorption at different sorbate and sorbent concentrations increased below the pHzpc for the kaolinite edge, suggesting the formation of weak surface complexes. If CrO42− and SO42− were present at equal concentration (5.0 × 10−7 M), the two solutes sorbed independently, suggesting binding to separate sites. The presence of excess SO42− (5.0 × 10−4 M), however, unexplainably enhanced CrO42− adsorption. The adsorption of both Chromate and sulfate can be described in terms of a site-binding model of the kaolinite edge, in which the edge is viewed as composite layers of Al and Si oxide. Surface complexation constants for CrO42− on kaolinite were similar to those for alumina, pointing to the importance of Al-OH edge sites in Chromate adsorption.
Hydrothermal Alterations of Hisingerite Material from a Basalt Quarry Near Geelong, Victoria, Australia
Authors: Shayan Ahmad , Sanders John V. , Lancucki Christopher J.
Published: August 2006

To understand the genetic relationship between hisingerite material in the joints of an overlying grey basalt and nontronite and Fe-rich saponite in the joints and matrix of a more deuterically altered, underlying green basalt, the hisingerite material was treated in a series of hydrothermal experiments. No well-ordered clay mineral was produced at temperatures <340°C, although extended treatment for 445 days and at 110°C or 42 days at 180°C resulted in the formation of materials that gave broad, weak, basal X-ray powder diffraction (XRD) reflections characteristic of 2:1 phyllosilicates. Hematite did not form at 110°C, but it did form at 180°C in 1- and 6-week runs. Treatments at 340°C in Pt, Ag-Pd, and Au containers resulted in mixtures of Fe-rich saponite + hematite, but the same starting material treated at 340°C in stainless steel yielded, in addition, some chlorite, probably due to the more reducing conditions in the stainless steel container. Treatment of the unaltered grey basalt at 340°C and 50 MPa for 10 days resulted in complete alteration of olivine (and probably glass) to a trioctahedral smectite.

The Fe-rich saponite produced by the hydrothermal treatment of the hisingerite material has a composition and XRD pattern similar to the Fe-rich saponite found in the green basalt and an XRD pattern similar to that produced by the hydrothermal treatment of the grey basalt; thus these clays may have had a similar origin. The compositions and XRD patterns of these clays are not similar, however, to those of the nontronite in the joints of the green basalt. The nontronite probably formed during a subsequent low-temperature alteration.
Comparison of Clay and Zeolite Mineral Occurrences in Neogene Age Sediments From Several Deep Wells
Authors: Velde B. , Iijima A.
Published: August 2006

Clay and zeolite mineral assemblages were determined for five deep wells in volcano-clastic sediments (Japan) and for one well in mudstones (California). The clay mineral suites in these wells showed a gradual change with depth of illite/smectite (I/S) composition, which increases in smectite content in the upper portion towards a fully expandable mineral (2–3-km depth) and then decreases in smectite content with depth (2–5 km). The temperature of transformation or recrystallization to a fully expandable smectite mineral is about 60°–70°C in non-zeolite bearing rocks and 70°–90°C in zeolite-bearing rocks, with no apparent dependence on time. Comparison is made between the I/S smectite content in the lower part of the wells (i.e., below the occurrence of the fully expandable mineral) and the zeolite mineral zone boundaries. The 60% smectite composition was found at 108°–118°C maximum burial temperatures. The zeolite II/III zone boundary, i.e., the onset of the analcime zone, occurs between 85° and 95°C and may be slightly time-related in the span of 1–15 Ma. The clay and zeolite minerals can be used as temperature indicators in the range of the Neogene age.
Evidence for the Formation of Interlayer Polyacrylonitrile in Kaolinite
Authors: Sugahara Yoshiyuki , Satokawa Shigeo , Kuroda Kazuyuki , Kato Chuzo
Published: August 2006

A kaolinite-polymer intercalation complex was apparently formed for the first time by the polymerization of acrylonitrile between the kaolinite layers. A kaolinite-ammonium acetate intercalation complex was dispersed in acrylonitrile monomer. The monomer was apparently incorporated between the layers by displacing intercalated ammonium acetate. After the removal of excess monomer, the intercalation complex was heated to cause polymerization. The resulting kaolinite-polyacrylonitrile (PAN) intercalate showed a basal spacing of ∼ 13–14 Å. On heating the complex at 220°C for 1 hr in air, the spacing decreased slightly. The hydrogen bond between the hydroxyls of kaolinite and probably the C≡N group of PAN was not affected after heating at 220°C. Even after heating at 400°C, the layers expanded. Because the starting kaolinite-ammonium acetate intercalation complex decomposed at a much lower temperature, these observations strongly suggest the presence of PAN between the layers.
Sintering of Montomorillonites Pillared by Hydroxy-Aluminum Species
Authors: Tichit D. , Fajula F. , Figueras F. , Ducourant B. , Mascherpa G. , Gueguen C. , Bousquet J.
Published: August 2006

The sintering of montmorillonites pillared by hydroxy-Al species was investigated by several techniques. The change of the microporosity of the pillared interlayer clay with temperature shows that sintering was mainly due to the loss of microporosity. On calcination of the parent clay at 760°C, the X-ray powder diffraction pattern did not change; the 060 line shifted only slightly from 8.988 to 9.017 Å. The infrared (IR) spectrum suggested some dehydroxylation, but the structure appears to have been preserved. On calcination of the pillared clay at >700°C, the intensity of the 001 line decreased steadily, the 060 line broadened, and the b parameter decreased slightly from 8.988 to 8.928 Å. Fe3+ ions apparently occupied only one site after calcination at 300°C and two sites after calcination at 700°C. Smaller isomer shifts and higher quadrupole splittings in the Mössbauer spectra suggest that calcination produced more covalent bonding of Fe3+ and a highly distorted structure. The IR spectrum was significantly modified by calcination of the sample, and the 935- and 1125-cm−1 bands disappeared and the 1035-cm−1 band broadened. These results suggest that at <700°C the pillars sintered and that the clay progressively decomposed at >750°C. The pillaring-induced decrease of thermal stability of the clay was likely due to the introduction of protons during the first step of the preparation. The thermal stability of these Al-pillared interlayer complexes is comparable to that reported for hydroxy-silicoaluminum montmorillonites and fluorhectorites.
Mössbauer Spectroscopic Identification of Iron Oxides in Nontronite From Hohen Hagen, Federal Republic of Germany
Authors: Lear Paul R. , Komadel Peter , Stucki Joseph W.
Published: August 2006

Iron impurities in the Hohen Hagen nontronite (NG-1) were identified as maghemite and goethite. The phase identified as maghemite was magnetically ordered at both room temperature and 87 K, with hyperfine magnetic fields of 48.6 and 50.7 tesla, respectively. Due to the magnetic properties of this phase, it was easily separated from aqueous dispersions of the clay using a hand magnet. X-ray powder diffraction analysis revealed maghemite, quartz, and phyllosilicate in the magnetically separated phase. The impurity identified as goethite remained in the non-magnetic <2-μm fraction of the clay, displayed magnetic order only at 87 K (47.44 tesla hyperfine field), and accounted for about 8% of the total area of the Mössbauer spectrum.
Relative Solubility of Corundum, Gibbsite, Boehmite, and Diaspore at Standard State Conditions
Authors: Peryea F. J. , Kittrick J. A.
Published: August 2006

The solubilities of HCl-treated samples of corundum, gibbsite, boehmite, and diaspore in aqueous solutions at 298 K and one atmosphere pressure were determined from undersaturated and supersaturated initial conditions. Solution characteristics at apparent equilibrium were measured and used to calculate equilibrium constants (Kr) for mineral dissolution reactions:
$$\begin{array}{l} A{l_2}{O_3}\left( {corundum} \right) + 3{H^ + } = A{l^3} + 1.5\,{H_2}O,\\ Al{\left( {OH} \right)_3}\left( {gibbsite} \right) + 3{H^ + } = A{l^3} + 3\,{H_2}O,\\ and\\ AlOOH\left( {boehmite\,or\,diaspore} \right) + 3{H^ + } = A{l^3} + 2{H_2}O, \end{array}$$
Assuming solid phase and water activities of unity, log Kr = 3pH - pAl3+ for all three equations. The calculated log Kr values were: 9.01 ± 0.05 (corundum), 7.76 ± 0.14 (gibbsite), 7.49 ± 0.09 (boehmite), and 6.75 ± 0.24 (diaspore), indicating that the relative thermodynamic stabilities under the experimental conditions were: corundum < gibbsite < boehmite < diaspore. The gibbsite value agreed well with that determined independently by another research group using acid-treated subsamples of the same source mineral (7.70 ± 0.02). The calculated Gibbs free energies of formation (kJ/mole) were: -1587.4 ± 2.1 (corundum), -1156.7 ± 1.6 (gibbsite), -921.0 ± 1.5 (boehmite), and -925.1 ± 2.0 (diaspore). The Δ Gfo values of the acid-treated minerals were 1.8 to 12.4 kJ/mole more negative than values recently compiled for untreated mineral samples. This result is attributed to the removal of reactive surface coatings that isolated the bulk mineral phases from the solution phase.
Modified Clays for the Adsorption of Environmental Toxicants: Binding of Chlorophenols to Pillared, Delaminated, and Hydroxy-Interlayered Smectites
Authors: Zielke Richard C. , Pinnavaia Thomas J.
Published: August 2006

Due to their unique polarity, pore-size distribution, and high surface areas, pillared and delaminated clays are potentially useful materials for the adsorption of environmental toxicants. To determine their properties for adsorption of chlorinated phenols, alumina-pillared montmorillonite (APM), chromia-pillared montmorillonite (CPM), and alumina-delaminated Laponite (ADL) were reacted with aqueous pentachlorophenol (PCP) solutions in batch equilibrium experiments. An hydroxy-Al Laponite (HAL) in which the Na+ exchange ions were replaced by ions of the type Al13O4(OH)(24+x)(H2O)(12-x)(7-x)+ was included in the study. With ADL as the adsorbent, the extent of PCP adsorption increased with decreasing pH, and then became constant at pH ≤ pKa. Thus, the neutral phenol was preferred over the phenolate form. Binding of neutral PCP at pH 4.7 to all adsorbents never reached saturation values, and the loadings achieved were limited by the water solubility of the adsorbate. Among the pillared and delaminated clays investigated, ADL exhibited the largest capacity for physical adsorption of PCP at pH 4.7. Differences in the PCP binding capacities for APM, CPM, and ADL suggested that adsorption was dependent on the pore structure and surface composition of the modified clay adsorbent, not on surface area alone. HAL exhibited quantitative uptake of PCP at the 8 µmole/g level, indicating that a chemi-sorption mechanism may operate for PCP binding to this adsorbent. Adsorption of 3-chlorophenol, 3,5-dichlorophenol, and 3,4,5-trichlorophenol by ADL at pH 7.4 increased as the degree of hydrophobicity and chlorination of the phenol increased; hence, the binding capacity was not limited by the molecular size of the adsorbate. In contrast to the adsorption properties observed for pillared, delaminated, and hydroxy-interlayered clays, Na+-montmorillonite and Na+-Laponite did not adsorb PCP from aqueous solution.
Cacoxenite in Miocene Sediments of the Maryland Coastal Plain
Authors: Hearn Paul P. , McCartan Lucy , Soller David R. , Krohn M. Dennis , Gonzalez Virginia M.
Published: August 2006

Cacoxenite having the composition (Al4.0Fe22.5O7.1(OH)14.3(PO4)17(H2O)23.7)·50.3H2O was identified in a bed of mature quartz sand in the Miocene Calvert Formation near Popes Creek, Maryland. This is the first reported occurrence of this mineral in Atlantic Coastal Plain sediments north of Florida. The cacoxenite occurs as silt-size to sand-size grains, both as irregularly shaped aggregates and as radiating arrays of delicate acicular crystals. The presence of discrete cores and overgrowths in some grains indicates at least two generations of crystal growth. Electron microprobe analyses reveal excess Si and Al (relative to the ideal composition), which is believed to reflect ultra-fine clay particles within the cacoxenite grains. Admixed clays probably served as a substrate for the formation of ferric oxyhydroxides, which were subsequently converted to cacoxenite through the addition of dissolved phosphorus.
Celadonite and its Transformation to Smectite in an Entisol at Red Rock Canyon, Kern County, California
Authors: Reid D. A. , Graham R. C. , Edinger S. B. , Bowen L. H. , Ervin J. O.
Published: August 2006

A green, Lithic Torriorthent soil derived from a celadonite-rich, hydrothermally altered basalt immediately north of the Mojave Desert region in southern California was studied to investigate the fate of the celadonite in a pedogenic weathering environment. Celadonite was found to be disseminated in the highly altered rock matrix with cristobalite, chalcedony, and stilbite. X-ray powder diffraction (XRD) showed the soil material to contain celadonite having a d(060) value of 1.510 Å, indicative of its dioctahedral nature. Very little smectite was detected in the parent material, whereas Fe-rich smectite was found to be abundant in the soil. The Fe-smectite and celadonite were identified as the sole components of the green-colored clay fraction (<2 µm) of all soil horizons. The soil clay showed a single d(060) value of 1.507 Å, indicating that the smectite was also dioctahedral and that its b-dimension was the same as that of the celadonite. Mössbauer spectroscopy showed that the chemical environments of Fe in the rock-matrix celadonite and in the smectite-rich soil clay were also nearly identical. These data strongly suggest a simple transformation of the celadonite to an Fe-rich smectite during soil formation.

Supporting evidence for this transformation was obtained by artificial weathering of celadonite, using sodium tetraphenyl boron to extract interlayer K. The intensity of the 001 XRD peak (at 10.1 Å) of celadonite was greatly reduced after the treatment and a peak at 14.4 Å, absent in the pattern of the untreated material, appeared. On glycolation of the sample, this peak expanded to 17.4 Å, similar to the behavior of the soil smectite. The alteration of celadonite to smectite is a simple transformation requiring only the loss of interlayer K. The transformation is apparently possible under present-day conditions, inasmuch as the erosional landscape position, shallow depth, and lack of significant horizonation indicate that the soil is very young.
Determination of Surface Free Energy of Kaolinite
Authors: Chibowski Emil , Staszczuk Piotr
Published: August 2006

The adsorption of n-octane and water vapor on natural kaolinite was measured. From adsorption isotherms film pressures were determined which were then used to calculate the dispersion and nondispersion components of the kaolinite surface free energy. In addition, thermodesorption of water from the kaolinite surface was determined. These results suggest that physically adsorbed water remained on the kaolinite surface, even at temperatures as great as 125°C. Therefore, experimentally determined dispersion and nondispersion components appear to relate to the surface precovered with a film of water. These values are: γSf(w)d = 34.4 mJ/m2 for dispersion interactions and γSf(w)n = 60.2 mJ/m2 for nondispersion interactions. Assuming a kaolinite surface precovered with a film of water, which decreased the free energy by the work of spreading, the following components of the energy for the bare surface were calculated: γSd = 67.6 mJ/m2 and γSn = 103.4 mJ/m2, for dispersion and nondispersion components, respectively.
Mobilization of Quartz Fines in Porous Media
Authors: Cerda César M.
Published: August 2006

The onset of the mobilization of fine particles of quartz (fines) in sandpacks was determined by comparing the theoretically calculated hydrodynamic and colloidal forces acting on a fines particle near a representative sand grain. The results show that the mobilization of fines depends strongly on the chemistry of fluids present in the reservoir. Specifically, a critical electrolyte concentration exists for mobilization, which depends on the pH. For large particles of fines and relatively high fluid velocity, the mobilization of fines may depend on the fluid velocity, but in a narrow range of electrolyte concentration. The types of interactions between the fines and sand grain surfaces were corroborated by direct visual observations using a traveling microcell pack.

The mobilization of fines in sandstones leads to a reduction of permeability (i.e., a reduction of the hydraulic conductivity).
Coprecipitation of Iron and Aluminum During Titration of Mixed AP+, Fe3+, and Fe2+Solutions
Authors: Bertsch P. M. , Miller W. P. , Anderson M. A. , Zelazny L. W.
Published: August 2006

Potentiometric titration analysis was used to examine the hydrolysis behavior of Fe2+Fe3+, and Al3+in pure solution and in mixture, in order to evaluate the potential for coprecipitation and mixed solid-phase formation. Mixtures of Fe3+and Al3+did not interact during neutralization; base consumed in their respective buffer regions was equivalent to the total metal added. Fe2+-Al3+solutions, however, showed excess base consumption in the Al3+buffer region, indicating hydrolysis of Fe2+at lower than normal pH. Ferric/ferrous iron analyses of systems at the Al endpoint (pH 5.5) showed amounts of oxidized Fe equivalent to the excess base consumption (∼10% of total Fe), with substantial amounts of Fe2+sorbed to or occluded within Al polymers present. Increased electrolyte levels or the presence of SO42-inhibited oxidation and sorption of Fe2+on Al surfaces, suggesting that Fe hydrolysis and oxidation was catalyzed at the surfaces. Increasing Al3+: Fe2+ratios in the titrated solutions also increased the amount of Fe2+coprecipitation, supporting a surface-mediated reaction mechanism. Ferrous iron oxidation was sensitive to O2levels, which also affected the amount of coprecipitation. These findings suggest that surface-facilitated oxidation of Fe2+may be important in the formation of mixed Fe-Al mineral phases in dilute soil solutions.
Weathering of Iron-Bearing Minerals in Soils and Saprolite on the North Carolina Blue Ridge Front: I. Sand-Size Primary Minerals
Authors: Graham R. C. , Weed S. B. , Bowen L. H. , Buol S. W.
Published: August 2006

The weathering products of primary biotite, chlorite, magnetite, and almandine in mica gneiss and schist in the North Carolina Blue Ridge Front were determined. Sand-size grains of biotite, the most abundant, readily weathered mineral in the parent rock, have altered to interstratified biotite/vermiculite, vermiculite, kaolinite, and gibbsite in the saprolite and soil. Fe2+-chlorite in the parent rock was relatively resistant to chemical weathering, which appears to be confined to the external surfaces of particles. Magnetite grains in the saprolite are essentially unaltered, but those in the soil contain abundant crystallographically controlled etch pits and are coated with oxidation crusts. Almandine altered to goethite, hematite, and gibbsite as the rock weathered to saprolite. Extensively weathered almandine grains were found to contain etch pits and what appeared to be oxide coatings. Apparently, a rapid release of Fe during weathering produced hematite, whereas slower release of Fe favored the formation of goethite.
Alcohothermal Treatments of Gibbsite: Mechanisms for the Formation of Boehmite
Authors: Inoue Masashi , Kitamura Kazuhisa , Tanino Hirokazu , Nakayama Hiroyuki , Inui Tomoyuki
Published: August 2006

Gibbsite samples of various particle sizes (0.2–80 μm) were heated at 250°C in a series of straight-chain primary alcohols under the autogenous vapor pressure of the alcohol (alcohothermal treatment of gibbsite). The treatment in ethanol yielded pure boehmite, the morphology of which was similar to that of the boehmite obtained by hydrothermal treatment of gibbsite. In middle-range alcohols, the boehmite yields were low (50% if 80 μm gibbsite was used), and the products were contaminated by a poorly crystallized phase, having a χ-alumina-like structure. The products preserved the morphology of the originating gibbsite, this feature being similar to the thermal dehydration of gibbsite. Complete conversion to boehmite was also attained in mineral oil (a hydrocarbon mixture, which was used as a limit of higher alcohol. The morphology of the boehmite formed in this medium was identical to that of the product prepared by thermal dehydration of gibbsite in a sealed bomb without a medium. If fine particle-size gibbsite was used, the yield of boehmite decreased and the yield of the poorly crystallized phase increased in all the media.

The reaction mechanisms may be discussed in terms of the reported mechanisms for the thermal and hydrothermal formations of boehmite from gibbsite. Thus, in lower alcohols boehmite formed by a dissolution-recrystallization mechanism, whereas in middle-range or higher alcohols it formed by intra-particle hydrothermal reaction mechanism proposed by de Boer and coworkers for the thermal dehydration of gibbsite. The difference in behavior in middle-range and higher alcohols can be explained in terms of the solubility of water in the medium: In the middle-range alcohols, water molecules formed by partial dehydration of gibbsite were removed from the gibbsite particles into the medium so that dehydration proceeded in a manner similiar to that of thermal dehydration, whereas in the higher alcohols, the low solubility of water in the medium allowed the water molecules to remain on the surface of the particles, thereby promoting the complete hydrothermal formation of boehmite.
Structure of a 1,4-Diazabicyclo[2,2,2]Octane-Vermiculite Intercalate
Authors: Slade P. G. , Schultz P. K. , Tiekink E. R. T.
Published: August 2006

1-4-diazabicyclo[2,2,2]octane dihydrochloride (DABCO·2HC1) was reacted with two vermic-ulite samples to produce intercalates which, at room temperature, had relatively sharp, single crystal X-ray diffraction patterns. At higher temperatures (250°C) the stacking order decreased, and consequently the 0kl reflections with k ≠ 3n became increasingly diffuse. The stacking order of previously heated samples returned when they were cooled. A superstructure was present in which DABCO cations occupied the corners and center of a cell 3a × b, compared with the standard vermiculite cell.

DABCO-intercalated Nyasaland vermiculite had the following monoclinic subcell (symmetry C1) parameters under ambient conditions: a = 5.341(2), b = 9.249(3), c = 14.50(1) Å, and ß = 96.98(5)°. Differential Fourier analyses and least-squares refinement led to a final R value of 12.6% for 1814 reflections. The crystal structure analysis showed that individual DABCO ions were not symmetrically positioned between the silicate layers. A network of inorganic cations and water molecules was also present and governed the interlayer separation. At 250°C the d value was 13.7 Å, consistent with a dehydrated structure, in which each organic pillar has one amino group keyed into a ditrigonal cavity and the other amino group riding on the basal oxygens of an opposite tetrahedron.
Solid State Reaction of Sodium Carbonate with Montmorillonite at 550°C
Authors: Natale I. M. , Helmy A. K.
Published: August 2006

The isothermal solid state reactions of Na2CO3 and other salts at 550°C with montmorillonite and with 1:1 mixtures of montmorillonite-illite and montmorillonite-chlorite were investigated. At a concentration of 20 wt. %, Na2CO3 caused the complete destruction of the X-ray powder diffraction (XRD) pattern of montmorillonite alone and in mixtures with other clays. Less deterioration of the XRD pattern was found for NaOH, NaF, K2CO3, and Li2CO3. NaCl, Na2SO4, Na3PO4, MgCO3, and CuCO3 had no effect on the XRD traces of montmorillonite. The time dependence of the Na2CO3-montmorillonite interaction at 550°C suggested that the reaction is diffusion controlled in three dimensions, i.e., diffusion was directed from the surface of the particle towards its center.
Stacking Faults in Kaolin-Group Minerals in the Light of Real Structural Features
Authors: Bookin A. S. , Drits V. A. , Plançon A. , Tchoubar C.
Published: August 2006

A comparison of the structural characteristics of the kaolin-group minerals, mainly kaolinite and dickite, shows that they differ in both the two-dimensional periodicity in the 1:1 layers and the rotation angles of the polyhedra. Distortions in a real 1:1 layer, compared with an idealized layer, do not allow such stacking faults as ± 120° layer rotations and vacancy displacements, because the second layer is incommensurable with the first. The 1:1 layer structure and the fact that the unit cell is symmetrical with respect to the plane passing through the long diagonal of the unit cell suggest the possibility of defects resulting from the two stacking sequences for the same layers. For a regular alternation of translations, a halloysite-like structure should be the end-member of such a series of defect kaolinite types.

The formation of layers having vacant octahedral C-sites is another possible type of fault. Because of the minor dilference between γ and 90°, dickite-like layers should exist. A regular alternation of B and C layers yields dickite as the end-member structure. In materials containing few defects, stacking faults of both types lead to similar X-ray powder diffraction patterns. Thus, the nature of the stacking faults is difficult to determine experimentally. In materials containing many defects, however, the two models lead to different calculated diffraction patterns. Therefore, only a study of defect-rich types of kaolinite can determine which types of defects exist in natural kaolinite samples.
Cation Migration in Smectite Minerals: Electron Spin Resonance of Exchanged Fe3+ Probes
Authors: Luca V. , Cardile C. M.
Published: August 2006

The migration of interlayer Fe3+ cations into the structure of heated montmorillonite and Laponite has been studied by electron spin resonance (ESR), Mössbauer spectroscopy, and magnetic susceptibility measurements. The intensity of the ESR signal corresponding to interlayer Fe3+ in air-dried montmorillonite and Laponite increased linearly as the amount of interlayer Fe3+ increased. Changes in the spectra after thermal treatment indicate that Fe3+ cations migrated into the pseudohexagonal cavities of dehydrated montmorillonite and Laponite. The electrostatic interaction between the Fe3+ and the oxygen atoms defining the entrance to these cavities and the proton of the structural OH groups at the bottom of the cavities differ for the two smectites. Ferric cations were apparently bound more strongly within the pseudohexagonal cavities of the dehydrated montmorillonite than within the cavities of Laponite, because the montmorillonite did not rehydrate after heating. The differences in the binding of Fe3+ cations within the pseudohexagonal cavities of montmorillonite and Laponite were probably due to variations in the ability of the protons of the structural OH groups to reorient. An additional electronic interaction occurred in the heated Laponite, in which small cations were able to promote the formation of structural defects, which gave rise to a sharp ESR signal at g = 2.00. No evidence for the penetration of Fe3+ cations into the vacant octahedral sites of montmorillonite was found.
Oxidation of Dihydroxybenzenes in Aerated Aqueous Suspensions of Birnessite
Authors: McBride M. B.
Published: August 2006

The oxidation of 1,2- and 1,4-dihydroxybenzenes (1,2-DHB and 1,4-DHB) by unbuffered aerated suspensions of synthetic bimessite was studied by continuously monitoring the H+, Mn2+, dissolved O2, and organic radical concentration of the aqueous phase during the reaction. The reaction rapidly generated a very high pH, attributed to oxide dissolution, and the alkaline conditions prevented Mn2+ release into solution over the entire reaction period. Semiquinone radical anions accumulated early in the reaction and then diminished. A secondary radical product appeared in solution during the reaction of the oxide with 1,2-DHB, and was tentatively identified as an hydroxylated semiquinone. The oxide/DHB ratio controlled the maximum concentration and persistence of these radicals in solution as well as the degree to which O2 was consumed as an electron donor. In general, low oxide/DHB ratios promoted O2 uptake by the system, consistent with the subordinate role of O2 as a competing electron acceptor in the presence of excess Mn oxide. Soluble phosphate suppressed O2 consumption, but the mechanism by which it interacted with the reaction system was not determined.
Quantification of Crystalline and Noncrystalline Material in Ground Kaolinite by X-Ray Powder Diffraction, Infrared, Solid-State Nuclear Magnetic Resonance, and Chemical-Dissolution Analyses
Authors: Kodama Hideomi , Kotlyar Luba S. , Ripmeester John A.
Published: August 2006

The capabilities of X-ray powder diffraction (XRD), infrared absorption (IR), solid-state magicangle-spinning nuclear magnetic resonance (MAS-NMR), and chemical dissolution methods were assessed for estimating the amount of noncrystalline material in a ground kaolinite. The Georgia kaolinite was ground in a mechanical mortar for various lengths of time to produce a set of ground samples containing different amounts of the resulting noncrystalline material. In the XRD method, the intensities of characteristic reflections at 7.2 and 4.47 Å did not respond proportionally to the amount of crystalline kaolinite. Although a transmission-type X-ray diffraction method using the hk reflection gave a slightly better estimate than the reflection-type X-ray diffraction method using the basal reflection, both methods gave overestimated values for the amount of noncrystalline material. This overestimation may have been caused by a masking effect due to coaggregation. Using the characteristic IR absorption band at 3700 cm-1 underestimated the amount of the noncrystalline material, if the proportion of this material <50%.

Extraction with NaOH gave estimations 15 to 20% greater than extraction with alkaline Tiron, except for the sample ground for 24 hr, for which both extractions indicated the presence of about 50% noncrystalline material. X-ray powder diffraction data of the residues after these extractions indicated that they consisted of crystalline kaolinite. 29Si NMR spectra of samples ground for ≥ 30 hr suggested that SiO4 tetrahedra were considerably distorted.27 Al NMR spectra showed a signal for tetrahedral A1 for the sample ground for 10 hr, which increased with an increase in grinding time. Plots of the Al(IV)/[Al(IV) + Al(VI)] ratios vs. time were similar to those of chemical extraction curves. Inasmuch as extraction with hot 0.5 M NaOH is a rather harsh treatment, the composition of the noncrystalline material must have been similar to that of the crystalline kaolinite. The chemical dissolution using alkaline Tiron appeared to be superior to other methods, such as XRD, IR, and NaOH extraction, for estimating the amount of noncrystalline material in kaolinite.
Expandable Sepiolite from Ninetyeast Ridge, Indian Ocean
Authors: Argast Scott
Published: August 2006

The structure of sepiolite from a piston core obtained on Ninetyeast Ridge in the Indian Ocean was modified by exposure to ethylene glycol vapor. With ethylene glycol, the sepiolite Oil X-ray powder diffraction peak expanded from 12.4 to 12.8 Å, and the 130 peak contracted from 4.53 to about 4.45 Å. The cell modification is consistent with concomitant expansion along the c-axis and contraction along the b-axis. This structural distortion is not permanent, however, inasmuch as the sepiolite returned to its original state 6 to 12 hr after it was removed from the ethylene glycol-saturated atmosphere.
Oxygen Isotope Measurements of Albite-Quartz-Zeolite Mineral Assemblages, Hokonui Hills, Southland, New Zealand
Authors: Stallard Mary L. , Boles J. R.
Published: August 2006

The oxygen isotopes of albite, quartz, and zeolites from the Hokonui Hills, New Zealand, constrain crystallization temperatures and the type of pore fluids present during diagenesis. A section of altered vitric tuffs in this region contains an extremely sharp reaction boundary between a heulandite-chlorite assemblage containing fresh detrital plagioclase and a laumontite-albite-quartz assemblage. A laumontite vein follows the local joint pattern and forms the reaction boundary, suggesting that laumontitization occurred as a result of fracturing and increased fluid flow during uplift. The albite (δ18O = +15.0)-quartz (δ18O = +19.9 to +20.5) geothermometer constrains the temperature of alteration between 145° and 170°C with a pore water δ18O of +1.8 to +3.5. The tuff was buried to an estimated maximum temperature of about 225°C, indicating that alteration occurred after maximum burial.

Framework oxygen was extracted from zeolites by reaction with ClF3 after the zeolites were thermally dehydrated in a vacuum. Laumontite was dehydrated at 300°C, and stilbite at 150°C. The precision of the method is typically about ±0.45‰. Fractionation curves for dehydrated zeolites are based on a general expression from the literature for feldspars, which depends only on the Si/Al ratio of the mineral. Measured δ18O values for laumontite in the groundmass of the altered tuff were +14.4‰. The laumontite-quartz pair constrains the temperature to between 139° and 162°C, in excellent agreement with the albite-quartz pair, and supporting the petrographic observation of co-crystallizing albite-laumontite.

Oxygen isotope values for fracture-filling laumontite in the vitric tuff, as well as those for groundmass and vein laumontite from other parts of the stratigraphic section, cluster around +14.5, suggesting that laumontite probably crystallized under similar conditions throughout much of the section. Oxygen isotope values for stilbite veins from various parts of the section indicate that this mineral crystallized at lower temperatures than the laumontite, for a given fluid isotopic composition, in agreement with the observed cross-cutting of laumontite by stilbite.