Cambridge University Press (CUP)
0009-8604
1552-8367
Cơ quản chủ quản: SPRINGER , Clay Minerals Society
Lĩnh vực:
Water Science and TechnologyGeochemistry and PetrologySoil ScienceEarth and Planetary Sciences (miscellaneous)
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Iron Substitution in Soil and Synthetic Anatase
Tập 43 - Trang 599-606 - 1995
IronIII for TiIV substitution in the structure of pedogenic and synthetic anatase of up to Fe/ (Ti+Fe) 0.1 mol/mol was indicated by an increase in unit cell size as measured by XRD line shifts. Mössbauer- and electron paramagnetic resonance spectra at both, 298 K and 4.2 K supported this by the presence of signals typical for octahedrally coordinated FeIII in a diamagnetic matrix. Charge compensation was achieved by structural OH, as indicated by FTIR bands at 3360 and 960 cm−1, which were absent in pure anatase and which disappeared on heating. The weight loss on heating amounted to ca. 0.5 mol H2O/mol Fe. At 600°C structural Fe was ejected, the unit cell size decreased to that of pure anatase, and pseudobrookite, Fe2TiO5, was formed.
Incorporation of Radioactive Contaminants into Pyroaurite-Like Phases by Electrochemical Synthesis Abstract During electrochemical remediation of radionuclide, 235 U, 238 U, and 99 Tc-contaminated aqueous solutions, pyroaurite-like phases, ideally [M(II)M(III)(OH)16 CO3 ·4H2 O] where M = Fe, were synthesized following coprecipitation with iron from metal iron electrodes. The effect of radionuclides on the transformation of amorphous precipitates to crystalline pyroaurite-like phases was investigated using X-ray diffraction (XRD), scanning electron microscopy with energy dispersive X-ray analysis, Fourier-transform infrared (FTIR) spectroscopy, and fluorescence spectroscopy. The synthetic iron carbonate hydroxide phases showed primary XRD peaks at 0.7 and 0.35 nm and FTIR spectra that indicated the presence of a brucite-like sheet structure with carbonate anions occupying the interlayer. Divalent and trivalent iron, eroded from the electrode, occupies the octahedral sites of the brucite-like sheets. The carbonate anions in the interlayer balance the excess positive charge from isomorphous substitution of the Fe2+ or Fe3+ by reduced uranium (U4+ ) and technetium (Tc4+ ). Because of the lower solubility associated with crystalline phases than amorphous phases, incorporation of radioactive contaminants into pyroaurite-like phases by electrochemical syntheses represents a more effective approach for removing U and Tc from contaminated aqueous solutions than traditional technologies.
Tập 48 Số 2 - Trang 266-271 - 2000
Clay Minerals in Hydrothermally Altered Rocks at Wairakei, New Zealand Abstract Geothermal fluid discharged by steam wells, which have been core drilled to depths as much as 4500 ft at Wairakei, New Zealand, has altered Pliocene to Pleistocene, silicic, mainly glassy volcanics and related aqueous tuffs and breccias. Measured temperatures (max. 265°C) indicate epithermal to mesothermal conditions in buried fault fissures, the locus of both the hydrothermal fluid and most intense alteration. A supergene kaolinite alteration zone is distinguished from hypogene Ca-montmorillonite and combined micaceous and chloritic zones. The hypogene zones are usually wide and are temperature dependent and localized along fault fissures. Other common hypogene minerals are alkali feldspars, wairakite, epidote, quartz, calcite, laumontite, ptilolite, pyrite and pyrrhotite. Prehnite is rare. The micaceous clay minerals include illite (about 10 Å) and a series of random mixed-layer illite-montmorillonites with d (001) values ranging from 10·28 to 12·45 Å. The amount of interstratified montmorillonite is related to temperature and fault fissures. Apart from rare mixed-layer swelling chlorite, the Fe-rich chloritic clay shows little or no variation in its composition. Both the micaceous clays and the chloritic clay result from alteration of earlier formed Ca-montmorillonite. The stability of hydrothermal minerals is controlled by the temperature and chemical composition of the geothermal fluid ascending along the fault fissures. K-feldspar but not albite is deposited on fissure walls, but both alkali feldspars replace primary soda-lime plagioclase in the wall rock. The absence of albite on fissure walls is ascribed to low aqueous mNa+ /mK+ ratio. Primary quartz is not affected by the altering solution but hydrothermal quartz is deposited on fissure walls and in the wall rock.
Tập 16 Số 3 - Trang 193-213 - 1968
Kaolinite/Montmorillonite Resembles Beidellite Abstract A number of smectitic samples from Almeria (SE Spain) were studied by chemical analysis, DTA, TG, XRD (oriented aggregates with ethylene glycol treatment and Greene-Kelly test), FTIR and MAS NMR. Chemically they resembled a beidellite-montmorillonite series, displaying DTA/TG characteristics already quoted in the literature in beidellite descriptions. They did not swell after the Greene-Kelly test, as it has also been reported for some beidellites. Nevertheless XRD of the oriented, glycolated samples, FTIR, MAS NMR and revision of the chemical analysis demonstrated that they were mixed-layered kaolinite/montmorillonite. It is possible that some of the reported beidellites in the literature are kaolinite/montmorillonite. Beidellite characterization must be supported by several different techniques.
Tập 42 Số 5 - Trang 643-651 - 1994
Contribution to the Adsorption Mechanism of Acetamide and Polyacrylamide on to Clays Abstract While studying the retention of additives used in tertiary recovery of petroleum (waterflooding) on minerals present in a rock reservoir, an investigation has been undertaken into the adsorption mechanism of Polyacrylamides on to clays. The adsorption of amides and Polyacrylamides takes place exclusively on the external surfaces of the clay particles. The organic molecules are protonated on the surface and adsorbed by ionic forces. There is a linear relationship between the adsorption ratio and the polarizing power of the exchangeable cations of the clay mineral. The adsorption isotherms and the thermal analyses reveal the existence of two adsorption mechanisms: (i) a strong, irreversible adsorption, which corresponds to the formation of a monolayer of chemisorbed molecules, (ii) a more important adsorption of molecules retained by hydrogen bonding, which can be eliminated by heating at low temperature. The retention ratio in the irreversible process, which is practically identical both for acetamide and Polyacrylamide, is low (3 mg/g). It depends on the external cation exchange capacity (CEC) of the mineral and increases with the surface area. The Polyacrylamide adsorption depends on the physico-chemical characteristics of the macromolecule, more particularly on the CONH2 /COO− ratio, which determines the extent of the carbon chain, and the molecular weight. The accessibility of the organic macromolecule to the clay particle is controlled by the preceding factors. The quantity of Polyacrylamide irreversibly adsorbed by clay minerals is important in the context of the use of the polymer on a petroleum field. It may be reduced to a minimum by working at low concentrations with a weakly hydrolyzed Polyacrylamide solution.
Tập 25 Số 6 - Trang 392-406 - 1977
Ferrihydrite: Surface Structure and Its Effects on Phase Transformation Abstract X-ray absorption fine structure (XAFS) spectra were collected on a series of ferrihydrite samples prepared over a range of precipitation and drying conditions. Analysis of the XAFS pre-edge structures shows clear evidence of the presence of lower coordination sites in the material. These sites, which are most likely tetrahedral, are believed to be at the surface and become coordination unsaturated (CUS) after dehydroxylation. With chemisorbed water molecules, the CUS sites become the crystal growth sites responsible for the phase transformation of ferrihydrite to hematite at low temperatures. On the other hand, when impurity anions such as SiO4 −4 are present in the precipitation solution, the CUS sites may instead absorb the impurity anions, thereby blocking the crystal growth sites and inhibiting the formation of hematite.
Tập 42 Số 6 - Trang 737-746 - 1994
Effects of Temperature on the Sorption of Lanthanides by Montmorillonite Abstract The diffusion of exchanged Yb, Ho, and Eu from interlayer positions in montmorillonite was studied using infrared spectroscopy (IR), X-ray powder diffraction, and cation-exchange measurements. Dehydration of exchanged montmorillonite between 100° and 280°C caused the ions to diffuse into the hexagonal rings of surface oxygens. Subsequent migration into vacant octahedral sites was small regardless of the radius of the cation. Considerable ion fixation in excess of the cation-exchange capacity of the clay was observed at 20°C in both water and a 1:1 water:95% ethanol mixture. Evidence for hydrolysis as a possible mechanism for cation fixation was obtained by observing frequency shifts for deuterated hydroxyl groups using IR spectroscopy. A major IR band centered at 2680 cm−1 was observed for all three lanthanide-exchanged montmorillonites studied and assigned to the OH-stretching frequency of a lanthanide hydroxide. This band intensified on heating at 300°C for 1 hr. An IR band between 690 and 710 cm−1 also was observed for all three lanthanide-exchanged montmorillonites and was assigned to a lanthanide-hydroxyl deformation mode. No hydrolysis was observed for Na-montmorillonite, as expected from the very low hydration energy of Na+ .
Tập 30 Số 2 - Trang 111-122 - 1982
Synthesis and Characterization of Zn-Al Layered Double Hydroxides Intercalated With 1- to 19-Carbon Carboxylic Acid Anions
Tập 58 - Trang 596-605 - 2010
Layered double hydroxides (LDHs) are layered ion exchangers, with a large surface-charge density, which react easily with organic anions. Various types of organics are rapidly substituted in the interlayer space of inorganic precursor LDHs. ZnAl-LDHs were intercalated with 1- to 19-carbon monocarboxylic acid anions by anion exchange of NO3-saturated LDH precursor phases in order to study the dependence of exchange reactions on synthesis parameters (temperature, pH, and interlayer anion). The carboxylic acid anion-LDHs synthesized were characterized using X-ray diffraction, infrared spectroscopy, thermal analysis, scanning electron microscopy, chemical analysis, and N2 adsorption. Carboxylic anion quantities in excess of the LDH anion exchange capacity easily replaced exchangeable nitrate anions at moderate pH. The intercalated LDH interlayer space depended on the alkyl chain length and orientation (inclination angle) of thecarboxylic-acid anion. Thelatticeparameter c0 ranged from 3.4 to 13.5 nm, but the a0 lattice parameter remained constant at 0.31 nm. Crystallographic analyses indicated a monomolecular arrangement of intercalated short-chain fatty-acid anions. At pH < 7, intercalated long-chain carboxylates showed a preferred bimolecular interlayer orientation. Carboxylic-acid anion exchange with LDHs at pH 7 resulted in the formation of two different sets of basal spacings, which indicated the coexistence of LDHs intercalated with monomolecular and bimolecular arrangements of interlayer carboxylic compounds. Thermal treatment of the carboxylic acid anion-intercalated LDHs indicated stability up to ~140ºC. The release of interlayer water led to distortion of the crystallographic units and resulted in smaller basal spacings without collapse of the layered structure. Heat treatment re-oriented alkyl-chain carbon carboxylates (with >10 carbons) to a more upright interlayer position.
Clay Swelling and Colloid Stability. Martin Smalley. CRC Press, Taylor and Francis Group, 2006, 272 pp. [ISBN 0-8493-8079-0] Price $139.95
Tập 54 - Trang 773-775 - 2006
Ion Exchange and Intersalation Reactions of Hectorite with Tris-Bipyridyl Metal Complexes Abstract The binding of tris-bipyridyl metal complexes of the type M(bp)3 2+ (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: SO4 2- , Br- > CIO4 − , Cl− . The homoionic M(bp)3 2+ -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)3 2+ , 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)3 2+ -hectorite.
Tập 26 Số 5 - Trang 318-326 - 1978