bluuebunny/crossref_metadata_2025_split huggingface dataset:
Mineral-Content and Particle-Size Effects on the Colloidal Properties of Concentrated Lateritic Suspensions
Authors: Cerpa A. , García-González M. T. , Tartaj P. , Requena J. , Garcell L. , Serna C. J. 
Published: August 2006

AbstractThe rheological behavior of concentrated lateritic suspensions from Cuba is affected by mineral composition and particle size. Electrophoretic mobility and yield stress were considered. The lateritic samples were found to be mostly composed of mixtures of serepentine and goethite in varying proportions. The flow properties of the lateritic suspensions are strongly affected by the mineral composition and particle size. This result was determined by comparison of flow properties of the bulk sample and the colloidal fraction. The electrokinetic curves suggest that heterocoagulation is present in all samples, with a zeta potential minimum at the isoelectric point (IEP), which varies with the serpentine to goethite ratio. A relationship between yield stress (τ0) and the sample volume fraction (ϕ) and particle size (d) was obtained at the IEP from the expression τ0 = kϕ3/d0.5, with the constant k dependent on the sample serpentine to goethite ratio.
Synthesis of Smectite Clay Minerals: A Critical Review
Authors: Kloprogge J. Theo , Komarneni Sridhar , Amonette James E. 
Published: August 2006

AbstractSmectites are one of the most important groups of phyllosilicates found in soils and sediments, and certainly one of the most difficult to study. New information about the formation mechanisms, impact of structural features on surface properties, and long-term stability of smectites can best be gained from the systematic study of single-phase specimens. In most instances, these specimens can only be obtained through synthesis under controlled conditions. Syntheses of smectites have been attempted (1) at ambient pressure and low-temperature (<100°C), (2) under moderate hydrothermal conditions (100–1000°C, pressures to several kbars), (3) under extreme hydrothermal conditions (>1000°C or pressures >10 kbars), and (4) in the presence of fluoride. Of these approaches, syntheses performed under moderate hydrothermal conditions are the most numerous and the most successful in terms of smectite yield and phase-purity. Using hydrothermal techniques, high phase-purity can be obtained for beidellites and several transition-metal smectites. However, synthesis of montmorillonite in high purity remains difficult. Starting materials for hydrothermal syntheses include gels, glasses, and other aluminosilicate minerals. The presence of Mg2+ seems to be essential for the formation of smectites, even for phases such as montmorillonite which contain low amounts of Mg. Highly crystalline smectites can be obtained when extreme temperatures or pressures are used, but other crystalline impurities are always present. Although the correlation between synthesis stability fields and thermodynamic stability fields is good in many instances, metastable phases are often formed. Few studies, however, include the additional experiments (approach from under-and over-saturation, reversal experiments) needed to ascertain the conditions for formation of thermody-namically stable phases. Thorough characterization of synthetic products by modern instrumental and molecular-scale techniques is also needed to better understand the processes leading to smectite formation.
Removal of Nickel and Cobalt from Aqueous Solutions by Na-Activated Bentonite
Authors: Triantafyllou Stella , Christodoulou Eirini , Neou-Syngouna Paraskevi 
Published: August 2006

AbstractThe ability of Na-activated bentonite to remove Ni2+ and Co2+ from aqueous solutions at room temperature (22 ± 1°C) was studied under various experimental conditions. The parameters studied were solid-to-liquid ratios and initial cation concentrations. Experiments involved the behavior of bentonite vs. Ni and Co separately and where Ni and Co were present in solution at different concentrations and ratios. Bentonite retained substantial amounts of both metals readily, but it showed a higher affinity for Ni. Over-exchange appears when initial metal concentration exceeds the concentration corresponding to the cation exchange capacity (CEC) of bentonite. The presence of both metals in solution may be either synergistic or antagonistic sorption, depending on the initial ion concentrations.
Methods for Performing Atomic Force Microscopy Imaging of Clay Minerals in Aqueous Solutions
Authors: Bickmore Barry R. , Hochella Michael F. , Bosbach Dirk , Charlet Laurent 
Published: August 2006

AbstractThree methods were developed that allow for the imaging of any clay mineral in aqueous solutions with atomic force microscopy (AFM). The methods involve fixing the particles onto special substrates that do not complicate the imaging process, but hold the particles sufficiently so that they do not move laterally or float away during imaging. Two techniques depend on electrostatic attraction under circumneutral pH conditions, between the negatively charged clay particles and the high point of zero charge substrate (either aluminum oxide or polyethyleneimine-coated mica) whereas the third technique depends on adhesion to a thermoplastic film. The first electrostatic technique involves a polished single crystal α-Al2O3(sapphire) substrate. This was used successfully as a substrate for clay-sized minerals with high permanent layer charge localized on the basal planes (phlogopite and vermiculite) and when the AFM was operated in TappingMode to limit the lateral forces between the probe tip and the particles. However, electrostatic attraction between the sapphire surface and clay minerals such as smectite and kaolinite (low or no permanent layer charge) is not sufficiently strong to adequately fix the particles for imaging. The second electrostatic technique involves a polyethyleneimine-coated mica surface designed to immobilize a larger variety of clay minerals (phlogopite, vermiculite, montmorillonite, and kaolinite), and in this technique weak bonding between the clay and the organic film is also a factor. The third technique, which does not depend on electrostatic attraction, fixes clay particles into the surface of a thermoplastic adhesive called Tempfix. This has proven useful for fixing and imaging relatively large clay particles with well-defined morphology. The Tempfix mount also requires imaging in TappingMode because the Tempfix is relatively soft.
Crystal Chemistry of Layer Silicates of the Miocene Green Grain (Congo Basin) from Transmission Electron Microscopy (TEM) and Analytical Electron microscopy (AEM) Observations
Authors: Wiewióra A. , Giresse P. , Jaunet A. M. , Wilamowski A. , Elsass F. 
Published: August 2006

AbstractTransmission electron microscopy (TEM) and analytical electron microscopy (AEM) methods were used to study the crystal chemistry of phyllosilicates occurring in green grains of Miocene sediments from the Congo continental shelf. Using diagrams based on wt. % K and the (Fe + Mg)/Al ratio, minerals were distinguished from mixed-layer phases. The most abundant detrital mineral is Fe-kaolinite. The morphology and composition identify this mineral as a component of ferralitic soils. This Fe-rich kaolinite has undergone a complex process of partial dissolution and recrystallization and further enrichment in Fe and, to a lesser extent, in Mg in the marine environment. The detrital mica observed with TEM retains the original morphology and chemistry of muscovite. Alteration processes resulted in the crystallization of 1:1 trioctahedral Fe2+ and Mg-rich minerals and interstratified phases with 1:1 and 2:1 layers in varying proportions observed with the aid of high-resolution transmission electron microscopy (HRTEM) imaging. Included among the newly formed 7-Å phases are those apparently containing excess Si. The smectites are apparently neoform, and chemical analyses showed that these marine K-smectites belong to the beidellite-nontronite series and have tetrahedral substitutions similar to muscovite. Their compositions are closer to beidellite than to nontronite, although the latter was observed in association with goethite. The TEM observations and crystallochemical data show that mineral alteration ceased after forming mixed-layer minerals, and alteration did not reach the glauconitization stage. Apparently, the Miocene assemblages experienced rapidly changing environmental conditions and high sedimentation rates that continue today.
Structural Fe3+ in Natural Kaolinites: New Insights from Electron Paramagnetic Resonance Spectra Fitting at X and Q-Band Frequencies
Authors: Balan Etienne , Allard Thierry , Boizot Bruno , Morin Guillaume , Muller Jean-Pierre 
Published: August 2006

AbstractStructural Fe3+ in kaolinites and dickites covering a broad range of disorder was investigated using electron paramagnetic resonance (EPR) spectroscopy at both the X and Q-band frequencies. A procedure based on a numerical diagonalization of the spin Hamiltonian was used to accurately determine the second and fourth-order fine-structure parameters. A least-squares fitting method was also developed to model the EPR spectra of Fe3+ ions in disordered local environments, including multimodal site-to-site distributions. Satisfactory fits between calculated and observed X and Q-band spectra were obtained regardless of the stacking order of the samples.In well-ordered kaolinite, Fe3+ ions are equally substituted in sites of axial symmetry (Fe(II)sites, namely Fe(II)a and Fe(II)b) which were determined to be the two non-equivalent Al1 and Al2 sites of the kaolinite structure. In dickite, Fe3+ ions were also found to be equally substituted for Al3+ in the two non-equivalent Al sites of the dickite structure. In poorly ordered kaolinites, the distribution of the fine-structure parameters indicates that Fe3+ ions are distributed between Fe(II) sites and other sites with the symmetry of the dickite sites.Hence, when stacking disorder prevails over local perturbations of the structure, the near isotropic resonance owing to Fe3+ ions in rhombically distorted sites (Fe(I) sites) is a diagnostic feature for the occurrence of C-layers in the kaolinite structure, where C refers to a specific distribution of vacant octahedral sites in successive layers.
Sorption of Heavy-Metal Cations by Al and Zr-Hydroxy-Intercalated and Pillared Bentonite
Authors: Matthes Winnie , Madsen Fritz T. , Kahr Guenther 
Published: August 2006

AbstractThe sorption of Cd, Cu, Pb, and Zn ions by Na-rich bentonite, Al and Zr-pillared Na-rich bentonite (Al-MX80, Zr-MX80), the uncalcined hydroxy-intercalated precursors (HAl, HZr-MX80), and commercial Al-pillared bentonite EXM 534 was investigated. Experiments were conducted in ultrapure water and artificial leachate with varying pH. The experiments were performed over periods to 30 wk. Sorption characteristics were described with one and two-site Langmuir isotherms. The non-exchangeable quantities of heavy metals were determined by fusion of the sorbents after ion exchange with ammonium acetate.The sorption of Cd, Cu, Pb, and Zn by bentonite was dominated by cation exchange. In artificial leachate, the sorption was reduced due to competition with alkali and alkaline-earth cations. The sorption of Cu, Zn, and Pb at pH 4.9 and Cd at pH 6.9 by Al and Zr-hydroxy-intercalated and pillared MX80 was governed also by cation exchange. In contrast, the sorbed quantities of Zn at pH 6.9 exceeded the cation exchange capacity (CEC) of HAl, HZr, Al, Zr-MX80, and EXM 534 and were partially non-exchangeable. The increase of the sorption of Zn with pH and its independence of the ionic strength of the solution at neutral pH suggest a complexation of Zn ions to surface hydroxyl groups of the intercalated Al and Zr-polyhydroxo cations and pillars. This complexation is the dominating sorption mechanism. Removal of dissolved Zn from solution with time is attributed to surface precipitation. Al-hydroxy and pillared bentonites are considered potential sorbents of Zn ions from neutral pH aqueous solutions, such as waste waters and leachates.
Transmission X-ray Diffraction of Undisturbed Soil Microfabrics Obtained by Microdrilling in Thin Sections
Authors: Denaix L. , van Oort F. , Pernes M. , Jongmans A. G. 
Published: August 2006

AbstractClay mineralogical studies by X-ray diffraction performed on extracted <2-µm fractions do not always represent all clay mineral constituents present in the soil. In this work, transmission X-ray diffraction (TXRD) was applied to undisturbed microsamples of optically homogeneous mineral soil fabrics and features. These microsamples were isolated by microdrilling their periphery in soil thin sections, then removing them, and transferring them to glass capillaries for TXRD analysis. The usefulness of this technique for supplying in situ mineralogical information on identification, structure, and natural orientation of soil constituents was tested on mineral microfabrics and features of primary and secondary phyllosilicates. The study demonstrated that TXRD allowed detailed, representative interpretations of undisturbed mineral features and fabrics. In particular, this technique allowed us (1) to compare mineralogical compositions at selected microlocalities, (2) to study natural preferred orientations, and (3) to detect small amounts of minor mineral interstratification phases. In addition, complementary information on crystallography and crystal chemistry may be obtained by performing analytical transmission electron microscopy on the same microsample.
Selective Gas Adsorption by Amorphous Clay-Mineral Derivatives
Authors: Volzone Cristina , Thompson John G. , Melnitchenko Alexandra , Ortiga José , Palethorpe Stephen R. 
Published: August 2006

AbstractAmorphous derivates prepared by aqueous reaction of various aluminosilicate clay minerals with concentrated KF solution at 80–110°C were studied for their gas adsorption properties. The four clay minerals studied are halloysite, a well-crystallized kaolinite, a poorly crystallized kaolinite, and a montmorillonite. The gases tested are N2, O2, CH4, CO, CO2, and C2H2. The kaolin-group mineral derivatives are characterized by substantial reduction in particle size, high specific surface, and significant selectivity towards CO2 and C2H2 relative to the other gases. The montmorillonite derivative shows no increase in adsorption over the starting material, however, for all the materials high adsorption of CO2 and C2H2 was observed. Levels of gas adsorption and gas adsorption ratios are comparable to pillared clays.
Role of Tartaric Acid in the Inhibition of the Formation of Al13 Tridecamer using Sulfate Precipitation
Authors: Krishnamurti G. S. R. , Wang M. K. , Huang P. M. 
Published: August 2006

AbstractPolynuclear Al13 tridecamer species are the major hydrolyzed species of aluminum, but their occurrence in terrestrial environments has not been established. X-ray diffraction (XRD), 27Al nuclear magnetic resonance (NMR), and scanning electron microscope (SEM) analyses show that the presence of tartaric acid (concentration range of 10−5–10−3 M), one of the commonly occurring low-molecular-weight organic acids, inhibits the formation of the Al13 tridecamer species.In the absence of tartaric acid, the basic aluminum sulfate crystals were of tetrahedral morphology and conformed to isometric symmetry with a = 17.748 Å and space group of P4232. Increasing amounts of tartaric acid [tartaric acid/Al molar ratio (R) ranging from 0.01 to 0.05] modified the crystal morphology from the tetrahedral particles of isometric symmetry (R = 0) to rod-shaped particles of monoclinic symmetry (R = 0.01) to irregularly shaped X-ray noncrystalline microparticles (R = 0.05). Failure to detect the presence of Al13 tridecamer, the dominant hydrolyzed species of aluminum, in terrestrial environments may be partially attributed to the presence of low-molecular-weight organic acids, which inhibit the formation of Al13 tridecamer species.
Effects of Exchange Cations and Layer-Charge Location on Cysteine Retention by Smectites
Authors: Brigatti Maria Franca , Lugli Cristina , Montorsi Stefano , Poppi Luciano 
Published: August 2006

AbstractThis study investigates the complexes formed between amino acids, which are the natural degradation products of organic matter, and smectites. Thus, the adsorption and desorption behavior of cysteine and Na-, Ca-, Cu-homoionic smectites with different layer-charge location, a montmorillonite, and a beidellite, were studied. The clay samples were treated with Na, Ca, and Cu 1 N solutions and then with a 0.2 M cysteine solution. To test smectite-cysteine stability at acidic pH, the solids obtained were repeatedly treated with distilled water acidified to pH = 5. All treated samples were characterized by thermal, X-ray diffraction, chemical, and infrared analyses. The results showed that: 1) Na- and Ca-rich smectites adsorbed and retained small amounts of cysteine, and did not show interlayer cation-cysteine complexes, whereas the amino acid was strongly retained in the interlayer by Cu-rich smectites; 2)d(001)-values for Na- and Ca-rich smectites showed little or no expansion, whereas for the Cu-rich smectites the intercalation of the organic molecule produced a swelling of the structure; 3) the interaction mechanism of homoionic smectites with cysteine in an aqueous medium occurs by weak interactions, (e.g., van der Waals interactions, hydrogen bonding, dipole-dipole interactions, and other electrostatic forces such as entropy-driven hydrophobic bonding), and/or by complexes involving interlayer cations and organic ligands. The formation of a stable chelate complex with the saturating ion permits cysteine to be adsorbed by Cu(II)-rich smectites and to be resistant to migration in soils and groundwaters.
Complex Formation of Cation-Exchanged Montmorillonites with Propylene Carbonate: Osmotic Swelling in Aqueous Electrolyte Solutions
Authors: Onikata Masanobu , Kondo Mrrsuji , Hayashi Naoki , Yamanaka Shoji 
Published: August 2006

AbstractMontmorillonites saturated with Li+, Na+, K+, NH4+, Mg2+, Ca2+, Ba2+, or Ni2+ ions can form complexes with propylene carbonate (PC) by intercalation; the d(001) of montmorillonite expands to 19 Å. In the infrared absorption spectra of these complexes, the C=0 stretching band of the intercalated PC molecules shifts to lower frequencies, and the amount of the shift increased with the increase of the polarizing power of the interlayer cations. Water molecules were strongly bound to the cations. The PC molecules interacted with the cations by way of H2O molecules. With the removal of H2O, the PC molecules directly coordinate to the cations and the PC molecules show a much larger red-shift in the C=O frequency. The PC-montmorillonite complexes exhibited osmotic swelling, even in aqueous electrolyte solutions. This finding is interpreted in terms of the formation of thick electric double-layers consisting of PC and H2O between the 2:1 layers.
Cation-Exchange Capacity (CEC) of Zeolitic Volcaniclastic Materials: Applicability of the Ammonium Acetate Saturation (AMAS) Method
Authors: Kitsopoulos Konstantinos P. 
Published: August 2006

AbstractThe ammonium acetate saturation (AMAS) method was used to study the cation-exchange capacity (CEC) of zeolitic volcaniclastic materials from Santorini and Polyegos Islands, Greece. The AMAS method was tested with respect to the time required to saturate the samples of zeolites with ammonium (NH4+) ions, the efficient liberation of NH4+ ions, and the suitability of two widely used techniques to measure ammonia (NH3) (Kjeldahl ammonia distillation technique and the ammonia electrode technique). By using the inductively coupled plasma-mass spectrometry (ICP-MS) technique and measuring the number of cations exchanged during ammonium acetate (NH4OAc) saturation, it was found that the saturation period for zeolitic materials must be increased to 12-day cycles to ensure effective saturation. Following NH4OAc saturation, the AMAS method produces NH4+ solutions, after the NH4+-saturated samples of zeolites are washed with 10% NaCl. The amount of the NH4+ ions in solution (i.e., exchangeable cations) is a measure of the CEC. The NH4+ ions can not be directly measured and must be converted to NH3. The Kjeldahl ammonia distillation technique and the ammonia electrode technique for measuring NH3 give identical CEC results. However, the ammonia electrode technique, when used directly with the NH4+ samples of zeolite without 10% NaCl treatment, generally gives higher CEC values. The amount of NH4+ treated (converted to NH3), when the NH4+-saturated zeolitized samples were used directly, was higher than the amount of the NH4+ treated when the NH4+ solutions were obtained after washing the NH4+-saturated zeolitized samples with 10% NaCl. Therefore, washing with 10% NaCl does not facilitate the release of all NH4+ initially within the zeolite structure. A modified AMAS technique is proposed for measuring the CEC of zeolitic material.
Impact of Different Asbestos Species and Other Mineral Particles on Pulmonary Pathogenesis
Authors: van Oss C. J. , Naim J. O. , Costanzo P. M. , Giese R. F. , Wu W. , Sorling A. F. 
Published: August 2006

AbstractFactors that are potentially important in the pulmonary pathogenesis of asbestos and other mineral particles are: 1) morphology, 2) Fe-content, 3) solubility under intraphagosomal conditions, 4) value and sign of the surface potential of the particle, 5) hydrophobicity or hydrophilicity, 6) capacity to activate phagocytic leukocytes, and 7) duration of exposure to the particles. The order of importance of these factors in causing severe or fatal pulmonary pathogenicity is estimated to be: 1 > 3 > 7 > 6 ≫ 5 > 4 > 2. The order of pathogenicity of the minerals is estimated as: amphibole asbestos: crocidolite, tremolite, amosite > erionite > serpentine asbestos: chrysotile > talc > silica > simple metal oxides. Particle length, duration of exposure to the particles, and pre-treatment of the particles may however enhance the pathogenic potential of any of the lower-ranked particles.
Clay Minerals in Hydrothermally Altered Volcanic Rocks, Eastern Pontides, Turkey
Authors: Çelik Muazzez , Karakaya Necati , Temel Abidin 
Published: August 2006

AbstractExtensive hydrothermal alteration is observed around volcanogenic massive sulfide deposits. These deposits are related to Late Cretaceous volcanism in various parts of the Eastern Pontide province. Mineral assemblages resulting from alteration consist of mostly clay minerals and silica polymorphs, some sulfate minerals, and scarce zeolite minerals. The clay minerals are kaolinite, illite, and smectite. These minerals were examined using X-ray diffraction (XRD), scanning electron microscopy (SEM)-energy dispersive spectrometry (EDS), X-ray fluorescence spectroscopy (XRF), and differential thermal analysis (DTA)-thermal gravimetry (TG) techniques. The illite and the toseki deposits are a result of hydrothermal alteration of dacitic-andesitic volcanites. Two groups of bentonite deposits occur; the first mainly formed by hydrothermal solution whereas the second group resulted from halmyrolysis.The smectite in these alteration zones is generally montmorillonitic in composition and the interlayer cation is mostly Ca and lesser amounts of Na. The SiO2 and Fe2O3 contents of the hydrothermal bentonites are higher than those of the halmyrolysis smectites; however, the MgO content of both groups is similar. The Na2O and K2O contents of both groups are generally <0.5%. The hydrothermal bentonites are not plastic and have open honeycomb microtextures, although the halmyrolitic smectites are plastic with ultrafine and rod-shaped textures. Illite, which contains some smectite layers, is a 1M polymorph, and has an asymmetry to the low-angle side of the XRD peaks. The impure illite deposits contain various combinations of smectite, kaolinite and gypsum, galena, sphalerite, pyrite, goetite, and quartz. The illite has >35 wt. % Al2O3. The toseki raw material, which may be possibly useful as a porcelain raw material, is composed mainly of illite, kaolinite and quartz, or illite and quartz. The crystallinity of the kaolinite is poor.