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Showing 1 to 20 of 20 for “"Smectites"”.
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Physical chemistry of microbially-reduced smectites
… 0.4 mmol g$\sp{-1}$ than in chemically-reduced smectites. The presence of structural Fe(II) apparently overcomes the opposing effect of organics on the ability of clay gels to retain water. The flow behavior of microbially-reduced smectite suspensions depended on smectite, medium used, …
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Abiotic nitrate reduction by redox activated iron-bearing smectites
Nitrate is a contaminant of interest in soils and water. It has been linked to chronic human illness and a variety of environmental problems, including hypoxia in coastal waters. Previous work has shown that nitrate is naturally removed from soils below the redox interface of the soil profile. A …
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The Toxicity of Pesticides to Mammalian Cells as Altered by Redox-Modified Smectites
… have found that the iron (Fe) oxidation state in smectites directly affects the degradation of pesticides without microbial intervention. Yet, what does degradation mean when attempting to assess toxicologic risk? The objective of this study was to measure the influence of Fe oxidation state on …
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Dry Oxidation of Ferrous and Mixed-valence Smectites and Its Implications for the Oxidative History of Mars
… A range of ferrous and mixed-valence smectites were synthesized and then exposed to varying O2 fluxes under dry conditions to determine if Fe/Mg trioctahedral smectites can be oxidized without an aqueous medium to form dioctahedral smectites like those observed on the surface of Mars. …
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Untersuchungen zur Dehydroxilierung dioktaedrischer Smectite
Due to their special features smectites, dioctahedral smectites in particular, are widely used in a broad spectrum of technical applications and processes. They seem to be one of the most important indsutrial minerals. By using smectites in thermal technology processes their behaviour plays an …
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The adsorption of phenolic and organotin compounds by clays and cation exchanged clays
… of phenols and chlorinated phenols by Quat-smectites is greater than that by the Bi Quat-Smectites prepared in this study. It is thought that the quaternary ammonium exchanged smectite components of the Bi Quat-smectites interact with each other (adsorbent-adsorbent interactions) reducing …
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The Effects of Iron Oxidation State on Surface Chemistry and Structure of Iron-Bearing Smectites: Cation Fixation and Selectivity, Structural Iron Environment, and Dissolution
Smectites are widespread as a major constituent of soils and sediments and include a substantial amount of structural Fe. The reduction of structural Fe(III) invokes partial dehydroxylation, protonation, and site translocation of Fe(II) to alter the crystal structure. The structural changes, …
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Caesium and strontium exchange at specific clay mineral sites
… increases. For this reason, caesium exchange on smectites does not fit Langmuir nor Freundlich plots. Also, the selectivity coefficient was found to vary widely with loading, compared with potassium exchange on smectites or caesium exchange on non-swelling minerals. Complete caesium exchange on …
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Transformation of Trichloromethanes in Iron(ii)-Containing Environments
… reduced, and reoxidized forms of three different smectites, montmorillonite (Upton), ferruginous smectite (SWa-1), and nontronite (NG-1), in aqueous suspension. The adsorption rate of RCCl3 in clay minerals showed a strong correlation with the iron(II) content of the clay (r2 = 0.94). The clay …
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The relationship of the Yucca Mountain repository block to the regional groundwater system: A geochemical model
… the next part. Minerals consisted of zeolites, smectites, authigenic feldspars and quartz polymorphs from described diagentic mineral zones. Reaction steps were ion exchange with zeolites. (Abstract shortened with permission of author.).
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Sorption mechanisms of dibenzo-p-dioxin/furan from water by smectite clays and theoretical studies on formation pathways of chlorodibenzo-p-dioxins from precursor chlorophenols on smectite clays
… deposits. Sorption experiments demonstrated that smectites, especially Cs-saponite, effectively adsorbed dibenzo-p-dioxin /furan from water. Adsorption was promoted by exchangeable cations with low hydration energies, and negative charge in the smectite arising from the tetrahedral siloxane …
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Structure property and deformation analysis of polypropylene montmorillonite nanocomposites.
Nanocomposites with expandable smectites such as montmorillonite layered silicates (MLS) in polymer matrices have attracted extensive application interest. Numerous MLS concentrations have been used with no particular justification. Here, we investigate the effects of MLS dispersion within the …
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Laboratory characterization of a highly weathered old alluvium in San Juan, Puerto Rico
… quartz and orthoclase; (2) kaolinite and smectites as major clay minerals; and (3) Fe-oxides (goethite and hematite) as special fine-grained minerals, which give the soil distinct red, brown, and yellow coloration. The subsequent quantitative analysis yields high accuracy results, such …
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Untersuchungen zur Eignung von natürlich alterierten sowie mit Oxalsäure aktivierten Bentoniten als Bleicherde für Pflanzenöle
… CEC-determination: The octahedral layering of smectites is dissolved during acid attack. The remaining tetrahedral layer forms an x-ray amorphous, in a sodium-carbonate-solution soluble and porous phases which provides most of the activity. The natural acid alteration of the milosbentonites is …
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Hydrated silica on Mars: Global comparison and in-depth analysis at Antoniadi Crater
… this site. There is also spectral evidence for smectites beneath the silica-bearing rocks, in the lowermost exposed Noachian-aged breccia. A similar stratigraphic sequence -- smectite-bearing breccias beneath deposits containing minerals indicating a greater degree of alteration -- has also been …
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The role of soil clays and clay-humic complexes in processes controlling colloidal stability and the sorption and degradation of tetracyclines
… the dissertation addresses the influence of soil smectites and humic substances and their interactions on sorption and desorption of tetracyclines. Tetracyclines are important in human medicine and are also used extensively in livestock production. Chlortetracycline and tetracycline are routinely …
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Studies in clay chemistry
… NMR. TTF was intercalated by smectites containing different interlayer and lattice cations. Evidence from ESR and 57Fe Mossbauer indicated charge-transfer from TTF to structural iron in natural montmorillonite, and to interlayer Cu2+ in Cu2+ exchanged laponite. No charge …
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Melt Synthesis, Structural, Characterization and Scaling of Swelling 2:1-Layer Silicate Materials
… Generally, natural swelling layer silicates (smectites) usually contain impurities such as iron oxide (pigmentation material), quartz, and carbonate. However, these impurities hinder the employment of swelling layer silicates in industry for cutting edge and advanced applications. In addition, …
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Interaction of aqueous U(VI) with goethite, montmorillonite, and UO2(s)
… of structural Fe(II) in low iron content smectites in controlling uranium mobility in subsurface environments. Finally, uranium atom exchange between aqueous U(VI) and the solid associated uranium species was probed using a 236U isotope tracer at pH 7 and 1 mM dissolved inorganic carbon …