Search results for "clay minerals"

Past, Present and Future Perspectives on Halloysite Clay Minerals

2020

Halloysite nanotubes (HNTs), clay minerals belonging to the kaolin groups, are emerging nanomaterials which have attracted the attention of the scientific community due to their interesting features, such as low-cost, availability and biocompatibility. In addition, their large surface area and tubular structure have led to HNTs’ application in different industrial purposes. This review reports a comprehensive overview of the historical background of HNT utilization in the last 20 years. In particular it will focus on the functionalization of the surfaces, both supramolecular and covalent, following applications in several fields, including biomedicine, environmental science and catalysis.

Retention of Vanadium(V), Molybdenum(VI) and Tungsten(VI) by Kaolin

1993

Abstract The ability of kaolin (approximately H2Al2Si2O8 · H2O), a well known clay mineral constituent, to retain V(V) andMo(VI) species from 10−5 and 10−4 M solutions, and W(VI) species from 10−4 M solutions was investigated in the pH range 2–7.5 using a solid/liquid ratio 1:100 (w:v). The equilibration time in the adsorption studies was 72 h, and the shaking time in the desorption studies was 17 h. 0.02 M KCl was used as ionic medium and desorbing liquid. V(V), Mo(VI) and W(VI) were all retained by kaolin to some extent, and the amounts of the elements which could be washed away from kaolin with 0.02 M KCl were very small. The pH dependence of the adsorption was considerable: when added a…

Distribution of clay minerals in Early Jurassic Peritethyan seas: palaeoclimatic significance inferred from multiproxy comparisons.

2009

13 pages; International audience; A set of published, unpublished, and new clay mineral data from 60 European and Mediterranean localities allows us to test the reliability of clay minerals as palaeoclimatic proxies for the Pliensbachian–Toarcian period (Early Jurassic) by reconstructing spatial and temporal variations of detrital fluxes at the ammonite biochronozone resolution. In order to discuss their palaeoclimatic meaning, a compilation of low-latitude belemnite δ18O, δ13C, Mg/Ca, and 87Sr/86Sr values is presented for the first time for the whole Pliensbachian– Toarcian period. Once diagenetic and authigenic biases have been identified and ruled out, kaolinite content variation is cons…

Evidence for montmorillonite or its compositional equivalent in Columbia Hills, Mars

2007

During its exploration of the Columbia Hills, the Mars Exploration Rover ‘‘Spirit’’ encountered several similar samples that are distinctly different from Martian meteorites and known Gusev crater soils, rocks, and sediments. Occurring in a variety of contexts and locations, these ‘‘Independence class’’ samples are rough-textured, iron-poor (equivalent FeO 4 wt%), have high Al/Si ratios, and often contain unexpectedly high concentrations of one or more minor or trace elements (including Cr, Ni, Cu, Sr, and Y). Apart from accessory minerals, the major component common to these samples has a compositional profile of major and minor elements whic…

2012

Abstract. Mineral dust is a major fraction of global atmospheric aerosol, and the oxidation of SO2 on mineral dust has implications for cloud formation, climate and the sulfur cycle. Stable sulfur isotopes can be used to understand the different oxidation processes occurring on mineral dust. This study presents measurements of the 34S/32S fractionation factor α34 for oxidation of SO2 on mineral dust surfaces and in the aqueous phase in mineral dust leachate. Sahara dust, which accounts for ~60% of global dust emissions and loading, was used for the experiments. The fractionation factor for aqueous oxidation in dust leachate is αleachate = 0.9917±0.0046, which is in agreement with previous m…

Hydrothermal macroscopic Fe-sepiolite from Oujda Mounts (Middle Atlas, Eastern Morocco)

2008

The Triassic-Jurassic series in the Oujda Mounts (Middle Atlas, NE Morocco) includes two basaltic units. The whole sequence is crosscut by veins filled with Fe-sepiolite + chalcedony + calcite + smectite and mixed layer talc-saponite. Fe-sepiolite occurs as macroscopic fibres and is one of the latest mineral phases in the filling sequence of the veins. The compositional relationships and crystallographic parameters obtained on carefully selected samples of sepiolite are compared with previous data, and support the actual development of Mg-Fe substitution in this clay mineral, given the adequate hydrothermal conditions. Genesis of this uncommon variety of sepiolite in veins is interpreted as…

Mineralogical variability of Callovo-Oxfordian clays from the Paris Basin and the Subalpine Basin.

2006

High-resolution clay mineralogical data at the Middle/Upper Jurassic boundary from the French Subalpine Basin, the Jura Mountains and the Paris Basin (ANDRA boreholes) from Callovo-Oxfordian clayey deposits allow spatial and temporal terrigenous flux evolution to be considered over a period of 6 to 7 Myr. Recorded diachronisms of major mineralogical changes and complex clays distribution at the Paris Basin scale result to combined palaeogeographic/eustatic variations and climate input. In the French Subalpine Basin, mineralogical homogeneity confirms the burial diagenesis influence, but other terrigenous supplies must be involved in contrast to the Paris Basin domains. Volcanogenic clays (b…

The influence of natural trace element distribution on the mobility of radionuclides. The exemple of nickel in a clay-rock

2015

International audience; The natural distribution of nickel (Ni) in the Callovian–Oxfordian clay-rich rock of Bure (France) was investigated, together with that of cobalt (Co), zinc (Zn) and lead (Pb). The most Ni-enriched phases are pyrite (∼400 × 10−6 g g−1 Ni), sphalerite (∼300 × 10−6 g g−1), chlorite (∼285 × 10−6 g g−1), organic matter (∼300 × 10−6 g g−1), muscovite (100–200 × 10−6 g g−1) and possibly carbonate minerals (mainly calcite and minor dolomite, ∼10 × 10−6 g g−1). Despite their high abundance (up to ∼80% in the upper part of the formation), carbonate minerals are quantitatively a minor Ni reservoir; most of the Ni is borne by chlorite and pyrite, which are minor mineral phases.…

A new simple approach to evaluate pedogenic clay transformation in a Vertic Calcisol

2006

The aim of this study is to characterize the pedogenic clay minerals by using simple approach: Mixing mineralogical and geochemical findings. The fine clay fractions (< 0.1 μm) of a Vertic Cambisol profile were studied by means of X-ray diffraction (XRD), infrared spectroscopy (FTIR) and cation exchange capacity (CEC). Qualitative and quantitative mineralogical compositions of the clay mixture were determined. Moreover, chemical equilibria and thermodynamic stabilities of minerals (calcite, gypsum, kaolinite, smectites and illites) were studied using results of ionic activities obtained from total concentration of various aqueous species in water extracts from soil-saturated pastes. XRD ana…

Hydrogeochemistry and fractionation pathways of Mg isotopes in a continental weathering system: Lessons from field experiments

2012

Abstract The potential of magnesium isotope records from cave carbonate archives (speleothems) has been documented but remains underexplored. This is due to the limited knowledge regarding the complex suite of physico-chemical and biological disequilibrium fractionation processes affecting meteoric fluids in the soil zone, the carbonate hostrock and calcite precipitation in the cave. This study presents δ 26  Mg data from a monitored cave in Germany (Bunker Cave) including rain water (δ 26  Mg: − 0.70 ± 0.14‰), soil water (δ 26  Mg: − 0.51 ± 0.10‰) and drip waters (δ 26  Mg: − 1.65 ± 0.08‰) sampled between November 2009 and May 2011. Field precipitation experiments, i.e., calcite precipitat…