Vermiculite

About: Vermiculite is a research topic. Over the lifetime, 2320 publications have been published within this topic receiving 37142 citations.

Mineralogical composition of the clay fraction of two fluvio-glacial sediments from east greenland

Abstract: The < 2 #m fractions of two fluvio-glacial sediments from East Greenland have been analysed chemically and by XRD and M6ssbauer spectroscopy. The bulk of each < 2 #m fraction consists of feldspars and micas (biotite) which are important constituents of the Pre- cambrian igneous and metamorphic rocks of the area. Significant amounts of vermiculitic and smectitic minerals are also present. Compared with similar minerals present in Danish soil clays, the Greenland vermiculite and smectite are characterized by a high degree ofcrystallinity and it is concluded that these minerals have been formed from biotite through K release and lattice expansion. These processes appear to have proceeded at a sufficiently high rate to yield significant amounts of vermiculite and smectite despite the cold climate prevailing in the area. The major part of Greenland is covered by inland glaciers, and exposed rocks and soils occur only in a rather narrow belt along the coasts. The surface of this ice-free belt consists mostly of solid rock although some sediments have been deposited by the glaciers either as moraines or melt-water deposits. The moraines are invariably coarse-grained and consist mainly of boulders. Most of the melt-water deposits also consists of rather coarse particles, but deposits containing significant amounts of < 2 #m material do occur (Jensen, 1965), these generally forming in glacial lakes at or near the edge of the glaciers (Weidick, 1976). Clay-size particles are also found in suspended state in present-day glacial streams. In general it is assumed that the clay-size material occurring in Greenland and other cold regions consists to a large extent of chemically unaltered fragments of the original rocks rather than of true clay minerals. For example, Jensen (1965) found that clay from a presumed glacial lake deposit near Godth~tb contained 15-30~o vermiculite, 25-40~o biotite, 25-30~ oligoclase and small amounts of quartz and hornblende. All these minerals, including vermiculite, were present in the gneisses in the vicinity of the lake. However, work by Claridge (1965), Reynolds (1971) and Foged (1975) have shown that a certain amount of chemical weathering occurs in a cold climate, this involving, particularly, the formation of expandable clay minerals from biotite. In the present investigation the mineralogical composition of two < 2 pm separates from contemporary fluvio-glacial sediments from an East Greenland glacier has been determined, particular attention being paid to the possible presence of true clay minerals. SAMPLES

Fe2+-modified Vermiculite for the Removal of Chromium (VI) from Aqueous Solution

Abstract: A novel adsorbent: Fe2+-modified vermiculite was prepared in a two-step reaction. Adsorption experiments were carried out as a function of pH, contact time, and concentration of Cr(VI). It was found that Fe2+-modified vermiculite was particularly effective for the removal of Cr(VI) at pH 1.0. The adsorption of Cr(VI) reached equilibrium within 60 min, and the pseudo-second-order kinetic model best described the adsorption kinetics. The adsorption data follow the Langmuir model more than the Freundlich model. At pH 1.0, the maximum Cr(VI) sorption capacity (Q max ) was 87.72 mg · g−1. Desorption of Cr(VI) from Fe2+-modified vermiculite using NaOH treatment exhibited a higher desorption efficiency by more than 80%. The sorption mechanisms including electrostatic interaction and reduction were involved in the Cr (VI) removal. The results showed that Fe2+-modified vermiculite can be used as a new adsorbent for Cr(VI) removal which has a higher adsorption capacity and a faster adsorption rate.

Transition Metals in Llano Vermiculite Samples: an EPR Study

Abstract: Continuous wave and pulsed electron paramagnetic resonance spectroscopies combined with thermal and chemical methods were used to identify and characterize V(IV), Fe(III), Mn(II) and Cr(III) in a multimineral system that consists of vermiculite and impurities of carbonates. All of these transition metals were structure-bound in mineral phases. The V(IV) was located in octahedral layers of the vermiculite and became oxidized to V(V) during the transformation of the host mineral to enstatite at about 800 °C. The Fe(III) was associated with the vermiculite as well as the carbonate impurities. The Fe(III) identified in the vermiculite was transferred into the enstatite structure during the thermal conversion. An indirect proof of Fe(III) and Cr(III) in the impurities was found in the heated samples in which these cations occurred in Ca and/or Mg oxides that were formed by transformation of the carbonates. The Mn(II) in the untreated samples was associated with the impurities and was also detected in oxides formed from the samples heated at 600 °C.

Improve the thermal and mechanical properties of poly(L-lactide) by forming nanocomposites with pristine vermiculite

Abstract: Poly(L-lactide) (PLLA)/pristine vermiculite nanocomposites were prepared by melt blending in a twin-screw extruder, and the detailed information of vermiculite dispersion state and effect of vermiculite on thermal and mechanical properties were systematically studied. The results show that the dispersion of vermiculite in the matrix is quite well when the loading content does not exceed 3 wt%. Pristine vermiculite can obviously improve the melt-crystallization temperature during the nonisothermal crystallization. Both crystallization time span and spherulitic size of PLLA decrease with the increasing amount of vermiculite under isothermal crystallization condition by enhancing the primary nucleation of PLLA. And the adding vermiculite can also improve the tensile modulus and Izod impact strength of PLLA. The intrinsic mechanism for the nucleating effect of vermiculite on PLLA is proposed to be the epitaxial crystallization and specific interaction between vermiculite and PLLA.