Characterization of rectorite from the Beatrix Gold Mine in South Africa

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Authors

Atanasova, Maria T.
Vyalikh, Anastasia
Scheler, Ulrich
Focke, Walter Wilhelm

Journal Title

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Publisher

Elsevier

Abstract

Three rectorite samples from the Beatrix Gold Mine, South Africa were characterized. Scanning electron microscopy revealed a layered morphology. High resolution transmission microscopy showed well distinguished light and dark layers of about 2.20 nm consistent with the 1:1 interstratified mica-smectite nature. X-ray diffraction measurements confirmed the basal spacing d001 of 2.20 nm consistent with a one-water-layer structure. Unit cell parameters, for a monoclinic unit cell with primitive lattice, refined to a = 5.177 Å; b = 8.980 Å; c = 22.489 Å and β = 97.335° with mean crystallite size around 14 nm and calculated cell volume of 1045 Å3. The Greene-Kelly test suggested that the expandable smectite layers have montmorillonite-beidellite composition. Nuclearmagnetic resonance spectroscopy indicated a high degree of Al substitution and the presence of two different Al sites corresponding to six- and four-fold octahedral and tetrahedral aluminumrespectively. The chemical composition and diffraction data suggest that the mica is Na-Ca-rich, i.e. of paragonite-margarite series. The fixed interlayer regions (mica interlayers) contains proportionally dominant Na+ and Ca2+ and minor amounts of K+. The exchangeable smectitic interlayers contain almost equal amounts of Na+ and Ca2+ ions. The distribution of the interlayer Na+ ions was quantified by 23Na solid-state NMR spectroscopy. It points to a three component mixed-layer structure with considerable variation in the composition of the mica layer of the different samples.

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Keywords

Rectorite, Mixed-layer, Interstratification, Solid-state NMR, Thermal analysis, Scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray powder diffraction (XRD)

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Citation

Atanasova, MT, Vyalikh, A, Scheler, U & Focke, WW 2016, 'Characterization of rectorite from the Beatrix Gold Mine in South Africa', Applied Clay Science, vol. 126, pp. 7-16.