Characterization of rectorite from the Beatrix Gold Mine in South Africa
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Date
Authors
Atanasova, Maria T.
Vyalikh, Anastasia
Scheler, Ulrich
Focke, Walter Wilhelm
Journal Title
Journal ISSN
Volume Title
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.
Description
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.