Abstract
Vermiculite is a mineral with many potential uses in various industrial areas, such as in insulation, horticulture, and environmental applications. The regolith of the Sokli carbonatite intrusion in northern Finland consists of weathered micas which reportedly contain vermiculite. The aim of the present study was to characterize the weathered mica in order to determine if the weathered regolith contains vermiculite. If so, the value of the apatite-rich Sokli intrusion may increase, because the vermiculite could be classified as an ore in Sokli. For the characterization, mica fractions were investigated using electron probe microanalysis (EPMA), X-ray diffraction (XRD), and thermogravimetric analysis (TGA). The EPMA results show that the potassium (K2O) content of the mica investigated varies between 6.20 and 0.31 wt.%. The XRD results provided evidence that the interlayer distances in the mica vary between 10.1 and 14.7 Å. The TGA shows that the dehydration of the samples varies between 6 and 12 wt.% for temperatures up to 170°C. Dehydroxylation takes place in three steps, as is characteristic for vermiculite. The results from this study revealed that mica in the weathered parts of the Sokli carbonatite is mostly vermiculite, and that the vermiculite was formed by the weathering of phlogopite. These results can be used to determine whether vermiculite is a possible future commodity at the Sokli carbonatite complex.
Highlights
The demand for vermiculite has increased recently
Vermiculite is not mined in Finland even though it has been reported to exist at the Sokli carbonatite intrusion (Vartiainen 1974; Kresten & Berggren 1978; O'Brien & Hyvönen 2015)
The purpose of the present study was to test the hypothesis that mica flakes from Sokli are mostly vermiculite by performing detailed mineralogical analyses of mica flakes from the weathered surface of the Sokli massif, using a battery of methods, including electron probe microanalysis (EPMA), thermogravimetric analysis (TGA) and X-ray diffraction (XRD)
Summary
The physical and chemical properties of natural vermiculite, such as low density, high cation exchange capacity, and high adsorption ability (Bergaya & Lagaly 2013), are the reasons for using vermiculite in building materials, the chemical industry, and in various applications in environmental protection and agriculture (Huo et al 2012). Among these uses are as nonflammable packing material, water purification by ion exchange (Rama et al 2019), and thermal insulation (Bergaya & Lagaly 2013). The term Fhydrobiotite_ was interpreted as regular 1:1 interstratification of biotite (or interlayerdeficient biotite) and vermiculite (Rieder et al 1998; Valášková et al 2018)
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