Glass foams from acid-leached phlogopite waste
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Glass foams from acid-leached phlogopite waste Helena Maria Deysel1 , Kent Berluti1 and Walter Wilhelm Focke1,* 1
, Barend Jacobus du Plessis1
,
Department of Chemical Engineering, Institute of Applied Materials, University of Pretoria, Private Bag X20, Hatfield 0028, Pretoria, South Africa
Received: 11 February 2020
ABSTRACT
Accepted: 19 March 2020
XRD analysis and exfoliation behaviour of Palabora phlogopite flakes supplied by PMC indicate a heterogeneous mineralogical composition dominated by phlogopite and hydrobiotite. 4 M nitric acid leaching for 6 h at 65 °C resulted in amorphous silica flakes with a very high surface area (\ 450 m2 g-1). This was used to produce lightweight and high-strength glass foams via a direct foaming method. The best results were obtained with a formulation with borax:waterglass:amorphous silica 23:46:31 wt%. A closed-cell foam with a density of 0.326 g cm-3 and compressive strength of 2.09 MPa was obtained by heating a compacted mixture at ca. 6 K min-1 to 525 °C and keeping it at that temperature for 30 min before allowing it to cool down. These results suggest that the silica waste, obtained from acid leaching of phlogopite waste from mine tailings, could provide a valuable raw material for the manufacture of low-density glass foams.
Published online: 30 March 2020
Ó
Springer Science+Business
Media, LLC, part of Springer Nature 2020
Introduction Phlogopite is a constituent of the pegmatoid ultrabasic rocks found in the Palabora igneous complex [1]. Surface weathering under the influence of percolating water has, over geological time, led to the progressive vermiculitisation of the phlogopite [1]. According to Muiambo et al. [2], Palabora ‘‘vermiculite’’ is chiefly an interstratified material. Hillier et al. [3] identified it as mainly composed of hydrobiotite, a regular 1:1 interstratified vermiculite–biotite previously defined by Brindley et al. [4]. Operations at the Palabora open-pit mine centre on the extraction of copper and phosphate. This has led to the accumulation of an extensive stockpile of
‘‘phlogopite’’. For now, this is regarded as a waste, but in future, it could be exploited as a potential source of potassium and magnesium. Acid leaching of phlogopite has a long history [5–10], and it provides a possible route to the recovery of these elements. The acid-leached residue is a hydrated, layered but disordered, silica with a ‘‘distorted’’ structure [10]. However, macroscopically it still resembles the silicate sheets of the original mineral. Wypych et al. [10] proposed the following model for the formation of this ‘‘disordered’’ silica structure. The removal of the octahedral sheet from the original structures induces distortion in the silica sheets with the tilting of some bonds to produce alternate apical silanol groups. The bonds, which previously
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https://doi.org/10.1007/s10853-020-04589-4
8051
J Mater Sci (2020) 55:8050–8060
connected the octahedral sheet, end up being partially hydroxylated. T
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