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Geological controls on kaolin particle shape and consequences for mineral processing

Published online by Cambridge University Press:  09 July 2018

A. Psyrillos ,
J. H. Howe ,
D. A. C. Manning  and
S. D. Burley
A. Psyrillos
Affiliation:
Department of Earth Sciences, Oxford Road, University of Manchester, Manchester M13 9PL, UK
J. H. Howe
Affiliation:
English China Clays International Ltd., John Keay House, St. Austell, Cornwall PL25 4DJ, UK
D. A. C. Manning*
Affiliation:
Department of Earth Sciences, Oxford Road, University of Manchester, Manchester M13 9PL, UK
S. D. Burley
Affiliation:
Department of Earth Sciences, Oxford Road, University of Manchester, Manchester M13 9PL, UK
*
2Corresponding author
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Abstract

The kaolinized granites of St. Austell, England, are worked to produce a range of china clay products, for some of which the kaolin has to meet stringent particle shape and size specifications. Systematic petrographic study indicates that kaolin occurs in the form of two textural types: (i) finely crystalline kaolin (typically <5 µm in average diameter), which infills dissolution porosity of granitic feldspars, and (ii) coarsely crystalline vermiform aggregates (up to 100 µm or more in length), which are closely associated with expanded micas. The vermiform aggregates are characterized by an intergrowth of mica and kaolin crystals, which can be observed at scales of resolution offered by TEM. Textural and chemical evidence suggest that the expanded mica texture is probably the result of preferential precipitation of kaolin along mica cleavage planes and is not simply a process of chemical replacement.

Petrographic examination of kaolin slurries sampled at different points in a typical refinery circuit indicates that platy products with high aspect ratio are derived exclusively from raw materials rich in vermiform aggregates. The fine scale intergrowth of kaolin and mica within the aggregates results in circumstances where mica persists through to fine grained products. Furthermore, the absence of Fe or other chemical components in the kaolin structure suggests that any iron reported for the final products may be a consequence of the presence of Fe-bearing mica within a very fine grained intergrowth.

Type
Research Article
Information
Clay Minerals , Volume 34 , Issue 1 , March 1999 , pp. 193 - 208
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1999

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Footnotes

1

Venizelou 48, Nea Smyrni GR-17122, Athens, Attiki, Greece

3

BG Technology, Ashby Road, Loughborough, Leicestershire LE11 3QU, UK

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