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Use of hydrofluoric acid dissolution for the concentration of dickite and nacrite from kaolin deposits: an FTIR study

Published online by Cambridge University Press:  09 July 2018

A. R. Fraser ,
M. J . Wilson ,
M. J . Roe  and
Z. Y. Shen
A. R. Fraser*
Affiliation:
Macaulay Land Use Research Institute, Craigiebuckler, Aberdeen, UK
M. J . Wilson
Affiliation:
Macaulay Land Use Research Institute, Craigiebuckler, Aberdeen, UK
M. J . Roe
Affiliation:
Macaulay Land Use Research Institute, Craigiebuckler, Aberdeen, UK
Z. Y. Shen
Affiliation:
Department of Earth Sciences, Zhejiang University, Hangzhou, China
*
*E-mail: a.fraser@macaulay.ac.uk
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Abstract

A series of kaolin-rich mineral samples was treated with hydrofluoric acid (HF) and the residual material characterized using infrared (IR) spectroscopy, supplemented by scanning electron microscope (SEM) observations. By examining the hydroxyl-stretching region of the IR spectra before and after treatment with hydrofluoric acid, it was possible to identify the three kaolin polytypes – kaolinite, dickite and nacrite – with greater certainty. The SEM observations suggested that the rate of dissolution of the kaolin phase was largely dependent on particle size. In general, dickite and nacrite tend to occur in the coarser clay fractions, and for this reason the finer-grained kaolinite is preferentially dissolved by the HF treatment. However, in the Keokuk kaolinite, which occurs in exceptionally large particles, it was still possible to concentrate a dickitic fraction by HF treatment, suggesting that in some cases kaolinite may be more susceptible to HF dissolution for reasons other than particle size. The IR spectra of disordered kaolinite could be interpreted as arising from a mixture of kaolinite and dickite components. However, both components dissolve at the same rate in HF, supporting the idea that disordered kaolinite consists of an intimate association of randomly stacked dickite-like and kaolinite-like components.

Keywords

Hydrofluoric acidinfrared spectroscopykaolinitedickitenacrite
Type
Research Article
Information
Clay Minerals , Volume 37 , Issue 3 , September 2002 , pp. 559 - 570
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2002

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