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Nickel-bearing clay minerals: II. Intracrystalline distribution of nickel: an X-ray absorption study

Published online by Cambridge University Press:  09 July 2018

A. Manceau  and
G. Calas
A. Manceau
Affiliation:
Laboratoire de Minéralogie-Cristallographie, UA CNRS 09, Universités Paris 6 et 7, 4 place Jussieu, 75230 Paris Cedex 05, and Laboratoire pour l'Utilisation du Rayonnement Electromagnétique (LURE), CNRS, 91405 Orsay, France
G. Calas
Affiliation:
Laboratoire de Minéralogie-Cristallographie, UA CNRS 09, Universités Paris 6 et 7, 4 place Jussieu, 75230 Paris Cedex 05, and Laboratoire pour l'Utilisation du Rayonnement Electromagnétique (LURE), CNRS, 91405 Orsay, France
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Abstract

The mechanism of Ni-Mg substitution has been studied by X-ray absorption spectroscopy in phyllosilicates belonging mainly to the lizardite-nepouite and kerolite-pimelite series. Two types of information were obtained: (1) Analysis of nickel K-edge spectra under high resolution confirmed that Ni atoms were substituted for Mg atoms. There was no evidence for 4-fold coordinated Ni. (2) Extended X-ray absorption fine structure (EXAFS) was sensitive to atomic pair-correlations and gave access to the radial distribution function around Ni atoms. For all samples, this function gave two peaks. The first one was related to the (O,OH) coordination shell and analysis confirmed that Ni atoms were 6-fold coordinated. The amplitude of the second peak was very sensitive to the atomic composition of the Ni-Mg second shell. It is shown that the intracrystalline distribution of Ni is never random within the octahedral sheet; Ni atoms are segregated into domains, the minimum size of which has been calculated. In the kerolite-pimelite series the mean domain size is at least 30 Å and EXAFS could not exclude the existence of pure Ni sheets. X-ray dispersive spectroscopy combined with TEM suggested that the minerals in this series have pure Ni layers associated with pure Mg layers. In the lizardite-nepouite series, Ni atoms are segregated into specific Ni-enriched areas, the exent of which depends on the specific chemical constitution of the sample. Distribution patterns are discussed with respect to the formation mechanisms of these ore minerals.

Type
Research Article
Information
Clay Minerals , Volume 21 , Issue 3 , September 1986 , pp. 341 - 360
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1986

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