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A Mössbauer study of green rust precipitates: I. Preparations from sulphate solutions

Published online by Cambridge University Press:  09 July 2018

A. H. Cuttler ,
V. Man ,
T. E. Cranshaw  and
G. Longworth
A. H. Cuttler
Affiliation:
Polytechnic South West, Plymouth, Devon PL4 8AA, UK
V. Man
Affiliation:
Polytechnic South West, Plymouth, Devon PL4 8AA, UK
T. E. Cranshaw
Affiliation:
AEA Technology, Harwell, Didcot, Oxfordshire, OX11 0RA, UK
G. Longworth
Affiliation:
AEA Technology, Harwell, Didcot, Oxfordshire, OX11 0RA, UK
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Abstract

The preparation of green rusts from sulphate solutions and representative Mössbauer spectra are described. As the samples oxidized readily, attention focused on the Mössbauer parameters at liquid nitrogen and helium temperatures. The spectra recorded at 77 K could be fitted satisfactorily with one ferrous iron quadrupole doublet with a separation of 2·93 mms−1 and one ferric iron quadrupole doublet with a separation of 0·45 mms−1. In some spectra a ferric iron magnetic hyperfine of strength 49·2 T was also apparent. At 4·2 K, the ferrous iron exhibited a hyperfine splitting with a field of 12·4 T whilst the ferric iron exhibited a hyperfine splitting with a field of strength 50·4 T. The ratio of ferrous to ferric ions was 2·25 ± 0·25 at 77 K and at 4·2 K, and ∼1·6 with a large variation at room temperature. The liquid helium spectra did not always give a good chi-squared fit, the main reason being attributed to relaxation. The line-width of the ferrous iron site at 77 K is slightly larger than that for iron metal and could be explained by a variation in the number of near Fe3+ neighbours at different Fe2+ sites, consistent with the assumption that the ferrous iron site is in the hydroxide sheet. The effect of different numbers of Fe2+ and Fe3+ neighbours probably contributed to the increase in line-widths at 4·2 K compared with those at 77 K. The ferrous iron doublet is marginally different to those of chloride and hydroxy-carbonate green rusts and the aluminium analogues.

Type
Research Article
Information
Clay Minerals , Volume 25 , Issue 3 , September 1990 , pp. 289 - 301
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1990

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