A Mössbauer study of green rust precipitates: I. Preparations from sulphate solutions
| Autor: | G. Longworth, T. E. Cranshaw, A. H. Cuttler, V. Man |
|---|---|
| Rok vydání: | 1990 |
| Předmět: |
Inorganic chemistry
chemistry.chemical_element 020101 civil engineering 02 engineering and technology 010502 geochemistry & geophysics 01 natural sciences Chloride 0201 civil engineering Ferrous chemistry.chemical_compound chemistry Geochemistry and Petrology Aluminium Mössbauer spectroscopy medicine Hydroxide Ferric Partial oxidation Hyperfine structure 0105 earth and related environmental sciences medicine.drug |
| Zdroj: | Clay Minerals. 25:289-301 |
| ISSN: | 1471-8030 0009-8558 |
| Popis: | The preparation of green rusts from sulphate solutions and representative M6ssbauer spectra are described. As the samples oxidized readily, attention focused on the M6ssbauer 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 rams -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 Fe 3+ neighbours at different Fe e+ sites, consistent with the assumption that the ferrous iron site is in the hydroxide sheet. The effect of different numbers of Fe 2+ and Fe 3+ 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. Green rusts are unstable compounds containing a mixture of ferrous and ferric iron and were first described by Keller (1948) who produced a chloride and a sulphate green rust. The ratio of ferrous to ferric iron was found to lie between 0.8 and 4-0. A study by Bernal et al. (1959) of iron oxyhydroxides, which included green rusts, identified two forms of the sulphate species as well as the chloride form. These green rusts were prepared "by the partial oxidation of ferrous iron solutions" but the method was not described in sufficient detail to enable repeat studies to be made. Misawa et al. (1973, 1974) made a study by ultra-violet spectroscopy and chemical analysis of the aerial oxidation of neutral and slightly alkaline ferrous sulphate solutions. An intermediate green complex was observed which was shown to be a precursor of green rust II and on that basis the ferrous to ferric ratio was estimated to be about unity. |
| Databáze: | OpenAIRE |
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