Structural vanadium in synthetic goethite
1994; Elsevier BV; Volume: 58; Issue: 20 Linguagem: Inglês
10.1016/0016-7037(94)90338-7
ISSN1872-9533
Autores Tópico(s)Geochemistry and Elemental Analysis
ResumoA significant correlation between Fe and V in many weathered profiles suggests a close geochemical association of the two elements. Because V3+ is the dominant form of V in primary rocks, and because an isostructural VOOH (montroseite) exists, we suspect that goethite, FeOOH, might incorporate V3+ in its structure. We synthesized Fe1−xVxOOH with x up to 0.06. Because the ionic radii of V3+ and high spin Fe3+ are very similar (64.5 vs. 64.0 pm), even a careful measurement of the unit cell parameters did not reveal a statistically significant difference. Structural incorporation was, therefore, demonstrated by congruent dissolution in 6 M HCl. Equivalent amounts of Fe2+ and V found in the acid digest were presumably formed by the reaction V3+ + Fe3+ + H2O = VO2+ + Fe2+ + 2H+. An EPR spectrum did not indicate V 4+. For these and steric reasons, it is postulated that V is incorporated into goethite as a trivalent cation rather than as a combination of V 4+ and Fe2+.
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