8-FeOOH cation substitution

Scheinost A. C. and Schwertmann U. (1997) VIS-NIR reflectance spectra of goethite (a-FeOOH) as a function of particle size, luiit-cell size, and cation substitution. 28 Limar and Planetary Science Conference, March 17-21, Houston, TX. 

Extensive replacement of Fe by transition metal cations and alkaline earth ions has been reported for b-FeOOH (Okamoto, 1968). Muller et al. (1979) found incorporation of up to 0.4 mol moF Ca solid solutions with the formula Fei xKxOi x(OH)i+x could be identified. Jimenez-Mateos et al. (1990) reported that Co and Mn, respectively, could replace up to 0.3 and 0.5 mol mol Fe. The unit cell parameters decreased in both cases with increasing substitution. These Mn- and Co-substituted 5-FeOOHs decomposed at 200 °C to give poorly crystalline, substituted hematites. 

The Fe in the octahedral position may be partly replaced by other triva-lent metal cations of similar size, for example, Mn ", Cr and without modifying the structure isomorphous substitution). In this way solid solutions between pure end members (such as FeOOH and... 

Influence of Trivalent Cations Due to the common presence of Al-substituted a-FeOOH in natural samples (well oxidized soils), the Impact of Al-substitution on the properties of natural and synthetic goethite was... 

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