Original paper

Crystallization of hematite and goethite in the presence of soil minerals

Boero, Valter; Franchini-Angela, Marinella

European Journal of Mineralogy Volume 4 Number 3 (1992), p. 539 - 546

26 references

published: Jun 11, 1992
manuscript accepted: Oct 17, 1991
manuscript received: Dec 21, 1990

DOI: 10.1127/ejm/4/3/0539

BibTeX file

ArtNo. ESP147050403015, Price: 29.00 €

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Abstract Freshly precipitated ferrihydrite 5Fe2O3-9H2O was stored at pH 7 and 40°C alone and in the presence of muscovite, kaolinite, quartz, gibbsite and soil clay at various mg mineral per mole Fe ratios (20, 200 and 500). The crystallization of ferrihydrite into hematite and goethite was monitored after 20, 50, 100, 148 and 210 days using Feo/Fed ratios and XRD. After 210 days, the ferrihydrite suspension free of soil minerals was nearly completely (Feo/Fed = 0.10) converted into a mixture of goethite and hematite. The following materials retarded the crystallization of the iron oxides: deferrated soil clay > kaolinite > gibbsite > quartz. On the contrary, muscovite seems to promote the crystallization and induce a faster transformation of ferrihydrite into goethite and hematite. Also, the soil mineral/Fe ratio influences the crystallization of the iron oxides. The best differentiation between the studied minerals is observed when the amount of soil mineral is 200 mg per mole Fe. At 40°C and pH 7, all soil minerals, except the soil clay, induce the preferential crystallization of hematite possibly via an epitaxial mechanism rather than through ion interference. The best developed morphologies of hematite plates, also with 120° oriented goethite needles, were observed in the presence of muscovite, suggesting a strong template effect