Characteristics of Ferrihydrites Formed by Oxidation of FeCl2 Solutions Containing Different Amounts of Silica

Zahurul Karim
Bangladesh Agricultural Research Institute, Joydebpur, Dhaka, Bangladesh

Abstract: Well-crystallized ferrihydrite as indicated by its X-ray powder diffraction pattern and low solubility in acidified oxalate (Feo/Fet = 0.27) was formed by the oxidation of FeCl2 solution containing Si/Fe = 18 × 10−3. The crystallinity of ferrihydrites formed from the solutions containing Si/Fe > 18 × 10−3 was lowered as indicated by weaker and broader XRD lines and increased oxalate solubility. Ferrihydrites formed in the presence of silica did not give the differential thermal analysis exothermic peak between 350° and 450°C that is found for ferrihydrites prepared from the hydrolysis of Fe(III) salts. The transformation of ferrihydrite (formed at Si/Fe = 18 × 10−3) to hematite was inhibited by the presence of 1.48% SiO2 in the oxidation products.

Key Words: Ferrihydrite • Hematite • Iron • Lepidocrocite • Oxidation • Silica

Clays and Clay Minerals; June 1984 v. 32; no. 3; p. 181-184; DOI: 10.1346/CCMN.1984.0320304
© 1984, The Clay Minerals Society
Clay Minerals Society (www.clays.org)