INFRARED VIBRATIONS OF HEMATITE FORMED FROM AQUEOUS-THERMAL AND DRY-THERMAL INCUBATION OF SI-CONTAINING FERRIHYDRITE

Ferrihydrite samples having Si/Fe molar ratios ranging from 0 to 1 were synthesized by the reaction of Fe2(SO4)3 and Na2SiO3 with NaOH to an equilibrium pH of 8.2. Hematite formed by incubating the ferrihydrite (Si/Fe molar ratios 0.05) at pH 12.5 and 91C for 36 hr had a globular morphology. Hematite formed from Si-free ferrihydrite gave infrared (IR) bands at 548, 471, 397, and 337 cm-1, whereas, hematite formed from Si-containing ferrihydrite having 0.001 to 0.05 Si/Fe molar ratios gave broad IR bands at about 550, 450, and 330 cm-1. Ferrihydrite having Si/Fe molar ratios 0.10 did not transform to hematite following the aqueous-thermal treatment. Differences in the IR vibrations of hematite formed during aqueous- and dry-thermal treatments of the ferrihydrite samples were probably due to differences in the particle size and morphology of the product. The Si content influenced the IR pattern of the product. Particle morphology and IR spectroscopy may therefore by useful indicators of the precursor of hematite and the conditions of hematite formation in soil. -from Authors

INFRARED VIBRATIONS OF HEMATITE FORMED FROM AQUEOUS-THERMAL AND DRY-THERMAL INCUBATION OF SI-CONTAINING FERRIHYDRITE Academic Article