Synthesis of ferrihydrite and feroxyhyte

Ferrihydrite and feroxyhyte were synthesized at room temperature from 0.1 M FeSO 4 . Ferrihydrite, with 6 to 7 diffraction lines, formed at pHs 5-11 in the presence of Si (Fe:Si = 10:1). The use of Ge, in place of Si, resulted in the same, with the same d-spacings of the diffraction peaks. This indicates that the Si or Ge is not in the structure of ferrihydrite, but forms Fe-O-Si (or Ge) at the periphery of «domain» of ferrihydrite. The presence of Si or Ge was a requisite for the formation of ferrihydrite, because their absence led, at the pHs investigated, to the formation of goethite or lepidocrocite