抄録
Ferrihydrite and feroxyhyte were synthesized at room temperature from 0.1M FeSO4. Fcrrihydrite, 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. Synthetic products at pH 7 from Fe (NO3) 3 and Fe (CIO4) 3 were 2-line ferrihydrites irrespective of the presence of Si, and those from FeCl2 were lepidocrocitc in the presence and magnetite in the absence of Si.
The products from FeSO4 at pH 12 yielded 4 diffraction lines for feroxyhyte. Either Si or Gc seemed to effect the formation of the mineral, because, in the absence of these cations at the same pH, the oxidation of Fe (II) never proceeded from the stage of green rust. Electron microscopic examination showed that ferrihydrite appears as shapeless assemblies of granular texture, and feroxyhyte consists of numerous “rod-like” particles about 4 nm wide and 70 nm long.
