MATSUE Naoto Ehime Univ., Fac. Agric., Asst. Professor, 農学部, 助手 (90199753)
HENMI Teruo Ehime Univ., Fac. Agric., Assoc. Professor, 農学部, 助教授 (40093942)
|Budget Amount *help
¥6,900,000 (Direct Cost : ¥6,900,000)
Fiscal Year 1991 : ¥300,000 (Direct Cost : ¥300,000)
Fiscal Year 1990 : ¥300,000 (Direct Cost : ¥300,000)
Fiscal Year 1989 : ¥6,300,000 (Direct Cost : ¥6,300,000)
(1) Occurrence: Volcanic ash and non-volcanic ash soils were examined by means of selective dissolution combined with difference X-ray diffraction and Moessbauer spectroscopy. It was shown that ferrihydrite of various crystallinity were presented in ash soils, but it was absent or very small in amount in non-ash soils. Its presence in ash soils was considered to be related to ample supply of Si, as well as Fe, from volcanic glass in the early stage of weathering.
Field and laboratory observations suggested that ferrihydrite forms rapidly when the underground water containing ferrous iron exposed to air. Ferrihydrite formed this way is usually poorly-ordered in the sense that it shows only two X-ray diffractions at about 0.25 and 0.15 nm.
(2) Synthetic work: Well-crystallized ferrihydrite was synthesized from the solution containing Fe and Si in the ratios 10:1-2 and in the pH range 6-8. In the range lower or higher than these limits, ferrihydrite was not formed, or was coexisted with other iron minerals such as goethite or lepidocrocite formed. In the pH range > 11 feroxyhite was formed, suggesting that the mineral cannot form in the soils of usual pH range. Use of Ge, in the place of Si, results completely in the same as above. Comparison of d-spacings between synthetic Si- and Ge-ferrihydrite indicated that Si (and Ge) are not held in the structure of ferrihydrite, but held in the "outsides" of the crystal domains.
Organic anions, such as acetate and citrate, interfered with the formation of ferrihydrite, even though the interference may be different among the kind of anions.
(3) Attempts of measuring CEC and AEC, P-retention, and specific surface area for ferrihydrite in soils failed due to the lack of appropriate procedure. However, it was inferred that P-retention and specific surface area may be larger than or equal to, in magnitude, to clay constituents (aluminosilicates).