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This article in SSSAJ

  1. Vol. 27 No. 6, p. 632-635
    Received: Dec 26, 1962
    Accepted: Apr 9, 1963

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Gibbsite Formation From Aluminum-Interlayers in Montmorillonite1

  1. R. I. Barnhisel and
  2. C. I. Rich2



Gibbsite crystallized from hydroxy-Al which previously had been precipitated on the interlayer surfaces of the 2 to 0.2µ fraction of montmorillonite. Hydroxy-Al interlayers were prepared with OH/Al molar ratios of 0.38, 0.75, 1.50, 2.25, and 3.00 and were aged 1, 3, and 6 months. In the samples that were not aged, the CEC decreased from 78 to 2 me. per 100 g. as the OH/Al molar ratio increased. In addition, the basal spacing increased from 10.2 to 14.7Å. (K-saturated, 300°C.) as the OH/Al molar ratio increased.

X-ray diffraction, thermo-gravimetric, and differential thermal analysis studies indicated that the hydroxy-Al interlayers formed with OH/Al molar ratios of 0.38, 0.75, and 1.50 were stable when aged 6 months; whereas, samples with OH/Al molar ratios of 2.25 and 3.00 were not. Gibbsite formed after 1 month in the sample with an OH/Al ratio of 3.00 and after 3 months in the sample with an OH/Al ratio of 2.25, and the amount of gibbsite increased with time. Gibbsite formed in the presence of montmorillonite at a pH of < 4.3. After the Al-interlayers were removed through gibbsite formation, the montmorillonite regained its cation-exchange capacity. The crystallization of gibbsite from Al-interlayers may be one mechanism for the formation of this mineral in some acid soils.

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