Interpretation of Alkylammonium Characterization of Soil Clays1
- D. A. Laird,
- A. D. Scott and
- T. E. Fenton2
The alkylammonium method of characterizing the charge of layer silicates has recently been applied to soil clays containing mixed mineral assemblages. Various sharp, low-angle x-ray diffraction (XRD) peaks (e.g., 2.5 nm for tetradecylammonium-treated samples) have been attributed to vermiculite or high-charge smectite. To the degree that alkylammonium cations can replace interlayer K+, however, the observed low-angle peaks may represent K+-depleted soil illite as well as vermiculite. This hypothesis was tested by treating two reference illites with alkylamine hydrochlorides. The treated illites exhibited low-angle XRD peaks similar to those observed in the soil clays. Moreover, the occurrence of these low-angle peaks coincided with the release of K+ from the illites. Similarly, the alkylamine hydrochloride treatments for layer-charge determinations released as much as 49% of the K+ from a soil clay. These data clearly show that the alkylammonium method can expand soil illites to give low-angle XRD peaks, which may be misinterpreted as evidence of soil vermiculite.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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