Mineralogical Properties of Clays from Panama Soils
1972
Reneau, , R. B. | Fiskell, J. G. A.
Panama soil clays from eight Alfisols were studied extensively by X-ray diffraction, DTA, and infrared spectroscopy. Composition of these clays was examined before and after sequential selective dissolution with citrate-dithionite and hot 0.5N NaOH for removal of amorphous components. Vermiculite was the dominant mineral in three clays, and smectite in four others. In one soil, a poorly crystalline mineral was present and this clay had an unusally large low-temperature endotherm which was attributed to a combination of halloysite, an expandable phyllosilicate, and amorphous materials. In the other clays the shape of the high-temperature endotherms indicated presence of kaolinite ranging in content from 19 to 27%. Infrared spectra showed a large absorption band of 3,450 cm⁻¹ for water adsorbed to clay surfaces indicating the presence of halloysite and/or 2:1 expanding phyllosilicates. Absorption bands at 910 cm⁻¹ found for some clays was attributed to A1-O-H bending presumably from halloysite. Mica content ranges from 1.4 to 12.0%. Considerable interlayer hydroxy-A1 and hydroxy Fe appears to be present in the expanding phyllosilicates from incomplete collapse of spacings after K saturation and heating to 550C. After sequential dissolutions, and allowing for CEC of kaolinite and mica, CEC of the expanding phyllosilicate fractions ranges from 61 to 152 meq/100 g at pH 4.8 and increased about 15% more when measured at pH 8.2.
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