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Effect of Iron Removal and Dispersion Methods on Clay Mineral Identification by X-Ray Diffraction¹

ABSTRACT

The clay minerals identified in soil samples were found to be dependent on the pretreatment of samples for iron removal and dispersion. Treatments affected the characterization for chlorite, montmorillonite-type minerals, vermiculite, and intergrade components. Increases in the degree of expansion upon solvation and in degree of collapse upon K-saturation and heating were related to the severity of treatments used for dispersion. Iron removal treatments also increased the ease of expansion and collapse to 2:1 lattice clays. It was concluded that certain pretreatments tended to remove interlayered materials which were present in these samples.

The degree to which clay mineral interpretation was affected by methods of pretreatment was not the same for all soils. Samples of the Astoria soil exhibited the greatest differences in diffraction patterns as a result of dispersion and Fe removal treatments while the Aiken was the least affected. The Willamette was found to be intermediate. The evidence suggested that the Astoria samples contained interlayer materials (intergrade components) which were poorly crystallized and thus more labile and subject to removal. On the other hand, the interlayer material in the Aiken seemed to be better crystallized and more toward the chlorite end of the spectrum.

It has sometimes been assumed that the methods which permit the identification of the largest number of components with "clean-sharp" peaks are the ones which should be used in sample preparation. It is suggested that the objective should be to obtain methods which permit the identification and reflect the properties of clay minerals as they existed in situ.

¹ Contribution from Dept. of Soils, Oregon State University, Corvallis. Technical Paper No. 1496, Oregon Agr. Exp. Sta. Presented before Western Soil Science Society, June 16, 1960, Eugene, Ore.

² Associate Professor; formerly Instructor, now Soil Mineralogist, Scott Lab., Nairobi, Kenya; and Associate Professor of Soils, respectively.

Received for publication January 18, 1962. Accepted for publication June 8, 1962.