Quantification of Crystalline and Noncrystalline Material in Ground Kaolinite by X-ray Powder Diffraction, Infrared, Solid-State Nuclear Magnetic Resonance, and Chemical-Dissolution Analyses1

Hideomi Kodama2, Luba S. Kotlyar3 and John A. Ripmeester3
2 Land Resource Research Centre, Research Branch, Agriculture Canada Ottawa, Ontario K1A 0C6, Canada
3 National Research Council of Canada, Division of Chemistry, M-12 Montreal Road Ottawa, Ontario K1A 0R9, Canada
1 Land Resource Research Centre Contribution LRRC89-11, a joint contribution with National Research Council of Canada.

Abstract: The capabilities of X-ray powder diffraction (XRD), infrared absorption (IR), solid-state magic-angle-spinning nuclear magnetic resonance (MAS-NMR), and chemical dissolution methods were assessed for estimating the amount of noncrystalline material in a ground kaolinite. The Georgia kaolinite was ground in a mechanical mortar for various lengths of time to produce a set of ground samples containing different amounts of the resulting noncrystalline material. In the XRD method, the intensities of characteristic reflections at 7.2 and 4.47 Å did not respond proportionally to the amount of crystalline kaolinite. Although a transmission-type X-ray diffraction method using the hk reflection gave a slightly better estimate than the reflection-type X-ray diffraction method using the basal reflection, both methods gave overestimated values for the amount of noncrystalline material. This overestimation may have been caused by a masking effect due to coaggregation. Using the characteristic IR absorption band at 3700 cm-1 underestimated the amount of the noncrystalline material, if the proportion of this material <50%.

Extraction with NaOH gave estimations 15 to 20% greater than extraction with alkaline Tiron, except for the sample ground for 24 hr, for which both extractions indicated the presence of about 50% noncrystalline material. X-ray powder diffraction data of the residues after these extractions indicated that they consisted of crystalline kaolinite. 29Si NMR spectra of samples ground for ≥30 hr suggested that SiO4 tetrahedra were considerably distorted. 27Al NMR spectra showed a signal for tetrahedral Al for the sample ground for 10 hr, which increased with an increase in grinding time. Plots of the Al(IV)/[Al(IV) + Al(VI)] ratios vs. time were similar to those of chemical extraction curves. Inasmuch as extraction with hot 0.5 M NaOH is a rather harsh treatment, the composition of the noncrystalline material must have been similar to that of the crystalline kaolinite. The chemical dissolution using alkaline Tiron appeared to be superior to other methods, such as XRD, IR, and NaOH extraction, for estimating the amount of noncrystalline material in kaolinite.

Key Words: Chemical dissolution • Dry grinding • Infrared spectroscopy • Kaolinite • Noncrystalline • Nuclear magnetic resonance • X-ray powder diffraction

Clays and Clay Minerals; August 1989 v. 37; no. 4; p. 364-370; DOI: 10.1346/CCMN.1989.0370410
© 1989, The Clay Minerals Society
Clay Minerals Society (www.clays.org)