Kaolins: Sources of Differences in Cation-Exchange Capacities and Cesium Retention

C. H. Lim, M. L. Jackson, R. D. Koons and P. A. Helmke
Department of Soil Science, University of Wisconsin Madison, Wisconsin 53706

Abstract: Seven kaolins from Georgia (southeastern U.S.A.), ranging from high to low commercial grade, were characterized by X-ray powder diffraction and chemical techniques to establish that the variation in quality was caused by impurities. The Ca and Cs cation-exchange capacities (CEC) varied from 2.67 to 8.17 and from 3.29 to 8.77 meq/100 g, respectively. Selective dissolution and correlation analyses strongly indicated that expandable 2:1 minerals, particularly smectite (1.2–5.9%), were responsible for most of the observed variations in Ca CEC (r = 0.85*). The external surface CEC of kaolinite ranged from 0 to 1 meq/ 100 g. The positive significant correlation (r = 0.90**) between the Ca CEC and the K-mica content (0–3.9%) suggested that Ca CEC may be related to the degree of mica weathering through an expandable mineral stage.

The Cs-retention capacity (0.19–1.14 meq/100 g) was closely related to Cs-measured vermiculite content (r = 0.80*), and this content plus specific surface (R = 0.93**) or mica content (R = 0.86*). The Cs retention appeared to be primarily related to the presence of interlayer wedges at mica/vermiculite XY interfaces.

Key Words: Cation-exchange capacity • Cs retention • Interlayer wedges • Kaolinite • Vermiculite

Clays and Clay Minerals; June 1980 v. 28; no. 3; p. 223-229; DOI: 10.1346/CCMN.1980.0280309
© 1980, The Clay Minerals Society
Clay Minerals Society (www.clays.org)