The Effect of Heat Treatments on the Total Charge and Exchangeable Cations of Ca-, Na-, and Li-Saturated Kaolinite

Kurt D. Pennell1, R. Dean Rhue2 and Willie G. Harris2
1 Department of Civil Engineering, The University of Michigan, Ann Arbor, Michigan 48109
2 Soil Science Department, University of Florida, Gainesville, Florida 32611

Abstract: The effect of heat treatments on the total charge and water adsorption by Ca-, Na- and Li-saturated kaolinite was studied using extraction techniques and thermal gravimetric analysis, respectively. Measurements of cation exchange capacity indicated that the total charge of Li-kaolinite was reduced by approximately 50% after heating to 110 or 130°C. In contrast, the total charge of Ca-kaolinite remained essentially constant while that of Na-kaolinite decreased slightly. Water adsorption and desorption on Ca- and Li-kaolinite following heat treatments at 150°C were consistent with the total charge of the respective kaolinites. Ion extraction of Li-kaolinite using NH4Cl revealed that only 6% of the Li remained exchangeable after heating, while Al and H were released. Thus, non-exchangeable Li ions not only reduced the total charge of the kaolinite but also displaced Al and H from the kaolinite structure. Infrared spectroscopy also indicated that Li migrated into the kaolinite structure and replaced a portion of the Al from the octahedral sheet. The results presented here indicate that Li-kaolinite represents a surface of reduced charge rather than a surface free of cation-hydration effects. Therefore, Li-kaolinite is not recommended as a reference for the study of vapor-phase adsorption, and conclusions based on such a reference material should be reevaluated.

Key Words: Kaolinite • Cation exchange capacity • Water adsorption • Lithium retention

Clays and Clay Minerals; June 1991 v. 39; no. 3; p. 306-315; DOI: 10.1346/CCMN.1991.0390311
© 1991, The Clay Minerals Society
Clay Minerals Society (www.clays.org)