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

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~ 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~ were consistent with the total charge of the respective kaolinites. Ion extraction of Li-kaolinite using NH4C1 revealed that only 6% of the Li remained exchangeable after heating, while A1 and H were released. Thus, non-exchangeable Li ions not only reduced the total charge of the kaolinite but also displaced AI and H from the kaolinite structure. Infrared spectroscopy also indicated that Li migrated into the kaolinite structure and replaced a portion of the A1 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 rec- ommended as a reference for the study of vapor-phase adsorption, and conclusions based on such a reference material should be reevaluated.