Long-term thermal loading study on the dehydration behavior of Ca-bentonites of unye (Ordu, NE Turkey)

Abstract

The aim of this study is to monitor the changes in physicochemical and mineralogical properties of three Ca-bentonite samples from unye (Ordu, NE Turkey). The effect of long-term (20, 30 and 40 days) thermal loading (100, 150 and 200 degrees C) treatments on the dehydration behavior of Ca-bentonites (CaB) was characterized in terms of the variations in the cation exchange capacity (CEC), specific surface area (SSA), pH, swelling index (SI), crystal structure and molecular fingerprints. CEC of raw CaB samples (52.3-62.7 meq/100 g) shows maximum decrease at 40 days to 29.9-37.3 meq/100 g at 100 degrees C, 19.4-25.4 meq/100 g at 150 degrees C and 20.9-23.9 meq/100 g at 200 degrees C. Long-term thermal loading also lowers the SSA of CaB samples from 42.8-51.4 m(2)g(-1) to 19.6-30.6 m(2)g(-1) at 100 degrees C, 15.9-20.8 m(2)g(-1) at 150 degrees C and 17.1-19.6 m(2)g(-1) at 200 degrees C. The strong alkalinity of the CaB samples (pH 9.3-9.7) changes from slight to moderate (7.7-8.6) at 200 degrees C. The swelling index of CaB samples shows narrow-range variations from 4.4-7.5 mL/2 g (raw) to 4.2-5.3 mL/2 g at 100 degrees C, 4.2-5.8 mL/2 g at 150 degrees C and 3.7-5.8 mL/2 g at 200 degrees C at 40 days. Thermal loading has also the imprints on the molecular scale in the loss of capillary condensed and adsorbed water vibrations (similar to 3388 cm(-1)). The dehydration effect at 100 and 150 degrees C thermal loadings is revealed by the broadening and asymmetry of the basal reflection with a decrease in the intensity; on the other hand, 200 degrees C treatment at 40 days results in the appearance of similar to 1 nm reflection which is suggested to be the beginning of illitization.