Thermal and chemical stability of Romanian bentonite

Ca-bentonite originating from a Romanian deposit was leached in 0.5-8.0 M HCl solution at 90 A degrees C for 4 h. This material was fully characterized through BET, thermogravimetry, X-rays diffraction, and elemental analysis. The acid treatment at high temperature altered the crystallinity, but produced an increase in the surface area and thermal stability. The resulting acid-treated bentonite turned out to be an efficient adsorbent in both liquid and gaseous media. The changes of the clay mineral properties were discussed in terms of structural modification of the bulk material and increase in the number of edge terminal aluminol and silanol sites. The kinetic parameters of first dehydration step, reaction order (n), apparent activation energy (E (a)) and pre-exponential factor (ln A) were calculated by the Freeman-Carroll method.