A study of the mineralogical alteration of bentonite in saline water

The mineralogical alteration of bentonite was studied in saline water at 60 and 90 °C. To obtain the altered bentonite, a crude bentonite (Kunigel V1) was dispersed into simulated sea-water, and maintained at 60 or 90 °C over 6000 h. Magnesium was accumulated into bentonite during the experiments at levels over the cation exchange capacity (CEC; 0.78 meq/g for the original bentonite) at only 90 °C. The excess Mg was not replaced by ammonium ions, suggesting that the precipitation of Mg solid in bentonite occurred. The IR spectra and the thermogravimetric/differential Thermal Analysis (TG-DTA) profiles show the neo-formation of magnesium hydroxide in the altered bentonite. The CEC decreased from 0.78 to 0.45 meq/g as the amount of accumulated Mg increased. The distribution coefficient K_d for Cs in the altered bentonite was half of that in the original bentonite. It is conjectured that the thermal alteration of bentonite in saline water affects the sorption capacity of Cs onto smectite.