Effect of heating temperature on Li-fixation, layer charge and properties of fine fractions of bentonites

The fine fractions (<2 mum) of four bentonites, in which the dominant miner als were Al-rich montmorillonites of various chemical compositions, have be en Li-saturated. The admixtures identified in the fine fractions include py rophyllite in Otay (USA), amorphous SiO2 in Ivancice (Czech Republic) and o pal CT in Sarigus (Armenia) samples, while the Kriva Palanka sample (Macedo nia) was a pure montmorillonite. The sample portions were heated at differe nt temperatures (110 to 300 degreesC) for 24 h to promote Li-fixation in th e layers in order to reduce the negative charge on the layers in a systemat ic manner. Hence a series of materials with gradually decreasing charge, ca tion exchange capacity (CEC) and swelling ability were prepared. The CEC of the prepared samples was affected by the admixtures present and by the ext ent of Li+ for Ca2+ exchange in the starting material. The largest reductio n in CEC (by 81%) was obtained for Otay montmorillonite, the mineral with t he lowest tetrahedral and the highest octahedral charge, heated at 300 degr eesC. The extent of Li-fixation was very sensitive to the treatment tempera ture in the range 110-200 degreesC. The development of uncharged layers wit h non-swelling interlayers occurred in all materials heated above 150 degre esC. The shift of the OH-stretching band to higher wavenumber and a new ban d due to an AlMgLiOH stretching vibration in the infrared spectra confirmed the penetration of Li into the previously vacant octahedral sites.