The microstructural study of thermal treatment montmorillonite from Heping, China

The montmorillonite samples from Heping, China had been studied by chemical analysis, DAT, TG, XRD and MAS NMR. The results showed that the hydroxyl in octahedra sheets begins dehydrating, when the thermal treatment temperature reaches 650 °C, but the layer structure remains, the corresponding Al(VI) was turned into Al(IV) in octahedra sheets. When the temperature reaches 900 °C, the layer structure of montmorillonite is destroyed, and the new mineral phase μ-cordierite is found. When the temperature reaches 1200 °C, the μ-cordierite phase loses stability, and decomposes into cristobalite phase and mullite phase, meanwhile, the recrystallization phenomena in thermal treatment products is obvious. There is a small quantity of Al(VI) signal in MAS NMR spectrum, this Al(VI) corresponds to the Al of mullite. When the temperature reaches 1350 °C, the cristobalite and mullite phases reduce slightly, and more Fe-cordierite phase appear. There is corresponding Fe-cordierite spectrum in XRD and MAS NMR.