Thermal Decomposition of Şaphane Alunite Ore

The thermal decomposition of Şaphane alunite from Kütahya, Turkey, has been studied using ambient- and high-temperature X-ray diffraction analysis, differential thermal analysis, and thermogravimetric analysis. The alunite content in the ore was about 47.5%. The first endothermic peak at about 545 °C is due to the dehydration of the structural water and the transformation of alunite into KAl(SO 4 ) 2 and amorphous Al 2 O 3 . The small exothermic peak at about 712 °C is probably caused by the recrystallization of KAl(SO 4 ) 2 into K 3 Al(SO 4 ) 3 and Al 2 (SO 4 ) 3 . So far, no work has reported this new phase, K 3 Al(SO 4 ) 3, resulting from the exothermic reaction of alunite. Moreover, the d and I values of unidentified peaks in the previous literature gave reflections that were surprisingly identical to those of the K 3 Al(SO 4 ) 3 peaks. The second endothermic peak at about 810 °C is due to the desulfurization by which K 3 Al(SO 4 ) 3 and amorphous Al 2 (SO 4 ) 3 decompose into K 2 SO 4 (arcanite) and two polymorphic varieties of Al 2 O 3 (κ and γ). Above 800 °C, only γ-alumina and arcanite were observed.