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• Polyhalite ore started to decompose into anhydrite and langbeinite at 573 K. • The changes of internal models of vibration of SO 4 indicated a phase transformation. • The most probable mechanism function matched D3 Janders diffusion mechanism. • Calcination and hot-leaching could improve the extraction of potassium. In this paper, the thermal decomposition of polyhalite ore from Dayantan Playa in Qaidam Basin of China was investigated by X-ray powder diffractometry (XRD), Raman spectroscopy (Raman), and thermal analysis techniques (TG-DTG). The dehydration reaction of polyhalite ore takes place with the release of water and starts at about 510 K. The results of X-ray diffraction of roasting sample showed that polyhalite ore starts to decompose into anhydrite and langbeinite at 573 K. Raman spectroscopy, in conjunction with X-ray diffraction, was also used to follow the thermal decomposition of polyhalite ore. The changes of internal models of vibration of the SO 4 ions in sulfates indicated the phase transformation polyhalite, langbeinite, and anhydrite. The reaction kinetics of thermal decomposition of polyhalite ore were successfully modeled by a Coats-Redfern equation (ln g (α) T 2 = ln A R β E 1 − 2 R T E − E R T ) and the activation energy is found to be 208 kJ·mol−1. Additionally, the effect of roasting temperature on potassium extraction from polyhalite ore was studied. [ABSTRACT FROM AUTHOR]