The pentlandite exsolution from monosulfide solid solution (mss)/pyrrhotite exsolution is a complex multi-step process, including nucleation, new phase growth and atomic diffusion, and lamellae coarsening. Some of these steps occur in sequence, others simultaneously. These make its kinetic analysis difficult, as the mechanisms cannot be elucidated in detail. In mineral reactions of this type, the true functional form of the reaction model is almost never known, and the Arrhenius parameters determined by the classic Avrami method are skewed to compensate for errors in the model. The model-free kinetics allows a universal de-termination of activation energy. Kinetic study of pentlandite exsolution from mss/pyrrhotite was performed over the temperature range 200 to 300 ℃. For mss/pyrrhotite with bulk composition (Fe0.77Ni0.19)S, activation energy of pentlandite exsolution, Ea, varies from 49.6 kJ·mol1 at the beginning of reaction (nucleation is dominant) to 20.7 kJ·mol1 at the end (crystal growth is dominant). In general, the activation energy varies during the course of solid reaction with the extent of reaction. The surrounding environment of reactant at-oms affects the atom’s activity and more or less accounts for changes of activation energy Ea. The pentlandite exsolution from monosulfide solid solution (mss) / pyrrhotite exsolution is a complex multi-step process, including nucleation, new phase growth and atomic diffusion, and lamellae coarsening. Some of these steps occur in sequence, others simultaneously. These make its kinetic analysis difficult, as the mechanisms can not be elucidated in detail. the true functional form of the reaction model is almost never known, and the Arrhenius parameters determined by the classic Avrami method are skewed to compensate for errors in the Kinetic study of pentlandite exsolution from mss / pyrrhotite was performed over the temperature range 200 to 300 ° C. For mss / pyrrhotite with bulk composition (Fe 0.77 Ni 0.19 ) S, activation energy of pentlandite exsolution, Ea, varies from 49.6 kJ · mol1 at the beginning of reaction (nucleation is dominant) to 20.7 kJ · mol1 at the end (cr The general environment of reactant at-oms affects the atom’s activity and more or less accounts for changes of activation energy Ea.