Abstract: The effects of SiO₂, Al₂O₃ and MgO on the hydration of lime were investigated by isothermal calorimetry, and the results were validated by 5 types of lime used in the sintering plant. It is found that the total hydrating heat of lime has positive relationship with CaO content, and decreases with increasing SiO₂, Al₂O₃ and MgO contents. The contents of SiO₂, Al₂O₃ and MgO also have important effect on the hydrating speed of lime. When the mass fraction of SiO₂ increases to 1%, the hydrating speed of lime dramatically decreases, and then slowly drops with increasing SiO₂ content. A small amount of Al₂O₃ has no significant effect on the hydrating speed of lime, but when the mass fraction of Al₂O₃ is more than 2%, the hydrating speed of lime sharply decreases. With the increase of MgO content, the hydrating speed of lime significantly decreases.