In this article, the effects of calcination temperature and calcination atmosphere on the properties of the lime produced during flash calcination of industrial lime mud samples in a pilot-sized drop tube furnace have been studied. Flash calcination was performed at a wide range of temperatures between 800 and 1300 °C and different gas mixtures containing N2, CO2, and H2O in the calcination atmosphere. The effect of the calcination condition on the key conditions of the produced CaO, such as chemical composition, surface area, porosity, and particle morphology, has been shown. The addition of CO2 to the inert atmosphere led to slower calcination rates and a higher onset temperature for the calcination, but no changes to morphology. Furthermore, the addition of H2O to the calcination atmosphere generally led to lower calcination rates at higher temperatures and smoother particles in comparison to CO2 and N2.