In order to control the properties of hydroxyapatite particles, the method based on neutralization of a suspension of lime with orthophosphoric acid is studied. The dissolution of lime is the first step in the process and is described here. After a preliminary study of the hydrodynamics of the reactor, a kinetic model, based on diffusion theory; was developed. It describes the increase of calcium concentration in a dynamic system. The effects of stirring rate, temperature and acid flow rate on the dissolution of lime were determined experimentally. The acid flow rate influenced the reaction rate the most.