Reaction of calcium hydroxyapatite with Cd2+ and Pb2+ ions

Calcium hydroxyapatite (CaHap) particles with different atomic Ca/P ratios were immersed into the solutions containing Cd2+ or Pb2+ ions at 30 °C for different periods. The compositions of the solutions and particles before and after immersing were determined. The sorption of Cd2+ reached equilibrium within a short time of ca. 15 min without changing the morphology and crystal structure of CaHap particles. The sorption of Pb2+ continued for ca. 180 min, followed by coating of the CaHap particles with PbHap and formation of PbHap particles. The amount of incorporated Cd2+ was almost independent of the Ca/P ratio of CaHap while that of incorporated Pb2+ was decreased with the increase in Ca/P ratio. The reaction with Cd2+ took place through the surface layer dissolution of CaHap particles and recrystallization of a new layer of CdCaHap solid solution onto the particles.