Preparation of spherical apatite particles by the homogeneous precipitation method in the presence of magnesium ions and their ion-exchange properties

Spherical apatite particles were prepared by the homogeneous precipitation method in the presence of magnesium ions. The starting solutions were prepared by mixing 0.167 mol·L−1 of Ca(NO3)2, 0.100 mol·L−1 of (NH4)2HPO4, 1.00 mol·L−1 of (NH2)2CO, 0.10 mol·L−1 of HNO3, and a small amount of Mg(NO3)2. The carbonate-containing apatite powders were obtained by heating these solutions at 80∼95°C for 48∼192 h. Although fibrous particles with long-axis lengths of 30 to 60 μm were obtained from the magnesium-free solution, spherical agglomerates with diameters of ∼10 μm, which contained minute plate-like particles, were present in the apatite powders derived from the solutions with 5 mass% of magnesium ions. The ion-exchange test for the harmful ions (Pb2+, Cd2+, and Ni2+) showed that the ion-exchange abilities of the apatite powders containing magnesium ions were much better than the ability of the magnesium-free apatite powder. The ion-exchanged amounts of the apatite powder containing magnesium ions were arranged in the following order: Pb2+ >> Cd2+ > Ni2+.