Exchange characteristics of carbonate-containing apatite for Al³⁺, La³⁺ and Y³⁺ ions

The exchange characteristics of synthetic carbonate-containing apatite for Al³⁺, La³⁺ and Y³⁺ ions in aqueous solutions have been investigated by a normal batch method at 25 °C, and compared with those of hydroxy-apatite. From the results, it was found that the exchange characteristics for Al³⁺ ions increased with CO₃^2- ion content, and the uptake of Al³⁺ ions in aqueous solution with low initial concentrations was driven forward by the cation-exchange reaction between Ca²⁺ ions in the apatite sample and Al³⁺ ions in aqueous solution. On the other hand, the exchange characteristics of both the apatites for Al³⁺ ions were found to be reduced considerably in the system in which Al³⁺ and Pb²⁺ ions coexist. In the reactions with La³⁺ and Y³⁺ ions, a significant difference between the removal characteristics of both apatites was not observed, and crystalline LaPO₄ and Y³⁺ ion-exchanged apatites were produced by the uptake of La³⁺ and Y³⁺ ions, respectively. These results should lead to important information for the clinical investigations of the roles played by the trivalent cations in inhibiting dental caries and for medical investigations of the behaviour of Al³⁺ ions in the human body.