Synthetic carbonate apatites as inorganic cation exchangers. Exchange characteristics for toxic ions

The ion-exchange characteristics between Ca²⁺ ions in carbonate apatites containing 6 and 16 wt % CO₃^2- ions and toxic ions (Zn²⁺, Cd²⁺, Hg²⁺, and Pb²⁺) in aqueous solution have been investigated in detail at 25 °C. From the results, it was found that the ion-exchange removal characteristics for Zn²⁺, Cd²⁺ and Pb²⁺ ions were enhanced with increasing CO₃^2- ion content; however, those for Hg²⁺ ions were similar for different CO₃^2- content. The reaction with Pb²⁺ ions was especially remarkable and formed Pb²⁺ ion-exchanged carbonate apatites. The effect of substitution of CO₃^2- for PO₄^3- ions was concluded to be a loosening effect on the skeletal structure of the apatite.