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

Abstract

The ion-exchange characteristics between Ca²⁺ ions in carbonate apatites containing 6 and 16 wt % CO^2–₃ 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 CO^2–₃ ion content; however, those for Hg²⁺ ions were similar for different CO^2–₃ content. The reaction with Pb²⁺ ions was especially remarkable and formed Pb²⁺ ion-exchanged carbonate apatites. The effect of substitution of CO^2–₃ for PO^3–₄ ions was concluded to be a loosening effect on the skeletal structure of the apatite.