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 % CO2–3 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 CO2–3 ion content; however, those for Hg2+ ions were similar for different CO2–3 content. The reaction with Pb2+ ions was especially remarkable and formed Pb2+ ion-exchanged carbonate apatites. The effect of substitution of CO2–3 for PO3–4 ions was concluded to be a loosening effect on the skeletal structure of the apatite.