REACTION OF Ca-DEFICIENT HYDROXYAPATITE WITH HEAVY METAL IONS ALONG WITH METAL SUBSTITUTION

抄録

Reaction of Ca-deficient hydroxyapatite, HAP-400, with heavy metals, Pb (II), Fe (III), Fe (II), Cu (II), Cd (II), Cr (II), Co (II), Ni (II), and Zn (II) was investigated at 25^oC for 4 h in water, compared with stoichiometric hydroxyapatite HAP-300. From heavy metal consumption and [Ca]/[Metal], which is defined by molar ratio of eluted Ca and consumed heavy metal, the reactions of HAP-400 with the heavy metals except for Pb (II) and Fe (III) proceed via metal-adsorptive substitution mechanism. In the reactions of HAP-400 with Pb (II) and Fe (III), the metals were completely consumed with equivalent elution of Ca, but these reactions proceeded by no simple substitution mechanism to afford Pb (II)- and Fe (III)-bearing HAP-400 with specific structures, namely HAP-400-Pb and HAP-400-Fe. By XRD and FT-IR microspectroscopy, it was found that HAP-400-Pb is constituted of both newly formed lead apatite crystal and the original apatite crystal, and that HAP-400-Fe is constituted of much amorphous FePO₄ phase around the original apatic phase. Therefore, it was concluded that the reactions of HAP-400 with Pb (II) and Fe (III) proceed by the following mechanism: erosion of the apatic structure and formation of a brand-new structure containing metal. This mechanism can be named apatite-erosive substitution mechanism.