No abstract

We studied on adsorbability of alizarin red S (ARS) on Fe(III)-and Pb(II)-treated hydroxyapatites in distilled water (H 2 O) and phosphate buffer solution (PBS). The Fe(III)-treated apatites indicated high adsorption capacity from their isothermic curves both in H 2 O and PBS: The capacities in PBS were larger than those in H 2 O. On the other hand, adsorption capacities of Pb(II)-treated apatites in PBS were much lower than those in H 2 O. Surface analysis of those treated apatites by electron probe micro analysis and FT-IR microspectroscopy affords significant information on surface element (P, Ca, Fe, or Pb) distribution and interaction patterns between ARS and the corresponding metal (Fe or Pb) sites. Eventually, predominant adsorption mechanisms were elucidated as follows, chelate form adsorption for Fe(III)-treated apatites and salt form adsorption for Pb(II)-treated apatites.

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˚C 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 FePO 4 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.

The lead removal ability of two kinds of board-shape hydroxyapatites with different Ca/P molar ratio were evaluated. The samples reacted with Pb(NO3)2 in an aqueous solution produced a mixture of hydroxyapatite and hydroxypyromorphite. The results showed that Board-shape Ca-deficient type HAP(HAP-400) has Pb2+ removal ability superior to Board-shape HAP with stoichiometric composition(HAP-300).

Adsorption of humic acid (commercially available) on hydroxyapatites