Effect of calcination and sieving of calcium hydroxyapatite on ion-exchangeability with lead cation in the presence and absence of HCl

摘要

The properties of calcium hydroxyapatite (CaHAp) for cation exchange with Pb~(2+) in aqueous solution have been investigated in the presence and absence of HCl at 293 K. Cation exchange of CaHAp with divalent cations such as Pb~(2+) in aqueous solution has received attention since it may control hazardous quantities of Pb~(2+) in the environment. However, to the best of our knowledge, the effects of the sieving of CaHAp and the calcination procedure in the preparation step for ion exchangeability have not been focused on. In the present paper, these factors were examined and it was found that ion exchangeability of CaHAp with Pb~(2+) was strongly influenced by the preparation procedure. The ion exchangeability of CaHAp was strongly influenced by sieving of the apatite, and CaHAp with a size fraction between 0.85 and 1.70 mm were found to have a lower exchangeability than that with a size fraction of less than 0.85 mm. Although it is generally accepted that the cation exchangeability of CaHAp with Pb~(2+) is improved by the addition of HCl, the quantity of Pb~(2+) exchange into CaHAp decreased with the addition of HCl, except when CaHAp treated by double calcination at 773 K was employed. In order to investigate the influence of calcination and sieving on the nature of CaHAp, X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) have been employed, together with typical measurements for the ion exchange.