Enhancement of Lead-Barium Exchangeability of Barium Hydroxyapatite

In order to improve lead-barium exchangeability of barium hydroxyapatite (BaHAp), the effects of the recycle employment of BaHAp and the introduction of HCl into the exchange solution have been investigated at 293 K. The ion exchange capacity of BaHAp was evidently improved by use of the recycle experiments to reach levels approximately twice that obtained via the batch experiment. XPS analyses revealed that the ion exchange appears to proceed from the surface to the bulk of the apatite. The addition of HCl to the exchange solution also resulted in the enhancement of the ion exchangeability of BaHAp. Based on the apparent solubility of BaHAp, which was estimated from the dissolution of BaHAp for 4 h, together with the results of that experiment, it is suggested that the dissolution-precipitation mechanism appears to be possible for ion exchange. Copyright 2001 Academic Press.