Sorption and ion-exchange properties of barium hydroxyapatite with divalent cations

The properties of barium hydroxyapatite (BaHAp) for ion exchange with Pb2+, Cu2+, Zn2+, Cd2+ and Co2+ have been investigated, with particular emphasis on the former two cations. Under similar conditions the exchange capacities followed the order Cu2+>Pb2+>Zn2+>Cd2+>Co2+. After exchange with Pb2+, lead hydroxyapatite was identified in the solid but with Cu2+ no copper analogue of BaHAp was found, although Ba3(PO4)2 was formed. With solutions containing both Pb2+ and Cu2+ only the former exchanged into BaHAp. With HCl in the exchanging solutions the capacities of BaHAp for both Pb2+ and Cu2+ were enhanced, while copper hydroxyapatite was not found in the solid. Discussions of possible mechanisms are included.