Interdependence of anion and cation exchanges in calcium hydroxyapatite: Pb2+ and Cl-

The ion exchange of Pb2+ and Cl- into calcium hydroxyapatite from aqueous s olutions is studied at 293 K. Although the exchange of Cl- into CaHAp and P bHAp was not observed, in the presence of both Pb2+ and Cl- in aqueous solu tion the exchange of both Pb2+ and Cl- into CaHAp occurred, and, at least a t intermediate concentrations of HCl, a proportionality between the sorbed quantities of these two ions was observed. The dissolution of CaHAp is show n to be dependent upon the pH, while the quantity of Pb2+ exchanged into th e solid is not a function of the proton content; consequently, the exchange is not primarily a dissolution-precipitation process. (C) 1999 Academic Pr ess.