Synthetic hydroxyapatites employed as inorganic cation-exchangers

Abstract

The manner in which ions such as Cd²⁺, Zn²⁺, Ni²⁺, Mg²⁺ and Ba²⁺ in aqueous solution are removed by synthetic hydroxyapatites has been probed by using both batch and column methods. The behaviour is not merely an adsorption effect but a type of ion-exchange reaction between the ions in solution and the Ca²⁺ ions of the apatites. The ranking of the ions according to amount exchanged was as follows: Cd²⁺, Zn²⁺ > Ni²⁺ > Ba²⁺, Mg²⁺. These results suggest that the apatites have a selectivity for metallic cations and can be employed as a new inorganic cation-exchanger for recovering valuable ions in waste water.