Preparation of a hydroxyapatite film and its application in th...

Aqueous Pb(2+), Cd(2+), Co(2+), and Cu(2+) were continuously removed and regenerated using a bulk powder of calcium hydroxyapatite (Ca(10)(PO(4))(6)(OH)(2), CaHAp) and a glass plate coated with a thin film of CaHAp. Although use of CaHAp effectively removed aqueous Pb(2+) from the wastewater, lead cations immobilized on CaHAp could not be regenerated in an aqueous solution due to the formation of lead hydroxyapatite (Pb(10)(PO(4))(6)(OH)(2)), which is insoluble in water at acidic and neutral pH. In contrast, Co(2+) and Cu(2+) immobilized on CaHAp were easily regenerated in an aqueous solution by treatment with an acidic aqueous solution containing Ca(NO(3))(2), as previously reported for the CaHAp-Cd(2+) system. We found that the combination of the removal of the aqueous divalent cations by the CaHAp film and subsequent regeneration of the immobilized divalent cations from the film allowed for recycling of the film and for removal and regeneration of aqueous Cd(2+), Co(2+), and Cu(2+).