Removal of heavy metal ions from aqueous solutions by alkaline-earth metal phosphates

The possibility of utilization of calcium or magnesium phosphates of various composition for heavy and non-ferrous metal extraction from aqueous solutions has been studied. The efficiency of the phosphates in removal of Pb(II), Cr(III) and Fe(III) ions has been shown to decrease in the following sequence: Mg-3(PO4)(2) > MgNH4PO4 > Ca-3(PO4)(2) > CaHPO4 > Ca-10(PO4)(6)(OH)(2) which is inverse to their hydrolytic stability series. It has been established that phosphates of non-apatite structure are capable of binding up to 12 mmol g(-1) of the named heavy metals by a chemical interaction. Hydroxyapatite interacts with the polyvalent metal ions via either the above mentioned or ion-exchange mechanism, depending on preparation method used for the apatite and the nature of metal. (C) 1999 Elsevier Science B.V. All rights reserved.