EFFECTS OF AQUEOUS AL, CD, CU, FE(II), NI, AND ZN ON PB IMMOBILIZATION BY HYDROXYAPATITE

The effects of aqueous Al, Cd, Cu, Fe(II), Ni, or Zn on Pb immobilization by hydroxyapatite [Ca10(PO4)6(OH)2] were studied. Lead was removed mainly via hydroxyapatite dissolution and hydroxypyromorphite [Pb10(PO4)6(OH)2] precipitation in the presence of these metals with a Pb removal efficiency of 37-100%. These metals inhibited Pb immobilization by hydroxyapatite in the order: Al > Cu > Fe(II) > Cd > Zn > Ni and Cu > Fe(II) > Cd > Zn > Al > Ni at high and low initial Pb concentrations, respectively. The inhibition was probably through the precipitation of amorphous to poorly crystalline metal phosphates, decreasing the amount of dissolved P available for precipitation with dissolved Pb ions. Hydroxyapatite was effective in removing these added metals, especially at low concentrations. Hydroxyapatite selectively removed Pb from solution in the presence of aqueous Al, Cd, Cu, Fe(II), Ni, or Zn. The results support our earlier finding that hydroxyapatite has the potential to be used for in situ immobilization of Pb in Pb contaminated soils and wastes.