Pb2+, Cu2+ and Cd2+ ions uptake by Brazilian phosphate rocks

In this work Brazilian phosphate rocks, PRs, were used to reduce Pb2+, Cu2+ and Cd2+ concentrations from aqueous solutions. We concluded that these metals were mainly immobilized by fluorapatite but other minerals such as calcium carbonate also contribute to their immobilization. In the case of lead two mechanisms are proposed: the Ca-10(PO4)(6)F-2 dissolution followed by the precipitation of (Ca,Pb)(10)(PO4,CO3)(6)(OH,F,Cl)(2.56).1.5H(2)O and CaCO3 dissolution with the formation of a PbCO3. The occurrence of this second mechanism improves the uptake efficiency but contribute to the increases of lead bioavailability because lead carbonate is more soluble than fluorpyromorphite. This fact could limit the use of PRs for remediation of contaminated soils and wastes. The Cu2+ and Cd2+ removal by PRs is controlled by adsorption mechanisms but dissolution/precipitation mechanisms also occur. In the case of Cu2+, fluorapatite dissolution followed by Cu-2(PO4)(OH) precipitation.