Abstract

MAVROPOULOS, Elena et al. Pb ²⁺, Cu ²⁺and Cd ²⁺ ions uptake by Brazilian phosphate rocks. J. Braz. Chem. Soc. [online]. 2005, vol.16, n.1, pp. 62-68. ISSN 0103-5053.  http://dx.doi.org/10.1590/S0103-50532005000100010.

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 Ca₁₀(PO₄)₆F₂ dissolution followed by the precipitation of (Ca,Pb)₁₀(PO₄,CO₃) ₆(OH,F,Cl)_2.56.1.5H₂O 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 Cu₂(PO₄)(OH) precipitation.

Keywords : lead; cadmium and cooper immobilization; phosphate rock; hydroxyapatite.