Heavy metal contamination of waters and soils can seriously affect living organisms. The bioavailability of metal ions can be reduced immobilizing them in minerals with low solubility. In this process some cations of the mineral are substituted by the metallic cations present in the solution. The removal of Cd, Cu, Zn and Pb from aqueous solutions by sorption onto synthetic hydroxyapatite (HA) surfaces has been investigated in batch conditions at 25±2 °C. The metals were applied both as single or multi-metal (Cd+Cu+Zn+Pb) systems with initial metal concentrations ranging from 0 to 8 mmol/L. The removal capacity of HA in single-metal systems was 0.058-1.681 mmol of Cd/g, 0.016-0.764 mmol of Cu and 0.015-0.725 mmol of Zn/g of HA. In the multi-metal systems competitive metal sorption reduced the removal capacity by 63-83% for Cd, 13-76% for Cu and 10-63% for Zn, compared to the single-metal systems. The sorption of heavy metals by HA follows the Langmuir model. Heavy metal immobilization occurs through a two-step mechanism: first rapid surface complexation followed by partial dissolution of HA and ion exchange with Ca resulting in the formation of a heavy metal-containing HA.

The incorporation site of the metals in HA has been investigated by Extended X-ray Absorption Spectroscopy in the case of the four cited metals. Different situations appear for the various metals with detection of a metal-oxygen first coordination shell in all cases and a visible second coordination shell only for Pb and Cd. The metals appear to have a low coordination with O at distances much shorter than those typical of Ca. As a general finding, we observe different sites around the metal than that expected for a simple substitution of Ca and the possible scenarios will be described in detail for each case.

• Legal notice:
  

  Copyright (c) Pielaszek Research, all rights reserved.
  The above materials, including auxiliary resources, are subject to Publisher's copyright and the Author(s) intellectual rights. Without limiting Author(s) rights under respective Copyright Transfer Agreement, no part of the above documents may be reproduced without the express written permission of Pielaszek Research, the Publisher. Express permission from the Author(s) is required to use the above materials for academic purposes, such as lectures or scientific presentations.
  In every case, proper references including Author(s) name(s) and URL of this webpage: https://science24.com/paper/11307 must be provided.

1. Silver and copper ions and nanoparticles in the glaze of Renaissance majolica
2. Characterization of silicate glasses doped with transition metals by field-assisted ion exchange
3. Solid state silver ion exchange in Er:glass sol-gel films: an EXAFS study of the Er environment