Cadmium removal from single- and multi-metal (Cd+Pb+Zn+CuCd+Pb+Zn+Cu) solutions by sorption on hydroxyapatite

Heavy metal contamination of waters and soils is particularly dangerous to the living organisms. Different studies have demonstrated that hydroxyapatite has a high removal capacity for divalent heavy metal ions in contaminated waters and soils. The removal of Cd from aqueous solutions by hydroxyapatite was investigated in batch conditions at 25±2°C. Cadmium was applied both as single- or multi-metal (Cd+Pb+Zn+CuCd+Pb+Zn+Cu) systems with initial concentrations from 0 to 8 mmol L−1. The adsorption capacity of hydroxyapatite in single-metal system ranged from 0.058 to 1.681 mmol of Cd/g of hydroxyapatite. In the multi-metal system competitive metal sorption reduced the removal capacity by 63–83% compared to the single-metal system. The sorption of Cd by hydroxyapatite follows the Langmuir model. Cadmium immobilization occurs through a two-step mechanism: rapid surface complexation followed by partial dissolution of hydroxyapatite and ion exchange with Ca resulting in the formation of a cadmium-containing hydroxyapatite.

Graphical abstractThe sorption of Cd by hydroxyapatite occurs through a two-step mechanism: rapid surface complexation followed by partial dissolution of hydroxyapatite and ion exchange with Ca.Figure optionsDownload full-size imageDownload as PowerPoint slide