title: Cadmium removal from single- and multi-metal (Cd + Pb + Zn + Cu) solutions by sorption on hydroxyapatite.
abstract: 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 degrees C. Cadmium was applied both as single- or multi-metal (Cd + 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.
authors.affiliation: Department of Earth Sciences, University of Rome La Sapienza, Piazzale Aldo Moro 5, 00185 Rome, Italy.
authors.forename: Alessia
authors.initials: A
authors.lastname: Corami
authors.forename: Silvano
authors.initials: S
authors.lastname: Mignardi
authors.forename: Vincenzo
authors.initials: V
authors.lastname: Ferrini