Removal of Lead (Pb) by Hydroxyapatite Sorbent

The capacity of hydroxyapatite (HA) for removal of lead from aqueous solution was investigated under different conditions, namely initial metal ion concentration and reaction time. The sorption of lead solution by synthetic hydroxyapatite was investigated with initial concentration in the solution containing Pb 2+ varying from 1000 to 8000 mgl −1 . Pb and Ca analysis in the solutions, X-ray diffractometry associated with SEM-WDS and XPS analysis characterized the mechanisms of lead uptake. It was shown that the dissolution of hydroxyapatite is followed by the formation of hydroxypyromorphite, a solid solution of Pb 10−x Ca x (P0 4 ) 6 (OH) 2 formula, with Pb ions mostly occupying Ca(II) sites, and that the Ca/P molar ratio of this solid solution decreases continuously. Classical adsorption isotherms were used to describe adsorption data. The adsorption capacity, k LF , of 320 mg Pb g −1 HA and the adsorption intensity, n LF , of 2.5 were calculated from Langmuir–Freundlich. This isotherm was at an initial pH 5 and 25°C for 16 mm mean particle size. This shows significant affinity of HA to Pb 2+ according to literature data.