Some factors affecting the removal of lead(II) ions from aqueous solution by porous calcium hydroxyapatite: Relationships between surface and adsorption properties

A porous hydroxyapatite (p-HAp) was prepared and employed for the removal of lead(H) ions at different concentrations from aqueous solution to determine the adsorption properties of p-HAp and compare them with those of a commercial hydroxyapatite (CAp) sample. The kinetic data obtained indicated that the adsorption performances of the adsorbents depended both on their specific surface area and crystallinity. Complexation of the Pb(II) ion on the adsorbent surface favoured the dissolution of hydroxyapatites characterized by a Ca/Pb molar ratio in the 0.85-1.5 range. The maximum adsorption capacity of p-Hap for Pb(II) ions at 30 +/- 2 degrees C was 2.30 mmol/g relative to 1.38 mmol/g for the commercial compound Cap at the same temperature. The higher capacity of p-HAp was explained in terms of its porosity and crystallinity. The Pb(II) ions sorption results could be modelled by the Langmuir and Freundlich isotherms.