Sorption behavior of Zn(II) ions on synthesized hydroxyapatites.

Calcium hydroxyapatite (CaHAP) and barium hydroxyapatite (BaHAP) have been prepared by a wet method from aqueous solutions with cation/P molar ratio of 1.67. The prepared particles were characterized using XRD, IR, TG-DTA and BET-N(2) adsorption measurements. The potential of the synthesized hydroxyapatites to remove Zn(II) from aqueous solutions was investigated in batch reactor under different experimental conditions. Both hydroxyapatites remove Zn(II) from aqueous solutions with an efficiency higher than 98% at initial pH around 6-8. The data reveal that the initial uptake was rapid and equilibrium was established in 20 and 60 min for CaHAP and BaHAP. The sorption process follows the pseudo-first-order kinetic with a rate constant (k(ads)) equals to 1.06x10(-2) and 1.91x10(-2) min(-1) for CaHAP and BaHAP, respectively. Zn(II) removal was quantitatively evaluated using Langmuir isotherm model and the monolayer sorption capacity (Q(max)) shows the values 102.04 and 36.62 mg g(-1) for CaHAP and BaHAP clarifying the high affinity of these novel sorbents for Zn(II) ions. Kinetically, the prepared apatites are feasible sorbents retain Zn(II) ions through a favorable and spontaneous sorption process. The possibility of metal recovery and regeneration of hydroxyapatites were investigated using several eluting agents include hydrochloric acids, double distilled water, calcium chloride, barium hydroxide, and copper chloride. Different desorption levels were obtained with the different adsorbents and the maximum recovery yield was achieved with copper chloride.