Lead sorption properties of nanohydroxyapatite–alginate composite adsorbents

In the present work bio-composite adsorbents were prepared by incorporating natural nano-sized hydroxyapatite (nHAp) into alginate polymer. Bead and film form composite adsorbents with two different compositions were used for the Pb2+ removal from aqueous solutions. The adsorption results were compared with the results obtained by using pure alginate films and beads as well as pure nHAp particles. In case of bead form adsorbents, incorporating nHAp particles into alginate decreased the adsorption capacity. SEM and EDX analysis proved that it was due to agglomeration of nHAP particles on the bead surface and reduction in Pb2+ diffusion in the beads. However, composite films had greater sorption capacities than pure alginate film and nHAp powder. Maximum equilibrium capacity of 270.3 mg g−1 was obtained after 6 h for composite film from adsorbent containing 50 wt% of nHAp. Kinetics studies showed that the pseudo-second-order kinetic model was able to describe the dynamic behavior of the adsorption process by composite adsorbents used in this work. Also the Langmuir isotherm model is very well fitted to the equilibrium data. The mechanism of Pb2+ adsorption by the composite adsorbents was described. Finally, the film type nHAp–alginate composite adsorbents were found to be promising for lead ions removal from aqueous solutions.

► Composite adsorbents were prepared from natural hydroxyapatite and alginate.
► The adsorbents were used for Pb+2 removal from aqueous solutions.
► Film type adsorbents had better performance than bead shape adsorbents.
► Removal performance improved by increasing nHAP content of adsorbent films.
► Adsorption capacity of the adsorbents was higher than other composite adsorbents made by other researchers.