Polymeric sponges coated with hydroxyapatite for metal immobilization

Polymeric sponges coated with hydroxyapatite (S-HA) were used in lead and cadmium uptake experiments to study the sorption capacity for possible in situ metal remediation. S-HA metal sorption was compared with synthetic hydroxyapatite (HA) powder behavior to evaluate metal uptake efficiency. The coated sponges were produced by a two-step process consisting of monetite coating and further conversion to HA. Aqueous solutions containing nearly 1000 mg L− 1 of Cd2+ and 1000 mg L− 1 of Pb2+ were shaken for 24 hours with 0.4 g of each sample (HA and S-HA). The metal uptake experiments using polymeric sponges (S-HA) coated with HA accounted for nearly 96% of Pb2+ removal and 65% of Cd2+ removal after a 24-hour sorption experiment, while the hydroxyapatite (HA) powder sorbed 100% of Pb2+ and almost 50% of Cd2+. Scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDS) analyses of polymeric sponges coated with HA after the Pb2+ uptake experiment showed needle-like crystals on the material surface, identified by X-ray diffraction (XRD) as pyromorphite, Pb10(PO4)6OH2. An initial stage of nucleation after Cd2+ uptake (24 hours) on the S-HA sample surface was observed by SEM images and EDS analysis, indicating formation of a new phase.