Terbium adsorption onto polyhydroxyethylmethacrylatehydroxyapatite composite and its modified composition by phytic acid
Hydroxyapatite (Hap) was entrapped in poly(hydroxyethylmethacrylate) P(HEMA) by direct polymerization and P(HEMA-Hap) was obtained in aqueous solution. Phytate (phy) was immobilized by phytic acid (phy) modification onto the poly(hydroxyethylmethacrylate-hydroxyapatite), P(HEMA-Hap). The adsorptive features of P(HEMA-Hap) composite and its modified form P(HEMA-Hap)-phy, were investigated by using Tb analogues, rare earth elements (REE), by isotopic tracer method, Tb-160 was used as the radiotracer. It was observed that P(HEMA-Hap) composite had a higher affinity for Tb3+ than bare Hap, as well as its modified composition P(HEMA-Hap)-phy. Adsorption data obtained, fitted well to the classical Lagmuir, Freundlich, and Dubinin-Radushkevich (D-R) sorption models. Changes in enthalpy and entropy values showed that the overall adsorption process was endothermic (H>0), increasing entropy (S>0), and spontaneous (G<0), as expected. The adsorption kinetics following the pseudo-second order model indicated that the rate-controlling step was the chemical adsorption. Reusability of the adsorbent was also investigated and it was found that the adsorbent could be used at least for five times.