Kinetic, Equilibrium and Thermodynamic Studies of Uranium (VI) Adsorption from Aqueous Solutions by PVA/TEOS Hybrid Adsorbent Functionalized with Mercapto Group

Poly (vinyl alcohol) / tetraethyl orthosilicate (PVA/TEOS) hybrid adsorbent modified with 3-mercaptopropyltrimethoxysilane (TMPTMS) was prepared by the sol-gel method, and its application for the adsorption of uranium ions from aqueous solutions in a batch sorption process was studied. The functional groups of the hybrid adsorbents were characterized by the FTIR analysis. The batch adsorption studies such as TEOS content, TMPTMS content, pH, adsorbent dosage, contact time, initial concentration and temperature were investigated. The maximum adsorption capacity of uranium ions was found to be 39.08 mg g-1 at pH of 4.5 and temperature of 25˚C. The kinetic data were analyzed by Pseudo-first-order, Pseudo-second-order and Double-exponential kinetic models. The Freundlich, Langmuir and Dubinin-Radushkevich isotherm models were applied to describe the equilibrium data. Thermodynamic parameters indicated that the uranium sorption onto the adsorbent was an endothermic and spontaneous process. The PVA/TEOS/TMPTMS hybrid adsorbent was regenerated by 0.5 M HNO3/0.1 M HCl in an equal ratio solution and the adpsorption capacity did not change remarkably after five sorption-desorption cycles.