Adsorptive removal of U(VI) and Th(IV) from aqueous solutions using polymer-based electrospun PEO/PLLA fibrous membranes Ioanna Savva • Maria Efstathiou • Theodora Krasia-Christoforou • Ioannis Pashalidis Received: 26 May 2013 / Published online: 31 October 2013 Ó Akade ´miai Kiado ´, Budapest, Hungary 2013 Abstract Fibrous membranes based on poly(ethylene oxide) and poly(L-lactide) fabricated by electrospinning were evaluated for the first time as substrates for the adsorption of tetravalent thorium (Th(IV)) and hexavalent uranium (U(VI)) from aqueous media. The membranes consisted of microfibers with diameters of approximately 2 lm as revealed by scanning electron microscopy. The adsorption of Th(IV) and U(VI) on the membrane was investigated as a function of pH, ionic strength and initial metal concentration under normal atmospheric conditions. The experimental data indicated increased affinity of the membrane for Th(IV) and U(VI), which was pH depended and reaches maximum values ( [ 90 %) for Th(IV) and U(VI) at pH 3 and pH 6.5, respectively. The maximum adsorption capacity (q max ) at optimum conditions was evaluated from the Langmuir isotherm and was found to amount 50.08 and 9.3 mmol kg -1 for Th(IV) and U(VI), respectively. In addition, studies on the effect of ionic strength on the adsorption efficiency did not show any significant effect indicating that the adsorption of Th(IV) and U(VI) on the membrane was most probably based on specific interactions and the formation of inner-sphere surface complexes. The significantly higher adsorption efficiency of the membrane for Th(IV) in acidic media (pH B 3) could be utilized for a pH-triggered, selective separation of Th(IV) from U(VI) from aqueous media. Keywords U(VI) Á Th(IV) Á Adsorption Á Electrospun membrane Á Aqueous solution Á pH triggered selectivity Introduction Uranium and thorium are naturally occurring radioactive elements widely distributed over the earth’s crust [1]. However, anthropogenic activities such as nuclear weapons testing, nuclear power generation and the use of depleted uranium in armor-piercing munitions are associated with increased nuclear waste production and radioactive relea- ses into environment [2]. Because of their toxicity radio- nuclides, even at trace levels, are considered to be major public health concern and therefore contaminated envi- ronmental compartments (e.g. soils, waters) have to be properly treated. There is particular interest in actinides (e.g. U, Th), because of the amounts produced in fission reactors and their long-lived radionuclides, which are generally highly radiotoxic alpha radiation emitters [3]. The chemical behaviour of uranium in aqueous solu- tions, particularly of hexavalent uranium, is governed by hydrolysis, complexation with naturally occurring ligands, colloid generation and solid phase formation [3]. Thorium exists only in the tetravalent state and is capable of forming both mono-and polymeric hydrolysis products, which govern the chemical behavior of Th(IV) in aqueous solu- tions. Th(IV) hydrolysis starts at pH 2 and results eventu- ally in the formation of the very stable Th(OH) 4(s) species that limits the Th(IV) solubility even in the acidic pH range. I. Savva Á T. Krasia-Christoforou Department of Mechanical and Manufacturing Engineering, School of Engineering, University of Cyprus, P.O. Box 20537, 1678 Nicosia, Cyprus e-mail: krasia@ucy.ac.cy M. Efstathiou Á I. Pashalidis (&) Department of Chemistry, University of Cyprus, P.O. Box 20537, 1678 Nicosia, Cyprus e-mail: pspasch@ucy.ac.cy 123 J Radioanal Nucl Chem (2013) 298:1991–1997 DOI 10.1007/s10967-013-2657-x