Research paper Adsorptive removal of 134 Cs + , 60 Co 2+ and 152 + 154 Eu 3+ radionuclides from aqueous solutions using sepiolite: Single and multi-component systems Mamdoh R. Mahmoud a, ⁎, Ghada M. Rashad a , Essam Metwally a , Ebtissam A. Saad b , Ahmed M. Elewa a a Nuclear Chemistry Department, Hot Laboratories Center, Atomic Energy Authority, P.O. Box 13759, Inshas, Cairo, Egypt b Chemistry Department, Faculty of Science, Ain Shams University, Cairo, Egypt abstract article info Article history: Received 31 May 2016 Received in revised form 2 December 2016 Accepted 14 December 2016 Available online xxxx Single and multi-component adsorptive removal of 134 Cs + , 60 Co 2+ and 152+154 Eu 3+ from aqueous solutions onto sepiolite are studied in the present study. Removal of these radionuclides in single systems is found to be strongly dependent on the initial pH on the solution. Removals N 99% (for 60 Co 2+ and 152+154 Eu 3+ ) and of about 82% (for 134 Cs + ) are achieved at initial pH values higher than 4 and 5, respectively. The kinetic data and the equilibrium isotherms are modeled by two kinetic models, the pseudo-first-order and the pseudo-second-order, and two iso- therm models, Langmuir and Freundlich, respectively. The effect of various coexisting cations, Na + , Ca 2+ and Al 3+ , at different concentrations on the adsorption processes of the concerned radionuclides in single systems was evaluated. Desorption studies of radionuclide-loaded sepiolite are studied using different concentrations of organic, EDTA and HA (strong complexing agents for radionuclides), and inorganic, HCl, NaCl, CaCl 2 , Mg(NO 3 ) 2 and AlCl 3 , desorbing agents. Adsorption mechanisms of radionuclides onto sepiolite are deeply discussed. Multi-component adsorptive removal of 134 Cs + , 60 Co 2+ and 152+154 Eu 3+ onto sepiolite as a function of adsorbent weight and time was also studied. The influence of the solution pH on co-removal efficiency of ra- dionuclides was investigated in presence of EDTA. Furthermore, the present investigation evaluated the removal efficiency of radionuclides, in multi-systems, in presence of different concentrations either of NaCl or CaCl 2 . © 2017 Elsevier B.V. All rights reserved. Keywords: Radionuclide Sepiolite Adsorption Removal Clay 1. Introduction The application of radionuclides in medicine, industry, agriculture and research generates large volumes of radioactive wastewaters which have dangerous effects on the environment. The radionuclides 134 Cs + , 60 Co 2+ and 152+154 Eu 3+ are commonly present in radioactive wastewaters. Owing to their relatively long half-lives (2.06, 5.27, 8.59 and 13.54 for 134 Cs + , 60 Co 2+ , 154 Eu 3+ and 152 Eu 3+ , respectively) as well as their radiotoxicity, these radionuclides must be removed from radioactive wastes for safe discharge. The traditional chemical and physical methods used for removing radionuclides from aqueous solu- tions include chemical precipitation, evaporation, solvent extraction, foam separation, membrane separation and adsorption. However, most of these technologies have some disadvantages such as generation of toxic byproduct, generation of high volumes of sludge or solid wastes, low efficiency, time consuming and high energy requirements (Yu et al., 2016; Uzal et al., 2011; Zhu et al., 2014). Alternatively, adsorption is considered the most efficient and extensively used technique for treat- ment of radioactive wastewater due to its simplicity and efficiency (El Afifi et al., 2016; Zhu et al., 2016; Metwally and Ayoub, 2016; Sun et al., 2014). In the last decades, clay minerals have been widely utilized as adsorbents for the removal of radionuclides from aqueous solutions due to their low cost, availability and high efficiency (Hongxia et al., 2016; Reinoso-Maset and Ly, 2016; Yu et al., 2015; Zong et al., 2015; Sun et al., 2014; Fan et al., 2009). Sepiolite, a natural clay mineral, is a hydrated magnesium silicate with the unit cell formula of Mg 8 Si 12 O 30 (OH) 4 (OH 2 ) 4 (H 2 O) 8 (Bergaya et al., 2006). Unlike other layer silicate, sepiolite has not continuous oc- tahedral sheets. Structurally, it contains ribbons of a 2:1 phyllosilicates. One ribbon is linked to the next by inversion of SiO 4 tetrahedral along a set of Si-O-Si bonds (Sparks, 2003). Each structure block of sepiolite is composed of two tetrahedral silica sheets sandwiching a central sheet of magnesium oxide-hydride. Due to the discontinuity of octahedral sheet, oxygen atoms in the octahedral at the edge of the ribbons are co- ordinated to cations on the ribbon side only, while coordination and charge balance are completed along the channels by protons, coordinat- ed waters and a small number of exchangeable cations (Bergaya et al., 2006). In addition to the exchangeable cations (Ca and Mg), the chan- nels of sepiolite contain two types of water: bound water (molecules co- ordinating Mg atoms at the broken bond surfaces of the channels) and zeolitic water (clusters filling the empty space in the channels and Applied Clay Science 141 (2017) 72–80 ⁎ Corresponding author. E-mail address: mamdohrefaat@yahoo.com (M.R. Mahmoud). http://dx.doi.org/10.1016/j.clay.2016.12.021 0169-1317/© 2017 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Applied Clay Science journal homepage: www.elsevier.com/locate/clay