Sorption of uranyl ions on organosepiolite Agnieszka Gajowiak a , Agnieszka Gładysz-Płaska a,⇑ , Dariusz Sternik a , Stanisław Pikus a , Eyup Sabah b , Marek Majdan a a Faculty of Chemistry, Maria Curie Skłodowska University, PL MC Skłodowskiej 2, 20-031 Lublin, Poland b Engineering Faculty, Mining Engineering Department, Afyon Kocatepe University, 03200 Afyon, Turkey highlights " HDTMA–sepiolite is found to be efficient sorbent for U(VI) acetates/ nitrates. " The linear increase of U(VI) sorption with its concentration is evident. " The maximum of U(VI) sorption percentage P near 90% appears at pH > 9. " Solid/liquid ratio S = 1 is sufficient for effective U(VI) removal. graphical abstract article info Article history: Received 1 May 2012 Received in revised form 6 June 2012 Accepted 6 June 2012 Available online 15 June 2012 Keywords: Sepiolite HDTMA Uranium Sorption abstract Sorption of U(VI) on sepiolite and HDTMA–sepiolite was studied by investigating sorption isotherms and the influence of pH on sorption percentage P for initial U(VI) concentrations of 0.0001–0.001 mol/dm 3 . Sorption isotherms were linear both for nitrates and acetate solutions, which was explained as a conse- quence of the precipitation of U(VI) hydroxycomplexes on the surface of the mineral. pH > 9 was optimal for U(VI) sorption on HDTMA–sepiolite, and this fact was related to the sorption of U(VI) anionic com- plexes on the positively charged surface of the sorbent. The respective chemical reactions for the sorption of different species were proposed. Ó 2012 Published by Elsevier B.V. 1. Introduction Sepiolite is a porous magnesium silicate which, owing to the presence of channels in its structure, has a high specific surface area. There are many reports concerning the application of sepio- lite in the removal of different inorganic and organic impurities from aqueous solutions [1]. Zhou studied sorption by sepiolite of heavy metals (Cu 2+ , Pb 2+ , Zn 2+ and Cd 2+ ) from simulated metallur- gical wastewater under different adsorbent dosage, pH, adsorption time and temperature conditions. That author found that the adsorption increased with the adsorbent dosage. At pH 6, the adsorption of heavy metal ions by sepiolite was in the order Cu 2+ > Zn 2+ > Pb 2+ > Cd 2+ [2]. Brigatti and coworkers investigated the interaction between sepiolite and Zn 2+ and Pb 2+ ions [3]. The release of these ions to the aqueous phase depended on the adsorp- tive site. The ions were relatively weakly bound within structural channels and on the surface of sepiolite, but strongly bound within the octaeders on the edges of the channels. Bektas and co-workers studied Pb 2+ sorption on zeolite using the Langmuir and Freundlich models [4]. Enthalpy changes of the adsorption process indicated its endothermic character. Celis et al. [5] used sepiolite modified with thiol groups for the adsorption of Hg(II), Pb(II) and Zn(II). Among studies of adsorption of organic substances on sepiolite [6–13], the most important is the work of Sabah and Majdan [13] concerning chlorophyll from rapeseed oil. The author found that 1385-8947/$ - see front matter Ó 2012 Published by Elsevier B.V. http://dx.doi.org/10.1016/j.cej.2012.06.022 ⇑ Corresponding author. Tel.: +48 81 537 57 29; fax: +48 81 533 33 48. E-mail address: agnieszka.gladysz.plaska@onet.pl (A. Gładysz-Płaska). Chemical Engineering Journal 219 (2013) 459–468 Contents lists available at SciVerse ScienceDirect Chemical Engineering Journal journal homepage: www.elsevier.com/locate/cej