Journal of Colloid and Interface Science 295 (2006) 303–309 www.elsevier.com/locate/jcis Priority communication Modiﬁcation of a montmorillonite–illite clay using alkaline hydrothermal treatment and its application for the removal of aqueous Cs + ions B. Öztop, T. Shahwan ∗ Department of Chemistry, Faculty of Science, Izmir Institute of Technology, 35430 Urla, Izmir, Turkey Received 31 October 2005; accepted 2 December 2005 Available online 18 January 2006 Abstract A montmorillonite–illite clay was modiﬁed using alkaline hydrothermal treatment (reﬂux method) and applied to the removal of aqueous Cs + ions. The alkaline solutions were prepared by dissolving NaOH in seawater and in distilled water, and the effect of the two alkaline media on the sorption capacities of the modiﬁed clay was discussed. The modiﬁed materials were characterized using XRD, SEM/EDS, and FTIR. As a result of the modiﬁcation, the original mineral was partially transformed into a zeolitic material with spherical morphology. The results showed that the modiﬁcation improved the Cs + uptake capacity of the starting clay, with the clay modiﬁed in distilled water medium demonstrating higher sorption capacity. The sorption data were adequately described using the Freundlich and Dubinin–Radushkevich isotherm models.  2006 Elsevier Inc. All rights reserved. Keywords: Montmorillonite; Illite; Alkaline hydrothermal treatment; Sorption; Cs + 1. Introduction Montmorillonite and illite are among the best-known clay minerals, which are widely studied by many researchers as Cs + sorbents (e.g., [1–6]). The alkaline hydrothermal treatment of montmorillonite is less common than that of kaolinite, where such treatment leads to the formation of hydrated feldspathoid or hydroxysodalite [7]. The aim of this treatment is to con- vert the layered (lamellar) structure of the clay into a porous structure composed of channels and cavities that can provide sorption locations for sorbate ions/molecules. During the hy- drothermal alkaline treatment, ions such as Na + and K + act as templates around which the aluminosilicate units polymerize to produce large pores in the structure [8]. The morphology and grain size of the produced zeolitic material depend on the re- action conditions and the silica content of the starting material. This modiﬁcation aimed at increasing the uptake capacity of the solid and obtaining products that can behave selectively toward a particular cation. Zeolitic material synthesized in seawater medium from bentonite using reﬂux and autoclave methods was reported to show selectivity toward NH + 4 ions in seawater [8]. * Corresponding author. Fax: +90 232 750 7509. E-mail address: talalshahwan@iyte.edu.tr (T. Shahwan). Cesium is important from a radioactive waste viewpoint. It has several radioactive isotopes, the most important of which are 134 Cs (t 1/2 = 2.06 years), 135 Cs (t 1/2 = 3.0 × 10 6 years), and 137 Cs (t 1/2 = 30.17 years), produced in nuclear ﬁssion. Due to their long half-lives, both 135 Cs and 137 Cs are principal ra- diocontaminants. In this study, hydrothermal alkaline treatment was performed using the reﬂux method. Seawater and distilled water were used in the preparation of the alkaline solutions and their ef- fect on the modiﬁed clay was discussed. The produced ma- terial was characterized using X-ray diffraction (XRD), scan- ning electron microscopy (SEM), energy dispersive X-ray spec- troscopy (EDS), and infrared spectroscopy (FTIR). The syn- thesized solids were then tested as sorbents for Cs + ions and their uptake capacity was compared with that of the starting montmorillonite–illite clay. The concentrations of both ions in the ﬁltrates following the sorption experiments were deter- mined using atomic absorption spectroscopy (AAS). 2. Experimental The clay mineral used in this study was obtained from Aldrich (Cat. 28,152-2). The alkaline solutions were prepared with a concentration of 3.75 M NaOH dissolved in seawater, 0021-9797/$ – see front matter  2006 Elsevier Inc. All rights reserved. doi:10.1016/j.jcis.2005.12.008