Separation and Purification Technology 28 (2002) 103 – 116 Removal of 137 Cs from aqueous solutions using different cationic forms of a natural zeolite: clinoptilolite Abdelrahim Abusafa, Hayrettin Yu ¨ cel * Chemical Engineering Department, Middle East Technical Uniersity, Ankara 06531, Turkey Received 14 February 2001; received in revised form 25 February 2001; accepted 10 March 2002 Abstract Distribution coefficients of cesium on natural and cation-enriched (Na + ,K + , NH 4 + and Ca +2 ) forms of clinoptilolite were measured by batch, radioactive tracer technique. The measurements were carried out for an initial cesium concentration range of 10 -6 –10 -1 mol/dm 3 and at temperatures of 25, 40, 60 and 80 °C. Experimental isotherms evaluated from distribution coefficients were fit to Langmuir, Freundlich and Dubinin-Radushkevich (D-R)models. Of the models tested, D-R model was found to represent the isotherms better in a wider range of concentrations than either Langmuir or Freundlich model. Breakthrough behavior of cesium on natural and cation-enriched forms of clinoptilolite for a particular set of conditions were also determined in a small size column. Column parameters were evaluated using mass transfer zone concept. © 2002 Elsevier Science B.V. All rights reserved. Keywords: Clinoptilolite; Cesium; Sorption isotherm; Dubinin-Radushkevich isotherm www.elsevier.com/locate/seppur 1. Introduction 137 Cs is one of the most abundant radionuclides in nuclear fission products that are routinely or accidentally released [1 – 3]. It has a relatively long half-life of about 30 years and is considered as one of the most hazardous radiotoxic elements for the environment. One of the most effective meth- ods for the treatment and disposal of radioactive wastes has been based on ion-exchange using inorganic ion-exchangers [1]. The desirable char- acteristics of high exchange capacity and favor- able selectivity for some radioisotopes have made certain zeolites quite useful for the treatment of radioactive wastes. Thermal, mechanical and radi- ation stability are further advantages of these materials. A zeolite can also be incorporated into a cement matrix and easily stored in stainless drums which is a common practice for long term storage of radioactive waste. Radioactive waste- treatment processes utilizing zeolites have been developed and used successfully since the intro- duction of atomic energy installations [1]. Natural zeolites which have been considered for radioac- tive waste-treatment include mordenite, erionite, chabazite and clinoptilolite [2 – 9]. Among these, clinoptilolite has received much attention due to its widespread occurrence and high selectivity * Corresponding author. Tel.: +90-312-210-26-35; fax: + 90-312-210-12-64. E-mail address: hyucel@metu.edu.tr (H. Yu ¨ cel). 1383-5866/02/$ - see front matter © 2002 Elsevier Science B.V. All rights reserved. PII:S1383-5866(02)00042-4