Fast and efficient cesium removal from simulated radioactive liquid waste by an isotope dilution–precipitate flotation process Mohamed A. Soliman a , Ghada M. Rashad b , Mamdoh R. Mahmoud b,⇑ a Egypt Second Research Reactor, Atomic Energy Authority, P.O. Box 13759, Cairo, Egypt b Nuclear Chemistry Department, Hot Laboratories Center, Atomic Energy Authority, P.O. Box 13759, Cairo, Egypt highlights  Removal of Cs-137 by an isotope dilution–precipitate flotation was studied.  Sodium tetraphenylborate precipitating agent was used with SLS and CPC surfactants.  Lower remaining Cs-137 activity values than the permissible value are obtained.  CsTPB precipitate was efficiently separated within half a minute.  The removal mechanism of cesium by SLS and CPC was proposed at different pH values. graphical abstract article info Article history: Received 10 February 2015 Received in revised form 28 March 2015 Accepted 30 March 2015 Available online 15 April 2015 Keywords: Cesium Precipitation Flotation Removal Radioactive liquid waste abstract The performance of an isotope dilution–precipitate flotation process for Cs-137 removal from low-level liquid radioactive waste is evaluated in this study using sodium tetraphenylborate (NaTPB) as the precip- itating agent. In absence of Fe(III), neither the anionic sodium lauryl sulfate (SLS) nor the cationic cetylpyridinium chloride (CPC) could float the CsTPB precipitate over the studied pH range of 2.5–11.9. It is proposed that iron oxide coated CsTPB particles are formed upon addition of Fe(III) solution and their floatability is greatly dependent on the solution pH and the Fe(III) content. At the optimum conditions, remaining Cs-137 activity values <1.3 nCi/L (SLS, pH 6.8) and <2.3 nCi/L (CPC, pH 10.2) are achieved from radioactive wastewater within half a minute which are below its discharge limits. The mechanism of flotation is proposed and cesium removal is suggested to proceed via flotation of iron oxide coated CsTPB. Flotation technique is compared to other conventional solid–liquid separation processes (decanta- tion, centrifugation and filtration) for separation of the iron oxide coated CsTPB particles. The results showed that the best separation was attained by flotation process. The data obtained by the present com- bined process, precipitation followed by flotation, for Cs-137 from radioactive wastewater are also com- pared to those reported by other treatment methods. Based on the data obtained, the combined process has great potential as a radioactive wastewater treatment technology. Ó 2015 Elsevier B.V. All rights reserved. 1. Introduction Due to its long half-life (T 1/2 = 30.17 years), high fission yield (6.5%), high solubility/mobility and high radiotoxicity, the Cs-137 radionuclides-contaminated radioactive liquid wastes must be effectively treated prior its release into the environment. Chemical precipitation, ion exchange, membrane separation sol- vent extraction and adsorption are the usual methods used for the treatment of radioactive liquid wastes [1–4]. Among them, chemical precipitation method is a well-established method for the removal of radionuclides from radioactive wastewaters and is http://dx.doi.org/10.1016/j.cej.2015.03.136 1385-8947/Ó 2015 Elsevier B.V. All rights reserved. ⇑ Corresponding author. Tel.: +20 1221925641. E-mail address: mamdohrefaat@yahoo.com (M.R. Mahmoud). Chemical Engineering Journal 275 (2015) 342–350 Contents lists available at ScienceDirect Chemical Engineering Journal journal homepage: www.elsevier.com/locate/cej