RESEARCH ARTICLE An assessment of strontium sorption onto bentonite buffer material in waste repository Pankaj Pathak 1,2 Received: 29 August 2016 /Accepted: 31 January 2017 # Springer-Verlag Berlin Heidelberg 2017 Abstract In the present study, changes occurring in sorption characteristics of a representative bentonite (WIn-BT) ex- posed to SrCl 2 (0.001–0.1 M) under the pH range of 1–13 were investigated. Such interaction revealed a significant var- iation in surface charge density and binding energy of ions with respect to bentonite, and alteration in their physicochem- ical properties viz., specific surface area, cation exchange ca- pacity, thermal and mechanical behaviour were observed. The distribution coefficients (k d ) calculated for sorption onto vir- gin (UCBT) and contaminated bentonite (CBT) indicated a greater influence of mineralogical changes occurred with var- iance of pH and strontium concentration. Notably, the sorption mechanism clearly elucidates the effect of structural negative charge and existence of anionic metal species onto CBT, and depicted the reason behind significant k d values at highly acid- ic and alkaline pH. The maximum k d of UCBT and CBT (0.001M SrCl2) were 8.99 and 2.92 L/kg, respectively, at the soil pH 8.5; whereas it was 2.37 and 1.23 L/kg at pH 1 for the CBT (0.1M SrCl2) and CBT (0.01M SrCl2) , respectively. The findings of this study can be useful to identify the physico- chemical parameters of candidate buffer material and sorption reversibility in waste repository. Keywords Strontium . Bentonite . Buffer material . Distribution coefficient . Sorption mechanism Introduction 90 Sr, the β-emitter radionuclide with a half-life of 28.8 years, average biological half-life ∼18 years and decay energy 546 KeV, is the foremost isotope of strontium (Alfredo et al. 2014; Glasstone and Dolan 1977; Guimaraes et al. 2014; IAEA 2006; Keceli 2015; Smiciklas et al. 2015). The signif- icant amounts of 90 Sr radionuclides produced from nuclear reactors and/or fallout from weapon testing remained in the spent fuels were identified as a serious threat to the sustainable world (IAEA 2006; Mckinley et al. 2007; Zhijian 2008). The mobility of radiation emitted by nuclear wastes (containing strontium isotopes) can only be prevented by their decay and decontamination. For this, deep geological disposal has remained in-practice wherein the radioactive wastes are kept prolonged in isolation in the multi-barrier repository (IAEA 2006; Zhijian 2008). In such repositories, bentonite has remained a prime can- didate buffer material, often surrounded by the packaging ma- terial either of concrete at low pH < 4 or cement at high pH > 10 (IAEA 2006; Kwon et al. 2013; Mckinley et al. 2007; Till and Grogan 2008; Zhijian 2008). Owing to the exceptional characteristics of high swelling potential, low per- meability, self-sealing capacity, higher cation exchange capac- ity, specific surface area and active mineralogy, the bentonite exhibits high sorption capacity (commonly determined as a distribution coefficient, k d ) to facilitate the proper functioning of waste repository (Caglar et al. 2009; Mckinley et al. 2007; Zhijian 2008). The development of engineered multi-barrier waste repositories was pioneered albeit the adversity caused by natural and/or manmade intrusion, due to potential leakage Responsible editor: Georg Steinhauser Electronic supplementary material The online version of this article (doi:10.1007/s11356-017-8536-1) contains supplementary material, which is available to authorized users. * Pankaj Pathak pankajpathak18@gmail.com 1 Department of Environmental Science and Engineering, Marwadi Education Foundation, Gauridad, Rajkot, Gujarat 360003, India 2 Department of Civil Engineering, Indian Institute of Technology (IIT) Bombay, Powai, Mumbai -400076, India Environ Sci Pollut Res DOI 10.1007/s11356-017-8536-1