Sorption separation of cobalt and cadmium by straw-derived biochar: a radiometric study Martin Pipı ´s ˇka 1,2 • Barbora Micha ´lekova ´ Richveisova ´ 1 • Vladimı ´r Fris ˇta ´k 3 • Miroslav Hornı ´k 1 • Lucia Remena ´rova ´ 1 • Richard Stiller 1 • Gerhard Soja 3 Received: 14 April 2016 / Published online: 19 September 2016 Ó Akade ´miai Kiado ´, Budapest, Hungary 2016 Abstract Biochar prepared from Triticum aestivum straw (SB) was used to investigate the sorption separation of Cd 2? and Co 2? ions in single and binary systems. The maximum adsorption capacity of SB was higher for Cd 2? ions and the process was strongly pH dependent. Adsorp- tion data in the binary system Cd 2? –Co 2? were well described by the extended Langmuir model and the values of affinity parameter b indicate a higher affinity of SB to Cd 2? in comparison with Co 2? ions. The mechanisms for the removal of Cd and Co by biochar were evidenced by the different instrumental analyses as well as by chemical speciation modeling. Elemental mapping of SB revealed spatial distributions of cobalt and cadmium on biochar surfaces. The role of functional groups in metal sorption was confirmed by FTIR. Results demonstrate that SB is a promising heavy metal-immobilizing agent for contami- nated soils or water. Keywords Straw biochar  60 Co  109 Cd  Adsorption  Binary system  Mechanism Introduction Sorption separation of heavy metals and radionuclides has appeared as a highly competitive method to conventional methods of waste water treatment. Despite high effectivity of ion-exchange, electro-coagulation, precipitation, and membrane separation, currently sorption with application of low-cost materials represents a promising alternative separation technology. Many publications on the topic of sorption separation ([44, 45], Fris ˇta ´k et al. [14]) showed the potential of natural and artificial sorbents to purify large volumes of radioactively contaminated aqueous solutions from nuclear industry and from water bodies or seepage waters of contaminated areas [54]. Additionally, natural sorption materials (zeolites, bentonites) found utilization as engineered barriers to mitigate radionuclide migration in the deep geological repositories of high-level radioactive waste and spent nuclear fuel [1, 17]. Carbon-based sorption materials such as activated carbon, carbon fibers or carbon nanotubes revealed the option to apply thermochemical conversion processes to different input materials, thereby producing sorbents with various properties and sorption characteristics. Recently, biochar as a solid by-product from slow or fast pyrolysis processes established its posi- tion in the system of carbon sorption materials and thus opened a new direction in the portfolio of sorbents [15]. Input feedstock and pyrolysis conditions such as tempera- ture (300–700 °C), highest temperature holding time, pressure or presence of chemical agents (catalysts) affect the physicochemical transformation of biomass and its subsequent ability to sorb contaminants. It is important to notice that after the pyrolysis process biochar derived from various feedstocks has a highly porous structure and con- tains oxygen-containing functional groups, which are most responsible to bind inorganic and organic pollutants on & Martin Pipı ´s ˇka pipiska@ucm.sk; pipiskam@gmail.com 1 Department of Ecochemistry and Radioecology, Faculty of Natural Sciences, University of SS. Cyril and Methodius in Trnava, J. Herdu 2, 917 01 Trnava, Slovak Republic 2 Department of Chemistry, Trnava University in Trnava, Priemyselna ´ 4, 918 43 Trnava, Slovak Republic 3 Energy Department, AIT Austrian Institute of Technology GmbH, Konrad-Lorenz-Straße 24, 3430 Tulln an der Donau, Austria 123 J Radioanal Nucl Chem (2017) 311:85–97 DOI 10.1007/s10967-016-5043-7