SORPTION AND KINETICS OF Eu(III) ON BENTONITE/PHYLLITE BARRIERS Joanna KYZIOŁ-KOMOSIŃSKA 1 , Monika FABIAŃSKA 2 , Janusz JANECZEK 2 1 Institute of Environmental Engineering, Polish Academy of Sciences, M. Skłodowskiej-Curie St. 34., 41-819 Zabrze, Poland, joanna.kyziol-komosinska@ipis.zabrze.pl 2 University of Silesia, Faculty of Earth Sciences, Będzińska St. 60, 41-200 Sosnowiec, Poland Introduction The key function of a nuclear waste repository is to isolate radionuclides from the biosphere by preventing their migration via groundwater to the surrounding environment (IAEA 2011). Since the distribution, mobility, and bioavailability of radionuclides are controlled by the sorption properties of barrier materials, it is vital to find efficient and mechanically and thermally stable, high capacity sorbents (Itälä 2009, Yang et al. 2014). Currently, bentonite or bentonite mixed with quartz sand is used in the majority of programs for radioactive-waste disposal. However, bentonites undergo dehydration, mechanical degradation, and structural transformation decreasing their sorption capacity at a temperature above 100 o C expected at the contact with waste containers. Previous studies show that phyllites, while less efficient sorbents than bentonites, have high sorption capacity for actinides and some nuclear fission products. Moreover, they are thermally stable up to 400°C. Therefore, they can be considered as a component of a mixture with bentonite instead of sand to take advantage of phyllite sorption. The main goal of the research is to determine the removal efficacy of Eu(III) ions - an analog of nuclear fission-originated isotopes of rare earth elements and analog of Am - by bentonite/phyllite (B/Ph) mixtures compared to bentonite as potential repository buffer and/or backfill materials for engineered barriers in a radioactive waste repository. Moreover, the research allowed for choice the Ph/B mixture of the best removal efficacy of Eu(III) ions at with high content of phyllite. Samples and methods Sorbents Mixtures of B/Ph at ratios 75%/25%, 50%/50% and 25%/75% (wt.) were prepared. Bentonite was from the Miocene Kopernica deposit in Slovakia and phyllite from the Dewon–Pokrzywna phyllite deposit from the northern base of the Opava Mountains in Eastern Polish Sudetes. The main properties which decide on the sorption properties are shown in Table 1. Table 1. Physico-chemical properties of Ph/B mixtures B B/Ph=75/25 B/Ph=50/50 B/Ph=25/75 Ph Specific surface area, m 2 /g 58.24 44.82 31.24 18.55 3.64 Cation exchange capacity, cmol + /kg 79.55 60.44 42.11 21.61 3.55 pH 7.41 7.15 6.97 6.87 6.85 pH PZC 5.95 6.01 6.08 6.14 6.21 Methods of sorption/desorption Sorption experiments were performed with the batch equilibration method under atmospheric pressure and at room temperature from Eu(III) initial concentration ranging from 0.005 mg/L to 205 mg/L at pH of 4.5 and 7.0 and solid (S):solution (L) ratio of 1:100. The initial (C 0 ) and equilibrium (C eq ) concentrations of Eu(III) were measured either by the ICP-OES or by the ICP-MS spectrometry depending on the Eu(III) concentration. The results allow to calculate removal efficacy (RE) of Eu(III) ions, RE=(C 0 -C eq )/C 0 . 100 (%) and determine of initial concentration ranges for which Eu(III) ions were sorbed completely, i.e. RE=99.9% and C eq ≤0.005 mg/L. Sorption rate constants were determined for C 0 of 10 mg/L and 205