Sorption and redox speciation of plutonium at the illite surface under highly saline conditions

Remi Marsac (1, 2, 3) , Nidhu Lal Banika (4, 2) , Johannes Luetzenkirchen (2) , Alexandre Diascorn (2, 5) , Kerstin Bender (2) , Christian Michael Marquardt (2) , Horst Geckeis (2)

1 ISCR - Institut des Sciences Chimiques de Rennes
2 Karlsruhe Institute of Technology (KIT), Institute for Nuclear Waste Disposal (INE)
3 GR - Géosciences Rennes
4 ITU - JRC Institute for Transuranium Elements [Karlsruhe]
5 EAMEA - Ecole des applications militaires de l'énergie atomique

Natural groundwater may contain high salt concentrations, such as those occurring at several potential deep geological nuclear waste repository sites. Actinide sorption to clays (e.g. illite) under saline conditions has, however, been rarely studied. Furthermore, both illite surface and ionic strength may affect redox speciation of actinides like plutonium. In the present study, Pu sorption to illite is investigated under anaerobic conditions for 3 < pH(m) (=-log m(H+)) < 10 and m(Nacl) = 1.0 and 3.2 molal (m). Results are compared with previous data for m(Nacl) = 0.1 m. According to redox potential measurements and based on Eu(III)-illite sorption data (taken as analogue of Pu(III)), the strong effect of m(Nacl) on overall Pu uptake observed for pH(m) < 6 is mainly attributed to the presence of Pu(III) and its competition with Na+ for ion exchange sites. For pH(m) > 6, overall Pu uptake is largely insensitive to m(Nacl) due to the prevalence of strongly adsorbed Pu(IV). By applying appropriate corrections to the activity coefficients of dissolved ions and using the 2-site protolysis non-electrostatic surface complexation and cation exchange (2 SPNE SC/CE) model, experimental data on Pu sorption to illite as a function of pH, Eh and m(Nacl) can be very well reproduced. (C) 2016 Elsevier Inc. All rights reserved.

Keywords: montmorillonite; adsorption; reduction; behavior; pu(v); ulva-lactuca; high ionic-strength; equilibria; np(v); actinides

Domains: Chemical Sciences; Theoretical and/or physical chemistry; Sciences of the Universe [physics]; Earth Sciences; Applied geology; Sciences of the Universe [physics]; Earth Sciences; Hydrology

Remi Marsac, Nidhu Lal Banika, Johannes Luetzenkirchen, Alexandre Diascorn, Kerstin Bender, et al.. Sorption and redox speciation of plutonium at the illite surface under highly saline conditions. Journal of Colloid and Interface Science, 2017, 485, pp.59-64. ⟨10.1016/j.jcis.2016.09.013⟩. ⟨hal-01438105⟩