期刊
GEOCHIMICA ET COSMOCHIMICA ACTA
卷 215, 期 -, 页码 421-431出版社
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.gca.2017.08.008
关键词
Neptunium; Illite; Redox; Saline; High ionic strength; Surface complexation; Spectroscopy; Geochemical modeling
资金
- Federal Ministry of Economic Affairs and Energy (Germany) [02E10206, 02E10961]
- European Union's European Atomic Energy Community's (Euratom) Seventh Framework Program [249624]
Neptunium (Np) uptake on illite is investigated in 1 and 3.2 molal (m) NaCl solutions under inert (Ar) atmosphere for 4 < pH(m) < 10 (pH(m) = -log(mH+) ) and 5 x 10(-8) < [Np(V)](tot) < 3 x 10(-4) M. In agreement with a previous study in 0.1 m NaCl solutions (Marsac et al., 2015a), Np(V) is the prevailing oxidation state in the aqueous solution, but Np uptake by illite is affected by surface induced reduction. The extent of Np(V) reduction to Np(IV) follows the measured redox potential (or the pe = -log a(e-)), which is influenced by the introduced Np(V) amount, because of the low redox capacity of the illite. The presence of Np(IV) on the solid phase is verified by X-ray Absorption Near Edge Spectroscopy (XANES). We can conclude that Np uptake by illite is not significantly affected by the variation of m(Nacl) from 0.1 to 3.2 m and thus is in agreement with reports on tetravalent actinide and Np(V) sorption to clays at high ionic strength. The combination of (i) the two site protolysis non-electrostatic surface complexation and cation exchange model, (ii) the specific ion interaction theory to calculate activity coefficients for dissolved species and (iii) by accounting for redox equilibria and the stability of surface Np species, the overall Np uptake by illite can be simulated as a function of pH(m), pe m(Nacl) and using a single set of parameters. The present experimental and modeling results are particularly important in the context of deep geological nuclear waste disposal since many sedimentary rocks or clay formations that are deemed suitable for this purpose exhibit highly saline porewaters. (C) 2017 Elsevier Ltd. All rights reserved.
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