Neptunium(V) transport in granitic rock : A laboratory scale study on the influence of bentonite colloids

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Elo , O , Hölttä , P , Kekäläinen , P , Voutilainen , M & Huittinen , N M 2019 , ' Neptunium(V) transport in granitic rock : A laboratory scale study on the influence of bentonite colloids ' , Applied Geochemistry , vol. 103 , pp. 31-39 . https://doi.org/10.1016/j.apgeochem.2019.01.015

Title: Neptunium(V) transport in granitic rock : A laboratory scale study on the influence of bentonite colloids
Author: Elo, O.; Hölttä, P.; Kekäläinen, P.; Voutilainen, M.; Huittinen, Nina Maria
Contributor: University of Helsinki, Department of Chemistry
University of Helsinki, Department of Chemistry
University of Helsinki, Department of Chemistry
University of Helsinki, Department of Chemistry
University of Helsinki, Institute of Resource Ecology, Dresden
Date: 2019-04
Language: eng
Number of pages: 9
Belongs to series: Applied Geochemistry
ISSN: 0883-2927
URI: http://hdl.handle.net/10138/301163
Abstract: In the present study neptunium(V) uptake by crystalline granitic rock (Kuru Grey granite) and the role of stable and mobile bentonite colloids (MX-80) on the migration of neptunium(V) was investigated. Two different experimental setups were utilized, batch-type experiments under stagnant conditions and column experiments under flowing water conditions. The uptake of 10(-6) M neptunium(V) by 40 g/L crushed granite in 10 mM NaClO4 was found to be pH-dependent, whereas neptunium(V) uptake by MX-80 bentonite colloids (0.08-0.8 g/L) was pH-independent up to a pH-value of approximately 11. Column experiments were conducted in the presence and absence of colloids at two pH values (pH = 8 and 10) and two flow rates (0.3 and 0.8 mL/h) in 10 mM NaClO4. The injected neptunium(V) concentration was 2x10(-4) M and the colloid concentration ranged from 0.08 to 0.32 g/L. The properties of the flow field in the columns were investigated with a conservative chloride tracer, at the same two flow rates of 0.8 and 0.3 mL/h. The resulting breakthrough curves were modeled using the analytical solution of advection-matrix diffusion equation. A tailing of neptunium(V) breakthrough curves in comparison to the conservative tracer was observed, which could be explained by a slightly higher retardation of neptunium(V) in the column caused by sorption on the granite. The sorption was in general lower at pH 8 than at pH 10. In addition, the tailing was almost identical in the absence and presence of MX-80 bentonite colloids, implying that the influence of colloids on the neptunium(V) mobility is almost negligible.
Subject: 116 Chemical sciences
1171 Geosciences
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