TY - JOUR
T1 - Neptunyl (NpO2+) interaction with green rust, GRNa,SO4
AU - Christiansen, Bo C.
AU - Geckeis, Horst
AU - Marquardt, Christian
AU - Bauer, Andreas
AU - Römer, Jürgen
AU - Wiss, Thierry
AU - Schild, Dieter
AU - Stipp, Susan Louise Svane
PY - 2011/3/1
Y1 - 2011/3/1
N2 - Green rust (GR), a member of the Fe(II),Fe(III) layered double hydroxide mineral family, forms in groundwater and during steel corrosion. It has high surface area and is very reactive, especially for redox-sensitive elements such as some actinides. During neutron irradiation of nuclear fuel in a reactor, 237Np develops. Although the abundance of Np in spent nuclear fuel is only about 0.05% by mass, it has a very long half life, 2.14 × 106 years, so there is concern about its mobility in the distant future, when radioactive storage sites might be expected to degrade. Under oxidizing conditions, as are expected from radiolysis in a repository, the very mobile neptunyl-ion, NpO2+, would be the dominant aqueous neptunium species. In this work, we investigated the interaction of NpO2+ with green rust sodium sulphate (GRNa,SO4). The aim of the study was to define the processes involved, to determine the final redox speciation of Np, hence its potential mobility, and to characterise changes in the green rust. The GRNa,SO4 sorbed and reduced NpO2+ within minutes. Reduced Np(IV) was primarily found as precipitated nanoparticles at the edges of the GRNa,SO4 crystal platelets. The position of the particles at the crystal edges suggests initial sorption of Np(V) and subsequent reduction at GR edge sites. In further experiments, Np-containing GR was allowed to oxidise completely in aqueous suspension. Surprisingly, about 50% of the Np remained associated with the oxidised product and about 75% of the associated Np was still present as Np(IV).
AB - Green rust (GR), a member of the Fe(II),Fe(III) layered double hydroxide mineral family, forms in groundwater and during steel corrosion. It has high surface area and is very reactive, especially for redox-sensitive elements such as some actinides. During neutron irradiation of nuclear fuel in a reactor, 237Np develops. Although the abundance of Np in spent nuclear fuel is only about 0.05% by mass, it has a very long half life, 2.14 × 106 years, so there is concern about its mobility in the distant future, when radioactive storage sites might be expected to degrade. Under oxidizing conditions, as are expected from radiolysis in a repository, the very mobile neptunyl-ion, NpO2+, would be the dominant aqueous neptunium species. In this work, we investigated the interaction of NpO2+ with green rust sodium sulphate (GRNa,SO4). The aim of the study was to define the processes involved, to determine the final redox speciation of Np, hence its potential mobility, and to characterise changes in the green rust. The GRNa,SO4 sorbed and reduced NpO2+ within minutes. Reduced Np(IV) was primarily found as precipitated nanoparticles at the edges of the GRNa,SO4 crystal platelets. The position of the particles at the crystal edges suggests initial sorption of Np(V) and subsequent reduction at GR edge sites. In further experiments, Np-containing GR was allowed to oxidise completely in aqueous suspension. Surprisingly, about 50% of the Np remained associated with the oxidised product and about 75% of the associated Np was still present as Np(IV).
U2 - 10.1016/j.gca.2010.12.003
DO - 10.1016/j.gca.2010.12.003
M3 - Journal article
SN - 0016-7037
VL - 75
SP - 1216
EP - 1226
JO - Geochimica et Cosmochimica Acta
JF - Geochimica et Cosmochimica Acta
IS - 5
ER -