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Effect of ISA and chloride on the uptake of niobium(V) by hardened cement paste and C-S-H phases: quantitative description and mechanistic understanding

Jo, Y.; Çevirim-Papaioannou, N.; Franke, K.; Fuss, M.; Pedersen, M.; Lothenbach, B.; de Blochouse, B.; Altmaier, M.; Gaona, X.


The uptake of niobium by hardened cement paste (HCP) a calcium silicate hydrate (C-S-H) phases was investigated with ⁹³Nb and ⁹⁵Nb (t₁/₂=35.0 days). Structural materials used in nuclear reactors as well as cements contain the naturally occurring isotope ⁹³Nb, while radioactive ⁹⁴Nb with t₁/₂=2×10⁴ years is relevant in the context of nuclear waste disposal. Strong uptake of Nb was observed for both materials, confirming that C-S-H are the main sink of Nb in cement. Isotopic exchange with ⁹³Nb in cement can play a role in the uptake of ⁹⁴Nb under repository conditions. The formation of complexes with isosaccharinic acid (ISA) decreases the Nb uptake, although sorption remains strong up to [ISA]tot=0.1 M. Chloride has a negligible effect on the uptake of Nb up to [NaCl] = 2 M. This work provides a sound basis for the quantitative description and mechanistic understanding of ⁹⁴Nb retention in L/ILW repositories.

Keywords: Niobium; Hardened cement paste (HCP); Limestone; Calcium silicate hydrate (C15 S-H) phases; Sorption

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