Crystal Structure and Stability in Aqueous Solutions of Na0.5[NpO2(OH)1.5]·0.5H2O and Na[NpO2(OH)2]

David Fellhauer; Jun-Yeop Lee; Nicole A DiBlasi; Olaf Walter; Xavier Gaona; Dieter Schild; Marcus Altmaier

doi:10.1021/jacs.2c03479

Crystal Structure and Stability in Aqueous Solutions of Na_0.5[NpO₂(OH)_1.5]·0.5H₂O and Na[NpO₂(OH)₂]

J Am Chem Soc. 2022 Jun 1;144(21):9217-9221. doi: 10.1021/jacs.2c03479. Epub 2022 May 19.

Authors

David Fellhauer¹, Jun-Yeop Lee², Nicole A DiBlasi¹, Olaf Walter³, Xavier Gaona¹, Dieter Schild¹, Marcus Altmaier¹

Affiliations

¹ Institute for Nuclear Waste Disposal, Karlsruhe Institute of Technology, P.O. Box 3640, 76021 Karlsruhe, Germany.
² School of Mechanical Engineering, Pusan National University, 2, Busandaehak-ro 63beon-gil, Geumjeong-gu, Busan 46241, South Korea.
³ Joint Research Centre Karlsruhe, European Commission, P.O. Box 2340, 76125 Karlsruhe, Germany.

PMID: 35588478
DOI: 10.1021/jacs.2c03479

Abstract

The ternary neptunium(V) (Np(V)) hydroxides Na_0.5[NpO₂(OH)_1.5]·0.5H₂O (I) and Na[NpO₂(OH)₂] (II) were synthesized in aqueous NaOH solutions at T = 80 °C, and their crystal structures were determined to be monoclinic, P2₁, Z = 2, a = 5.9859(2), b = 10.1932(3), c = 12.1524(4) Å, β = 98.864(1)°, V = 732.63(4) Å³ for (I) and orthorhombic, P2₁2₁2₁, Z = 4, a = 5.856(7), b = 7.621(9), c = 8.174(9) Å, V = 364.8(7) Å³ for (II). By combining the detailed structural information with results from systematic solubility investigations, a comprehensive chemical and thermodynamic model of the Np(V) behavior in NaCl-NaOH solutions was evaluated. The results reveal a great stability of the ternary Na-Np(V)-OH solid phases that significantly enhances the predominance field of the entire Np(V) redox state to high alkalinity.