Np(V) solubility, speciation and solid phase formation in alkaline CaCl2 solutions. Part II

• Verfasst von: Fellhauer, David [VerfasserIn]
• Verfasst von: Altmaier, Marcus [VerfasserIn]
• Verfasst von: Gaona, Xavier [VerfasserIn]
• Verfasst von: Lützenkirchen, Johannes [VerfasserIn]
• Verfasst von: Fanghänel, Thomas [VerfasserIn]
• Titel: Np(V) solubility, speciation and solid phase formation in alkaline CaCl2 solutions. Part II
• Titelzusatz: thermodynamics and implications for source term estimations of nuclear waste disposal
• Verf.angabe: David Fellhauer, Marcus Altmaier, Xavier Gaona, Johannes Lützenkirchen und Thomas Fanghänel
• E-Jahr: 2016
• Jahr: 17.02.2016
• Umfang: 17 S.
• Fussnoten: Gesehen am 15.05.2020
• Titel Quelle: Enthalten in: Radiochimica acta
• Ort Quelle: Berlin : De Gruyter, 1962
• Jahr Quelle: 2016
• Band/Heft Quelle: 104(2016), 6, Seite 381-397
• ISSN Quelle: 2193-3405
• DOI: doi:10.1515/ract-2015-2490
• Datenträger: Online-Ressource
• Sprache: eng
• K10plus-PPN: 1698319975

Abstract

<section class="abstract"><h2 class="abstractTitle text-title my-1" id="d465e2">Abstract</h2><p>The results of comprehensive solubility experiments with Np(V) in dilute to concentrated - CaCl₂ solutions which included the spectroscopic investigation of the predominant aqueous - Np(V) species and the thorough analysis of the solubility controlling Np(V) solid - phases [1](Fellhauer, D., Rothe, J., Altmaier, M., Neck, V., Runke, J., Wiss, T., - Fanghänel, Th., Np(V) solubility, speciation and solid phase formation in alkaline - CaCl₂ solutions. Part I: Experimental solubility (Radiochim. Acta, DOI 10.1515/ract-2015-2489), in the - following referred to as “Part I”), showed that the concentration of Np(V) in these - systems is limited by equilibrium reactions between previously unknown (qua)ternary solid - compounds, CaNpO₂(OH)_2.6Cl_0.4 · 2H₂O(s) <strong>(I)</strong>, - Ca_0.5NpO₂(OH)₂ · 1.3H₂O(s) <strong>(II)</strong> and Ca_0.5NpO₂(OH)₂(s) <strong>(III)</strong>, and ternary aqueous complexes of Np(V) with - the general formulae Ca_<em>x</em>[NpO₂(OH)₂]^{2<em>x-</em>1}, Ca_<em>y</em>[NpO₂(OH)₅]^{2<em>y-</em>4} with <em>y</em> ≈ 2.4 ± 1.5 (EXAFS result) and innersphere Np(V) chloro complexes, - Ca_<em>z</em>[NpO₂Cl]^2<em>z</em>+ with <em>z</em> = 0 and 1 (EXAFS result). A systematic thermodynamic - evaluation of the experimental solubility data based on the specific ion interaction theory (SIT) - and the Pitzer approach is performed. The stoichiometries of the ternary hydrolysis complexes are - assessed as Ca[NpO₂(OH)₂]⁺ and Ca₃[NpO₂(OH)₅]²⁺. The corresponding - thermodynamic solubility and complex formation constants at <em>I</em> = 0 as well as the ion interaction - parameters (SIT and Pitzer) were derived yielding a comprehensive geochemical model for the - Np(V) solubility behavior in pH neutral and alkaline CaCl₂ solutions over a large - range of ionic strengths. This significantly improves source term estimations for scenarios with - calcium dominated aquatic systems. The principally different behavior of Np(V) in - NaCl and CaCl₂ solutions is highlighted, and the impact of the new findings on - geochemical modelling of systems relevant for nuclear waste disposal is discussed.</p></section>