Np(V) solubility, speciation and solid phase formation in alkaline CaCl2 solutions. Part II: thermodynamics and implications for source term estimations of nuclear waste disposal
<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 - CaCl<sub>2</sub> solutions which included the s...
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| Main Authors: | , , , , |
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| Format: | Article (Journal) |
| Language: | English |
| Published: |
17.02.2016
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| In: |
Radiochimica acta
Year: 2016, Volume: 104, Issue: 6, Pages: 381-397 |
| ISSN: | 2193-3405 |
| DOI: | 10.1515/ract-2015-2490 |
| Online Access: | Verlag, lizenzpflichtig, Volltext: https://doi.org/10.1515/ract-2015-2490 Verlag, lizenzpflichtig, Volltext: https://www.degruyterbrill.com/view/journals/ract/104/6/article-p381.xml 
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| Author Notes: | David Fellhauer, Marcus Altmaier, Xavier Gaona, Johannes Lützenkirchen und Thomas Fanghänel |
| Summary: | <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 - CaCl<sub>2</sub> 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 - CaCl<sub>2</sub> 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, CaNpO<sub>2</sub>(OH)<sub>2.6</sub>Cl<sub>0.4</sub> · 2H<sub>2</sub>O(s) <strong>(I)</strong>, - Ca<sub>0.5</sub>NpO<sub>2</sub>(OH)<sub>2</sub> · 1.3H<sub>2</sub>O(s) <strong>(II)</strong> and Ca<sub>0.5</sub>NpO<sub>2</sub>(OH)<sub>2</sub>(s) <strong>(III)</strong>, and ternary aqueous complexes of Np(V) with - the general formulae Ca<sub><em>x</em></sub>[NpO<sub>2</sub>(OH)<sub>2</sub>]<sup>2<em>x-</em>1</sup>, Ca<sub><em>y</em></sub>[NpO<sub>2</sub>(OH)<sub>5</sub>]<sup>2<em>y-</em>4</sup> with <em>y</em> ≈ 2.4 ± 1.5 (EXAFS result) and innersphere Np(V) chloro complexes, - Ca<sub><em>z</em></sub>[NpO<sub>2</sub>Cl]<sup>2<em>z</em>+</sup> 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[NpO<sub>2</sub>(OH)<sub>2</sub>]<sup>+</sup> and Ca<sub>3</sub>[NpO<sub>2</sub>(OH)<sub>5</sub>]<sup>2+</sup>. 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 CaCl<sub>2</sub> 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 CaCl<sub>2</sub> solutions is highlighted, and the impact of the new findings on - geochemical modelling of systems relevant for nuclear waste disposal is discussed.</p></section> |
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| Item Description: | Gesehen am 15.05.2020 |
| Physical Description: | Online Resource |
| ISSN: | 2193-3405 |
| DOI: | 10.1515/ract-2015-2490 |