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Thermodynamic description of Tc(IV) solubility and hydrolysis in dilute to concentrated NaCl, MgCl₂ and CaCl₂ solutions

Yalcintas, Ezgi 1; Gaona, Xavier ORCID iD icon 1; Altmaier, Marcus 1; Dardenne, Kathy ORCID iD icon 1; Polly, Robert ORCID iD icon 1; Geckeis, Horst 1
1 Institut für Nukleare Entsorgung (INE), Karlsruher Institut für Technologie (KIT)

Abstract (englisch):

We present the first systematic investigation of Tc(IV) solubility, hydrolysis and speciation in dilute to concentrated NaCl, MgCl2 and CaCl2 systems, and comprehensive thermodynamic and activity models for the system Tc4+–H+–Na+–Mg2+–Ca2+–OH−–Cl−–H2O using both SIT and Pitzer approaches. The results are advancing the fundamental scientific understanding of Tc(IV) solution chemistry and are highly relevant in the applied context of nuclear waste disposal. The solubility of Tc(IV) was investigated in carbonate-free NaCl–NaOH (0.1–5.0 M), MgCl2 (0.25–4.5 M) and CaCl2 (0.25–4.5 M) solutions within 2 ≤ pHm ≤ 14.5. Undersaturation solubility experiments were performed under an Ar atmosphere at T = 22 ± 2 °C. Strongly reducing conditions (pe + pHm ≤ 2) were imposed with Na2S2O4, SnCl2 and Fe powder to stabilize technetium in the +IV redox state. The predominance of Tc(IV) in the aqueous phase was confirmed by solvent extraction and XANES/EXAFS spectroscopy. Solid phase characterization was accomplished after attaining thermodynamic equilibrium using XRD, SEM–EDS, XANES/EXAFS, TG–DTA and quantitative chemical analysis, and indicated that TcO2·0.6H2O(s) exerts solubility-control in all evaluated systems. ... mehr

Volltext §
DOI: 10.5445/IR/1000056227
DOI: 10.1039/c6dt00973e
Zitationen: 26
Web of Science
Zitationen: 25
Zitationen: 28
Cover der Publikation
Zugehörige Institution(en) am KIT Institut für Nukleare Entsorgung (INE)
Publikationstyp Zeitschriftenaufsatz
Publikationsjahr 2016
Sprache Englisch
Identifikator ISSN: 1477-9226
KITopen-ID: 1000056227
HGF-Programm 32.01.01 (POF III, LK 01) Grundl. Unters. - Geochemie v. Actiniden
Erschienen in Dalton Transactions
Verlag Royal Society of Chemistry (RSC)
Band 45
Heft 21
Seiten 8916-8936
Bemerkung zur Veröffentlichung RSC geförderter Open Access-Artikel
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