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Radiochimica Acta

International Journal for chemical aspects of nuclear science and technology

Ed. by Qaim, Syed M.

12 Issues per year


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2193-3405
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Volume 105, Issue 5 (May 2017)

Issues

Hafnium(IV) complexation with oxalate at variable temperatures

Mitchell T. Friend
  • Department of Chemistry, Washington State University, Pullman, WA, United States of America
/ Nathalie A. Wall
  • Corresponding author
  • Department of Chemistry, Washington State University, Pullman, WA, United States of America
  • Email:
Published Online: 2016-11-09 | DOI: https://doi.org/10.1515/ract-2016-2686

Abstract

Appropriate management of fission products in the reprocessing of spent nuclear fuel (SNF) is crucial in developing advanced reprocessing schemes. The addition of aqueous phase complexing agents can prevent the co-extraction of these fission products. A solvent extraction technique was used to study the complexation of Hf(IV) – an analog to fission product Zr(IV) – with oxalate at 15, 25, and 35°C in 1 M HClO4 utilizing a 175+181Hf radiotracer. The mechanism of the solvent extraction system of 10−5 M Hf(IV) in 1 M HClO4 to thenoyltrifluoroacetone (TTA) in toluene demonstrated a 4th-power dependence in both TTA and H+, with Hf(TTA)4 the only extractable species. The equilibrium constant for the extraction of Hf(TTA)4 was determined to be log Kex=7.67±0.07 (25±1°C, 1 M HClO4). The addition of oxalate to the aqueous phase decreased the distribution ratio, indicating aqueous Hf(IV)-oxalate complex formation. Polynomial fits to the distribution data identified the formation of Hf(ox)2+ and Hf(ox)2 (aq) and their stability constants were measured at 15, 25, and 35°C in 1 M HClO4. van’t Hoff analysis was used to calculate ΔrG, ΔrH, and ΔrS for these species. Stability constants were observed to increase at higher temperature, an indication that Hf(IV)-oxalate complexation is endothermic and driven by entropy.

This article offers supplementary material which is provided at the end of the article.

Keywords: Hafnium(IV); oxalate; complexation; stability constants; solvent extraction; van’t Hoff

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About the article

Received: 2016-08-24

Accepted: 2016-10-06

Published Online: 2016-11-09

Published in Print: 2017-05-01


Citation Information: Radiochimica Acta, ISSN (Online) 2193-3405, ISSN (Print) 0033-8230, DOI: https://doi.org/10.1515/ract-2016-2686.

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