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A density-functional theory approach to the separation of K2ZrF6 and K2HfF6 via fractional crystallization

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dc.contributor.author Branken, David Jacobus
dc.contributor.author Krieg, Henning Manfred
dc.contributor.author Lachmann, Gerhard
dc.contributor.author Bruinsma, O.S.L.
dc.date.accessioned 2012-10-22T07:57:34Z
dc.date.available 2012-10-22T07:57:34Z
dc.date.issued 2011
dc.identifier.citation Branken, D.J et al. 2011. A density-functional theory approach to the separation of K2ZrF6 and K2HfF6 via fractional crystallization. International journal of quantum chemistry, 111(3):682-693. [http://onlinelibrary.wiley.com/journal/10.1002/%28ISSN%291097-461X/] en_US
dc.identifier.issn 0020-7608
dc.identifier.issn 1097-461X (Online)
dc.identifier.uri http://hdl.handle.net/10394/7535
dc.description.abstract Because of the low absorption cross-section for thermal neutrons of zirconium (Zr) as opposed to hafnium (Hf), Zr-metal must essentially be Hf-free (<100 ppm Hf) to be suitable for use in nuclear reactors. However, Zr and Hf always occur together in nature, and due to very similar chemical and physical properties, their separation is particularly difficult. Separation can be achieved by traditional liquid–liquid extraction or extractive distillation processes, using Zr(Hf)Cl4 as feedstock. However, the production of K2Zr(Hf)F6 via the plasma dissociation route, developed by the South African Nuclear Energy Corporation Limited (Necsa), could facilitate the development of an alternative separation process. In this theoretical study, the results of density-functional theory (DFT) simulations of K2Zr(1-z)HfzF6 solid solutions [using Cambridge Serial Total Energy Package (CASTEP)] are presented, for which the supercell approach was applied in an attempt to determine whether solid solution formation during crystallization from aqueous solutions (fractional crystallization) is thermodynamically possible, which would hinder the separation efficiency of this method. Consequently, the calculated thermodynamic properties of mixing were used to evaluate the separation efficiency of Zr and Hf by fractional crystallization using a thermodynamic model to calculate the relative distribution coefficients. The small mixing enthalpies that were calculated from the DFT results, indicates that lattice substitution of Zr(IV) by Hf(IV) in K2ZrF6 could occur with relative ease. This is not surprising, considering the close similarities between Zr and Hf, and it was therefore concluded that K2Zr(1-z)HfzF6 solid solution formation might well restrict the separation efficiency of Zr and Hf by fractional crystallization of K2Zr(Hf)F6. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2011 en_US
dc.description.uri http://dx.doi.org/10.1002/qua.22448
dc.language.iso en en_US
dc.publisher Wiley-Blackwell en_US
dc.subject Zirconium and hafnium separation en_US
dc.subject fractional crystallization of K2Zr(Hf)F6 en_US
dc.subject solid solutions en_US
dc.subject density-functional theory simulation en_US
dc.subject thermodynamic properties of mixing en_US
dc.title A density-functional theory approach to the separation of K2ZrF6 and K2HfF6 via fractional crystallization en_US
dc.type Article en_US


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