Thermodynamic Stability of Zirconium(IV) Complexes with Hydroxy Ions

Abstract

A protometric study on the speciation of zirconium(IV) was computed and refined, by the program PROTAF, for each ionic strength. The solubility product Ks of Zr(OH) 4 was performed in an aqueous solution at 25°C in KNO 3 and four ionic strengths (0.2, 0.5, 1, and 2 mol·dm -3 ). This study calculated by taking these β mlh constants into account. . Increasing zirconium concentration induces the formation of polynuclear species outstanding resistance to corrosion, as well as to a low neutron capture cross-section. It is an essential constituent of Zr m (OH) h (4mϪh)ϩ . In accordance with studies from Zielen and Connick [2] , Johnson and Kraus [11] , and Angstadt and the core of the nuclear power station and for confining fissile materials.Tyree [12] , Baes and Mesmer conclude that the existence of a trimer, Zr 3 (OH) 4 8ϩ or Zr 3 (OH) 5 7ϩ , and of the tetramer The running of nuclear installations relies on the proZr 4 (OH) 8 8ϩ is probable. cessing of nuclear fuels and fission by-products, but also on the long-term storage, in protected sites, of confined materiAja et al. [13] also published a review concerning the aqueals which have acquired an appreciable radioactivity.ous chemistry of zirconium(IV). They principally take into In the long-term one may expect the possibility of cor-account the results obtained by Russian scientists [5] [6] [8] [14] . rosion and fissuring of the confining containers leading to They consider that the values of the formation constants of a contamination of soils and waters.the mononuclear hydroxide complexes depend little on the ionic strength and the nature of the supporting electrolyte. Modelling programs which take into account the whole For these constants, they have retained average values which local physical parameters as well as the physicochemical are very different from those given by Baes and Mesmer. data allow the quantification of these contamination risks. The values used for these simulations, especially those relatMore recently, Adair et al. [15] published an article entitled ing to zirconium, have to be as reliable as possible in order "A review of the aqueous chemistry of the zirconium-water to yield realistic estimations.system" in which they simply give the same values of conThe chemistry of zirconium(IV) in aqueous media is stants that Baes and Mesmer indicated for the mono-and dominated by the complexation of Zr 4ϩ with OH Ϫ . The polynuclear zirconium hydroxide complexes at 25°C. data currently available on zirconium hydroxide complexes In short, numerous studies deal with the formation of comes from studies carried out (essentially) before zirconium-hydrolysed complexes in aqueous solution but. The advanced species formulae many discrepancies exist from one author to another conand, above all, the values of the corresponding comcerning the major species formed and the values of the corplexation constants, seem questionable.responding constants of formation. It must be pointed that Baes and Mesmer [10] have reviewed bibliographical re-in these studies the stoi...

Rational Design, Synthesis, and Evaluation of Tetrahydroxamic Acid Chelators for Stable Complexation of Zirconium(IV)

“…The calculated Δ G for the complexation [see Eq. (1)] in the reaction field of water was −56.1 kcal mol −1 , underestimating the experimental Δ G by 6.6 kcal mol −1 20. The calculated Δ H and T Δ S at 298.15 K were −68.9 and −12.8 kcal mol −1 , respectively, indicating that the reaction is entirely enthalpy driven. …”

Detection of Polynuclear Zirconium Hydroxide Species in Aqueous Solution by Desktop ESI-MS

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Computational Study of the Zr4+ Tetranuclear Polymer, [Zr4(OH)8(H2O)16]8+

“…The structure of this species [Zr 4 (OH) 8 (H 2 O) 16 Cl 8 ] was determined by early X-ray 5,6 and some later experiments . X-ray scattering studies have shown that this species is the major form present in solutions. , Spectrophotometric and ultracentrifugation studies also suggest the presence of the tetramer, which has been confirmed by several recent publications. , We have obtained and characterized the gas-phase and solution structures of the tetramer using the CPMD approach and conducted an analysis of its stability and chemical behavior in aqueous solution.…”