827. Some aspects of the solution chemistry of zirconium

Selective extraction of Hf(IV) over Zr(IV) from aqueous H2SO4 solutions by solvent extraction with acidic organophosphorous based extractants

“…Pershina et al reported that the preferential complex formation of Hf(IV) over Zr(IV) was observed in lower concentration H 2 SO 4 solutions for macro‐concentrations of hydrolyzed cations, whereas a quite opposite trend was detected for Zr(IV) and Hf(IV) in higher concentrations of H 2 SO 4 . In fact, the tendency shown in both Cyanex 272 and D2EHPA experimental results in the present investigations is in good agreement with the reported experimental observations . Finally, the overall results for the influence of Cyanex 272 and D2EHPA concentrations on the extraction of Hf(IV) over Zr(IV) from 0.5 to 4 mol L ‐1 H 2 SO 4 concentrations suggest that it is possible to extract Hf(IV) selectively over Zr(IV).…”

“…However, it is generally assumed that the complex chemistry of Zr(IV) and Hf(IV) and their activity in strong H 2 SO 4 solutions may be responsible for this lower extraction tendency of Zr(IV) and Hf(IV) towards the extractants from H 2 SO 4 solutions. According to the information available in the literature, the general form of Zr(IV) and Hf(IV) complexes in sulphate media is M(SO 4 ) n (4‐2n)+ (H 2 O) m. When the H 2 SO 4 concentration increases, the step‐wise formation of complexes also increases, with larger negative charges . Pershina et al reported that the preferential complex formation of Hf(IV) over Zr(IV) was observed in lower concentration H 2 SO 4 solutions for macro‐concentrations of hydrolyzed cations, whereas a quite opposite trend was detected for Zr(IV) and Hf(IV) in higher concentrations of H 2 SO 4 .…”

“…However, it is generally assumed that the complex chemistry of Zr(IV) and Hf(IV) and their activity in strong H 2 SO 4 solutions may be responsible for this lower extraction 41 When the H 2 SO 4 concentration increases, the step-wise formation of complexes also increases, with larger negative charges. [41][42][43][44][45][46][47] reported that the preferential complex formation of Hf(IV) over Zr(IV) was observed in lower concentration H 2 SO 4 solutions for macro-concentrations of hydrolyzed cations, whereas a quite opposite trend was detected for Zr(IV) and Hf(IV) in higher concentrations of H 2 SO 4 . 41,42 In fact, the tendency shown in both Cyanex 272 and D2EHPA experimental results in the present investigations is in good agreement with the reported experimental observations.…”

Separation of Hf(IV)–Zr(IV) in H2SO4 solutions using solvent extraction with D2EHPA or Cyanex 272 at different reagent and metal ion concentrations

“…Moreover, the decrease in the extraction percentage of Zr(IV) with the sulfuric acid concentration was more remarkable as the concentration ratio of the metal ions also decreased. This is in agreement with the data reported for the formation of negatively charged species which were predominant at a lower metal ion concentration ratio than at a high metal ion concentration ratio (Pershina et al, 2002;Caletka et al, 1980;Ryabchikov et al, 1964;Kubica et al, 1999;Lister and McDonald, 1952;Hurst, 1983).…”

Engineering New Defective Phases of UiO Family Metal-Organic Frameworks with Water

“…9,21,22 Defects can therefore be deliberately introduced via the inclusion of these species in the reaction mixture. [23][24][25][26][27][28] In 'modulated' synthesis, a monocarboxlic acid modulator is included in the synthesis, giving a ready source of monocarboxylate groups that compete with the linker to coordinate to the cluster, thereby creating missing-linker defects. 1,14,21,29 While modulated synthesis was originally devised as a method of controlling the morphology of MOF crystals via capping coordination sites on the faces of the MOF crystal, [30][31][32] the linker vacancies introduced by modulated synthesis can be incorporated within the framework, leading to a defective structure.…”