Studies on extraction of zirconium(IV) by tricapryl methyl ammonium chloride from sulphate media and its separation from hafnium(IV)

The distribution of Zr(IV) between aqueous H₂SO₄ solutions and organic phases of tricapryl methyl ammonium chloride has been described. The dependence of extraction on acidity, metal and solvent concentration, diluent type and temperature was thoroughly investigated. The possible extraction mechanism is discussed in the light of results obtained. A method for the separation of Hf(IV) from Zr(IV) is also suggested.     

The adsorption behaviour of99Mo(VI),238U(VI),95Zr(IV) and95Nb(V) on alumina

The distribution of Mo(VI) and the interfering radiocontaminants U(VI), Zr(IV) and Nb(V) have been investigated between chromatographic alumina and aqueous hydrochloric acid solutions of concentrations ranging from 0.5M to 11M. At low acidities (less than 1M HCl) the distribution coefficients increase with the decrease of acid concentration, while in the region of 2–4M they increase with the increase of the acid concentration. Above 4M HCl, the increase inK _D continues with the acid concentration for both Zr(IV) and Nb(V), but constant values are reached for U(VI) and Mo(VI).     

Film-Forming Capacity of Sn(II), Zr(IV), and Hf(IV) Acetylacetonates

Zr(acac)₄, Hf(acac)₄, and SnHacacCl₂ · 2H₂O were prepared in the solid state and in enthanol solutions. The film-forming capacity and thermal stability of these compounds were studied. Films of ZrO₂, HfO₂, and SnO₂ were prepared from film-forming solutions of the corresponding acetylacetonates.     

Selective separation and reversed phase extraction of zirconium and hafnium from a multitracer solution

The solvent extraction of Zr and Hf was studied using 444-trifluoro-1-(2-thienyl)-1,3-butanedione (TTA) from a multitracer solution containing carrier-free radioisotopes of Zr, Hf, and other elements. The multitracer was prepared from Au foil irradiated with high-energy heavy-ion beams. Effects of HCl and HNO₃ concentrations and organic solvent on the extraction and coextraction of other radionuclides have been studied. It was found that decalin (decahydronaphthalene) was the best solvent among 14 solvents studied and the optimum aqueous phase was 2 mol·dm^–3 HCl or HNO₃. About 2–10% of Sr, Rb, Sc and Nb were coextracted with Zr and Hf. The reversed phase extraction of Zr and Hf was also developed by using ethylenediaminetetraacetic acid (EDTA) solution at pH range of 8.5–10.     

Untersuchungen in den Systemen Titan (Zirkonium,Hafnium)-Niob-Kohlenstoff

Zusammenfassung Die Aufteilung der Phasenfelder in den Dreistoffen: Titan (Zirkonium, Hafnium)-Niob-Kohlenstoff wird mit Hilfe gesinterter Proben bei je einer Temperatur ermittelt. Alle drei Systeme sind durch das Auftreten großer homogener Bereiche der Mischcarbide (Ti, Nb) C_1-x , (Zr, Nb) C_1-x und (Hf, Nb) C_1-x charakterisiert. Nb₂C löst wenig von dem Zweitcarbid. Eine thermodynamische Betrachtung führt zu einer Abschätzung der Stabilitätsdifferenz zwischen NbC_1-x und Nb₂C.

---

The ternary systems: Ti(Zr, Hf)–Nb–C have been examined by means of sintered specimens. The equilibria of the above mentioned systems are characterized by the occurrence of a large domain of the respective solid solutions (Ti, Nb) C_1-x , (Zr, Nb)C_1-x and (Hf, Nb)C_1-x . Nb₂C dissolves very little of the second carbide. Thermodynamic considerations lead to an evaluation of the difference of stability between NbC_1-x and Nb₂C.

---

---

Mit 6 Abbildungen     

Catenated polysulfur ligands: the pentasulfides of di-η5-cyclopentadienyl-zirconium(IV) and -hafnium(IV)

The thiols Cp₂M(SH)₂, where M = Ti and Zr, react to form the complexes Cp₂MS₅ when treated with mono- and di-sulfur transfer reagents. Treatment of Cp₂MCl₂ with Li₂S₂ and sulfur gave Cp₂MS₅, M = Ti, Zr and Hf, in better yield. The new Zr and Hf complexes have a six-membered MS₅ ring in a chair conformation similar to the previously observed for M = Ti. Variable temperature NMR studies show that the barriers to MS₅ ring inversion decrease in the order Ti > Hf > Zr.     

Extraction-chromatographic behavior of Zr(IV) and Hf(IV) on TRU and LN resins in mixtures of HNO3 and HF

The behavior of group-4 homologs Zr and Hf on extraction-chromatographic sorbents LN resin and TRU resin in mixtures of HF and HNO₃ is considered. Distribution coefficients of the elements in the mixtures of 5·10⁻⁴ M–1 M HF and 0.01 M–5 M HNO₃ are determined. Strong retention of both elements was found on LN resin in the range of concentrations c(HF) ≤ 0.01 M for all concentrations of HNO₃. Retention tends to gradually disappear while increasing c(HF) to 0.5 M. On TRU resin retention is observed only in solutions with c(HNO₃) ≥ 2 M and c(HF) ≤ 0.01 M. The possibility of separating Zr(IV) and Hf(IV) on LN resin is illustrated in two different acid mixtures, whereas their separation on TRU resin under the conditions studied in this work is difficult. The results obtained can be used to isolate analytes from multicomponent mixtures during analytical tasks, as well as to separate them from each other.

     

Behaviour of 18 elements in HF and HF−NH4F media on anion exchanger in various ionic forms

The behaviour of the elements As, Ba, Cr, Fe, Eu, Hf, La, Mo, Nb, Pa, Re, Sb, Sc, Sn, Ta, Tc, W, and Zr on Dowex-1X8 in 0.1 to 29.5M HF and mixed solutions of HF and NH₄F of different concentration combinations varying for both reagents from 0.1 to 10M has been studied. The influence of the ionic form of Dowex-1 on the distribution of elements has also been examined. The distribution ratio for the mixed solutions are given in form of adsorption contour lines.     

Study of group IV–VI B metal extraction by easily melting acid extractants

The melt extraction of Ti, Zr, Hf, Nb, Cr and Mo with β-diketones in naphthalene-biphenyl eutectics has been studied and the temperature dependence of the equilibrium constants obtained. X-ray fluorescence determination of the elements in the solidified organic extract is convenient.     

Anion-exchange behaviour of 12 elements in H2SO4 and HF−H2SO4 medium

Anion-exchange data have been obtained for the elements As, Hf, Mo, Nb, Pa, Re, Sb, Sn, Ta, Tc, W, and Zr in 0.1 to 10M H₂SO₄ and in HF–H₂SO₄ mixtures of combination extending from 0.1 to 10M HF and from 0.1 to 10M H₂SO₄. The distribution ratios for mixed solutions are presented in form of adsorption contour lines.     

Zr(IV) and Hf(IV) based metal-organic frameworks with reo-topology

Zr and Hf based MOFs with enhanced pore accessibility for large molecules and good hydrothermal stability were obtained using a bent dithienothiophene dicarboxylate and Zr(4+) or Hf(4+) source. A modulator (benzoic acid) facilitates formation of an eight-connecting cluster leading to a new framework which adopts reo topology.     

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

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)Hf_zF₆ 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)Hf_zF₆ 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     

Solvent extraction of hafnium(IV)

^{175, 181}Hafnium(IV) was extracted by HDBP in 2-ethylhexanol from 1–10M solutions of HClO₄, HCl and HNO₃, and 1–8M H₂SO₄. As with low polar organic phase diluents, the acidity dependence of the distribution ratio of Hf, D, passes through a minimum for HClO₄, HCl, and H₂SO₄ whereas only an increase of D can be observed with increasing HNO₃ concentration. From the slope analysis the following complexes were found to be extracted (HDBP=HA): HfA₄ at <4M HClO₄ and <5M HCl, lg K_extr=9, HfX₄(HA)₄ (X=ClO ₄ ⁻ , Cl⁻ or NO ₃ ⁻ ) at >5M HClO₄, >7M HCl and 1–10M HNO₃, Hf(SO₄)A₂(HA)_3–4 at <3M H₂SO₄, and Hf(SO₄)₂ (HA)₄ at >6M H₂SO₄. Coextraction of sulphate with hafnium from H₂SO₄ solutions was evidenced in experiments with macro concentrations of Hf(IV) and³⁵SO ₄ ²⁻ . Part XX: Coll. Czech. Chem. Commun., 40 (1975) 3617.     

A chelating resin containing 1-(2-thiazolylazo)-2-naphthol as the functional group; synthesis and sorption behavior for trace metal ions

A new polystyrene-divinylbenzene resin containing 1-(2-thiazolylazo)-2-naphthol (TAN) functional group was synthesized and its sorption behavior for 19 metal ions including Zr(IV), Hf(IV) and U(VI) was investigated by batch and column experiments. The chelating resin showed a high sorption affinity for Zr(IV) and Hf(IV) at pH 2. Some parameters affecting the sorption of the metal ions are detailed. The breakthrough and overall capacities were measured under optimized conditions. The overall capacities of Zr(IV) and Hf(IV) that were higher than those of the other metal ions were 0.92 and 0.87 mmol/g, respectively. The elution order of metal ions at pH 4 was evaluated as: Zr(IV)>Hf(IV)>Th(IV)>V(V)>Nb(V)>Cu(II)>U(VI)>Ta(V)>Mo(VI)>Cr(III)>Sn(IV)>W(VI). Quantitative recovery of most metal ions except Zr(IV) was achieved using 2 M HNO₃. Desorption and recovery of Zr(IV) was successfully performed with 2 M HClO₄ and 2 M HCl.     

Extraction of thiocyanate complexes of cobalt(II) by diphenyl-2-pyridylmethane in benzene from mineral acid solutions

Extraction of Co(II) by diphenyl-2-pyridylmethane (DPPM) in benzene form mineral acid solutions containing potassium thiocyanate has been studied at room temperature (23±2°C). Its extraction from mineral acids alone is rather poor. Optimal aqueous phase composition for the quantitative extraction of Co(II) by 0.1M DPPM is 0.1M acid+0.2M KSCN. Stoichiometric studies indicate that an ionic type complex, (DPPM·H)₂·Co(SCN)₄, is responsible for extraction. The metal can be back-extracted from the organic phase by aqueous acetate, citrate or oxalate solutions. Separation factors from other metals determined under optimal conditions reveal that Co(II) can be quantitatively separated from CsI), Sr(II), Cr(III), Ln(III), Zr(IV), Hf(IV), Cr(VI) and Tc(VII), Mo(VI), Zn(II), Au(III), Hg(II) and U(VI) are, however, coextracted and hence should be previously removed by other techniques or reagents.     

Consecutive thin-layer chromatographic separation of Zr(IV), Hf(IV) and many other ions on silica gel in nitric acid-hydrogen peroxide media

The thin-layer chromatographic (TLC) behaviour of 64 ions including Zr(IV) and Hf(IV) has been surveyed on systems composed of silica gel and of nitric acid and nitric acid-hydrogen peroxide media. In the 0.5 mol 1(-1) HNO(3)-3% (w/v) H(2)O(2) solution, only Hf(IV) adsorbed very strongly, whereas Zr(IV) and many other ions showed no or weak adsorption. Stepwise development with diluted nitric acid and subsequently with nitric acid-hydrogen peroxide solution allowed the consecutive separation of three-component mixtures consisting of Zr(IV), Hf(IV) and one of many other accompanying elements, such as Mo(VI), Nb(V), Th(IV), Ti(IV), U(VI) and rare earths(III), to be conducted simply and effectively.     

Extraction and separation of Zr,Nb and Hf by Aliquat 336 and its mixtures with TOPO from acidic thiocyanate media

Presence of thiocyanate ions results in appreciable extraction of Zr(IV) by Aliquat 336 from low aqueous HCl acidities, i.e., 0.1 to 4.5M. The variation of concentrations of HCl, thiocyanate and Aliquat 336 greatly influences the extent of extraction. Mixtures of Aliquat 336 and TOPO result in synergistic extraction of Zr and Hf from acidic thiocyanate media, the extracted species being the disolvate with TOPO. By controlled adjustment of HCl, SCN^– and Aliquat 336 concentrations, separation of Zr, Nb and Hf is possible. A maximum separation factor (D_Nb/D_Zr) of 3675 has been achieved under certain conditions.     

Syntheses and X-ray crystal structures of zirconium(IV) and hafnium(IV) complexes containing monovacant wells-Dawson and Keggin polyoxotungstates

The syntheses and crystal structures of a series of zirconium(IV) and hafnium(IV) complexes with Dawson monovacant phosphotungstate [alpha2-P2W17O61](10-) and in situ-generated Keggin monovacant phosphotungstate [alpha-PW11O39](7-), which was obtained by a reaction of [alpha-PW12O40](3-) with Na2CO3, are described. K15H[Zr(alpha2-P2W17O61)2].25H2O (K-1), K16[Hf(alpha2-P2W17O61)2].19H2O (K-2), (Et2NH2)10[Zr(alpha-PW11O39)2].7H2O (Et2NH2-3), and (Et2NH2)10[Hf(alpha-PW11O39)2].2H2O (Et2NH2-4), being afforded by reactions in aqueous solutions of monolacunary Dawson and Keggin polyoxotungstates with ZrCl2O.8H2O and HfCl2O.8H2O followed by exchanging countercations, were obtained as analytically pure, homogeneous colorless crystals. Single-crystal X-ray structure analyses revealed that the Zr(IV) and Hf(IV) ions are in a square antiprismatic coordination environment with eight oxygen atoms, four of them being provided from each of the two monovacant polyanion ligands. Although the total molecular shapes and the 8-coordinate zirconium and hafnium centers of complexes 1-4 are identical, the bonding modes (bond lengths and bond angles) around the zirconium(IV) and hafnium(IV) centers were dependent on the monovacant structures of the polyanion ligands. Additionally, the characterization of complexes 1-4 was accomplished by elemental analysis, TG/DTA, FTIR, and solution (31P and 183W) NMR spectroscopy.     

Solvent extraction of Hf(IV) from mixed electrolyte solutions into di-2-ethylhexylphosphoric acid (HDEHP)

Extraction of hafnium(IV) from aqueous sulfuric and sulfuric-nitric acid solutions into di-2-ethylhexylphosphoric acid (HDEHP) in xylene has been investigated. The Hf(IV) species extracted from 5M sulfuric acid was found to be HfY₂(HY₂)₂ where Y and HY₂ represent the anions of monomeric HY and dimeric H₂Y₂ forms of HDEHP, respectively. In the presence of nitrate ion the species extracted are found to be Hf(NO₃)Y(HY₂)₂ and Hf(NO₃)₂)(HY₂)₂. But when the aqueous phase is 3.0M HNO₃+2.5M H₂SO₄ only one species, Hf(NO₃)₂(HY₂)₂ was extrated. No synergism was observed from 5M H₂SO₄ by HDEHP with the addition of thenoyltrifluoracetone (HTTA).     

Separation of Zr and Hf from strong hydrochloric acid solution by solvent extraction with TEHA

In order to separate Zr(IV) and Hf(IV) from chloride solutions, TEHA (tri 2-ethyl hexyl amine) was used as an extractant. The aqueous phase consisted of 200 ppm of Zr and Hf in strong HCl solution. In our solvent extraction system, the extractability of the constituents by TEHA was found to be in the following order, HCl > Zr(IV) > Hf(IV). The highest separation factor between the two metals was obtained from 8 M HCl solution. Based on the selectivity towards Zr over Hf with TEHA, McCabe–Thiele plot was constructed and batch simulation of counter-current extraction studies has been conducted. Scrubbing results from the loaded TEHA showed that Hf was selectively scrubbed over Zr by strong HCl solution (9 M). Complete stripping of Zr was possible from the organic phase with distilled water after scrubbing of Hf. The extraction behavior of Zr and Hf by TEHA was compared with that by TiOA and TOA. Our results can be utilized in developing a solvent extraction process to separate Zr and Hf from concentrated chloride solutions by using TEHA.