Tracer scale solvent extraction separation of tantalum from niobium using di-(2-ethylhexyl)-phosphoric acid as extractant

A simple solvent extraction procedure for the efficient separation of the radioactive tracers⁹⁵Nb and¹⁸²Ta from each other in a mixture using di-(2-ethylhexyl)phosphoric acid (HDEHP) as extractant is described. Tantalum was found to be quantitatively extracted from an aqueous madium, which is 1.6N in HCl and 10^?2 M in oxalic acid, with a HDEHP solution of 0.1 M concentration. Extractabilities of both niobium and tantalum in mineral acids like HCl, H₂SO₄ and HNO₃ and in some organic acids like oxalic, citric, etc., in HDEHP under the experimental conditions were also studied. The reliability of the separation procedure was verified further by γ-ray spectrometry.     

Extraction Recovery of Tantalum(V) and Niobium(V) from Hydrofluoric and Hydrofluoric-Sulfuric Acid Aqueous Solutions with Octanol

Comparative study of extraction of tantalum(V) and niobium(V) with octanol and tributyl phosphate was made. The data on distribution of tantalum(V) and niobium(V) between octanol and hydrofluoric and hydrofluoric-sulfuric acid aqueous solutions were obtained. The flowsheet for preparation of pure tantalum and niobium oxides was developed.     

Solvent extraction of protactinium(v) with bis(2-ethylhexyl)phosphoric acid in toluene

The extraction of Pa(V) from 1M perchloric acid medium with HDEHP in toluene was carried out. The different factors affecting the metal distribution coefficient such as HDEHP concentration in the organic phase, pH of the aqueous phase and the equilibrium temperature were followed. From the data obtained the equilibrium constants of the extraction reaction were calculated. From the temperature variation, the corresponding thermodynamic parameters (G, H and S) were also derived. In the same way, the effect of addition of some N-and 0-containing solvents such as pyridine, 2,2-dipyridyl, n-amyl alcohol, n-decyl alcohol and n-butyl acetate, to the HDEHP organic phase was demonstrated. From the data obtained the suggested mechanisms for the synergistic extraction reactions were discussed together with the corresponding values of the thermodynamic parameters.     

Alternative spectrophotometric determination of niobium and tantalum with o-hydroxyhydroquinonephthalein in cationic surfactant micellar media

Summary The alternative and simultaneous spectrophotometric determination of niobium and tantalum was examined by using the colour development between o-hydroxyhydroquinonephthalein (Qnph) and niobium or tantalum in the presence of hexadecyltrimethylammonium chloride (HTAC) in strong acidic media. Beer's law was obeyed up to 10.0 g of niobium and up to 18.0 g of tantalum in a final volume of 10.0 ml. The apparent molar absorption coefficients for niobium and tantalum were 2.18×10⁵ and 2.09×10⁵ l mol^–1 cm^–1 with Sandell's sensitivities of 0.00042 g/cm² niobium at 520 nm and 0.00085 g/cm² tantalum at 510 nm, respectively. The alternative assay of niobium and tantalum was possible by using two methods: Method A — masking method with oxalic acid, Method B — acid adjusting-method using 50% sulfuric acid. These methods were 2–6-times more sensitive than other methods.Application of xanthene derivatives in analytical chemistry. Part XC. Part LXXXIX see ref [1]     

Decrease of HF Concentration in Process Solutions before Extractive Separation of Tantalum(V) from Niobium(V)

To improve separation of tantalum(V) from niobium(V) in their extraction from fluoride solutions, different ways for decreasing the fluoride ion concentration in the aqueous phase were tested. The efficiency of decomposition of rare-metal concentrate in continuous countercurrent process with several equilibrium decomposition stages was studied.     

Separation of niobium and tantalum through solvent extraction and reversed phase extraction chromatography using Aliquat 336 as an anion exchanger

Niobium and tantalum which have close chemical similarities have been separated through two different methods, viz. solvent extraction and reversed phase extraction chromatography (RPEC) in tracer scale using Aliquat 336 as a liquid anion exchanger. Quantitative extraction of tantalum in the organic phase from 0.05M HF solution by 5·10^–4M Aliquat 336 solution was achieved leaving niobium in the aqueous phase. In RPEC, hydrophobized kieselguhr impregnated with Aliquat 336 was used as the stationary phase in the column from which niobium was first eluted with 0.1M HF and then tantalum with 10M HNO₃ solution. The purity of the separated isotopes in both the procedures were verified by means of gamma-ray spectrometry.     

Extraction of Tantalum(V) Impurities from Niobium(V) Fluoride Solutions with Octanol

Fine purification of niobium(V) to remove tantalum(V) by extraction was studied at various compositions of solutions and ratios of phase volumes. Washing of tantalum(V) and niobium(V) extracts with aqueous solutions of their fluorides was considered.     

Eu(III) extraction by bis(2-ethylhexyl)phosphoric acid and 8-hydroxyquinoline in dodecane from perchlorate medium

Europium(III) was extracted by bis(2-ethylhexyl)phosphoric acid (HDEHP) and 8-hydroxyquinoline (HQ) in dodecane from aqueous perchlorate media of constant ionic strength (0.1M; H⁺, NaClO₄). Slope analysis of the data indicate that three molecules of HDEHP or HQ are attached to Eu³⁺. Extraction constants were obtained at different temperatures. The data were used to calculate the thermodynamic parameters (G, H and S) for the extraction process in the two systems. When using mixtures of crown ethers with HDEHP no synergism was observed.     

Gel formation in extraction of terbium by bis(2-ethylhexyl) hydrogen phosphate

Gel formation has been studied in the bulk of the organic phase and in the interphase of the Tb(OH)₃ (Tb(NO₃)₃)-bis(2-ethylhexyl) hydrogen phosphate-decane-water systems. In the Tb(OH)₃-HDEHP-decane-water system, gel formation is observed over the bulk of the organic phase when $c_{HDEHP} /c_{Tb(OH)_3 } $ ≤ 1.8. A structured layer several tens of micrometers thick is formed when an aqueous Tb(NO₃)₃ solution is in contact with an HDEHP solution in decane. The share of the structured layer in the interphase increases from 0 to about 90% as the terbium concentration increases. The structured layer that appears during the extraction of terbium by HDEHP in decane consists of both amorphous portions and portions dominated by acicular crystals.     

Reversed phase chromatographic separation of zirconium,niobium and hafnium tracers with HDEHP

Effective separation of the congeneric pair of elements, zirconium and hafnium and also niobium which was in admixtures with zirconium as daughter in its isotopic form were achieved through reversed phase column and paper extraction chromatographic procedures using di-(2-ethylhexyl)phosphoric acid (HDEHP) as the liquid exchanger. In reversed phase column chromatographic separation, the tracers,⁹⁵Zr,⁹⁵Nb and^175,181Hf, were extracted by HDEHP impregnated on kieselguhr and were sequentially eluted with 6N H₂SO₄+xN oxalic acid+H₂O₂(where x=0.1, 0.5 and 2). Similarly, in reversed phase paper chromatographic study in which a coating of HDEHP on Whatman No. 1 chromatographic paper was used as stationary phase, the mobile phase, 18N H₂SO₄+0.1N oxalic acid + H₂O₂, helped in separating the elements with favorable separation factors. Under the optimal conditions, the separation and decontamination of the elements in both methods were found to be quantitative, as verified by -spectrometric studies.     

Isolation of niobium,tantalum, and titanium complex fluoride salts with alkali metal cations

Fluoride and oxofluoride salts of niobium, tantalum, and titanium were isolated. They precipitated from aqueous solutions and upon washing of organic extracts with aqueous solutions of ammonium, potassium, and sodium salts. The compositions of the isolated compounds were studied. Different compositions were established for the niobium salts that precipitated upon the dissolution of unwashed niobium hydroxide in hydrofluoric acid under the atmospheric pressure, in an autoclave, and upon addition of sodium, potassium, and ammonium salts to purely fluoride solutions of niobium, as well as for the tantalum ammonium and sodium salts isolated from aqueous and organic solutions. The data obtained can be used for the synthesis of niobium, tantalum, and titanium complex fluoride salts with various compositions.     

Extractive Recovery of Tantalum(V) and Niobium(V) with Octanol from Hydrofluoric Acid Solutions Containing Large Amounts of Titanium(IV)

Extractive recovery with n-octanol of tantalum(V) and niobium(V) from hydrofluoric acid solutions containing large amounts of titanium (up to 2-3 M) was studied. The conditions were found for separation of tantalum(V) and niobium(V) from titanium(IV), allowing recovery of 95.7 and 84.1% of tantalum and niobium fluoride complexes, respectively, in one extraction cycle, with 2.6% recovery of titanium.     

Separation of rhodium from ruthenium and iridium by fast solvent extraction with HDEHP

Solvent extraction of rhodium, ruthenium and iridium with di(2-ethylhexyl)phosphoric acid (HDEHP) has been investigated. Under the conditions [Cl^–1]=0.20M, [(HDEHP)₂]=0.30M, pH 4.05, phase contact time 1 minutes, Rh(III) is extracted 90.7%, Ru(III) and Ir(III) 20.0% and 11.5%, respectively, at phase ratio 11. The distribution ratio of rhodium is proportional to [(HDEHP)₂]³ for a freshly prepared aqueous phase with low chloride concentration but might drop to [(HDEHP)₂]^1to2 for an aqueous phase high in chloride concentration and after standing. The spectroscopic studies indicate that the extracted compound of rhodium is Rh(H₂O)_6–x Cl _x [H(DEHP)₂]_3–x (x=0, 1, 2).     

Selective liquid scintillation method of uranium α-spectrometry

A selective liquid scintillation method is proposed for the determination of uranium in geological samples by -counting. This method permits the determination of uranium in presence of other radionuclides. The extraction of uranium with HDEHP into the scintillator is conducted in the presence of DTPA in the aqueous phase. The optimum conditions provide quantitative extraction of uranium while masking the other -emitters.     

Europium isotope separation in the HCl/HDEHP extraction system

The^153/151Eu isotope separation factor (q) for the Eu(II)/Eu(III) chemical exchange in the liquid-liquid extraction system, containing Eu (III) in di (2-ethylhexyl) phosphoric acid (HDEHP) and Eu(II) in water acidified with hydrochloric acid, was found to be 0.9993±0.0002 (2) for the single stage. Some theoretical aspects of separation of the Eu isotopes are discussed. The decisive role of the electron exchange reaction and complexation by the counter-ion in the aqueous phase is emphasized.     

Extraction of Am(III) from different acid media by di-2-ethyl hexyl phosphoric acid containing phosphorous pentoxide

The extraction of Am(III) from nitric, hydrochloric, oxalic, phosphoric and hydrofluoric acids was studied using 0.4F di-2-ethyl hexyl phosphoric acid (HDEHP) containing 0.1M phosphorous pentoxide (P₂O₅) in dodecane/xylene. The extraction with pure 0.4F HDEHP was found to be negligible from all the media studied. However, the presence of a small amount of P₂O₅ in it increased the extraction substantially. The distribution ratios of Am(III) obtained for HDEHP - P₂O₅ mixture 3M nitric acid containing different concentrations of oxalic acid/phosphoric acid/hydrofluoric acid are in the order of 200-250. The same for 3M hydrochloric acid is very high (800). These distribution ratios are sufficiently high for the quantitative extraction of Am(III) from all the acid media studied. Different reagents such as ammonium oxalate, sodium oxalate, oxalic acid, hydrofluoric acid, sodium carbonate and potassium sulphate were explored for the back extraction of Am(III) from 0.4F HDEHP + 0.1M P₂O₅ in dodecane/xylene. Of these, 0.35M ammonium oxalate and 1M sodium carbonate were found to be most suitable. The back extraction of Am(III) was also attempted with water and 1M H₂SO₄, HNO₃, HClO₄ and HCl solutions after allowing the extracted organics to degrade on its own. It was found that more than 90% of Am could be back extracted with these acids. Using this method more than 90% of Am(III) was recovered from nitric acid solutions containing calcium and fluoride ions.     

Cerium isotope partition in HNO3/TBP or HDEHP extraction systems

The^142/140Ce unit separation factors (q) for cerium(III)-cerium(IV) exchange reaction in an extraction system containing Ce(IV) in tri-n-butyl phosphate (TBP) or di(2-ethylhexyl) phosphoric acid (HDEHP) and Ce(III) in nitric acid were determined. The value of q was found to be 1.00054±0.00012 (2) in 6M HNO₃/TBP and 1.00078±0.00028 in 6M HNO₃/HDEHP extraction systems. The dehydration and complex formation processes and their contribution to reduced partition function ratios (RPFR's) are discussed.     

Solvent extraction of rhodium,ruthenium, and iridium with HDEHP

Solvent extraction of rhodium, ruthenium, and iridium with HDEHP from thioureachloride media was investigated. Under the conditions ([Cl^–]=0.50 M, [HDEHP]=1.0M, [SC(NH₂)₂]=0.50M, pH=4.50, phase contact time 1 min), Rh(III) is extracted 88.3%, Ru(III) and Ir(III) 40.8% and 28.5% respectively at phase ratio 11. The formation of rhodium-thiourea complexes in aqueous solutions, even at 5M chloride concentration, with the possible composition Rh[SC (NH₂)₂]₆ ³⁺ is confirmed by the observed molar ratio of thiourea to rhodium and UV-spectra.     

Substoichiometric extraction of tantalum with diantipyrylmethane

Diantipyrylmethane is used for substoichiometric extraction of tantalum from 1—4M hydrofluoric acid into 1,2-dichlorethane. The selectivity of the method is good, niobium and antimony(V) being the main inteferences. The stoichiometric composition of the tantalum/diantipyrylmethane complex is 1:1. The method was usef for the determination of trace amounts of tantalum (0.52 ± 0.05 μ g^?1) in a lake sediment (Bodensee/Lake Constance) by neutron activation/μ-spectrometry. Tantalum was determined in niobium samples by an isotope dilution procedure after separation of the matrix on a polyurethane foam column loaded with diantipyrylmethane.