Gravimetric separation of titanium and zirconium from Niobium with Phenylacetylhydroxamic acid

Phenylacetylhydroxamic acid is used to separate titanium and zirconium from niobium in an oxalate medium at pH 6.5–7.5 in presence of ammonium chloride at room temperature. The method is accurate when the ratio of (TiO₂ + ZrO₂) : Nb₂O₅ is 10 : 1 to 1 : 1 ; when the niobium concentration is higher, reprecipitation is necessary. Tantalum, citrate, tartrate, lactic acid, EDTA, and a large excess of oxalate interfere.     

1-(o-Carboxyphenyl)-3-hydroxy-3-phenyltriazene,a new reagent for the direct gravimetric determination of titanium(IV)

A direct gravimetric method for the determination of titanium with a new reagent, 1-(o-carboxyphenyl)-3-hydroxy-3-phenyltriazene, is proposed. The titanium is precipitated at the pH range 2.0–5.0 and weighed as TiO(C₁₃H₁₀N₃O₃)₂ after drying at 115–120°. In the presence of EDTA, only niobium and tantalum interfere.     

Separation of niobium and tantalum with n-benzoyl-n-phenylhydroxylamine

The use of N-benzoyl-N-phenylhydroxylamine for the separation of niobium and tantalum, allows a satisfactory estimation of niobium from a tartrate solution at an acidity of 2.0N. The pH range for complete precipitation can be extended to 6.5. For tantalum precipitation, the pH of the solution should be below 1.5 and the acidity may even be above 2.0N. At pH 3.5–6.5, niobium is completely precipitated and tantalum remains in solution; the latter is precipitated by lowering the pH. Niobium and tantalum in ratios of 1:16 to 100:1 can be separated by a single precipitation, in the case of a ratio of 1:100 precipitation must be carried out twice. Titanium, zirconium, vanadate and molybdate interfere with the determination of niobium though other ions have no effect in the presence of complexone III and tartaric acid. The precipitates are granular and easy to filter and wash. The time taken for a complete analysis is much less than that of other methods     

The extraction of niobium (V) and Tantalum (V) by Octylarsinic acid in chloroform

Dioctylarsinic acid (HDOAA) in chloroform solution extracts Nb(V) and Ta(V) efficiently from solutions containing oxalate and oxalic acid at hydrochloric acid concentrations greater than 1M.The extraction coefficients are 92.5 at 7M hydrochloric acid and 251 at 6M hydrochloric acid for niobium and tantalum, respectively. These metals can be extracted even more efficiently from sulfuric acid solutions. The results of the reagent- and pH-dependence studies suggested that a trimeric, monobasic oxoacid of niobium, associated with ten HDOAA molecules, is extracted. Tantalum appears to be present in the organic phase as (H₂DOAA)⁺ [Ta(C₂O₄)₃ (HDOAA_n] (n=l or 2).     

Separation and determination of tantalum and niobium by precipitation from homogeneous solution

An attempt to separate niobium and tantalum by precipitation from homogeneous solution by thermal decomposition of their peroxy complexes, in the presence of tannin and oxalate, has been only moderately successful. A more satisfactory separation of tantalum and niobium for ratios from 50:1 to 1:30 is obtained by extracting the bisulphate melt with ammonium oxalate before adding hydrogen peroxide, hydrochloric acid and tannin. For a tantalum/niobium ratio of 1:1 the niobium coprecipitation is reduced to 5 %. Furthermore, two alternative possibilities are presented: (1) a quantitative recovery of a tantalum precipitate at small oxalate and high tannin concentration, leaving 90% of the tantalum-free niobium in solution; (2) an 85 % recovery of niobium-free tantalum at high oxalate and small tannin concentration. A study of the coprecipitation process of niobium shows that the distribution coefficients follow a logarithmic pattern, true homogeneous mixed crystals being formed.     

Niobium,tantalum, and titanium fluoride solutions

Parameters for the preparation of concentrated tantalum, niobium, and titanium fluoride solutions by dissolution of their oxides or hydroxides in hydrofluoric acid were studied. Anatase titania, niobium oxide, and tantalum oxide calcined to 900°C were found to have high dissolution rates. Solid phases separated upon the dissolution of niobium, tantalum, and titanium oxides in hydrofluoric acid were identified as NbO₂F, TaO₂F, Ta₃O₇F, and TiOF₂. Niobium hydroxide dissolution in an autoclave at the atmospheric pressure gave various complex salts: NH₄NbOF₄ and (NH₄)₃Nb₂OF₁₁.     

N-acetylsalicyloyl-N-phenylhydroxylamine as an analytical reagent Determination of niobium and tantalum in the presence of each other

N-Acetylsalicyloyl-N-phenylhydroxylamme is proposed for the separation of niobium(V) and tantalum(V) and their gravimetric determination. Niobium is precipitated at pH 5.5-6.5 by the reagent and the complex is weighed directly. Tantalum is precipitated from 1-2M hydrochloric acid solutions and the complex is ignited to tantalum pentoxide. The method is fairly selective. In the presence of thiocyanate the reagent forms an extractable complex with niobium. The reaction forms the basis of a selective and sensitive spectrophotometric determination of niobium.     

Identification of phosphate anions in niobium and tantalum phosphates by means of infra-red spectra

Some niobium and tantalum phosphates have been prepared and their infra-red spectra have been recorded and compared with those of reference substances. It has been possible to identify P0₄^-3, P₂O₇^-4 and possibly P₃O10^-5 groups in different samples of niobium and tantalum phosphates.     

Separation of niobium and tantalum with benzo- and phenylacetylhydroxamic acids

Benzohydroxamic acid (I) or phenylacetylhydroxamic acid (II) is suggested for the quantitative separation of tantalum from niobium in an oxalate solution. The tantalum precipitate must be ignited for weighing; niobium is determined in the filtrate with another reagent. The pH range for complete separation is 4.0–6.4 for I and 4.5–6.2 for II. Single precipitation is satistactory for Nb: Ta ratios of 18 : 1 to 1 : 20 for I, and 8 : 1 to 1 : 23 for II. Titanium, zirconium, tartrate, citrate and a large excess of oxalate interfere.     

Fabrication and characterization of three-dimensionally ordered macroporous niobium oxide

Three-dimensionally ordered macroporous (3-DOM) niobium oxide was fabricated by aqueous organic gel method through the interstitial spaces between polystyrene spheres assembled on glass substrates. Freshly precipitated hydrous niobium oxide (Nb₂O₅·nH₂O), which was prepared starting from Nb₂O₅, was used in combination with citric acid in an aqueous solution and then was transferred as a niobium source to synthesize 3-DOM Nb₂O₅. The morphologies of porous Nb₂O₅ were characterized by scanning electron microscope (SEM). The thermal decomposition and phase composition of 3-DOM Nb₂O₅ were investigated by Fourier transform infrared spectroscopy (FT-IR), Thermogravimetric–differential thermal analysis (TG–DTA), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS).     

Separation and gravimetric determination of niobium,tantalum and titanium by precipitation with n-benzoyl-n-phenylhydroxylamine

A method is described for the separation and gravimetric determination of niobium, tantalum and titanium by precipitation with N-benzoyl-N-phenylhydroxylamine. Titanium is kept in solution with EDTA and hydrogen peroxide, and the earth acids are precipitated in 1N sulphuric acid Niobium and tantalum are separated and determined by a modification of the method of MAJUMDAR AND MUKHERJEE. All three metals are finally precipitated with N-benzoyl-N-phenyl-hydroxylamine. In the analysis of complex materials niobium, tantalum and titanium are separated from other constituents by a double precipitation with N-benzoyl-N-phenylhydroxylamine in the presence of EDTA and tartaric acid     

Solvent extraction and separation of zirconium,niobium and tantalum by 2-carbethoxy-5-hydroxy-1-(4-tolyl)-4-pyridone

Summary Extraction of zirconium, niobium and tantalum from oxalic and hydrofluoric acid solutions, by 2-carbethoxy-5-hydroxy-1-(4-tolyl)-4-pyridone (HA) dissolved in chloroform was studied. Extraction mechanism for the extraction of zirconium from oxalate solutions and of niobium from fluoride solutions is proposed. Separation of zirconium and niobium from oxalate solution as well as from fluoride solution and tantalum and niobium from fluoride solution is described. Back-extraction of these metals is possible by hydrofluoric and oxalic acid. Results obtained show that the efficiency of extraction by HA decreases in the sequence tantalum > niobium > zirconium.

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Zusammenfassung Die Extraktion von Zirkonium, Niob und Tantal aus oxalsauren und fluorwasserstoffsauren Lösungen mit Hilfe einer chloroformischen Lösung von 2-Carbäthoxy-5-hydroxy-(4-tolyl)-4-pyridon wurde untersucht. Ein Extraktionsmechanismus für Zirkonium aus Oxalatlösungen und für Niob aus Fluoridlösungen wurde vorgeschlagen. Die Trennung von Zirkonium und Niob aus einer Oxalatlösung oder aus einer Fluoridlösung sowie von Tantal und Niob aus einer Fluoridlösung wurde beschrieben. Die Rückextraktion dieser Metalle mit Flußsäure und Oxalsäure ist möglich. Die Ergebnisse zeigen, daß die Effizienz der Extraktion in der Reihenfolge Tantal > Niob > Zirkonium abfällt.

     

Oxidchloride, -bromide und -iodide des Niobs und Tantals

Oxidechlorides, -bromides, and -iodides of Niobium and Tantalum We report on oxidehalides of the 5- and 4-valent niobium and tantalum, the most of which are chemically transportable. A new class of compounds (mNb₂O₅ + NbOCl₃) is indicated.     

The determination of zirconium in its binary alloys with niobium and tantalum

A procedure is presented for the determination of zirconium in the presence of niobium or tantalum. The bulk of the niobium or tantalum is first removed by extracting with hexone from a 10M hyclrofluoric acid, 6M sulphuric acid solution of the sample. The zirconium is then. separated from any unextractcd earth, acid element by precipitation with ammonium hydroxide followed by the addition of hydrogen peroxide. Under these conditions, both the niobium and tantalum form soluble peroxy complexes whereas the zirconium is completely precipitated from solution. After the separation of the precipitate by filtration, it is re-dissolved in hydrochloric acid and the zirconium concentration is finally determined by titration with ethylenediaminetetraacetic acid.     

On the separation of cesium and strontium from oxalate filtrate by neutralization

At the treatment of HLLW (high-level liquid radioactive waste) by oxalate precipitation, the filtrate is occured as a waste. But various elements including Cs and Sr are contained in the oxalate filtrate. It is very important, therefore, to separate from each other in a viewpoint of ultimate isolation of heat generating nuclides such as Cs and Sr from HLLW. In this study, the simulated oxalate filtrate, consisted of five elements (Cs, Sr, Ru, Fe and Mo) and organics (oxalic acid and ascorbic acid), was prepared, from which the separation of Cs and Sr was carried out by neutralization with NaOH. As a result, the simulated solution could be divided into Cs, Sr and Ru containing groups with pH. Sr was readily precipitated as forms of Sr(C₂O₄)·nH₂O at pH 3. Iron and ruthenium were also co-precipitated around pH 8, and Cs and Mo remained in the resulting solution.     

Comparative study of bimetal alkoxo complexes of rhenium,niobium, and tantalum by single-crystal x-ray diffraction and IR spectroscopy

Bimetal alkoxo complexes of rhenium, niobium, and tantalum with the general formula M₄O₂(OR)₁₄(ReO₄)₂, where M = Nb or Ta and R = Me or Et, were prepared in ～80% yield by reacting niobium or tantalum alkoxide M(OR)₅ (R = Me or Et) with rhenium heptoxide Re₂O₇ in toluene. Comparative analysis of the molecular structures of the complexes was carried out by means of single-crystal X-ray diffraction and IR spectroscopy. The effect of the organic ligand and crystallization temperature on the geometry of the perrhenate group was studied. The solubility of the aforementioned alkoxo complexes in organic solvents increases with increasing hydrocarbon chain length of the ligand.     

Spektrochemische Analyse der Mischpentoxide Nb2O5 + Ta2O5

Zusammenfassung Zur spektrochemischen Analyse der Mischpentoxide von Niob und Tantal wurde ein Verfahren ausgearbeitet, das die Anregung im Gleichstrom-Kohlebogen nach Addink u. Mitarb. benutzt. Für die Niobbestimmung werden die bekannten K-Werte verwendet, während die K-Werte für Ta 2681,87, Ta 2684,28 sowie einige schwächere Nb- und Ta-Linien erst gefunden werden mußten. Die Reproduzierbarkeit des Verfahrens beträgt 10–11%; es erlaubt eine bequeme und rasche Analyse, besonders in Verbindung mit einer chemischen Isolierung von (Nb, Ta)₂O₅.

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Summary A spectrochemical method utilizing the Addink's Constant Temperature D.C. Arc Method has been worked out for the determination of Nb₂O₅ and Ta₂O₅ in combined pentoxides. For the determination of niobium the known K-values are employed, while the K-values for Ta 2681.87, Ta 2684.28 and for some weaker niobium and tantalum lines had to be found. The reproducibility being 10–11%, the method has proved to be convenient for a rapid and simple niobium and tantalum analysis, especially in combination with a chemical isolation of (Nb,Ta)₂O₅.

     

Thermodynamic modeling of magnesiothermic reduction of niobium and tantalum from pentoxides

Results obtained in thermodynamic modeling of the magnesiothermic reduction of niobium and tantalum from pentoxides under adiabatic conditions are given. The dependences of equilibrium temperature of the reactions on the composition and initial temperature of the raw material, along with the equilibrium composition, were determined in the systems Nb₂O₅-Mg-NaCl and Ta₂O₅-Mg-NaCl in the temperature range 1200–3000 K.     

Formation of PPy/Ta2O5/Ta structure by electropolymerization

Electropolymerization of pyrrole on tantalum (Ta) electrodes was carried out in buffer solutions (0.04 M phosphoric acid, 0.04 M acetic acid, 0.04 M boric acid and 0.2 M sodium hydroxide) containing 0.1 M sodium ptoluenesulfonate (TsONa) under galvanostatic conditions and it was found that a polypyrrole (PPy) and a tantalum oxide (Ta₂O₅) layer are formed on a Ta electrode by an electrochemical oxidation process. The conditions of this simultaneous formation were studied in respect to current density (i_d), pyrrole concentration ([Py]), pH and the amount of electricity. Under certain conditions ([Py] = 0.25 M, pH = 1.8, i_d = 10–20 mA cm^?2, the amount of electricity = 1 C), 6–8 μm thick PPy films were efficiently formed on homogeneous 30–50 nm thick Ta₂O₅ layers. The PPy film showed a high electrical conductivity (110 s cm^?1), adhered well and covered the Ta₂O₅ layer. The resulting PPy/Ta₂O₅/Ta system is therefore proved to have excellent properties as a capacitor.     

Determination of niobium and tantalum in some ores and special alloys by inductively coupled plasma atomic emission spectrometry

A fast analytical method for the determination of niobium and tantalum in ores and special alloys by inductively coupled plasma atomic emission spectrometry has been developed. Optimum conditions for the determination of both metals in the plasma were worked out and possible interferences were studied before attempting the determination in the real samples. Ores are dissolved in a mixture of HCl, HF and H₃PO₄ acids while for the special alloy a HCl+H₂O₂ mixture is used. The resulting solutions are diluted to the mark with tartaric acid before their final direct nebulization into the plasma. Other elements present did not interfere in the determination of Nb or Ta at concentration levels similar to those found in the analyzed samples. The results obtained determining niobium and tantalum in pyrochlore and special alloys by the proposed procedure are in good agreement with the certified values.