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.     

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.     

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.     

Tantalum(V) or niobium(V) catalyzed oxidation of sulfides with 30% hydrogen peroxide

Tantalum(V) and niobium(V) are effective catalysts for the oxidation of sulfides with 30% hydrogen peroxide. The reaction of sulfides with 30% hydrogen peroxide catalyzed by tantalum(V) chloride or niobium(V) chloride in acetonitrile, i-propanol or t-butanol selectively provided the corresponding sulfoxides in high yields. The corresponding sulfones are efficiently obtained from the reaction of sulfides with 30% hydrogen peroxide in methanol catalyzed by tantalum(V) or niobium(V).     

Conversion of Tantalum(V), Niobium(V), and Titanuim(IV) Sulfates and Chlorides to Their Fluorides

A process was developed for converting tantalum(V), niobium(V), and titanium(IV) sulfate and chloride to their fluorides in order to improve separation of these elements.     

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.     

Processing of Precipitates of Hydrated Tantalum(V), Niobium(V), and Titanium(IV) Oxides in Loparite Technology

Conditions were studied for the dissolution in HF of hydrated tantalum(V), niobium(V), and titanium(IV) oxides, which are formed by acid decomposition of loparite, and also for the selective extraction of Ta(V) with octanol from the resulting fluotitanic solutions.     

Deprotection of dithioacetals with 30% hydrogen peroxide catalyzed by tantalum(V) chloride–sodium iodide or niobium(V) chloride–sodium iodide

The reaction of dithioacetals with 30% hydrogen peroxide in the presence of catalytic amounts of tantalum(V) and iodide ion effectively produced carbonyl compounds in high yields. Dithioacetals also can be deprotected using the niobium(V) catalyzed oxidation of iodide ion by hydrogen peroxide under mild conditions.     

Liquid-liquid extraction of niobium(V) in the presence of other metals with high molecular mass amines and ascorbic acid

A novel method is proposed for the solvent extraction of niobium(V). A 0.1M solution of Aliquat 336S in xylene quantitatively extracts microgram quantities of niobium(V) from 0.01M ascorbic acid at pH 3.5-6.5. Niobium from the organic phase is stripped with 0.5M nitric acid and determined spectrophotometrically in the aqueous phase as its complex with TAR. The method permits separation of niobium not only from tantalum(V) but also from vanadium(IV), titanium(IV), zirconium(IV), thorium(IV), chromium(III), molybdenum(VI), uranium(VI), iron(III), etc. Niobium from stainless steel was determined with a precision of 0.42%.     

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).     

Adsorption behavior of Zr, Hf, Nb, Ta and Pa on macroporous anion exchanger in NH4SCN/HClO4 and NH4SCN/HF media

The possible use of thiocyanate and ammonium thiocyanate-hydrofluoric acid mixtures for quantitative anion exchange separation of zirconium from hafnium and niobium from tantalum and protactinium has been investigated. Distribution coefficients of zirconium(IV), hafnium(IV), niobium(V), tantalum(V) and protactinium(V) on macroporous BIO-RAD AGMP1 resin over a wide range of SCN and SCN/HF concentrations have been determined. The simultaneous presence of these two complexing agents causes a strong decrease of the adsorption phenomena.     

Determination of V(V), Nb(V), and Ta(V) with 2-(2-Thiazolylazo)-5-diethylaminophenol by Reversed-Phase High Performance Liquid Chromatography

The simultaneous determination of vanadium, niobium, and tantalum by reversed-phase high performance liquid chromatography (HPLC) with 2-(2-thiazolylazo)-5-diethylaminophenol (TADAP) as the precolumn chelating reagent has been established. Optimum conditions for the separation, such as the methanol content, the addition of tartaric acid, pH, and the concentration of acetate buffer, were investigated. The metal chelates were eluted in 8 min with a mobile phase of methanol–water (55/45, v/v) containing tartaric acid (0.1%, m/v) and acetate buffer (pH 3.5, 10 mmol/liter) on an ODS column at 568 nm. The detection limits (signal-to-noise RATIO = 3) for V(V), Nb(V), and Ta(V) were 0.16, 0.32, and 1.77 ng/ml, respectively. The proposed method was applied to the analyses of a reference of mineral and synthetic samples. The result was in accord with the certified value, and the recoveries were 98.9–101.8%.     

Composés d'addition des halogénures de niobium(V) et de tantale(V). V. Stabilité relative des composés des chlorures avec quelques oxydes et sulfures organiques

The adducts of niobium(V) and tantalum(V) chlorides with some aliphatic and cyclic oxides and sulfides, studied by NMR. spectroscopy in CHCl₃, are found to have 1:1 stoechiometry, at room temperature and lower. In the thioxane complex TaCl₅ · C₄H₈OS two species are present with the ligand coordinated by the sulfur atom or by the oxygen atom, respectively, in a proportion which has been determined. The thioxane adduct of niobium(V) chloride, however, is preferentially coordinated by the sulfur atom. There is also evidence for the species 2MCl₅ · C₄H₈OS. The relative basicity of each donor atom in dioxane, thioxane and dithiane is calculated and discussed. In contrast to the nitrile adducts, whose stability was found earlier to be controlled by inductive factors, the steric factors are more important for the ether and sulfide adducts: MCl₅ · Me₂X is more stable than the corresponding MCl₅ · Et₂X (M = Nb, Ta; X = O, S). Both niobium(V) and tantalum(V) chlorides have a soft behaviour, but NbCl₅ is a weaker Lewis acid than TaCl₅ and shows also a softer behaviour.     

Extraction of molybdenum(VI) from fluoride niobium-tantalum solutions with a high content of titanium(IV)

Distribution of molybdenum(VI) (0.05 M) upon extraction with tributyl phosphate from fl uoride solutions with a content of titanium(IV), niobium(V), and tantalum(V) of up to 3.0, 0.7, and 0.7 M, respectively, was studied.     

Adducts of niobium(V) and tantalum(V) halides. XIV. Structure and relative stability of the adducts with some phosphoryl compounds

The adducts of niobium(V) and tantalum(V) halides with some phosphoryl compounds have been studied in chloroform solution by ¹H- and ¹⁹F-FT-NMR. spectroscopy. These octahedral adducts of general formula MX₅ · L (M = Nb, Ta; X = F, Cl, Br; L = phosphoryl ligand) are monomeric and neutral. Their relative stability constants have been determined at ?60°. The stabilities are controlled by electronic effects of substituents on the phosphoryl group.     

Spectrophotometric Determination of Simultaneously Present Niobium and Tantalum

The formation of niobium(V) and tantalum(V) complexes of 2,3,4-trioxyphenylazo-5-sulfonaphthalene in the presence of cetyltrimethylammonium bromide was studied by spectrophotometry. The effect of surfactants on the chemical and analytical properties of niobium(V) and tantalum(V) complexes of this reagent was studied. Procedures were developed for the spectrophotometric determination of niobium and tantalum present simultaneously as mixed-ligand complexes. The procedures were tested on model solutions.     

Composés d'addition des halogénures de niobium (V) et de tantale(V): III. Détermination de constantes de stabilité par résonance magnétique nucléaire

In view of a systematic study of the Lewis acidity of niobium (V) and tantalum (V) halides, NMR. methods for the determination of stability constants are discussed. In the case of rapid exchange chemical shifts are used to determine the relative amounts of adduct(s) and free base(s) in equilibrium. In the case of slow exchange the relative concentrations of the species are given by the peak areas.     

Preparation of alkaline solutions of niobium(V)

Alkaline niobium(V) solutions containing up to 190 g l⁻¹ of niobium oxide were prepared by sintering niobium(V) oxide with potassium carbonate and following leaching of the sinters with water.     

Mass spectral studies of some complexes of niobium(V) and tantalum(V) with chloro,alkoxy, acetylacetonato or salicylaldehydato ligands

Mass spectra of complex compounds of niobium (V) and tantalum (V) of the type MCl₂(OR)₂L have been measured, where M = Nb and Ta; HL = 2,4-pentanedione, R = CH₃, C₂H₅ and HL = Salicyladehyde, R = CH₃. The fragmentation upon electron-impact depends on the nature of the ligands and to a minor extent on the central metal atom. A fragmentation scheme has been constructed on the basis of measurements of metastable transitions and accurate masses of important fragment ions. Rearrangement reactions involving hydrogen migration among ligands have been observed.     

Fast simultaneous determination of niobium and tantalum by Kalman Filter analysis with flow injection chemiluminescence method.

A fast and highly efficient Kalman Filter analysis-flow injection chemiluminescence (FI-CL) method was developed to simultaneously determine trace amounts of niobium and tantalum in geological samples. The method, without the boring process of separation and dear instruments, is suitable for field scene analysis. The mixed chemiluminescence kinetic curve was analyzed by a Kalman Filter (KF) in this method to realize the simultaneous determination of niobium and tantalum. Possible interference elements in the determination were investigated. Under the selected conditions, the detection limits (3sigma, n = 11) of niobium(V) and tantalum(V) were 2.1 x 10(-3) microg g(-1) and 4.0 x 10(-3) microg g(-1), respectively, and the relative standard deviations were 4.9% and 3.3% (n = 9). The method was applied to the determination of niobium and tantalum in geological samples with satisfactory results.