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.     

Redox Behavior of Neptunium(V) in Tributyl Phosphate and <Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>-Dihexyl Octanamide Extractants Dissolved in <Emphasis Type="Italic">n</Emphasis>-Dodecane

Spectrophotometric investigations have been carried out on the disproportionation of Np(V) to form Np(IV) and Np(VI) in 1.1 mol⋅L⁻¹ solutions of tributyl phosphate (TBP) and in N,N-dihexyl octanamide (DHOA) in n-dodecane medium. The Np(V) was found to coordinate with Np(IV) in 1.1 mol⋅L⁻¹ TBP solution in n-dodecane to form a mixed valence “cation–cation” complex by bonding through an axial oxo group on Np(V). By contrast, this interaction was less prominent in the case of 1.1 mol⋅L⁻¹ DHOA solutions. The effect of 1-octanol, added as phase modifier, on the disproportionation behavior of Np(V) was also investigated. An attempt was made to calculate the disproportionation/reduction rate constants for Np(V) under the conditions of these studies. Absorbance measurements on the Np stripped from organic phases revealed the occurrence of Np(V) in the aqueous phase.     

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).     

Interaction of tantalum fluoride with organic solvents

A systematic study on the extraction of tantalum fluoride from various acidic solutions and mixed media has been given using HDEHP, TBP and LA-2 as solvents. The results obtained for these three solvents clarify the ionic behaviour of tantalum. The separation of tantalum from other elements is discussed.     

The solvent extraction of trace antimony(V)

An investigation of the extraction of trace amounts of antimony(V) from aqueous hydrochloric acid solutions into various others and chloroform has been carried out. Before extractions were made, mutual solubility studies of the two-phased systems were conducted. Then extraction experiments were performed using original aqueous acid concentrations from 0 to 12N and non-aqueous phases of ethyl ether, isopropye ether, isoamyl ether, n-hexyl ether, and chloroform. Dielectric constant determinations were made in the equilibrated non-aqueous phases, and spectrophotormetric and salting-out studies were carried out on the ethyl ether system. It was found that the isopropyl ether system presents the most advantageous conditions for the extraction of trace antimony(V)     

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.     

Comparative studies on radiolytic degradation of deuterium labeled and unlabeled tributyl phosphates

Deuterium labeled tributyl phosphates were synthesized and their solutions in n-dodecane have been investigated for γ-radiolytic degradation up to an absorbed dose of 2,000 kGy from a ⁶⁰Co source. The performance was compared with undeuterated TBP. Radiolysis extent and pattern of formation of major degradation products, viz. dibutyl hydrogen phosphate and monobutyl dihydrogen phosphate were found to be very similar from deuterated or undeuterated samples. Extraction behavior for UO₂ ²⁺ and Pu(IV) was studied after the radiolysis, and the results showed similarity in extraction/stripping behavior for all labeled or unlabeled TBP samples. The isotope effect (k _H/k _D) observed is minimal in this γ-radiolytic degradation study.     

An electrochemical method for determination of the standard Gibbs energy of anion transfer between water and n-octanol

The transfer of the ions Cl⁻, Br⁻, I⁻, ClO₄⁻, SCN⁻, NO₃⁻, BF₄⁻, and (C₆H₅)₄B⁻ across the water|n-octanol (W|OC) liquid interface was studied and the standard Gibbs energies of ion transfer were determined. The ion transfer was achieved by oxidation of decamethylferrocene dissolved in a droplet of n-octanol that was attached to a graphite electrode immersed in the aqueous solutions of the respective alkali salts of the anions. The electrode reaction can be described by the equation: dmfc_(OC)+X_(W)⁻⇄dmfc⁺_(OC)+X⁻_(OC)+e⁻, where X⁻ is the transferred anion. Square-wave voltammetry at this three-phase arrangement was utilised to determine the formal potential of the decamethylferrocene/decamethylferrocenium (dmfc/dmfc⁺) couple under the condition of ion transfer across the water|n-octanol interface. For calibration the standard Gibbs energies of ion transfer have been extrapolated to octanol from the series of known data for methanol, ethanol, n-propanol, and n-butanol. All these data are consistent and the experimental dependence of the formal potentials on the standard Gibbs energies is as predicted by theory. The validity of data is further supported by calculations of Gibbs energies of ion transfer using the Born theory. Until now it was not possible to perform electrochemical measurements at the water|n-octanol interface because in the conventional four-electrode cells this interface cannot be polarised. With the new method it is now for the first time possible to determine the Gibbs energies of transfer of ions across the water|n-octanol interface. These values are of very wide use for assessing the lipophilicity of compounds in chemistry, medicine, and pharmacology.     

A novel rapid detection approach for the analysis of radionuclides in environmental samples using graphite MALDI mass spectrometry

In nuclear technology, tri-n-butyl phosphate (TBP) diluted with a hydrocarbon diluent such as n-dodecane or NPH is the most frequently used solvent in liquid–liquid extraction for fuel reprocessing. This extraction, known as the plutonium uranium refining by extraction, is still considered as the most dominant process for the extraction of uranium and plutonium from irradiated fuels. The solubility of pure TBP in water is about 0.4 g/L at 25 °C. This is enough to create trouble during evaporation of raffinate and product solutions. Solubility data for undiluted TBP and TBP (diluted in inert hydrocarbon diluent) in various concentrations of nitric acid is not adequate in the literature. The solubility data generated in the present study provide complete information on the solubility of TBP in various nitric acid concentrations (0–15.7 M) at room temperature. The effect of heavy metal ion concentration such as uranium and various fission products on the solubility of TBP in nitric acid is also presented. The results obtained from gas chromatographic technique were compared with spectrophotometric technique by converting the organic phosphate into inorganic phosphate. The generated data is of direct relevance to reprocessing applications.     

The study of radiolytic stability of 25,27-bis(2-propyloxy)calix[4]-26,28-crown-6(iPr-C[4]C-6)

The radiolytic stability of 25,27-bis(2-propyloxy)calix[4]-26,28-crown-6(iPr-C[4]C-6) was studied. The radiation source was ⁶⁰Co and its dose rate was 437?Gy/min and the total absorbed dose was from 10⁴ to 10⁶?Gy. The iPr-C[4]C-6 solid and 0.025?mol/L iPr-C[4]C-6/n-octanol which were pre-equilibrated with 0.01 and 3?mol/L nitric acid, respectively, were absorbed different dose and their extraction performance were researched. The degradation mechanism of them was investigated by mass spectrometry and infrared spectrum. The results show that radiolytic stability of the iPr-C[4]C-6 solid and 0.025?mol/L iPr-C[4]C-6/n-octanol are good when their absorbed dose was less than 10⁶?Gy. The extracting system of iPr-C[4]C-6/n-octanol is promising for separating cesium from high level liquid waste.     

Comparative studies on co-extraction of uranium(VI) and different mineral acid from aqueous feed solutions using TBP,TOPO and TOA

Equilibrium and kinetics of co-extraction of hexavalent uranium and mineral acids from aqueous solutions into a hydrocarbon phase (paraffin) using tri n-butyl phosphate (TBP), tri-n-octyl phosphine oxide (TOPO) and tri-n-octyl amine (TOA) has been studied. Relative rates of extraction of uranium(VI) and mineral acid by different complexing ligands were measured simultaneously using bulk-liquid membrane system. Acid extraction by complexing ligands was found to be significant. Wherever there was a possibility of the formation of the third phase, isodecanol was used as an organic phase modifier. Study revealed that isodecanol promotes acid extraction and substantially reduces distribution coefficient of U(VI) into the hydrocarbon phase. The rate of acid extraction by different ligand was in the order of TOPO > TOA > TBP–isodecanol > TBP, whereas the rate of extraction of uranium(VI) was in the order TOPO > TOA > TBP > TBP–isodecanol. A kinetic model was developed to predict concentration of acid and U(VI) in the feed, organic and the strip phase during extraction. The mass transfer coefficients for acid and metal were determined by fitting the model to the observed concentration–time data.     

Sodium-reduced tantalum powders produced from plumbomicrolite raw materials

Effect of various extractive systems (triisoamyl phosphate/HF+H₂SO₄, n-octanol/HF+H₂SO₄, n-octanol/HF+HNO₃) used to obtain potassium heptafluorotantalate from plumbomicrolite-based raw materials on the purity and characteristics of sodium-reduced tantalum powders was studied. Application of the extractive systems provides production of high-purity potassium heptafluorotantalate from raw materials based on products formed in processing of the plumbomicrolite concentrate.     

A cloud point extraction for spectrophotometric determination of ultra- trace antimony without chelating agent in environmental and biological samples

We report on a simple, sensitive and reliable method for the cloud point extraction of antimony (Sb) and its subsequent spectrophotometric detection. It is based on the color reaction of Sb (III) with iodide in acidic medium and subsequent micelle-mediated extraction of tetraiodoantimonate using a non-ionic surfactant in the absence of any chelating agent. The effects of reaction and extraction parameters were optimized. The calibration plot is linear in the range of 0.80–95?ng?mL^?1 of antimony in the sample solution, with a regression coefficient (r) of 0.9994 (for n?=?9). The detection limit (at SNR?=?3) is 0.23?ng?mL^?1, and the relative standard deviations at 10 and 70?ng?mL^?1 of antimony are 3.32 and 1.85?% (at n?=?8), respectively. The method compared favorably to other methods and was applied to determine antimony in seawater, anti-leishmania drug (glucantime), and human serum.

Speciation analysis of antimony in marine biota by HPLC-(UV)-HG-AFS: Extraction procedures and stability of antimony species

Speciation analysis of antimony in marine biota is not well documented, and no specific extraction procedure of antimony species from algae and mollusk samples can be found in the literature. This work presents a suitable methodology for the speciation of antimony in marine biota (algae and mollusk samples). The extraction efficiency of total antimony and the stability of Sb(III), Sb(V) and trimethylantimony(V) in different extraction media (water at 25 and 90 °C, methanol, EDTA and citric acid) were evaluated by analyzing the algae Macrosystis integrifolia (0.55 ± 0.04 μg Sb g⁻¹) and the mollusk Mytilus edulis (0.23 ± 0.01 μg Sb g⁻¹). The speciation analysis was performed by anion exchange liquid chromatography (post-column photo-oxidation) and hydride generation atomic fluorescence spectrometry as detection system (HPLC-(UV)-HG-AFS). Results demonstrated that, based on the extraction yield and the stability, EDTA proved to be the best extracting solution for the speciation analysis of antimony in these matrices. The selected procedure was applied to antimony speciation in different algae samples collected from the Chilean coast. Only the inorganic Sb(V) and Sb(III) species were detected in the extracts. In all analyzed algae the sum of total antimony extracted (determined in the extracts after digestion) and the antimony present in the residue was in good agreement with the total antimony concentration determined by HG-AFS. However, in some extracts the sum of antimony species detected was lower than the total extracted, revealing the presence of unknown antimony species, possibly retained on the column or not detected by HPLC-(UV)-HG-AFS. Further work must be carried out to elucidate the identity of these unknown species of antimony.     

Inversvoltammetrische spurenbestimmung von Antimon(III) und Antimon(V) in aquatischen umweltproben nach selektiver extraktionStripping Voltammetry of Traces of Antimony(III) and Antimony(V) in Natural Waters After Selective Extraction

The biological activity of antimony depends on the oxidation state. The Sb(III) and Sb(V) states can be distinguished, even in the ng l^?1 range, by coupling extraction with ammonium pyrrlidenedithiocarbamate into methyl isobutyl ketone (APDC/MIBK), or N-benzoyl-N-phenylhydroxylamine (BPHA) into chloroform, with anodic stripping voltammetry (a.s.v.). After complex formation with APDC in acetate-buffered medium, Sb(III), but not Sb(V), is extracted into MIBK and quantified by a.s.v. Antimony(V) is quantified in the aqueous phase after removal of Sb(III) by extraction with BPHA into chloroform from the medium acidified with nitric acid. The applicability of the proposed separation/a.s.v. method is demonstrated for samples of rain, snow and water from a dredging operation. The stability of the two antimony species is examined for natural waters with Sb(III) and Sb(V) added; possibilities of stabilization are described. The precedures should be suitable for speciation of antimony in relatively unpolluted waters.     

Thermodynamics of solvent extraction of thorium by solutions of HHTA and mixtures of HHTA and TBP

The changes in free energy, enthalpy and entropy for the extraction of thorium by solutions of thenoyltrifluoroacetone (HTTA) and mixtures of solutions of HTTA and tri-n-butylphosphate (TBP), in three diluents, viz. cyclohexane, benzene and chloroform, were determined using the solvent extraction data obtained at different temperatures. From these data the thermodynamic parameters associated with the formation of Th(TTA)₄ · TBP in the respective organic diluents were evaluated. Trends in the enthalpy changes were attributed to different degrees of association of the diluents with themselves and with the solutes present in them.     

Excess partial molar values of ibuprophene enantiomer and racemate in n-octanol

n-Octanol vapor pressures over solutions of (+)-and (±)-ibuprophene were measured at 25, 30, 35, 40, and 45°C by the effusion method. The excess partial molar values of ibuprophene in n-octanol at 25°C were calculated. The conclusion of n-octanol destructuring in solutions of (+)-ibuprophene was drawn. The suggestion was made that the pharmacological activity of (+)-ibuprophene was related to n-octanol destructuring caused by its solution.     

Squeezing Fluoride out of Water with a Neutral Bidentate Antimony(V) Lewis Acid

Because of hydration, fluoride ions in water typically elude complexation by neutral Lewis acids. Here, we show how this limitation can be overcome with a bidentate Lewis acid containing two antimony(V) centers. This derivative ( 2 ) is obtained by the simple reaction of 4,5‐bis(diphenylstibino)‐9,9‐dimethylxanthene ( 1 ) with two equivalents of 3,4,5,6‐tetrachlorobenzoquinone (o‐chloranil). It features two square‐pyramidal stiborane units oriented in a face‐to‐face fashion. Titration experiments show that this new bidentate Lewis acid binds fluoride in aqueous solutions containing 95 % water with a binding constant (K) of 700±30 M ^?1. The structure of the fluoride adduct confirms fluoride anion chelation between the two antimony centers.     

Synergic extraction of Cd(II) with mixtures of 4-methyl-N-8-quinolinylbenzenesulphonamide and tri-n-butylphosphate or tri-n-octylphosphine oxide dissolved in toluene

The distribution equilibria of Cd(II) from 0.1 mol dm⁻³ KNO₃ with mixtures of 4-methyl-N-8-quinolinylbenzenesulphonamide and the organophosphorus compounds tri-n-butylphosphate (TBP) or tri-n-octylphosphine oxide (TOPO) dissolved in toluene have been investigated. The composition of the extracted species and values of the corresponding stoichiometric extraction constants have been deduced following both graphical and numerical treatments of experimental data. Synergic effects are bigger with TOPO than with TBP in agreement with its greater ability to displace water molecules from the coordination sphere of the metal ion.     

Spectroscopic and structural characterization of pure and FeCl<Subscript>3</Subscript>-containing tri-<Emphasis Type="Italic">n</Emphasis>-butyl phosphate

The spectroscopic properties and liquid structure of pure tri-n-butyl phosphate (TBP) and FeCl₃/TBP solutions have been investigated by Uv–Vis and Raman spectroscopies, X-ray diffraction and conductometry. Uv–Vis and Raman spectra, supported by conductometric measurements, consistently indicate that the solubilized salt is present mostly as TBP _n [FeCl_3???n ] ⁿ⁺ and FeCl₄ ^? complex ions due to specific interaction with the TBP phosphate group. Thanks to this interaction, a high amount of salt (up to 13 % w/w) can be dissolved despite the relatively low dielectric constant of TBP. The X-ray diffractogram of pure TBP has been interpreted in terms of three main contributions which can be attributed to spatial pair correlations between atoms of interacting TBP molecules. In the presence of increasing FeCl₃ amounts, it has been observed a progressive structuring effect, exerted by the dissolved salt, on the layers of opportunely oriented TBP molecules due to the formation of the complex ionic species. By simple treatment with NaBH₄, the synthesis of Fe nanoparticles has been achieved. The absence of water, the easiness of preparation, the high amount of salt which can be suspended and the peculiar physico-chemical properties of such systems are all elements worth of note for the fields of nanoparticle synthesis and for specialized technological applications.