The extraction of trace amounts of tantalum(V) from different mineral acid solutions by 4-(5-nonyl)pyridine oxide and trioctylamine oxide

Data are presented on the distribution of trace amounts of tantalum (V) between different mineral acid solutions and 0.1M solutions of N-oxides of 4-(5-nonyl)pyridine and trioctylamine. The optimal acidity is 0.01–0.5M, depending on the nature of the acid. Common anions have little effect on extraction. Possible mechanisms of extraction are suggested making use of slope analysis data. Separation factors for a number of metal ions with respect to tantalum are reported for the 0.1M 4-(5-nonyl)pyridine oxide—1M sulphuric acid extraction system. Separation from uranium(VI), thorium(IV) and a number of fission products is suggested. where a part of the work was done.     

N-oxides of 4-(5-nonyl)pyridine and trioctylamine as extractants for cerium(IV) and its separation from thorium(IV)

Trace level cerium has been oxidized to the quadrivalent state with potassium dichromate and shown to be preferentially extracted from very dilute mineral acid solutions and also from moderate nitric acid media by 0.1M solutions of 4-(5-nonyl)pyridine oxide and trioctylamine oxide dissolved in xylene. The dependence of extraction on the type of N-oxide, acid concentration and the N-oxide concentration has been investigated. The influence of the concentration of salting-out agents is described. Separation factors for a number of metal ions relative to cerium(IV) are reported for 0.1 M 4-(5-nonyl)pyridine oxide/xylene-0.1M sulphuric acid system. The ratio of the D for Ce(IV) to that of Ce(III) is greater than 10⁵, and the D for Ce(IV) is much greater than that for thorium(IV). Separation of cerium(IV) from thorium has been achieved from 0.1M sulphuric acid solutions using 0.1M 4-(5-nonyl)pyridine oxide/xylene as an extractant.     

Spectrophotometric determination of tantalum in ores and mill products with brilliant green after separation by methyl isobutyl ketone extraction of tantalum fluoride

A method for determining ~ 0.001% or more of tantalum in ores and mill products is described. After fusion of the sample with sodium carbonate, the cooled melt is dissolved in dilute sulphuric-hydrofluoric acid mixture and tantalum is separated from niobium and other matrix elements by methyl isobutyl ketone extraction of its fluoride from 1M hydrofluoric acid-0.5M sulphuric acid. The extract is washed with a hydrofluoric-sulphuric acid solution of the same composition to remove co-extracted niobium, and tantalum is stripped with dilute hydrogen peroxide. This solution is acidified with sulphuric and hydrofluoric acids and evaporated to dryness, and the residue is dissolved in oxalic-hydrofluoric acid solution. Tantalum is ultimately determined spectrophotometrically after extraction of the blue hexafluorotantalate-Brilliant Green ion-association complex into benzene from a 0.05M sulphuric acid-0.5M hydrofluoric acid-0.2M oxalic acid medium. The apparent molar absorptivity of the complex is 1.19 x 10(4) l.mole(-1).mm(-1) at 640 nm, the wavelength of maximum absorption. Common ions, including iron, aluminium, manganese, zirconium, titanium, molybdenum, tungsten, vanadium, tin, arsenic and antimony, do not interfere. Results obtained by this method are compared with those obtained by an X-ray fluorescence method.     

Separation of niobium and tantalum with phenylarsonic acid

Phenylarsonic acid permits satisfactory separation of niobium and tantalum and estimation of tantalum from an oxalate solution containing sulphuric acid up to pH 5.8. For complete precipitation of niobium the pH should exceed 4.8. In mixtures, tantalum is precipitated below pH 3.0 and niobium is then precipitated above pH 5.0. When the oxalate concentration is high, recovery of niobium with cupferron is recommended. When the ratio of Nb₂O₅, to Ta₂O₅ exceeds 2:1, reprecipitation of tantalum is necessary. The effect of interfering ions is studied.     

Extraction studies of Pu(IV) with octylphenyl acid phosphate

Octylphenyl acid phosphate, the commercially available mixture of monooctylphenylphosphoric acid (MOPPA) and dioctylphenylphosphoric acid (DOPPA) in xylene medium has been employed as an extractant for distribution studies on Pu(IV) in different mineral acids including phosphoric acid. It was found possible to extract Pu quantitatively from an acid mixture comprising 2.5M H₃PO₄, 0.75M H₂SO₄ and 0.5M HNO₃. Quantitative stripping was observed with a mixture of 0.25M oxalic acid and 0.2M ammonium oxalate.Parts of this work have been reported at symposie (Refs^1,2)     

Spectrophotometric determination of tantalum with 4,5-dibromo-o-nitrophenylfluorone

Micro amounts of tantalum can be determined directly by spectrophotometry with 4,5-dibromo-o-nitrophenylfluorone, citric acid, hydrogen peroxide and Triton X-100 in 0.5–5 mol l^?1 sulphuric acid. The apparent molar absorptivity of tantalum at 530 nm is 1.84 × 10⁵ l mol^?1 cm^?1. Beer's law is obeyed for 0–10 μg of tantalum in 25 ml of solution at 530 nm and a large amount of niobium and most foreign ions can be tolerated. Results obtained by applying the proposed method to niobium oxide, ferroniobium, nickel-base alloy and a mineral are satisfactory. The synthesis of the complexing agent is described.     

Separation of niobium and tantalum by extraction chromatography with bis(2-ethylhexyl)phosphoric acid

A novel method is developed for the reversed-phase extractive chromatographic separation of niobium and tantalum with bis(2-ethylhexyl)phosphoric acid. Niobium is extracted from 1-10M hydrochloric acid and can be stripped with 3M sulphuric acid containing 2% hydrogen peroxide. Tantalum is extracted from 0.1-2M hydrochloric acid and can be stripped with 0.1M hydrochloric acid containing 2M tartaric acid. It is possible to separate niobium and tantalum, in different ratios, from multicomponent mixtures.     

Solvation of cobalt-thiocyanate complexes by 2-hexylpyridine from aqueous mineral acid solutions

A study of the distribution of cobalt between mineral acid solutions containing potassium thiocyanate and 0.1M 2-hexylpyridine in benzene has been undertaken. Cobalt can be quantitatively extracted as its thiocyanate complex from very dilute acid solutions containing 0.1–1M KSCN. Variation of the distribution coefficient D_Co in terms of the ligand concentration in the organic phase has allowed the formula of the extracted species to be determined as Co(HPy)₄ (SCN)₂. The effects of oxalate, acetate, fluoride, ascorbate, sulphate and thiosulphate ions on the extraction of cobalt from three mineral acid solutions have been reported. The extraction coefficients of several elements are given for the 0.1M 2-hexylpyridine in three systems containing 0.5M KSCN with 0.25M HNO₃, 0.05M HCl and 0.05M H₂SO₄ respectively; and their factors for separation from cobalt are estimated.     

Extraction of trace amounts of cerium(III) by oxides of amines and its separation from cerium(IV)

The solvent extraction of cerium(III) from nitric, hydrochloric and sulphuric acid solutions by 4-(5-nonyl)pyridine oxide and trioctylamine oxide in xylene has been studied. The influence of the concentration of the solvents and salting-out agents is described. From the results of partition experiments attempts have been made to deduce the nature of the extracted species. The investigation shows that cerium(III) can be separated from cerium(IV) from very dilute solutions of mineral acids and also from moderate nitric acid media.     

Monte Carlo simulations of corrosion inhibition of mild steel in 0.5 M sulphuric acid by some green corrosion inhibitors

Atomistic modelling and simulations are becoming increasingly important in the field of corrosion inhibition. New research and development efforts and new possibilities for using computational chemistry in studying the behaviour of corrosion inhibitors on the metal surfaces are introduced. In this study, Monte Carlo simulations technique incorporating molecular mechanics and molecular dynamics were used to simulate the adsorption of methionine derivatives, namely l-methionine, l-methionine sulphoxide and l-methionine sulphone, on iron (110) surface in 0.5 M sulphuric acid. Adsorption energy as well as hydrogen bond length has been calculated. Results show that methionine derivatives have a very good inhibitive effect for corrosion of mild steel in 0.5 M sulphuric acid solution. Tafel polarisation studies have shown that methionine derivatives act as mixed-type inhibitors, and their inhibition mechanism is adsorption assisted by hydrogen bond formation. Impedance results indicate that the values of the constant phase element tend to decrease with increasing methionine derivatives concentrations due to the increase in the thickness of the electrical double layer. In addition, both polarisation resistance and inhibition efficiency E _i(%) tend to increase with increasing inhibitors concentrations due to the increase of the surface coverage, i.e., the decrease of the electrochemical active surface area. The quantum mechanical approach may well be able to foretell molecular structures that are better for corrosion inhibition.     

Sorption of uranium and thorium from sulphuric acid using TVEX-PHOR resin

Summary Solid-liquid extraction has been used to study the uptake of uranium(VI) and thorium(IV) from sulphuric acid using a TVEX-PHOR resin. The experimental results were found to fit the BET isotherm and show a higher affinity of the TVEX-PHOR resin towards the extraction of uranium than thorium under similar experimental conditions. The best separation of uranium from thorium is obtained from 3M sulphuric acid at V/m ratio of 20 ml/g. Elution of loaded uranium and thorium was carried out with 1M sodium carbonate and 0.075M sulphuric acid, respectively. After the elution of both elements, the regenerated resin could be reused with high efficiency.     

Determination of spatial distribution of oxidation products in ultra-high molecular weight polyethylene by staining with sulphur dioxide or hydrochloric acid

Treating a sample of oxidised ultra-high molecular weight polyethylene (UHMWPE) with SO₂ will cause a reaction between SO₂ and hydroperoxides in the sample, forming a hydrosulphate group. During subsequent heat treatment the hydrosulphate group will leave as sulphuric acid, and a double bond will form in the polymer chain. During this step the sample turns brown. This browning has previously been used to determine the spatial distribution of oxidation in PP. The aim of this work was to apply this also to UHMWPE and to determine what causes the browning and how well it corresponds to the true distribution and concentration of hydroperoxides. The possible future use of the technique to determine the spatial distribution of oxidation in UHMWPE has also been evaluated.The true nature of the browning has been difficult to establish, but it seems to originate from a charge transfer complex between the double bonds and the sulphuric acid. A similar type of coloration develops in oxidised UHMWPE, when it is treated with hot hydrochloric acid. However, in that case the coloration is proportional to the carbonyl concentration and has been concluded to originate from the oxonium ion formed by protonation of ketones. The coloration of both SO₂/heat-treated samples and samples treated with hot hydrochloric acid can be used to give a qualitative picture of the spatial distribution of oxidation in UHMWPE. The techniques have been applied to study the heterogeneous oxidation in badly consolidated UHMWPE. It was found that the very good spatial resolution gave information about the heterogeneous oxidation that is not possible to obtain when using other techniques, such as FTIR mapping and imaging chemiluminescence.     

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.     

Solvent extraction of Tc(VII) by the mixture of TBP and 2-nitrophenyl octyl ether

The extraction of Tc(VII) by the mixture of tri-n-butyl phosphate (TBP) and 2-nitrophenyl octyl ether (NPOE) has been studied. 0.2M NPOE-TBP can extract Tc(VII) effectively from 1M HNO₃ and 1M NaOH solutions with distribution ratios of 57.1 and 12.3, respectively. The distribution ratio of Tc(VII) decreases with increasing (>0.5M) HNO₃ concentration but increases with the increase of NaOH concentration. A pH 9 NaOH solution has proven to be suitable for Tc(VII) stripping. A simple extraction-stripping cycle can remove Tc(VII) from a sodium hydroxide solution. A more sophisticated extraction process is proposed to remove Tc(VII) from nitric acid solution because the co-extracted HNO3 prevents the direct stripping of Tc(VII) by NaOH solution of pH 9.     

Extraction of rare earth elements by high molecular weight amines from nitric acid solutions

Extraction of trivalent rare earth elements by a high molecular weight primary amine /decylamine/ from 0.5–3M nitric acid solutions, containing potassium phosphotungstate /K₁₀P₂W₁₇O₆₁/, has been investigated. The effect of nitric acid and potassium phosphotungstate concentration of the organic solvent, and lanthanides ionic radii upon distribution coefficients has been studied. It has been established that decylamine solutions in chloroform can be used for the group isolation of rare earth elements and for their separation.     

Partial electro-neutralisation of -α-p-hydroxyphenylglycine in sulphuric acid medium

In the industrial synthesis of -α-p-hydroxyphenylglycine the separation of amino acid is carried out by precipitation. During this process, a mother liquor is produced with a high salt content (2 M phosphates and sulphates) and an amino acid concentration of 0.11–0.12 M. The disposal of this mother liquor causes an environmental problem and an economic loss. The salt content of this mother liquor can be reduced in 70% of the initial by means of an electrodialysis process previously carried out by us, with only an amino acid loss of 15% of the initial. To improve and simplify this process, an electro-electrodialysis process (a membrane electrolysis process; the electrode processes and the transport process across the membrane are used) has been developed in which as a first step, the electro-neutralisation of solutions containing sulphuric acid and -α-p-hydroxyphenylglycine is studied. The sulphuric acid content is reduced to 87% of the initial, without detected loss of amino acid. The final solution is posteriorly neutralised by working up the pH of the solution for precipitating the amino acid, and a mother liquor with approximately 0.10 M -α-p-hydroxyphenylglycine and a low salt content (0.08 M Na₂SO₄) is produced. This mother liquor with low salinity can be recirculated again to a new electro-electrodialysis process.     

Methyl isobutyl ketone extraction of iodide complexes from sulphuric acid-potassium iodide media and back-extraction into an aqueous phase

The methyl isobutyl ketone extraction of 15 elements (Cu, Ag, Zn, Cd, In, Tl, Ge, Sn, As, Sb, Bi, Se, Te, Mo and Pd) as iodide complexes from 0.1-5 M sulphuric acid/0.01-0.5M potassium iodide media has been studied. At the optimum potassium iodide concentrations, and a 1:2 v v ratio of organic to aqueous phase, Cu(II), Ag, Cd, In(III), Tl(III), Sb(III), Bi, Te(IV) and palladium(II) are completely extracted in a single step from 1-5M sulphuric acid. All these elements except palladium are also quantitatively extracted from 0.05-0.5M iodide/2M sulphuric acid. Zn, Sn(IV) and As(III) are completely extracted at high acid and iodide concentrations, and at the highest concentrations of acid and iodide investigated, Ge is partly extracted and Mo(VI) is slightly extracted. The extraction of Se(IV) is incomplete because of its reduction to the elemental state by iodide. The back-extraction of the elements has also been investigated and the forms in which they are extracted and potential analytical separations and interferences are discussed.     

Comparison of standards in the Karl Fischer method for water determination.

The use of 4-(5-nonyl)pyridine oxide and trioctylamine oxide for the extraction of niobium(V) from different mineral acid solutions is described. The influence of the concentration of the solvents, acids and salting-out agents is discussed. Separations of niobium(V) from tantalum(V) and zirconium(IV) have been achieved.     

Adsorption of radioisotopes from their organic solutions on filter papers the Sb(III)-nonpolar solvents-system

The extraction of Sb(III) chloride by nonpolar solvents from 0.15M HCl was studied as a function of sulphuric acid concentrations in the aqueous phase. The distribution of Sb(III) chloride between the nonpolar solvents benzene, toluene, xylene, nitrobenzene, cyclohexane, chloroform and carbon tetrachloride and filter paper is reported. In case of benzene the Sb(III) activity (given in counts·s^–1·ml^–1) decreases from 1500 to 200 after 24 hours. The corresponding values are about 1200 and 540 for toluene, 1330 and 50 for xylene, 1050 and 700 for nitrobezene, 1080 and 22 for cyclohexane, 330 and 30 for chloroform and 130 and 40 for carbon tetrachloride. More than 95% of the adsorbed Sb(III) is desorbed by 1M HNO₃, 1M HCl or 0.5M H₂SO₄ by contacting the loaded filter paper with any of these acids for 27 hours.