Liquid-liquid extraction of Th(IV) with Cyanex302

Summary Th(IV) was quantitatively extracted from 1 ^. 10^-3M HNO₃ using 1 ^. 10^-3M Cyanex302 in xylene and was stripped from the organic phase with 5M HCl. The effect of different parameters affecting the extraction was systematically studied to achieve optimum conditions for the extraction of thorium. Based on the data some separations of thorium from binary and complex mixtures and its recovery from monazite sand were achieved. The method is reproducible with a relative standard deviation of 0.4%.     

Column chromatographic separation of thorium(IV) from ascorbic acid medium using poly-(dibenzo-18-crown-6)

A simple separation method has been developed for thorium(IV) using poly-(dibenzo-18-crown-6) and column chromatography. The separation was carried out from ascorbic acid medium. The adsorption of thorium(IV) was quantitative from 0.001-0.01M ascorbic acid. The elution of thorium(IV) was quantitative with 4.0-8.0M HCl, 3.0-6.0M HClO₄, 4.0-8.0M H₂SO₄ and 1.0-8.0M HBr. The capacity of poly-(dibenzo-18-crown-6) for thorium(IV) was found to be 1.379±0.01 m^.mol/g of crown polymer. Thorium(IV) was separated from a number of cations in binary as well as in multicomponent mixtures. The method was extended to the determination of thorium in monazite sand. It is possible to separate and determine 5 ppm of thorium(IV) by this method. The method is very simple, rapid, selective and has good reproducibility (approximately ±2%).     

Conductometric estimation of thorium in dilute thorium chloride

Summary Conductometric titrations of thorium chloride against oxalic acid, ammonium oxalate and silver nitrate have been carried out at high dilutions (0.001, 0.0005 and 0.00033 M) of the chloride. Oxalic acid is found to be a suitable titrant for rapid estimation of thorium, the minimum error being +0.5%. The other titrants do not give good results. The titrations with ammonium oxalate indicate the step-wise ionisation of ThCl₄ into ThCl₂ ²⁺, ThCl³⁺ and Th⁴⁺. For mixtures of thorium chloride and cerous chloride, only the equivalence point corresponding to complete precipitation of both thorium and cerium is indicated.The authors express their sincere thanks to Prof. S. S.Joshi for his keen interest in this work and to Dr. G. S.Deshmukh for his advice and help in so many ways during the progress of these studies.     

Analytical application of poly [dibenzo-18-crown-6] for chromatographic separation of thorium(IV) from uranium(VI) and other elements in glycine medium

A selective and effective chromatographic separation method for thorium(IV) has been developed by using poly [dibenzo-18-crown-6] as stationary phase. The separations are carried out from glycine medium. The sorption of thorium(IV) was quantitative from 1 × 10^?2 to 1 × 10^?4 M glycine. The elution of thorium(IV) was quantitative with 2.0–8.0 M HCl, 4.0–7.0 M HBr, 1.0–2.0 M HClO₄ and 5.0 M H₂SO₄. The capacity of poly [dibenzo-18-crown-6] for thorium(IV) was found to be 0.215 ± 0.01 mmol/g of crown polymer. The effect of concentration of glycine, metal ion, foreign ion and eluents has been studied. Thorium(IV) was separated from a number of cations in ternary as well as in multicomponent mixtures. The applicability of the proposed method was checked for the determination of thorium(IV) in real as well as geological sample. The method is simple, rapid, and selective with good reproducibility (approximately ±2 %).     

Novel Thorium Membrane Sensors with Anionic Response Based on Trioctylphosphine Oxide and Toluate Ionophores

Two novel potentiometric polymeric membrane sensors for rapid and accurate determination of thorium are described. These are based on the use of trioctylphosphine oxide (TOPO) and thorium toluate (Th‐TA) as ionophores dispersed in poly(vinyl chloride) matrix membranes plasticized with nitrophenyloctyl ether. In strong nitric acid medium, Th(IV) nitrate is converted into [Th(NO₃)₆]^2? complex and sensed as anionic divalent ion which exclude most cationic effect. Validation of the assay methods using the quality assurance standards (linearity range, accuracy, precision, within‐day variability, between‐day‐repeatability, lower detection limit and sensitivity) reveals excellent performance characteristics of both sensors. The sensors exhibit near‐Nernstian response for 1.0×10^?6–1.0×10^?1 M Th over the pH range 2.5–4.5. Calibration slopes of ?32.3±0.3 and ?27.2±0.2 mV/decade, precision of ±0.5 and ±0.8% and accuracy of 98.8±0.9 and 97.9±0.7% are obtained with TOPO and Th‐TA based sensors, respectively. Negligible interferences are caused by most interfering mono‐, di‐, tri‐, tetra‐, penta‐, and hexa‐valent elements commonly associated with thorium in naturally occurring minerals and ores. High concentrations of Cl^?, F^?, SO₄^2?, and NO₃^? ions have no diverse effect. Complete removal of the effect of the interferents in complex matrices is achieved by retention of [Th(NO₃)₆]^2? complex from 5 M nitric acid/methanol mixture (1 : 9 v/v) on a strong anion exchanger, washing out the cationic interferents followed by stripping off thorium anion complex and measurements. Both sensors are used for determining thorium in certified thorium ore samples (20–120 mg Th/kg) and some naturally occurring ores (200–600 mg Th/kg). The results obtained agree fairly well with the certified labeled values or the data obtained using X‐ray fluorescence spectrometry     

Extraction of thorium from aqueous nitric acid solution by bis-2-(butoxyethyl ether) (DBC)

The solvent extraction of thorium(IV) (4.3·10^–4M) from nitric acid solution by bis-2-(butoxyethyl ether) (butex or DBC) has been studied. It has been investigated as a function of nitric acid, extractant and metal ion concentration. The effect of equilibration time, diverse ions and salting-out agent on the extraction has also been examined. Among anions, fluoride, phosphate, oxalate and perchlorate have reduced the extraction. Cations such as Na(I), K(I), Ca(II), Zn(II), Al(III), Ti(IV), Zr(IV) except Sr(II) and Pb(II) do not interfere in the extraction. The extraction is enhanced upto 97% in three stages at 6M HNO₃ having 2.94M NaNO₃ as salting-out agent. The extraction is found to be independent of thorium concentration in the range studied (4.3·10^–4–4.3·10^–2M). The temperature (18–45°C) has an adverse effect on the extraction. A 1% solution of ammonium bifluoride is found to be a good stripping solution and recovery of thorium is >98%.     

Selective adsorption of thorium on activated charcoal from electrolytic aqueous solution

The adsorption of thorium on activated charcoal has been studied as a function of shaking time, amount of adsorbent, pH, concentration of adsorbate and temperature. Adsorption of thorium obeys the Langmuir isotherm. H⁰ and S⁰ were calculated from the slope and intercept of ln K_D vs. 1/T plots. The influence of different anions and cations on thorium adsorption has been examined. The adsorption of other metal ions on activated charcoal has been studied under specified conditions to check its selectivity. Consequently, thorium was removed from Cs, Co, Ba, Cr, Sr, Cd, Cu, Mn and Zn. More than 98% adsorbed thorium on activated charcoal can be recovered with 55 ml 3M HNO₃ solution. Wavelength dispersive X-rays fluorescence spectrometer was used for measuring thorium concentration.     

Extraction properties of octaethyltetraamidopyrophosphate (OETAPP)

The extraction of thorium and hafnium was studied in the system of 0.1M OETAPP in CHCl₃/HCl or HNO₃ at acid concentrations of 1–10 M. It has been found by the dilution method that under the experimental conditions mono- and disolvates of thorium nitrate or hafnium chloride, the disolvate of thorium chloride or the monosolvate of hafnium nitrate are formed. The solvation and hydration energies of thorium chloride in the system of 1M ThCl₄ in 1M HCl−1M OETAPP in CHCl₃ as well as their difference were calculated.     

Peptization of Thorium Hydroxide and Thorium Oxide Sols with Nitrate

The peptization of thorium hydroxide and thorium oxide sol on the preparation of microsphere of nuclear fuels are studied. These sols are prepared mainly by dispersing hydrated thorium oxide in nitric acid. A main character of ThO₂ sol is its NO₃^?/Th mole ratio. After peptization, the nitrate is presented as two forms; i. e., sorbed by particles of the sol and free in the aqueous solutions. The adsorbed NO₃^?/Th mole ratio depends on the average crystallite size of thorium oxide. In certain size range, the adsorbed NO₃^?/Th of ThO₂ sol prepared from thorium oxalate is inversely proportional to the crystallite size. The different series of thorium oxide are made by different methods. In this paper the crystallite size is obtained from 33 to 84 A by changing calcination temperatures.     

Extractive separation of Th(IV), U(VI), Ti(IV), La(III) and Fe(III) from Zarigan ore

In this study, the effects of various extraction parameters such as extractant types (Cyanex302, Cyanex272, TBP), acid type (nitric, sulfuric, hydrochloric) and their concentrations were studied on the thorium separation efficiency from uranium(VI), titanium(IV), lanthanum(III), iron(III) using Taguchi^??s method. Results showed that, all these variables had significant effects on the selective thorium separation. The optimum separations of thorium from uranium, titanium and iron were achieved by Cyanex302. The aqueous solutions of 0.01 and 1 M nitric acid were found as the best aqueous conditions for separating of thorium from titanium (or iron) and uranium, respectively. The combination of 0.01 M nitric acid and Cyanex272 were found that to be the optimum conditions for the selective separation of thorium from lanthanum. The results also showed that TBP could selectively extract all studied elements into organic phase leaving thorium behind in the aqueous phase. Detailed experiments showed that 0.5 M HNO₃ is the optimum acid concentration for separating of thorium from other elements with acidic extractants such as Cyanex272 and Cyanex302. The two-stage process containing TBP-Cyanex302 was proposed for separation thorium and uranium from Zarigan ore leachate.     

Effect of complexants on the adsorption and color reactions of lanthanum(III), uranium(VI), thorium(IV), and zirconium(IV) with Arsenazo M in the solid phase of an ANKB-50 fibrous ion-exchanger

The effect of complexants—acetic, aminoacetic, tartaric, malonic, and oxalic acids; EDTA; and Na₂CO₃—on the adsorption and subsequent determination of thorium(IV), lanthanum(III), uranium(VI), and zirconium(IV) with Arsenazo M in the solid phase of polyacrylonitrile fiber filled with an ANKB-50 anion exchanger was studied. Complexing agents were introduced into the solution at the step of metal ion adsorption. It was shown that zirconium and uranium interacted with the iminodiacetate groups of the adsorbent in the course of adsorption; the adsorption of elements from 10^?3 to 10^?2 M complexant solutions (except for tartaric and oxalic acids and EDTA) under the optimum conditions was enhanced as compared to their adsorption from pure solutions; complexation with Arsenazo M in the solid phase proceeded at a higher acidity than in the solution. When the elements were present simultaneously, their total concentration and individual thorium could be determined from malonic acid solutions with Arsenazo M by varying the concentration of acid and the adsorption pH.     

Secondary ion mass spectrometry and alpha-spectrometry of electrodeposited thorium films

The main aim of this work was the preparation of samples with thorium content on the steel discs by electrodeposition for determination of natural thorium isotope by alpha spectrometry and secondary ion mass spectrometry and finding out their possible linear correlation between these methods. The analysis of the composition of surface was other aim of study. Discs were measured by alpha spectrometer. After that, alpha spectrometry discs were analyzed by TOF-SIMS IV, which is installed in the International Laser Centre in Bratislava. The integral and normalized intensities of isotope of ²³²Th and intensities of ions of ThO⁺, ThOH⁺, ThO₂H⁺, Th₂O₄H⁺, ThO₂ ^?, ThO₃H^?, ThH₃O₃ ^? a ThN₂O₅H^? were measured. The linear correlation is between surface’s weights of Th and intensities of ions of Th⁺ from identified in SIMS spectra. We found out the chemical binding between thorium and oxygen and hydrogen on the surface of samples by SIMS method. Obtained intensities of ions ²³²ThO⁺, ²³²ThOH⁺, ²³²ThO₂H⁺ prove the presence of oxidized forms of thorium in the upper layers of surface. The oxidized ions predominate in univalent form of thorium up to deep about 3,000 nm.     

Separation studies of uranium and thorium using tetra(2-ethylhexyl) diglycolamide (TEHDGA) as an extractant

The extraction behavior of uranium, thorium and nitric acid has been investigated for the TEHDGA/isodecyl alcohol/n-dodecane solvent system. Conditional acid uptake constant (K _H) of TEHDGA/n-dodecane and the ratio of TEHDGA to nitric acid were obtained as 1.72 and 1:0.96, respectively. The extracted species of uranium and thorium in the organic phase were found to be UO₂(NO₃)₂·2TEHDGA and Th(NO₃)₄·2TEHDGA. A workable separation factor (D _Th/D _U) of the order of 300 was observed between thorium and uranium in the nitric acid range of 0.5M to 1.5M. Similar separation factor was also achieved at higher acidity when thorium was present in large concentration compared to uranium. These results indicate that TEHDGA solvent system could be a potential candidate for separation of thorium from uranium.     

Extraction of thorium using primary amine N1923 levextrel resin by a micro-column

The extraction behavior of thorium from Baotou iron ore with primary amine N1923 levextrel resins by a micro-column was investigated under the decompression technology. Thorium was adsorbed on the micro-column conditioned by 3 mol L⁻¹ HCl solution before use. The washing liquor of 0.5 mol L⁻¹ H₂SO₄–0.1 mol L⁻¹ H₃PO₄ solution was used to wash impurity elements and the solution of 3 mol L⁻¹ HCl was used as the eluent for thorium. The method was applied to analyze thorium in the Baotou iron ore sample. The relative standard deviations of thorium in R-715 standard sample, Baotou main ore standard sample and Baotou west ore were of 0.49%, 1.63%, 1.16%, respectively. The accuracy of the method was satisfactory.

     

Stabilization of Th ions into mixed-valence thorium fluoride

The unusual oxidation state +3 of the thorium has been stabilized into a lithium containing non-stoichiometric mixed-valence (III/IV) thorium fluorinated phase with formula Li_2+xTh₁₂F₅₀ (0<x<1.8). This phase is closely related to the Li_5.5Ce₁₂F₅₀ one, the structure of which has been determined from the combined single-crystal X-ray diffraction and high resolution synchrotron powder diffraction. In these phases, the Li⁺ ions can be divided into two groups and are located either in locked positions or in open channels of the three dimensional framework. The amount of Li⁺ ions in open channels can be variable, so that the afore mentioned single phase may be considered as an insertion compound. The Li⁺ insertion is accompanied by the simultaneous reduction of a part of the Th⁴⁺ ions, resulting in a mixed-valence III/IV thorium fluoride. The electrochemical insertion of Li⁺ ions into the open channels of the host matrix has been carried out at 60 °C, using an alkylcarbonate PC-LiClO₄ 1 M electrolyte. The Li⁺ and Th³⁺ contents, both in the starting composition and the Li⁺ inserted ones, were investigated by high resolution solid state ⁷Li NMR and EPR, respectively.     

Liquid-liquid extraction of Th4+ and UO 2 2+ by LIX-26 and its mixtures

Solvent extractions of thorium(IV) and uranium(VI) by a commercially available chelating extractant LIX-26 (an alkylated 8-hydroxyquinoline) or 8-hydroxyquinoline, benzoic or salicylic acid, dipentyl sulphoxide (DPSO) and their mixtures with butanol as modifier in benzene/methylisobutyl ketone (MIBK) as the diluent have been studied. Extraction of uranium(VI) by 10% LIX-26 and 10% butanol in benzene becomes quantitative at pH 5.0. The pH 0.5 values for the extraction of thorium(IV) and uranium(VI) are 4.95 and 3.35, respectively. Quantitative extraction of thorium(IV) by the mixture of 0.1 M oxine and 0.1 M salicylic acid in methylisobutyl ketone was observed at pH 5.0. The influence of concentration of various anions on the extraction of Th⁴⁺ by mixtures of LIX-26 and benzoic acid has been studied. Studies on extraction of thorium(IV) and uranium(VI) by mixtures of LIX-26 (HQ) and DPSO show that the extracted species are possibly of the type [ThQ₂/DPSO/₂/SCN/₂] and [UO₂Q₂/DPSO/], respectively.     

Sequential separation and determination of uranium and thorium isotopes in soil samples with Microthene-TOPO chromatographic column and alpha-spectrometry

In the method, soil was fused together with Na₂CO₃ and Na₂O₂ at 600 °C, uranium and thorium were leached out with HCl, HNO₃ and HF, and HClO₄ was used to eliminate the residual HF through evaporation. The leaching solution (2 M HNO₃) was passed through a Microthene-TOPO column to adsorb uranium and thorium. Thorium was first eluted with 2 M HCl and electrodeposited in 0.025 M H₂C₂O₄ + 0.15 M HNO₃ on a stainless steel disc. Uranium was eluted with a 0.025 M ammonium oxalate solution and also electrodeposited. Both thorium and uranium isotopes on the discs were measured separately by α-spectrometry.     

Assignment of complex species by affinity capillary electrophoresis: The case of Th(IV)-desferrioxamine B

The electrophoretic mobility change of desferrioxamine B (DFO) was monitored by UV absorption spectrophotometry upon increasing the thorium(IV) concentration in the background electrolyte at two acidities ([HClO₄]_Tot = 0.0316 and 0.0100 M). These data enabled to assess the speciation model and to determine the equilibrium constant of [Th(DFO)H₂]³⁺ at fixed ionic strength (I = 0.1 M (H,Na)ClO₄). Affinity capillary electrophoresis (ACE) turned out to be most helpful in identifying the complexed species by ascertaining its charge and protonation state. The assignment of the correct stoichiometry relied on the reliable estimation of the electrophoretic mobility by assuming similar hydrodynamic radii for (DFO)H₄⁺ and the chelate. The value of the apparent equilibrium constant (log β₁₁₂ = 38.7 ± 0.4) obtained by ACE compares favorably well with those reported in the literature for thorium and a range of other metal ions, according to a linear free-energy relationship. This method is useful for studying metal-ligand binding equilibria and provides valuable information for further modelling the behavior of tetravalent actinides under environmental conditions. Structural information about the prevalent solution species in acidic conditions was gained by DFT calculations, confirming the bishydroxamato coordination mode of Th⁴⁺ by the diprotonated ligand.     

Coated wire thorium ion selective electrode: Part I

Coated wire ion selective electrode for thorium ion selective potentiometry was developed. Thorium ion selective coated wire electrodes were prepared by depositing a membrane comprising of Aliquat-336 loaded with Th(NO₃)₆²⁻ ions and poly vinyl chloride in varying proportion. A linear near-Nernstian response with a slope of −29.5 ± 0.3 mV over thorium concentration range of 1 × 10⁻¹–3 × 10⁻⁵ M in constant total nitrate concentration of 6 M was obtained for the electrodes of almost all the composition studied. In spite of small drift in response potential from composition to composition, day to day as well as from electrode to electrode, the slope of potential response line was constant within experimental error. Moreover, the electrode once prepared could be conveniently used over a period of one and half month.     

Determination of 237 Np in marine sediment and seawater

Procedures for determination of neptunium in marine sediment and seawatersamples are described. Iron hydroxide Fe(OH)₂ –Fe(OH)₃ is used for preliminary pre-concentration of neptunium. Secondly,neptunium Np⁴⁺ and Pu³⁺ are separated by tri-isooctylamine-(TIOA)extraction in 8–10M HCl by redox with SO₃ ^2–-Fe³⁺ Neptunium Np⁴⁺ and uranium U⁶⁺ areseparated by back extraction the Np⁴⁺ with 2M HCl. Finally, theneptunium is purified from the uranium and thorium by anion exchange in 8MHNO₃ and 12M HCl. The stripping of 6M HCl + NH₂ OH HClfurther separates the neptunium Np³⁺ and uranium. Reduction bySO 3_2– –Fe³⁺ appeared to be an efficientway to obtain Np⁴⁺ The decontamination factors of the procedureare 4.0. 10⁴ for ²³² Th, 5.6 . 10⁴ for uraniumand 1.6 . 10⁴ for plutonium.