Extraction of U(VI), Th(IV) and some fission products from nitric acid medium by sulfoxides and effect of γ-irradiation on the extraction

The extracting abilities for thorium, uranium and some fission products by five sulfoxides are given. The results show that di(2-ethylhexyl) sulfoxide (DEHSO) is not only completely miscible with kerosene, but also superior to tri-n-butyl phosphate in some properties. The extraction behavior of uranium, thorium and some fission products such as zirconium, niobium and ruthenium from aqueous nitric acid with DEHSO in kerosene has been studied over a wide range of conditions. DEHSO extracted uranium and fission products better than TBP under all conditions and is similar to TBP in extraction of thorium. A study of extraction mechanism indicates that U and Th are extracted as disolvates, whereas HNO₃ is extracted as monosolvate. Extraction of the two actinides decreases with increasing temperature, indicating the extraction to be exothermic. Preliminary studies show that -ray irradiated DEHSO extracts Zr and Nb to a smaller extent than irradiated TBP in the range of 10⁴–10⁷ rad.     

Extraction studies of uranium into a third-phase of thorium nitrate employing tributyl phosphate and <Emphasis Type="Italic">N,N</Emphasis>-dihexyl octanamide as extractants in different diluents

Extraction behavior of 1 × 10⁻²–0.1 M U(VI) from aqueous phases containing 0.86 M Th(IV) at 4 M HNO₃ in 1.1 M tributyl phosphate (TBP) and 1.1 M N,N-dihexyl octanamide (DHOA) solutions in different diluents viz. n-dodecane, 10% 1-octanol + n-dodecane, and decahydronaphthalene (decalin) was studied. Third-phase formation was observed in both the extractants using n-dodecane as diluent. There was a gradual decrease in Th(IV) concentration in the third-phase (heavy organic phase, HOP) with increased aqueous U(VI) concentration [0.71 M (no U(VI))–0.61 M (0.1 M U(VI)) for TBP; 0.27 M (no U(VI))–0.22 M (0.1 M U(VI)) for DHOA]. The HOP volume in case of DHOA was ~2.2 times of that of TBP. Uranium concentration in HOP increased with its initial concentration in the aqueous phase [from 1.8 × 10⁻² M (0.01 M U(VI))–0.162 M (0.1 M U(VI)) for TBP; from 1.4 × 10⁻² M (0.01 M U(VI))–0.14 M (0.1 M U(VI)) for DHOA] suggesting that Th(IV) was being replaced by U(VI). An empirical correlation was developed for predicting the concentrations of uranium and thorium in HOP for both the extractants. No third-phase appeared during the extraction of uranium and thorium from the aqueous phases employing 10% 1-octanol + n-dodecane, or decalin as diluents, and therefore, were better choices as diluent for alleviating the third-phase formation during the reprocessing of spent thorium based fuels, and for the recovery of thorium from high-level waste solutions.     

Separation and spectrophotometric determination of thorium contained in uranium concentrate

A method for the determination of thorium in uranium concentrate by spectrophotometry with Arsenazo III has been developed. Preliminary solvent extraction procedures were used to eliminate interfering species. Samples were dissolved in nitric, perchloric and sulfuric acid and the uranium extracted from the solution using tri-octylamine. The aqueous layer was evaporated to dryness and the residue re-dissolved with hydrochloric acid, thorium was extracted by tri-n-octyl phosphine oxide and stripped with oxalic acid. For a typical uranium concentrate produced from the phosphate rock of Itataia, Brazil, concentrations of thorium as low as 5 g·g^-1 can be determined.     

Determination of uranium and thorium in phosphate rocks by a combined ion-exchange — Spectrophotometric method

Summary Determination of Uranium and Thorium in Phosphate Rocks by a Combined Ion-Exchange — Spectrophotometric Method A selective anion-exchange separation and Spectrophotometric method has been developed for the determination of uranium and thorium in phosphate rocks. About 0.2 g of rock sample is decomposed with nitric acid. Uranium and thorium are adsorbed by anion-exchange on an Amberlite CG 400 (NO₃ ^–) column from the sample solution adjusted to 2.5M in magnesium nitrate and 0.1M in nitric acid. Uranium and thorium are eluted consecutively with 6.6M nitric acid and 0.1M nitric acid, respectively. Uranium and thorium in the respective effluents are determined spectrophotometrically with Arsenazo III. Results are quoted on uranium and thorium in NBS standard phosphate rock and others.     

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.     

Thorium determination in water samples by liquid scintillation counting after its separation by cloud point extraction

The aim of this study is the separation and pre-concentration of thorium from aqueous solutions by cloud point extraction (CPE) and its the radiometric determination by liquid scintillation counting (LSC). For CPE, tributyl phosphate (TBP) was used as the complexing agent and (1,1,3,3-Tetramethylbutyl)phenyl-polyethylene glycol (Triton X-114) as the surfactant. The radiometric measurements were performed after phase separation by mixing of the surfactant phase with the liquid scintillation cocktail. The effect of experimental conditions such as pH, ionic strength (e.g. [NaCl]) and the presence of other chemical species (e.g. Ca²⁺ and Fe³⁺ ions, and humic acid colloids) on the CPE separation recovery have been investigated at constant reactant ratio (m(TBP)/m(Triton) = 0.1). According to the experimental results the maximum chemical recovery is (60 ± 5)% at pH 3. Regarding the other parameters, generally Ca²⁺ and Fe³⁺ ions as well as the presence of colloidal species in solution (even at low concentrations) results in significant decrease of the chemical recovery of uranium. On the other hand increasing NaCl concentration leads to enhancement of chemical recovery. Generally, the method could be applied successfully for the radiometric determination of thorium in water solutions with relatively increased thorium content.     

Extrapolation studies on adsorption of thorium and uranium at different solution compositions on soil sediments

Study on adsorption of thorium and uranium radionuclides by a soil sediment as a function of ionic composition of Ca, Mg and Na has been carried out. Experimentally determined slopes represents an average of adsorption on soil sediments having different relative affinities for thorium, uranium, calcium and magnesium. Both thorium and uranium were found to be adsorbed to ion-exchange sites together with calcium and magnesium cations as effective competitors An extrapolated equation for the distribution coefficientK _d was formed for both radionuclides thorium and uranium at the specified site where the soil sediments were sampled. The combined cation concentration of both calcium and magnesium in solution correlates linearly with the measuredK _d ^Th,U values.     

On-stream nuclear activation of trace uranium and thorium using a 14 MeV neutron generator

A method for the continuous on-stream determination of trace concentrations of uranium and thorium in flowing streams is developed. The 14 MeV neutron generator was used for irradiation and the delayed neutron counting technique was employed in counting the induced neutron activity. The dependence of the minimum detectable concentration on the irradiation, decay and counting times, liquid flow-rate and the background was studied. At optimal conditions, uranium and thorium concentrations were determined down to 20 and 100 ppm, respectively. The interference of the neutron emitting nuclide^17m O was reduced to an insignificant level by optimizing the decay time.     

The Comprehensive Nuclear Test-Ban-Treaty and the radiological risk to on-site inspection teams

The solvent extraction behavior of thorium traces from the hydrochloric acid media with 1-phenyl-3-methyl-4-benzoyl-5-pyrazolone (PMBP) is described using ²³⁴Th as a tracer. The influence of certain variables such as extractant concentration, acidity, equilibrium time as well as UO₂ ²⁺ ions on the extraction of thorium has been investigated systematically. The back-extraction behavior of thorium from the organic phase has also been tested. The results reveal that the percent extraction of ²³⁴Th decreases with increasing hydrochloric acid concentration and thorium is easily back-extracted with an 4-6 mol/l aqueous HCl solution. At the same time, the effect of thorium extraction with PMBP was tested employing radioisotopes as multi-tracers in the irradiation of natural uranium with 14-15 MeV neutrons. The results show that thorium can be completely separated from a large amount of uranium and most of the other main reaction products.     

Smart thorium and uranium determination exploiting renewable solid-phase extraction applied to environmental samples in a wide concentration range

A smart fully automated system is proposed for determination of thorium and uranium in a wide concentration range, reaching environmental levels. The hyphenation of lab-on-valve (LOV) and multisyringe flow injection analysis (MSFIA), coupled to a long path length liquid waveguide capillary cell, allows the spectrophotometric determination of thorium and uranium in different types of environmental sample matrices achieving high selectivity and sensitivity levels. Online separation and preconcentration of thorium and uranium is carried out by means of Uranium and TEtraValents Actinides resin. The potential of the LOV–MSFIA makes possible the full automation of the system by the in-line regeneration of the column and its combination with a smart methodology is a step forward in automation. After elution, thorium(IV) and uranium(VI) are spectrophotometrically detected after reaction with arsenazo-III. We propose a rapid, inexpensive, and fully automated method to determine thorium(IV) and uranium(VI) in a wide concentration range (0–1,200 and 0–2,000 μg L^-1 Th and U, respectively). Limits of detection reached are 5.9 ηg L^-1 of uranium and 60 ηg L^-1 of thorium. Different water sample matrices (seawater, well water, freshwater, tap water, and mineral water), and a channel sediment reference material which contained thorium and uranium were satisfactorily analyzed with the proposed method.     

Successive uranium and thorium adsorption from Egyptian monazite by solvent impregnated foam

The present work deals with uranium and thorium recovery from the Egyptian monazite sulfate leach liquor using the extraction chromatography technique (solvent impregnated material), where tributylamine (TBA) and di-n-octylamine (DOA) solvents were impregnated onto foam uranium and thorium separate recovery. The calculated theoretical capacities of the latter solvents were about 1.4 gU/g foam and 1.6 gTh/g foam, respectively. The attained uranium and thorium adsorption efficiencies (using ion-exchange columnar technique) were about 75 and 70% of its theoretical capacities, respectively. Using 1 M NaCl–0.1 M H₂SO₄ and 2 M H₂SO₄ as eluent solutions for uranium and thorium from the loaded solvents impregnated foam gave 95.8 and 98.7% elution efficiencies, respectively.     

Alpha spectroscopic analysis of actinides (Th,U and Pu) after separation from aqueous solutions by cation-exchange and liquid extraction

The radioactivity concentration of ²³⁶Pu, ²³²U and ²²⁸Th in aqueous samples has been determined by means of alpha spectroscopy after chemical separation and pre-concentration of the radionuclides by cation exchange and liquid–liquid extraction using the Chelex-100 resin and 30% TBP/dodecan, respectively. Method calibration using a ²³⁶Pu standard solution containing the daughter radionuclides results in a detector efficiency of 18% and in a chemical recovery for cation-exchange which is (30 ± 7)%, (90 ± 5)% and (20 ± 5)% for plutonium, uranium and thorium, respectively. The chemical recovery for liquid–liquid extraction is found to be (60 ± 7)%, (50 ± 5)% and (70 ± 5)%, for plutonium, uranium and thorium, respectively. The differences in the efficiencies can be ascribed to the oxidation states, the different actinides present in solution. Taking into account that the electrodeposition of the radionuclides under study is quantitative, the total method efficiency is calculated to be (18 ± 15)%, (46 ± 7)% and (15 ± 5)%, for plutonium, uranium and thorium, respectively, at the mBq concentration range. The detection limit of the alpha spectrometric system has been found to be 0.2 mBq/L, suggesting that the method could be successfully applied for the radiometric analysis of the studied radionuclides and particularly uranium in aqueous samples.     

Simultaneous Spectrophotometric Determination of Uranium and Thorium Using Arsenazo III by H‐Point Standard Addition Method and Partial Least Squares Regression

Simultaneous determination of uranium and thorium using arsenazo III as a chromogenic reagent at pH 1.70 by H‐point standard addition method (HPSAM) and partial least squares (PLS) calibration is described. Under optimum conditions, the simultaneous determinations of uranium and thorium by HPSAM were performed. The absorbencies at one pair of wavelengths, 649 and 669 nm, were monitored with the addition of standard solutions of uranium. The results of applying the HPSAM showed that uranium and thorium can be determined simultaneously with weight concentration ratios of uranium to thorium varying from 20:1 to 1:15 in the mixed sample. By multivariate calibration methods such as PLS, it is possible to obtain a model adjusted to the concentration values of the mixtures used in the calibration range. In this study, the calibration model is based on absorption spectra in the 600–750 nm range for 25 different mixtures of uranium and thorium. Calibration matrices contained 0.10–21.00 and 0.25–18.5 μg mL^?1 of uranium and thorium, respectively. The RMSEP for uranium and thorium were 0.7400 and 0.7276, respectively. Both proposed methods (HPSAM and PLS) were also successfully applied to the determination of uranium and thorium in several synthetic and real matrix samples.     

Transfer of uranium and thorium from soil to different parts of medicinal plants using SSNTD

The uptake of ²³⁸U and ²³²Th in different parts of some selected plants used in traditional treatment of hypertension and diabetes in south-eastern Morocco (Errachidia area) has been studied using two different types of solid state nuclear track detectors (SSNTDs) LR-115 type II and CR-39. Plant uptake of radionuclides is one of many vectors for introduction of contaminants into the human food chain. Thus, it is critical to understand soil–plant relationships that control nuclide bioavailability. Soil concentrations of uranium ranged from 6.10 to 11.62 ppm, with a mean of 7.90 ppm. Soil concentrations of thorium ranged from 2.70 to 4.80 ppm, with a mean of 3.41 ppm. Mean uranium specific activities were 8.38 Bq kg⁻¹ in root tissue, 5 Bq kg⁻¹ in stem tissue and 6.02 Bq kg⁻¹ in leaf tissue. Mean thorium specific activities were 2.53 Bq kg⁻¹ in root tissue, 1.64 Bq kg⁻¹ in stem tissue and 1.96 Bq kg⁻¹ in leaf tissue. The transfer factors of ²³⁸U and ²³²Th from soil to different parts (root, stem, leaf, seed and fruit) of studied plant samples have been investigated. The transfer factors obtained for root plants were markedly higher than those for leaf, stem, fruit and seed plants. Soil-to-plant transfer factor (TF) is one of the most important parameters to be used in transfer models for predicting the concentration of radionuclides in agricultural crops and for estimating dose impacts to man. This study of uranium and thorium uptake in plants used in traditional medicine is also significant as far as the health hazard effects of uranium and thorium in human being are concerned.     

Determination of trace concentrations of thorium in uranium oxide matrix by epithermal instrumental neutron activation analysis

An epithermal instrumental neutron activation analysis (EINAA) method using cadmium filter was standardized to determine trace concentrations of thorium in four samples of uranium oxide (U₃O₈) samples. Samples and thorium standards, wrapped with cadmium foil, were irradiated at a reactor neutron flux of about 10¹² cm^?2 s^?1. Radioactive assay was carried out using a Compton suppressed anticoincidence gamma ray spectrometer consisting of HPGe-BGO detectors coupled to MCA. Concentrations of thorium in these samples were found to be in the range of 15–72 mg kg^?1. EINAA results were validated by determining thorium concentrations in uranium matrix by standard addition method. EINAA results were compared with those obtained by two wet chemical methods namely ion chromatography (IC) and inductively coupled plasma atomic emission spectrometry (ICP-AES). The results obtained by the three methods were found to be in good agreement, indicating further validity of the proposed EINAA method.     

Simultaneous extraction and preconcentration of uranium and thorium in aqueous samples by new modified mesoporous silica prior to inductively coupled plasma optical emission spectrometry determination

A new synthesized modified mesoporous silica (MCM-41) using 5-nitro-2-furaldehyde (fural) was applied as an effective sorbent for the solid phase extraction of uranium(VI) and thorium(IV) ions from aqueous solution for the measurement by inductively coupled plasma optical emission spectrometry (ICP OES). The influences of some analytical parameters on the quantitative recoveries of the analyte ions were investigated in batch method. Under optimal conditions, the analyte ions were sorbed by the sorbent at pH 5.5 and then eluted with 1.0 mL of 1.0 mol L⁻¹ HNO₃. The preconcentration factor was 100 for a 100 mL sample volume. The limits of detection (LOD) obtained for uranium(VI) and thorium(IV) were 0.3 μg L⁻¹. The maximum sorption capacity of the modified MCM-41 was found to be 47 and 49 mg g⁻¹ for uranium(VI) and thorium(IV), respectively. The sorbent exhibited good stability, reusability, high adsorption capacity and fast rate of equilibrium for sorption/desorption of uranium and thorium ions. The applicability of the synthesized sorbent was examined using CRM and real water samples.     

Insights into the Mechanism of Extraction of Uranium (VI) from Nitric Acid Solution into an Ionic Liquid by using Tri‐n‐butyl phosphate

We present new results on the liquid–liquid extraction of uranium (VI) from a nitric acid aqueous phase into a tri‐n‐butyl phosphate/1‐butyl‐3‐methylimidazolium bis(trifluoromethylsulfonyl)imide (TBP/[C₄mim][Tf₂N]) phase. The individual solubilities of the ionic‐liquid ions in the upper part of the biphasic system are measured over the whole acidic range and as a function of the TBP concentration. New insights into the extraction mechanism are obtained through the in situ characterization of the extracted uranyl complexes by coupling UV/Vis and extended X‐ray absorption fine structure (EXAFS) spectroscopy. We propose a chemical model to explain uranium (VI) extraction that describes the data through a fit of the uranyl distribution ratio D_U. In this model, at low acid concentrations uranium (VI) is extracted as the cationic complex [UO₂(TBP)₂]²⁺, by an exchange with one proton and one C₄mim⁺. At high acid concentrations, the extraction proceeds through a cationic exchange between [UO₂(NO₃)(HNO₃)(TBP)₂]⁺ and one C₄mim⁺. As a consequence of this mechanism, the variation of D_U as a function of TBP concentration depends on the C₄mim⁺ concentration in the aqueous phase. This explains why noninteger values are often derived by analysis of D_U versus [TBP] plots to determine the number of TBP molecules involved in the extraction of uranyl in an ionic‐liquid phase.     

Radiological measurement of phosphate rock and phosphogypsum from fertilizer industries in India

Phosphate deposits are generally characterized by high levels of natural radionuclide concentrations. Natural radionuclides from the uranium and thorium series were measured, using high-resolution gamma-spectrometry in phosphate rock and phosphogypsum samples from the phosphate fertilizer industry in India. Equilibrium was found to be disrupted during the chemical processing of phosphate rock with 83 % of the ²²⁶Ra and only 5 % of ²³⁸U fractionating to phosphogypsum. Activity concentrations of ²³⁸U and ²²⁶Ra in phosphogypsum produced from various fertilizer industries of India showed levels < 1,000 Bq kg^?1 and pose no restriction for use in building/construction material.     

Sorption of uranium by non-living water hyacinth roots

Summary Many studies have shown that water hyacinth (Eichhornia crassipes) roots can be used to accumulate high concentrations of organic as well as inorganic pollutants. They are currently used to remediate aquatic environments and aqueous solutions. In the present study, sorption of uranium from aqueous solutions by using dried roots of water hyacinth has been investigated. The sorption of uranium was examined as a function of initial concentration, pH, weight of roots and contact time. Five different concentrations 20, 40, 60, 80, and 100 μg ^. ml^-1 were used. Sorption proves to be very rapid and depend on pH, weight of roots and concentration of uranium. Maximum sorption capacity of water hyacinth roots was 64,000 U⁶⁺ μg/g. The sorption of uranium by water hyacinth roots follows a Langmuir isotherm.     

Determination of radioactive nuclides of uranium and thorium series and estimation of α-flux in LSI constituent materials

Gamma-rays of nuclides of uranium and thorium series in silicone resin and ceramics were measured with a Ge(Li) detector. The state of radioactive equilibrium was determined by comparing the concentrations of uranium and thorium with the radioactive concentrations of²¹⁴Pb and²¹²Pb. The radioactive equilibrium was attained in silicone resin but not in ceramics. The -flux was calculated from the concentrations of uranium and thorium and their daughter nuclides. The calculated values of -flux agreed with that of -flux measured.