Determination of ultratrace boron concentrations in uranium oxide by isotope dilution-thermal ionization mass spectrometry using a simplified separation procedure

Boron was determined at sub-ppm levels in uranium oxide by ID-TIMS. Following nitric acid dissolution, a solvent extraction method was adapted for extraction of boron by 5% 2-ethylhexane-1,3-diol in chloroform followed by evaporation of the extractant in presence of sodium carbonate and mannitol. This procedure allowed TIMS analysis of boron by monitoring the Na₂BO ₂ ⁺ ions formed from the sodium borate salt in the ion source. Reproducibility of about 1% was obtained for boron determination in the three different uranium oxide samples containing sub-ppm amounts of boron.     

Separation and Recovery of Uranium and Plutonium from Oxalate Supernatant

The separation of uranium and plutonium from oxalate supernatant, obtained after precipitating plutonium oxalate, containing ~10 g/l uranium and 30–100 mg/l plutonium in 3M HNO₃ and 0.10–0.18M oxalic acid solution has been carried out. In one extraction step with 30% TBP in dodecane: ~92% of uranium and ~7% of Pu is extracted. The raffinate containing the remaining U and Pu is extracted with 0.2M CMPO+1.2 M TBP in dodecane and near complete extraction of both the metal ions is achieved. The metal ions are back extracted from organic phases using suitable stripping agents. The recovery of both the metal ions separately is >99%. The uranium species extracted into the TBP phase from the HNO₃+oxalic acid medium was identified as UO₂(NO₃)₂·2TBP.     

Optimization of operating parameters and rate of uranium bioleaching from a low-grade ore

In this study the bioleaching of a low-grade uranium ore containing 480 ppm uranium has been reported. The studies involved extraction of uranium using Acidithiobacillus ferrooxidans derived from the uranium mine samples. The maximum specific growth rate (µ ^max) and doubling time (t _d) were obtained 0.08 h^?1 and 8.66 h, respectively. Parameters such as Fe²⁺ concentration, particle size, temperature and pH were optimized. The effect of pulp density (PD) was also studied. Maximum uranium bio-dissolution of 100 ± 5 % was achieved under the conditions of pH 2.0, 5 % PD and 35 °C in 48 h with the particles of d ₈₀ = 100 μm. The optimum concentration of supplementary Fe²⁺ was dependent to the PD. This value was 0 and 10 g of FeSO₄·7H₂O/l at the PD of 5 and 15 %, respectively. The effects of time, pH and PD on the bioleaching process were studied using central composite design. New rate equation was improved for the uranium leaching rate. The rate of leaching is controlled with the concentrations of ferric and ferrous ions in solution. This study shows that uranium bioleaching may be an important process for the Saghand U mine at Yazd (Iran).     

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.     

Synergistic extraction of uranium(VI) with tri-n-butyl phosphate and i-butyldodecylsulfoxide

Summary The synergistic extraction of uranium(VI) from aqueous nitric acid solution with a mixture of tri-n-butyl phosphate (TBP) and i-butyldodecylsulfoxide (BDSO) in toluene was investigated. The effects of the concentrations of extractant, nitric acid, sodium nitrate and sodium oxalate on the distribution ratios of uranium(VI) have been studied. The values of enthalpy change for the extraction reactions with BDSO, TBP and a mixture of TBP and BDSO in toluene were -23.2±0.8 kJ/mol, -29.2±1.4 kJ/mol and -30.6±0.6 kJ/mol, respectively. It has been found that the maximum synergistic extraction effect occurs when the molar ratio of TBP to BDSO is close to 1. The composition of the complex of the synergistic extraction is UO₂(NO₃)₂ ^. BDSO ^. TBP.     

Removal of uranium from sulfate leach liquor of salcrete deposits using tri-n-octyl amine

A uranyl sulfate leach liquor obtained by uranium leaching of a technological sample of salcrete deposits of Gabal Qatrani ore was subjected to uranium extraction using the liquid–liquid technique. Uranium was effectively extracted from sulfate leach liquor by [(10 %) tri-n-octylamine (TOA)] dissolved in xylene as a diluent. The extraction efficiency was markedly enhanced as the concentration of TOA increases from 1 to 10 %. The relevant factors controlling the extraction process of uranium using tri-n-octylamine were studied. These factors include the effect of diluents used, TOA concentration, contact time, settling time and phase ratio (O/A) v/v. The optimum extraction conditions were chosen. Stripping of uranium from the loaded TOA has been carried out using 5 % Na₂CO₃ as an effective stripping agent. More than 97 % of uranium was extracted by 10 % TOA, at contact time 10 min, settling time 5 min, phase ratio (V_O/V_A) 1/1 and at room temperature. The feasibility of using the TOA for preconcentration-separation of uranium was assessed by stripping studies. The loaded uranium onto TOA has been stripped by 100 % when using 5 % Na₂CO₃ as an efficient eluting agent at 15 min contact time, 5 min settling time and phase ratio (O/A) 2/1.     

Extraction-separation of Eu(III) and Th(IV) ions from nitrate media into a room-temperature ionic liquid

Application of a room-temperature ionic liquid (RTIL), 1-butyl-3-methylimidazolium hexafluorophosphate ([C₄mim⁺][PF₆ ^?]), in the extraction of Eu(III) and Th(IV) ions from nitrate media using tri-n-octylphosphine oxide (TOPO) as extractant is investigated. The results are compared with those obtained in dichloromethane. It is shown that the europium ions are extracted via a solvation mechanism by formation of [Eu(TOPO) ₃ ³⁺ ](NO₃ ^?)₃ species in both [C₄mim⁺][PF₆ ^?] and dichloromethane. Nevertheless, application of the studied RTIL makes a significant improvement in the extraction efficiency of europium ions. A different attitude was observed for the extraction of thorium ions. In fact, although the analysis of the extraction data of these ions from sodium nitrate solutions confirms the formation of [Th(TOPO) ₃ ⁴⁺ ](NO₃ ^?)₄ species in dichloromethane, the extraction of these ions into the ionic liquid was not affected by the presence of TOPO. This latter outcome states the process takes place by a cation-exchange mechanism. It is found that the extraction of thorium ions diminishes in the presence of nitric acid. Interestingly, in contrast to the results observed in the extraction of thorium ions from sodium nitrate solutions, TOPO shows a co-operative effect on the extraction of these ions from nitric acid media. This allows considering the mechanism of the extraction of Th⁴⁺ ions from nitric acid media as a mixed ion exchange-solvation mechanisms by formation of [Th(TOPO)⁴⁺](NO₃ ^?)(PF₆ ^?)₃ species.     

Development of an integrated flow injection system for the electro-oxidative leaching of uranium from geological samples and its spectrophotometric determination with Arsenazo III

This work proposes a new procedure for on-line electro-oxidative leaching and spectrophotometric determination of uranium in ore samples. By associating a conventional flow injection system, used for uranium determination with Arsenazo III, with an on-line system for electro-oxidative leaching, a fully integrated system was assembled. The systems were integrated after achieving optimum conditions for uranium determination and leaching. According to the results obtained in the present work, a current density of 280 mA cm⁻² generated enough hypochlorite ions in the electrolyte solution (3.6 mol L⁻¹ HCl + 2% (w/v) NaCl) to promote quantitative oxidation of U(IV) to U(VI) thus improving the extraction efficiency. The slurry density did not significantly affect the performance of the system and the increasing temperature resulted in a decrease in extraction efficiency. This methodology was applied in the determination of U₃O₈ in four ore samples and the results obtained agreed with those obtained by ICP-MS after conventional wet acid digestion of the samples.     

Preparation of carbon coated Fe3O4 nanoparticles for magnetic separation of uranium

Uranium(VI) was removed from aqueous solutions using carbon coated Fe₃O₄ nanoparticles (Fe₃O₄@C). Batch experiments were conducted to study the effects of initial pH, shaking time and temperature on uranium sorption efficiency. It was found that the maximum adsorption capacity of the Fe₃O₄@C toward uranium(VI) was ∼120.20 mg g⁻¹ when the initial uranium(VI) concentration was 100 mg L⁻¹, displaying a high efficiency for the removal of uranium(VI) ions. Kinetics of the uranium(VI) removal is found to follow pseudo-second-order rate equation. In addition, the uranium(VI)-loaded Fe₃O₄@C nanoparticles can be recovered easily from aqueous solution by magnetic separation and regenerated by acid treatment. Present study suggested that magnetic Fe₃O₄@C composite particles can be used as an effective and recyclable adsorbent for the removal of uranium(VI) from aqueous solutions.     

Extraction of uranium by amine, amide and benzamide grafted covalently on silica gel

Organic complexing moieties such as amine, 2°-amide and benzamide functional groups were covalently linked to silica gel by performing organomodification on commercially available silica gel. The extraction of uranium as a function of pH, time, concentration of uranium and the effect of ions such as Fe²⁺, Co²⁺, Ni²⁺ and CO₃ ^2- on the distribution coefficient of uranium by sorbent was studied. The data was fitted into Langmuir adsorption isotherm. The selectivity of the sorbents towards uranium were found to decrease in the order gel-amine >> gel-benzamide ≅ gel-2°-amide at all pHs. The presence of metal ions such as Fe²⁺, Co²⁺, Ni²⁺ and CO₃ ^2- were found to decrease the distribution coefficients (K _d, ml/g) of uranium and the decrease was very high when Fe²⁺ was present. The performance of the sorbent, gel-amine, under a given column condition was tested by following the breakthrough curve of uranium up to C/C ₀ = 0.025. The sorbent was found to be good for the quantitative pre-concentration of uranium from a large amount of sodium. This revised version was published online in July 2006 with corrections to the Cover Date.     

A fast and sensitive method for the determination of uranium in the Thorex Process streams

This paper presents a simple, rapid and sensitive radiometric method for the determination of uranium in Thorex Process stream containing large amount of thorium. This method involves the extraction of uranium into 0.05M tri-n-octyl phosphine oxide (TOPO) in xylene at 2M HNO₃. The extraction of thorium is prevented by masking them with suitable quantity of fluoride ions. The optimum experimental parameters for extraction of ²³³U were evaluated and using the most suitable experimental conditions the extracted uranium is radiometrically determined by α-counting in proportional counter with a prior knowledge of specific activity of uranium. Simultaneously in the same sample uranium was determined by spectrophotometric method using 2-(5bromo-2 pyridylazo)-5-diethylaminophenol (Bromo-PADAP) as chromogenic reagents. Simulated as well as actual samples of dissolver, conditioner and raffinate tank of Thorex stream have been analyzed by both these methods. The method was tested for as low as 0.15 μg of uranium and the results of these analyses were found to be satisfactory within the experimental limits.     

Ion‐pair cloud‐point extraction: A new method for the determination of water‐soluble vitamins in plasma and urine

A novel, simple, and effective ion‐pair cloud‐point extraction coupled with a gradient high‐performance liquid chromatography method was developed for determination of thiamine (vitamin B₁), niacinamide (vitamin B₃), pyridoxine (vitamin B₆), and riboflavin (vitamin B₂) in plasma and urine samples. The extraction and separation of vitamins were achieved based on an ion‐pair formation approach between these ionizable analytes and 1‐heptanesulfonic acid sodium salt as an ion‐pairing agent. Influential variables on the ion‐pair cloud‐point extraction efficiency, such as the ion‐pairing agent concentration, ionic strength, pH, volume of Triton X‐100, extraction temperature, and incubation time have been fully evaluated and optimized. Water‐soluble vitamins were successfully extracted by 1‐heptanesulfonic acid sodium salt (0.2% w/v) as ion‐pairing agent with Triton X‐100 (4% w/v) as surfactant phase at 50°C for 10 min. The calibration curves showed good linearity (r² > 0.9916) and precision in the concentration ranges of 1‐50 μg/mL for thiamine and niacinamide, 5–100 μg/mL for pyridoxine, and 0.5–20 μg/mL for riboflavin. The recoveries were in the range of 78.0–88.0% with relative standard deviations ranging from 6.2 to 8.2%.     

Direct determination of U(VI) in TBP-kerosene extracts using first derivative ultraviolet spectroscopy

Summary The extractive first order derivative spectrophotometry is a selective method for the separation and determination of U(VI) using tri-n-butyl phosphate (TBP), which combines the roles of solvent and complexing agent. The complex is formed by extracting U(VI) from an aqueous 6M sodium nitrate solution at initial pH 3.0 into a 25% solution of TBP in kerosene. This extraction also separates U(VI) from many diverse ions that interfere. After extraction, the determination of uranium shows good accuracy and precision with relative standard deviation of 1.5% (n = 5) at 20 ppm using zero-order spectrum at l_max = 250 nm. Calibration curve was also found to obey Beer's law in the range of 10-100 ppm with 3.33 ppm detection limit. However, these accuracy and precision have been improved to give relative standard deviation of 0.7% (n = 5) at 20 ppm with a lower detection limit of 2.24 ppm using the first-derivative spectrum at l = 263 nm comparing to the normal one.     

Nitrate ion transport across TBP-kerosene oil supported liquid membranes coupled with uranyl ions

The role of nitrate ions in uranyl ions transport across TBP-kerosene oil supported liquid membranes (SLM) at varied concentrations of HNO₃ and NaNO₃ has been studied. It has been found that nitrate ions move faster compared to uranyl ions at the uranium feed solution concentrations studied. The nitrate to uranyl ions flux ratio vary from 355 to 2636 under different chemical conditions. At low uranium concentration the nitrate ions transport as HNO₃ · TBP, in addition to as UO₂(NO₃)₂ · 2TBP type complex species. The flux of nitrate ions is of the order of 12.10 · 10^–3 mol · m^–2 · s^–1 compared to that of uranium ions (4.56 · 10^–6 mol · m^–2 · s^–1). The permeability coefficient of the membrane for nitrate ions varies with chemical composition of the feed solution and is in the order of 2.5 · 10^–10 m^–2 · s^–1. The data is useful to estimate the nitrate ions required to move a given amount of uranyl ions across such an SLM and in simple solvent extraction.     

Electrosorption of uranium ions on activated carbon fibers

A study on the electrosorption of uranium (U(VI)) ions onto a porous activated carbon fiber was performed to treat lagoon sludge containing 100 mg/L uranium and high concentration of chemical salts composed 3.8% NaNO₃, 19.8% NH₄NO₃, 1.9% Ca(NO₃)₂. The applied negative potential increased the adsorption kinetics and capacity in comparison to the open-circuit potential adsorption for uranium ions. When applying potential at −0.9 V (vs. Ag/AgCl) and pH 4, above 99% of the uranium is selectively removed from the 100 mg/L influent by electrosorption, and the cumulative amount of uranium for 50 h is about 600 mg_uranium/g_ACF. The high selectivity of elctrosorption process for uranium was probably caused by the difference of charge density of cations. More than 99% of adsorbed uranium ions was desorbed at a potential of +1.2 V and pH 3. The electrosorption of uranium onto the porous activated carbon fiber electrode is due to an ion exchange type reaction between the uranium ions and surface acid groups on carbon surface. Cyclic electrosorption test consisting of adsorption and desorption step shows that the activated carbon fiber electrode is easily regenerated in situ, indicating it is a reversible process.     

Solvent Extraction and Spectrophotometric Determination of Uranium Using α-Benzoin Oxime as Chelating Agent

Solvent extraction of uranium by a chloroform solution of α-benzoin oxime was studied and the formation of uranium-α-benzoin oxime complex described. The uranium-α-benzoin oxime complex has two maximum absorbance at 350 nm and 427 nm. A constant absorbance was obtained for 1 × 10^?3 M uranium when the concentration of α-benzoin oxime was higher than 1.2 × 10^?2 M. Ions of Ag⁺, Fe³⁺, V⁵⁺, Cu²⁺, and W⁶⁺ were found to have interference. A solution containing 0.1–10 mg uranium at pH 1.6–6.8 was extracted with 1 × 10^?3 M ?2 × 10^?3 M α-benzoin oxime solution in chloroform. With single extraction, the maximum amount of uranium passing into organic layer was at least 98%. Under this condition the presence of diverse ions except V⁵⁺ does not significantly interfere the extraction of uranium.     

<Superscript>99m</Superscript>Tc production via the (<Emphasis Type="Italic">γ, n</Emphasis>) reaction on natural Mo

In this paper, cheap liquorice residue was used to prepare activated carbon (AC), thioacetamide (TAA) was used to modify the AC, and the adsorption experiments were conducted in the simulated acid radioactive wastewater with low uranium concentration to study the adsorption behavior and mechanism for uranium by TAA modified AC (TAA–AC). The removal efficiency by TAA–AC was 92.1–98.2% from the 1 mg L^?1 uranium solution at pH 2–6. The adsorption equilibrium data were well fitted by Dubinin–Radushkevich model, and the maximum adsorption capacity was estimated to be 340 mg g^?1. TAA–AC showed an enhanced selectivity for uranium in the presence of competitive ions. Furthermore, the adsorption experiments were conducted in the actual acid radioactive wastewater with low uranium concentration from an in situ leach uranium mine. The high adsorption rate (98.3%) and selectivity (K_d?=?3.78×10⁴ mL g^?1) for uranium were observed in the actual acid radioactive wastewater, and the adsorption rate was found to maintain 96.2% over six cycles of adsorption–desorption.     

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.     

Electrochemical-Mediated Regenerable FeII Active Sites for Efficient Uranium Extraction at Ultra-Low Cell Voltage

Nano-reduced iron (NRI) is a promising uranium adsorbent due to its strong reducibility and good selectivity, but it still faces the challenges of slow kinetics, limited and non-renewable active sites. In this work, we realized high efficiency uranium extraction under ultra-low cell voltage (−0.1 V) in seawater with 20 ppm UO₂(NO₃)₂ solution by coupling electrochemical mediated Fe^II/Fe^III redox and uranium extraction. The adsorption capacity and extraction efficiency of NRI after electrochemical uranium extraction (EUE) could reach 452 mg/g and 99.1 %, respectively. Combined with quasi-operando/operando characterization technologies, we clarified the mechanism of EUE and revealed that continuously regenerating Fe^II active sites by electroreduction could significantly enhance the property of EUE. This work here provides a new electrochemical mediated and low energy consumption uranium extraction strategy which also provides a reference for other metal resource recovery.     

Solid Phase Extraction of Uranium by Naphthalene‐Methyltrioctylammonium Chloride and Arsenazo(III) Adsorbent and Subsequent Spectrophotometric Determination

A simple and effective method has been presented for the preconcentration of uranium by solid phase extraction. For this purpose arsenazo(III) supported on naphthalene‐methyltrioctylammonium chloride was used as an adsorbent and uranium solution at pH 3.5 with flow rate of 1 mL·min⁻¹ was passed through the column. Therefore, uranium‐arsenazo(III) complex was formed onto column. Uranium was quantitatively eluted with 5 mL of a 0.1% ammonium tetraphenylborate and determined by spectrophotometric method at 652 nm. Several parameters such as pH, amount of reagents, sample volume, etc. were investigated. The effect of diverse ions on the preconcentration has also been studied and the optimized conditions developed have been utilized for the trace determination of uranium. A preconcentration factor of 100 was achieved. The relative standard deviation (N=8) was 0.5% for 3 ng· mL⁻¹ of uranium. The three sigma detection limit (36) was 0.045 ng·mL⁻¹