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.     

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).     

Sorption of uranium on lead hydroxyapatite

The uranium sorption from diluted aqueous solution onto lead hydroxyapatite was studied by using a batch-mode technique and the fluorimetric determination of uranium mass concentration. Partially crystallised lead hydroxyapatite [Pb₁₀(PO₄)₆(OH)₂] was obtained by direct precipitation and mild heating. This material presents very high specific surface, which is the key factor in the sorption of uranium from diluted solution. This material has a high ability to remove uranium (K _d,max from 5,661 to 18,833 ml/g, at 4 and 60 °C, respectively) in the chosen setup conditions (initial concentration of uranium 5 × 10^?6 M and pH 5.65).     

Estimation of distribution coefficient of uranium around a uranium mining site

Distribution coefficient (K _d) of uranium and its daughter products are very important for migration study around uranium mining sites. Since the distribution coefficient depends very much on the soil and groundwater chemistry, generation of site specific K _d is very important. In the literature there is a large variation of K _d values of uranium. For realistic prediction of contaminant migration, literature K _d value is not very effective. So site specific experimental K _d values are required. The present study emphasizes on the estimation of site specific distribution coefficient for uranium around a uranium mining site. The soil and groundwater parameters which affect the K _d value of uranium have also been estimated. Soil and groundwater samples from nine locations around Turamdih uranium mining site were collected and chemically characterized for various parameters. The distribution coefficient of uranium in top and one meter depth soil samples from above locations were estimated using laboratory batch method. The distribution coefficient of uranium varies from 69 ± 4 to 5524 ± 285 l/kg. No significant difference in uranium K _d values was observed for top and one meter depth soil samples. In the top and one meter depth soil samples uranium K _d values vary from 129 ± 8 to 5524 ± 285 and 69 ± 4 to 3862 ± 195 l/kg respectively. For the estimation of distribution coefficient of uranium different parameters like equilibration time, solid to solution ratio, method of tracer addition to solution, solid-solution separation method etc. have been optimized. The distribution coefficient of uranium determined in the present study will be used for the migration study of uranium around uranium mining sites.     

Bioleaching of low grade uranium ore containing pyrite using A. ferrooxidans and A. thiooxidans

A process of uranium extraction from ore containing 3.1 % pyrite by bacterial leaching was investigated in shaken flasks during 90 days. The highest uranium recovery amounting to 85.1 % was obtained using binary mixture of Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans that was exceeding results obtained by traditional acid leaching technique up to 27 %. High uranium recovery was founded to be due to the high degree of pyrite dissolution that can be readily achieved by bacterial leaching (up to 98.0 %).     

Uranium (VI) recovery from saline environment by a marine unicellular cyanobacterium, Synechococcus elongatus

Sequestration of uranium from simulated sea water and reverse osmosis concentrates by the marine cyanobacterium, Synechococcus elongatus was assessed. Short term experiments established removal of 90–98 % uranium by the strain from simulated sea water containing 13 nM uranyl carbonate at pH 7.8, resulting in a loading of 7–42 μg U g^?1 over a period of 1–5 days respectively. Long term experiments involving repeated exposure of Synechococcus biomass to fresh simulated sea water every third day, showed a loading of 2,960 μg U g^?1 in 4 weeks. Nearly 85–90 % of cell bound uranium could be desorbed using 0.1 N HCl. The organism could sequester uranium (13,306 μg U g^?1 in 24 h) from aqueous solutions supplemented with 0.6 M NaCl and 21 μM [UO₂(CO₃)₂]^2? at pH 7.8. The results demonstrate noteworthy potential of this organism for harnessing uranium from marine environments.     

Spectroscopic determination of U(VI) species sorbed by the Chlorella (Chlorella pyrenoidosa) fresh water algae

The green algae Chlorella (Chlorella pyrenoidosa) have the ability to bind high amounts of uranium(VI) in the pH range from 3 to 6. At pH 3 up to 20 % of the uranium is bound by the algal cells whereas the uranium removal by algal cell is almost complete at pH 5 and 6 in the concentration range of 4 × 10^?4 to 1.6 × 10^?3 M. Sorption capacities are in the range of 300–350 mg g^?1 and 250–280 mg g^?1 for fresh water and seawater respectively. Concentration of uranium was measured by inductively coupled plasma optical emission spectroscopy (ICP-OES) by using two different emission spectral lines at 409.014 and 424.167 nm. Environmental scanning electron microscopy (ESEM) complimented with energy dispersive X-ray (EDX) is used to characterize the binding sites of uranyl species on algal cell in the selected pH range. The micrographs show a regular distribution of U(VI) on the cell surface. Attenuated total reflectance-fourier transform infrared (ATRFTIR) spectrum of Chlorella indicates that the binding of U(VI) either to phosphodiesters (P–O–aryl/P–O–alkyl), and combination of amine, secondary amine and imine = NH respectively. These sites in Chlorella groups are mainly responsible for the removal and binding of U(VI) by formation of organic and/or inorganic uranyl phosphates.     

Synthesis of phosphorus-modified poly(styrene-co-divinylbenzene) chelating resin and its adsorption properties of uranium(VI)

A new phosphorus-modified poly(styrene-co-divinylbenzene) chelating resin (PS–N–P) was synthesized by P,P-dichlorophenylphosphine oxide modified commercially available ammoniated polystyrene beads, and characterized by Fourier transform infrared spectroscopy and elemental analysis. The adsorption properties of PS–N–P toward U(VI) from aqueous solution were evaluated using batch adsorption method. The effects of the contact time, temperature, pH and initial uranium concentration on uranium(VI) uptake were investigated. The results show that the maximum adsorption capacity (97.60 mg/g) and the maximum adsorption rate (99.72 %) were observed at the pH 5.0 and 318 K with initial U(VI) concentration 100 mg/L and adsorbent dose 1 g/L. Adsorption equilibrium was achieved in approximately 4 h. Adsorption kinetics studied by pseudo second-order model stated that the adsorption was the rate-limiting step (chemisorption). U(VI) adsorption was found to barely decrease with the increase in ionic strength. Equilibrium data were best modeled by the Langmuir isotherm. The thermodynamic parameters such as ?G ₀, ?H ₀ and ?S ₀ were derived to predict the nature of adsorption. Adsorbed U(VI) ions on PS–N–P resin were desorbed effectively (about 99.39 %) by 5 % NaOH–10 % NaCl. The synthesized resin was suitable for repeated use.     

Quasirelativistic energy-consistent 5f-in-core pseudopotentials for pentavalent and hexavalent actinide elements

Quasirelativistic energy-consistent 5f-in-core pseudopotentials modeling pentavalent (5f ^n?2 occupation with n = 2–6 for Pa–Am) and hexavalent (5f ^n?3 occupation with n = 3–6 for U–Am) actinides have been adjusted. Energy-optimized (6s5p4d) and (7s6p5d) valence basis sets contracted to polarized double- to quadruple-zeta quality as well as 2f1g correlation functions have been derived. Corresponding smaller basis sets (4s4p3d) and (5s5p4d) suitable for calculations on actinide(V) and actinide(VI) ions in crystalline solids form subsets of these basis sets designed for calculations on neutral molecules. Calculations using the Hartree–Fock and the coupled-cluster method with single and double excitation operators and a perturbative estimate of triple excitations for actinide pentafluorides show satisfactory agreement with calculations using 5f-in-valence pseudopotentials and experimental data, respectively. However, in the hexavalent case the 5f-in-core approximation seems to reach its limitations except for hexavalent uranium (5f⁰), where results for both uranium hexafluoride and the uranyl ion deviate only slightly from the 5f-in-valence reference data.     

Properties of PAN-TBP extraction chromatographic material

Three production routes of the preparation of a solid extractant based on tributylphosphate (TBP) embedded in the polyacrylonitrile matrix (PAN) have been studied. The method of direct PAN coagulation with TBP was found to be not viable due to the significant TBP solubility in the coagulation bath. The most suitable PAN-TBP solid extractant was prepared by the well-known impregnation method of ready-made neat PAN beads. The kinetics of uranium extraction from 3 mol L^?1 HNO₃, the effect of nitrate and nitric acids concentrations on the value of weight distribution coefficients D _g as well as the uranium “extraction isotherm” were determined for this material. Uranium extraction was rather fast, approximately 1 h was sufficient for the equilibrium achievement. Capacity for the uranium uptake, measured in batch experiments on PAN-TBP for 0.048 mol L^?1 of uranium in 3 mol L^?1 nitric acid, was found to be q = 0.363 mmol g^?1 (58 % of the theoretical capacity). It was concluded that PAN-TBP material behaves like TBP in liquid–liquid extraction. Extraction capacity determined in column experiments was lower (by about 23 %) than expected from the “extraction isotherm” due to the TBP leaching out of the column. The thus prepared material is therefore not very suitable for multicycle extraction and stripping and can be used once, particularly for the analytical purposes.     

Sorption of uranium using silica gel with benzoylthiourea derivatives

Benzoylthiourea derivatives (N,N-diphenyl-N′-(3-methylbenzoyl)thiourea and diphenyl-N′-(4-methylbenzoyl)thiourea) were impregnated onto silica gel. The preconcentration of uranium(VI) from aqueous solution was investigated. Extraction conditions were optimized in batch method prior to determination by uv–visible absorption spectrometry using arsenazo(III). The optimum pH for quantitative adsorption was found as 3–7. Quantitative recovery of uranium (VI) was achieved by stripping with 0.1 mol L^?1 HCl. Equilibration time was determined as 30 min for 99% sorption of U(VI). Under optimal conditions, dynamic linear range of for U(VI) was found as 0.25–10 μg mL^?1. The relative standard deviation as percentage and detection limit were 5.0% (n = 10) for 10 μg mL^?1 U(VI) solution and 8.7 ng mL^?1, respectively. The method was employed to the preconcentration of U(VI) ions in soil and tap water samples.     

Adsorption of uranium from aqueous solution using biochar produced by hydrothermal carbonization

The ability of biochar produced by hydrothermal carbonization (HTC) has been explored for the removal and recovery of uranium from aqueous solutions. The micro-morphology and structure of HTC were characterized by Fourier transform infrared spectroscopy and scanning electron microscopy. The influences of different experimental parameters such as solution pH, initial concentration, contact time, ionic strength and temperature on adsorption were investigated. The HTC showed the highest uranium sorption capacity at initial pH of 6.0 and contact time of 50 min. Adsorption kinetics was better described by the pseudo-second-order model and adsorption process could be well defined by the Langmuir isotherm. The thermodynamic parameters, △G°(298 K), △H° and △S° were determined to be ?14.4, 36.1 kJ mol^?1 and 169.7 J mol^?1 K^?1, respectively, which demonstrated the sorption process of HTC towards U(VI) was feasible, spontaneous and endothermic in nature. The adsorbed HTC could be effectively regenerated by 0.05 mol/L HCl solution for the removal and recovery of U(VI). Complete removal (99.9 %) of U(VI) from 1.0 L industry wastewater containing 15.0 mg U(VI) ions was possible with 2.0 g HTC.     

Sorption study of uranium on carbon spheres hydrothermal synthesized with glucose from aqueous solution

The ability of oxygen-rich carbon spheres (CSs) produced by hydrothermal carbonization with the glucose has been explored for the removal and recovery of uranium from aqueous solutions. The micro-morphology and structure of CSs were characterized by FT-IR and SEM. The influences of different experimental parameters such as solution pH, initial concentration, contact time, ionic strength and temperature on adsorption were investigated. The CSs showed the highest uranium sorption capacity at initial pH of 6.0 and contact time of 25 min. Adsorption kinetics was better described by the pseudo-second-order model and adsorption process could be well defined by the Langmuir isotherm. The thermodynamic parameters, △G°(298 K), △H° and △S° were determined to be ?16.88, 12.09 kJ mol^?1 and 197.87 J mol^?1 K^?1, respectively, which demonstrated the sorption process of CSs towards U(VI) was feasible, spontaneous and endothermic in nature. The adsorbed CSs could be effectively regenerated by 0.05 mol/L HCl solution for the removal and recovery of U(VI). Complete removal (99.9 %) of U(VI) from 1.0 L industry wastewater containing 15.0 mg U(VI) ions was possible with 3.0 g CSs.     

Enhancement of uranium(VI) biosorption by chemically modified marine-derived mangrove endophytic fungus Fusarium sp. #ZZF51

Fusarium sp. #ZZF51, mangrove endophytic fungus originated from South China Sea coast, was chemically modified by formaldehyde, methanol and acetic acid to enhance its affinity of uranium(VI) from waste water. The influencing factors about uranium(VI) adsorption such as contact time, solution pH, the ratio of solid/liquid (S/L) and initial uranium(VI) concentration were investigated, and the suitable adsorption isotherm and kinetic models were determined. In addition, the biosorption mechanism was also discussed by FTIR analysis. Experimental results show that the maximum biosorption capacity of formaldehyde-treated biomass for uranium(VI) at the optimized condition of pH 6.0, S/L 0.6 and equilibrium time 90 min is 318.04 mg g^?1, and those of methanol-treated and HAc-treated biomass are 311.95 and 351.67 mg g^?1 at the same pH and S/L values but different equilibrium time of 60 and 90 min, respectively. Thus the maximum biosorption capacity of the three kind of modified biomass have greatly surpassed that of the raw biomass (21.42 mg g^?1). The study of kinetic exhibits a high level of compliance with the Lagergren’s pseudo-second-order kinetic models. Langumir and Freundlich models have proved to be well able to explain the sorption equilibrium with the satisfactory correlation coefficients higher than 0.96. FTIR analysis reveals that the carboxyl, amino and hydroxyl groups on the cell wall of Fusarium sp. #ZZF51 play an important role in uranium(VI) biosorption process.     

Determination of Ultra Trace Amounts of Uranium (VI) by Adsorptive Stripping Voltammetry Using L-3-(3, 4-dihydroxy phenyl) Alanine as a Selective Complexing Agent

Abstract

The spectrophotometric behavior of uranium (VI) with L-3-(3, 4-dihydroxy phenyl) alanine (LDOPA) reagent revealed that the uranium can form a ML₂ complex with LDOPA in solution. Thus a highly sensitive adsorptive stripping voltammetric protocol for measuring of trace uranium, in which the preconcentration was achieved by adsorption of the uranium-LDOPA complex at hanging mercury drop electrode (HMDE), is described. Optimal conditions were found to be a 0.02 M ammonium buffer (pH 9.5) containing 2.0 × 10^?5 M (LDOPA), an accumulation potential of ? 0.1 V (versus Ag/AgCl) and an accumulation time of 120 sec.

The peak current and concentration of uranium accorded with linear relationship in the range of 0.5–300 ng ml^?1. The relative standard deviation (at 10 ng ml^?1) is 3.6% and the detection limit is 0.27 ng ml^?1. The interference of some common ions was studied. Applicability to different real samples is illustrated. The attractive behavior of this reagent holds great promise for routine environmental and industrial monitoring of uranium.     

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.     

Removal, preconcentration and spectrophotometric determination of U(VI) from water samples using modified maghemite nanoparticles

Arsenazo III modified maghemite nanoparticles (A-MMNPs) was used for removing and preconcentration of U(VI) from aqueous samples. The effects of contact time, amount of adsorbent, pH and competitive ions was investigated. The experimental results were fitted to the Langmuir adsorption model in the studied concentration range of uranium (1.0 × 10^?4–1.0 × 10^?2 mol L^?1). According to the results obtained by Langmuir equation, the maximum adsorption capacity for the adsorption of U(VI) on A-MMNPs was 285 mg g^?1 at pH 7. The adsorbed uranium on the A-MMNPs was then desorbed by 0.5 mol L^?1 NaOH solution and determined spectrophotometrically. A preconcentration factor of 400 was achieved in this method. The calibration graph was linear in the range 0.04–2.4 ng mL^?1 (1.0 × 10^?10–1.0 × 10^?8 mol L^?1) of U(VI) with a correlation coefficient of 0.997. The detection limit of the method for determination of U(VI) was 0.01 ng mL^?1 and the relative standard deviation (R.S.D.) for the determination of 1.43 and 2.38 ng mL^?1 of U(VI) was 3.62% and 1.17% (n = 5), respectively. The method was applied to the determination of U(VI) in water samples.     

Separation and inductively coupled plasma optical emission spectrometric (ICP-OES) determination of trace impurities in nuclear grade uranium oxide

A simple and rapid inductively coupled plasma optical emission spectrometric method for the determination of trace level impurities like REEs, Y, Cd, Co, V, Mg, B, Ca, Cr, Mn, Ni, Cu, Zn and Al in uranium oxide samples is described. The method involves solvent extraction separation of uranium from 6 M HNO₃ acid medium using di (2-ethyl hexyl) phosphoric acid in toluene, which selectively separates uranium leaving behind the trace impurities in the aqueous media, for quantification by ICP-OES. The method has been applied to few synthetic samples and five certified reference U₃O₈ standards. The results are compared with other methods such as TBP-TOPO-CCl₄ and 1,2 diaminocyclohexane N,N,N′,N′-tetra acetic acid (CyDTA)–ammonium hydroxide (NH₄OH) separation techniques. Different experimental parameters like contact time, acidity, aqueous to organic ratio etc., are optimized for better and accurate results. The method is simple, rapid, accurate and precise for all the studied elements, showing a relative standard deviation of 1.5–12.0% at trace levels studied (5.5–12% at 0.2 μg/mL and 1.5–6.0% at 0.5 μg/mL), on the synthetic samples prepared from high purity oxides.     

Uranium concentration in blood samples of Southern Iraqi leukemia patients using CR-39 track detector

The simple and effective technique of fission track etch has been applied to determine trace concentration of uranium in human blood samples taken from two groups of male and female participants: leukemia patients and healthy subjects group. The blood samples of leukemia patients and healthy subjects were collected from three key southern governorates namely, Basrah, Muthanna and Dhi-Qar. These governorates were the centers of intensive military activities during the 1991 and 2003 Gulf wars, and the discarded weapons are still lying around in these regions. CR-39 track detector was used for registration of induced fission tracks. The results show that the highest recorded uranium concentration in the blood samples of leukemia patients was 4.71 ppb (female, 45 years old, from Basrah) and the minimum concentration was 1.91 ppb (male, 3 years old, from Muthanna). For healthy group, the maximum uranium concentration was 2.15 ppb (female, 55 years old, from Basrah) and the minimum concentration was 0.86 ppb (male, 5 years old, from Dhi-Qar). It has been found that the uranium concentrations in human blood samples of leukemia patients are higher than those of the healthy group. These uranium concentrations in the leukemia patients group were significantly different (P < 0.001) from those in the healthy group.     

An investigation on the subcellular distribution and compartmentalization of uranium in Phaseolus vulgaris L.

Phaseolus vulgaris L. (bean) is a promising species for uranium rhizofiltration with high tolerance and accumulation ability. To further understand the mechanisms involved in uranium tolerance and detoxification, the present study investigated subcellular distribution and compartmentalization of uranium in bean. Subcellular fractionation of uranium containing tissues indicated that both in roots and shoots, the concentration of uranium in each subcellular fractions increased evidently with increasing solution uranium level, and the majority of uranium was located in cytosol and cell wall fraction, while a minor part of uranium associated with the organelle fraction. Meanwhile, with uranium concentration increasing from 100 to 1,000 μM, the proportion of uranium distribution in cytosol fraction was decreased but it was increased in cell wall fraction. However, the proportion of uranium distribution in organelle fraction is always less than 5 %. These results suggest that stored in the cytosol (such as uranium compartmentalization with organo-ligands in vacuole) and bound to the cell walls (may be integrated with polyose and protein) might play an important role in tolerance and detoxification of uranium in bean.