Rapid and interference free determination of ultra trace level of uranium in potable water originating from different geochemical environments by ICP-OES

Direct determination of uranium in the concentration range of 8 μg L⁻¹ to mg L⁻¹ in water samples originating from different geochemical environments has been done using Inductively Coupled Plasma-Optical Emission Spectroscopy (ICP-OES). Uranium detection with 2–3% RSD (relative standard deviation) has been achieved in water samples by optimizing the plasma power, argon and sheath gas flow. These parameters were optimized for three different emission lines of uranium at 385.958, 409.014 and 424.167 nm. Interference arising due to the variation in concentration of bicarbonate, sodium chloride, calcium chloride, Fe and dissolved organic carbon (DOC) on the determination of uranium in water samples was also cheeked as these are the elements which vary as per the prevailing geochemical environment in groundwater samples. The concentration of NaHCO₃, CaCl₂ and NaCl in water was varied in the range 0.5–2.0%; whereas Fe ranged between 1 and 10 μg mL⁻¹ and DOC between 0.1–1%. No marked interference in quantitative determination of uranium was observed due to elevated level of NaHCO₃, CaCl₂ and NaCl and Fe and DOC in groundwater samples. Concentration of uranium was also determined by other techniques like adsorptive striping voltametry (AdSv); laser fluorimetry and alpha spectrometry. Results indicate distinct advantage for uranium determination by ICP-OES compare to other techniques.     

Separation of uranium from different uranium oxide matrices employing supercritical carbon dioxide extraction

Uranium from different uranium oxide matrices was extracted with tri-n-butyl phosphate–nitric acid (TBP–HNO₃) adduct using supercritical carbon dioxide (SC CO₂). While 30 min dissolution time at 323 K was sufficient for U₃O₈ and UO₂ powder, UO₂ granule (at 333 K) and crushed green pellet (at 353 K) required 40 min. Crushed sintered pellet required 60 min at 353 K for complete dissolution. Influence of various experimental parameters such as temperature, pressure, volume of TBP–HNO₃ adduct, acidity of nitric acid used for preparing TBP–HNO₃ adduct and extraction time on uranium extraction efficiency was also investigated. For UO₂ powder, temperature of 323 K, pressure of 15.2 MPa, 1 mL TBP–HNO₃ adduct, 10 M nitric acid and 30 min extraction time was found to be optimum. ~70% uranium extraction efficiency was obtained on extraction with SC CO₂ alone which increased to 90% with the addition of 2.5% TBP in SC CO₂ stream. Extraction efficiency was found to vary linearly with TBP percentage and nearly complete uranium extraction (~99%) was observed with 20% TBP. Nearly complete extraction was also achieved with addition of 2.5% thenoyltrifluoroacetylacetone (TTA) in methanol. The optimized procedure was extended to remove uranium from simulated tissue paper waste matrix smeared with uranium oxide solids.     

Selective ion exchange separation of uranium from concomitant impurities in uranium materials and subsequent determination of the impurities by ICP-OES

An ion exchange method has been developed for the separation of uranium from trace level metallic impurities prior to their determination by inductively coupled plasma optical emission spectrometry (ICP-OES) in uranium materials. Selective separation of uranium from trace level metallic impurities consisting Cr, Co, Cu, Fe, Mn, Cd, Gd, Dy, Ni, and Ca was achieved on anion exchange resin Dowex 1 × 8 in sulphate medium. The resin (100–200 mesh, in chloride form) was packed in a small Teflon column (7.8 cm × 0.8 cm I.D.) and brought into sulphate form by passing 0.2 N ammonium sulphate solution. Optimum experimental conditions including pH and concentration of sulphate in the liquid phase were investigated for the effective uptake of uranium by the column. Uranium was selectively retained on the column as anionic complex with sulphate, while impurities were passed through the column. Post column solution was collected and analyzed by ICP-OES for the determination of metallic impurities. Up to 2,500 μg/mL of uranium was retained with >99% efficiency after passing 25 mL sample through the column at pH 3. Percentage recoveries obtained for most of the metallic impurities were >95% with relative standard deviations <5%. The method established was applied for the determination of gadolinium in urania–gadolinia (UO₂–Gd₂O₃) ceramic nuclear fuel and excellent results were achieved. Solvent extraction method using tributylphosphate (TBP) as extractant was also applied for the separation of uranium in urania–gadolinia nuclear fuel samples prior to the determination of gadolinium by ICP-OES. The results obtained with the present method were found very comparable with those of the solvent extraction method.     

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.     

Recovery of uranium from phosphate by carbonate solutions

Uranium concentrations were analyzed in the Syrian phosphate deposits. Mean concentrations were found between 50 and 110 ppm. As a consequence, an average phosphate dressing of 22 kg/ha phosphate would charge the soil with 5–20 g/ha uranium when added as a mineral fertilizer. Fine grinding phosphate produced at the Syrian mines was used for uranium recovery by carbonate leaching. The formation of the soluble uranyl tricarbonate anion UO₂(CO₃)₃ ⁴⁻ permits using alkali and sodium bicarbonate salts for the nearly selective dissolution of uranium from phosphate. Separation of iron, aluminum, titanium, etc., from uranium during leaching was carried out. Formation of some small amounts of molybdates, vanadates, phosphates, aluminates, and some complex metals was investigated. This process could be used before the manufacture of Tri-Super Phosphate (TSP) fertilizer, and the final products would contain less uranium quantities.     

Extraction behaviour of uranium,zirconium and ruthenium with gamma-irradiated sulfoxides and tri-n-butyl phosphate

The extraction, scrubbing and stripping behaviour of uranium, zirconium and ruthenium with di-n-hexyl and di-n-octyl sulfoxides in Solvesso-100 and tri-n-butyl phosphate (TBP) in shell Sol-T irradiated by various gamma doses (0–169 Mrads) have been investigated. 2M HNO₃ was used for extraction and scrubbing and 0.01M HNO₃ for stripping purposes. Results indicate that the extraction of uranium with TBP increases and that with sulfoxide decreases with dose. This is reflected in their corresponding scrubbing percentages too. The stripping percentage of uranium with TBP decreases with dose while the reverse is the case with sulfoxide. The extraction of zirconium with TBP increases sharply with dose as compared to sulfoxides. The extraction scrubbing and stripping of ruthenium remain almost unaffected by dose both in the case of TBP and sulfoxides. These results lead to much higher overall decontamination factors for uranium with respect to zirconium as well as ruthenium with irradiated sulfoxides as compared to those with irradiated TBP.     

Preconcentration of uranium(VI) and thorium(IV) from aqueous solutions using low-cost abundantly available sorbent

Olive cake as low-cost abundantly available sorbent has been characterized by N₂ at 77 K adsorption, porosity analysis, elemental analysis and IR spectra and has been used for preconcentrating of uranium(VI) and thorium(IV) ions prior to their determination spectrophotometrically. The optimum pH values for quantitative sorption of U(VI) and Th(IV) are 4–7 and 3–7, respectively. The enrichment factor for the preconcentration of U(VI) and Th(IV) were found to be 125 and 75 in the given order. The sorption capacity of olive cake is in the range of 2,260–15,000 μg g⁻¹ for Th(IV) and in the range of 1,090–17,000 μg g⁻¹ for U(VI) at pH 3–7. The sorbent exhibits good reusability and the uptake and stripping of the studied ions were fairly rapid. The elution of U(VI) and Th(IV) was performed with 0.3–1 M HCl/1–2 M HNO₃ and 0.3–0.8 M HCl/1 M HNO₃, respectively. The precision of the method was 1.8 RSD% for U(VI) and 2.5 RSD% for Th(IV) in a concentration of 1.00 μg mL⁻¹ for 10 replicate analysis. The influence of some electrolytes and cations as interferents was discussed. Separation of U(VI) and Th(IV) from other metal ions in synthetic solution was achieved.     

Comparative extraction efficiencies of tri-<Emphasis Type="Italic">n</Emphasis>-butyl phosphate and <Emphasis Type="Italic">N,N</Emphasis>-dihexyloctanamide for uranium recovery using supercritical CO<Subscript>2</Subscript>

Extraction of uranium from tissue paper, synthetic soil, and from its oxides (UO₂, UO₃ and U₃O₈) was carried out using supercritical carbon dioxide modified with methanol solutions of extractants such as tri-n-butyl phosphate (TBP) or N,N-dihexyl octanamide (DHOA). The effects of temperature, pressure, extractant/nitric acid (nitrate) concentration, and of hydrogen peroxide on uranium extraction were investigated. The dissolution and extraction of uranium in supercritical CO₂ modified with TBP, from oxide samples followed the order: UO₃ ≫ UO₂ > U₃O₈. Addition of hydrogen peroxide in the modifier solution enhanced the dissolution/extraction of uranium in dynamic mode. DHOA appeared better than TBP for recovery of uranium from different oxide samples. Similar enhancement in uranium extraction was observed in static mode experiments in the presence of hydrogen peroxide. Uranium estimation in the extracted fraction was carried out by spectrophotometry employing 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (Br-PADAP) as the chromophore.     

A combined method of neutron activation analysis and radiometric measurements for <Superscript>234</Superscript>U and <Superscript>238</Superscript>U determination in soil samples of low uranium concentration

A method that combines the use of non-destructive neutron activation analysis and high-resolution α spectrometry has been developed for determination of the activities of ²³⁴U and ²³⁸U in geological samples of low uranium content. The ²³⁸U content is determined by k₀-based neutron activation analysis, whereas the ²³⁴U/²³⁸U relationship is measured by α spectrometry after isolation and electrodeposition of the uranium extracted from a lixiviation with 6 M HCl. The main advantage of the method is the simplicity of the chemical operations, including the fact that the steps destined to assure similar chemical state for the tracer and the uranium species present in the sample are not necessary. The method was applied to soil samples from sites of the North Peru Coast. Uranium concentration range 3–40 mg/kg and the isotopic composition correspond to natural uranium, with about 10% uncertainty.     

Synergistic extraction of uranium with mixtures of PC88A and neutral oxodonors

The extraction of uranium(VI) from nitric acid medium is investigated using 2-ethylhexyl phosphonic acid-mono-2-ethylhexyl ester (PC88A in dimeric form, H₂A₂) as extractant either alone or in combination with neutral extractants such as tri-n-butyl phosphate (TBP), trioctyl phosphine oxide (TOPO), and dioctyl sulfoxide (DOSO). The effects of different experimental parameters such as aqueous phase acidity (up to 10 M HNO₃), nature of diluent [xylene, carbon tetrachloride (CCl₄), n-dodecane and methyl iso-butyl ketone (MIBK)] and of temperature (303–333 K) on the extraction behavior of uranium were investigated. Synergistic extraction of uranium was observed between 0.5 and 6 M HNO₃. Use of MIBK as diluent was also studied. Temperature variation studies using PC88A as extractant showed exothermic nature of extraction process. Studies were carried out to optimize the conditions for the recovery of uranium from the raffinate generated during the purification of uranium from nitric acid medium. Inductively Couple Plasma Atomic Emission Spectroscopy (ICP-AES) and Energy Dispersive X-Ray Fluorescence (EDXRF) techniques were employed for analysis of uranium in equilibrated samples.     

Uranium uptake from acidic solutions using synthetic titanium and magnesium based adsorbents

Uranium uptake from acidic solutions is comprised practically in this study into three main steps namely; adsorbent synthesis, uranium uptake procedure, and desorption step. In this respect, two uranium adsorbents were synthesized from mineral processing of ilmenite and talc. Titanium phosphate adsorbent (TP) was deposited from titanium sulfate solution obtained from ilmenite sands processing. On the other hand, magnesium silicate adsorbent (MS) is prepared by sodium metasilicate neutralization of the acidic magnesium bearing waste solution resulted from talc whitening process. Structurally and chemically the two adsorbents were investigated by XRD, IR and SEM-EDX analyses. The studied factors affecting the uranium uptake onto TP and MS adsorbents were uranium concentration (10–1000 ppm), acidic pH range (1–6), contact time, shaking time and solid to liquid ratio. The uranium analysis was determined spectrophotometrically using arsenazo(III) dye where SEM-EDX analysis confirmed the uranium uptake by adsorbents. The optimum conditions obtained were applied to uranium bearing, highly mineralized granite samples (5200 ppm U) and black shale (40 ppm U). The uranium uptake was more than 98% for the mineralized granite samples and more than 97% for shale. The loaded uranium was recycled by using 0.5 and 1M HNO₃ in case of TP and MS with percentage recovery of 96 and 98% respectively.     

Composition and structure of complexes formed in the reaction of uranyl di(2-ethylhexyl)phosphate and tributyl phosphate or di-N-octyl sulfoxide in benzene solutions

This paper reprots of³¹P NMR and IR studies of the interaction of tributyl phosphate (TBP) and di-n-octyl sulfoxide (DOSO) with polymer molecules of uranyl di-2-ethylhexyl phosphate (UO₂X₂)_p (I) in C₆H₆ sulutions. Detailed interpretations of the³¹P NMR spectra and the v_as(POO) IR bands and determination of the fraction of nonequivalent phosphorus atoms of X⁻ anions and uranium (VI) atoms as well as the concentration of U(VI)-bonded TBP in I have shown that only a single TBP or DOSO molecule is coordinated to the uranium atoms of polymer I at C_TBP=0.1–2 M or C_DOSO=0.1–0.5 M. In the case of 100% TBP, two TBP molecules are coordinated to some U(VI) atoms. Distribution of TBP (DOSO) molecules along the polymer chain agrees with the mean statistical value. The portion of terminal chalate POO-groups of X⁻ anions is determined. The dependence of the degree of (UO₂X₂)_p·nL (L=TBP, DOSO) polymerization on C_L is obtained. Saturation of solutions with water only slightly affects the terminal POO-groups and has no effects on the distribution of L along the polymer chain of I. Institute of Catalysis, Siberian Branch, Russian Academy of Sciences. Translated fromZhurnal Strukturnoi Khimii, Vol. 35, No. 6, pp. 66–73, November–December, 1994. Translated by K. Shaposhnikova     

An investigation of the biogeochemistry of the uranium radionuclide in the munitions testing contaminated soil of Kirkcudbright, New Galloway, SW Scotland

The understanding of the bio-geochemical behavior of the uranium radionuclides in the environmental matrices is crucial for the health safety point of view. The research was carried out in munitions testing sites New Golloway (SW) of Scotland at the Dunderann firing range which is contaminated with depleted uranium and site is particularly important because it provides a controlled environment for the investigation of post depositional association of Depleted Uranium (DU) in contaminated soils. This study used the modified BCR sequential extraction method to investigates the association of DU in at the different sampling location and in a control soil and were followed by elemental analysis using inductively coupled-optical Emission spectroscopy (ICP-OES).The Certified Reference Material (CRM) were used for the validation of the concentration. The concentrations of (Bureau of Reference) BCR-extracted Uranium (U) were in the range of 4–40 (±13.2) mg kg⁻¹ for the DU-contaminated sites whilst U was barely detectable in the soil from the control site (Rebury Gun) RGW. With the exception of RGH and RGW, the values for BCR-extracted U compared well with those obtained using Aqaua-regia. The obtained result showed that the maximum Uranium deposition is at RGE and it is 20 mg kg⁻¹ before hitting the target, the 6 mg kg⁻¹ at RGH and minimum is at RGG and RGW control site.     

Multisyringe flow injection spectrophotometric determination of uranium in water samples

A multisyringe flow injection analysis method for the determination of uranium in water samples was developed. The methodology was based on the complexation reaction of uranium with arsenazo (III) at pH 2.0. Uranium concentrations were spectrophotometrically detected at 649 nm using a light emitting diode. Under the optimized conditions, a linear dynamic range from 0.1 to 4.0 μg mL⁻¹, a 3σ detection limit of 0.04 μg mL⁻¹, and a 10σ quantification limit of 0.10 μg mL⁻¹ were obtained. The reproducibility (%) at 0.5, 2.5, and 4.0 μg mL⁻¹ was 2.5, 0.9, and 0.6%, respectively (n = 10). The interference effect of some ions was tested. The proposed method was successfully applied to the determination of uranium in water samples.     

Selective uptake of plutonium (IV) on calcium alginate gel polymer and TBP microcapsule

The uptake behavior of Pu(IV) has been investigated by using calcium alginate gel polymer (CaALG) and TBP microcapsules (TBP-CaALG). The characterization of CaALG and TBP-CaALG was examined by SEM and IR, and the uptake properties and distribution of Pu(IV) ions were estimated by batch method. The uptake rate of Pu(IV) on CaALG and TBP-CaALG in the presence of 5 M HNO₃ was attained within 6 and 4 h, respectively, and K _d values for CaALG and TBP-CaALG after 7 h-shaking were 50.2 and 53.2 cm³/g, respectively. Relatively large K _d values (90.3–425 cm³/g) were obtained for fresh CaALG and TBP-CaALG in the presence of 0.5–2 M HNO₃. Thus CaALG and TBP-CaALG are effective for the separation of Pu(IV) in the presence of highly concentrated HNO₃.     

A simplified determination of uranium in phosphate rock and phosphogypsum by alpha-spectroscopy after its separation by liquid-extraction

A relatively rapid, economic and robust procedure is described for the radiometric analysis of uranium in phosphate rock and phosphogypsum. The analysis is performed by alpha spectroscopy after pre-concentration and separation of uranium by liquid-extraction using tributyl-phosphate (30% TBP in dodecan) and finally its electrodeposition on stainless steel discs. The method has been successfully applied to 0.1 g samples of phosphate rock and phosphogypsum resulting in high-quality spectra for measurement times ≥15 h. The main advantage of the procedure is the use of tracer solution (²³²U) that allows reliable measurements and evaluation of the separation procedure. The separation efficiency of the proposed method has been estimated to be (75 ± 20)%.     

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.     

Uranium in natural waters sampled within former uranium mining sites in Kazakhstan and Kyrgyzstan

New data are presented on ²³⁸U concentrations in surface and ground waters sampled at selected uranium mining sites in Kazakhstan and Kyrgyzstan and in water supplies of settlements located in the vicinity of these sites. Radiochemical neutron activation analysis (RNAA) was used for ²³⁸U determination in all cases. In addition, for data accuracy assessments purposes, a sub-set of these samples was analysed by high-resolution alpha spectrometry, following standard radiochemical separation and purification. Our data show that drinking waters sampled at various settlements located close to the uranium mining sites are characterised by relatively low uranium concentrations (1.9–35.9 μg L⁻¹) compared to surface waters sampled within the same sites. The latter show high concentrations of total uranium, reflecting the influence from the radioactive waste generated as a result of uranium ore production.     

Determination of Cd, Co, Cr, Cu, Fe, Ni and Pb in Milk, Cheese and Chocolate

 Combined analytical procedures consisting of wet digestion step followed by instrumental determination – differential pulse cathodic stripping voltammetry (DPCSV) or electrothermal atomic absorption spectrometry (ETAAS) – as well as a direct analysis method – slurry sampling ETAAS – for the determination of Cd, Co, Cr, Cu, Fe, Ni and Pb in milk, cheese and chocolate are described and compared. Wet digestion using a mixture of HNO₃-HClO₄-H₂O₂ is proposed for complete matrix decomposition prior to trace analyte determinati on by DPCSV or ETAAS. A mixture of HNO₃-H₂O₂ is used for slurry preparation. Optimal instrumental parameters for trace analyte measurements are presented. The reliability of the procedures has been verified by analyzing standard reference materials. Results obtained are in good agreement with the certified values and the relative standard deviations (for these results) are in the range 5–10% for wet digestion DPCSV or ETAAS and 3–9% for slurry sampling ETAAS in the range of 2 μgċg⁻¹ (Cd) to 12 μgċg⁻¹ (Fe). Received August 24, 1999. Revision January 20, 2000.     

Electro-oxidative process for the mineralization of solvent and recovery of plutonium from organic wastes

Mediated electrochemical oxidation is a promising technique for the destruction of organic compounds. Destruction of tributyl phosphate (TBP) in normal paraffin hydrocarbon (NPH) in nitric acid medium containing electro-generated Ag(II) was studied. Initially, the effect of uranium, presence of DBP along with uranium in the organic phase and direct electrochemical oxidation without catalyst (Ag) on the destruction of 30% TBP/NPH system was evaluated. For a comparison, the rate of destruction of NPH alone was studied. Further, radioactive laboratory waste solution was tested for the destruction of organic waste under similar experimental conditions. The electrolyte used in the system was 0.5 M AgNO₃ in 8 M HNO₃ at 333 K. The uniqueness in all these experiments is the use of a double end open porcelain diaphragm for the isolation of electrodes. Though there would be a slight reduction in the efficiency, two major hurdles viz., reduction in the concentration of nitric acid and reduction in the volume of catholyte resulting in an increase in cell voltage were avoided. The problem of the migration of Ag⁺/Ag²⁺ and accumulating at the cathode site was overcome by using double end open diaphragm and thorough mixing. The results revealed that the rate of destruction of organics is favoured in the presence of uranium in organic phase and with increase in temperature.