Showing papers in "Journal of Radioanalytical and Nuclear Chemistry in 2013"

Adsorption of uranium, cesium and strontium onto coconut shell activated carbon

Abstract: The adsorption of uranium (VI), cesium and strontium ions from aqueous solutions onto a commercial activated carbon obtained by physical activation of coconut shell has been studied in batch systems. In particular the adsorption of uranium, studied as a function of contact time and metal ion concentration, followed pseudo-first-order kinetics. Equilibrium adsorption data were fitted by Langmuir and Freundlich isotherm models and the maximum adsorption capacity of the activated carbon resulted to be 55.32 mg/g. The study showed that the considered activated carbon could be successfully used for uranium adsorption from aqueous solutions. Feasibility of cesium and strontium adsorption onto the same activated carbon has been also investigated. Results showed that no affinities with both of these ions exist.

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

Abstract: 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.

Distribution of 137Cs and 134Cs in the North Pacific Ocean: impacts of the TEPCO Fukushima-Daiichi NPP accident

Abstract: Impact of the TEPCO Fukushima-Daiichi NPP accident, FNPP1, to the North Pacific Ocean occurred through two pathways, namely direct release and atmospheric deposition to wide ocean surface. We collected more than 100 seawater samples in the North Pacific Ocean in April and May 2011 by seven commercial ships as VOS. Since the sample volume was 2 l each, we measured radiocaesium activity at Ogoya Underground Facility to obtain reliable activity. 137Cs was detected at all stations and 134Cs was detected at most of the stations in the North Pacific Ocean. The 137Cs activity ranged from around 1 to 1,000 Bq m−3 with activity ratios of 134Cs/137Cs close to 1 which is a signature of radiocaesium originated from the FNPP1 accident. At east of the International Date Line north of 40°N in the Pacific Ocean in April 2011, the 134Cs activity ranged from 2 to 12 Bq m−3.

The worldwide NORM production and a fully automated gamma-ray spectrometer for their characterization

Abstract: Materials containing radionuclides of natural origin and being subject to regulation because of their radioactivity are known as Naturally Occurring Radioactive Material (NORM). By following International Atomic Energy Agency, we include in NORM those materials with an activity concentration, which is modified by human made processes. We present a brief review of the main categories of non-nuclear industries together with the levels of activity concentration in feed raw materials, products and waste, including mechanisms of radioisotope enrichments. The global management of NORM shows a high level of complexity, mainly due to different degrees of radioactivity enhancement and the huge amount of worldwide waste production. The future tendency of guidelines concerning environmental protection will require both a systematic monitoring based on the ever-increasing sampling and high performance of gamma-ray spectroscopy. On the ground of these requirements a new low-background fully automated high-resolution gamma-ray spectrometer MCA_Rad has been developed. The design of lead and cooper shielding allowed to reach a background reduction of two order of magnitude with respect to laboratory radioactivity. A severe lowering of manpower cost is obtained through a fully automation system, which enables up to 24 samples to be measured without any human attendance. Two coupled HPGe detectors increase the detection efficiency, performing accurate measurements on small sample volume (180 cm3) with a reduction of sample transport cost of material. Details of the instrument calibration method are presented. MCA_Rad system can measure in less than one hour a typical NORM sample enriched in U and Th with some hundreds of Bq kg−1, with an overall uncertainty less than 5 %. Quality control of this method has been tested. Measurements of three certified reference materials RGK-1, RGU-2 and RGTh-1 containing concentrations of potassium, uranium and thorium comparable to NORM have been performed. As a result, this test achieved an overall relative discrepancy of 5 % among central values within the reported uncertainty.

Cesium removal from solution using PAN-based potassium nickel hexacyanoferrate (II) composite spheres

Abstract: A polyacrylonitrile–potassium nickel hexacyanoferrates composite adsorbent was prepared to remove cesium ion in aqueous solution. The dual nozzle technique was applied to prepare a composite sphere. The physicochemical behavior of the ion exchanger was specified with different techniques including Fourier transform infrared spectroscopy, X-ray powder diffraction, specific surface analysis, scanning electron microscopy, and X-ray fluorescence spectroscopy analysis. The effects of contact time, solution initial pH, presence of various cations and initial cesium concentration on the adsorption was also investigated and the optimum conditions for separation of cesium were determined. In addition, adsorption kinetics and adsorption mechanism were studied by modeling the experimental data and related parameters were also evaluated, which showed that sorption data fitted to pseudo-second-order and film diffusion models. Adsorption isotherm in batch experiments showed that the sorption data were successfully fitted with Langmuir model. Finally the adsorption dynamic capacities of the synthesized composite in column experiments were evaluated at 139.925 and 119.539 mg/g for flow rate of 1 and 3 BV/min, respectively.

Heterogeneous distribution of radiocesium in aerosols, soil and particulate matters emitted by the Fukushima Daiichi Nuclear Power Plant accident: retention of micro-scale heterogeneity during the migration of radiocesium from the air into ground and river systems

Abstract: We analyzed 137Cs in aerosols, rock, soil and river suspended sediment collected after the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident. Based on the results, we discuss the post-event behavior and transportation of radiocesium in the environment from the air into ground and river systems. First, radionuclides were emitted from the FDNPP as airborne ‘hot’ particles, which contained water-soluble fractions of radiocesium. Radiocesium was still present in a water-soluble fraction after deposition on the ground. Subsequent interaction of the ‘hot’ particles with water (e.g. rainfall) dissolved and strongly fixed the radiocesium on rock and soil particles, thus changing the radiocesium into insoluble forms. The distribution of ‘hot spots’ was possibly controlled by the initial position of deposition on the ground. Consequently, ‘hot spots’ were studded on the rock surface rather than being uniformly distributed. The distribution of radiocesium in river suspended particles was not homogeneous during water transportation, reflecting the heterogeneity of radiocesium in rock and soil. Leaching experiments demonstrated that radiocesium in rock, soil and river suspended sediment was fairly insoluble, showing that the adsorption reaction is irreversible. The micro-scale heterogeneous distribution of radiocesium in aerosols, soil and suspended particles was due to the presence of ‘hot’ particles in aerosols. Dissolution of radiocesium in the ‘hot’ particles in the aerosols and subsequent irreversible adsorption onto the soil particle complex are responsible for the preservation of the heterogeneity both in soil and in river suspended particles.

Separation and recovery of ruthenium: a review

Abstract: The chemistry of the noble metal fission product, ruthenium is very complex due to the existence of many oxidation states in addition to forming a large number of co-ordination complexes. In the PUREX process for the separation of U and Pu from the spent nuclear fuels from fast breeder reactors, owing to the high volatile nature of RuO4 problems arise not only during the extraction stages but also in the treatment of high active liquid waste and subsequent vitrification. As this volatile RuO4 can deposit in cooler parts, there is an increase in the radiation field due to the presence of 106Ru. The problem is very acute in the reprocessing of fast reactor fuels due to the increased concentration of ruthenium in the spent fuel. In nitric acid medium Ru can exist in various nitroso nitrate complexes and nitroso complexes are more stable than nitrates. The nitrates are non-extractable by the solvent TBP; however, they are extractable to a higher degree by DBP (the primary degradation product of TBP). The extractability of Ru nitrates into the solvent is inhibited by high acid content, temperature and prolonged hold-up time. Nevertheless, these factors promote the volatilization of Ru as RuO4. The volatilization is enhanced by the addition of phosphate ions, but is suppressed by phosphite or hypophosphite ions. Thus, it would be advantageous if ruthenium is removed so that not only the purity of the product (Pu) is improved, but also the problem related to volatilisation can be resolved. High molecular weight amines (tertiary amines) capable of forming co-ordinate bonds are reported to be ideal extractants for Ru. Gas phase separation is an effective method for the recovery of Ru from catalysts, lead button and from other platinum group metals. Separation and pre-concentration of noble metals can be accomplished from non-metals by simple sorbents like coconut shell activated carbon to complicated chelating resins, aromatic polymers and zeolites. In the electro-oxidation of active Ru from nitroso salts, Pd was found to interfere and removal of Pd prior to oxidation of Ru is recommended. Redox catalysts such as Ag2+ and Ce4+ are found to play a prominent role in the electro-oxidation of Ru. Though, various methods and extractants are reported in the literature for the separation of Ru, R&D is being pursued for the removal of Ru during aqueous reprocessing of spent fuels using extractants and methods which are conducive to plant conditions. Hence, an exhaustive survey of literature was made and the different methods reported for the removal of Ru with emphasis towards reprocessing applications are discussed in this report as a review. Attempts made by the authors in separating Ru from simulated waste solution are also included in this review.

Uranium extraction from aqueous solution using dried and pyrolyzed tea and coffee wastes

Abstract: The adsorption of U(VI) onto dried and pyrolyzed tea and coffee wastes was investigated. The adsorption properties of the materials were characterized by measuring uranium uptake as a function of solution pH, kinetics and adsorption isotherms. pH profile of uranium adsorption where UO2 2+ is expected to be the predominant species was measured between pH 0 and 4. Both Langmuir and Freundlich adsorption models were used to describe adsorption equilibria, and corresponding constants evaluated. Using the Langmuir model, the maximum adsorption capacity of uranium by dried tea and coffee wastes was 59.5 and 34.8 mg/g, respectively at 291 K. Adsorption thermodynamic constants, ΔH° ΔS° and ΔG° were also calculated from adsorption data obtained at three different temperatures. Adsorption thermodynamics of uranyl ions on dried tea and coffee systems indicated spontaneous and endothermic processes. Additionally, a Lagergren pseudo-second-order kinetic model was used to fit the kinetic experimental data for both adsorbents and the constants evaluated. Dried tea and coffee wastes proved to be effective adsorbents with high capacities and significant advantage of a very low cost.

A brief introduction to analytical methods in nuclear forensics

Abstract: Nuclear forensic (NF) techniques are critical in responding to both environmental releases of nuclear materials and illicit trafficking activities involving both nuclear and counterfeit materials. Despite rising need, however, significant barriers exist to the future success of such research. This subset of analytical chemistry contains unique concerns (e.g. chronometry and impurity signatures), a wide variety of preparatory/instrumental approaches, and is in need of innovative solutions to current problems both in and out of the lab. The present work introduces existing NF research, development challenges and notes potential areas for advancement by highlighting several key analytical approaches. Examples of concerns and techniques discussed in this review include: chronometry, reference materials, separations, counting spectrometry, mass spectrometry and more.

Tuning the diglycolamides for modifier-free minor actinide partitioning

Abstract: The unsymmetrical diglycolamides (DGAs) such as N,N-dihexyl-N′,N′-dioctyl-3-oxapentane-1,5-diamide (DHDODGA), N,N-didecyl-N′,N′-dioctyl-3-oxapentane-1,5-diamide (D2DODGA), N,N-didodecyl-N′,N′-dioctyl-3-oxapentane-1,5-diamide (D3DODGA), were synthesized, and characterized by IR, NMR, and mass spectroscopic techniques. The extraction behaviour of Am(III), Eu(III), and Sr(II) by the solutions of these unsymmetrical DGAs in n-dodecane was studied as a function of concentration of nitric acid and DGA. The distribution ratio of Am(III) and Eu(III) increased with increase in the concentration of nitric acid; whereas, the distribution ratio of Sr(II) reached a maximum at 4 M nitric acid followed by decrease at higher acidities. The extraction of Am(III) and Eu(III) in 0.1 M DGA/n-dodecane decreased in the order DHDODGA > D2DODGA > D3DODGA. However, the order changed upon lowering the concentration of DGA. The third-phase formation behaviour of nitric acid and neodymium(III) in 0.1 M DGA/n-dodecane was studied as a function of concentration of nitric acid. The limiting organic concentration of nitric acid and neodymium increased with increase in the chain length of alkyl group attached to amidic nitrogen. Near stoichiometric amount of neodymium(III) was loaded in 0.1 M D3DODGA/n-dodecane without the formation of third-phase from 3 to 4 M nitric acid medium. The study revealed that the unsymmetrical diglycolamides D2DODGA and D3DODGA are superior candidates for partitioning the minor actinides from high-level liquid waste.

Removal of uranium (VI) from aqueous solutions by adsorption using a novel electrospun PVA/TEOS/APTES hybrid nanofiber membrane: comparison with casting PVA/TEOS/APTES hybrid membrane

Abstract: Polyvinyl alcohol/tetraethyl orthosilicate/aminopropyltriethoxysilane (PVA/TEOS/APTES) nanofiber membrane was prepared by the sol–gel/electrospinning method and its application for adsorption of uranium from aqueous solutions was compared with PVA/TEOS/APTES membrane prepared by sol–gel/casting method. The prepared membranes were characterized by Fourier transform infrared, scanning electron microscope and Brunauer–Emmert–Teller analysis. The surface area of electrospun and casting hybrid membranes obtained were 153 and 282 m2 g−1, respectively. Experiments were carried out to investigate the influence of different sorption parameters, such as pH, contact time, initial concentration and temperature in a batch system. Results indicated that the pH of 4.5 and high temperature (45 °C at studied condition) proceeded earlier than the adsorption of uranium ions onto the both of prepared membranes. Langmuir, Freundlich and Dubinin–Radushkevich (D–R) isotherm models were applied to describe the equilibrium data of uranium to the prepared membranes at different temperatures (25–45 °C) and the kinetic data were analyzed by pseudo-first-order and pseudo-second-order kinetic models. The maximum adsorption capacity of uranium ions onto the PVA/TEOS/APTES hybrid nanofiber membrane was found to be 168.1 mg g−1 with the optimum pH of 4.5 and at the optimum temperature of 45 °C which is more than five-fold greater to that of uranium sorption onto the PVA/TEOS/APTES hybrid membrane (33.61 mg g−1 with pH of 4.5 and at a temperature of 45 °C). Thermodynamic parameters were evaluated to understand the nature of adsorption process for uranium ions. The negative values of Gibbs free energy change (∆G°) and positive value of enthalpy change (∆H°) showed that the adsorption of uranium onto both of the electrospun and casting hybrid membranes was feasible, spontaneous and endothermic in studied conditions. The reusability of hybrid membranes was determined after five sorption–desorption cycles and the results showed that these membranes can be utilized extensively in industrial activities.

Removal of U(VI) from aqueous solutions by using MWCNTs and chitosan modified MWCNTs.

Abstract: In this paper, the multiwalled carbon nanotubes (MWCNTs) were modified with chitosan (CS) by using low temperature plasma grafting technique (denoted as MWCNT-CS). The prepared MWCNTs and MWCNT-CS were characterized by SEM, TEM, FTIR and Raman spectroscopy in detail and the results suggested that CS molecules were successfully grafted on the surfaces of MWCNTs. The materials were applied as adsorbents in the removal of U(VI) ions from large volumes of aqueous solutions as a function of environmental conditions. The removal of U(VI) from aqueous solution to MWCNTs and MWCNT-CS increased with increasing pH values at pH 7. The sorption of U(VI) on MWCNTs and MWCNT-CS was strongly dependent on pH and independent of ionic strength. The sorption of U(VI) on MWCNTs and MWCNT-CS was dominated by inner-sphere surface complexation rather than by ion exchange or outer-sphere surface complexation. The surface grafted chitosan molecules can enhances U(VI) sorption on MWCNTs obviously, which was also evidenced from the XPS spectroscopy analysis. The results of high sorption capacity of U(VI) on MWCNT-CS suggest that the MWCNT-CS nanomaterial is a suitable candidate in the preconcentration of U(VI) ions from large volumes of aqueous solutions.

Removal of radioactive cesium, strontium, and iodine from natural waters using bentonite, zeolite, and activated carbon

Abstract: Cs-134, Sr-85, and I-131 were produced by neutron irradiation of CsCl, SrCl2, and K2TeO3, respectively, using the Kyoto University Reactor. These radioactive nuclides were added to river water and seawater to prepare artificially contaminated samples, and the removal of these nuclides using bentonite, zeolite, and activated carbon was then investigated. In the river water samples, Cs-134 and Sr-85 were successfully removed using bentonite and zeolite, and I-131 was removed using activated carbon. In the seawater samples, Cs-134 was removed using bentonite and zeolite, whereas Sr-85 and I-131 were hardly removed at all by these adsorbents.

Adsorption of uranium from aqueous solution by graphene oxide nanosheets supported on sepiolite

Abstract: Adsorptive behavior of uranium from aqueous solution on graphene oxide supported on sepiolite composites (GO@sepiolite composites) as a function of pH, ionic strength, temperature and initial uranium concentration was carried out by the batch techniques. GO@sepiolite composites was synthesized and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and potentiometric acid–base titration. According to XRD patterns and SEM images, the graphene oxide nanosheets were grafted on sepiolite surface successfully. The macroscopic results showed that the adsorption of uranium on GO@sepiolite composites was significantly depended on pH, whereas no effect of ionic strength on uranium adsorption at high pH and high ionic strength conditions was observed. The uptake equilibrium is best described by Langmuir adsorption isotherm, and the maximum adsorption capacity (Qe) of GO@sepiolite composites at pH 5.0 and T = 298 K were calculated to be 161.29 mg/g. Thermodynamic results indicated that the adsorption of uranium on GO@sepiolite composites is the spontaneous and exothermic process.

Local distribution of radioactivity in tree leaves contaminated by fallout of the radionuclides emitted from the Fukushima Daiichi Nuclear Power Plant

Abstract: We analyzed fresh and dead leaves collected in forests in Fukushima after the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident, using autoradiography. Both fresh and dead leaves of Cryptomeria japonica were contaminated by radionuclides (134Cs and 137Cs). Contamination of the fresh leaves was possibly attributed to interception of radionuclides by tree canopies, whereas the dead leaves indicated the direct deposition of radionuclides by fallout and/or washout of radionuclides intercepted by tree canopies. Translocation of radiocesium from a contaminated branch to new leaves growing after the FDNPP accident was not clearly observed, although transfer of radiocesium from leaf parts to male flowers occurred. Fallen leaves of Quercus serrata, which started growing after the FDNPP accident, did not show radioactivity, indicating that significant amounts of translocation from other parts to new leaves did not occur. Fallen leaves of Q. serrata collected from a litter showed hot spots originating from direct fallout. Needles of Pinus densiflora were also contaminated by fallout. Leaching with pure water removed soluble fractions of radiocesium and hot particles from the surface of the contaminated leaves, but significant amounts of radioactivity remained. This means that foliar absorption occurred in both fresh and dead leaves. Further leaching experiments using surfactant and acetone could not remove the remaining radiocesium from the leaves. The leaching experiments indicate that radiocesium in the contaminated leaves is strongly fixed in leaf tissues and is not readily released unless leaf tissues are decomposed.

Investigation of the polymorphs and hydrolysis of uranium trioxide

Abstract: This work focuses on the polymorphic nature of the UO3 and UO3–H2O system, which are important materials associated with the nuclear fuel cycle. The UO3–water system is complex and has not been fully characterized, even though these species are key fuel cycle materials. Powder X-ray diffraction, and Raman and fluorescence spectroscopies were used to characterize both the several polymorphic forms of UO3 and the certain UO3-hydrolysis products for the purpose of developing predictive capabilities and estimating process history; for example, polymorphic phases of unknown origin. Specifically, we have investigated three industrially relevant production pathways of UO3 and discovered a previously unknown low temperature route to the production of β-UO3. Several phases of UO3, its hydrolysis products, and key starting materials were synthesized and characterized as pure materials to establish optical spectroscopic signatures for these compounds for forensic analysis.

Biosorption behaviors of uranium (VI) from aqueous solution by sunflower straw and insights of binding mechanism

Abstract: Uranium (VI)-containing water has been recognized as a potential longer-term radiological health hazard. In this work, the sorptive potential of sunflower straw for U (VI) from aqueous solution was investigated in detail, including the effect of initial solution pH, adsorbent dosage, temperature, contact time and initial U (VI) concentration. A dose of 2.0 g L−1 of sunflower straw in an initial U (VI) concentration of 20 mg L−1 with an initial pH of 5.0 and a contact time of 10 h resulted in the maximum U (VI) uptake (about 6.96 mg g−1) at 298 K. The isotherm adsorption data was modeled best by the nonlinear Langmuir–Freundlich equation. The equilibrium sorption capacity of sunflower straw was observed to be approximately seven times higher than that of coconut-shell activated carbon as 251.52 and 32.37 mg g−1 under optimal conditions, respectively. The positive enthalpy and negative free energy suggested the endothermic and spontaneous nature of sorption, respectively. The kinetic data conformed successfully to the pseudo-second-order equation. Furthermore, energy dispersive X-ray, fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy demonstrated that U (VI) adsorption onto sunflower straw was predominantly controlled by ion exchange as well as complexation mechanism. The study revealed that sunflower straw could be exploited for uranium remediation of aqueous streams as a promising adsorbent.

Environmental assessment of heavy metal and natural radioactivity in soil around a coal-fired power plant in China

Abstract: Concentrations of heavy metals and natural radionuclides in soil around a major coal-fired power plant of Xi’an, China were determined by using XRF and gamma ray spectrometry, respectively. The measured results of heavy metals show that the mean concentrations of Cu, Pb, Zn, Co and Cr in the studied soil samples are higher than their corresponding background values in Shaanxi soil, while the mean concentrations of Mn, Ni and V are close to the corresponding background values. The calculated results of pollution load index of heavy metals indicate that the studied soils presented heavy metal contamination. The concentrations of 226Ra, 232Th and 40K in the studied soil samples range from 27.6 to 48.8, 44.4 to 61.4 and 640.2 to 992.2 Bq kg−1 with an average of 36.1, 51.1 and 733.9 Bq kg−1, respectively, which are slightly higher than the average of Shaanxi soil. The air absorbed dose rate and the annual effective dose equivalent received by the local residents due to the natural radionuclides in soil are slightly higher than the mean values of Shaanxi. Coal combustion for energy production has affected the natural radioactivity level and heavy metals (Cu, Pb, Zn, Co and Cr) concentrations of soil around the coal-fired power plant.

Adsorption of uranium(VI) by grapefruit peel in a fixed-bed column: experiments and prediction of breakthrough curves

Abstract: Adsorbent, natural grapefruit peel (GFP) exhibit good efficacy to adsorb a highly toxic radioactive heavy metal, uranium(VI). Through the fixed-bed column technique adsorption characteristics of uranium(VI) is observed at different flow rate, bed depth, influent uranium(VI) concentration and particle size of adsorbent. The results showed that adsorption reached saturation faster with increasing the flow rate and influent uranium(VI) concentration while it was the advantage of column adsorption with the increase in the GFP bed. The data were fitted to the Thomas model, the Yan model, the Clark model and the mass transfer model by nonlinear regressive analysis. When the flow rate was 8.0 mL min−1 and the influent concentration of uranium(VI) was 90 mg L−1, the maximum adsorption quantity reached 104.1 mg g−1 according to the Thomas model. The bed depth service time model was applied to predict the service times with other flow rate and initial concentration. The theoretical breakthrough curve was compared with experimental breakthrough curve profile in the dynamic process. The results showed that the Yan model was better for the description of breakthrough curves at the experimental conditions than the Thomas and the Clark models. The saturated column was regenerated by 0.05 mol L−1 hydrogen chloride solution and GFP could be reused in uranium(VI) removal.

Adsorption of uranium(VI) from aqueous solution by diethylenetriamine-functionalized magnetic chitosan

Abstract: In this paper, the modified magnetic chitosan resin containing diethylenetriamine functional groups (DETA-MCS) was used for the adsorption of uranium ions from aqueous solutions. The influence of experimental conditions such as contact time, pH value and initial uranium(VI) concentration was studied. The Langmuir, Freundlich, Sips and Dubinin–Radushkevich equations were used to check the fitting of adsorption data to the equilibrium isotherm. The best fit for U(VI) was obtained with the Sips model. Adsorption kinetics data were tested using pseudo-first-order and pseudo-second-order models. Kinetic studies showed that the adsorption followed the pseudo-second-order kinetic model, indicating that the chemical adsorption was the rate-limiting step. The present results suggest that DETA-MCS is an adsorbent for the efficient removal of uranium(VI) from aqueous solution.

Batch and continuous fixed-bed column adsorption of Cs + and Sr 2+ onto montmorillonite–iron oxide composite: Comparative and competitive study

Abstract: A montmorillonite–iron oxide composite (MIOC) was prepared to assess its effectiveness in the removal of Cs+ and Sr2+ from aqueous solution. A comparative and competitive adsorption study was conducted in single and binary systems. Used materials have been characterized by X-ray diffraction (XRD) and Infrared spectroscopy. Adsorption of Cs+ and Sr2+ as a function of contact time and pH was investigated, adsorption data of single metal solutions were well fitted to the Freundlich–Langmuir isotherm models. Equilibrium isotherms for the binary removal of Cs+ and Sr2+ by MIOC have been analyzed by using non modified and extended Langmuir models with a satisfactory R 2 values. Neutral solution pH was found to be favorable for both single and binary systems. The adsorption model analysis revealed that MIOC was more selective for Sr than Cs. The maximum adsorption capacities for individual Cs+ and Sr2+ solutions were 52.6 and 55.5 mg g−1, respectively. While the maximum uptakes in the binary system were 41.6 and 47.6 mg g−1 for Cs+ and Sr2+, respectively. Column adsorption experiments were carried out at room temperature under the effect of various operating parameters such as bed depth, initial cation concentration and flow rate, Breakthrough curves were well fitted to the Thomas model. Desorption experiments were also conducted to assess the possibility for the reuse of adsorbent and the recovery of cations.

Uranium adsorption by non-treated and chemically modified cactus fibres in aqueous solutions

Abstract: The adsorption efficiency of Opuntia ficus indica fibres regarding the removal of hexavalent uranium [U(VI)] from aqueous solutions has been investigated prior and after the chemical treatment (e.g. phosphorylation and MnO2-coating) of the biomass. The separation/removal efficiency has been studied as a function of pH, uranium concentration, adsorbent mass, ionic strength, temperature and contact time. Evaluation of the experimental data shows that biosorption is strongly pH-depended and that the MnO2-coated product presents the highest adsorption capacity followed by the phosphorylated and non-treated material. Experiments with varying ionic strength/salinity don’t show any significant effect on the adsorption efficiency, indicating the formation of inner-sphere surface complexes. The adsorption reactions are in all cases exothermic and relatively fast, particularly regarding the adsorption on the MnO2-coated product. The results of the present study indicate that adsorption of uranium from waters is very effective by cactus fibres and particularly the modified treated fibres. The increased adsorption efficiency of the cactus fibres is attributed to their primary and secondary fibrillar structure, which result in a relative relative high specific surface available for sorption.

INAA application in the assessment of Ag, Co, Cr, Fe, Hg, Rb, Sb, Sc, Se, and Zn mass fraction in pediatric and young adult prostate glands

Abstract: The effect of age on trace element contents in intact prostate of 50 apparently healthy 0–30 year old males was investigated by neutron activation analysis with high resolution spectrometry of long-lived radionuclides. Mean values (M ± SEΜ) for mass fraction (milligram per kilogram, on dry-weight basis) of trace elements were: Ag 0.0708 ± 0.0096, Co 0.0348 ± 0.0040, Cr 0.466 ± 0.069, Fe 100 ± 10, Hg 0.0258 ± 0.0025, Rb 12.6 ± 0.8, Sb 0.0576 ± 0.0066, Sc 0.0125 ± 0.0016, Se 0.478 ± 0.031, and Zn 273 ± 31, respectively. A strongly pronounced tendency of age-related increase in Se and Zn mass fraction and of age-related decrease in Co, Cr, Fe, and Sc mass fraction was observed in period of life from 0 to 30 years.

Methodological advances for measuring low-level radium isotopes in seawater

Abstract: A new approach for quantifying radium isotopes in seawater was developed in advance of the international GEOTRACES program, which has the goal of identifying processes and quantifying fluxes that control the distribution of trace elements and isotopes (TEIs) in the ocean. High-resolution water column samples were collected via a commercially available in situ pump modified to accept multiple filter media including a manganese-oxide (MnO2) impregnated acrylic cartridge for extracting dissolved radionuclides from seawater. The modifications mitigated prefilter clogging and allowed for up to 1,800 L filtrations in 4 h of pumping. Different MnO2 cartridge preparation methods were investigated to achieve maximum radium (Ra) extraction efficiency under high sample flow rates. Full-ocean depth profiles were measured for short-lived radium isotopes (223Ra and 224Ra) in shipboard laboratories using a delayed coincidence alpha scintillation counter (RaDeCC). Samples were reanalyzed 4 weeks and 2 months after collection for 228Th and 227Ac to correct for supported 224Ra and 223Ra, respectively. Finally, the cartridges were measured on a gamma-ray spectrometer for the long-lived radium isotopes (226Ra and 228Ra). Parallel 20 L samples at each pumping depth were collected from Niskin bottles and analyzed via alpha scintillation for 226Ra to determine radium extraction efficiencies for the cartridges. These modified methods will allow for increased sample throughput, and hence higher spatial resolution for radium isotopes in the ocean. Such resolution will greatly improve the determination of oceanic vertical and horizontal mixing rates over small and large scales, which in turn can be used to calculate fluxes of TEIs into the ocean.

Role of solution chemistry on the trapping of radionuclide Th(IV) using titanate nanotubes as an efficient adsorbent

Abstract: Titanate nanotubes (TNTs) have attracted great interest in multidisciplinary study since their discovery. The adsorption of thorium [Th(IV)] onto TNTs in the absence and presence of humic acid (HA)/fulvic acid (FA) was studied by batch technique. The influence of pH from 2.0 to 10.0, ionic strength from 0.001 to 0.1 mol L−1 NaClO4, and coexisting electrolyte cations (Li+, Na+, K+) and antions (ClO4 −, NO3 −, Cl−) on the adsorption of Th(IV) onto TNTs was tested. The adsorption isotherms of Th(IV) was determined at pH 3.0 and analyzed with Langmuir and Freundlich adsorption models, respectively. The results demonstrated that the adsorption of Th(IV) onto TNTs increases steeply with increasing pH from 2.0 to 4.0. Generally, HA/FA was showed to enhance Th(IV) adsorption onto TNTs at low pH values, but to reduce Th(IV) adsorption onto TNTs at high pH values. The adsorption of Th(IV) onto TNTs was also dependent on coexisting electrolyte ions in aqueous solution under our experimental conditions. The adsorption of Th(IV) onto TNTs is exothermic and spontaneous. The findings indicating that TNTs can be used as a promising candidate for the enrichment and solidification of Th(IV) or its analogue actinides from large volume solution in real work.

Removal of Th4+ ions from aqueous solutions by graphene oxide

Abstract: The removal of Th4+ ions from aqueous solutions was investigated using single-layer graphene oxide (GO) as a sorbent which was prepared by the modified Hummers’ method through batch adsorption experiments at room temperature. Structural characterizations of the sorbent were also investigated. The influences of the pH value of solution, contact time, sorbent dose, ionic strength, the initial metal ion concentration and temperature on the adsorption of Th4+ were also investigated. These results indicated that the adsorption of Th4+ was dependent on the pH and independent on the ionic strength. The sorbent provided significant Th4+ removal (>98.7 %) at pH 3.0 and the adsorption equilibrium was achieved after only 10 min. The Langmuir adsorption isotherm fit the absorption profile very closely, and indicated that a maximum adsorption capacity of 1.77 mmol g−1 of GO (411 mg g−1) after 2 h. The thermodynamic parameters showed that this adsorption process was endothermic and spontaneous. Moreover, the desorption level of Th4+ from GO, by using 0.1 mol L−1 H2SO4 as a stripping agent, was 84.2 ± 1.2 %, and that of 0.5 mol L−1 HNO3 as a stripping agent, was 79.8 ± 3.0 %.

Fast concentration of dissolved forms of cesium radioisotopes from large seawater samples

Abstract: The method developed for cesium concentra- tion from large freshwater samples was tested and adapted for analysis of cesium radionuclides in seawater. Concen- tration of dissolved forms of cesium in large seawater samples (about 100 L) was performed using composite absorbers AMP-PAN and KNiFC-PAN with ammonium molybdophosphate and potassium-nickel hexacyanofer- rate(II) as active components, respectively, and polyacry- lonitrile as a binding polymer. A specially designed chromatography column with bed volume (BV) 25 mL allowed fast flow rates of seawater (up to 1,200 BV h -1 ). The recovery yields were determined by ICP-MS analysis of stable cesium added to seawater sample. Both absorbers proved usability for cesium concentration from large sea- water samples. KNiFC-PAN material was slightly more effective in cesium concentration from acidified seawater (recovery yield around 93 % for 700 BV h -1 ). This material showed similar efficiency in cesium concentration also from natural seawater. The activity concentrations of 137 Cs determined in seawater from the central Pacific Ocean were 1.5 ± 0.1 and 1.4 ± 0.1 Bq m -3 for an off- shore (January 2012) and a coastal (February 2012) locality, respectively, 134 Cs activities were below detection limit (\0.2 Bq m -3 ).

Radioactive cesium deposition on rice, wheat, peach tree and soil after nuclear accident in Fukushima

Abstract: We present how radioactive Cs was deposited on wheat, rice, peach tree and soil after nuclear accident in Fukushima. The deposition of radioactive Cs was found as spots at the surface of the leaves, branch or trunk of the trees, as well as in soil using one of the imaging method, autoradiography. The deposited radioactive Cs was not easily washed out, even with the treatment of acid solution. When the wheat was harvested 2 months after the accident, high radioactivity of Cs was found only on the leaves developed and expanded at the time of the accident. In the case of the rice grain, most of the radioactivity was found in bran and the radioactivity was drastically reduced in milled rice. Most of the radioactive Cs accumulation in rice plants was estimated from the absorption of the Cs ion dissolved in water, rather than Cs adsorbed in soil.

Characterization and properties of Pleurotus mutilus fungal biomass as adsorbent of the removal of uranium(VI) from uranium leachate

Abstract: Removal and recovery of uranium from dilute aqueous solutions by dead fungal biomass (Pleurotus mutilus) have been studied by biosorption. The parameters that affect the uranium(VI) adsorption, such as: pH solution, temperature, biomass particle size and speed of stirring have been investigated and optimized. The experimental data were analyzed using pseudo-first-order and pseudo-second-order equations. The Freundlich and Langmuir adsorption models have been used for the mathematical description of the adsorption equilibrium. The maximum uranium biosorption capacity has been calculated. The value obtained (636.9 mg g−1) showed that P. mutilus is a good adsorbent. Also, the chemical bands involved in uranium link have been identified. We have applied this biosorption to actual waste uranium leachate, the results are satisfactory and promising.

Occurrence of uranium in groundwater of a shallow granitic aquifer and its suitability for domestic use in southern India

Abstract: Groundwater used for domestic purpose without proper treatment should be free from chemical and biological contaminants. This study was carried out to assess the groundwater quality with respect to uranium in a part of Nalgonda district, Andhra Pradesh, India. Groundwater was regularly monitored for uranium concentration by collection of samples once every two months from March 2008 to November 2009 from 44 wells. The concentration of uranium in groundwater ranged from 0.2 to 118.4 ppb. Groundwater is unsuitable for domestic use in 2 % of this area based on the limit of 60 ppb prescribed by the Atomic Energy Regulatory Board of India. However, due the wide variation in limit suggested by different organizations and countries, the no-observed-adverse-effect level and lowest-observed-adverse-effect level (in mg/kg day) was used to understand the dosage of uranium that reaches the people through drinking water pathway. This level varied from 0 to 0.02 mg/kg day and 0 to 0.08 mg/kg day based on an uncertainty factor of 10 and 50 respectively for the mean uranium concentration in groundwater in each well. With an uncertainty factor of 50, 5 groundwater samples had uranium above 0.06 mg/kg day which is the lowest-observed-adverse-effect level. This study showed that with the presence of present level of uranium concentration in groundwater of this area there is no major threat to humans through the drinking water pathway.