Showing papers in "Journal of Radioanalytical and Nuclear Chemistry in 2012"

Sorption of anthropogenic radionuclides on natural and synthetic inorganic sorbents

Abstract: The history of sorption and ion-exchange processes starts with the use of natural materials which properties were discovered coincidentally and ends with the age of polymer and anorganic—or synthetic sorbents specifically made for a particular project. Its objectives are focused on sorption of anthropogenic radionuclides originating from nuclear power plant operations (fission, activation, corrosion products and transuranium elements) on bentonites, zeolites, hydroxyapatites, magnetic sorbent, ferrocyanides, and silica sorbent. Bentonites from Slovak deposits should be used as part of multi-barrier system in deep geological repository for spent nuclear fuel and high level radioactive waste. Zeolites are used as molecular sieves, catalysts, ion-exchangers, sorbents, water softeners, in wastewater treatment, in chemistry industry, buildings. Hydroxyapatite is a suitable sorbent for heavy metals and radionuclides due to its low water solubility, high stability under reducing and oxidizing conditions, high specific surface area and good buffering properties. The leaching wastes from the Sereď hydrometallurgical plant represent a large stock of inexpensive, ready-to-use magnetic sorbent for the decontamination of soil or sediments in their common suspensions, followed by the magnetic separation and sorbent recycling. Insoluble ferrocyanides of nickel are highly selective sorbents for heavy alkali metals ions, and therefore can be used to separate cesium from liquid radioactve waste. Silica sorbents modified with imidazole can be used for the separation of cobalt ions from aqueous solution.

A high efficient sorption of U(VI) from aqueous solution using amino-functionalized SBA-15

Abstract: Uranium is one of the most hazardous heavy metal due to its long half-life radioactivity, high toxicity and mobility as aqueous uranyl ion (UO22+) under ordinary environmental conditions. Herein, amino functionalized SBA-15 (APSS) was developed as a rapid and efficient sorbent for removal of U(VI) from the environment. The APSS sample was synthesized by grafting method and was characterized by SEM, NMR, SAXS, and N-2 sorption/desorption isothermal experiments. The sorption of U(VI) by APSS was investigated under different conditions of pH, contact time, initial U(VI) concentration, ionic strength and solid-liquid ratio. The results show that the sorption of U(VI) by APSS is strongly dependent on pH but independent of ionic strength and solid-liquid ratios (m/V). The sorption is ultrafast with an equilibrium time of less than 30 min, and the sorption capacity is as large as 409 mg/g at pH 5.3 +/- 0.1. Besides, the U(VI) sorption by APSS from extremely diluted solution and the desorption of U(VI) from APSS were also studied. It is found that 100 mg of APSS can almost completely remove the U(VI) ions from 4 L aqueous solution with the U(VI) concentration as low as 4.2 ppb and the sorbed U(VI) can be completely desorbed by 0.1 mol/L nitric acid. The results strongly reveal the high performance of the APSS material in the removal and preconcentration of U(VI) from the aqueous solution.

Chemistry and analysis of radionuclides

Abstract: The book is the result of the concerted effort of Professor Lehto of the Laboratory of Radiochemistry at the Department of Chemistry, University of Helsinki, Finland; as well as of Dr. Hou of Riso National Laboratory, Technical University of Denmark, Roskilde, Denmark. The volume fits a series of related titles from the same publisher starting with Lieser’s Nuclear and Radiochemistry (2001), continuing with Prussin’s Nuclear Physics for Applications (2007), and completed with Radiochemistry in the Environment edited by Atwood (2010) and Nuclear Materials edited by Lambert (2011). Being a chemist myself, I can appreciate the text printed on the back cover of the book:

Diglycolamide functionalized multi-walled carbon nanotubes for removal of uranium from aqueous solution by adsorption

Abstract: Diglycolamide functionalized multi-walled carbon nanotubes (DGA-MWCNTs) were synthesized by sequential chemical reactions for removal of uranium from aqueous solution. Characterization studies were carried out using FT-IR spectroscopy, XRD and SEM analysis. Adsorption of uranium from aqueous solution on this material was studied as a function of nitric acid concen- tration, adsorbent dose and initial uranium concentration. The uranium adsorption data on DGA-MWCNTs followed the Langmuir and Freundlich adsorption isotherms. The adsorption capacity of DGA-MWCNTs as well as adsorp- tion isotherms and the effect of temperature on uranium ion adsorption were investigated. The standard enthalpy, entropy, and free energy of adsorption of the uranium with DGA-MWCNTs were calculated to be 6.09 kJ mole -1 , 0.106 kJ mole -1 K -1 and -25.51 kJ mole -1 respectively at 298K. The results suggest that DGA-MWCNTs can be used as efficient adsorbent for uranium ion removal.

Adsorption of La(III) onto GMZ bentonite: effect of contact time, bentonite content, pH value and ionic strength

Abstract: Bentonite has been studied extensively because of its strong adsorption capacity. A local Na-bentonite named GMZ bentonite, collected from Gaomiaozi County (Inner Mongolia, China), was selected as the first choice of buffer/backfill material for the high-level radioactive waste repository in China. In this research, the adsorption of La (ΙΙΙ) onto GMZ bentonite was performed as a function of contact time, pH, solid content and metal ion concentrations by using the batch experiments. The results indicate that the adsorption of La (III) on GMZ bentonite achieves equilibration quickly and the kinetic adsorption follows the pseudo-second-order model; the adsorption of La (III) on the adsorbent is strongly dependent on pH and solid content, the adsorption process follows Langmuir isotherm. The equilibrium batch experiment data demonstrate that GMZ bentonite is effective adsorbent for the removal of La (III) from aqueous solution with the maximum adsorption capacity of 26.8 mg g−1 under the given experimental conditions.

Efficient uranium(VI) biosorption on grapefruit peel: kinetic study and thermodynamic parameters

Abstract: The uranium(VI) biosorption by grapefruit peel was studied from aqueous solutions. Batch experiments was conducted to evaluate the effect of contact time, initial uranium(VI) concentration, initial pH, adsorbent dose, salt concentration and temperature. The equilibrium process was well described by the Langmuir, Redlich–Peterson and Koble–Corrigan isotherm models, with maximum sorption capacity of 140.79 mg g−1 at 298 K. The pseudo second order model and Elovish model adequately describe the kinetic data in comparison to the pseudo first order model and the process involving rate-controlling step is much complex involving both boundary layer and intra-particle diffusion processes. The effective diffusion parameter Di and Df values were estimated at different initial concentration and the average values were determined to be 1.167 × 10−7 and 4.078 × 10−8 cm2 s−1. Thermodynamic parameters showed that the biosorption of uranium(VI) onto grapefruit peel biomass was feasible, spontaneous and endothermic under studied conditions. The physical and chemical properties of the adsorbent were determined by SEM, TG-DSC, XRD and elemental analysis and the nature of biomass–uranium (VI) interactions was evaluated by FTIR analysis, which showed the participation of COOH, OH and NH2 groups in the biosorption process. Adsorbents could be regenerated using 0.05 mol L−1 HCl solution at least three cycles, with up to 80% recovery. Thus, the biomass used in this work proved to be effective materials for the treatment of uranium (VI) bearing aqueous solutions.

Environmental condition effects on radionuclide 64Cu(II) sequestration to a novel composite: polyaniline grafted multiwalled carbon nanotubes

Abstract: This work examines the sequestration of 64Cu(II) by sorption process onto plasma-induced polyaniline (PANI)-grafted multiwalled carbon nanotubes (denoted as MWCNTs/PANI) prepared by an plasma-induced grafting technique. The role of a variety of environmental conditions such as pH, ionic strength, natural organic matter (NOM) in the sorption of 64Cu(II) onto MWCNTs/PANI is studied. The results indicate that the sorption is strongly dependent on pH but independent of ionic strength. A positive effect of NOM on 64Cu(II) sorption is found at pH 7.5. The sorption isotherms in the absence and presence of NOM can be better described by Freundlich model than Langmuir model. Sorption isotherms of 64Cu(II) at higher initial NOM concentrations are higher than those at lower NOM concentrations. The thermodynamic data calculated from temperature-dependent sorption suggest that the sorption is spontaneous and enhanced at higher temperature. Results of this work suggest that MWCNTs/PANI may be a promising candidate for cost-effective treatments of 64Cu(II)-contaminated wastewaters.

Treatment of phosphogypsum waste using suitable organic extractants

Abstract: Phosphogypsum (PG) is a residue of the phosphate fertilizer industry that has relatively high concentrations of harmful radioactive materials. The reduction in concentration of the radionuclides from PG was investigated. The removal process is based on leaching of radionuclides using suitable organic extractants. The studied radionuclides were 226Ra, 210Pb, 238U and 40K. The factors affect the leaching process such as type of leaching materials, contact time, concentration of the desired solvent, liquid to solid ratio, and temperature were studied. Based on the experimental results, about 71.1, 76.4, 62.4, and 75.7% of 226Ra, 210Pb, 238U and 40K respectively were successfully removed from the PG. The reduction in the concentration of radionuclides was accompanied by reduction in the concentration of rare earth elements (∑REE) equals to 69.8%. Using the desired organic extractant under optimum conditions for treatment of the PG waste leads to obtain a decontaminated product that can be safely used in many industrial applications.

Removal of Zn(II) from aqueous solution by natural halloysite nanotubes

Abstract: Clay minerals have been widely used in wastewater disposal due to their strong sorption and complexation ability towards various environmental pollutants. In this study, the removal of Zn(II) from aqueous solution by natural halloysite nanotubes (HNTs) was studied as a function of various solution chemistry conditions such as contact time, pH, ionic strength, coexisting electrolyte ions and temperature under ambient conditions. The results indicated that the removal of Zn(II) by HNTs was strongly dependent on pH and ionic strength. Langmuir and Freundlich models were used to simulate the sorption isotherms of Zn(II) at three different temperatures of 293, 313 and 333 K. The thermodynamic parameters (ΔH 0, ΔS 0 and ΔG 0) calculated from the temperature dependent sorption isotherms indicated that the removal process of Zn(II) by HNTs was endothermic and spontaneous. At low pH, the removal of Zn(II) was dominated by outer-sphere surface complexation and/or cation exchange with Na+/H+ on HNT surfaces, whereas inner-sphere surface complexation was the main removal mechanism at high pH. From the experimental results, one can conclude that HNTs may have a good potentiality for the disposal of Zn(II)-bearing wastewaters.

Biosorption of uranium(VI) by a mangrove endophytic fungus Fusarium sp. #ZZF51 from the South China Sea

Abstract: The uranium(VI) accumulation was studied in detail by using the biomass of mangrove endophytic fungus Fusarium sp.#ZZF51 from the South China Sea. The uranium(VI) biosorption process onto the tested fungus powders was optimized at pH 4.0, adsorption time 60 min, and uranium(VI) initial concentration 50 mg L−1 with 61.89% of removal efficiency. According to Fourier transform infrared spectra for the tested fungus before and after loaded with uranium(VI), the results showed that both of hydroxyl and carboxyl groups acted as the important roles in the adsorption process. In addition, the experimental data were analyzed by using parameter and kinetic models, and it was obtained that the Langmuir isotherm model and the pseudo-second-order kinetic model provided better correlation with the experimental data for adsorption of uranium(VI).

Removal of uranium(VI) from aqueous solution using citric acid modified pine sawdust: batch and column studies

Abstract: This study described adsorption of uranium(VI) by citric acid modified pine sawdust (CAMPS) in batch and fixed-bed column modes at 295 K. The equilibrium adsorption data were analyzed by Langmuir, Freundlich, Koble–Corrigan and Dubinin–Radushkevich isotherm models. The results indicated that the Langmuir and Koble–Corrigan models provided the best correlation of the experimental data. The Elovish model was better to fit the kinetic process, which suggested that ion exchange was one of main mechanism. The effective diffusion parameter Di values indicated that the intraparticle diffusion was not the rate-controlling step. In fixed-bed column adsorption, the effects of bed height, feed flow rate, and inlet uranium (VI) concentration were studied by assessing breakthrough curve. The Thomas, the Yan and the bed-depth/service time (BDST) models were applied to the column experimental data to determine the characteristic parameters of the column adsorption. The results were implied that CAMPS may be suitable as an adsorbent material for adsorption of uranium (VI) from an aqueous solution.

Preliminary studies on 226Ra, 228Ra, 228Th and 40K concentrations in foodstuffs consumed by inhabitants of Accra metropolitan area, Ghana

Abstract: Knowledge of radioactivity levels in human diet is of particular concern for the estimation of possible radiological hazards to human health. However, very few surveys of radioactivity in food have been conducted in Ghana. The natural radionuclides 226Ra, 228Ra, 228Th and 40K were measured in the foodstuffs using gamma ray spectrometry. All samples were found to contain high 40K content in the range 87.77–368.50 Bq kg−1. The maximum concentration of 228Th and 40K were found in cassava to be 14.93 ± 3.86 and 368.50 ± 19.20 Bq kg−1, respectively. The total annual committed effective dose was estimated to be 4.64 mSv. The daily intake of radionuclides from food consumption reveals that cassava and plantain are the highest contributors, while millet is the lowest. The daily radionuclide intake from the foodstuffs consumed by the general public was 411.32 Bq and the daily internal dose resulting from ingestion of the radionuclides in the foodstuffs was 0.01 mSv. The radionuclide concentrations were comparable with those reported from other countries.

Study of uranium contamination of ground water in Punjab state in India using X-ray fluorescence technique

Abstract: The elemental concentration of uranium in the samples collected from the ground water and the canal water in the Bathinda district of Punjab state, India, have been investigated using X-ray fluorescence technique. The residues obtained after drying the water samples were analysed using the energy dispersive X-ray fluorescence spectrometer consisting of Mo-anode X-ray tube equipped with selective absorbers as an excitation source and an Si(Li) detector. The uranium concentration values in significant fraction of the shallow ground water samples from the hand pumps is found to be above the permissible level of 15 ppb recommended by World Health Organisation for the drinking water, and its values in the canal water samples are below 5 ppb. To investigate the flyash from the coal-fired thermal power plants as a possible source of ground water contamination, the water samples collected from the surroundings of the power plants and the flyash samples were also analyzed. The results rule out flyash as a source of uranium contamination. Agrochemical processes occurring in the calcareous soils in the region are the favoured potential source of uranium contamination of the ground water.

Biosorption characteristics of uranium(VI) from aqueous solution by pummelo peel

Abstract: The biomass pummelo peel was chosen as a biosorbent for removal of uranium(VI) from aqueous solution. The feasibility of adsorption of U(VI) by Pummelo peel was studied with batch adsorption experiments. The effects of contact time, biosorbent dosage and pH on adsorption capacity were investigated in detail. The pummelo peel exhibited the highest U(VI) sorption capacity 270.71 mg/g at an initial pH of 5.5, concentration of 50 μg/mL, temperature 303 K and contacting time 7 h. The adsorption process of U(VI) was found to follow the pseudo-second-order kinetic equation. The adsorption isotherm study indicated that it followed both the Langmuir adsorption isotherm and the Freundlich adsorption isotherm. The thermodynamic parameters values calculated clearly indicated that the adsorption process was feasible, spontaneous and endothermic in nature. These properties show that the pummelo peel has potential application in the removal of the uranium(VI) from the radioactive waste water.

Uranium and lead adsorption onto bentonite and zeolite modified with polyacrylamidoxime

Abstract: Polyacrylonitrile (PAN) and bentonite (B)/zeolite (Z)-PAN composites were prepared by direct polymerization of acrylonitrile (AN) and AN adsorbed onto B and Z. PAN and the composites were subjected to amidoximation procedure to obtain polyacrylamidoxime (PAO), B-PAO and Z-PAO compositions. The structural features were evaluated by FT-IR, XRD and SEM analysis. The adsorption dependency of the materials on ion concentration, temperature and time were investigated for Pb2+ and UO2 2+. The adsorption capacities of B/Z-PAO composites were higher than those of pure PAO. The values of enthalpy and entropy changes were positive. The kinetics of the adsorption was well defined by the pseudo second order rate model. For the use of 1 M HCl as a regenerative effluent, the composites were reusable for five sequential treatments without any change in their structures whereas PAO completely gelled in the first use.

Removal of radiocobalt from aqueous solution by oxidized MWCNT

Abstract: The study was undertaken to evaluate the feasibility of oxidized multiwalled carbon nanotube (oxidized MWCNT) for the removal of radiocobalt (60Co) from aqueous solutions. The oxygen functional groups of oxidized MWCNT were characterized by FT-IR and XPS. Batch experiments were performed to study the sorption of cobalt as a function of contact time, solid contents, pH, ionic strength, foreign ions, and temperature. Two kinetic models viz. pseudo-first-order and pseudo-second-order were used to determine kinetic sorption parameters, and the kinetic sorption could be described more favorably by the pseudo-second-order model. The thermodynamic parameters (∆G°, ∆S°, ∆H°) calculated from the temperature-dependent sorption isotherms indicated that the sorption of Co(II) on oxidized MWCNT was an endothermic and spontaneous processes. The results suggest that oxidized MWCNT can be used efficiently in the treatment of industrial effluents containing radioactive and heavy metal ions.

99mTc–meropenem as a potential SPECT imaging probe for tumor hypoxia

Abstract: Meropenem was successfully radiolabeled with 99mTc in high labeling yield (92 ± 2%) and stability (~6 h). 99mTc–meropenem showed high accumulation in tumor hypoxic tissue (4.193% injected dose/g organ). 99mTc–meropenem showed high ability to differentiate the tumor tissue from inflamed or infected tissues in different mice models as its T/NT ratio ~4 in case of tumor mice model while T/NT ratio ~1 in case of inflamed mice model. So, 99mTc–meropenem showed high selectivity in comparison with FDG-PET and 99mTc-nitroimidazole analogues. Thus, 99mTc–meropenem could be used as a selective potential imaging agent for diagnosis of tumor hypoxia.

Nuclear forensics: searching for nuclear device debris in trinitite-hosted inclusions

Abstract: This study documents the 3D morphology of trinitite-hosted metallic inclusions and the first observations of alloys consisting primarily of Pb, Ta, Ga, and W. Scanning electron and backscatter electron imaging, as well as energy dispersive X-ray spectra chemical composition data are reported for heavy metal inclusions in 14 different samples of trinitite. Inclusions consisting of Fe–Ti–Si are the most abundant and presumably derived predominantly from the explosion tower. Grains of Cu, Pb, Ta + Ga + W were also observed and are likely derivatives of the trinitite device wiring, tamper, and tamper and core, respectively. Additionally, a Ba-rich grain and multiple zircons (ZrSiO4) were observed in a large majority of samples. The spherical morphology and the ubiquitous positioning of the heavy metal inclusions on the crater walls of the glassy trinitite surfaces indicate a two-step formation. Stage one involves formation of the glassy trinitite, while the second stage involved the precipitation of the inclusions that were incorporated onto the surface of the trinitite. Furthermore, the precarious positioning of these inclusions further emphasizes the need for analysis using non-destructive techniques prior to methods employing a bulk sample digestion approach.

Development of a cosmic veto gamma-spectrometer

Abstract: Cosmic radiation contributes significantly towards the background radiation measured by a gamma-spectrometer. A novel cosmic veto gamma-spectrometer has been developed that provides a mean background reduction of 54.5%. The system consists of plastic scintillation plates operated in time-stamp mode to detect coincident muon interactions within an HPGe gamma-spectrometer. The instrument is easily configurable and provides improved sensitivity for radionuclides indicative of nuclear weapons tests and reactor incidents, including 140Ba, 95Zr, 99Mo, 141Ce, 147Nd, 131I, 134Cs and 137Cs. This has been demonstrated for Comprehensive Nuclear-Test-Ban Treaty applications to obtain the required 140Ba MDA of 24 mBq within 2 days counting. Analysis of an air filter sample collected during the Fukushima incident indicates improved sensitivity compared to conventional gamma-spectrometers.

Hybrid grafted ion exchanger for decontamination of radioactive cesium in Fukushima Prefecture and other contaminated areas

Abstract: We have developed a material that can be used to remove cesium (Cs) in Fukushima Prefecture and other contaminated areas. The developed material was prepared by radiation-induced graft polymerization of ammonium 12-molybdophosphate and acrylonitrile onto nonwoven polyethylene fabric. To evaluate the adsorption performance of the developed material, we conducted batch and column experiments by using a Cs solution with a concentration of 1 ppm at pH 7. In the batch study, the adsorbent was able to remove 90, 87 and 64 % of Cs from pure water, acidic water and seawater, respectively. In the column study, adsorbent packed in a column with a diameter of 7 mm and a height of 5 cm was able to remove nearly the entire amount of dissolved Cs. The solution (1 ppm Cs at pH 7) was pumped into the column at a space velocity of 300 h−1, in which the Cs adsorption capacity at the breakthrough point reached 54 g-Cs/kg-adsorbent. Adsorbent grafted into a cartridge with a diameter of 4 cm and a height of 3.8 cm was used in a field test on removing dissolved radioactive Cs in Iitate-mura, and this test was conducted successfully.

Comparative study of strontium adsorption on dioctahedral and trioctahedral smectites

Abstract: Bentonites which are characterized by good rheological, mineralogical and chemical stability is considered used as sealing barriers in multibarrier Slovak system of deep geological repository for high-level radioactive waste and spent nuclear fuel. In Slovak Republic there are several significant deposits of bentonite, which are characterized by appropriate adsorption properties and meet the geotechnical requirements for this type of barriers. Study of adsorption properties of bentonites and other smectites is an essential step for developing the migration model long-lived corrosion and activation products, and fission products of uranium. Nuclear wastes contain the most important nuclear fission products, radioisotopes 134Cs and 137Cs. The present paper investigates and compares the cesium adsorption properties of Slovak and North America bentonites composed mainly of dioctahedral smectite montmorillonite (J, L, SAz-1 and STx-1) and trioctahedral smectites saponite (SapCa-2) and hectorite (SHCa-1).

Removal and recovery of uranium from aqueous solution by tea waste

Abstract: Experiments on the removal and recovery of U(VI) from aqueous solution by tea waste were conducted. The adsorbent was characterized by scanning electron microscope and energy dispersive spectrometer before and after the adsorption treatment. The removal of U(VI) amounts to 86.80 % at optimum pH 6. The adsorption process reaches its equilibrium in 12 h at 308 K, and the kinetic characteristic can be described by the pseudo-second-order kinetic equation. The amount of adsorption increases from 22.92 to 142.21 mg g−1 with the decrease of tea waste dosage from 100 to 10 mg for solution with an initial uranium concentration of 50 mg L−1. Desorption for the four strippants is higher than 80 %. The equilibrium data are more agreeable with Freundlich isotherm than Langmuir isotherm.

Solvent extraction of uranium from lean grade acidic sulfate leach liquor with alamine 336 reagent

Abstract: This paper describes the solvent extraction studies carried out on an acidic low assay uranium bearing leach liquor generated during sulfuric acid leaching of a refractory uranium ore using alamine 336–isodecenol–kerosene reagent combine. The leach liquor has a U3O8 content of about 270 mg/L, free acidity 2.4 N H2SO4 and total dissolved solids concentration of 260 g/L. Process parameteric variation studies indicated strong influence of free acidity of the leach liquor, alamine 336 concentration and aqueous to organic phase ratio on the extraction efficiency of uranium. An extraction efficiency of about 95% was achieved when the free acidity of leach liquor was 1 N H2SO4 or lower, using 2% (v/v) alamine 336 at ambient temperature with an aqueous to organic phase ratio of 1:1. The loading capacity under these conditions was 1.2 g/L of U3O8. About 98% of the uranium values could be stripped from the loaded organic using 1 N NaCl in 0.2 N H2SO4. The solvent extraction studies aided in developing a suitable process flowsheet for treating refractory uranium ores which need high acidity during leaching and relatively lower acidity for purification by solvent extraction.

Monitoring of radon anomalies in South-Eastern part of Romania for earthquake surveillance

Abstract: South-Eastern part of Romania has a highest potential seismic risk in Europe due to the earthquake-prone Vrancea zone placed at conjunction of four tectonic blocks in the South-Eastern part of Carpathian Arc. This paper is an attempt to analyze the development of radon pre-earthquake anomaly in relation with moderate seismic events in Vrancea area through permanent monitoring with solid state nuclear track detectors CR-39 detectors. Radon in air above the ground was measured during 1 year period (November 2010–October 2011) in four selected test sites: Vrancioaia (VRI) and Plostina (PLOR) located in Vrancea zone, and Muntele Rosu-Cheia and Bucharest. During sampling period recorded earthquakes that occurred mostly in Vrancea epicentral region were minor-moderate of moment magnitudes in range of \( 2.0 \le M_{w} \le 4.9 \). The average radon concentration in air above the ground measured with CR-39 detectors and 10 days period recorded simultaneously at all test sites, registered the following values: (1) in Vrancea area (similar in VRI and PLOR) was 1094.58 \( \pm \) 150.3 Bq/m3; (2) at Muntele Rosu-Cheia seismic station measured in a mountain tunnel laboratory was 3695.91 ± 440 Bq/m3; (3) at Bucharest station was 380.53 \( \pm \) 69.17 Bq/m3, and 10 days CRn fluctuations in the range of (88 \( \pm \) 40 to 912 \( \pm \) 130 Bq/m3). Clear radon anomalies, mostly at VRI and PLOR in Vrancea epicentral area as well as at Muntele Rosu-Cheia have been measured before seven minor earthquakes which were recorded in the range of moment magnitude \( 4 \le M_{w} \le 4.9 \) in Vrancea area. Temporal variation of radon in air near the ground have been examined in relation with meteorological parameters like as air temperature, relative humidity, air pressure and wind velocity. Permanent monitoring of radon concentration anomalies in seismic area Vrancea is an important issue as surveillance tool in the field of earthquake hazard for Romania.

Gamma-ray absorption using rubber—lead mixtures as radiation protection shields

Abstract: In the present study five samples of special rubber–lead were fabricated each of them consists of lead and rubber with different weight ratios. The fabrication was carried out through the process of mixing under compression pressure. Gamma-ray transmission method was employed to determine the linear attenuation coefficient for narrow collimated mono-energetic beams of gamma-rays emitted from 241Am 0.059, 152Eu 0.13 and 137Cs 0.662 MeV. The linear attenuation coefficient of standard rubber–lead shield was also experimentally determined. The percentage of lead in standard rubber–lead shield was determined through the calibration curve or by a simple computer program written in MATLAB. All prepared samples are characterized as flexible and gives a good homogeneity. samples no. 4 & 5 offers the best performance as a radiation protection shields. The results showed an inverse proportionality between the linear attenuation coefficient μl and E, and μl has a direct proportionality with mixing ratios (sample density). The results showed an inverse proportional between the half value layers and the average linear attenuation coefficients of the various samples.

Effect of gamma-irradiation on adsorption properties of Slovak bentonites

Abstract: One of the basic prerequisites for the use of bentonite as engineering barrier in deep geological repositories for radioactive waste and spent nuclear fuel is their stability against ionizing radiation stemming from radionuclides present in radioactive waste and spent nuclear fuel. The aim of this study was to compare the changes in the adsorption properties of selected Slovak bentonites in relation to uranium fission products (137Cs and 90Sr), prior to and after irradiation of bentonites with a 60Co γ-source and specifying the changes in the structure of Slovak bentonites induced by γ-radiation. The changes in irradiated natural forms of Slovak bentonites and the changes in their natrified analogues and fractions with different grain sizes were studied from five Slovak deposits: Jelsový potok, Kopernica, Lastovce, Lieskovec and Dolna Ves. The EPR spectra of bentonites from deposits Jelsový potok and Lieskovec with absorbed doses of 104 and 105 Gy γ-rays showed no changes in the structure of the studied Slovak bentonites. The changes, which in terms of structure destabilization can be considered insignificant, occurred only in bentonites with absorbed doses of γ-radiation as much as 1 MGy. The absorbed dose of 1 MGy γ-radiation did not have an effect on the adsorption of cesium on every studied bentonite. Changes that can also be regarded as insignificant occurred only during strontium adsorption, especially on Fe–bentonite from deposit Lieskovec and Ca–Mg–bentonite from deposit Jelsový potok, when an increase in the adsorption capacity occurred. Attention should be paid in further research of this topic which would require carrying out experiments on bentonite samples with absorbed doses higher by several orders of magnitude.

Adsorption of uranium from aqueous solution using HDTMA + -pillared bentonite. Isotherm, kinetic and thermodynamic aspects

Abstract: The ability of hexadecyltrimethylammonium cation pillared bentonite (HDTMA+-bentonite) has been explored for the removal and recovery of uranium from aqueous solutions. The adsorbent was characterized using small-angle X-ray diffraction, high resolution transmission electron microscopy, and Fourier transform infrared spectroscopy. The influences of different experimental parameters such as solution pH, initial uranium concentration, contact time, dosage and temperature on adsorption were investigated. The HDTMA+-bentonite exhibited the highest uranium sorption capacity at initial pH of 6.0 and at 80 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° (308 K), ΔH°, and ΔS° were determined to be −31.64, −83.84 kJ/mol, and −169.49 J/mol/K, respectively, which demonstrated the sorption process of HDTMA+-bentonite towards U(VI) was feasible, spontaneous, and exothermic in nature. The adsorption on HDTMA+-bentonite was more favor than Na-bentonite, in addition the saturated monolayer sorption capacity increased from 65.02 to 106.38 mg/g at 298 K after HDTMA+ pillaring. Complete removal (≈100%) of U(VI) from 1.0 L simulated nuclear industry wastewater containing 10.0 mg U(VI) ions was possible with 1.5 g HDTMA+-bentonite.

Sorptive removal of cobalt, strontium and cesium onto manganese and iron oxide-coated montmorillonite from groundwater

Abstract: Applicability of montmorillonite, manganese oxide-coated montmorillonite (MOCM) and iron oxide-coated montmorillonite (IOCM) as backfill materials in permeable reactive barrier (PRB) to remediate contaminated groundwater was investigated. Single- and bi-solute competitive sorptions of Co, Sr and Cs were conducted. The Freundlich, Langmuir and Dubinin-Radushkevich models fitted the single-solute sorption data well (R 2 > 0.95). Maximum sorption capacities (q mL) of Co and Sr predicted by the Langmuir model were in the order of MOCM (0.37 mmol/g for Co and 0.28 mmol/g for Sr) > montmorillonite (0.27 mmol/g for Co and 0.19 mmol/g for Sr) ≈ IOCM (0.23 mmol/g for Co and 0.21 mmol/g for Sr), while those of Cs were in the order of montmorillonite (1.11 mmol/g) > MOCM (0.68 mmol/g) > IOCM (0.62 mmol/g). In the bi-solute sorptions, the sorbed amount of one solute decreased due to the presence of the other competing metal ion. Langmuir model parameters for single-solute (q mL and b L) and bi-solute ( $$ q_{\text{mL}}^{*} $$ and $$ b_{\text{L}}^{ *} $$ ) sorptions were compared to analyze the effect of competition between the metal ions. The competitive Langmuir (R 2 > 0.81) and P-factor (R 2 > 0.82) models predicted the bi-solute competitive sorption data well but not the SRS model (0.003 < R 2 < 0.97).

Lichens as biomonitors at indoor environments of primary schools

Abstract: A biomonitoring study, using transplanted lichens Flavoparmelia caperata, was conducted to assess the indoor air quality in primary schools in urban (Lisbon) and rural (Ponte de Sor) Portuguese sites. The lichens exposure period occurred between April and June 2010 and two types of environments of the primary schools were studied: classrooms and outdoor/courtyard. Afterwards, the lichen samples were processed and analyzed by instru- mental neutron activation analysis (INAA) to assess a total of 20 chemical elements. Accumulated elements in the exposed lichens were assessed and enrichment factors (EF) were determined. Indoor and outdoor biomonitoring results were compared to evaluate how biomonitors (as lichens) react at indoor environments and to assess the type of pollutants that are prevalent in those environments.

Study on selective separation of cesium from high level liquid waste using a macroporous silica-based supramolecular recognition absorbent

Abstract: A macroporous silica-based supramolecular recognition absorbent (Calix[4] + Dodecanol)/SiO2–P, was prepared by successive impregnation and fixing the 1,3-[(2,4-diethylheptylethoxy)oxy]-2,4-crown-6-Calix[4]arene (Calix[4]arene-R14) and its molecule modifier 1-Dodecanol onto SiO2 silica-based polymer support. The characterization of (Calix[4] + Dodecanol)/SiO2–P was examined by thermal gravimetry and differential thermal analysis and electron probe microanalysis. Relatively large separation factors of Cs and other metal ions (α Cs/M + ) above 60 were obtained in the presence of 3 M HNO3. The adsorption data of Cs(I) fitted well with Langmuir isotherm and the maximum adsorption capacity was estimated to be 0.19 mmol g−1. The Cs(I) in 3 M HNO3 were also effectively adsorption on (Calix[4] + Dodecanol)/SiO2–P in the column operation, and the loaded Cs(I) was successfully eluted with an eluent of H2O. The column packed with (Calix[4] + Dodecanol)/SiO2–P had excellent reusability after three cycles.