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1.
Adsorption and desorption of uranium(VI) from dilute aqueous solutions by Eucalyptus citriodora distillation sludge was studied in a batch mode. The potential of Eucalyptus citriodora distillation sludge to remove uranium(VI) from aqueous solutions has been investigated at different conditions of solution pH, metal ion concentrations, biosorbent dosage, biosorbent particle size, contact time and temperature. The results indicated that biosorption capacity of Eucalyptus citriodora distillation sludge was strongly affected by the medium pH, the biosorbent dose, metal ion concentrations and medium temperature. Reduction in particle size increased the biosorption capacity. Langmuir and Freundlich isotherm models were applied to biosorption data to determine the biosorption characteristics. An optimum biosorption capacity (57.75 mg/g) was achieved with pH 4.0, particle size 0.255 mm, biosorbent dose 0.5 g/100 mL and initial uranium(VI) concentration of 100 mg/L. Uranium(VI) removal by Eucalyptus citriodora distillation sludge was rapid, the equilibrium was established within 60 min and pseudo-second-order model was found to fit with the experimental data. The biosorption process decreased with an increase in the temperature indicating its exothermic nature. Pretreatments of biomass with different reagents affected its biosorption capacity. A significant increase (34 %) in biosorption capacity (83.25 mg/g) was observed with benzene treatment. Fourier-transform infra-red studies showed the involvement of carbonyl, carboxyl and amide groups in the biosorption process. The results indicated that sulfuric acid had the best effects as an eluent showing 93.24 % desorption capacity.  相似文献   

2.
The degradation of organic wastes and the corrosion of metallic wastes and steel containers in low and intermediate level radioactive waste (LLW/ILW) repositories are important processes that affect repository geochemistry and the speciation and transport of radionuclides. Gas is generated in association with these degradation processes and this has the potential to overpressure the repository, which can promote transport of groundwater and gas, and consequently radionuclide transport. Microbial activity plays an important role in organic degradation, corrosion and gas generation through the mediation of reduction–oxidation reactions.  相似文献   

3.
The goal of the paper was to determine the activity of 137Cs and 40K radionuclides as well as heavy metals Zn, Cr, Pb in soil samples taken from the Tatra National Park in the south of Poland. The samples were obtained as cores (10 cm in diameter) from the top 10-cm layer of the soil. Each sample was divided into three subsamples (a, b and c), where a was the subsample closest to the surface and c was the deepest one. Activity of the radionuclides was determined by means of gamma spectrometry, while analysis of heavy metals was performed (after microwave digestion) using atomic absorption spectrometry technique. The highest activity of cesium-137 was detected (5112 ± 120 Bq kg?1) in the “a” layer of the core with the peak concentration of cesium-137 (14,452 ± 278 Bq m?2) in the whole soil core. The highest detected concentration of heavy metals was: Zn—52.8 ± 4.4 mg kg?1, Pb—260.1 ± 9.4 mg kg?1, Cr—52.8 ± 4.4 mg kg?1, respectively. Cluster analysis and principal component analysis were used to examine the obtained data. Application of statistical analysis tools allowed specifying the interdependencies between the examined variables.  相似文献   

4.
Iron and Mn oxides and associated radionuclides in soils and sediments from the radioactive waste burial grounds at Oak Ridge National Laboratory have been selectively extracted using wet chemical techniques. Product-moment-correlation analyses have demonstrated that 60Co and various actinides, principally 244Cm, 241Am and 238Pu are dominantly associated with Mn oxides. Correlation coefficients between these radionuclides and Fe oxides and organic C are generally very low. The important role of Mn oxides in radionuclide adsorption is attributed to their unique surface and colloidal properties. The data illustrate the importance of the Mn oxide component of soils and sediments in controlling transition metal and actinide solubility.These results suggest two major implications for the disposal of radioactive waste. First, in order to minimize future 60Co and actinide mobilization from disposal sites, a chemical environment in which Mn oxides are least soluble should be maintained. Second, the liberal use of Mn oxides in waste management operations might improve long-term retention of these radionuclides. Deep-sea Mn modules, which may in the future be mined for their trace metal contents, could serve as a ready supply of Mn oxide for waste disposal applications.  相似文献   

5.
Nuclear facilities in coastal locations often discharge low‐level liquid wastes into the sea and the radioisotopes in these discharges are of interest both in assessing possible environmental impacts and as tracers for coastal processes. The distributions of a range of artificial radionuclides, derived from the authorized discharges from British Nuclear Fuels (BNFL) Sellafield, have been determined in the sediments of an intertidal salt marsh in the Esk Estuary, Cumbria, UK. Where published discharge histories exist (for 137Cs, 238Pu, 239,240Pu and 241Am), the sediment core‐profile distributions of these radionuclides have been compared with the releases from Sellafield, and consistent values of the accumulation rate (0·226 ± 0·007 g cm?2 yr?1) are obtained. A quantitative model has been developed, describing association of radionuclides with suspended particulate material, which is then accumulated and mixed in an offshore mud patch before resuspension and deposition in the salt marsh. The model has been used to describe radionuclide distributions observed in both the mud patch and the salt marsh, and to identify isotopes for which post‐depositional remobilization or solution transport from the discharge point are important. The behaviour of the commonly studied isotopes (137Cs, 238Pu, 239,240Pu and 241Am) is similar to that observed at this and other nearby locations. The activation product isotope 236U is enhanced in these sediments over the natural baseline by four to eight orders of magnitude, and the results suggest that Sellafield‐derived uranium is comparably mobile to 137Cs in these sediments although the processes governing the behaviour of these two elements may be different. In situ production of 241Am by decay of its 241Pu parent has generated only 17% of the current sediment inventory of this isotope, insufficient to account for the increase over the last 20–25 years, and suggesting that the input material for these sediments is preferentially enriched in Am relative to Pu during transport from the offshore mud patch. The discharge history of 244Cm, which is unknown, has also been reconstructed from the sediment profile and the model.  相似文献   

6.
Biosorption is a promising technology for the removal of heavy metals from industrial wastes and effluents. In the present study, biosorption of Pb2+, Cu2+, Fe2+ and Zn2+ onto the dried biomass of Eucheuma denticulatum (Rhodophyte) was investigated as a function of solution pH, contact time, temperature and initial metal ion concentration. The experimental data were evaluated by Langmuir, Freundlich, Temkin and Dubinin–Radushkevich isotherm models. The sorption isotherm data followed Langmuir and Freundlich models, and the maximum Langmuir monolayer biosorption capacity was found as 81.97, 66.23, 51.02 and 43.48 mg g?1 for Pb2+, Cu2+, Fe2+ and Zn2+, respectively. The sorption kinetic data followed pseudo-second-order and intraparticle diffusion models. Thermodynamic study revealed feasible, spontaneous and endothermic nature of the sorption process. Fourier transform infrared analysis showed the presence of amine, aliphatic, carboxylate, carboxyl, sulfonate and ether groups in the cell wall matrix involved in metal biosorption process. A total of nine error functions were applied in order to evaluate the best-fitting models. We strongly suggest the analysis of error functions for evaluating the fitness of the isotherm and kinetic models. The present work shows that E. denticulatum can be a promising low-cost biosorbent for removal of the experimental heavy metals from aqueous solutions. Further study is warranted to evaluate its potential for the removal of heavy metals from the real environment.  相似文献   

7.
Uranium is a common contaminant of concern in the aquifers of nuclear waste management facilities around the world. The Electrochemical Plant (ECP) (Krasnoyarsk Krai, Russia) and the Angarsk Electrolysis Chemical Complex (AEСC) (Irkutsk Region, Russia) have produced enriched uranium and related nuclear wastes (sludge materials) since the 1960s. The results of the detailed sampling of groundwater and waste solutions near the storage sites of radioactive waste are presented elsewhere (Gaskova et al., 2011, Boguslavskiy et al., 2012). A number of experimental studies were conducted in the laboratory (a) to investigate the uranium-containing sludge leaching by regional groundwater and (b) to understand the ability of host sediments to retain major and minor components from drainage solutions as a function of the water/rock ratio (indicating the timescale over which the behavior is observed). The geochemical modeling code “HCh” was applied to simulate these processes and to predict the long-term environmental impact of residual uranium. The experimental and thermodynamic results indicate that U leaching from the sludge materials is less dependent on the specific solubility of the sludge sediments and more dependent on the solid uranium species in this sludge. The model simulation of uranium sorption in dynamic experiments was successful only in the case of the permanent filtration of less mineralized groundwater in fine-grained clay rocks. To more accurately describe the potential future release of U from the residual waste sites, a series of batch reactor experiments needs to be conducted.  相似文献   

8.
陈璋如  赵云龙 《铀矿地质》1992,8(4):223-227
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9.
放射性废物处置研究进展   总被引：1，自引：0，他引：1  
放射性废物的处置是制约核能可持续发展的关键因素,目前已成为国际社会关注的热点问题之一.针对处置场地核素运移污染的风险问题,对放射性废物的处置及其选址、核素运移试验和核素运移模型进行了回顾和论述.指出采用多重屏障系统进行放射性废物的处置,其安全性是可以得到保障的;处置场的选址应遵循就近原则,并应从环境水文地质的角度来构建...  相似文献   

10.
The principal aspects of reconstruction of conditions and paths of fluid migration in massifs of crystalline rocks are considered. The spatiotemporal relationships between stress fields, brittle failure, and migration of radionuclides are discussed. The main attention is focused on the staged character of tectonic events, fluid circulation conditions, and the sequence of uranium mineral formation as determined with structural, geological, tectonophysical, petrophysical, petrographic, mineralogical and geochemical, microstructural, microthermometric, and radiographic methods. As is exemplified in uranium deposits and massifs of silicic igneous rocks, the comprehensive consideration of the tectonodynamics of fluid-conducting structural elements and radionuclide migration is necessary for providing insights into the localization and redistribution of uranium, the PT conditions of uranium ore formation, and the forecast for long-term safety of disposal of radioactive wastes in crystalline rocks.  相似文献   

11.
Asexual spores of the filamentous fungus Rhizopus arrhizus were used as the resting biomass as they tolerate chitosan gelling for mycelia growing in chitosan beads. Biosorption of lead using the dead detergent pre-treated chitosan-immobilised and grown fungal beads was performed with initial lead (II) nitrate concentrations ranging from 9.02 to 281.65 mg/L. The adsorption data were best correlated with equilibrium adsorption isotherms in the order Redlich–Peterson, Langmuir, Freundlich and Fritz–Schlünder by non-linear regression. The biosorption kinetic model of pseudo second-order (R 2 > 0.99) fitted better than pseudo first-order and modified pseudo first-order models. Among the four pseudo second-order kinetic models, the Blanchard model was the best fit for the experimental biosorption data. The rate-limiting step of biosorption of lead was shown to be intraparticle diffusion controlled according to Weber and Morris model fitting. The beads could be regenerated using 1 M nitric acid solution. This illustrated the good performance of the beads for regenerated sorption/desorption at least five cycles.  相似文献   

12.
Assuring safe disposal and long-term storage of radioactive and toxic wastes corresponds to a primary environmental task of present societies. To improve any technical limitation, a mechanistic understanding of the processes governing the binding of heavy metals and radionuclides is required. In this study, the significance of synchrotron-based X-ray microprobes for elucidating the spatial distribution and the speciation of radionuclides in highly heterogeneous waste repository materials will be outlined. A case study on the uptake process of Co in cementitious engineered barrier materials exposed to microbial degradation will be presented.  相似文献   

13.
The transportation of colloidal radionuclides by groundwater was subject to theoretical analysis. The far field of radioactive contamination of the underground environment (liquid waste pumping sites or storage of solidified waste) is dominated by pseudocolloids, i.e., colloidal particles of natural origin contaminated with radionuclides upon contact of groundwater with radioactive materials. Properties of real pseudocolloids were analyzed at sites of radioactive contamination of the underground environment. Based on a probabilistic approach, we developed a mathematical model of pseudocolloid transportation by groundwater, taking into account the difference in size of colloidal particles and the occurrence of nonradioactive natural particles with a similar composition in the groundwater. It is proved that nonuniform dimensions of the particles considerably affect the water transportation rate.  相似文献   

14.
Two types of Shrimp Chitin derivatives and two types of Iranian natural Zeolite derivatives (Firuzkooh Clinoptiliolite) were studied for adsorption and treatment of low-level radioactive liquid waste (LLW). Chitin with lowers than 10% and Chtiosan with higher than 90% deacetylation factor were selected as natural organic adsorbents. Natural Cliniptilolite of Firuzkooh area and Na form derivatives of it were selected as natural inorganic adsorbents. The static and dynamic ion exchange experimental results show that the adadsorption efficiency depend on particle size, PH, adsorbent type, deacetylation factor (in Chitin adsorbents) and cation type. The best Cs adsorption occurred in Na form Clinoptilolite. Nevertheless Chitin derivatives, particularly Chitosan, are more efficient than Zeolite adsorbents for removing of radionuclides such as 137Cs, 54Mn, 90Sr and 60Co. Adsorption performance was discussed and compared with each other.  相似文献   

15.
High concentrations of several radionuclides were reported in the sea near the Fukushima Daiichi Nuclear Power Station (FDNPS) in Japan due to the nuclear accident that occurred on 11 March 2011. The main source of these concentrations was leakage of highly radioactive liquid effluent from a pit in the turbine building near the intake canal of Unit-2 of FDNPS through a crack in the concrete wall. In the immediate vicinity of the plant, seawater concentrations reached 68 MBq m?3 for 134Cs and 137Cs, and exceeded 100 MBq m?3 for 131I in early April 2011. These concentrations began to fall as of 11 April 2011 and, at the end of April, had reached a value close to 0.1 MBq m?3 for 137Cs. Following the nuclear accident, the Tokyo Electric Power Company (TEPCO) had initiated intense monitoring of the environment including the Pacific Ocean. Seawater samples were collected and the concentrations of few radionuclides were measured on a wide spatial and temporal scale. In this study, the measured concentrations of different radionuclides near the south discharge canal of the FDNPS were used to estimate their leakages into the Pacific Ocean. The method is based on estimating the release rates that reproduce the concentration of radionuclides in seawater at a chosen location using a two-dimensional advection–dispersion model in an iterative manner. The radioactive leakages were estimated as 5.68 PBq for 131I, 2.24 PBq for 134Cs and 2.25 PBq for 137Cs. Leakages were also estimated for 99mTc, 136Cs, 140Ba and 140La and they range between 0.02 PBq (99mTc) and 0.53 PBq (140Ba). It was estimated that about 11.28 PBq of radioactivity in total was leaked into the Pacific Ocean from the damaged FDNPS. Out of this, 131I constitutes 50.3 %; 134Cs 20 %; 137Cs 20 %; 140Ba 4.6 %; 136Cs 2.6 %; 140La 2.3 % and 99mTc 0.2 % of the total radioactive leakage. Such quantitative estimates of radioactive leakages are essential prerequisites for short-term and local-scale as well as long-term and large-scale radiological impact assessment of the nuclear accident.  相似文献   

16.
In this study, dried anaerobic digested sludge (DADS) was utilized to remove 4-chlorophenol (4-CP) from aqueous solutions. Batch biosorption experiments were carried out to investigate the effects of physicochemical parameters such as pH, contact time, biosorbent dosage, and initial concentration. Artificial neural network (ANN) was then used to predict the removal efficiency of the process. The comparison between predicted and experimental results provided a high degree of determination coefficient (R2 = 0.98), indicating that the model could predict the biosorption efficiency with reasonable accuracy. Biosorption data were successfully described by the Freundlich isotherm and pseudofirst-order model. The Weber–Morris kinetic model indicated that intraparticle diffusion was not the only rate-controlling step, and other mechanisms may be involved in the biosorption process. The optimum pH was detected to be 3 for DADS. By increasing contact time and biosorbent dosage, the removal efficiency of 4-CP increased. Also, a decreasing trend was observed when initial concentrations were increased. The findings suggested that the results predicted by ANN are very close to the experimental values, and DADS as an available adsorbent can efficiently remove 4-CP from aqueous solutions.  相似文献   

17.
The candidate repository for high-level nuclear waste in the Gorleben salt dome, Germany, is expected to host 8,550 tonnes of uranium in burnt fuel. It has been proposed that 5,440 waste containers be deposited at a depth of about 800?m. There is 260?C280?m of siliciclastic cover sediments above the proposed repository. The potential groundwater contamination in the siliciclastic aquifer is simulated with the TOUGHREACT and TOUGH2-MP codes for a three-dimensional model with 290,435 elements. Two deterministic cases are simulated. The single-phase case considers the transport of radionuclides in the liquid phase only. The two-phase case accounts for hydrogen gas generated by the corrosion of waste containers and release of gaseous C-14. The gas release via a backfilled shaft is assumed to be steady (non-explosive). The simulation period is 2,000,000 years for the single-phase case and 7,000 years for the two-phase case. Only the radioactive dose in the two-phase case is higher than the regulatory limit (0.1?mSv/a).  相似文献   

18.
Fernald site produced over 500 million pound of uranium metal products from 1952 to 1989 resulting in a huge quantity of hazardous waste to be stored, treated and transported for final disposal. The structural integrity evaluation of specific types of waste containers used in the Fernald Closure Project are briefly presented in this paper. Metal containers of various shapes and sizes, concrete silos, gondola rail cars were successfully used for storage and disposal of low-level waste. Computer solutions were obtained using finite element analyses techniques, destructive and non-destructive tests were used to get a realistic response to complex loading conditions. Structural integrity is evaluated for concrete silos built in the fifties, unique metal containers and fiberglass rail car lid. A failure modes and effects analysis was also made for the railcar lid to identify the weak link for postulated failure mechanisms. Establishing the structural integrity was a key to the reliability of the various containment systems for a successful storage, transportation and final disposal of the low-level radioactive wastes.  相似文献   

19.
Arsenic is a ubiquitous element in the environment and occurs naturally in both organic and inorganic forms. Under aerobic condition, the dominant form of arsenic in waters is arsenate, which is highly mobile and toxic. Arsenic poisoning from drinking water remains a serious world health issue. There are various standard methods for arsenic removal from drinking waters (coagulation, sorption, ion-exchange reactions or methods of reverse osmosis) and alternative methods, such as biosorption. Biosorption of arsenic from natural and model waters by native or chemically modified (with urea or ferric oxyhydroxides) plant biomass prepared from sawdust of Picea abies was studied. The kinetic of the adsorption process fitted well the pseudo second order adsorption model and equilibrium was achieved after 2 h. The results showed that biosorption was well described by both Langmuir and Freundlich isotherms. The maximum biosorption capacity of the sawdust modified with ferric oxyhydroxides, evaluated by Langmuir adsorption model, was 9.259 mg/g, while the biosorption capacity of unmodified biosorbent or biosorbent modified with urea was negligible. The adsorption capacity is comparable to results published by other authors, suggesting that the prepared chemically modified biosorbent has potential in remediation of contaminated waters.  相似文献   

20.
This paper reports the results of the investigations of 2006–2007 on the distribution and migration forms of artificial radionuclides and chemical elements in the Ob-Irtysh water system. Three regions were studied. One of them is a local segment of the Ob River upstream from the confluence with the Irtysh River; its investigation allowed us to estimate the general radioecological state of the aquatic environment affected by the activity of the Tomsk 7 plant. The second region is a local segment of the Irtysh River upstream from its confluence with the Ob River, where the influence of emissions from the NPO Mayak could be estimated. The third region is the water area of the Ob River after its confluence with the Irtysh River. It characterizes the real level of radioactive and chemical contamination of the middle reaches of the Ob River.In order to explain horizontal variations in the distribution of radionuclides in the upper layer of bottom sediments collected at various sites, the results of sorption-kinetic experiments with radioactive tracers in the precipitate-solution system were used. The investigation of the migration forms of trace elements and radionuclides occurring in river water was based on the method of tangential-flow membrane filtration.Chemical element contents were determined in 400-ml water samples. A set of Millipore polysulfone membranes with pore sizes of 8, 1.2, 0.45, 0.1, and 0.025 μm was employed. Taking into account the ultralow specific concentrations of radionuclides in the water, they were analyzed in 300–500 litre samples using Millipore polysulfone membranes with pore sizes of 0.45 μm and 15 kDa. This allowed us to estimate the percentages of cesium-137 and plutonium-239, 240 in the suspended particulate fraction, colloids, and dissolved species.  相似文献   

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