RESUMO
The effect of three chelating agents (citrate, EDTA, and EDDS) on the solubilization of radium from a granitic soil was studied systematically, considering different soil pH values, chelating agent concentrations, and leaching times. For all the chelating agents tested, the amount of radium leached proved to be strongly dependent on the pH of the substrate: only for acidic conditions did the amount of radium released increase significantly relative to the controls. Under the best conditions, the radium released from the amended soil was greater by factors of 20 in the case of citrate, 18 for EDTA, and 14 for EDDS. The greatest improvement in the release of radium was obtained for the citrate amendment at the highest concentration tested (50 mmol kg(-1)). A slightly lower amount of radium was leached with EDTA at 5 mmol kg(-1) soil, but the solubilization over time was very different from that observed with citrate or EDDS. With EDTA, a maximum in radium leaching was reached on the first day after amendment, while with citrate, the maximum was attained on the fourth day. With EDDS, radium leaching increased slightly but steadily with time (until the sixth day), but the net effect for the period tested was the lowest of the three reagents.
Assuntos
Quelantes/química , Ácido Edético/química , Etilenodiaminas/química , Succinatos/química , Ácido Cítrico/química , Concentração de Íons de Hidrogênio , Chumbo/análise , Rádio (Elemento)/análise , Solo/análise , Poluentes Radioativos do Solo/análise , Urânio/análiseRESUMO
A systematic study was made of the effects of three soil amendments on the solubilization of uranium from a granitic soil. The aim was to optimize solubilization so as to enhance bioavailability for the purposes of remediation. The three amendments tested were with citrate, EDTA, and EDDS as chelating agents. The effects of pH, chelator concentration, and leaching time were studied. The most important factor in uranium solubilization was found to be the pH. In the absence of chelating agents, the greatest solubilization was obtained for alkaline conditions, with values representing about 15% of the total uranium activity in the bulk soil. There were major differences in uranium solubilization between the different amendments. The citrate treatment was the most efficient at acidic pH, particularly with the greatest concentration of citrate tested (50 mmol kg(-1)) after 6 days of treatment. Under these conditions, the uranium concentration in solution was greater by a factor of 356 than in the control suspension, and represented some 63% of the uranium concentration in the bulk soil. Under alkaline conditions, the EDTA and EDDS treatments gave the greatest uranium activity concentrations in solution, but these concentrations were much lower than those with the citrate amendment, and were not very different from the control results. The uranium extraction yield with EDDS amendment was greater than with EDTA.
Assuntos
Quelantes/química , Ácido Cítrico/química , Ácido Edético/química , Etilenodiaminas/química , Poluentes do Solo/química , Succinatos/química , Urânio/química , Concentração de Íons de Hidrogênio , SolubilidadeRESUMO
A procedure for the determination of (210)Pb, and alpha-emitting radioisotopes of uranium, thorium, and radium from the same aliquot of a sample has been proposed. The key step consisted in the recovery of Pb(II) and Ra by precipitation of insoluble Pb(NO(3))(2), the uranium and thorium radioisotopes remaining in solution. Afterwards, the fractions were handled by specific, well consolidated procedures. Lead-210 was determined by the LSC technique while the uranium, thorium, and radium radioisotopes were measured with silicon alpha-spectrometers. The procedure was applied to a reference sample and several environmental samples obtaining satisfactory results.
Assuntos
Algoritmos , Misturas Complexas/análise , Radioisótopos/análise , Radiometria/métodos , Análise Espectral/métodos , Partículas alfa , Doses de Radiação , Reprodutibilidade dos Testes , Sensibilidade e EspecificidadeRESUMO
The elimination of natural uranium and (226)Ra from contaminated waters by rhizofiltration was tested using Helianthus annuus L. (sunflower) seedlings growing in a hydroponic medium. Different experiments were designed to determine the optimum age of the seedlings for the remediation process, and also to study the principal way in which the radionuclides are removed from the solution by the sunflower roots. In every trial a precipitate appeared which contained a major fraction of the natural uranium and (226)Ra. The results indicated that the seedlings themselves induced the formation of this precipitate. When four-week-old seedlings were exposed to contaminated water, a period of only 2 days was sufficient to remove the natural uranium and (226)Ra from the solution: about 50% of the natural uranium and 70% of the (226)Ra were fixed in the roots, and essentially the rest was found in the precipitate, with only very small percentages fixed in the shoots and left in solution.
Assuntos
Helianthus/metabolismo , Rádio (Elemento)/metabolismo , Urânio/metabolismo , Poluentes Radioativos da Água/metabolismo , Precipitação Química , Filtração , Raízes de Plantas/metabolismo , Brotos de Planta/metabolismo , Rádio (Elemento)/química , Plântula/metabolismo , Urânio/química , Poluentes Radioativos da Água/química , Purificação da Água/métodosRESUMO
The linearity assumption of the validation of soil-to-plant transfer factors of natural uranium and (226)Ra was tested using Helianthus annuus L. (sunflower) grown in a hydroponic medium. Transfer of natural uranium and (226)Ra was tested in both the aerial fraction of plants and in the overall seedlings (roots and shoots). The results show that the linearity assumption can be considered valid in the hydroponic growth of sunflowers for the radionuclides studied. The ability of sunflowers to translocate uranium and (226)Ra was also investigated, as well as the feasibility of using sunflower plants to remove uranium and radium from contaminated water, and by extension, their potential for phytoextraction. In this sense, the removal percentages obtained for natural uranium and (226)Ra were 24% and 42%, respectively. Practically all the uranium is accumulated in the roots. However, 86% of the (226)Ra activity concentration in roots was translocated to the aerial part.
Assuntos
Helianthus/metabolismo , Rádio (Elemento)/análise , Urânio/análise , Biodegradação Ambiental , Helianthus/crescimento & desenvolvimento , Hidroponia , Raízes de Plantas/química , Raízes de Plantas/crescimento & desenvolvimento , Raízes de Plantas/metabolismo , Brotos de Planta/química , Brotos de Planta/crescimento & desenvolvimento , Brotos de Planta/metabolismo , Rádio (Elemento)/metabolismo , Plântula/crescimento & desenvolvimento , Plântula/metabolismo , Solo , Urânio/metabolismo , Purificação da Água/métodosRESUMO
A new version of a classical method was applied to study the distribution of natural radionuclides (238U, 230Th, and 226Ra) in the soil fractions obtained by a sequential extraction procedure. The potential significance of the fractions obtained with this method was tested on two very similar soils but with very different contents of the three radionuclides, collected in the proximity of a disused uranium mine located in the Extremadura region in the south-west of Spain. The results confirmed that, if only non-residual fractions are considered, the sequential method applied shows a characteristic speciation pattern of these natural radionuclides in this soil matrix, i.e., the distribution of each of the three radionuclides was very similar for the two soil samples.
Assuntos
Rádio (Elemento)/análise , Poluentes Radioativos do Solo/análise , Tório/análise , Urânio/análise , Monitoramento Ambiental , Rádio (Elemento)/química , Espanha , Tório/química , Urânio/químicaRESUMO
Two sequential extraction procedures, Tessier's method (Anal. Chem. 51(7) (1979) 844), and a current version known as Schultz's method (J. Environ. Radioact. 40(2) (1998) 155), were compared. The two procedures were applied to a natural soil sample that presents high activity concentrations in natural radionuclides of the 238U series. Reproducibility studies of each method and a comparison between the two sets of results were performed for uranium, thorium, and radium. The results were different for each radionuclide. Analysis of the extracted fractions was carried out by alpha spectrometry.
Assuntos
Fracionamento Químico/métodos , Poluentes Radioativos do Solo/análise , Análise Espectral/métodos , Urânio/análise , Partículas alfa , Reprodutibilidade dos Testes , Sensibilidade e Especificidade , Urânio/classificaçãoRESUMO
A simple procedure for the determination of 226Ra in geological samples using alpha-spectrometry is presented. The method uses 225Ra as yield tracer, and microprecipitation of Ba(Ra)SO(4) for source preparation. Extensive studies were performed in order to determine the chemical yield of the proposed procedure with precision. The method was tested on a geological reference sample, and gave satisfactory results and high reproducibility.
RESUMO
A study is presented on the distribution and mobilization of the natural U isotopes (238U and 234U), 230Th, and 226Ra in the sediments of a small river crossing an uranium mineralized zone where a disused uranium mine is located. Due to the preferential directions for surface run-off waters and to the mine's situation, one sampling point along the river bed was identified as a point of accumulation of radionuclides. The average values of the activity concentrations (Bq/kg) in this sediment sample were 5,025, 5,055, 5,915 and 1,694 for 238U, 234U, 230Th and 226Ra, respectively, while the respective average values of the activity concentrations (Bq/kg) for the sediment sample considered to give the background level were 125, 124, 131 and 370. Isotopic ratios between the descendants of 238U served to clarify some paths of distribution, involving the soils nearest to the sampling points and the location of these points with respect to the disused mine. The differences in behaviour found between the uranium, thorium and radium isotopes were associated to the mobility of these radionuclides in the fluvial system studied. Correlations between the radionuclide activity concentration ratios and stable element concentrations in the sediment samples were also investigated.