Leaching dynamics of uranium in a contaminated soil site

Samples from a potentially contaminated industrial area were analyzed for uranium using neutron activation analysis (NAA). Uranium concentration values had a typical uncertainty of 2 % and a detection limit of 1 Bq/kg. To investigate the potential leaching dynamics into ground water two techniques were employed. The US EPA Toxicity Characterization Leaching Procedure (TCLP) and the Sequential Extraction Procedure (SEP) were used to determine the concentration of uranium in the leachates. TCLP and SEP showed that very little of the uranium leached into solution under different chemical conditions. Values of uranium leachates ranged from 0.05 to 3.5 Bq/L; a concentration much lower than the results found in the soil concentrations which ranged from 29 to 155 Bq/kg. NAA showed an 8 % uncertainty for leachates with a detection limit of 0.13 Bq/L. To mimic environmental conditions and acid rain, pH 4.3 water was used as the extraction solvent instead of the acetic acid routinely used in TCLP. Results confirmed that very low amounts of uranium leached with values ranging from 0.0002 to 0.0122 Bq/L. These values represent 0.01–1 % of the uranium in the soil samples. The distribution of uranium in soil according to particle size was also investigated to evaluate its potential movement and possible contamination of the water table. Particles below 250 μm in diameter showed a linear increase in uranium concentration whereas those with a larger diameter had constant uranium content.     

Development of radiochemical analysis of uranium isotopes in highly contaminated soil samples

An accurate and reliable analytical technique of uranium isotopes in highly contaminated soil samples was developed and applied to the IAEA reference samples. The conventional TBP method of uranium isotopes is insufficient to completely purify uranium from actinides such as plutonium and americium isotopes in highly contaminated soil samples. For overcoming the demerits of the conventional TBP extraction method, sample materials were decomposed with HNO₃ and HF, and uranium isotopes were purified by TBP extraction and anion exchange columns and extraction chromatography. Among the purifying methods of uranium, with a TRU Spec resin column after TBP solvent extraction, uranium was completely separated from the radionuclides in a highly contaminated samples. With the modified TBP extraction method, it was found that the concentrations of uranium isotopes were consistent with the reference values reported by the IAEA.     

TRLFS study on the speciation of uranium in seepage water and pore water of heavy metal contaminated soil

In situ leaching of uranium ores with sulfuric acid during active uranium mining activity on the Gessenheap has caused longstanding environmental problems of acid mine drainage and elevated concentrations of uranium. To study there remediation measures the test site Gessenwiese, a recultivated former uranium mining heap near Ronnenburg/East Thuringia/Germany, was installed as a part of a research program of the Friedrich-Schiller University Jena to study, among other techniques, the phytoremediation capacity of native and selected plants towards uranium. In the first step the uranium speciation in surface seepage and soil pore waters from Gessenwiese, ranging in pH from 3.2 to 4.0, were studied by time-resolved laser-induced fluorescence spectroscopy (TRLFS). Both types of water samples showed mono-exponential luminescence decay, indicating the presence of only one major species. The detected emission bands were found at 477.5, 491.8, 513.0, 537.2, 562.3, and 590.7 nm in case of the surface water samples, and were found at 477.2, 493.2, 513.8, 537.0, 562.4, and 590.0 nm in case of the soil water samples. These characteristic peak maxima together with the observed mono-exponential decay indicated that the uranium speciation in the seepage and soil pore waters is dominated by the uranium (VI) sulfate species UO₂SO_4(aq). Due to the presence of luminescence quenchers in the natural water samples the measured luminescence lifetimes of the UO₂SO_4(aq) species of 1.0–2.6 μs were reduced in comparison to pure uranium sulfate solutions, which show a luminescence lifetime of 4.7 μs. These results convincingly show that in the pH range of 3.2–4.0 TRLFS is a suitable and very useful technique to study the uranium speciation in naturally occurring water samples.     

Arsenic speciation in multiple metal environments II. Micro-spectroscopic investigation of a CCA contaminated soil

The speciation of arsenic (As) in a copper-chromated-arsenate (CCA) contaminated soil was investigated using micro-focused X-ray fluorescence (microXRF) and micro-focused X-ray absorption fine structure (microXAFS) spectroscopies to determine if and how the co-contaminating metal cations (Cu, Zn, Cr) influenced the speciation of As. 15 microXRF images were collected on 30-mum polished thin sections and powder-on-tape samples from which Pearson correlation coefficients (rho) between As and various metal species were determined based on the fluorescence intensity of each element in each image pixel. 29 microXAFS and two bulk-XAFS spectra were collected from depths of 0-20 cm (LM-A) and 20-40 cm (LM-B) to determine the chemical speciation of As in the soil by target analyses of principal components with circa 52 reference spectra and linear least-square combination fitting of individual experimental spectra with a refined reference phase list (32) of likely As species. Arsenic and metal cations (Cr, Mn, Fe, Cu, Zn) accumulated in distinct, isolated areas often not larger than 50 x 50 microm in which the Pearson correlation between the elements was strongly positive (rho>0.75). The correlation of As to Zn and Cr decreased from >0.9 to <0.8 and increased to Cu from approximately 0.6 to >0.8 with depth. Arsenic occurred predominantly in the +5 oxidation state. Abstract factor analysis and linear least square combination fit analysis suggested that As occurred as a continuum of fully and poorly-ordered copper-arsenate precipitates with additional components being characterized by surface adsorption complexes on goethite and gibbsite in the presence and absence of Zn. Precipitates other than copper-based ones, e.g., scorodite, adamite and ojuelaite were also identified. The significant co-localization and chemical speciation of As with Cu suggest that the speciation of As in a contaminated soils is not solely controlled by surface adsorption reactions, but significantly influenced by the co-contaminating metal cation fraction. Future studies into As contaminated soil therefore need to focus on identifying the speciation of As and the co-localizing metal cations.     

Biological effects of uranium in water,soil and rice in uranium deposits in southern China

Journal of Radioanalytical and Nuclear Chemistry - The content of radionuclide uranium in the water, soil and rice around the decommissioned uranium mine was analyzed, and the radioactive...     

An investigation on the subcellular distribution and compartmentalization of uranium in Phaseolus vulgaris L.

Phaseolus vulgaris L. (bean) is a promising species for uranium rhizofiltration with high tolerance and accumulation ability. To further understand the mechanisms involved in uranium tolerance and detoxification, the present study investigated subcellular distribution and compartmentalization of uranium in bean. Subcellular fractionation of uranium containing tissues indicated that both in roots and shoots, the concentration of uranium in each subcellular fractions increased evidently with increasing solution uranium level, and the majority of uranium was located in cytosol and cell wall fraction, while a minor part of uranium associated with the organelle fraction. Meanwhile, with uranium concentration increasing from 100 to 1,000 μM, the proportion of uranium distribution in cytosol fraction was decreased but it was increased in cell wall fraction. However, the proportion of uranium distribution in organelle fraction is always less than 5 %. These results suggest that stored in the cytosol (such as uranium compartmentalization with organo-ligands in vacuole) and bound to the cell walls (may be integrated with polyose and protein) might play an important role in tolerance and detoxification of uranium in bean.     

An investigation of radionuclide uptake into food crops grown in soils treated with bauxite mining residues

Sandy soils of the coastal plain area of Western Australia have poor phosphorous retention capacity which leads to pollution of surface water bodies in the region. Application of bauxite mining residues (termed red mud) to vegetable and crops has been proposed as a solution to increase the phosphorous and water retention and thereby reduce the leaching of nutrients. The thorium and radium-226 concentrations in the red mud residues are in excess of 1 kBq/kg and 300 Bq/kg, respectively. Potentially, the use of these residues on agricultural land could result in increased levels of radionuclides in food crops grown in amended soils. The transfer of long-lived radionuclides of both the natural thorium and uranium series to a variety of vegetable crops grown under controlled conditions is investigated. The effects of varying the rates of application of red mud and phosphate fertilisers on radionuclide uptake are studied. It has been shown previously that fallout caesium-137 in sandy soils of the region transfers readily to food and grazing crops. Some of the parameters which influence that transfer are also examined.     

Spatial dependency of the groundwater uranium in the alluvial soil region of Gunnaur,India

Journal of Radioanalytical and Nuclear Chemistry - GIS based groundwater uranium and other physico-chemical parameters pH, electrical conductivity, oxidation reduction potential, temperature,...     

Physicochemical fractionation of americium, thorium, and uranium in Chernozem soil after sharp temperature change and soil drought

A sequential extraction procedure was used to study the changes in the physicochemical forms of americium (Am), thorium (Th), and uranium (U) in laboratory-contaminated Chernozem soil as a result of sharp variations of the environmental temperature and soil moisture. The influence of freezing and soil drought on the radio-ecological hazard was evaluated three months after radioactive contamination with aqueous solutions of ²⁴¹Am, ²³⁴Th, and U. The subsequent changes in the physicochemical forms of the actinides, caused by sharp increases in the environmental temperature and soil moisture, were examined for one month. The data showed that continuous freezing increased the potentially mobile forms of Am and Th but had the opposite effect on U. Prolonged soil drought did not influence the fractionation of Am and Th but led to the redistribution of U between the carbonates and organic matter and caused its immobilisation. The sharp increase in the temperature of the frozen soil caused the immobilisation of Am and Th and increased the potential mobility of U. The warming and enhanced humidity of the dry soil led to the immobilisation of Am and redistribution of U between the soil phases.     

An experimental investigation of uranium redox reactions in an electrolytic cell with a cation exchange membrane

This paper investigates the simultaneous reduction and oxidation reactions of uranium in hydrochloric acid media. The redox reactions were carried out in a cell fitted with a cation exchange membrane and hexavalent uranium was reduced to the tetravalent state in the cathode chamber. The reverse reaction was carried out in the anode side of the cell. The reaction rate was found to be independent of the uranium concentration and the extent of reaction was linear with time. There is evidence of uranium flux across the membrane.     

The study of the distribution of arsenic, mercury, thorium, protactinium, uranium and neptunium under the ChemChar gasification process using radionuclide tracers

A experimental method to measure the fate and distribution of a variety of radionuclides under the ChemChar gasification process has been developed. The elements studied were arsenic, mercury, thorium, protactinium, uranium and neptunium. Results indicate that the ChemChar gasification system quantitatively retains these elements. In all of the cases except mercury the radiotracer was found to reside on the char matrix with small amounts (<1%) being found downstream in the condensation trap and char filter. Mercury, presumably as vapor, was entrained and distributed in significant amounts (≈40%) to the downstream char filter and its pre-filter. A methodology was developed to account for char height differences in quantifying the radiotracer on the char prior and subsequent to gasification. These results demonstrate the efficacy of using relatively short-lived radiotracers to characterize the behavior of hazardous elements during waste treatment via gasification.     

Quantum-chemical investigation of the nature of interatomic bonding in molybdenum and uranium clusters

Calculation of the electronic structure of regular and distorted octahedral clusters of uranium and molybdenum has been carried out by the relativistic Dirac-Slater X-SW method. The cluster model can describe the b.b.c. -uranium structure stabilization by molybdenum. The important role of the inner uranium 6p-AO in the interatomic bonding is pointed out.     

A preliminary investigation of the operational and isotopic speciation of uranium in sediments

Uranium was determined in extracts of inter-tidal sediment, obtained from a contaminated harbour, using the three-stage sequential extraction procedure recommended by BCR. The element was found mainly in association with reducible, or reducible and oxidisable, phases and the overall concentration was enhanced (up to 6.7 μg g^–1 dry weight) with respect to typical, UK levels. The ²³⁸U/²³⁵U ratio has been measured in digests of stream sediments obtained from the vicinity of a uranium enrichment plant. Significant enhancement in ²³⁵U with respect to the natural ²³⁸U/²³⁵U ratio (137.88:1) was observed at some locations.     

Analyses of radionuclides in soil,water, and agriculture products near the Urgeiriça uranium mine in Portugal

Analyses of soils, irrigation waters, agriculture products (lettuce), green pasture, and cheese were performed in samples collected in the area of the old Urgeiriça uranium mine and milling facilities, Centre-North of Portugal, in order to assess the transfer of uranium series radionuclides in the environment and to man. Soils close to milling tailings display an enhancement of radioactivity. In the drainage basin of the stream Ribeira da Pantanha, receiving drainage from the tailings piles and discharges from the acid mine water treatment plant, there was enhancement of uranium series radionuclide concentrations in water and suspended matter. Agriculture products from kitchen gardens irrigated with water from the Ribeira da Pantanha show an increase of radioactivity, mainly due to uranium isotopes. Agriculture products from other kitchen gardens in this area, irrigated with groundwater, as well pasture and cheese produced locally from sheep milk did not show enhanced radionuclide concentrations. In the Urgeiriça area, some soils display radionuclide concentrations higher than soils in reference areas and, in agriculture products grown there, ²²⁶Ra was the radionuclide more concentrated by vegetables. Through ingestion of these products ²²⁶Ra may be the main contributor to the increment of radiation dose received by local population.     

Pilot plant study of the microbial flora in a diesel fuel contaminated soil

This study focused on the impact of a recent soil pollution of diesel fuel on a site and its indigenous microbial flora. A pilot plant (0.5 m3) was set up and filled with a soil (about 700 kg), artificially and uniformly polluted with diesel fuel (7 g/kg). This plant was then chemically and biologically monitored during the whole experiment (about two years). During the monitoring, a morphological change of the microbial colonies was observed. This was probably due to the acclimation phenomena to the pollution. With batch kinetic studies (10 ml) and increasing the selective pressure of the pollutant, it was possible to select and isolate a microbial consortium and a single strain that developed the ability to use different diesel fuel fractions as carbon sources. GC-MS analytical techniques were used. Results showed that different fractions were degraded at different times. In the batch system, in 7 days, the microbial consortium degraded some aromatic hydrocarbons. The isolate strain, in 20 days, degraded linear hydrocarbons. After a two years acclimation, it was possible to obtain, from a pilot plant, a microbial consortium and a strain able to degrade diesel fuel, for a future bioremediation in situ process.     

Extraction procedures for the determination of heavy metals in contaminated soil and sediment

Extraction tests are commonly used to study the mobility of metals in soils and sediments by mimicking different environmental conditions or dramatic changes on them. The results obtained by determining the extractable elements are dependent on the extraction procedure applied. The paper summarises state of the art extraction procedures used for heavy metal determination in contaminated soil and sediments. Two types of extraction are considered: single and sequential. Special attention is paid to the Standard, Measurement and Testing projects from the European Commission which focused on the harmonisation of the extraction procedures and on preparing soil and sediment certified reference materials for extractable heavy metal contents.