环境中有机物和微生物对黄铁矿还原铀的影响

天然铀矿中铀常与黄铁矿共生,这两者之间存在着相互作用,而环境中有机物和微生物也会对此共生现象产生一些影响。本文采用循环伏安法(CV)研究了黄铁矿与U(VI)体系中的铀价态的变化及电子转移数,结果表明,黄铁矿可以自发把U(VI)还原到U(V)和U(IV)。腐殖酸(HA)存在时对黄铁矿还原铀有抑制作用,氧化亚铁硫杆菌(TF)存在时则有协同作用。光电子能谱研究表明,黄铁矿中的Fe²⁺和S^-对U(VI)的还原都起了作用。本文从电子、离子等微观角度研究了黄铁矿还原富集铀的反应机理,解释了天然铀矿中铀与黄铁矿共生这一现象,为铀成矿理论提供了新依据,并为黄铁矿在环境污染修复中的应用及周围环境影响程度的大小提供了理论依据。     

Determination of isotopic ratios of uranium samples using passive gamma spectroscopy with multiple detectors

Uranium samples of various enrichments have been passively counted on the University of Texas detector gamma–gamma coincidence system. By observing gamma rays emitted from ²³⁵U and its daughters compared to gamma rays emitted by ²³⁸U daughters and comparing the data to standards of known enrichments, a technique has been developed to take a uranium sample of unknown enrichment and passively count it to determine its uranium isotopic concentration. Because the gamma rays from ²³⁵U are generally in the low-energy regime, there is a strong susceptibility to background interferences, especially from the Compton background produced from higher energy gamma rays. Other interferences, such as those from the decay series of uranium also exist for ²³⁵U gamma rays. In this light, we have collected data using list-mode to produce two-dimensional gamma–gamma coincidence spectra, which allows us to gate the low-energy gamma rays from ²³⁵U with gamma rays that are in coincidence. In doing this, much of the low energy interferences are reduced, and one can analyze the ²³⁵U gamma rays with high precision. Because of the high density of uranium, self-shielding has significant effects especially in the low-energy regime. To correct for this attenuation the detector system has been modeled by MCNP and self-shielding factors have been calculated across the energy spectrum. A big advantage to this method is the capability of performing this analysis with small (<1 g) samples in a non-destructive and relatively inexpensive manner. If necessary, this analysis can be performed within 24 h if an urgent nuclear forensics scenario arises.     

A coincidence transmission electron microscope with digital waveform measuring system for analytical microscopy

We have been developing a new analytical transmission electron microscope (TEM), called a coincidence TEM, which in principle enables elemental mapping images to be observed at a high signal‐to‐noise (S/N) ratio under very low dose radiation conditions. In this paper, we report the development of a coincidence TEM with a digital waveform measuring system for obtaining a coincidence elemental mapping image. In this system, analog signals detected by a Si(Li) detector and a multianode, position‐sensitive photomultiplier (PSPM) are continuously converted into 12‐bit digital waveform data at a rate of 100 MHz, and transferred to a PC. From the transferred digital waveform data, information on X‐ray photon energy, electron incident position, and detection times of both X rays and electrons are calculated by digital waveform measurement, which lead to the observation of a successful coincidence elemental mapping image. Copyright © 2005 John Wiley & Sons, Ltd.     

Fission track mapping of uranium in black spruce (Picea Mariana) twigs

Fission track analysis (FTA) has been used to investigate the biological uptake of uranium. Examination of fission track maps of black spruce twigs (from areas of uranium mineralization and mill tailings) shows uranium to be concentrated in the inner bark while decreasing in the outer bark of the twigs. Track clusters in the bark, too large to be uraniferous airborne particulate matter, are identified as being associated with resin canals in the twigs. The results of this work help clarify the mechanisms by which uranium is incorporated in black spruce twigs. The observation of decreasing uranium content with the increasing age of black spruce twigs by an earlier worker, can now be explained by the relative reduction in volume of the uranium enriched inner bark with age.     

Insight of solvent extraction process: Reassessment of trace level determinations

Solvent extraction is hoary yet modern technique with great scope of research due to the various intriguing phenomena in the system. Tri-n-butyl phosphate (TBP) is a well known extractant which has been extensively used for separation of uranium matrix prior to elemental profiling. In this paper, one of the impurities namely Fe is being considered as it posed a challenge to the separation due to its co-extraction with TBP along with uranium. In these studies, for the first time, the existence of cation-cation inner sphere complexes between the UO₂²⁺and Fe³⁺ ions in both aqueous and organic phases have been establisted in addition to the selective separation of iron from uranium sample matrix using only TBP. The data from both spectrophotometric and thermophysical studies corroborated one another confirming the presence of cation-cation interactions (CCIs). The developed solvent extraction with only TBP showed almost no interferences on the iron extraction from matrix uranium and other co-ions like aluminum and copper. This has been the first time application of pure TBP for selective removal of iron from uranium samples. The procedure possessed excellent reproducibility and robustness.     

Use of the Eurachem guide on method validation for determination of uranium in environmental samples

Three analytical methods for determination of uranium in environmental samples by a fluorescence technique have been validated and compared in accordance with the Eurachem Guide on method validation. The first method depends on uranium separation from iron using the mercury anode technique; in the other two methods uranium is separated from iron on an anion exchange column by use of either a solution of hydrochloric acid containing ascorbic acid and hydrazine hydrate or a dilute sulfuric acid solution. Detection limits, repeatability, reproducibility, and recovery coefficient were the main validation characteristics. The results showed that better statistical values can be achieved by using the third method. Control charts for in-house control samples and international intercomparison samples have also shown that the third method is more statistically stable with time. In addition, uncertainties of measurement were estimated and compared for the three methods. It was found that the Eurachem Guide and comparison of quality statistical validation data can be good tools for selection of the appropriate method for an application.     

Seasonal variation, chemical behavior and kinetics of uranium in an unconfined groundwater system

The seasonal changes in the concentration of uranium in an unconfined groundwater system in Cyprus have been investigated and compared to corresponding changes of boron and salinity, to better understand the chemical behavior of uranium in the respective system. Uranium concentration measurements were performed by alpha spectroscopy after selective pre-concentration, whereas boron concentration analysis and electrical conductivity measurements were carried out by photometry using azomethine-H and an electrical conductivity electrode, respectively. The experimental data show that seasonal variations are mainly related to rainwater infiltration and the specific chemical behavior of a species. Increased levels of uranium and boron in natural water systems are attributed to the increased stability of the uranium(VI)-carbonato complexes and the boric acid, which are in natural waters the predominant chemical species for uranium and boron, respectively. Dilution/dissolution processes govern the seasonal concentration changes of uranium and boron in a groundwater system, however redox-reactions resulting in the reduction of U(VI) to U(IV) affect significantly the concentration of uranium in the respective system, particularly under suboxic conditions.     

Activity concentration of uranium in groundwater from uranium mineralized areas and its neighborhood

Uranium mineralization in parts of northeastern Nigeria necessitated its exploration during early eighties by the Nigeria Uranium Mining Company (NUMCO) which was later abandoned. During their course of decay, uranium isotopes pass through radioactive decay stage and eventually into stable isotope of lead. The course of concern for soluble uranium in groundwater especially from the mineralized areas include ionizing radiation, chemical toxicity and reproductive defects for which ingested uranium has been implicated to have caused. This study is aimed at assessing the levels of concentration of uranium in groundwater to ascertain its compliance with the World Health Organization’s (WHO) and the United State Environmental Protection Agency’s (EPA) guideline for uranium in drinking water. Thirty five groundwater samples were collected using EPA’s groundwater sampling protocol and analyzed at the Department of Geology, University of Cape Town using an Inductively Coupled Plasma Mass Spectrometric (ICP-MS) technique. Significant finding of this work was that there is radiological contamination of groundwater in the area. There is also an indication that the extent of radiological contamination is not much within the mineralized zones, therefore, there is likelihood that groundwater has acted as a medium of transporting and enhancing uranium in groundwater in an environment away from that of origin. About 5.7 % of the samples studied had uranium concentration above WHO and EPA’s maximum contaminant level of 30 μg/L which is a major concern for inhabitants of the area. It was also apparent that radiological contamination at the southwestern part of the study area extends into the adjacent sheet (sheet 152). Uranium concentration above set standards in those areas might have originated from rocks around established mineralized zones but was transported to those contaminated areas by groundwater that leaches across the host rock and subsequently mobilizing soluble uranium along with it.     

Estimation of uranium in bioassay samples of occupational workers by laser fluorimetry

A newly established uranium processing facility has been commissioned at BARC, Trombay. Monitoring of occupational workers is essential to assess intake of uranium in this facility. A group of 21 workers was selected for bioassay monitoring to assess the existing urinary excretion levels of uranium before the commencement of actual work. Bioassay samples collected from these workers were analyzed by ion-exchange technique followed by laser fluorimetry. Standard addition method was followed for estimation of uranium concentration in the samples. The minimum detectable activity by this technique is about 0.2 ng. The range of uranium observed in these samples varies from 19 to 132 ng/L. Few of these samples were also analyzed by fission track analysis technique and the results were found to be comparable to those obtained by laser fluorimetry. The urinary excretion rate observed for the individual can be regarded as a ‘personal baseline’ and will be treated as the existing level of uranium in urine for these workers at the facility.     

Study of uranium sorption and desorption on some Turkish clays

The sorption and desorption of uranium on two different clay samples which are obtained from the deposit located in Turgutlu and Kula have been studied by application of a batch technique. The two types of clay materials are Ca-montmorillonite. The uranium concentration range was between 200–3000 ppm. Experimental procedures are outlined and results for uranium contacted with montmorillonite are reported and discussed. The sorption/desorption isotherms were reversible and non-linear for this concentration range. The relative importance of test parameters e.g., pH, clay particle size, temperature, ground water composition, contact — time, solid/water ratio which require definition in order to arrive at meaningful distribution coefficients were carried out. The sorption coefficients varied between 0.65–1.45 and 0.45–1.14 for Kula clay and for Turgutlu clay, respectively. The data could be fitted to Freundlich and Langmuir isotherms. The quantity of the sorbed and desorbed uranium ions was much lower than its theoretical CEC's. This was attributed to a blocking of montmorillonite's CEC by uranium islands sorbed in interlayer. The results have shown that the test parameters can have a marked effect on sorption and the present work provides further evidence of the need to take account of the presence of such materials in safety assessment modeling.     

A comparative analysis of uranium in potable waters using laser fluorimetry and ICPMS techniques

The main objective of this work is the accurate measurement of uranium in the potable water sources of Muktsar district of Punjab, India. In the present work, a laser fluorimetry technique was used for the analysis of uranium. Inductively coupled plasma mass spectrometry (ICPMS) technique was also applied to verify and compare the uranium content analyzed using laser technique. About 16 samples from waterworks, bore wells, and hand pumps that supply the drinking water to local population were collected for this purpose. An indigenous laser fluorimeter supplied by RRCAT, Indore was employed for the analysis. Uranium concentrations obtained were in the range from 0 to 10???g?L^?1 in ten samples, 11?C30???g?L^?1 in three samples, and more than 100???g?L^?1 in three samples namely Channu ground water, Warning Khera pump, and Killanwale village hand pump. The USEPA guideline value for uranium in safe drinking water is 30???g?L^?1. Also, a data comparison with similar studies carried out in other countries is presented.     

Column reversed-phase partition chromatography for the isolation of some radionuclides from biological materials

Revised-phase partition chromatography is a very useful tool for selective isolation of radionuclides from biological materials. Some new applications of this technique to the resolution of practical problems in radiation protection are reported. Natural thorium and enriched uranium can be determined separately and together in urine by means of a column of Microthene-710 supporting a solution of tri-n-octyl-phosphine oxide (TOPO) in cyclohexane; batchwise extraction processes with Microthene supporting TOPO are also successful. Strontium-90 is determined in urine by a batch extraction of yttrium-90 with a slurry of Microthene supporting the liquid cation exchanger di-(2-ethylhexyl)phosphoric acid. Only a wet mineralization of the urines is required and the analyses are simple, rapid and sufficiently accurate. A method for the isolation of iodine from foodstuffs with a Microthene-benzene column is also described.     

Extraction of Uranium with 2-Ethylhexyl Phosphonic Acid Mono-2-Ethylhexyl Ester (PC-88A)

The extraction behavior of uranium (VI) from chloride medium with 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester (PC-88A) in dodecane has been investigated under wide range of conditions. Attempts have been made to establish the extraction mechanism of uranium(VI) with PC-88A. Treatment of the distribution data by slope analysis technique showed the formation of a monomeric complex of the nature [UO₂(A₂H)₂]. Formation of this species was also confirmed by non-linear least square regression of the distribution data to the mathematical expression correlating percentage extraction and acidity. In this investigation attempts have also been made to develop a mathematical model for the system (UO₂Cl₂-HCl-H₂O-PC-88A-dodecane) using experimental data on the distribution of uranium against initial aqueous acidity at different initial metal concentration. The mathematical model D = 37.547±0.223/C _i ^1/2×[H _i ]² can be used to predict the concentration of uranium in organic as well as in aqueous phases at any initial concentration of uranium [C _i ] and initial hydrogen ion concentration [H _i ]. The extraction constant (K _ex ) has been calculated.     

Resolution of uranium isotopes with kinetic phosphorescence analysis

This study was conducted to test the ability of the Chemchek? Kinetic Phosphorescence Analyzer Model KPA-11 with an auto-sampler to resolve the difference in phosphorescent decay rates of several different uranium isotopes, and therefore identify the uranium isotope ratios present in a sample. Kinetic phosphorescence analysis (KPA) is a technique that provides rapid, accurate, and precise determination of uranium concentration in aqueous solutions. Utilizing a pulsed-laser source to excite an aqueous solution of uranium, this technique measures the phosphorescent emission intensity over time to determine the phosphorescence decay profile. The phosphorescence intensity at the onset of decay is proportional to the uranium concentration in the sample. Calibration with uranium standards results in the accurate determination of actual concentration of the sample. Different isotopes of uranium, however, have unique properties which should result in different phosphorescence decay rates seen via KPA. Results show that a KPA is capable of resolving uranium isotopes.     

Solvent extraction of the lanthanide elements,scandium, uranium and thorium using tetracycline as complexing agent

Hydrogen ion dependence and extractant dependence of the extraction of the lanthanide elements, scandium, uranium and thorium into a solution of tetracycline in benzyl alcohol have been determined. Possiblity of using the tetracycline-benzyl alcohol system for separation of the lanthanide elements present in a mixture, as well as for the separation of uranium from those elements was tested. In the first case discontinuous countercurrent technique was used. In the second case a single step solvent extraction procedure was applied.     

CMOS image sensor for detection of interferon gamma protein interaction as a point-of-care approach

Complementary metal oxide semiconductor (CMOS)-based image sensors have received increased attention owing to the possibility of incorporating them into portable diagnostic devices. The present research examined the efficiency and sensitivity of a CMOS image sensor for the detection of antigen–antibody interactions involving interferon gamma protein without the aid of expensive instruments. The highest detection sensitivity of about 1 fg/ml primary antibody was achieved simply by a transmission mechanism. When photons are prevented from hitting the sensor surface, a reduction in digital output occurs in which the number of photons hitting the sensor surface is approximately proportional to the digital number. Nanoscale variation in substrate thickness after protein binding can be detected with high sensitivity by the CMOS image sensor. Therefore, this technique can be easily applied to smartphones or any clinical diagnostic devices for the detection of several biological entities, with high impact on the development of point-of-care applications.     

Adsorption and thermodynamic behaviour of U(VI) on the Tendurek volcanic tuff

In this work, sorption of uranium ions on volcanic tuff collected from the deposits located at the Tendurek of Eastern Turkey was investigated in batch technique. The effect of different parameters such as pH of the medium, contact time, uranium concentration and temperature were investigated. The maximum removal of U(VI) was found to be 68% at pH 5.0, initial U(VI) concentration of 75 mg L⁻¹ and 30 °C. Thermodynamic parameters, such as enthalpy of adsorption ∆H°, free energy change ∆G° and entropy change ∆S° have been also calculated and interpreted. The suitability of the Langmuir, Freundlich and Dubinin-Radushkhevic adsorption models to the equilibrium data was investigated for uranium-volcanic tuff system. The results suggest that volcanic tuff can be used as efficient and cost effective adsorbents for uranium ion removal.     

UF6 plasma chemistry reconstitution experiments using high-temperature fluorine

Prior results indicate techniques have been developed for fluid mechanical confinement of high-temperature uranium hexafluoride (UF₆) plasma for long test times while simultaneously minimizing uranium compound deposition on the walls. Follow-on investigations were conducted to demonstrate a UF₆/argon injection, separation, and reconstitution system for use with rf-heated uranium plasma confinement experiments applicable to UF₆ plasma core reactors. A static fluorine batch-type regeneration test reactor and a flowing preheated fluorine/UF₆ regeneration system were developed for converting all the nonvolatile uranium compound exhaust products back to pure UF₆ using a single reactant. Pure fluorine preheat temperatures up to 1000 K resulted in on-line regeneration efficiencies up to about 90%; static batch-type experiments resulted in 100% regeneration efficiencies but required significantly longer residence times. A custom-built, ruggedized time-of-flight (T.O.F.) mass spectrometer, sampling, and data acquisition system permitted on-line quantitative measurements of the UF₆ concentrations down to 30 ppm at various sections of the exhaust system; this system proved operational after long-time exposure to corrosive UF₆ and other uranium halides.     

Determination of uranium and radium concentrations in the waters of the Grand Canyon by alpha spectrometry

In order to establish baseline information for current and future mining operations, water samples from the Colorado River and its tributaries have been analyzed for Ra-226 and uranium isotopes. Ra-226 was separated by coprecipitation on BaSO₄ followed by alpha spectrometry. Ba-133 was used as a tracer for yield determination. Uranium was separated by a combination of BaSO₄ precipitation and solvent extraction followed by coprecipitation on CeF₃ for alpha spectrometry.Results indicate that radium and uranium levels in the Colorado River and its tributaries, except the Little Colorado River, are below the EPA specifications [1] for drinking water of 185 mBq/liter (5 pCi/1) for Ra-226 and 433 mBq/liter (11.7 pCi/1) for U-238. However, the specific sources for elevated uranium and Ra-226 concentrations in the Little Colorado River should be identified, and the potential impacts from leaching of the naturally exposed mineralization inside the Grand Canyon should be investigated.     

Recovery of Uranium(VI) from Sulfate Leach Liquor using Modified Duolite

Silicate mercapto Duolite composite ( SMDC ) and activated Duolite A 101 D ( AD ) were prepared, characterized, and tested for uranium removal from sulfate solution using batch experiment technique. The capability of newly adsorbents for sorption of uranium was estimated and optimized under different controlling variables, including the impact of uranium initial concentration, pH of the medium, equilibrium time, temperatures, dose and interfering ions. Testing of different adsorbents for adsorption isotherms revealed that the achieved experimental data were fitting well with the Langmuir isotherm model with 68.02 mg · g^–1 and 208.33 mg · g^–1 as theoretical capacity for AD and SMDC , respectively. Thermodynamic parameters have been resulted in negative values for ΔH and ΔS indicating an exothermic and decreased randomness behavior for uranium(VI) adsorption, while negative values of ΔG indicate spontaneous uranium adsorption. The kinetics studies showed that the adsorption process was controlled expressed by pseudo-second order model. Finally, the optimized factors have been applied for uranium(VI) recovery from Gattar leach liquor producing a uranium concentrate (Na₂U₂O₇) with uranium concentration of 70 % and purity of 93.33 %.