Uranium in waters

Uranium in water decays to form Zn24 and Sm by fission. Uranium has a half-life of 7 X 10s years. The zinc ions complex with water and act as a weak acid according to the following equation ... 

Table 1. Total uranium in water analyses, leaching experiments using rainwater. Green Street Occurrence, near Windsor Nova Scotia (after Parsons, 2007).

Dadfamia, S. and McLeod, C. W., On-line trace enrichment and determination of uranium in waters by flow injection inductively coupled plasma mass spectrometry, Appl. Spectrosc., 48, 1331-1336, 1994. 

Roane, J. E. and DeVol, T. A., Evaluation of an extractive scintillation medium for the detection of uranium in water, J. Radioanal. Nucl. Chem, 263, 51-57, 2005. 

Wrenn ME, Durbin PW, Willis DL, et al. 1987. The potential toxicity of uranium in water. J AWWA (April) 177-181. 

The principal abiotic processes that transform uranium in water are formation of complexes and oxidation-reduction reactions that have been described in Section 5.3.1. In seawater at pH 8.2, it was shown that U(IV) exists as 100% neutral hydroxo complexes, and U02 " and U(VI) exist as 100% carbonate complexes. In freshwater at pH 6, U(IV) was shown to exist as 100% hydroxo... 

Considerable work has been done to develop methods for analysis of uranium in water. In 1980, the EPA published standardized procedures for measurement of radioactivity in drinking water which included uranium analysis by both radiochemical and fluorometric methods (Krieger and Whittaker 1980), and more recently developed an ICP-MS method. An example of each is provided below. 

The ICP-MS method was developed for measuring total uranium in water and wastes. The sample preparation is minimal—filtration for dissolved uranium, acid digestion for total recoverable uranium. Recovery is quantitative (near 100%) for a variety of aqueous and solid matrices and detection limits are low, 0.1 pg/L for aqueous samples and 0.05 mg/kg for solid samples (Long and Martin 1991). 

Greene B, Uranga A, Sneddon J. 1985. Observations on the determination of uranium in waters by direct current argon plasma emission spectrometry. Spectroscopy Letters 18(6) 425-436. 

Van den Berg CMC, Nimmo M. 1987. Direct determination of uranium in water by cathodic stripping voltammetry. Anal Chem 59 924-928. 

The release of uranium and thorium from minerals into natural waters will depend upon the formation of stable soluble complexes. In aqueous media only Th is known but uranium may exist in one of several oxidation states. The standard potential for the oxidation of U in water according to equation (2) has been re-evaluated as E° - 0.273 0.005 V and a potential diagram for uranium in water at pH 8 is given in Scheme 3. This indicates that will reduce water, while U is unstable with respect to disproportionation to U and U Since the Earth s atmosphere prior to about 2 x 10 y ago was anoxic, and mildly reducing, U " would remain the preferred oxidation state in natural waters at this time. A consequence of this was that uranium and thorium would have exhibited similar chemistry in natural waters, and have been subject to broadly similar redistribution processes early in the Earth s history. Both U " and Th are readily hydrolyzed in aqueous solutions of low acidity. A semiquantitative summary of the equilibrium constants for the hydrolysis of actinide ions in dilute solutions of zero ionic strength has been... 

Chemical analyses were performed in accordance with ASTM Chemical Analysis of Gypsum and Gypsum Products (C 471). Fluoride and phosphorus were determined by the Association of Florida Phosphate Chemists Methods (7). Uranium was determined by ASTM Tests for Microquantities of Uranium in Water by Fluorometry (D 2907), and thorium was determined by ASTM Test Method for Thorium in Water and Waste Water (D 2333). Radium was determined by the radon emanation method (51, and uranium and thorium isotopes were determined by a chromatographic and radiological technique developed by the EPA. 

The 5-Br-PADAP method was used in the determination of uranium in waters [96], sewage [97,98], ores [3,95], and phosphoric acid [96]. 

Figure 18. Case study 2, contaminated situations geographic distribution of uranium in waters and sediments in the Martigny area (Rhone catchment. Western Switzerland). Sediment data from Woodtli et al. (1985) and water data from Baertschi and Keil (1992). Obviously the widespread uranium ore deposits (pitchblende/U02 veins) are at the origin of a widespread regional enrichment. The site described in detail in Fig. 19 (La Creusa-Les Marecottes) is marked with an asterisk.

D19.04 D2907-97 Standard Test Methods for Microquantities of Uranium in Water by Fluorometry... 

D19.04 D3972-97 Standard Test Method for Isotopic Uranium in Water by Radiochemistry... 

ASTM. 1982b. Standard test method for isotopic uranium in water by radiochemistry. ASTM standards designation D-3972-82. American Society for Testing and Materials, Philadelphia, PA, 1-6. 

The negative intercept indicated that the urinary excretion from a dietary source was not evident and that some retention may have occurred. The slope of the line indicated that about 5% of the uranium in water was absorbed into blood and excreted in urine. The authors concluded that for steady-state ingestion of uranium water is the primary pathway for absorption and not total dietary intake under normal chronic conditions. 

The absorption of uranium from water described above is valid for steady-state conditions over the measured range of values. There is some evidence that acute ingestion of high concentrations of uranium in water, of the order of 300 p,g/liter (3700 mBq/day), invokes a protective response in the body that markedly reduces absorption [25]. 

Measurements of Reactor Parameters in Subcritical and Critical Assemblies-Lot-ticesof Slightly Enriched Uranium in Water,... 

An SPE method for online preconcentration of uranium in water and effluent samples is based on amberlite XAD-4 resin functionalized with p-nitroso-a-naphtol (Lemos and Gama 2010). A preconcentration factor of 10 was achieved and with a colorimetric arsenazo-III spectrophotometry a detection limit 1.8 pg L" was reported. The online system included a mini-column through which the solution was passed for 180 s. In the elution step, the uranium was desorbed from the column and mixed with the colorimetric reagent and introduced into the spectrometer. The parameters were optimized and the effects of several interferences were examined. Recovery of spiked tap water, well water, and effluent samples was close to 100% (Lemos and Gama 2010). 

Jauberty, L., Droget, N., Decossas, J.L. et al. (2013). Optimization of the arsenazo-III method for the determination of uranium in water and plant samples, Talanta 115, 751-754. 

Lemos, V. A. and Gama, E.M. (2010). An online preconcentration system for the determination of uranium in water and effluent samples. Environ. Monit. Assess. 171, 163-169. 

The differences in sample size, sample preparation procedures, counting time, accuracy, isotope composition, and minimum detectable limits (MDL) should be noted. Some of these methods will be briefly surveyed here. The methods for determining uranium in urine are nsually also suitable for measuring the concentration of uranium in water, and those that are described in detail in Section 4.4.1 will not be discussed here to avoid duplication. 

Electroanalytical Methods Many publications described the use of electro-analytical methods for measuring uranium in water and some examples are discussed here. A detailed review article with illustrative tables that summarize the electroanalytical methods for the determination of uranium can be found elsewhere (Shrivastava et al. 2014). The tables in that review article list the method, the principles of the measurement technique, the linear range, limit of detection, tolerance to interferences (where defined), and the field in which the method is applied. 

Pulsed Laser Phosphorimetry. This is the basis for an ASTM standard test method for measurement of total uranium in water following wet ashing when impurities or suspended materials are present (D5174 2013). 

FTA has also been used to determine the concentration of uranium in water and urine (Sawant et al. 2011). The sample was placed in a polythene tube and a Lexan detector was also inserted in the tube so that it was submerged in the liquid sample. The tube was heat-sealed but a space of a few millimeters was intentionally left above the liquid. The urine samples and the calibration tubes were placed in a capsule that was then irradiated for 1 min with a flux of 5 10 n cm s". The Lexan detectors were removed from the capsule, etched with 6 M NaOH at 60°C for 1 h. The fission tracks in each detector were counted in 300-350 fields under a microscope at 400x magnification. The reported MDA was 3 ng per sample (Sawant et al. 2011), giving an MDL of 3 pg for a 1 mL urine sample. 

D5174, A. (2013). Standard test method for trace uranium in water by pulsed laser phospho-rimetry. West Conshohochen, PA ASTM. 

Sahoo, S., Satpati, A.K., and Reddy, A.V.R. (2013). Stripping voltammetric determination of uranium in water samples using Hg-thin film modified multiwall nanotube incorporated carbon paste electrode. Am. J. Anal. Chem. 4, 141-147 https //www.itia.ntua.gr/hsj/ redbooks/222/iahs 222 0071. pdf. 

Uranium occurs in natural waters as U", U" and U . Species relationships in aqueous equilibria of the U-O2-H2O-CO2 sub-system, as a function of Eh and pH, are shown in Fig. 3 for a temperature of 25°C and 1 atm pressure (the shaded area shows the stability field of uraninite (UO2)). Dissolved uranium in water is mainly in the form of stable uranyl dicarbonate and tricarbonate complexes. Fig. 3 shows that the field of existence of soluble uranium complexes becomes wider as pH increases. 

In addition to the usual analyses (dissolved uranium in water, uranium content of dry residues and stream sediments), sampling also includes radon, since its short half-life (3.8 days) limits its possible displacement from its source. For radon sampling a hypodermic syringe (30 cm ) is used to collect the water at the site of discharge and the sample is inserted into a vacuum-sealed test-tube. 

Fleischer R. L. and Delany A. C. Determination of suspended and dissolved uranium in water. Analyt. Chem., 48, 1976, 642-5. 

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