Uranium gravimetric

The only anhydrous trioxide is UO3, a common form of which (y-U03) is obtained by heating U02(N03).6H20 in air at 400°C six other forms are also known.Heating any of these, or indeed any other oxide of uranium, in air at 800-900°C yields U3O8 which contains pentagonal bipyramidal UO7 units and can be used in gravimetric determinations of uranium. Reduction with H2 or H2S leads to a series of intermediate... 

Elemental composition (anhydrous compound) U 60.41%, N 7.11%, O 32.48%. The compound may be identified by its physical properties and measured by gravimetric methods from its thermal decomposition to form uranium trioxide, UO3. The radioactivity may be measured by an alpha counter. 

Gravimetric Estimation.—Many methods for the quantitative determination of uranium have been described, but the follo%ving appear to be the most trustworthy (1) precipitation with ammonia as ammonium diuranate, and ignition to urano-uranie oxide (2) precipitation of uranyl ammonium phosphate by means of ammonium phosphate in presence of ammonium acetate, and ignition of the precipitate to uranyl pyrophosphate and (8) precipitation as uranyl sulphide by means of ammonium sulphide, and ignition to urano-uranie oxide. 

Phosphate. Because of interference by uranium in the usual magnesium ammonium orthophosphate procedure,5 uranium is first removed by a cation-exchange procedure. A column (2.5 by 36 cm.) of 50 to 75 cc. of Dowex-50 resin is washed with 200 ml. of Z N hydrochloric acid and then 200 ml. of water at flow rates of 2 to 3 ml./min. An acidic solution of the product, containing 100 to 150 mg. of orthophosphate, is passed through the column at a rate of 1 ml./min. The column is washed with water until the washings are neutral to litmus, and phosphate is determined in the combined eluate and washings by the usual gravimetric procedure.6 Uranium can be eluted from the... 

Thiocyanates. Anhydrous Th(NCS)4 has been reported, on the basis of thermo-gravimetric evidence, to be the product of the thermal decomposition of complexes of the type Th(NCS)4L2 (e.g. L = 2,6-lutidine A-oxide) it is said to decompose to ThO(NCS)2 above 49QOC 44 hydrate, [Th(NCS)4(H20)4], is better established the uranium(IV) analogue is known only as the solvate of composition [U(NCS)4(H20)4] (18-crown-6)l.s 3H20 MeCOBu in which the structure of the [U(NCS)4(H20)4] molecule is a distorted square antiprism in which the upper square comprises one 0(H20) and three N(NCS) atoms and the lower square three 0(H20) and one N(NCS) atoms." ... 

The final titration is usually performed with a commercial automatic volumetric titrator. Gravimetrically calibrated burettes yield coefficients of variation of 0.05% or less for the overall uncertainties of random or systematic nature in the assays of samples of uranium and mixed... 

The main specifications concern the uranium content in UFg by gravimetric and titrimetric methods, isotopic composition (as listed earlier), el ental impurities by atomic absorption, ICP-AES, spectrographic, colorimetric, titrimetric, spark source mass spectroscopy and radiochemical (alpha and gamma spectrometry and neutron absorption) methods, and organic impurities like hydrocarbons and their derivatives. Modern methods also deploy ICPMS techniques for the determination of impurities and isotopic composition (C1287 2010). It is beyond the scope of this book to present all these methods in detail so a number of examples are shown later. 

Some detailed examples of ASTM protocols for the characterization of UO2 are presented later in order to demonstrate the procedures. Determination of uranium, oxygen, and the 0 U atomic ratio by the ignition (gravimetric) impnrity correction method is part of the general test methods for UO2 (C696 2011). The sample (5-10 g of powdered... 

Uranium and oxygen uranium atomic ratio by the ignition (gravimetric) impurity correction method CI453 standard test method for the determination of uranium by ignition and oxygen to uranium ratio (0/U) atomic ratio of nuclear grade uranium dioxide powders and pellets Carbon (total) by direct combustion-thermal conductivity method... 

The amount of uranium In a sample may be determined by standard methods of analysis gravimetric, volumetric, colorimetric, spectrophotometrlc, etc. ... 

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