The gravimetric determination of uranium in uranyl nitrate

Abstract A study of the factors which affect the gravimetric determination of uranium in uranyl nitrate is described. In the gravimetry of uranium, the U 3 O 8 (weighing form) produced by ignition is usually assumed to deviate 3 0 8 matrix. It is shown that these assumptions are incorrect. Ignition temperature and time affect U 3 O 8 stoichiometry. Ignitions of uranyl nitrate for 1–3 h at 850° produce U 3 O 8 that deviates as much as 0.15% from stoichiometric U 3 O 8 ; deviations are negligible when uranyl nitrate is ignited at 1000° for 2 h. Elemental impurities, particularly calcium and phosphorus, affect the composition of U 3 O 8 formed in the ignition of uranyl nitrate. A variety of impurity complexes such as uranates and phosphates are found within the U 3 O 8 matrix. Formation of these impurity complexes depends on the elements present, their concentration, and ignition temperature. Therefore, in the gravimetric determination of uranium in uranyl nitrate, the effects of ignition parameters and nonvolatile impurities must be considered in order to obtain accurate uranium determinations.