Determination of Uranium as Pyrophosphate

Abstract

IN the gravimetric determination of uranium as phosphate, the ignited precipitate is commonly considered¹ to be the pyrophosphate (UO₂)₂P₂O₇ (U = 66.67 per cent). In recent work in these laboratories uranium was precipitated at pH 5.5 from solutions containing ethylenediaminetetraacetic acid, nitric acid and ammonium sulphate. The results were consistently low by 2.3 per cent relative when the precipitate was ignited to constant weight at 850° C.² and calculations made on the basis of the formula (UO₂)₂P₂O₇. As no significant quantities of uranium could be detected in the filtrates to explain the low results, the ignited precipitates were examined. They were dissolved in concentrated phosphoric acid and the solutions titrated with standard potassium dichromate solutions. From the observed titrations it was calculated that the ignited precipitates contained 33.2 ± 0.3 per cent quadrivalent uranium. For precipitates ignited at 1,000° C. the corresponding result was 33.9 ± 0.1 per cent quadrivalent uranium.