Spectrophotometric determination of uranium(VI) in phosphoric acid by means of solvent extraction with mixtures of TOPO and biphenyl

The variations in the distribution coefficients of twelve metals and uranium between nitric acid or hydrochloric acid - TOPO systems have been studied as functions of the concentration of nitric acid, hydrochloric acid and TOPO and temperature employing biphenyl as the diluent for TOPO. The formula UO2(NO3)2-(TOPO)2 can be assigned to the complex. Uranium in a phosphoric acid solution is quantitatively extracted from 2 mol dm-3 nitric acid into molten TOPO-biphenyl at about 700C. The organic phase separates out as a solid on cooling and is dissolved in ethanol. The uranium in this solution is then determined spectrophotometrically with 1-(2-pyridylazo)naphth-2-ol. Beer's law holds in the range 1 to 8 p.p.m. of uranium, and the relative standard deviation for 10 determinations was 2.1%. (author)