Estimation of uranium in leach liquors of low iron content : modification of a spectrophotometric method using 4-(2 pyridyl azo) resorcinol

The selective complexing property of the heterocyclic azo dye 4-(2-pyridyl azo) resorcinol (PAR) with uranium in presence of another complexing solution (ethylene diamine tetra acetic acid and sodium fluoride) in borate buffer (PH 7.8) has been employed for the rapid estimation of uranium present in carbonate leach liquors, in low acidity leach liquors and in ion exchange eluates where the content of dissolved iron is relatively low (≤2.5 gm/litre). The carbonate leach liquors are initially treated with nitric acid to destroy the carbonate radical. The extent of formation of the U-PAR complex (εm, without complexing solution is 38,700 at 530 nm) is reduced by about 40% in presence of the optimum concentration of the complexing solution and of the chromogenic reagent used for the analysis, and therefore, the sensitivity. However, the formation of the uranium-PAR is linear with the uranium concentration, even in presence of the complexing solutions, as was observed in absorption measurements at the peak wavelengths of both 530 nm and 540 nm. The calibration graph is linear for the range of 2 to 20 μg of uranium per ml when iron present is ≤ 50 μg per ml in the solution of measurements. Other interfering metal ions which may be present in small amounts in the above samples are also masked by the complexing solutions. The results compare well with those determined by the more sensitive fluorimetric method and the modified method enables the analysis, on a routine basis, of a wide variety of leach liquors of uranium. (author). 6 refs., 3 tabs