SPECTROPHOTOMETRIC DETERMINATION OF URANIUM(VI) IN BACTERIAL LEACH LIQUORS USING ARSENAZO-III

A highly sensitive and precise spectrophotometric method for the direct determination of uranium(VI) in bacterial leach liquors, obtained by the action of Thiobacillus ferrooxidans and T. thiooxidans, from low-grade sandstone uranium ores, has been developed. Arsenazo-III formed an intense pink-violet complex at pH 2.0 +/- 0.1, which showed maximum absorption at 655 nm. This method was found to obey Beer's law up to 6-mu-g cm-3, giving the values of molar absorptivity (epsilon) and Sandell sensitivity (S) as 4.6 x 10(4) mol-1 cm-1 and 0.0052-mu-g cm-2, respectively. Interference due to different metal ions, such as Al, Ca, Co, Cr, Fe, Mn, Mo, Zn, and Zr, was successfully masked by diethylenetriaminepenta-acetic acid without inhibiting the formation of the uranium(VI)-arsenazo-III complex. This method was also found suitable for detecting low levels of uranium(VI) in mine waters, acid leach liquors and tailings liquids. The results obtained were found to be in close agreement with the values determined by fluorometric and indirect spectrophotometric methods.