CATALYTIC DETERMINATION OF TRACES OF URANIUM IN ROCKS BY CHRONOCOULOMETRY

The chronocoulometric method for the determination of trace levels of uranium based on the catalytic reduction of nitrate, described in a pr eceding article, was applied and evaluated with real and synthetic sam ples. Samples with complex matrixes like rocks were first solubilized in hot acid (HF + HNO3) by digestion under pressure in a PTFE bomb. Wh en necessary, liquid-liquid extraction with tri-n-butyl phosphate (TBP ) followed by reversion to aqueous phase was used for previous separat ion of interferents. Results for a feldspar, a phosphorite, and three granitic rock samples, containing uranium in the range of 2 to 100 ppm , are in good agreement with those obtained by other techniques such a s X-rw fluorescence, isotopic dilution-mass spectrometry (ID-MS), and instrumental activation analysis (differences of 4 to 16% in relation to the unweighted mean for different techniques).