URANIUM(VI) SULFATE COMPLEXATION STUDIED BY TIME-RESOLVED LASER-INDUCED FLUORESCENCE SPECTROSCOPY (TRLFS)

The use of the OPO technique in laser induced spectroscopic instrument ation is a new and improved spectroscopic technique. Solid crystals fo r the tunable laser allows one to perform laser spectroscopy over a wi de wavelength range without the use of a dye laser. We have demonstrat ed that the laser output of the OPO-system (in our case 270 nm) is sui table for time-resolved laser-induced fluorescence measurements. The u ranyl sulfate complexation was investigated for the first time by fluo rescence measurements. Compared to spectrophotometric methods, lower u ranyl concentrations can be investigated and therefore measurements co uld be made in seepage waters of uranium mine tailing piles. The measu red lifetimes of the 1:1, 1:2, and 1:3 uranyl sulfate complexes are 4. 3 +/- 0.5 mu s, 11.0 +/- 1.0 mu s and 18.8 +/- 1.0 mu s, respectively. The main fluorescence bands of the sulfate complexes are centered at 498 nm, 515 nm and 538 nm and no significant shift of the fluorescence maxima was found between the three complexes. The complex formation c onstants of the first two uranyl sulfate complexes at an ionic strengt h of 0.2 M were measured as log beta(1(0.2 M)) = 2.42 and log beta(3(1 .0 M)) 3.30, respectively. The complex formation constants for the thr ee uranyl sulfate complexes at an ionic strength of 1 M were measured as log beta(1(1.0 M)) = 1.88, log beta(2,(1.0 M)) = 2.9 and log beta(3 (1.0 M)) 3.2, respectively. A speciation diagram was calculated from t he results of the time resolved measurements.