A series of feed solutions sequentially increasing in nitric acid and then increasing in UO2(NO3)2 concentration were introduced into the “hot” centrifugal contactor system to test the online performance of the spectro­scopic equipment as part of the centrifugal contactor system. At this stage, no contact with TBP/n-dodecane was done. Raman spectra were collected concurrent with the additions of HNO3 and UO2(NO3)2 into the feed. Figure 4.16 shows the accumulated Raman spectra taken over the time frame of the nitric acid and uranyl nitrate additions. Several spectral features are apparent: the water region at 3000-4000 cm-1; the nitrate band at 1050 cm-1; and the UO22+ at 871 cm-1. Collected spectra were subjected to a previously developed chemometric model, and a successful translation of the model based on static UO2(NO3)2/HNO3 measurements to the flow on-line moni­toring was achieved. Figure 4.17 contains the expected and predicted con­centrations of the Raman on-line measurements and shows excellent agreement between values. It is worth noting that the model is capable of not only predicting the UO22+ and nitrate concentrations but is also capable of differentiating between total nitrate and nitric acid. The distinction between nitrate and nitric acid is possible due to the inclusion of all the spectral data within the Raman spectrum, including the water region (3000­4000 cm-1) and multiple nitrate bands (of which 1050 cm-1 is the largest),

nitrate band at 1050 cm-1

0

Time (min)

4.16
On-line Raman monitoring of the composition of the raffinate solution in the centrifugal contactor extraction experiment. Fuel feed simulant solutions: 0-6 M HNO3 and 0-0.6 M UO2(NO3)2. Organic phase: 30% TBP-dodecane solution.

4.17 On-line PLS predictions of nitric acid, total nitrate, and uranyl concentrations based on on-line Raman measurements as a function of experimental time. Measured and predicted Raman on-line measurements showing excellent agreement between values. The light gray lines are the instantaneous concentrations of added analyte in solution (assuming zero mixing time); the dark gray lines are the predicted concentration of HNO3, total nitrate, and UO2(NO3)2 respectively.

which show subtle but reproducible changes based on acid content and the ionic strength of the solution.