Overcoming oxidation state dependent spectral interferences: On-line monitoring of U(VI) reduction to U(IV) via Raman and UV-vis spectroscopy

Analytical characterization of chemical constituents is an essential component of both industrial processes and fundamental studies. Applicable techniques abound, but optical spectroscopy has the unique combination of being easily incorporated into online (in situ) monitoring probes and can also provide abundant chemical information (concentration, oxidation state, speciation). However, this abundance of chemical information can make applying optical spectroscopy to complex chemical processes challenging. This is particularly evident in the bulk electrolysis of U(VI) to U(IV), an essential preparatory step in some nuclear fuel recycling schemes. Starting and product materials have interfering spectral signatures in both electronic and vibrational spectroscopies, making accurate and real-time analysis difficult to achieve. This spectral complexity was overcome through the use of chemometric models, multivariate analysis techniques that were built from spectral training sets and applied to process data in real-time for immediate process analysis. Here we discuss the application of optical spectroscopy to online monitoring of a bulk electrolysis process and the methods utilized to analyze data as well as characterize the efficiency of U(IV) generation.