PNNL

Abstract

The ability to run chemical processing more efficiently and cost effectively is a need that spans critical materials recovery to legacy nuclear waste cleanup. Sensors integrated to provide on-line monitoring are essential to addressing this need by providing near-real time feedback on process conditions, which can improve efficiency, aid in decision making, and reduce the need for grab sample measurements. Optical spectroscopy is well-suited for providing on-line chemical composition information and has been widely applied in varied chemical systems. However, applications in turbid matrices continue to represent substantial challenges to sensor performance, where absorption or scattering of excitation light can cause significant signal interference. Here, close-focus Raman probes are investigated for use in turbid media as a way to overcome the signal loss from scattering of the Raman excitation source. This, paired with advanced data science techniques, allowed for the development of chemometric models for the accurate quantification of several analytes of interest (NO3-, NO2-, and PO43-) in highly turbid solutions with solids loadings of up to 20 weight percent. Chemical systems of interest were focused on nuclear waste at the Hanford Site, which represents highly complex matrices that could realize significant processing benefits through the integration of on-line monitoring.