Effect of ion interactions on the Raman spectrum of NO₃⁻: Toward monitoring of low-activity nuclear waste at Hanford

Journal Article · 07 March 2022 · Chemical Engineering Research and Design

DOI: https://doi.org/10.1016/j.cherd.2022.03.002 · OSTI ID:1976959

Kocevska, Stefani  ^[1]; Maggioni, Giovanni Maria ^[2]; Crouse, Steven H.  ^[2]; Prasad, Rupanjali ^[2]; Rousseau, Ronald W.  ^[2]; Grover, Martha A.  ^[2]

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1. Georgia Institute of Technology, Atlanta, GA (United States); OSTI
2. Georgia Institute of Technology, Atlanta, GA (United States)

Raman spectroscopy is a valuable in-situ technique for many applications. The concentrations of species in complex ionic mixtures of nuclear waste can be estimated using Raman measurements. However, it has been experimentally observed that ion interactions can cause a modification of Raman peak intensities and positions. The present work explores the nonlinear behavior associated with the nitrate anion, NO₃⁻, which is present in abundance in low activity nuclear waste. We examine changes in the main Raman peak of the nitrate anion in the presence of other ions. A wide range of concentrations are covered, including those expected during direct-feed low-activity waste (DFLAW) processing at the Hanford site in the State of Washington. The experiments showed that the ions interact and associate to form ion pairs, which results in a blue shift (i.e., a shift towards higher wavenumbers) in the main Raman peak of nitrate. The results indicate that cation concentration is a better predictor of the peak shift, compared to ionic strength, both for binary and multicomponent mixtures. These findings have direct implications on the development of spectra-to-composition models for the DFLAW system, since they show deviations from the linearity assumptions used in common chemometric models.

• Research Organization: Vanderbilt University, Nashville, TN (United States)
• Sponsoring Organization: USDOE
• Grant/Contract Number: FC01-06EW07053
• OSTI ID: 1976959
• Journal Information: Chemical Engineering Research and Design, Journal Name: Chemical Engineering Research and Design Journal Issue: C Vol. 181; ISSN 0263-8762
• Publisher: ElsevierCopyright Statement
• Country of Publication: United States
• Language: English