Quantifying neptunium oxidation states in nitric acid through spectroelectrochemistry and chemometrics

Abstract

Controlled-potential in situ thin-layer spectropotentiometry was leveraged to generate visible/near-infrared (VIS/NIR) absorption spectral data sets for the development of chemometric models to quantify Np(III/IV/V/VI) oxidation states in HNO3. This technology would be valuable in laboratory studies and when monitoring process solutions to guide feed adjustments for radiochemical separations—the performance of which depends on oxidation state. This approach successfully isolated and stabilized Np species in pure (∼99%) oxidation states without compromising solution optical properties. Multivariate curve resolution–alternating least squares models were evaluated to resolve spectral and component concentrations from a scan that sequentially produced Np(VI), Np(V), Np(IV), and Np(III) spectra with mixtures of two valences at a time. Although it provided a useful approximation, the method was not able to quantitively resolve each component likely because of rotational ambiguity. Additionally, partial least squares regression models were built from artificial and electrochemically generated VIS/NIR spectral training sets to study the effect of interionic interactions on spectral characteristics. Models built with true Bi-chemical mixtures of coexisting Np oxidation states and spectra generated from additive combinations of pure end points had similar prediction performance. This methodology can be used to directly quantify Np concentration and the ratio of Np oxidation states and other actinides in remote settings such as hot cells.

Leveraging Calibration Transfer Techniques for Remote Monitoring of Samarium and Europium in LiCl Using Laser-Induced Florescence Spectroscopy for Radioisotope Production Applications

“…A plot comparing the two designs is shown in Figure S1. Transfer samples were selected using the KS algorithm which selects a user defined number of samples which are diverse from one another such that they represent the variability in the data set. ,, The KS-selected samples are annotated in Table S1.…”

Evaluating Optical Techniques to Characterize Solid State Samples for the Pu-238 Supply Program

“…Spectrophotometry is an important component of the 238 Pu Supply Program for measuring Np and Pu concentrations, oxidation state(s), and monitoring separations. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] Spectrophotometry, or absorption spectroscopy, is a technique that quantifies the amount of light absorbed by a sample as a function of wavelength. Ultraviolet (UV)-visible (Vis)-near-infrared (NIR) spectrometers collect spectra at relatively rapid intervals (e.g., 10-1,000 ms) and contain a wealth of information.…”