Insights for controlling plutonium behavior in hydrochloric acid solutions†

Abstract

Advancing understanding of aqueous chemistry for plutonium is important because it impacts energy production, environmental management, and national security. Unfortunately, plutonium's aqueous chemistry remains poorly characterized. We addressed this problem by characterizing Pu(IV) redox and coordination chemistry in aqueous solutions as a function of hydrochloric acid concentration using X-ray absorption spectroscopy, ultraviolet-visible near-infrared spectroscopy, and electrochemistry. The impact of Pu–Cl vs. Pu–O_H2O bonding was correlated with the stability of different plutonium oxidation states. We discovered that anionic Cl¹⁻ ligands stabilized electron-deficient Pu(IV) over Pu(III) and neutral H₂O ligands stabilized Pu(III) over Pu(IV). These findings offer a way to control plutonium electron transfer chemistry and imply that selective stabilization of Pu(IV) or Pu(III) may be achieved through tuning the electron donating ability of the ligand. Overall, this work advances predictive capabilities for aqueous plutonium chemistry, particularly within nuclear application spaces.