Chemical Understanding of Actinide Separations

Abstract

This article provides a broad overview of the separation processes used to isolate actinides and the experimentally and computationally determined chemical characteristics that define those separations. The redox chemistry of the actinides plays a pivotal role in both aqueous and pyrochemical processing separations. The nearoverlapping energies of the 6d and 5f orbitals in the light actinides allows for facile adjustment of actinide oxidation states, which is used in many established separation methods. In contrast, the stable, generally 3+oxidation states of the midand heavy actinides can make them difficult to separate from the similarly lanthanides(III). In aqueous separations, the tendency of the actinides to form anionic and neutral aqueous complexes with a variety of complexants (especially soft donors) is used to achieve high separation factors between chemically similar elements in both solid-liquid separations and liquid-liquid extraction. This selectivity can be further tuned through the use of specialized organic or solid phase ligands. Pyroprocessing separations utilize the unique redox behavior of the actinides to adjust their distribution between a molten salt electrolyte and either a solid electrode or molten metal phase. Atomic-level insights into the mechanisms underlying actinide separation processes, with the ultimate goal of predicting separation behavior, can be provided by electronic structure and statistical mechanicalbased calculation methods.

Critical fluctuations in liquid–liquid extraction organic phases controlled by extractant and diluent molecular structure

“…The selective recovery of critical materials, including metals, enables a wide range of important technologies. 1,2 Owing to its scalability and low input energy requirements, liquid-liquid extraction (LLE) is a predominant method for separations of metals, including rare earth elements, [3][4][5][6][7][8][9] actinides, 10,11 and platinum group elements. 12 In LLE, amphiphilic extractant molecules bind metals, transferring them from a polar aqueous phase to an immiscible nonpolar organic phase.…”

Critical Fluctuations in Liquid-Liquid Extraction Organic Phases Controlled by Extractant and Diluent Molecular Structure

“…The selective recovery of critical materials, including metals, enables a wide range of important technologies. 1,2 Owing to its scalability and low input energy requirements, liquid-liquid extraction (LLE) is a predominant method for separations of metals, including rare earth elements, [3][4][5][6][7][8][9] actinides, 10,11 and platinum group elements. 12 In LLE, amphiphilic extractant molecules bind metals, transferring them from a polar aqueous phase to an immiscible nonpolar organic phase.…”