The speciation of protactinium since its discovery: a nightmare or a path of resilience

Abstract

This review concerns the speciation of protactinium in aqueous solution under its both oxidation states +IV and +V. Emphasis is placed on experimental data obtained at trace level but also in macroscopic amount leading to the determination of thermodynamic and structural data. Thus, the complexation of Pa(V) with mineral acids and organic acids, mainly polyaminocarboxylic acids (iminodiacetic acid [IDA], nitrilotriacetic acid [NTA], ethylenediaminetetraacetic acid [EDTA] and diethylenetriaminepentaacetic acid [DTPA]) are highlighted and compared. The review also includes the actual knowledge about the Pa(IV) aqueous chemistry pinpointing its spectroscopic features.

Coordination and thermodynamic properties of aqueous protactinium(v) by first-principle calculations

“…Unfortunately, Pa( v ) and Pa( iv ) are prone to hydrolysis, polymerization and precipitation and other issues such as a strong tendency to adsorb into glass, etc. 6 Furthermore, the intrinsic radiations of its isotopes imply specific safety regulations to be followed. Consequently, the speciation of Pa( v ) and Pa( iv ) in aqueous solution is largely unknown, which further complicates the performance of a theoretical study dedicated to the coordination and thermodynamic properties of these; thus, one has to rely on ad hoc research hypotheses.…”

Stability of the Protactinium(V) Mono‐Oxo Cation Probed by First‐Principle Calculations

“…Both high‐level electronic structure calculations and experimental data suggest the monohydrate PaO 2 + (H 2 O) and the PaO(OH) 2 + dihydroxyl complex are isoenergetic [6–9] . However, in solution, the dioxo moiety PaO 2 + has not yet been identified [10–12] . Indeed the protactinyl(V) ion is a much stronger acid than its successors in the actinide series and, in fact, the least hydrolyzed species of Pa(V) appears to be PaO(OH) 2+ [10] .…”

“…has not yet been identified. [10][11][12] Indeed the protactinyl(V) ion is a much stronger acid than its successors in the actinide series and, in fact, the least hydrolyzed species of Pa(V) appears to be PaO(OH) 2 + . [10] Pa V may exist as a mono-oxo ion PaO 3 + , in highly acidic media, rendering it a truly unique actinide [12,13] or a solecation Pa 5 + .…”

“…[10][11][12] Indeed the protactinyl(V) ion is a much stronger acid than its successors in the actinide series and, in fact, the least hydrolyzed species of Pa(V) appears to be PaO(OH) 2 + . [10] Pa V may exist as a mono-oxo ion PaO 3 + , in highly acidic media, rendering it a truly unique actinide [12,13] or a solecation Pa 5 + . [14] However, studying Pa V presents formidable challenges due to its strong tendency towards hydrolysis, polymerization, precipitation and sorption on any solid.…”

“…[14] However, studying Pa V presents formidable challenges due to its strong tendency towards hydrolysis, polymerization, precipitation and sorption on any solid. [12] To mitigate these competitive reactions, careful control of Pa concentrations and complexing media is essential. Pa V displays high solubility in hydrofluoric and sulfuric acids, as well as in oxalic acids.…”