Hydrolysis of Np(IV) and Pu(IV) and their complexation by aqueous Si(OH)₄

Abstract

SummaryThe hydrolysis and interaction of Np(IV) and Pu(IV) with orthosilicic acid, Si(OH)Mat ionic strength

Neptunium(iv)-hydroxamate complexes: their speciation, and kinetics and mechanism of hydrolysis

“…9 below). This is in agreement with a recent paper by Yusov et al 44 that arrives at the same conclusion. Thus, of the Np(IV)-OH species studied only the NpOH 3+ complex may be present in significant quantities under the conditions studied here; the equilibrium constant, K 1,OH , for the formation of the monohydroxide complex by Np 4+ hydrolysis is given in eqn (7).…”

“…Neptunium(IV) forms a range of weak inner sphere complexes with nitrate ions of which the mono-and bis-nitrato species are the most important in the HNO 3 concentration range used in these experiments. [41][42][43][44] These complexes, for which the stability constants β 1,NO 3 and β 2,NO 3 are given by eqn (5) and (6), would form during PUREX/UREX-based reprocessing, limiting the availability of neptunium(IV) to complex with the hydroxamate ligand. Literature values for β 1,NO 3 and β 2,NO 3 are given in logarithmic form in Tables 2 and 3 Preliminary speciation diagrams (not shown) indicate that the formation of hydroxide complexes higher than NpOH 3+ is unlikely at pH < 2 and so can be neglected under the conditions used in PUREX/UREX-based reprocessing.…”

Long-term aqueous alteration kinetics of an alpha-doped SON68 borosilicate glass

“…Various hypothesis can be proposed to explain these higher concentrations. Small polynuclear species such as oligomers and colloids could be formed with diameters < 1 nm [16], or complex(es) with dissolved glass species could predominate and induce higher plutonium concentrations [19]. However these data show that plutonium releases remain three orders of magnitude lower than boron releases ( figure 3-B), suggesting strong plutonium retention in the alteration layer and/or sorption on the walls of the leaching reactor.…”

Complexation of tetravalent actinides (Th, U, Np, Pu) with 2,6-pyridinedicarboxylic acid in aqueous solutions

“…Experiments were performed in the pH range in which the hydrolysis of Th(IV) ions is insignificant (0.2-1.0 M HClO 4 solutions). In the case of U(IV), Np(IV), and especially Pu(IV), the first step of hydrolysis can be noticeable even under these conditions [6,7]; therefore, strictly speaking, by An 4+ in reaction (4) one should mean the sum of the aqua ion and hydrolyzed species An(OH) 3+ . However, this refinement does not affect essentially the subsequent reasoning and conclusions.…”

“…For the convenience of further interpretation of the data, let us rewrite the expression for the overall stability constant of the complexes An(PDCβ' (An) = logK 1 ' (An) + (-logK 1 ' (Th) + logK 1 ' (Th) ) + logK 2 ' (An) + (-logK 1 ' [U(VI)] + log K 1 ' [U(IV)] ) + log K 3 ' (An) = log (K 1 ' (An) /K 1 ' (Th) ) + log (K 2 ' (An) /K 1 ' [U(VI)] ) + log K 3 ' (An) + log (K 1 ' (Th) K 1 ' [U(VI)] ),(6) …”