Cyclic voltammetry of Pu and Np in nitric acid media

Electrochemical and spectroelectrochemical behaviour of Np(VI) ions in nitric acid solutions

“…The electrolytic redox method for controlling valence states without addition of any redox substances is one of the important techniques in the nuclear fuel reprocessing. There are many studies on electrochemical reactions of Np species in acidic [6][7][8][9][10] and alkaline solutions [11][12][13][14][15][16]. Plock measured the formal redox potential for Np(VI)/Np(V) at a glassy carbon (GC) *Author for correspondence (E-mail: skim@procsafe.tokai.jaeri.go.jp).…”

“…electrode in HClO 4 solution by using cyclic voltammetry (CV) [8], and confirmed that the redox system is reversible. Casadio et al investigated the Np(VI)/Np(V) couple by CV at a pyrolytic graphite electrode [9]. Niese et al characterized the charge transfers of Np(IV), Np(V), and Np(VI) in HClO 4 , HNO 3 , and H 2 SO 4 by CV with a GC electrode [10].…”

Reduction behavior of neptunium(V) at a gold or platinum electrode during controlled potential electrolysis and procedures for electrochemical preparations of neptunium(IV) and (III)

“…Electrode reactions of Np ions have been studied widely [2,6], and redox processes of NpO 2þ 2 /NpO þ 2 and Np 4+ /Np 3+ couples in acidic aqueous solutions were reported to be reversible or quasireversible [7][8][9][10][11][12][13]. The redox reaction of NpO þ 2 /Np 4+ , which accompanies the breaking or formation of an Np-O bond, is irreversible and requires considerably large overpotential [10].…”

“…Though HNO 3 system has been used most widely in various actinide processes, the acid adopted in the present work was HClO 4 because the acid composed of an anion that hardly complexes with Np species is considered to be preferable to use for the elucidation of fundamental reduction behavior. In this connection, electrode reactions of NpO 2þ 2 /NpO þ 2 and Np 4+ /Np 3+ couples were investigated in both HNO 3 [9][10][11][12][13]18] and HClO 4 [7,8,10,17,18] [21] (estimated under assumption that K 1 for Np 3+ is identical to that for Am 3+ ). The K 1 for NpO þ 2 was reported to be negligible [20].…”

“…The p was estimated to be 0.0145 s À1 from the i-t curve obtained by controlled potential electrolysis for the reduction of Np 4+ to Np 3+ at À0.250 V versus SSE based on Eqs. (4) and(9). The time course of i was calculated by substituting c à NpðIVÞ obtained by the simulation for c à NpðIVÞ ðtÞ in Eq (9)…”