Electrochemical and spectroscopic studies of neptunium in the aluminum chloride-1-n-butylpyridinium chloride melt at 40.degree.C

Abstract

The chemistry of neptunium in acidic and basic AlCl/sub 3/-1-n-butylpyridinium chloride melts at 40/sup 0/C has been investigated by means of electrochemical and spectral techniques. In acidic as well as in basic melts, the reduction of Np(IV) to Np(III) at glassy-carbon electrodes is quasi-reversible. Indirect measurements of the formal potential and spectroscopic results on the Np(IV)-Np(III) system as a function of the acidity indicate that Np(III) and Np(IV) exist as NpCl/sub 6//sup 3 -/ and NpCl/sub 6//sup 2 -/ and solvated Np/sup 3 +/ and NpCl/sub x//sup (4-x)+/ (with 3 greater than or equal to x greater than or equal to 1), respectively, in basic and acidic melts. The apparent rate constant K/sup 0/' has been measured on the basic and acidic sites. It depends on the melt acidity only in the latter melts. The Nugent linearization method has been applied to the standard potentials of Np(IV)-Np(III) and U(IV)-U(III) in 2:1 melts. A comparison with the results obtained from other room-temperature solvents shows, as already found with lanthanides, that the acidic melt is a very weak solvating medium.