Voltammetry of neptunium(VI) malonate at the rotated glassy carbon electrode

Abstract

The voltammetric behavior of the neptunium(VI)-malonate has been investigated over widely varying conditions of ligand concentration and pH. Under the conditions investigated, an irreversible wave was obtained when the pH was greater than 3·3 and the ligand concentration was less than 6·0 × 10 −2 M. In all other pH ranges and ligand concentrations, a reversible wave corresponding to the reduction of neptunium(VI) complex to the neptunium(V) complex was obtained. At acid concentrations greater than 1 M and less than a pH 3·3, the half wave potential was found to be independent of acid concentration. Inside this range the half wave potential is pH dependent, and one hydrogen ion is involved in the reduction. The metal-ligand ratio was found to be 1:2 by conductometric titrations. The limiting current is proportional to the concentration of the neptunium(VI) from 3·92 × 10 −5 to 1·96 × 10 −3 M. The diffusion coefficient is 0·28 × 10 −5 cm 2/sec at pH 1·3 and 0·22 × 10 −5 cm 2/sec at pH 4·6.