Electroreduction of pertechnetate ions in concentrated acetate solutions

Abstract

Electrochemical reduction of pertechnetate ions is studied in acetate solutions on both mercury dropping and solid electrodes. It is found that electroreduction of TcO4− ions on the mercury dropping electrode occurs stepwise via the following route Tc(VII) → Tc(IV) → Tc(III) → Tc(0). Ammonium ions affect the reduction of pertechnetate ions by shifting potentials of polarographic waves in a positive direction. Diffusion coefficients of Tc(VII) species in acetate solutions decreased from ~1 · 10−5 cm2 s−1 in a solution containing 2 mol dm−3 acetate ions to ~1.2 · 10−6 cm2 s−1 in a solution containing 8 mol dm−3 acetate ions. The Stokes radius of pertechnetate ion is 0.19 ± 0.01 nm. Technetium coatings were characterized using X-ray absorption spectroscopy (XANES/EXAFS). It is shown that technetium is in the metallic state in the electrolytic deposits; however, the obtained metal is amorphous. The Tc-Tc interatomic distances and coordination numbers of Tc atoms in the deposits are determined. The distance between technetium atoms in the electrodeposits is slightly less (0.262 nm) compared to technetium foil (0.272 nm).