Chemical and electrochemical behavior of metallic technetium in acidic media

The chemical and electrochemical properties of technetium metal were studied in 1-6 M HX and in 1 M NaX (pH 1 and 2.5), X = Cl, NO3. The chemical dissolution rates of Tc metal were higher in HNO3 than in HCl (i.e. 8.63 x 10(-5) mol cm(-2) h(-1) in 6 M HNO3 versus 2.05 x 10(-9) mol cm(-2) h(-1) in 6 M HCl). The electrochemical dissolution rates in HNO3 and HCl were similar and mainly depended on the electrochemical potential and the acid concentration. The optimum dissolution of Tc metal was obtained in 1 M HNO3 at 1 V/AgAgCl (1.70 x 10(-3) mol cm(-2) h(-1)). The dissolution potentials of Tc metal in nitric acid were in the range of 0.596-0.832 V/AgAgCl. Comparison of Tc behavior with Mo and Ru indicated that in HNO3, the dissolution rate followed the order: Mo > Tc > Ru, and for dissolution potential the order: E (diss)(Ru) > E (diss)(Tc) > E (diss)(Mo). The corrosion products of Tc metal were analyzed in HCl solution by UV-Visible spectroscopy and showed the presence of TcO4 (-). The surface of the electrode was characterized by microscopic techniques; it indicated that Tc metal preferentially corroded at the scratches formed during the polishing and no oxide layer was observed.