SYSTEMATIC EVALUATION OF Tc(VII)/Tc(IV) REDOX PROCESSES IN 0.1 M NaCl SOLUTIONS

The reduction of 1·10−5 mol/dm3 (M) Tc(VII) solutions in various reducing systems (homogeneous solutions with inorganic and organic reductants and heterogeneous suspensions containing Fe(II)/Fe(III) precipitates and Fe powder) was investigated in the pH range 2 – 13 in 0.1 M NaCl/NaOH at 22ºC under Ar atmosphere. The results were systematized according to Eh/pH conditions in solution and a general borderline for the reduction of Tc(VII) to Tc(IV) regardless the reducing systems was obtained according to the reaction (TcO4 – + 4H+ +3e– = TcO2(coll,hyd) + 2H2O). This experimental borderline was (about 100 mV) lower than the equilibrium line for the reduction of Tc(VII) (log [Tc(VII)]tot = −5.0) calculated from reported standard redox potential of TcO2(s) prepared electrochemically. This possibly implies the existence of more soluble solid phases such as small Tc(IV)oxyhydroxide particles under the given conditions. Reaction kinetics are also discussed and correlated to the measured redox potentials and the reduction borderline.

KOBAYASHI Taishi;  GAONA Xavier;  FELLHAUER David;  ALTMAIER M.; 

2012-02-07

Karlsruher Institut fuer Technologie

JRC68757

978-3-86644-756-1,   

1869-9669,