Cathodic reactions involving lead, cadmium and silver ions in NaNO3-KNO3 melts at 250°C

✍ Scribed by M.H. Miles

• Publisher: Elsevier Science
• Year: 1987
• Tongue: English
• Weight: 763 KB
• Volume: 32
• Category: Article
• ISSN: 0013-4686
• DOI: 10.1016/0013-4686(87)85031-4

✦ Synopsis

Cyclic voltammetric studies of Pb' + and Cd" ions on Pt and Hg electrodes suggest that the cathodic deposition of the metal does not occur in NaN03-KNO, melts. The new cathodic wave produced by the addition of these metal ions to the melt is due to the irreversible reduction of the nitrato complex, k (PbON02)+ +.2e-+ PbO + NO;. In contrast to metal deposition reactions, there is no oxidation state change for the metal ion since only the nitrate ligand is reduced. Irreversible cathodic waves were observed for Pb(NO& additions to molten NaN03-KN03 over the concentration range of 2.0 x 10m4 to 2.0 x lo-' m. Fast potential scan experiments from 1 to loo0 V S-I using a Pt microelectrode gave no indication of any Pb or Cd metal deposition. The exhaustive electrolysis of 0.10 m Pb(NO,), and 0.12 m Cd(NO& in molten NaNO --KN03 followed bv atomic absorbance analvses of the mercury cathodes showed that the amount of metal deposition is insignkcant. An investigation of Cd'+ .

-10"s in NaNOz-KNOs-NaNOJ suggests a similar reduction of nitrato or nitrito comolexes rather than metal deoosition. Silver ions are uniaue in that the reversible metal deposition reaction r&dily occurs in nitrate melt;. This is due to both the s&l1 electric field of this univalent cation and its favorable thermodynamics that places the reversible potential for the Ag+/Ag couple significantly more positive than the potentials required for the reduction of nitrate melts.