ISSN print edition: 0366-6352 ISSN electronic edition: 1336-9075 Registr. No.: MK SR 9/7 Published monthly

Anodic reactions of sulphate in molten salts

Marta Ambrová, Pavel Fellner, and Jomar Thonstad

Institute of Inorganic Chemistry, Technology and Materials, Slovak University of Technology, Radlinského 9, SK-812 37 Bratislava, Slovakia

E-mail: marta.ambrova@stuba.sk

Received: 17 February 2009  Revised: 6 July 2009  Accepted: 8 July 2009

Abstract: Electrochemical behaviour of sulphate under anodic polarization in molten sodium chloride, cryolite and sodium fluoride was investigated by cyclic voltammetry and chronopotentiometry at the temperatures of 820°C, 1010°C, and 1000°C, respectively. Using a platinum working electrode, two waves were observed on the chronopotentiograms in the systems: NaCl-Na₂SO₄ and Na₃AlF₆-Na₂SO₄. The first wave was attributed to the formation of oxygen. The second wave probably originated from the reaction of oxygen with platinum, or from oxidation of SO₃ decomposition products. Three waves were observed for the anodic process of sulphate ions dissolved in molten sodium fluoride. The first wave was attributed to the formation of oxygen. The second and the third wave were attributed to the formation of PtO and PtO₂. This conclusion was supported by cyclic voltammetry experiments of the in-situ formed sulphide in molten NaCl at 820°C and by chronopotentiometry on a gold working electrode in the system NaCl-Na₂SO₄, where no anodic wave was observed.

Keywords: anodic process - cryolite - sodium chloride - sodium fluoride - sodium sulphate

Full paper is available at www.springerlink.com.

DOI: 10.2478/s11696-009-0099-2

Chemical Papers 64 (1) 8–14 (2010)