Electrochemical Behaviour of Dissolved Iron Chloride in KCl+LiCl+NaCl Melt at 550ºC

Tuesday, 7 October 2014: 14:40
Expo Center, 1st Floor, Universal 3 (Moon Palace Resort)
B. Khalaghi, E. Kvalheim (Department of Materials Science and Engineering, Norwegian University of Science and Technology, 7491 Trondheim, Norway), M. Tokushige (Department of Fundamental Energy Science, Kyoto University, Kyoto 606-8501, JAPAN), L. Teng, S. Seetharaman (Royal Institute of Technology, SE 100 44, Stockholm, Sweden), and G. M. Haarberg (Norwegian University of Science and Technology)
Knowing the electrochemical behaviour of metallic ions in molten salts is crucial for electrometallurgical processes [1]. These processes include both extraction of metals from primary sources and recovery from wastes. Recently there has been a growing interest in developing an electrolytic process for iron production [2-3]. Furthermore, while an electrolytic process is used for treatment of wastes, iron is quite often present. Although, many studies have been done on iron in chloride melts [4-6], it seems little attention has been paid to FeCl3 behaviour and stability in these electrolytes.

In this study the electrochemical behaviour of iron in a salt bath composed of KCl+LiCl+NaCl was studied at 550°C by cyclic voltammetry and chronoamperometry. The working electrode was glassy carbon and iron was introduced to the melt by adding dehydrated FeCl3. Although FeCl3 is not fully stable in these types of solutions, both FeCl2 and FeCl3 showed to exist in the salt bath.  Based on cyclic voltammograms the Fe (II)/Fe (0) electron exchange is a soluble/insoluble diffusion controlled process, although it cannot be considered fully reversible. The nucleation of metallic iron on glassy carbon electrode showed instantaneous characteristics. From the cyclic voltammetry results, the calculated value for Fe (II) diffusion coefficient is equal to 1.4×10-5 cm2 s-1. Although FeCl3 is not fully stable in these types of solutions, the Fe (II)/Fe (III) exchange reaction was observed at potentials near the chlorine evolution reaction. The oxidation of Fe (II) to Fe (III) is followed by a chemical reaction consuming the as generated FeCl3 ions. The equilibrium between FeCl3 and FeCl2 is also briefly discussed.



  1. D. Inman, S.H. White, The production of refractory metals by electrolysis of molten salts design factors and limitations, Journal of Applied Electrochemistry 8 (1978) 375. 
  2. G.M. Haarberg, E. Kvalheim, S. Rolseth, T. Murakami, S. Pietrzyk, S. Wang, Electrodeposition of Iron from Molten Mixed Chloride/Fluoride Electrolytes, ECS Transactions 35 (2007) 341.
  3. D. Wang, A.J. Gmitter, D.R. Sadoway, Production of oxygen gas and liquid metal by electrochemical decomposition of molten iron oxide, Journal of the Electrochemical Society, 158 (2011) 51.
  4. D. Inman, J.C. Legey, R. Spencer, A chronopotentiometric study of iron in LiCl-KCl, Journal of Applied Electrochemistry 8 (1978) 269.
  5. Y. Castrillejo, A.M. Martínez, M. Vega, P. Sanchez Batanero, Electrochemical reduction of Fe(II) ions on different solid electrodes in fused ZnCl2-2NaCl mixture, Journal of Applied Electrochemistry  26 (1996) 1279.
  6. A. Lugovskoy, M. Zinigrad, D. Aurbach, Z. Unger, Electrodeposition of iron(II) on platinum in chloride melts at 700–750°C, Electrochimica Acta 54 (2009) 1904.