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

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.

References:

 

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