Direct electrochemical conversion of metal oxides to metal by molten salt electrolysis: a review

Abstract

Little over a decade ago, Professor Derek Fray's group at the University of Cambridge, UK, discovered that a solid metal oxide can be directly reduced to metal by cathodically polarising it in a molten salt electrolytic cell. The simple electrochemical process attracted worldwide attention and significant efforts have been made since then to study and develop the process for production of many metals/alloys from their oxides. The process, with necessary modifications, is being studied and adapted as a head-end step in the pyrochemical reprocessing of spent oxide nuclear fuels. This review discusses the solid-state electro-reduction process, its development and the present status in both public and nuclear domains.

Difference in the Mechanism of Electrochemical Deoxidation of Conducting and Non-conducting Solid Oxide Preforms: An Experimental Demonstration with TiO2 and SiO2 Pellet Electrodes in CaCl2 Melt

“…A solid metal part will be in close physical contact with the oxide preform through which the electrons from an external DC power source will be supplied to it. The thermodynamic stability and electrical characteristics of an oxide electrode are known to have strong influence on its electro-reduction behaviour [3,5,6] in addition to many other parameters such as applied voltage, duration of electrolysis, sintering temperature of the oxide performs etc. [3,7,8] .…”

“…The thermodynamic stability and electrical characteristics of an oxide electrode are known to have strong influence on its electro-reduction behaviour [3,5,6] in addition to many other parameters such as applied voltage, duration of electrolysis, sintering temperature of the oxide performs etc. [3,7,8] . Several studies have been reported on the electrochemical reduction of oxides such as TiO 2 [1,3,5,[8][9][10][11] , Nb 2 O 5 [7,12,13] , UO 2 [14][15][16] , SiO 2 [17][18][19][20][21][22][23][24][25][26] etc.…”

“…are of interest to conventional metallurgical industries for the production of metals. In this context, the direct oxide electrochemical reduction method, called the FFC Cambridge process [2,3] , is of interest.…”

“…Direct electrochemical reduction of oxides in the solid state to corresponding metals or elements using molten salts as the electrolyte medium is a recent development in electrometallurgy and significant R&D work has been reported in this field of study [1][2][3] . Conventionally, the metal production technologies are based on either chemical methods (e.g., metallothermic, carbothermic reduction) or electrochemical methods (in which the metal is produced cathodically from an electrolyte solution containing the metal in dissolved form, e.g., Hall-Heroults' process for the production of aluminium) [4] .…”

“…In FFC Cambridge process [2,3] , the electro-deoxidation of the oxide is carried out by configuring it as the cathode against graphite counter electrode in a cell in which molten CaCl 2 at ~1173 K is generally employed as the electrolyte. The solid oxide preform will be in physical contact with a metal part, which acts as the conduit for electrons between the external power supply and the oxide electrode.…”