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. 2020 Dec 30;27(12):1572–1587. doi: 10.1007/s12613-020-2202-1

Interactions of molten salts with cathode products in the FFC Cambridge Process

George Z Chen 1,2,✉
PMCID: PMC7772062

Abstract

Molten salts play multiple important roles in the electrolysis of solid metal compounds, particularly oxides and sulfides, for the extraction of metals or alloys. Some of these roles are positive in assisting the extraction of metals, such as dissolving the oxide or sulfide anions, and transporting them to the anode for discharging, and offering the high temperature to lower the kinetic barrier to break the metal-oxygen or metal-sulfur bond. However, molten salts also have unfavorable effects, including electronic conductivity and significant capability of dissolving oxygen and carbon dioxide gases. In addition, although molten salts are relatively simple in terms of composition, physical properties, and decomposition reactions at inert electrodes, in comparison with aqueous electrolytes, the high temperatures of molten salts may promote unwanted electrode-electrolyte interactions. This article reviews briefly and selectively the research and development of the Fray-Farthing-Chen (FFC) Cambridge Process in the past two decades, focusing on observations, understanding, and solutions of various interactions between molten salts and cathodes at different reduction states, including perovskitization, non-wetting of molten salts on pure metals, carbon contamination of products, formation of oxychlorides and calcium intermetallic compounds, and oxygen transfer from the air to the cathode product mediated by oxide anions in the molten salt.

Keywords: FFC Cambridge Process, molten salts, electrolysis, extraction, oxides, sulfides, metals, alloys, reaction mechanisms

Acknowledgements

This work was financially supported by the Darwin College Cambridge (Schlumberger Interdisciplinary Research Fellowship, 2000–2003), the Engineering and Physical Science Research Council of the UK (Nos. GR/J57650/02, GR/L08731/01, GR/S58447/01, EP/J000582/1, and EP/F026412/1), the Ministry of Education of China (2000–2003), the Natural Science Foundation of China (2002–2006), ZhejiangProvincial People’s Government, China(2015–2019), and 3315 Talents Program from Ningbo Municipal People’s Government, China (No. 2014A35001-1).

I would like to thank the editors of IJMMM for the invitation and patience in waiting for this manuscript, which has been written at a rather slow pace in the Covid-19 pandemic period following the UK policy of working from home. I fully appreciate the effort of the journal’s language editor for proof reading and style-conversion of some original texts in the manuscript, in line with the journal’s publishing tradition. I am sincerely grateful to my wife and children. Without their continuous understanding, support, and encouragement, pursuing my career in the research and development of the FFC Cambridge Process in the past two decades would have not been possible, particularly in the completion of this article in a locked down, uncertain, and depressing environment. I must express my great appreciation for the invaluable contribution from my past and present co-authors (whose names appear in the list of References) to the advancement of our understanding of the FFC Cambridge Process and of the relevant laboratory skills and equipment.

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