On the question of using solid electrodes in the electrolysis of cryolite-alumina melts. Part 1.

E S Gorlanov

doi:10.21285/1814-3520-2020-6-1324-1336

Abstract

This article is aimed at identifying issues associated with the use of solid cathodes in the electrolysis of cryolitealumina melts in order to determine conditions for their practical application. The contemporary technology of using solid anodes and cathodes is reviewed from its inception to the present time. The problems of stable electrolysis are discussed, such as effects of the electrode surface on the technological process. It is shown that all attempts undertaken over the recent 100 years to use solid electrodes, both reactive and inert, have been challenged with the emergence of electrolysis instability, formation of precipitates of varying intensity on the electrodes and impossibility of maintaining a prolonged process at current densities of above 0.4–0.5 A/cm2. Information is provided on the attempts to use purified electrolyte components with different ratios, metal-like and ceramic electrodes with a high purity and a smooth surface in order to approach real industrial conditions. However, to the best of our current knowledge, these experiments have not found commercial application. The authors believe that the most probable reason for the decreased current efficiency and passivation of solid electrodes consists in the chemical inhomogeneity and micro-defects of the bulk and surface structure of polycrystalline cathodes and anodes. It was the physical inhomogeneity of carbon electrodes that directed the development of the nascent electrolytic production of aluminium towards the use of electrolytic cells with a horizontal arrangement of electrodes and liquid aluminium as a cathode. This reason is assumed to limit the progress of electrolytic aluminium production based on the use of inert anodes and wettable cathodes in the designs of new generation electrolytic cells implying vertically arranged drained cathodes. The theoretical and experimental examination of this assumption will be presented in the following parts of the article.

Highlights

This article is aimed at identifying issues associated with the use of solid cathodes in the electrolysis of cry olite-alumina melts in order to determine conditions for their practical application
It can be assumed that the use of an electrolyte composition with a cryolite ratio of 0.5– 1.0 and a corresponding low solubility of aluminium oxide, an insufficient content of dissolved alumina in the melt made the electrolytic cell operate at limiting values of diffusion current densities
On the basis of the presented analysis of available publications, we attempted to establish a functional connection between various electrolysis parameters and the state of the electrode surface in the context of historical evolution of this research field

Summary

INTRODUCTION

Attempts to develop an approach to the elec- of cryolite-alumina melts using solid electrodes trolysis of cryolite-alumina melts using solid through the prism of contemporary knowledge electrodes have been ongoing since the incep- and achievements in the field. It can be assumed that the use of an electrolyte composition with a cryolite ratio of 0.5– 1.0 and a corresponding low solubility of aluminium oxide, an insufficient content of dissolved alumina in the melt made the electrolytic cell operate at limiting values of diffusion current densities. At Creil, Minet experimented with the electrolysis of cryolite-alumina melts containing sodium chloride, producing about 15–20 kg of aluminium per day [10] His process and industrial units differed from those proposed by Hall and Héroult only by the addition of NaCl to the electrolyte.

Process of electrolyzing fused salts of aluminium

CONCLUSION

Список литературы

INFORMATION ABOUT THE AUTHOR

Findings

СВЕДЕНИЯ ОБ АВТОРЕ