Recent trends in alumina and aluminium production technology

Abstract

For well over a century the Bayer process for the production of alumina from bauxite and the Hall-Heroult process involving the electrolysis of alumina dissolved in cryolite to produce aluminium have been commercially exploited. However, significant advances based on intense research and development activities in the last five decades have led to considerable improvements in operating parameters and productivity, efficient disposal and utilization of wastes. This review presents the developments that have taken place in technology, equipment and treatment of wastes in both the alumina and aluminium production processes. Technology and equipment developments in the field of alumina are concerned with usage of different qualities of bauxite, improvement in extraction efficiency of alumina from bauxite, obtaining better yield during precipitation, enhancing scale of operation and minimizing soda losses in the process. Improvements in electrolysis involve utilization of modified electrolytic baths, controlled feeding of alumina, better design of cell based on mathematical modelling of magnetic field and heat distribution and optimization of the performance of electrodes on the basis of good understanding of physical, mechanical and electrical properties. Information on the present situation in the Indian plants is also presented. Proper treatment and disposal of wastes generated in alumina and aluminium production are of great importance as they contain significant amounts of sodium hydroxide, fluorides, sulphur dioxide, oxides of carbon and cyanide. Some attempts made to utilize the waste material are briefly summarized.