Towards the Utilization of Fly Ash as a Feedstock for Smelter Grade Alumina Production: A Review of the Developments

The major commercial technology for the production of smelter grade alumina has conventionally been the Bayer process which converts bauxite ore, an aluminum containing ore which typically contains about 50 % Al2O3, into smelter grade alumina that contains over 99.0 % Al2O3. Another potential source of aluminum that is receiving renewed attention is coal fly ash (CFA), which is a by-product of coal combustion during electricity generation in power stations. Most coal fly ash found around the world contain typically between 25 and 35 % Al2O3, which is substantial to make CFA a potential alternative source of alumina. There has been some considerable research effort, in the last two decades, aimed at extracting aluminum from this semi-waste product. Much emphasis from the different workers has been on the leaching of the contained aluminum, while the purification and recovery of alumina from the liquor solution has received less attention. Notwithstanding that several patents on the processes to recover alumina from CFA exist, limited commercialisation of the processes has been reported. This paper seeks to review and discuss the hydrometallurgical extraction processes that have been formulated and tested by different workers and then assesses the available opportunities and the way forward on the prospects of commercially extracting alumina and other valuable components from this abundant resource.