Abstract
Sustainable utilization of Bauxite Residue (BR) is currently one of the greatest challenges being tackled by the alumina industry, due to its high production rates and limited reuse options. The present work is concerned with the use of BR as a candidate metallurgical raw material for iron (Fe) production and aluminum (Al) extraction. In more detail, at first, BR undergoes reductive smelting to extract its Fe content and produce a slag of mainly calcium aluminate composition. In a second step, Al contained in the calcium aluminate phases is extracted hydrometallurgically by leaching with a Na2CO3 aqueous solution. The focus of the current study is the optimization of this leaching process, and it was performed in two stages. The first was a laboratory scale investigation on the main parameters affecting the extraction rate of Al. The second stage was performed in pilot scale and incorporated observations and suggestions based on the laboratory scale investigation. Laboratory work showed that more than 50% of aluminum could be easily extracted in less than 1 h, in 5% S/L, at 70 °C and with an 20% excess of Na2CO3. Pilot scale work, by successfully applying the suggestions derived from laboratory scale work, achieved an average Al extraction of 68% from a 10% S/L pulp, with a slag of optimized composition in relation to the one used in the laboratory scale.
Highlights
Bauxite Residue (BR) is the term used to describe the solid residue produced from the alkaline digestion of bauxite in the Bayer Process for the production of aluminum oxide
The total extraction rate for any test is the sum of the extraction rates in the aluminate and the washing solution
On the other hand, based on the uniformity of the extraction rates in the washing solutions and due to the design of the Hydro-pilot facilities of MYTILINEOS, where these two streams would not be intermixed, focus will be placed on the results of the aluminate solution stream, which is of the main interest
Summary
Bauxite Residue (BR) is the term used to describe the solid residue produced from the alkaline digestion of bauxite in the Bayer Process for the production of aluminum oxide (alumina, Al2O3). BR is produced in large amounts in alumina refineries: about 0.9–1.5 tons of BR per ton of Al2O3, depending on bauxite quality and plant operating conditions. This by-product is currently one of the greatest sustainability challenges faced by the alumina industry [1]. Global production of alumina was estimated at 134 million metric tons for 2020, the majority of which was produced by Bayer plants [4]. On the road to sustainability and a zero-waste production process, the alumina industry is orienting its efforts on possible utilization processes for BR, among which are processes for the extraction of metal values from BR
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