Abstract
The disposal of voluminous, highly alkaline, bauxite residue (BR), the industrial by-product of alumina production by the Bayer process, constitutes an intricate global environmental problem. BR, containing valuable metals such as rare-earth elements (REEs)—in particular, scandium (Sc)—can be used as a secondary source for REE extraction. The scope of this study was the investigation of bioleaching as an innovative and environmentally friendly approach for the extraction of Sc from BR. The bioleaching parameters were studied on Greek BR and experiments were performed using different microbial cultures and solid to liquid ratios (S/L). The maximum extraction of Sc was 42% using Acetobacter tropicalis in a one-step bioleaching process at 1% S/L. The main organic acids produced were acetic, oxalic, and citric. The bioleaching data indicated a probable synergistic effect of the different organic acids produced by microorganisms along with a more targeted leaching mechanism.
Highlights
Bauxite residue (BR), called red mud, is a highly alkaline waste by-product generated from the Bayer process for alumina production
As far as the rare earth elements (REEs) concentrations are concerned, it has been found that the Greek bauxite residue (BR) is enriched by a factor of 2 compared with the original bauxite, reaching 1 kg/ton
The number of bacterial cells during bacterial growth of Acetobacter tropicalis was counted by a standard plate count (SPC) method
Summary
Bauxite residue (BR), called red mud, is a highly alkaline waste by-product generated from the Bayer process for alumina production. The disposal of BR constitutes a global environmental concern, as it is considered a hazardous material due to its alkalinity and volume. A huge quantity equaling 120 million tons (Mtpa) is generated annually and more than 3.5 billion tons have already been stockpiled in storage areas [1]. BR consists mainly of ferrous minerals, aluminum oxides, silicon, titanium, calcium, and sodium compounds [2]. Its composition varies and depends on the bauxite origin and the Bayer and sintering process parameters. As far as the rare earth elements (REEs) concentrations are concerned, it has been found that the Greek BR is enriched by a factor of 2 compared with the original bauxite, reaching 1 kg/ton.
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