Reprocessing of Aluminum Production Residues by Roasting and Magnetic Separation

Abstract

Objective: The aim of this work was to contribute for the development of a strategy for the reprocessing of red mud and marginal bauxite for iron recovery by magnetic roasting. Theoretical Framework: Red mud and marginal bauxite contain a considerable amount of iron, but it is not possible to recover this iron content with conventional mineral concentration techniques. Magnetic roasting is a process applied to alter the magnetic properties of minerals, typically aimed at the conversion of weakly magnetic iron oxides, such as goethite and hematite, into magnetite, a strongly magnetic phase. After roasting, iron can be recovered by magnetic separation even at low field intensities. Method: To achieve the purpose of this work, marginal bauxite and red mud samples were prepared, characterized chemically and mineralogically, roasted in a rotary kiln at different temperatures and with or without the addition of coke or hydrogen as reducing agents; and subjected to magnetic separation. The products of the roasting pre-treatment were characterized in terms of mineralogical composition by X-ray powder diffraction to assess the phase changes that occurred. Results and Discussion: The results obtained revealed that magnetic roasting is a promising technique to recover iron from marginal bauxite and red mud. Although recoveries higher than 90% were achieved, the selectivity of magnetic separation was low, indicating that Al was also being recovered in the magnetic product. Further conditions may be investigated. Research Implications: Tons of red mud are disposed of in tailing dams, and tons of marginal bauxite are stored in ore piles. Both pose environmental risks that might be significantly reduced if a strategy for reprocessing these aluminum production residues is applied. Originality/Value: The relevance and value of this research are evidenced by the promising results achieved, that showed that it is possible to recover iron from red mud and marginal bauxite by combining roasting pre-treatment and magnetic separation.