Assignment #03 Introduction
Red mud is a solid residue from processing bauxite ore into alumina. Red mud often comprises 20–40% by weight iron(III) oxide (Wang et al., 2019). Red mud is classified as hazardous waste because it contains heavy metals, and radioactive materials, and is highly alkaline. Red mud has been reused for a variety of purposes, including the production of building materials, raw materials for iron manufacturing plants, mixed materials for road construction, and reprocessing to extract major components such as Fe, Al, and Ti or minor components such as rare earth elements (Onghena et al., 2017).
The mineral content of red mud is hematite (Fe2O3), goethite (FeO(OH)), gibbsite (Al(OH)3), quartz (SiO2), and zeolite (Wang et al., 2019). The REE content in red mud is relatively high so it has the potential to be a secondary source of REE, especially scandium (Sc) with a content of around 60–160 g/t (Deng et al., 2017). Scandium and its compounds are widely applied in several high technologies such as aluminium alloys for aircraft bodies (Ahmad, 2003), dopants in lithium manganese oxide (LMO) battery cathodes (Borra et al., 2016), and as an alternative solid electrolyte in solid oxide fuel cells (SOFC) (Meng et al., 2020).
Scandium may be extracted from red mud using both direct leaching with acid or base reagents and melt-leaching. However, scandium extraction has low selectivity since Sc dissolution is followed by significant amounts of Fe, Al, and Ti. Sc extraction tests from red mud can also be done using the sulfation-roasting-water leaching technique. The sulfatization-roasting-leaching process produced high Sc extraction selectivity for Fe, Al, and Ti. Using the H2SO4 reagent for sulfurization resulted in the extraction of 60% Sc, less than 1% Fe and Ti, less than 20% Al, and no dissolved Si (Borra et al., 2016).
Roasting at a 1 ml/g H2SO4/red mud ratio resulted in an extraction percentage of 60% Sc, 0% Fe and Ti, 7% Al, and 3% Si (Liu et al., 2017). According to Meng et al. (2020), adding ammonium sulfate to red mud at a 1:1 ratio (g/g) results in a greater Sc extraction percentage of up to 90%.
The complex deportment of scandium complicates its separation and purification from other components within red mud. Scandium may form strong associations with specific minerals or be dispersed within the solution phase, posing challenges for efficient recovery and separation. This study intends to provide insights into the extraction and refining of scandium from red mud, with an emphasis on the complexity of scandium deportment. By explaining the obstacles and potential solutions to scandium deportment, we hope to contribute to the development of sustainable and economically feasible methods for extracting scandium from red mud resources.
