Abstract
Anticipated future demand and limited primary sources of Sc highlight the importance of secondary Sc resources such as bauxite residue (red mud). In this study, a process route starting from red mud aiming to recover Sc as a concentrate by a combination of pyrometallurgical and hydrometallurgical processes was developed. Bauxite residue was treated in an electric arc furnace (EAF) for Fe removal as well as slag conditioning with varying flux additions and various cooling conditions. 95% of iron recovery to the metal was achieved. Resulting slags were subjected to identical H2O2 supported H2SO4 leaching conditions at 75 °C. The effect of slag mineralogy and crystallinity on the leaching efficiencies were investigated using XRD and QEMSCAN analysis. As a result of the highly amorphous nature of acidic slags, maximum of 72% Sc leaching was obtained. For leached slags, water quenched basic slag was found to be the most promising condition resulting in an extreme Sc leaching yield of 97% and this slag was selected for the further Sc precipitation. High impurity removal rates and selective Sc separation were achieved with a triple-stage successive precipitation to synthesize a Sc concentrate. Starting from EAF treatment followed by leaching and precipitation, 85% of the initial Sc in the red mud was successfully recovered as Sc phosphate.
Highlights
Anticipated future demand and limited primary sources of Sc highlight the importance of secondary Sc resources such as bauxite residue
High alumina slags which are produced through direct smelting of red mud are highly viscous and this could lead to metal entrainment in the slag, additives during the smelting process are necessary[26,27]
A complete process route starting from red mud until Sc phosphate concentrate was investigated by means of pyrometallurgical and hydrometallurgical methods
Summary
Anticipated future demand and limited primary sources of Sc highlight the importance of secondary Sc resources such as bauxite residue (red mud). Different techniques based on hydrometallurgical processes for the Sc recovery had been studied before with low solid to liquid ratios (e.g. 1/50)[18,19] and pre-treatments such as microwave[20] to achieve higher leaching efficiencies. In these studies, by the help of extreme leaching conditions (high acid and energy consumption), substantial leaching efficiencies up to 70% of Sc were reported, with low selectivity over iron which is one of the main elements in bauxite residue. The proposed process is starting from red mud, recovering iron as pig iron and concentrating Sc in the resulting slag via smelting, followed by hydrometallurgical treatment of the separated slag ending up with a Sc enriched PLS and finalized by selective precipitation of the Sc concentrate
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