Abstract
A combination of pyrometallurgical and hydrometallurgical processes showed promising results for the sustainable valorisation of red mud with selective iron recovery. However; high Si content in red mud and its slags produced by pyrometallurgical treatment for the Fe removal makes these secondary resources untreatable with conventional acid leaching routes due to the formation of silica gel. In this study, red mud and slags synthesized by electric arc furnace smelting, which contain both moderate and extensive SiO2, were exposed to dry digestion aiming selective Sc recovery with suppressed Ti and Si dissolution. Various additions of concentrated sulfuric acid were investigated to find out the optimum acid consumption for this process. A promising Sc leaching efficiency was found for acidic slag (~80%), where Ti dissolution was suppressed to <10% and without Si gel formation. The mineralogical content of red mud and the two slags were analysed by QEMSCAN and XRD in order to elucidate the leaching mechanism. Using the findings of this study, an empirical dry digestion leaching model was proposed for each starting material in a comparative manner.
Highlights
Scandium (Sc), which is considered as one of the most promising candidates for future transportation and energy industry owing to its unique behaviours in both light weight alloys and Zr based solid oxide fuel cells, is an expensive metal due to inadequate primary sources, complex extraction and production routes (Marquis and Seidman, 2001; Røyset and Ryum, 2005; Yamamoto, 2000)
It is possible to smelt red mud via Electric Arc Furnace (EAF) by recovering pig iron wih 95% efficiency and yield in a slag enriched in terms of Sc, Ti and REE, whose crystallinity and chemistry can be controlled by fluxing agents and cooling rates
Hematite is the most dominant phase of red mud accompanied by goethite, boehmite, diaspore, gibbsite and other silicates and via depletion of iron this was replaced by Ca, Al, Si mixed oxides in both slags
Summary
Scandium (Sc), which is considered as one of the most promising candidates for future transportation and energy industry owing to its unique behaviours in both light weight alloys and Zr based solid oxide fuel cells, is an expensive metal due to inadequate primary sources, complex extraction and production routes (Marquis and Seidman, 2001; Røyset and Ryum, 2005; Yamamoto, 2000). Electric arc furnace (EAF) treated slags with depleted Fe content are enriched in terms of SiO2 content, especially for the cases where SiO2 is used as flux during pyrometallurgical treatment This causes significant processing difficulties for the direct acidic leaching which would magnify the common Si-gelation problem (Queneau and Berthold, 1986)
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