Recovery of scandium from sulfation-roasted leachates of bauxite residue by solvent extraction with the ionic liquid betainium bis(trifluoromethylsulfonyl)imide

Abstract

Bauxite residue (red mud) is a waste product of the alumina refining in the Bayer process and contains significant concentrations of critical metals, including scandium. Greek bauxite residue contains exploitable levels of scandium and is thus considered a suitable source for its production. A process was developed to recover scandium from Greek bauxite residue using a combination of sulfation-roasting-leaching and solvent extraction with the hydrophobic ionic liquid betainium bis(trifluoromethylsulfonyl)imide, [Hbet][Tf2N]. Sulfation-roasting-leaching was the preferred leaching technique to dissolve scandium from bauxite residue because of the low acid consumption, good selectivity towards scandium and low co-dissolution of the major elements. The scandium concentration in the leachate was increased by applying multistage leaching, during which the obtained leachate is contacted multiple times with freshly roasted material. In a next step, scandium was selectively extracted from the obtained leachate with [Hbet][Tf2N]. To improve the separation between scandium and iron, Fe(III) was reduced to Fe(II) by addition of ascorbic acid to the sulfate leachate prior to extraction. The phase ratio and pH of the extraction were optimized to achieve high extraction and the concentration of scandium in the ionic liquid phase. Co-extracted metal ions were scrubbed from the loaded ionic liquid phase by HCl and the purified scandium was removed by stripping with H2SO4. Scandium was recovered from the strip solution by precipitation together with sodium. Finally, the entire process was performed on lab scale as a proof-of-principle.

Effect of Aqueous Media on the Recovery of Scandium by Selective Precipitation

“…Previously, complete or partial recovery of Sc from bauxite residues was reported to be achieved mainly by solvent extraction, ion exchange, or the combination of these two techniques, as a result of its low concentration in the leachates [14][15][16][17][18][19][20]. Zhang et al recovered 91% of Sc from bauxite residue leachates by inorganic metal(IV)-phosphate ion exchangers, although Fe(III) was found to be an interfering ion in this process [20].…”

Extraction of scandium(III) from acidic solutions using organo-phosphoric acid reagents: A comparative study

“…On the other hand, the presence of considerable amount of Sc in Mg-Sc and Al-Sc scrap lured the metallurgists for its economic value [4]. Therefore, recycling of this industrial waste by recovering the valuable metals such as scandium and gallium while removing other toxic metal impurities through suitable process technology resulting zero waste would resolve environment issues [7][8][9][10]. It is often a challenging task for the researchers to produce pure scandium metal from low grade ores, secondary or red mud with an overall Sc concentration of ~100 g/t along with other impurities [6][7][8].…”

“…Ample amount work has been devoted by the researchers over the last few decades, on purification of leach liquor to separate scandium [7][8][9][10][11]. The liquid-liquid extraction (solvent extraction), ion exchange (IX), liquid membrane, adsorption, precipitation and co-precipitation are being applied to purify the leach liquors.…”

Selective Sc Recovery from Rare Earths in Nitric Acid Medium by Extraction Chromatography

“…Wide variety of compounds containing scandium (Sc) are recently attracted for various applications such as catalyst 1,2) , alloys 3,4) , lamp of laser 5) and etc. Rare earth elements (REs) involving 15 lanthanides, yttrium and Sc are chemically similar, technologies of scandium have been carried out [6][7][8][9] . However, an efficient process with releasing small amount of secondary wastes is desirable for practical operation.…”