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

Abstract

Chemical compounds containing scandium (Sc) are widely applied to various fields such as catalysts, alloys, lamps and etc. Sc is found in mineral ore, and it is necessary to develop efficient Sc separation and recovery technology for the industrial applications. N,N,N’,N’,N’’,N’’-hexaoctylnitrilotriacetamide (HONTA) extractant has been shown to be promising for selective Sc extraction. In this study, applicability of the extraction chromatography technology using HONTA impregnated adsorbent for the selective Sc recovery from other rare earth elements (REs) was experimentally evaluated through batch-wise adsorption/elution studies and column separation experiments. Batch-wise experiments showed that distribution coefficient of Sc onto the HONTA/SiO2-P adsorbent was far larger than those of other REs at acidity region with 0.001 < [HNO3] < 4 mol dm -3 and that the adsorbed Sc was efficiently eluted into 1 M H2SO4 solution. Appropriate experimental conditions for the column separation experiment were proposed based on those results, and performance of the flow-sheet was examined for laboratory scale column system. Only Sc in 4 mol dm HNO3 solution was adsorbed into a packed column with the adsorbent while other REs were discharged from the column with the feed solution, and then loaded Sc was properly eluted into 1 M H2SO4 solution. Purity of the Sc product solution obtained by the column separation experiment depended on Sc recovery ratio, and about 99.9 % purity was achieved with 97 % recovery ratio. The residual Sc was eluted from the column with other REs and did not remain inside the column, therefore repeated used of the column was shown to be possible. This process was shown to be promising for selective Sc recovery from mixture of REs in nitric acid.