SELECTIVE SEPARATION AND DETERMINATION OF SCANDIUM FROM YTTRIUM AND LANTHANIDES IN RED MUD BY A COMBINED ION EXCHANGE/SOLVENT EXTRACTION METHOD

Scandium, existing in economically interesting concentrations, in red mud, the byproduct of the alumina production, could be selectively separated from the main and minor elements, as well as from yttrium and the lanthanides by the development of a combined ion exchange-solvent extraction method. After a suitable borate/carbonate fusion of red mud, the sample solution was passed through the ion exchanger Dowex 50W-X8 and the main elements, such as Fe, Al, Ca, Si, Ti, Na as well as the minor ones Ni, Mn, Cr, V were removed by elution with 1.75 M HCl. Sc, Y and the lanthanides were quantitatively obtained by a subsequent elution with 6 M HCl. Using as extractant di(2-ethylhexyl)phosphoric acid in hexane, scandium could be selectively and nearly quantitatively extracted in the organic phase, while yttrium and the lanthanides remained in the aqueous phase. By suitable backstripping of the organic phase, scandium was finely quantitatively recovered in high purity in the aqueous phase. Experimental conditions, including the pH of the extracted solutions, the ratio of aqueous to organic phase and the contact time were investigated in order to achieve high distribution ratios and a selective extraction. In this way all spectral interferences for the inductively coupled plasma atomic emission spectrometric determination of scandium were eliminated and a very low detection limit in the ng/g range was achieved, allowing the determination of very low levels of scandium in complex matrices. The validity of the described process was tested on the bauxitic reference material BX-N from ANRT (Association Nationale de la Recherche Technique, France) and the procedure was applied on red mud samples coming from the Creek alumina production.