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 sep arated from the main and minor elements, as well as from yttrium and t he lanthanides by the development of a combined ion exchange-solvent e xtraction 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 elu tion with 6 M HCl. Using as extractant di(2-ethylhexyl)phosphoric acid in hexane, scandium could be selectively and nearly quantitatively ex tracted in the organic phase, while yttrium and the lanthanides remain ed in the aqueous phase. By suitable backstripping of the organic phas e, scandium was finely quantitatively recovered in high purity in the aqueous phase. Experimental conditions, including the pH of the extrac ted solutions, the ratio of aqueous to organic phase and the contact t ime were investigated in order to achieve high distribution ratios and a selective extraction. In this way all spectral interferences for th e inductively coupled plasma atomic emission spectrometric determinati on of scandium were eliminated and a very low detection limit in the n g/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 (Associa tion Nationale de la Recherche Technique, France) and the procedure wa s applied on red mud samples coming from the Creek alumina production.