Determination of scandium in geological materials, rare earth minerals andniobate/tantalate-type of samples by inductively coupled plasma atomic emission spectrometry after solvent extraction acid hydrolysis separation

Solvent extraction of scandium from 1.5 M HCl medium using di(2-ethyl hexyl ) phosphoric acid in hexane or benzene selectively separates Sc from the ac companying elements in rare-earth minerals (like monazite, xenotime, gadoli nite) and also in geological materials. Acid hydrolysis separation of Nb/Ta -type samples separates Sc from the major matrix elements and the remaining elements do not influence the Sc signal in inductively coupled plasma atom ic emission spectrometry or flame atomic absorption spectrometry. To avoid the matrix effect due to sodium that accompanies the analyte using the repo rted backstripping of Sc from the organic extract by 2M NaOH, the organic e xtract was evaporated off leaving the Sc in the residue which in turn was t reated with a mixture of HNO3-HClO4, dissolved in HCl (10%, v/v) and made u p to a known volume before aspiration in the plasma for estimation. The sil ica-rich geological materials were dissolved by HF-HCl-H2SO4 treatment and the rare-earth minerals (monazite/xenotime) were digested by H2SO4-HCl foll owed by dissolution in 1.5 M HCl before applying the solvent extraction pro cedure. In Nb/Ta-type of samples, Sc was separated from Nb and Ta by acid h ydrolysis, involving fusion with Na2O2, dissolution in HCl followed by NH3 precipitation and hydrolysis in HCl. The oxychloride precipitates of Nb and Ta are filtered off and the filtrates assayed for Sc. The proposed methods have been applied to some international geological reference standards (SY -2, SY-3, MRG-1, Mica-Fe, G-2, CH and ASK-2), rare-earth minerals like mona zite, xenotime and gadolinite and also to some Nb/Ta-type samples including reference standards IGS-33 and IGS-34, and the results are compared. Both methods are simple, rapid and accurate, showing a relative standard deviati on of less than 1% at the 55 mu g g(-1) level and 9.0% (at the 1.0 mu g g(- 1)). (C) 1998 Elsevier Science B.V. All rights reserved.