Determination of rare earth elements and yttrium in rocks by inductively coupled plasma atomic emission spectrometry after solvent extraction with a mixture of 2-ethylhexyl dihydrogenphosphate and bis(2-ethylhexyl) hydrogenphosphate

Abstract

The importance of rare earth elements in petrogenetic studies is well known. The inductively coupled plasma atomic emission spectrometry (ICP-AES) technique is mostly used for the determination of rare earth elements after its separation by the ion exchange method. An alternative, rapid, solvent extraction method involving a mixture of (2-ethylhexyl) dihydrogenphosphate and bis(2-ethylhexyl) hydrogenphosphate in kerosene suitable for the separation and preconcentration of REE in silicate rock is described. Major elements, such as Mg, Ca, Mn, Na and K, are not extracted appreciably from dilute hydrochloric acid solution. The extraction of the major fraction (>95%) of iron is prevented by its reduction with ascorbic acid. Titanium, Th, U and Zr are also extracted quantitatively and Al is extracted partially (∼6%). The REE are selectively stripped from the organic phase after the addition of tri-n-butyl phosphate with 4.5 mol dm ^–3 hydrochloric acid. Major fractions of co-extracted interfering elements (residual Fe, Th, U, Zr and Ti) remain in the organic phase. The aluminium is also stripped along with the REE; however, aluminium does not cause any interference in the determination of REE by ICP-AES. The method is applied for the preconcentration of REE in silicate rocks and its validity is checked by analyzing some Standard Reference Materials. The results are in good agreement with the recommended value. The method is simple, rapid, and suitable for the determination of REE in a silicate rock sample.