Extractive separation of rare earth elements and their determination by inductively coupled plasma optical emission spectrometry in geological samples
A simple, rapid and effective solvent extraction separation of rare earth elements (REEs) has been developed for their determination in geological samples such as rock, soil and core samples by inductively coupled plasma optical emission spectrometry (ICP-OES). Rare earth elements forms neutral complexes with bi-dentate ligand, 2,3-dihydroxynaphthalene (2,3-H2ND), which are extracted into ethyl acetate at the alkaline pH 9-10. All these elements are then quantitatively stripped off into aqueous phase using dilute hydrochloric acid and then determined by ICP-OES. The effects of different variables such as pH of the solution, reagent concentration, solvent, stripping solution, diverse ions etc. affecting the simultaneous quantitative extraction of lanthanides followed by their determination using ICP-OES have been studied in detail. The method has been validated by analyzing a set of certified reference materials of rock and soil samples such as SY-2, SY-3, GSP-2 and SO-2 respectively. The results obtained by the proposed method for a set of silicate rock and core samples are compared by other standard separation technique such as oxalate co-precipitation using calcium as a carrier. The precision (as % RSD) of the proposed method varied over the range of 1 to 10 % depending on the concentration of the lanthanides. The developed method involving simultaneous separation and determination of individual lanthanides by ICP-OES is an improved method of the existing method, where only total lanthanide was determined colorimetrically using arsenazo-III and do not required any counter cation. The proposed method is comparatively more environment friendly.