Liquid-liquid extraction of rare earth elements (total) using 2,3-dihydroxy-naphthalene as an extractant and its applications to the determination of REEs (total) in rock, soil and sediment samples by spectrophotometry

Chemistry Laboratory, Regional Center for Exploration and Research, Atomic Minerals Directorate, Eastern Region, AMD Complex, Khasmahal, Jamshedpur-831 002, Jharkhand, India

E-mail : ptarafder@sify.com

National Metallurgical Laboratory, Burmamines, Jamshedpur-831 007, Jharkhand, India

A simple and rapid separation procedure for the determination of total rare earth elements (lanthanides) including yttrium in geological samples such as rock, soil and sediments has been developed. Lanthanides form 1 : 3 complex with O-O' type hi-dentate ligand, 2,3-dihydroxynaphthalene (2,3-H₂ND) and are extracted in the ethyl acetate from aqueous solution at pH >8. Lanthanides from (lrganic phase are quantitatively and selectively stripped off at pH 6.3 ± 0.2 followed by its spectrophotometric determination using arsenazo-III.

The effects of different experimental parameters such as pH of aqueous solution, concentration of 2,3-H₂ND, electrolytes, equilibrium time, stripping agents, diverse ions etc. on the quantitative recoveries of lanthanides were studied in detail. The percentage recovery was checked by analyzing lanthanides in synthetic mixtures and it was found that more than 98% recovery of lanthanides was obtained by this method. The accuracy of the method was ascertained by analyzing some Certified Reference Materials (CRM) like syenite sample (SY/3) and gabro sample (MRG-1). The lanthanide values obtained for the CRMs were in excellent agreement with the recommended values, indicating that the method yields fairly accurate and the reproducible results as characterized by a relative standard deviation (RSD) of 1 to 5% (n = 4). The method was successfully applied to silicate rock, soil and sediment samples.