Preconcentration and ICP-OES determination of rare earth elements using silicas chemically modified with aminophosphonic groups in fossil raw materials

Silica-based adsorbents (Silica gel 60 and Silochrom S-80) chemically modified with aminophosphonic groups with various surface concentrations have been proposed for the preconcentration of rare earth elements (REE). The resulting adsorbents were studied by FT-IR, SEM, TGA and compared with unmodified matrices. Adsorbents quantitatively extracted REE from solutions with pH 1.0–5.0. Solid phase extraction at pH 1.0–2.0 made it possible to quantitatively separate rare earth elements from the predominant amounts of accompanying metal ions. An increase in the concentration of aminophosphonic groups on the silica surface led to an increase in the adsorption capacity of the adsorbent for Gd(III) both in batch and dynamic modes. A technique for solid-phase extraction followed by inductively coupled plasma optical emission (SPE-ICP-OES) determination of REE has been developed; it includes pumping 200 mL of the sample solution (pH 1) through a mini-column with an adsorbent at a flow rate of 1 mL min−1, eluting REE with 10 mL of 1 M HNO3 (preconcentration factor 20), and then determination of the elements in the eluate by ICP-OES. The technique was used for the determination of REE in lignite and coal from the Krasnoyarsk Krai (Russia). The accuracy of the results was confirmed by comparison with ICP-MS determination and by the analysis of certified reference material of coal ash.