Preconcentration and determination of the Yb(III) using transcarpathian clinoptilolite

Abstract

The sorption properties of Transcarpathian clinoptilolite towards trace amounts of Yb(III) under dynamic conditions have been studied. It is shown that the most effective sorption of this REE occurs from low alkaline solution (pH 10.0). The buffer solution has been used to maintain the constant value of pH, which permits to improve metrological characteristics of the preconcentration methods of Yb. Moreover, in this case the constant ionic strength minimizes influence of other water components on the sorption process of Yb(III) ions. The trace amounts of Yb(III) are sorbed most effectively with borate buffer solution. The final concentration of the borate buffer in the sample solution is 2.1·10 –4 М. It is known that such rare elements as Nd(III), Ce(III), Eu(III) and Gd(III) practically are not sorbed on Transcarpathian clinoptilolite from the solutions at pH 11.0. The differences in the sorption mechanisms of these REE give an opportunity to selectively preconcentrate Yb(ІІІ) from the solutions (рН 11.0) containing Nd(III), Ce(III), Eu(III) and Gd(III). Ytterbium is sorbed with the best efficiency on the uncalcined clinoptilolite samples. The calculation of the distribution of different forms of Yb(III) in aqueous solutions depending on pH at various values of the total concentration has been carried out. The sorption capacity of clinoptilolite under optimal conditions (diameter grains of sorbent – 0.200–0.315 mm; pH 10.0; low rate of the solution of Yb(III) with the concentration of 0.5 μg·mL –1 through the sorbent – 5 mL·min –1 ) is 13.2 μg·g –1 . The influence of the most common water ions on the preconcentration of Yb(III) on Transcarpathian clinoptilolite has been established. The most effective desorbent of Yb(III) from the clinoptilolite is1 М solution of NaCl, acidified with hydrochloric acid to рH 2.5, which provides a 100 % withdrawal of Yb from the zeolite matrix. The solid-phase extraction procedure with natural Transcarpathian clinoptilolite has been proposed for the preconcentration of trace amounts of Yb(III) ions from aqueous solutions for a final spectrophotometric determination using arsenazo III. Keywords: sorption, ytterbium, solid phase extraction, clinoptilolite.