Sorption of Yb(III) from aqueous solution on Na-clinoptilolite

Abstract

The sorptive properties of the Na-modified Transcarpathian clinoptilolite towards Yb(III) under dynamic conditions were investigated. The sorption capacity of the Na-form of Transcarpathian clinoptilolite towards Yb(III) significantly depends on the concentration of ytterbium salt, the pH of solution and the temperature of the preliminary calcination of the sorbent. The buffer solution has been used to maintain the constant value of pH, ioniс strength of the solutions and to improve the metrological characteristics of preconcentration methods of Yb. The trace amounts of Yb(III) most effectively are sorbed with borate buffer solution. The final concentration of the borate buffer in the sample solution is 4·10 - 4 М. The sorption capacity of Na-clinoptilolite under optimal conditions (diameter of zeolite grains was 0.20–0.31 mm; flow rate of ytterbium(III) solution with concentration 1.0 µg/mL through sorbent was 5 mL/min; temperature of preliminary thermal treatment ~ 50 ºC and pH 9.5) was 8.1 mg ytterbium per 1 g of Na-modified clinoptilolite. The sorption of Yb(III) is carried out mainly by means of the adsorption of soluble hydrolyzed forms of Yb(III) on the zeolite surface. The influence of the most common water ions on the preconcentration of Yb(III) on the Na-form of Transcarpathian clinoptilolite has been established. The solutions of 1 M KCl acidified by a hydrochloric acid to pH 4.0 are the most effective desorbents of ytterbium(III) ions from Na-clinoptilolite. It provides a 99 % withdrawal of Yb from the zeolite matrix. The method for ytterbium trace amounts preconcentration from aqueous solutions in a solid phase extraction mode with a further determination of this rare earth element by a spectrophotometric method was developed. Keywords: sorption, solid phase extraction, ytterbium, Na-clinoptilolite.