Preconcentration of the cobalt using modified forms of the transcarpathian clinoptylolite

Abstract

The sorption properties of Na- and H-forms of Transcarpathian clinoptilolite towards trace amounts of Co(II) under dynamic conditions were studied. Acid modified samples of clinoptilolite were obtained by treating this zeolite with solutions of different concentrations of nitric, chloride and sulfuric acids. The most effective acid modifier was 0.5 M HNO 3 . The effect of solution pH and pre-treatment temperature of sorbent samples on the sorption capacity of Na- and H-forms of clinoptilolite was investigated. It is established that the highest sorption capacity both modified forms of clinoptilolite occurs from neutral solutions on the the uncalcined samples. The urotropin buffer solution was used to ensure constant value of pH and ionic strength of the solution. The optimal sorption conditions both modified forms of clinoptilolite are as follows: pH 7.0; the flow rate of a solution of Co(II) with a concentration of 0.25 µg·mL –1 through the sorbent – 5 mL·min –1 ; the diameter of the sorbent grains is 0.200–0.315 mm. The maximum sorption capacity of Na- and H-clinoptilolite towards Co(II) are 3.25 µg·g –1 and 2.85 µg·g –1 , respectively, which exceeds the value of the sorption capacity of the natural form of this zeolite 1.5 and 1.3 times. It has been found that the most effective desorbent of Co(II) from the Na-clinoptilolite are HNO 3 solutions, in particular, a 4.5 M HNO 3 solution, which provides 97 % withdrawal of Co(II) from zeolite. The effective desorbents of Co(II) from the H-clinoptilolite are acidic solutions of alkali metals salts. 1 M NaCl solution acidified with hydrochloric acid to pH 4.0 provides 100% withdrawal of Co (II) from acid-modified clinoptilolite. The effect of common water ions on the maximum sorption capacity of Na- and H-clinoptilolite was investigated. The permissible multiple contents (C ion /C Co(II) ) of the common water ions for Na- and H-clinoptilolite are higher 1.5–4 times then for the natural clinoptilolite. The ability of modified forms of Transcarpathian clinoptilolite to sorb trace amounts of Co(II), high sorption capacity and the presence of effective desorbents give a reason to offer these sorbents for purification of water from Co(II) ions, including radioactive isotopes 60 Co, and also for preconcentration of Co(II) ions at the stage of waters samples preparation for analysis. Methods of Co(II) trace amounts preconcentration in the solid phase mode with its further determination using the atomic absorption method are proposed. Keywords: sorption, solid phase extraction, cobalt, Na-clinoptilolite, H-clinoptilolite.