Cation-exchange separation of thorium(zirconuim), scandium(uranium) and rare earth with arsenazo m as the eluant

Abstract

Strong inorganic acids [1,2] and organic complexing agents [3,4] have been usually used as eluants for cation-exchange separation of U(VI), Th, Zr, Sc and RE. However, the elution volume of strong inorganic acid is large, the organic complexing agents always interfere the determination of metals in the effluent. In this paper Arsenazo M has been developed as an eluant, the effluent may be used for direct spectrophotometric determination. The simple and rapid methods for cation-exchange and direct spectrophotometric determination of Zr/Sc/RE, Zr/U/RE, Th/Sc/RE mixture have been proposed. ▪ The ion exchange behaviour of U, Th, Zr, Y, La, Gd and Lu on the strong acidic cation exchange resin in Arsenazo M in various media (aqueous, acetic acidsodium acetate and hydrochloric acidsodium acetate buffer solution) has been investigated by equilibrium. The adsorption coefficients of the above metals have been measured. From the experimental results the acetic acidsodium acetate buffer solution is favourable for the metals (Fig. 1). The mechanism of the effects of the media has been studied, with La as a representation, because the media greatly affect the adsorption coefficients of the metals. When the Arsenazo M solution contains some single bonded ligands such as Ac −, we found that the shape and peak place of the absorption spectra of the complexes formed with La change distinctly (as shown in Fig. 2). It is clear that Lanthamum has formed a ternary complex, acetatemetal ion-Arsenazo M. Thus the adsorption coefficients of La are much smaller in the Arsenazo M solution containing Ac − medium. The results for the other elements (Th, Sc, etc.) are similiar to La. ▪ t001 TABLE I. Results for Separation of Determination of Mixtures. Mixtures Rations of metals Taken (μg) Found (μg) Recovery (%) ZrScRE 1000:1:1 Zr 2000 1967 98 Sc 2.0 2.1 105 RE 2.0 1.9 95 2:1:60 Zr 10 10.3 103 Sc 5.0 5.0 100 RE 300 290 97 ZrURE 500:5:1 Zr 1000 1000 100 U 10 9.8 98 RE 2.0 2.2 110 5:200:1 Zr 10 9.7 97 U 400 406 102 RE 2.0 2.0 100 ThScRE 40:4:1 Th 200 188 94 Sc 20 19 95 RE 5.0 5.0 100 1:3:10 Th 10 10 100 Sc 30 31 103 RE 100 95 95 ThRE 2000:1 Th 4000 3900 98 RE 2.0 2.2 110 1:100 Th 5.0 5.1 102 RE 500 500 100 URE 2000:1 U 4000 4100 102 RE 2.0 1.9 95 1:100 U 10 10 100 RE 1000 935 94 ScRE 2000:1 Sc 4000 4125 103 RE 2.0 2.1 105 1:500 Sc 2.0 2.0 100 RE 1000 975 98 ▪ According to the experimental results the complete separation of the ternary mixtures may be achieved by a column (0.8 cm × 10 cm). The flow rate was 0.5–1.0 ml/min. The elution was carried out at room temperature. Procedure of column separation: Solution of mixture of Zr/Sc(U)/RE (or Th/Sc/RE) added to the column. Elution was carried out with Arsenazo M in the different media and pH. Elution curves for these mixture are given in Fig. 3 and 4. The metals were directly determined by spectrophotometry. The spectrophotometric determination of each element is presented in the literature [5]. The results of percentage recovery are shown in Table I. The method was applied to the analysis of Th (0.017–0.17%) Sc (0.005–0.13%), and RE (0.6–2.9%) in ore samples with satisfactory results.