Determination of trace rare earth impurities in high-purity yttrium oxide by using ion-exchange separation and spectroscopic method

Abstract

Since the sensitivity of direct emission spectroscopic method is not enough to analize rare earth impurities in high-purity rare earth oxides, a separation and pre-concentration step is always required. In the present paper, a cation exchange spectroscopic method is described. α-Hydroxyisobutyric acid is used as an efficient eluant to separate La, Ce, Pr, Nd, ▪ ▪ Sam and Eu from matrix yttrium. The concentrate is then determined by using solution dry-residue method. The detection limits are located in the range of 0.008 to 0.03 ppm (for a concentration factor of 10 000), and the variation coefficients are from 12 to 15%. Ion-exchange Separation and Pre-concentration. α-Hydroxyisobutyric acid (α-HIBA) is and excellent eluent for the separation of Lanthanon [1]. Therefore, we selected α-HIBA as an eluent to separate La, Ce, Pr, Nd, Sm and Eu from matrix yttrium. In order to indicate the separation process, Eu (152, 154) t001 Sample Analysis Results Element Present μ/g Added μ/g Total μ/g Found μ/g Recovery % Average % La 2O 3 0.08 0.1 0.18 0.14 78 91 0.45 0.25 0.70 0.72 103 0.46 1.00 1.46 1.45 99 1.30 2.50 3.80 3.20 84 CeO 2 0.20 0.50 0.70 0.60 86 96 0.96 0.25 1.21 122 101 1.71 1.00 2.71 2.75 101 4.30 2.50 6.80 6.60 97 Pr 6O 11 0.05 0.40 0.40 0.36 90 94 0.20 0.25 0.45 0.42 93 1.30 1.00 2.30 2.30 100 3.25 1.50 4.75 4.40 94 Nd 2O 3 0.20 0.40 0.60 0.56 93 92 2.50 1.00 3.50 3.40 97 0.53 0.25 0.78 0.66 85 2.80 2.50 5.30 5.00 93 Sm 2O 3 0.05 0.40 0.40 0.34 85 95 0.30 0.50 0.80 0.72 90 1.20 1.00 2.20 2.20 100 0.98 2.50 3.48 3.60 103 Eu 2O 3 0.03 0.25 0.28 0.22 79 93 0.34 1.00 1.34 1.45 106 was used as a tracer. The comparison was made between porous cation resin (home made) and Zerolit 225 cation resin, and the experimental results are given in Fig. 1. The results obtained show that the porous resin has better properties than Zerolit 225 resin in the separation of rare earth impurities from matrix yttrium. The main separation parameters are as follows: column length: 2 × 50 cm; resin size: ∼200 mesh; concentration of the eluent (α-HIBA): 0.15 M (pH 5,4) for Y, 0.5 M (pH 5.4) for La, Ce, Pr, Nd, Sm, Eu. Under these conditions the rare earth impurities (LaEu) can be completely separated from matrix yttrium, the matrix residue amount is less than 100 μg for 1 g of Y 2O 3 on the column. Typical results are shown in Fig. 2. Spectroscopic Determination. The solution dry-residue method with high absolute sensitivity was adopted to analyze the concentrate of rare earths. The detailed studies on carrier influence, matrix effect, and controlled atmosphere ratio (Ar: O 2) were made in this paper, and the adequate conclusions are given below: 1. The addition of alkali elements increases the line intensities of rare earths, the increasing order is Cs > Rb > K > Na; 2. The line intensities of La, Ce, Pr, Nd, Sm and Eu are rising with the concentration of CsCl, the optimal concentration range of CsCl in solution dry-residue method is from 5 to 20 mg/ml. If its concentration is higher than 20 mg/ml, the increase of the background and the decrease of the line intensities of rare earths will be observed (Fig. 3). 3. The influence of matrix yttrium and third elements in concentrate should be considered. The experimental results show that the permissive maximum amounts of Y 2O 3 and CaO are 6 mg/ml and 5 mg/ml respectively. 4. Controlled atmosphere ratio of 4:1 (Ar:O 2) was employed, and the gas-chamber used is shown in Fig. 4. Sample Analysis. Analytical results for La, Ce, Pr, Nd, Sm, Eu in high-purity Y 2O 3 are listed in Table 1.