Simultaneous Determination of Dysprosium, Holmium and Erbium in High Purity Rare Earth Oxides by Second Order Derivative Spectrophotometry

Chern. Anal. (Warsaw), 41, 781 (1996)

by M. Anbu, T. Prasada Rao, C.S.P. Iyer and A.D. Damodaran

RegionalResearchLaboratory (CSIR) Trivandrum - 695 019, India

Key words: dysprosium, holmium, erbium, rare earth oxides, derivative spectrophotometry

High purity individual rare earth oxides are increasingly used as major components in lasers (YZ0 3), phosphors (YV03, EUZ03), magnetic bubble memory films (Gdz0 3) and refractive-index lenses and fibre optics ( La Z0 3)• The determination of individual lanthanides in high purity rare earth oxides is a more important and difficult task. This paper reports the utilization of higher order derivative spectrophotometry for the simultaneous determination of dysprosium, holmium and erbium in high purity rare earth oxides. The developed procedure is simple, reliable and allows the determination of 0.001 to 0.2% of dysprosium, holmium and erbium in several rare earth oxides.

Tlenki metali ziem rzadkich 0 wysokiej czystosci znajduj<\. rosnqce zastosowanie jako skladniki laser6w (YZ03), luminofor6w (YV03, EUZ03), w magnetycznych cylindrycz nych domenach pamietci (Gdz0 3) i optyce Swiatlowodowej (Laz03)' Oznaczanie po szczeg6lnych lantanowc6w w tlenkach metali ziem rzadkich wysokiej czystosci jest wainym i trudnym zadaniem. W tej pracy przedstawiono zastosowanie spektrofotome trU pochodnej do jednoczesnego oznaczania dysprozu, holmu i erbu w tlenkach metali ziem rzadkich wysokiej czystosci. Opracowana metoda jest prosta, niezawodna i po zwala na oznaczanie od 0,001 do 0,2% dysprozu, holmu i erbu w r6inych tlenkach ziem rzadkich.

All lanthanides have similar absorption spectra and it is very difficult to deter mine lanthanides in high purity rare earth ox ides [1]. However, two procedures have been described for the determination of neodymium in Y Z0 3 [2] and another one in yttrium aluminium garnet [3]. Derivative spectrometry finds increasing use for the determination of lanthanides in high purity rare earth oxides [4]. Prasada Rao and 782 M. Anbu et at.

Sukumar have described a higher order derivative spectrophotometric procedure for the simultaneous determination of lanthanum and europium [5]. Third order deriva tive spectrophotometric procedures were developed for praseodymium [6] and sama rium [7] in the presence ofmiddle and heavy rare earth oxides. Yan and Ren [8] have recently described a fourth order derivative spectrophotometric procedure for the determination of ytterbium and dysprosium in a mixture of rare earth metal oxides. This paper describes a second order derivative procedure for the simultaneous determination of dysprosium, holmium and erbium in high purity rare earth oxides.

EXPERIMENTAL

Reagents 0.01-20% dysprosium, holmium and erbium solutions were prepared by dissolving their oxides (RE Products, Cheshire, UK) in 5 mll:l HCl and diluting to 25 mt. Other rare earth oxides are prepared by dissolving 0.25 g of respective oxide (RE Products, Cheshire, UK) in 5 ml of 1:1 HCl and diluting to 25 mt. The Y203 concentrate was obtained from Indian Rare Earths Ltd., Alwaye.

Apparatus A computer controlled double beam spectrophotometer, Model 2000 (Shimadzu) was used in these studies. A pair of matched 10 mm quartz cuvettes which were periodically cleaned with H2S04 + HN03 mixture and thoroughly washed with distilled water was used in this study. ELICO digital pH meter was used for adjusting the pH. The notation for amplitude measurement is essentially the one recommended by Fasanmade and Fell [9]. The letter D is used to indicate that an amplitude of a peak has been measured in the derivative domain. The order of derivative (e.g., 1,2 etc.) is specified by a leading superscript to the letter D, e.g. 1D, 2D. The two wavelengths between which the derivative peak is measured are specified by subscripts separated by a comma. The first wavelength corresponds to the more positive amplitude value while the second defines the position of the more negative value. Hence, 2D628,644 describes the peak amplitude (usually in arbitrary units) that has been measured between the more positive displacement of peak at 628 nm and the more negative displacement at 644 nm in the seconder derivative spectrum.

Procedure Record second order derivative spectra of 0.001 to 0.2%(m/V) dysprosium, holmium and erbium in lO%(VIV) HCl solution in the wavelength range 700-300 nm. Draw a calibration graph by plotting the amplitudes measured at 2D338,346' 2D628,644 and 2D393,400 for dysprosium, holmium and erbium, respectively.

Procedure for the det~nnination of Dy, Do and Er in SS % Y203 concentrate 0.25 g of55% Y203 concentrate was dissolved in 5 ml of 1:1 HCl and diluted to 25 ml with distilled water. Record second order derivative spectrum in the wagvelength range 300-700 nm. Compute the concentrations of Dy, Ho and Er from the calibration graph as described above. Determination ofDy, Ho, Er by derivative spectrophotometry 783

RESULTS AND DISCUSSION

Figure 1 shows on absorption spectra of 0.1 %(mIV) dysprosium (curve a), holmium (curve b) and erbium (curve c) in 10%(VN) HCI against 10% HCI blank. Maximum absorbance was recorded at 350,537and 379om for dysprosium, holmium and erbium, respectively. Holmium and erbium interfere in the determination of dysprosium. Similarly, Er interferes in the determination of Ho, and Dy as well Ho interferes in the determination of Er. 0.05

< •() a ..c ..Q.. 0 ..Q• <

Wavelength. nm

Figure 1. Absorption spectra of 0.1% Dy (a), O.l%.Ho (b) and 0.1% Er (e) in 10% HCI

Figure 2 shows 2D absorption spectra ofthesame solution as employed in Fig.l. As follows from the figure the amplitudes at 2D338,346' 2D628,644 and 2D393,400 are selective for the determination of Dy, Ho and Er, respectively. By selecting these peaks, there is no mutual interference of Dy, Ho, Er which was checked using a mixture of these elements in 10%(V/V) HCI solution.

+0.04 r------, a d 2A dA2"

-0.04 30Q 500 700 Wavelength. nm

Figure 2. Second order derivative absorption spectra of0.1% Dy(a), 0.1% Ho (b) and 0.1% Er in.l0% HCI 784 M. Anbu et al.

Calibration graph and precision

Under the optimal conditions linear calibration graphs were obtained when the amplitudes at ZD338,346, zD6Z8,644 and zD393,400 for Dy, Ho and Er were measured and plotted against concentration of analytes in 10%(V/V) Hel. The precision of the developed procedure was· studied at the medium concentration of 0.01% Dy, lIo or Er. The relative standard deviations (RSD) for the 5 successive determinations are 0.5%, 0.6% and 0.8% for Dy, Ho and Er, respectively. This confirms the high precision attained in measuring the amplitude by the graphical method. The recovery of various amounts of Dy, Ho and Er added to various rare earth oxides is given in Table 1. It is clear that Dy, Ho and Er could be determinedin the presence of YZ03, LaZ03' Pr6011, GdZ0 3, Tb40 7, Yb20 3 and LU203' Further Ho could be determined in the presence of Sm203 and EU203'

Table 1. Recovery studies Rare earth Amount added, % Amount found, % oxide Dy Ho Er Dy Ho Er LaZ0 3 0.010 0.005 0.010 0.010 0.0040 0.010 Pr6011 0.005 0.010 0.005 0.005 0.010 0.006 SmZ03 - 0.010 - - 0.012 - EUZ03 - 0.050 - - 0.050 - Gdz0 3 0.10 0.010 0.010 0.104 0.010 0.009 Tb40 7 0.005 0.010 0.10 0.006 0.010 0.102 Yhz°3 0.010 0.020 0.05 0.010 0.018 0.052 LUZ03 0.010 0.050 0.08 0.10 0.050 0.084 YZ03 0.010 0.10 0.10 0.10 0.10 0.10

Application ofthe method

It follows from this study that the second order derivative spectra of Dy, Ho and Er obtained in Fig. 2 are unaffected in the presence of 1% Y203' Further, a number of other rare earth oxides which nonnally exist in 55% Y203 concentrate do not interfere in the determination. Hence, 55% Y203 concentrate was analysed by the developed procedure and also by energy dispersion X-ray fluorescence (EDXRF). The results obtained are shown in Table 2. It is clear from this Table that Dy, Ho and Er in Y203 could be reliably d~termined by the second order derivative spectro photometric procedure as described in this paper.

Table 2. Analysis of55% YZ0 3 concentrate ByEDXRF By present method Continues % % Y Z0 3 55.0 - Tb40 7 6.2 - Gdz0 3 9.0 - DYZ03 25.1 26.0 HoZ0 3 3.6 3.5 ErZ03 1.6 1.0 Determination olDy, Ho, Er by derivative spectrophotometry 785

REFERENCES

1. Bhagavathy V:, Prasada Rao 1: and Damodaran AD., in Handbook onPhysics and Chemistry ofRare Earths (K.A. Gschneidner and L Eyring Eds.), Vol. 21, Ch. 146, New York 1995. 2. Poluektov K.S., Lauer R.S. and Ovchar LA, Zh. Anal. Khim., 28, 1490 ( 1973). 3. Meliman M.A, Kohmitsev AI., Volodina I.S., Smagni AG., Bagdasarov Kh.s. and Keberkov AM ., Zh. Prild. Spekttosk., 38, 755 ( 1983). 4. Bhagavathy V:, Sukumar R., Prasada Rao T. and Damodaran AD.,Adv. in RareEarthsRes., 122 (1993). 5. Prasada Rao 1: and Sukumar R.,Anal. Lett., 19,1731 (1986). 6. Sukumar R., Prasada Rao T. and Damodaran AD.,Analyst, 113, 1061 (1988). 7. Bhagavathy V:, Prasada Rao 1: and Damodaran AD.,Anal. Lett., 21,901 (1988). 8. Yan ~ and Ren ~,FenxiHuaxue, 18, 897 ( 1990). 9. Fasanmade AA and Fell AF., Analyst, 110, 1117 (1985).

Received February 1996 AcceptedApril1996