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Preparation of high-purity europium oxide using combined reduction-ion exchange method
Journal
of the Less-Common
Metals,
112
(1985)
267
- 270
267
PREPARATION OF HIGH-PURITY EUROPIUM OXIDE USING COMBINED REDUCTION-ION EXCHANGE METHOD* M. ELBANOWSKI and J. BARANOWSKA Department of Poznaii (Poland)
Rare
Earths,
Faculty
of Chemistry,
A. Mickiewicz
University,
60-780
(Received December 11, 1984)
Summary
The separation of Y 3+, Gd3+ and other rare earths from Eu3+ ions using the combined reduction-precipitation and reduction-ion-exchange methods has been carried out. The elution of rare earth ions was done using EDTA solution after earlier reduction of Eu3+ to Eu*+. As a result of this process pure europium oxide containing no spectrographically discoverable traces of other rare earth elements was obtained.
1. Introduction
The main sources of raw material of europium compounds are mixtures of lanthanides containing relatively small amounts of europium. Of the separation techniques, McCoy’s reduction-precipitation method [l] and the reduction-ion-exchange method [ 21, combined, provide the possibility of enriching low-percentage mixtures of europium compounds to high-purity grade. The reduction-precipitation method is applied in the first stage of the separation process, giving a considerable enrichment of low-percentage europium materials. The reduction-ion-exchange method enables us to obtain high-purity grade europium oxide from Eu2O3 preparations containing more than 10% of other rare earth elements by using only one reduction-ion-exchange cycle with NTA solution as an eluent [2]. In the present work, by applying the combined reduction-precipitation and reduction-ion-exchange methods, the separation of Y3+, Gd3+ and other rare earth ions from Eu3+ was carried out using EDTA solutions as eluent. Separations of trace amounts, especially of Gd203 and Y3O3, from Eu3O3 is difficult. EDTA solution was chosen as an eluent for the ion-exchange process because the stability constants of the complex compounds Eu*+/EDTA and the trivalent rare earth ions/EDTA are greatly different [ 31. *Paper presented at the International land, March 4 - 8, 1985. 0022-5088/85/$3.30
Rare Earth Conference, ETH Zurich, Switzer-
@ Elsevier Sequoia/Printed in The Netherlands
268
2. Experimental
details
2.1. Chemical reagents The standards for the spectral analysis EuZ03, Gd,03, Y 203, Sm,03, Dy,Os, Yb,03, Laz03 and ZnO, were obtained from Johnson Matthey Chemicals Ltd., London; the gadolinium concentrate (75% Gd,03) from Koch-Light Laboratories, Colnbrook (Gt. Britain); spectroscopically pure samples of EuZ03, Gd,03 and Y,03 were obtained from the Department of Rare Earths, A. Mickiewicz University, Poznan; the remaining reagents were analytically pure from POCh, Gliwice. 2.2. Apparatus Quartz spectrograph, Q 24, C. Zeiss, Jena; a glass column (4.5 cm diameter) filled with amalgamated zinc (80 cm high); a glass column (6 cm diameter) filled with sulphonic cation exchange resin Zerolit 225 - ammonium form (100 cm high). 2.3. Procedure Isolation of europium compounds from low percentage concentrate was carried out using McCoy’s reduction-precipitation method. In this process we obtained a concentrate of Eu,Os containing from a few to -12% of accompanying elements. This Eu,O, concentrate was used for further purification by the reduction-ion-exchange method. The procedure was as follows: initially Eu3+ ions were reduced to Eu2+ using amalgamated zinc and then the Eu2+ ions were separated from the remaining trivalent rare earth ions by elution through an ion-exchange column. A thin layer of benzene on the surface of the solution in the column protected the Eu*+ from oxidation by atmospheric oxygen. Solutions of the ammonium salt of EDTA (0.5, 1 and 2%) with the addition of 6 g of concentrated CH,COOH and 1 g of hydroxylamine hydrochloride in 1 dm3 were used as eluent; the pH was adjusted to 6.5 by the addition of 25% ammonia water. The flow rate of the eluent through the column was 0.5 dm3/h. The collected fractions of eluate were acidified with HCl, Eu2+ was oxidized with hydrogen peroxide, and the oxalates were precipitated from hot solution. The oxalates were finally roasted to oxides at 900 “C. The oxides were purified from zinc and were tested by means of spectral emission analysis (high-voltage spark excitation, carbon rod electrodes). 3. Results and discussion 3.1. Elution curves of Eu2’, Eu3+, Gd3’ and Y3’ In order to determine the possibility of separating Eu2+ from other rare earth ions, the ions of Eu 2+, Eu3+, Gd3+ and Y3+ were subjected to elution. From the elution curves obtained it was determined that the Eu3+, Gd3+ and Y3+ ions (retention volume for each ion = 0.6 dm3) were eluted prior to Eu2+ (retention volume = 3.1 dm3).
269
The retention volumes of Eu2’ and Gd3+ or Y3+, obtained under optimal conditions, led to separation factors CQ~Z+~~~~+ and 1yxu~+,v3+ equal to 5. This value of ar suggested the possibility of separating Eu*+ from trivalent ions of rare earth elements. 3.2. Separation of artificial mixtures of europium with gadolinium and europium with yttrium In order to test, in practice, the usefulness of EDTA solution as eluent in the separation of europium from other rare earths in the reduction-ionexchange method, the separation procedure was applied to prepared mixtures of Eu,03 with Gdz03 and Eu,03 with Y,03. The elution of mixtures containing 95% Eu203 and 5% Gdz03 gave a few fractions of spectroscopically pure Eu,03 corresponding to 39% of the mass of the initial mixture. The remaining fractions consisted of Eu,03 contaminated (to different degrees) with Gdz03. Similarly, from a mixture of 99% Eu203 and 1% Gd,Os 70% of the mass was obtained as spectroscopically pure Eu,O,. Elution of a mixture containing 95% Eu,O, and 5% Y,03 gave spectroscopically pure Eu,Os (37% of the mass of the initial mixture), and a mixture containing 99% Eu,O, and 1% Y,Os yielded 65% spectroscopically pure Eu,03. The remaining fractions in both elutions contained Eu,03 contaminated to different degrees with Yz03. 3.3. Separation of a natural mixture of europium and other rare earth elements In the process of isolating europium from a mixture of natural origin, i.e., gadolinium concentrate (75% Gd203, 9% EuZ03, plus remaining rare earths) by means of the reduction-precipitation method, an enriched preparation was obtained containing 36% Euz03. This was purified from the accompanying elements by means of the ion exchange method after prior reduction of Eu3+ to Eu2’. The resu 1t o f the elution was several fractions with various europium contents. In the initial fractions, all the accompanying rare earth elements were present with the europium. The middle fractions contained only small amounts of gadolinium and yttrium in addition to the europium. The final fractions of the eluate consisted of pure Eu203, without spectroscopically detectable amounts of other rare earth elements. The spectrographic detection limits of yttrium and gadolinium, traces of which are most difficult to remove from europium preparations, are, under the given conditions, 0.01% Y,03 and 0.02% Gd,O;, in Eu,O,. Using this method, in a single elution process, 37% of the eluted amount of europium was obtained as spectroscopically pure Euz03. Several fractions of the eluate with small amounts of yttrium and gadolinium present (0.1 - l%), contained, together, 18.5% of Eu203. A repeat of the reduction-ion-exchange cycle on the preparations containing the contaminants, will greatly increase the resultant spectroscopically-pure Eu,O,. These experiments show that the reduction-ion-exchange procedure, with EDTA as eluent, may be used to remove rare earth elements present in
210
Eu,03 preparations up to -12%. In the case of low-percentage europium concentrates, before purification by means of the reduction-ion-exchange method, it is advisable to first undertake a preliminary enrichment employing the reduction-precipitation procedure.
Acknowledgment The authors are grateful helpful discussions.
to Drs. A. Borkowska
and B. Mqkowska
for
References 1 H. N. McCoy, J. Am. Chem. SOL, 57 (1935) 1756. 2 B. Borkowski, A. Borkowska, K. Bahczyk, J. Baranowska and B. Mgkowska, unpublished work. 3 J. Bjerrum, G. Schwarzenbach and L. G. Sill&, Stability Constants of Metal-Zon Complexes, Part I, The Chemical Society, London, 1957, p. 76.
of the Less-Common
Metals,
112
(1985)
267
- 270
267
PREPARATION OF HIGH-PURITY EUROPIUM OXIDE USING COMBINED REDUCTION-ION EXCHANGE METHOD* M. ELBANOWSKI and J. BARANOWSKA Department of Poznaii (Poland)
Rare
Earths,
Faculty
of Chemistry,
A. Mickiewicz
University,
60-780
(Received December 11, 1984)
Summary
The separation of Y 3+, Gd3+ and other rare earths from Eu3+ ions using the combined reduction-precipitation and reduction-ion-exchange methods has been carried out. The elution of rare earth ions was done using EDTA solution after earlier reduction of Eu3+ to Eu*+. As a result of this process pure europium oxide containing no spectrographically discoverable traces of other rare earth elements was obtained.
1. Introduction
The main sources of raw material of europium compounds are mixtures of lanthanides containing relatively small amounts of europium. Of the separation techniques, McCoy’s reduction-precipitation method [l] and the reduction-ion-exchange method [ 21, combined, provide the possibility of enriching low-percentage mixtures of europium compounds to high-purity grade. The reduction-precipitation method is applied in the first stage of the separation process, giving a considerable enrichment of low-percentage europium materials. The reduction-ion-exchange method enables us to obtain high-purity grade europium oxide from Eu2O3 preparations containing more than 10% of other rare earth elements by using only one reduction-ion-exchange cycle with NTA solution as an eluent [2]. In the present work, by applying the combined reduction-precipitation and reduction-ion-exchange methods, the separation of Y3+, Gd3+ and other rare earth ions from Eu3+ was carried out using EDTA solutions as eluent. Separations of trace amounts, especially of Gd203 and Y3O3, from Eu3O3 is difficult. EDTA solution was chosen as an eluent for the ion-exchange process because the stability constants of the complex compounds Eu*+/EDTA and the trivalent rare earth ions/EDTA are greatly different [ 31. *Paper presented at the International land, March 4 - 8, 1985. 0022-5088/85/$3.30
Rare Earth Conference, ETH Zurich, Switzer-
@ Elsevier Sequoia/Printed in The Netherlands
268
2. Experimental
details
2.1. Chemical reagents The standards for the spectral analysis EuZ03, Gd,03, Y 203, Sm,03, Dy,Os, Yb,03, Laz03 and ZnO, were obtained from Johnson Matthey Chemicals Ltd., London; the gadolinium concentrate (75% Gd,03) from Koch-Light Laboratories, Colnbrook (Gt. Britain); spectroscopically pure samples of EuZ03, Gd,03 and Y,03 were obtained from the Department of Rare Earths, A. Mickiewicz University, Poznan; the remaining reagents were analytically pure from POCh, Gliwice. 2.2. Apparatus Quartz spectrograph, Q 24, C. Zeiss, Jena; a glass column (4.5 cm diameter) filled with amalgamated zinc (80 cm high); a glass column (6 cm diameter) filled with sulphonic cation exchange resin Zerolit 225 - ammonium form (100 cm high). 2.3. Procedure Isolation of europium compounds from low percentage concentrate was carried out using McCoy’s reduction-precipitation method. In this process we obtained a concentrate of Eu,Os containing from a few to -12% of accompanying elements. This Eu,O, concentrate was used for further purification by the reduction-ion-exchange method. The procedure was as follows: initially Eu3+ ions were reduced to Eu2+ using amalgamated zinc and then the Eu2+ ions were separated from the remaining trivalent rare earth ions by elution through an ion-exchange column. A thin layer of benzene on the surface of the solution in the column protected the Eu*+ from oxidation by atmospheric oxygen. Solutions of the ammonium salt of EDTA (0.5, 1 and 2%) with the addition of 6 g of concentrated CH,COOH and 1 g of hydroxylamine hydrochloride in 1 dm3 were used as eluent; the pH was adjusted to 6.5 by the addition of 25% ammonia water. The flow rate of the eluent through the column was 0.5 dm3/h. The collected fractions of eluate were acidified with HCl, Eu2+ was oxidized with hydrogen peroxide, and the oxalates were precipitated from hot solution. The oxalates were finally roasted to oxides at 900 “C. The oxides were purified from zinc and were tested by means of spectral emission analysis (high-voltage spark excitation, carbon rod electrodes). 3. Results and discussion 3.1. Elution curves of Eu2’, Eu3+, Gd3’ and Y3’ In order to determine the possibility of separating Eu2+ from other rare earth ions, the ions of Eu 2+, Eu3+, Gd3+ and Y3+ were subjected to elution. From the elution curves obtained it was determined that the Eu3+, Gd3+ and Y3+ ions (retention volume for each ion = 0.6 dm3) were eluted prior to Eu2+ (retention volume = 3.1 dm3).
269
The retention volumes of Eu2’ and Gd3+ or Y3+, obtained under optimal conditions, led to separation factors CQ~Z+~~~~+ and 1yxu~+,v3+ equal to 5. This value of ar suggested the possibility of separating Eu*+ from trivalent ions of rare earth elements. 3.2. Separation of artificial mixtures of europium with gadolinium and europium with yttrium In order to test, in practice, the usefulness of EDTA solution as eluent in the separation of europium from other rare earths in the reduction-ionexchange method, the separation procedure was applied to prepared mixtures of Eu,03 with Gdz03 and Eu,03 with Y,03. The elution of mixtures containing 95% Eu203 and 5% Gdz03 gave a few fractions of spectroscopically pure Eu,03 corresponding to 39% of the mass of the initial mixture. The remaining fractions consisted of Eu,03 contaminated (to different degrees) with Gdz03. Similarly, from a mixture of 99% Eu203 and 1% Gd,Os 70% of the mass was obtained as spectroscopically pure Eu,O,. Elution of a mixture containing 95% Eu,O, and 5% Y,03 gave spectroscopically pure Eu,Os (37% of the mass of the initial mixture), and a mixture containing 99% Eu,O, and 1% Y,Os yielded 65% spectroscopically pure Eu,03. The remaining fractions in both elutions contained Eu,03 contaminated to different degrees with Yz03. 3.3. Separation of a natural mixture of europium and other rare earth elements In the process of isolating europium from a mixture of natural origin, i.e., gadolinium concentrate (75% Gd203, 9% EuZ03, plus remaining rare earths) by means of the reduction-precipitation method, an enriched preparation was obtained containing 36% Euz03. This was purified from the accompanying elements by means of the ion exchange method after prior reduction of Eu3+ to Eu2’. The resu 1t o f the elution was several fractions with various europium contents. In the initial fractions, all the accompanying rare earth elements were present with the europium. The middle fractions contained only small amounts of gadolinium and yttrium in addition to the europium. The final fractions of the eluate consisted of pure Eu203, without spectroscopically detectable amounts of other rare earth elements. The spectrographic detection limits of yttrium and gadolinium, traces of which are most difficult to remove from europium preparations, are, under the given conditions, 0.01% Y,03 and 0.02% Gd,O;, in Eu,O,. Using this method, in a single elution process, 37% of the eluted amount of europium was obtained as spectroscopically pure Euz03. Several fractions of the eluate with small amounts of yttrium and gadolinium present (0.1 - l%), contained, together, 18.5% of Eu203. A repeat of the reduction-ion-exchange cycle on the preparations containing the contaminants, will greatly increase the resultant spectroscopically-pure Eu,O,. These experiments show that the reduction-ion-exchange procedure, with EDTA as eluent, may be used to remove rare earth elements present in
210
Eu,03 preparations up to -12%. In the case of low-percentage europium concentrates, before purification by means of the reduction-ion-exchange method, it is advisable to first undertake a preliminary enrichment employing the reduction-precipitation procedure.
Acknowledgment The authors are grateful helpful discussions.
to Drs. A. Borkowska
and B. Mqkowska
for
References 1 H. N. McCoy, J. Am. Chem. SOL, 57 (1935) 1756. 2 B. Borkowski, A. Borkowska, K. Bahczyk, J. Baranowska and B. Mgkowska, unpublished work. 3 J. Bjerrum, G. Schwarzenbach and L. G. Sill&, Stability Constants of Metal-Zon Complexes, Part I, The Chemical Society, London, 1957, p. 76.