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Adsorption behaviour of some lanthanides on zirconium phosphate silicate (ZPS) in mineral acids
Talanta, Vol. 27, pp. 599 to 601 © Pergamon Press Ltd 1980. Printed in Great Britain
0039-9140/80/0701o0599502.00/0
ADSORPTION BEHAVIOUR OF SOME LANTHANIDES ON ZIRCONIUM PHOSPHATE SILICATE (ZPS) IN MINERAL ACIDS S. A. MAREI and N. BOTROS Nuclear Chemistry Department, Atomic Energy Establishment, Cairo, Egypt (Received 15 June 1979. Revised 11 November 1979. Accepted 27 November 1979)
Summary--The distribution coefficients of tervalent eruopium, terbium, thulium and scandium between zirconium phosphate silicate and mineral acids have been determined. The distribution coefficients were found to change from one element to another and to depend on the acid used and its concentration. Separation factors were calculated and a separation scheme for these elements was worked out.
Zirconium phosphate (ZP) is one of the most thoroughly investigated inorganic ion-exchangers. 1'2 Several zirconium phosphate derivatives have been prepared. Titanium phosphate silicate (TPS) has been prepared and used for separation of plutonium. 3 Zirconium titanium phosphate (ZTP) has been prepared and used for separation of rare earths and some other fission products from mineral acids. ~'s Zirconium phosphate silicate (ZPS) has been used for the isolation of plutonium from rare earths in nitric acid medium 6'7 and for separation of zirconium, ruthenium, neptunium and berkelium, s-l° The present investigation is part of a wider study planned to investigate the possible separation of the lanthanides and actinides from each other on zirconium phosphate derivatives. In this part the adsorption behaviour of tervalent Eu, Tb and T m (as representatives of the light, middle and heavy lanthanides) on ZPS in hydrochloric, nitric and sulphuric acid media was investigated. Scandium, which resembles the lanthanides in many respects, was also included in the investigation. EXPERIMENTAL
Apparatus An ECKO scintillation counter, type N 664 C, with a well-type NaI(TI) crystal, connected to an ECKO automatic scaler, type N 610 B, was used for gross activity measurements of the radioactive isotopes. A Telefunken type M~ Str. 1104/1 gamma-ray spectrometer connected to an M~ Zz 831/2 NaI(TI) detector was used for checking the isotope purity. Materials Unless otherwise stated, all chemicals used were of analytical grade; no further purification was done. The radioactive isotopes 15~'154Eu, ~6°Tb, ~°Tm and 465c were used as tracers. They were prepared by irradiating samples of the appropriate target materials, Eu20 3, Tb,,O7, Tm20 3 and Sc2Oa in the Egyptian ET-RR-1 reactor (neutron flux 1 x 10 t 3 n.cm-2, sec-t) for 48 hr. After a 599
sufficient cooling period, the targets were dissolved in the desired media. The gamma spectra of all the isotopes prepared showed that they were radiochemically pure. Zirconium phosphate silicate was prepared according to the procedure given by Naumann. It The 50-100 mesh fractions were used in this study. Determination of the distribution coefficients The distribution coefficients, D, were determined at room temperature (20 _+ 2 °) by the batch technique as detailed in a previous paper) Each D value reported is an average of three measurements, the deviation of the individual values from the average being about 10% for the highest D values.
RESULTS AND DISCUSSION
The uptake of Eu 3+, Tb 3+, Tm 3+ and Sc 3+ on zirconium phosphate silicate (ZPS) as a function of acid concentration is shown in Figs. 1-3. Generally, the distribution coefficients of the lanthanides (Eu 3÷, Tb 3 ÷ and Tm 3 +) are high at low acid concentrations and decrease with increase in acid concentrations. Therefore it may be deduced that exchangeadsorption is the ruling process, the lanthanides being exchanged for the protons in the resin. The flattening of the curves in the dilute acid range may be attributed to polymerization of the ions. At higher acid concentration, the deviation from mass-action law behaviour shown by some ions can be attributed to increase of cation-anion interaction in both aqueous and resin phases, together with possible invasion of the resin by the acid. The cation-anion interaction and the resin invasion may also explain the variation in behaviour of the distribution coefficients from one element to another and from one acid to another. The adsorption behaviour of Sc 3+ on ZPS differs according to the acid used. The distribution coefficient for Sc 3 ÷ generally increases with increasing acid concentration, passes through a maximum and then decreases. The scandium ion, being smaller, has a
600
SHORT COMMUNICATIONS
,o'
104
,o3
103
t~
102
t) e
10
10
I
I
I 10`2
I
I I0 - I
I~
i0-~
l
I0"3
10-2
I0 -I
I I
M L' SO 4
M HCI
Fig. I. Distribution of Eu, Tb, Tm and Sc between ZPS and hydrochloric acid • Eu 3+, A Tb 3÷, [] Tm 3+, x Sc 3+.
Fig. 3. Distribution of Eu, Tb, Tm and Sc between ZPS and sulphuric acid • Eu 3÷, A Tb 3+, [] Tm 3÷, x Sc 3÷.
much greater tendency to hydrolysis than the lanthanide ions. Therefore, at low acid concentration the scandium ions are hydrolysed and the increase of acid concentration will decrease the hydrolysis, increase
the percentage of free ions and consequently increase the adsorption of scandium on ZPS. The difference in the adsorption behaviour of Sc 3 ÷ and the lanthanides on ZPS from different acid solutions may facilitate the separation of Sc 3+ from the lanthanides. The separation factors (~L~,) between Sc 3÷ and the lanthanides investigated are calculated and collected in Table 1. Sc 3÷ is strongly retained on ZPS from 0.1M sulphuric acid, whereas the three lanthanides are much less adsorbed. Many schemes for separating Sc 3 ÷ from the investigated lanthanides can be deduced from Table 1. The separation of the lanthanides from each other with zirconium phosphate silicate may be achieved from different acid solutions. The separation factors were calculated from the distribution coefficients and are collected in Table 2. It is clear that they depend on the acid used and its concentration. Another useful feature seen from Table 2 is the variation of the separation factors from very high to very low values. This large variation illustrates the versatility of the ZPS. An element which is eluted first from one acid medium can be eluted last from another acid medium. Therefore, several separation schemes can be deduced from Table 2. An easy separation procedure is adsorption of the lanthanides at low acid concentration, then elution with 0.5M hydrochloric acid strips Eu 3+, elution with 0.5M nitric acid removes Tm 3÷ and finally Tb 3÷ can be collected by elution with 0.5M sulphuric acid. This is the simplest separation but many other schemes can be deduced from Table 2. It can be concluded that although the distribution
104
103
(~
i02
I0
I
lO-i tO-3
10-2
,05
I0"I
.5
i I
M HNO3
Fig. 2. Distribution of Eu, Tb, Tm and Sc between ZPS and nitric acid • Eu 3÷, A Tb 3÷, E3 Tm 3÷, x Sc3÷.
SHORT COMMUNICATIONS
601
Table 1. Separation factors between scandium and lanthanides on ZPS from different acids Separation factors Acid HCi
HNO3
H2SO 4
Concentration, M
~t~,
0.005 0.010 0.050 0.100 0.500 0.005 0.010 0.050 0.100 0.500 0.005 0.010 0.050 0.100 0.500
CtrbSC
a~r~
0.7 3.3 13.3 30.2 13.3 0.7 1.8 20.0 42.3 400
0.1 0.2 0.7 1.6 0.2 0.0 0.2 2.7 4.1 1.8
1.1 4.2 3.3 4.1 0.3 1.7 2.8 30.0 73.3 400
2.0 1.5 11.7 35.0 120
0.5 0.6 82.4 1400 120
5.3 3.3 8.2 11.7 0.3
Table 2. Separation factors of lanthanides on ZPS from different acids Separation factors Acid HCI
HNO3
H 2SO 4
Concentration, M
arT.b
~tT~
at~
0.005 0.010 0.050 0.100 0.500 0.005 0.010 0.050 0.100 0.500 0.005 0.010 0.050 0.100 0.500
7.1 21.3 20.0 18.3 73.3 25.0 13.7 7.3 10.4 220 4.3 2.3 0.1 0.0 1.0
0.6 0.8 4.0 7.3 40.0 0.4 1.0 0.7 0.6 1.0 0.4 0.5 1.4 3.0 430
11.4 26.7 5.0 2.5 2.5 62.5 14.5 11.0 18.0 220 11.3 5.0 0.1 0.0 0.0
coefficients of the lanthanides on Z P S are smaller than on Z T P or ZP, s the separation factors are sufficiently high. Therefore, a good mutual separation of the lanthanides may be achieved on zirconium phosptkate silicate. The practical application of the different separation schemes is in progress in our laboratory. REFERENCES
1. E. Akatsu, R. Ono, K. Tskuechi and H. Uchiyama~ J. Nucl. Sci. Technol., 1965, 2, 141. 2. C. B. Amphlett, Inorganic Ion Exchangers, Elsevier, Amsterdam, 1964.
3. S. J. Naqvi, D. Huys and L. H. Baetsle, J. lnorg. Nucl. Chem., 1971, 33, 4317. 4. S. A. Marei and S. K. Shakahooki, Radiochem. Radioanal. Lett., 1972, 11, 187. 5. S. A. Marei, M. EI-Garhy and N. Botros, Radiochim. Acta, 1978, 25, 37. 6. K. V. Barsukova and G. N. Radionova, Radiokhimiya, 1968, 10, 84. 7. Idera, Soy. Radiochem., 1972, 14, 237. 8. S. Naidyanathan and L. Baetsle, Radiochem. Radional. Lett., 1970, 5, 247. 9. R. Ooms, P. Schonken, W. D'olieslager, L. Baetsle and M. D'Hont, J. lnorg. Nucl. Chem., 1974, 36, 665. 10. B. F. Myasoedov, K. V. Barsukova and G. N. Radionova, Radiochem. Radioanal. Lett., 1971, 7, 269. 11. D. Naumann, Kernenergie, 1963, 6, 173.
0039-9140/80/0701o0599502.00/0
ADSORPTION BEHAVIOUR OF SOME LANTHANIDES ON ZIRCONIUM PHOSPHATE SILICATE (ZPS) IN MINERAL ACIDS S. A. MAREI and N. BOTROS Nuclear Chemistry Department, Atomic Energy Establishment, Cairo, Egypt (Received 15 June 1979. Revised 11 November 1979. Accepted 27 November 1979)
Summary--The distribution coefficients of tervalent eruopium, terbium, thulium and scandium between zirconium phosphate silicate and mineral acids have been determined. The distribution coefficients were found to change from one element to another and to depend on the acid used and its concentration. Separation factors were calculated and a separation scheme for these elements was worked out.
Zirconium phosphate (ZP) is one of the most thoroughly investigated inorganic ion-exchangers. 1'2 Several zirconium phosphate derivatives have been prepared. Titanium phosphate silicate (TPS) has been prepared and used for separation of plutonium. 3 Zirconium titanium phosphate (ZTP) has been prepared and used for separation of rare earths and some other fission products from mineral acids. ~'s Zirconium phosphate silicate (ZPS) has been used for the isolation of plutonium from rare earths in nitric acid medium 6'7 and for separation of zirconium, ruthenium, neptunium and berkelium, s-l° The present investigation is part of a wider study planned to investigate the possible separation of the lanthanides and actinides from each other on zirconium phosphate derivatives. In this part the adsorption behaviour of tervalent Eu, Tb and T m (as representatives of the light, middle and heavy lanthanides) on ZPS in hydrochloric, nitric and sulphuric acid media was investigated. Scandium, which resembles the lanthanides in many respects, was also included in the investigation. EXPERIMENTAL
Apparatus An ECKO scintillation counter, type N 664 C, with a well-type NaI(TI) crystal, connected to an ECKO automatic scaler, type N 610 B, was used for gross activity measurements of the radioactive isotopes. A Telefunken type M~ Str. 1104/1 gamma-ray spectrometer connected to an M~ Zz 831/2 NaI(TI) detector was used for checking the isotope purity. Materials Unless otherwise stated, all chemicals used were of analytical grade; no further purification was done. The radioactive isotopes 15~'154Eu, ~6°Tb, ~°Tm and 465c were used as tracers. They were prepared by irradiating samples of the appropriate target materials, Eu20 3, Tb,,O7, Tm20 3 and Sc2Oa in the Egyptian ET-RR-1 reactor (neutron flux 1 x 10 t 3 n.cm-2, sec-t) for 48 hr. After a 599
sufficient cooling period, the targets were dissolved in the desired media. The gamma spectra of all the isotopes prepared showed that they were radiochemically pure. Zirconium phosphate silicate was prepared according to the procedure given by Naumann. It The 50-100 mesh fractions were used in this study. Determination of the distribution coefficients The distribution coefficients, D, were determined at room temperature (20 _+ 2 °) by the batch technique as detailed in a previous paper) Each D value reported is an average of three measurements, the deviation of the individual values from the average being about 10% for the highest D values.
RESULTS AND DISCUSSION
The uptake of Eu 3+, Tb 3+, Tm 3+ and Sc 3+ on zirconium phosphate silicate (ZPS) as a function of acid concentration is shown in Figs. 1-3. Generally, the distribution coefficients of the lanthanides (Eu 3÷, Tb 3 ÷ and Tm 3 +) are high at low acid concentrations and decrease with increase in acid concentrations. Therefore it may be deduced that exchangeadsorption is the ruling process, the lanthanides being exchanged for the protons in the resin. The flattening of the curves in the dilute acid range may be attributed to polymerization of the ions. At higher acid concentration, the deviation from mass-action law behaviour shown by some ions can be attributed to increase of cation-anion interaction in both aqueous and resin phases, together with possible invasion of the resin by the acid. The cation-anion interaction and the resin invasion may also explain the variation in behaviour of the distribution coefficients from one element to another and from one acid to another. The adsorption behaviour of Sc 3+ on ZPS differs according to the acid used. The distribution coefficient for Sc 3 ÷ generally increases with increasing acid concentration, passes through a maximum and then decreases. The scandium ion, being smaller, has a
600
SHORT COMMUNICATIONS
,o'
104
,o3
103
t~
102
t) e
10
10
I
I
I 10`2
I
I I0 - I
I~
i0-~
l
I0"3
10-2
I0 -I
I I
M L' SO 4
M HCI
Fig. I. Distribution of Eu, Tb, Tm and Sc between ZPS and hydrochloric acid • Eu 3+, A Tb 3÷, [] Tm 3+, x Sc 3+.
Fig. 3. Distribution of Eu, Tb, Tm and Sc between ZPS and sulphuric acid • Eu 3÷, A Tb 3+, [] Tm 3÷, x Sc 3÷.
much greater tendency to hydrolysis than the lanthanide ions. Therefore, at low acid concentration the scandium ions are hydrolysed and the increase of acid concentration will decrease the hydrolysis, increase
the percentage of free ions and consequently increase the adsorption of scandium on ZPS. The difference in the adsorption behaviour of Sc 3 ÷ and the lanthanides on ZPS from different acid solutions may facilitate the separation of Sc 3+ from the lanthanides. The separation factors (~L~,) between Sc 3÷ and the lanthanides investigated are calculated and collected in Table 1. Sc 3÷ is strongly retained on ZPS from 0.1M sulphuric acid, whereas the three lanthanides are much less adsorbed. Many schemes for separating Sc 3 ÷ from the investigated lanthanides can be deduced from Table 1. The separation of the lanthanides from each other with zirconium phosphate silicate may be achieved from different acid solutions. The separation factors were calculated from the distribution coefficients and are collected in Table 2. It is clear that they depend on the acid used and its concentration. Another useful feature seen from Table 2 is the variation of the separation factors from very high to very low values. This large variation illustrates the versatility of the ZPS. An element which is eluted first from one acid medium can be eluted last from another acid medium. Therefore, several separation schemes can be deduced from Table 2. An easy separation procedure is adsorption of the lanthanides at low acid concentration, then elution with 0.5M hydrochloric acid strips Eu 3+, elution with 0.5M nitric acid removes Tm 3÷ and finally Tb 3÷ can be collected by elution with 0.5M sulphuric acid. This is the simplest separation but many other schemes can be deduced from Table 2. It can be concluded that although the distribution
104
103
(~
i02
I0
I
lO-i tO-3
10-2
,05
I0"I
.5
i I
M HNO3
Fig. 2. Distribution of Eu, Tb, Tm and Sc between ZPS and nitric acid • Eu 3÷, A Tb 3÷, E3 Tm 3÷, x Sc3÷.
SHORT COMMUNICATIONS
601
Table 1. Separation factors between scandium and lanthanides on ZPS from different acids Separation factors Acid HCi
HNO3
H2SO 4
Concentration, M
~t~,
0.005 0.010 0.050 0.100 0.500 0.005 0.010 0.050 0.100 0.500 0.005 0.010 0.050 0.100 0.500
CtrbSC
a~r~
0.7 3.3 13.3 30.2 13.3 0.7 1.8 20.0 42.3 400
0.1 0.2 0.7 1.6 0.2 0.0 0.2 2.7 4.1 1.8
1.1 4.2 3.3 4.1 0.3 1.7 2.8 30.0 73.3 400
2.0 1.5 11.7 35.0 120
0.5 0.6 82.4 1400 120
5.3 3.3 8.2 11.7 0.3
Table 2. Separation factors of lanthanides on ZPS from different acids Separation factors Acid HCI
HNO3
H 2SO 4
Concentration, M
arT.b
~tT~
at~
0.005 0.010 0.050 0.100 0.500 0.005 0.010 0.050 0.100 0.500 0.005 0.010 0.050 0.100 0.500
7.1 21.3 20.0 18.3 73.3 25.0 13.7 7.3 10.4 220 4.3 2.3 0.1 0.0 1.0
0.6 0.8 4.0 7.3 40.0 0.4 1.0 0.7 0.6 1.0 0.4 0.5 1.4 3.0 430
11.4 26.7 5.0 2.5 2.5 62.5 14.5 11.0 18.0 220 11.3 5.0 0.1 0.0 0.0
coefficients of the lanthanides on Z P S are smaller than on Z T P or ZP, s the separation factors are sufficiently high. Therefore, a good mutual separation of the lanthanides may be achieved on zirconium phosptkate silicate. The practical application of the different separation schemes is in progress in our laboratory. REFERENCES
1. E. Akatsu, R. Ono, K. Tskuechi and H. Uchiyama~ J. Nucl. Sci. Technol., 1965, 2, 141. 2. C. B. Amphlett, Inorganic Ion Exchangers, Elsevier, Amsterdam, 1964.
3. S. J. Naqvi, D. Huys and L. H. Baetsle, J. lnorg. Nucl. Chem., 1971, 33, 4317. 4. S. A. Marei and S. K. Shakahooki, Radiochem. Radioanal. Lett., 1972, 11, 187. 5. S. A. Marei, M. EI-Garhy and N. Botros, Radiochim. Acta, 1978, 25, 37. 6. K. V. Barsukova and G. N. Radionova, Radiokhimiya, 1968, 10, 84. 7. Idera, Soy. Radiochem., 1972, 14, 237. 8. S. Naidyanathan and L. Baetsle, Radiochem. Radional. Lett., 1970, 5, 247. 9. R. Ooms, P. Schonken, W. D'olieslager, L. Baetsle and M. D'Hont, J. lnorg. Nucl. Chem., 1974, 36, 665. 10. B. F. Myasoedov, K. V. Barsukova and G. N. Radionova, Radiochem. Radioanal. Lett., 1971, 7, 269. 11. D. Naumann, Kernenergie, 1963, 6, 173.