Radiochemical Sequential Separation of Tl(I), In(III) and Sr(II) from a Mixture by Adsorbing on Synthetic Inorganic Ion-Exchangers

 

Dr. S D Ajajekar

Asso. Professor, Thakur College of Science and Commerce, Shyamnarayan Thakur Marg,

Kandivli (E), Mumbai-400101

*Corresponding Author E-mail: shashiajagekar1@gmail.com

The present work aims at radiochemical sequential separation of Tl(I), In(III) and Sr(II) from a mixture by employing synthetic inorganic ion-exchanger. Zirconium phosphosilicate and zirconium phosphate has been synthesized and their composition has been determined.²⁰⁴Tl, ^114mIn and ⁸⁵⁺⁸⁹Sr have been used as tracers for optimizing the ideal conditions in the adsorption. Reproducibility of maximum adsorption at ideal conditions were found as 91.67 ± 2.08% for Tl(I) and 94.48 ± 2.8% for In(III) on zirconium phosphosilicate whereas 91.30 ± 2.0% for Sr(II) on zirconium phosphate. The radiochemical purity has been determined by gamma ray spectra or aluminium absorption curve after sequential separation.

 

 

INTRODUCTION:

In radioanalytical chemistry separation methods play an important role. The aim of any separation process is to isolate the chemical components of a mixture in their pure form. All the separation methods used from classical analytical chemistry can be applied to chemical separations of radionuclides and labelled compounds from samples to be analyzed such as ion-exchange, solvent extraction, precipitation, distillation etc. As only small amount of elements are to be separated, separation cannot usually be performed by methods whose success depends on the amount of component to be isolated. Therefore, methods which are independent of the amount such as ion-exchange, solvent extraction etc. are more advantages^1,2. These specific methods are time saving and allow the separation of carrier-free nuclides.

 

Adsorption studies of elements such as Zn(II), Co(II), Ni(II), C(II) and Fe(III) on the plant substrates has been reported in the literature^3,4,5. In the present investigation synthetic inorganic materials has been used for the adsorption and sequential separation of Tl(I), In(III) and Sr(II). Adsorption of indium from industrial waste water on the surface of modified saw dust has been studied recently⁶. Adsorption and oxidation of thallium by nanosized manganese dioxide has been reported by Huangfu, Xiaoliu⁷. The adsorption of Sr(II) from aqueous solution on activated carbon has been reported in the literature^8,9.Recently, E. Tereshatov et al. has separated In(III) and Tl(I) from chloride media using resin ion-exchange and liquid-liquid extraction¹⁰.

 

Investigation of adsorption of Tl(I) on zirconium phosphosilicate using batch adsorption method  revealed that 200.0 mg of zirconium phosphosilicate is adequate for maximum adsorption (91.67±2.08%) of 1.0 mg of Tl(I) at a pH of 4.0 and contact time of 5.0 minutes¹¹. From the adsorption studies of In(III) on zirconium phosphosilicate it has been observed that 1.0 mg In(III) has been quantitatively adsorbed (94.48±2.8%) on 200.0 mg of zirconium phosphosilicate at pH of 4.0 and contact time of 5.0 minutes¹².The quantitative adsorption and radiochemical separation of Sr(II) employing zirconium phosphate reveal that 50.0 mg of zirconium phosphate is sufficient for maximum adsorption of (91.30±2.0 %) of 1.0 mg of Sr(II) at pH 9.0 and contact time of 7.0 minutes¹³.

 

In the present investigation the methods thus developed and published has been applied for radiochemical sequential separation of Tl(I), In(III) and Sr(II) in the mixture. The recovery of the separated fraction also were evaluated. The objective of the work is to develop selective separation methods for Tl(I), In(III) and Sr(II) by adsorbing on synthetic inorganic ion exchange materials such as ZPS and ZP and to check radiochemical purity and recovery of the separated fraction after its sequential separation.

 

MATERIALS AND METHODS:

Chemicals and reagents:

All the chemicals and the reagents used were of A.R. grade. The concentration of various metal ion solutions were determined by standard methods^11,12 .The tracers ²⁰⁴Tl, ^114mIn and  ⁸⁵⁺⁸⁹ Sr were supplied by BRIT, BARC, Trombay. The salts of Tl(I), In(III) and Sr(II) used were of A.R. grade.

 

Instrumentation:

The activity in the effluent and on the exchanger was measured on a gamma–ray spectrometer coupled with high purity Germanium Detector, or by using G.M. counter in case of beta emitter.

 

Preparation and composition of Zirconium phosphosilicate and Zirconium phosphate:

The exchanger Zirconium phosphosilicate was prepared by the method as reported by Naumann¹⁴. The weight percentage of ZrO₂, P₂O₅ and SiO₂ were determined gravimetrically (Table 1) and was found to be in close agreement with the values reported in literature.

 

 

Table 1: Composition of Zirconium Phosphosilicate Ion-Exchanger

	Weight %
Composition	ZrO2	SiO2	P2O5
Observed	18.33	49.66	21.46
Expected	19.13*	48.18*	20.76*

* Result obtained by Baetsle et al¹⁵.

 

Table 2: Composition of Zirconium phosphate as Ion-Exchanger

Composition	Theoretical value (mg)	Observed value (mg)	Mean (mg)	% Variation
Zirconium	30.23	31.09 30.35	30.72	1.21
Phosphate	62.96	57.70 60.23	58.96	2.14

 

The method reported by C.B.Amphlett¹⁶ has been employed for the preparation of zirconium phosphate. A known amount of zirconium phosphate was dissolved in 1:1 HF solution and diluted to 100 cm³. Composition of zirconium and phosphate were estimated gravimetrically and results are as in Table 2.

 

Working standard solutions:

1 mg/cm³ of Tl(I),  In(III) and Sr(II) were prepared by diluting appropriate volume of standard solutions respectively in 100 cm³ standard measuring flasks.

 

Determination of gamma ray spectra of ⁸⁵⁺⁸⁹Sr(II) and ^114mIn(III):

An aliquot of ⁸⁵⁺⁸⁹Sr(II) was placed in the detector of gamma ray spectrometer and spectra was scanned from channel 0 to 2500. The photopeak of ⁸⁵⁺⁸⁹Sr(II) was observed at 0.514 MeV. All further radioactivity measurements after radiochemical separation of Sr(II) were counted on gamma ray spectrometer at channel number corresponding to 0.514 MeV.

 

An aliquot of ^114m In(III) was placed in the detector of gamma ray spectrometer and spectra was scanned from channel 0 to 2500. The photopeaks of ^11m In(III) was observed at 0.190 MeV, 0.558 MeV and 0.725 MeV. However, all further radioactivity measurements after radiochemical separation of In(III) were counted on gamma ray spectrometer at channel number corresponding to 0.190MeV.

 

Batch Adsorption Method and Tracer Technique:

A 10 cm³solution(whose pH is adjusted)  containing metal ion and its tracer was added to defined quantity of activated ion exchanger(ZPS or ZP).The mixture is equilibrated for sufficient time and centrifuged. The activity in the effluent and on the exchanger was measured on a gamma–ray spectrometer coupled with high purity Germanium Detector, or by using G.M. counter in case of beta emitter. The reproducibility of the adsorption was tested by evaluating the value five times.

 

Radiochemical Sequential Separation of Tl(I), In(III) And Sr(II) From A Mixture:

In a 25.0 cm³ cone, 1.0 mg carrier each of  Tl(I), In(III) and Sr(II) labeled with tracers ²⁰⁴Tl, ^114mIn and  ⁸⁵⁺⁸⁹ Sr respectively were taken.

 

Separation of Tl (I):

1.0 cm³ of 1.0 N hydrochloric acid was added to the above solution and its volume was made to 5.0 cm³ with distilled water. The mixture was chilled in an ice-bath and centrifuged. The precipitate of thallium chloride was washed with 2.0 cm³ of acidified distilled water. The supernatant along with washing was collected.

 

 

 

The precipitate of thallium chloride was dissolved in hot water. The volume was made to 10.0 cm³ and the pH was adjusted to 4.0 with dilute acetic acid. The solution was then transferred to 200.0 mg of zirconium phosphosilicate ion- exchanger and was contacted for 5.0 minutes. The ion- exchanger and the effluent were separated, dried and the beta activity of ²⁰⁴Tl was measured on a G.M. counter. The percentage adsorption was calculated in the usual manner. The contribution of ²⁰⁴ Tl to the indium fraction and strontium fraction was also evaluated.

 

Separation of In(III):

To the supernatant containing In(III) and Sr(II),  distilled water was added to make the volume to 10.0 cm³ and the pH of the solution was adjusted to 4.0 by using ammonia. The solution was then transferred to 200mg of zirconium phosphosilicate and was contacted for 5.0 minutes. The ion-exchanger and the effluent were separated. The exchanger was washed with 2.0 cm³ of distilled water. The eluant containing Sr(II) along with washing were collected. The ion-exchanger and the effluent were taken for counting on a gamma-ray spectrometer at the channel corresponding to the 0.190 MeV photopeak of ^114m In. The percentage adsorption was calculated in the usual manner. The contribution of ^114mIn to the thallium fraction and strontium fraction was also evaluated.

 

Separation of Sr(II):

The eluant containing Sr(II) was concentrated to 10.0cm³ and the pH was adjusted to 9.0 with ammonia solution. The solution was then transferred to 50.0mg of the zirconium phosphate ion-exchanger and was contacted for 7.0 minutes. The ion-exchanger and the effluent were separated and counted on a gamma-ray spectrometer at the channel number corresponding to 0.514MeV photopeak of ⁸⁵⁺⁸⁹Sr. The percentage adsorption of Sr(II) on the ion-exchanger was evaluated in the usual manner. The contribution of ⁸⁵⁺⁸⁹Sr(II) to the thallium fraction and indium fraction was also evaluated.

 

RESULTS AND DISCUSSIONS:

The results of the sequential separation of Tl(I), In(III) and Sr(II) are shown in Table 3.

 

It can be seen that Tl(I) was adsorbed to the extent of 90.77 % over an expected value of 91.67 %.

The separated component was found to be radiochemical pure and was confirmed by aluminium absorption curve (β_emax=0.76MeV), Fig.1.

 

 

Table 3: Sequential separation of Tl(I), In(III) and Sr(II) from a mixture by adsorption on inorganic ion exchanger:

		Percentage of Adsorption
Element	Tracer	Expected	Found	Thallium fraction	Indium fraction	Strontium fraction
Tl(I)	204Tl	91.67	90.77	------	1.55	2.36
In(III)	114mIn	94.48	92.88	1.58	------	2.43
Sr(II)	85+89Sr	91.30	90.83	1.53	1.79	-----

 

 

 

Fig. 1:Aluminium Absorption Curve of ²⁰⁴Tl after the separation from a mixture of Tl(I), In(III) and Sr(II)

 

It can be seen that In(III) was adsorbed to the extent of 92.88% over an expected value of 94.98%.The radiochemical purity of the separated component was confirmed by gamma-ray spectrum, Fig. 2.

 

 

Fig. 2:Gamma spectra of ^114mIn after the sequential separation from a mixture of Tl(I), In(III) and Sr(II)

 

 

From Table 3, it is observed that Sr(II) was adsorbed to the extent of 90.83% over an expected value of 91.30%. The radiochemical purity of the separated component was confirmed by gamma-ray spectrum, Fig. 3.

 

 

Fig. 3:Gamma spectra of ⁸⁵⁺⁸⁹Sr(II) after the sequential separation from a mixture of Tl(I), In(III) and Sr(II)

 

CONCLUSION:

From the results and discussion it can be concluded that using radiochemical separation procedure mentioned above. Tl(I), In(III) and Sr(II) can be separated sequentially from each other with adequate recovery and radiochemical purity. The sequential separation method is found to be rapid and quantitative. The synthetic ion exchange materials used were found to be selective, resistant to radiations and chemicals.

CONFLICT OF INTEREST:

The author declare no conflicts of interest.

 

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Received on 30.01.2018         Modified on 22.02.2018

Accepted on 07.04.2018         © AJRC All right reserved