The separation of terbium from gadolinium by solvent extraction

Abstract

¹⁶¹Tb is considered a promising alternative to ¹⁷⁷Lu in the treatment of neuroendocrine tumors and prostate cancer. It is produced via neutron irradiation of ¹⁶⁰Gd targets and its subsequent separation from said targets. Current separation methods have limitations so a fast removal method of the Gd bulk is desired. Such a method is developed in this research using solvent extraction techniques. Three extractants were investigated, the one with the highest potential, DEHPA, was used to optimize the extraction. This yielded a Tb extraction efficiency of 98.6 ± 0.2 % and a Gd extraction efficiency of 85.7 ± 5.5 % followed by a Tb back-extraction efficiency of 98.2 ± 0.1 % and a Gd back-extraction efficiency of more than 98.2 ± 0.1 %. The Tb/Gd separation was increased by adding the reverse size selective chelator MACROPA to the aqueous phase to preferentially complex Gd in the aqueous phase. This yielded a Tb and Gd extraction efficiency of 95.0 ± 0.2 % and 53.1 ± 3.0 % respectively. The ratio between total EEs of Tb and Gd after three subsequent extractions was approximately 10 demonstrating the potential of using sequential extractions to remove a bulk of Gd from Tb. The procedure of doing consecutive extractions must however be further optimized as nearly 80% of Tb was not extracted. Finally, it was shown that the resulting solution after bulk Gd removal can still be further purified using an ion exchange column. In future research, it is highly advised to investigate the recycling of Gd and MACROPA from the aqueous phase after extraction to allow for further irradiation of the Gd and re-usability of the MACROPA.