Crown ether-based cloud point extraction for lead-212 enrichment from thorium series

Abstract

An innovative cloud point extraction (CPE) method was proposed for the extraction and enrichment of medically valuable radionuclide lead-212 (²¹²Pb) from thorium decay series nuclides. This method employed 4′,4′′(5′′)-di-tert-butyldicyclohexyl-18-crown-6 (DtBuDC18C6) as the chelating agent, which exhibits high selectivity for Pb. This study systematically examined the effects of nitric acid, the non-ionic surfactant Triton X-114 (TTX-114), the chelating agent, and the ionic surfactant cetyltrimethylammonium bromide (CTAB) on Pb extraction efficiency, and optimization was performed. The results indicated that the optimal conditions were 0.1 mol L⁻¹ HNO₃, 370 μM DtBuDC18C6, 1200 μM TTX-114, and 30 μM CTAB. Even in the presence of high concentrations of thorium, this method achieved a Pb extraction efficiency of 96% and a recovery rate of 98 ± 5% through ammonium citrate stripping. Moreover, the ²¹⁰Pb tracer was used to study the CPE process, and gamma spectrometry revealed a chemical recovery rate of over 53.8% for ²¹⁰Pb. Finally, density functional theory (DFT) was used to calculate the interactions between thorium series nuclides and DtBuDC18C6, further validating the selective enrichment capability of the CPE system for ²¹²Pb. In conclusion, this was likely the first study to use CPE to extract the medical isotope ²¹²Pb from thorium decay series nuclides, highlighting its significant scientific and practical potential.