Highly efficient extraction of 212Pb/212Bi from natural thorium in halide medium based on an advanced anion exchanger

Although 212Pb and 212Bi have significant applications in targeted α-nuclide therapy for malignant tumors, their use is limited by the scarcity of 212Pb/212Bi resources. To address this bottleneck problem, we first proposed an advanced method for selectively extracting 212Pb and 212Bi from the decay chain of 232Th using an efficient porous silica-supported anion exchanger. The selective adsorption mechanisms of the resin for Pb(II) and Bi(III) were clarified through spectroscopic analyses and theoretical calculations. Using the new method, we successfully separated 2.07 MBq of 212Pb from 2 kg of Th(NO3)4·xH2O, achieving a record-breaking chemical yield of 88.2% and an estimated radionuclide purity of over 99.9%. Mechanistic analysis suggested that Pb(II) and Bi(III) could form anionic complexes in the HBr medium, with [PbBr3]− and [BiBr5]2− being the main species captured; while Th(IV), Ac(III) and Ra(II) mainly existed as cationic forms and thus could not be fixed. Unlike traditional extraction methods for 212Pb/212Bi, this method is not constrained by the supply of 224Ra or 228Th, giving this method significant theoretical and practical value. To date, this represents the first report of directly extracting MBq-level 212Pb from 232Th using anion exchanger or non-crown-ether materials.