Synthesis and evaluation of a camphorquinone-derived BTP for minor actinide separation from acidic high-level radioactive liquid waste

Abstract

A camphorquinone-derived bis-triazinylpyridine, bis-2,6-(5,6,7,8-tetrahydro-5,9,9-trimethyl-5,8-methano-1,2,4-benzotriazin-3-yl)pyridine (CA-BTP), was synthesised and systematically evaluated for the selective separation of minor actinides (MA: ²⁴¹Am and ¹⁵⁴Eu) from acidic high-level radioactive liquid waste (HLW). The extractant was purified by gradient polarity chromatography, with structure confirmation via FT-IR, ¹H NMR, ESI-MS, and TG-DSC, affirming chemical purity and thermal robustness. Extraction studies revealed excellent solubility and stability in 1-octanol and isodecyl alcohol (IDA), with sharp phase separation and no third-phase formation. Radiotracer experiments using ²⁴¹Am and ¹⁵⁴Eu demonstrated high selectivity, achieving separation factors (SF_Am/Eu) of 150–280 at 1 M HNO₃ using 0.1 M CA-BTP. Mechanistic investigations included acid uptake, nitrate ion dependence, temperature variation, and slope analysis, revealing a 3 : 1 ligand-to-metal stoichiometry and an exothermic extraction process (ΔH = −33.6 to −42.5 kJ mol⁻¹). CA-BTP also showed efficient back-extraction under mild acidic conditions (0.01 M HNO₃), without the need for synergists or complexing agents. These findings position CA-BTP as a robust, scalable, and selective extractant for advanced SANEX-type flowsheets aimed at minor actinide partitioning from chemically similar lanthanides.