Cloud point extraction of Sr(II) from simulated high-level liquid waste: Minimizing radioactive organic liquid volume

• Over 50% of Sr(II) is partitioned into the surfactant-rich phase accounting for approximately 5% of the total volume. • A recovery efficiency of 87% is achieved with Sr purity exceeding 94% in simulated high-level liquid waste. • Cloud point extraction for Sr separation is comprehensively compared with the conventional solvent extraction systems. Conventional solvent extraction for treating high-level liquid waste results in organic phases contaminated with radioactivity, posing challenges in disposing large volumes of radioactive organic liquid after their lifespan, it is thus critical to minimize organic liquid volume. This study presents the concept of separating Sr(II) from high-level liquid waste using cloud point extraction (CPE), where 18-crown-6 and its derivatives serve as complexing agents, while the surfactant Triton X-114 acts as both a temperature-driven phase-splitting agent and a cosolvent for the poorly water-soluble 18-crown-6 derivatives. After optimizing experimental conditions, >50 % of Sr(II) was partitioned into the surfactant-rich phase, constituting only 5 % of the total volume. A total Sr recovery yield of 87 % was achieved through four cross-flow extractions, with its purity exceeding 94 %. Furthermore, the CPE demonstrated extremely high concentration factors, satisfactory extraction efficiencies, short equilibrium times, and low chemical costs—which are difficult to achieve simultaneously with conventional solvent extraction.