Selective Extraction and Back-Extraction of Strontium Using Crown Ether in 1-Octanol/Dodecane Mixed Solvents: Control of Acid Co-Extraction and Separation from Multi-Element Systems

Efficient separation of Sr from multi-element mixtures is crucial in various industrial processes, including nuclear waste management. In this study, the solvent extraction behavior of Sr using a crown ether extractant, DtBuCH18C6, was systematically investigated with particular emphasis on controlling acid co-extraction using a 1-octanol/dodecane mixed solvent. The results revealed that increasing the 1-octanol volume ratio enhanced Sr extraction, which is attributed to improved solvation of the extractant and stabilization of extracted Sr species in the organic phase. However, this also led to the co-extraction of nitric acid, significantly hindering back-extraction of Sr due to acid accumulation in the organic phase. In contrast, reducing the 1-octanol content suppressed acid loading of the organic phase and facilitated efficient Sr back-extraction. Slope analysis indicated that the apparent dependence of Sr extraction on nitric acid concentration varied with solvent composition, reflecting changes in the extraction environment. Moreover, separation factors of Sr against various coexisting metals, including Ba, Mo, and Ag were evaluated. Back-extraction experiments under multi-element conditions demonstrated that a 1-octanol content of 10% provided high Sr stripping efficiency ( > 90%) in the recovered aqueous phase. The findings highlight solvent composition control as a complementary design parameter for achieving high Sr selectivity and recovery in separation systems treating complex multi-element solutions.