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

Saga, Kaname; Ban, Yasutoshi  

The solvent extraction behavior of Sr using a crown ether extractant, DtBuCHC, was systematically investigated with particular emphasis on controlling acid co-extraction through the use of a 1-octanol/dodecane mixed organic solvent. Increasing the 1-octanol volume ratio with dodecane improved solubility and complexation stability of DtBuCHC, enhancing Sr extraction. 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. The number of co-extracted nitric acid molecules was strongly dependent on the solvent composition, ranging from approximately 1 under 100% 1-octanol to 3 under 10% 1-octanol conditions. 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% also provided high Sr stripping efficiency (90%) in the recovered aqueous phase. The findings of this study highlight the importance of solvent composition control in designing extraction systems capable of achieving high selectivity and purity for Sr separation from complex multi-element solutions.