An ultra-high decontamination factor for yttrium(III) with strontium(II) via dissolution control and non-aqueous solvent extraction

A non‑aqueous separation strategy that combines acetonitrile (ACN) with 1, 3‑propanediol (PDO) is presented for the ⁹⁰yttrium(III)/⁹⁰strontium(II) (Y(III)/Sr(II)) separation. In an initial dissolution step, the ACN-PDO mixture displays a pronounced solubility contrast between Y nitrate (1.22 g/100 g) and Sr nitrate (0.09 g/100 g), enabling the selective dissolution of trace Y(III) while Sr(II) remains largely undissolved. Furthermore, ACN-PDO mixture also exhibits favorable physicochemical properties, e.g., relatively low viscosity (about 40 mPa·s), a suitable density difference (0.25 g/cm³) from n-octane, and lower miscibility with n-octane, for constituting an extraction system with N,N,N’,N’ tetra-octyl-3-oxopentanediamide in n-octane, in which both Y(III) extraction efficiencies and separation factors greatly exceed those of aqueous-based extraction systems. Density functional theory calculations also confirmed that the Y/Sr separation is more favorable in ACN-PDO/n-octane systems compared to water/n-octane systems due to differences in solvation effects and contact ion pairs. A practice integrated separation process achieved a Y(III) recovery of >90 % with product purity exceeding 99 %. The overall decontamination factor (>460,000) is markedly higher than the values reported for existing aqueous‑based methods.