Novel Polyethylene Glycol-Based Aqueous Biphasic Systems for the Extraction of Strontium and Cesium

Abstract

The partitioning behavior of Sr²⁺ and Cs⁺ in aqueous biphasic systems formed by the addition of polyethylene glycol (PEG)-2000 to either NaOH, (NH₄)₂SO₄, or K₂CO₃ was investigated. Phase diagram data reveal that on a weight percent basis the salting out effects of the three salts increase in the order (NH₄)₂SO₄ < K₂CO₃ < NaOH. In the presence of traditional extractants 12-crown-4, 15-crown-5, or 18-crown-6, only the partitioning of Sr²⁺ from (NH₄)₂SO₄ media using 18-crown-6 resulted in the expected 1:1 extractant dependency. All other measured distribution ratios in the presence or absence of extractants and regardless of salt system appear to be governed by cation enthalpy of hydration and system composition. The distribution ratio for cesium, D_Cs is greater than D_Sr due to cesium's lower enthalpy of hydration. D_M vs. percent salt and percent PEG both reveal an increase in D_M with decreasing salt or PEG.