Quantitative extraction of aqueous alkali metal ions using supercritical carbon dioxide and polyethylene glycol ligands

Abstract

Quantitative extraction (30–70%) of alkali metal ions (K⁺, Na⁺: 1.7 × 10⁻⁴ mol dm⁻³) from aqueous solutions with supercritical carbon dioxide (40 °C, 10–18 MPa) could be achieved using glymes (triethylene glycol dimethyl ether (triglyme: 3G), tetraethylene glycol dimethyl ether (tetraglyme: 4G)) and the addition of pentadecafluoro-n-octanoic acid (HPFOA) that supplies a CO₂-philic counter ion and makes the metal–ligand complex soluble in the CO₂ solvent via counter ion exchange.