Dominic BURNS1, John D. HOLBREY1, Hye-Kyung TIMKEN2
1Queens University Belfast, Belfast, United Kingdom
2Chevron Corporation, Richmond, United States
Extraction of hydrophilic oxyanions from aqueous solutions is a challenge across many areas from acid mine drainage to nuclear waste remediation, nuclear medicine, and general water treatment to address compliance with total discharge limits. The viability of hydrophobic ionic liquid (IL) media as liquid extractants for oxyanions from aqueous solution has been assessed, and it has been shown that environmentally relevant concentrations of sulfate ([SO4]2-) anions can be extracted and exchanged for chloride.
A series of long chain ammonium and phosphonium chlorides with functionality that mimics commercial ion-exchagne (IX) resins have been been obtained from commercial sources (Cyphos® 101 ([P66614]Cl) and Aliquat® 336 ([N1888]Cl)) or synthesised ([HN888]Cl, [N2OH888]Cl and [P1888]Cl) and examined as potential liquid anion exchangers for partitioning of sulfate from water. Sulfate was used a model due to its large hydration enthalpy and was successfully extracted primarily by an IX mechanism. The ionic liquid extracting phases were characterized by 1H and 13C NMR, FT-IR spectroscopy. Density and viscosity and mutual solubility with water were measured. The effects of aqueous sulfate concentration, phase-volume ratio and aqueous chloride concentration on the sulfate extraction efficiency were determined by ED-XRF and the data fitted to non-linear models.
Enhanced extraction of tetrahedral oxyanions was obtained by the addition of , weakly coordinating bis(urea) and bis(thiourea) receptors to the IL phase, leading to significant improvement in partition of sulfate ions from aqueous solution. High loadings of these receptors can be obtained through initial complexion with chloride which is then released upon contact with the sulfate solution. The mechanism and impact on sulfate anion extraction will be discussed.