Efficient extraction of gold from water by liquid-liquid extraction or precipitation using hydrophobic ionic liquids

Extraction of tetrachloroaurate or tetrabromoaurate anions has been carried out using several ionic liquids bearing trialkyl(2-ethoxy-2-oxoethyl)ammonium (alkyl group = C2H5 [EtGBOEt(+)], n-C3H7 [PrGBOEt(+)] or n-C4H9 [BuGBOEt(+)]) cations and halide (Cl- or Br-), bis(trifluoromethanesulfonyl)imide (Tf2N-) and dicyanamide (Dca(-)) anions. The removal of gold anionic moieties from water was first studied by mixing aqueous solutions containing gold complexes and water soluble bromide ionic liquids. This led to the formation of a solid precipitate corresponding to a hydrophobic ionic liquid based on a tetrahalogenoaurate anion. Liquid-liquid extraction of anionic gold complexes using hydrophobic ionic liquids was also investigated.