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

Abstract

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.