FTIR and EXAFS investigations of microstructures of gold solvent extraction: hydrogen bonding between modifier and Au(CN)2-

Abstract

The microstructures of loaded organic phases of three quaternary amine solvent extraction systems for gold, which were N263–xylene, N263–tributyl phosphate (TBP)–dodecane and N263–2-ethylhexanol (isooctanol)–dodecane (N263-trialkylmethylammonium chloride; alkyl=C₈–C₁₀), were studied by Fourier transform infrared (FTIR) spectroscopy and extended X-ray absorption fine structure (EXAFS) spectroscopy. According to the EXAFS results, it was found that the gold coordination environment was the same before and after extraction. However, the C3N stretching vibrations of Au(CN)₂^- in the three systems differed greatly. The second derivative spectra of C3N stretching bands of Au(CN)₂^- were also found to be different. In order to explain the differences in the IR characteristics of C3N in the three extraction systems, three microstructure models are proposed. For the N263–xylene system, the model is a simple ion pair. For the other two systems with a modifier (TBP and isooctanol), the models are two supramolecular structures based on hydrogen bonding between the modifier and Au(CN)₂^-. Some related work such as on the hydration of acetonitrile and the fine structure of C3N in solid KAu(CN)₂ was also performed in order to offer additional supporting evidence for the reliability of the proposed models.