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

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=C-8-C-10), 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 C=N stretching vibrations of Au(CN)(2)(-) in the three systems differed greatly. The second derivative spectra of C=N stretching bands of Au(CN)(2)(-) were also found to be different. In order to explain the differences in the IR characteristics of C=N 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 C=N in solid KAu(CN)(2) was also performed in order to offer additional supporting evidence for the reliability of the proposed models.