Extraction of Au(I) from aurocyanide solution by using a synergistic system of primary amine N1923/bis(2-ethylhexyl) sulfoxide: A mechanism study

Abstract

The synergistic effect of a mixture of bis(2-ethylhexyl) sulfoxide (BESO) and primary amine N1923 in kerosene on the extraction of Au(I) from alkaline cyanide solution was investigated. Experimental results demonstrate that addition of BESO into the organic phase can significantly enhance the basicity of amine N1923, in which the pH50 value can reach up to 11.91. Slope analysis suggested that the composition of the extracted complexes in the organic phase is [Au(CN)2−·RNH3+·2BESO]. The extracted complexes were characterized by FTIR spectroscopy, 1H NMR spectroscopy, mass spectrometry, and electrical conductivity analysis. FTIR and 1H NMR studies reveal strong interactions between BESO and N1923 molecules through hydrogen bonding between the O atoms in the SO groups and the H atoms in the –NH2 groups, forming SO…H–N. This hydrogen bonding enhances the basicity of N1923 and consequently the ability of N1923 to capture proton; Au(CN)2− serves as a counter anion against the protonated amine cation in the organic phase. Electrical conductivity measurements confirmed ionic character of the extracted complexes. The Au(I) extraction in the N1923/BESO system most probably involves the ion-association (ion pair) mechanism. A plausible microstructural model of the extracted complexes was proposed in the paper. Moreover, gold could be efficiently stripped from the loaded organic phase by using sodium hydroxide solution.