Extraction of Au(III) by ionic liquid from hydrochloric acid medium

• The IL/chloroform system shows high extractability and selectivity for Au(III).
• The mechanism of gold(III) extraction by [C16mim]Cl was studied.
• Thermodynamic parameters of the Au(III) extraction reaction were obtained.
• The Au stripping and the [C16mim]Cl regeneration can be achieved using oxalate.

The ionic liquid, 1-hexadecyl-3-methylimidazolium chloride/chloroform system was investigated for Au(III) extraction. In the extraction system, [C16mim]Cl bears a function of extractant. The effects of extraction time and [C16mim]Cl concentration were examined for Au(III) extraction. The anion-exchange mechanism of Au(III) extraction by [C16mim]Cl was confirmed by the method of continuous variation, UV–Vis and infrared spectrum analysis. According to the thermodynamics analysis, thermodynamic parameters of the Au(III) extraction reaction were obtained, which illustrates that higher temperature show negative effect for the Au(III) extraction. Under the experimental conditions, the [C16mim]Cl/chloroform system shows a high extractability for Au(III), also has high selectivity over some metals (Cu(II), Co(II), Ni(II), Fe(III), Al(III) and Sn(IV)). Moreover, oxalic acid is explored to reduce the Au–IL complex [C16mim]+AuCl4-, by which Au(III) is striped in the form of metallic gold precipitate and [C16mim]Cl also can be recycled.