Extraction of Ag and Au from chloride electronic waste leach solutions using ionic liquids

Abstract

Electronic waste (e-waste) contains valuable materials such as metals. These may be recovered using conventional pyrometallurgical or hydrometallurgical processes. However, these existing metal recovery techniques have a number of limitations such as adverse environmental footprints and high energy costs. This then necessitate an investigation into alternative methods or reagents. In this research, ionic liquids; [Bmim][Tf2N], [Bmim][PF6], and Cyphos 101 were investigated as extractants for Ag and Au from chloride aqua regia leach liquors of printed circuit board samples, with the composition of 162 gt−1 Au and 618 gt−1 Ag. The ionic liquids used were found to be efficient extractants for Au extraction from the leach liquor, with more than 90% of Au extracted in all the ionic liquids tested. Ag extraction was however, found to be lower compared to Au with no extraction recorded for [Bmim][Tf2N] but over 90% extraction was recorded for both Cyphos 101 and [Bmim][PF6]. This showed that ionic liquids are potential alternative extractants for the recovery of Au and Ag from chloride media. Considering both costs and efficiency, Cyphos 101 proved to be the most effective extractant for all metals from chloride solution at room temperature and 1:1 of the IL: sample ratio. The extractions were 95% Ag, 97% Au and 99% Cu under these conditions.