In-situ microwave-assisted leaching and selective separation of Au(III) from waste printed circuit boards in biphasic aqua regia-ionic liquid systems

Waste printed circuit boards (WPCBs) contain high amounts and various types of precious metals; thus, it is necessary to efficiently and selectively recover these metals by eco-friendly and economic means. An in-situ microwave-assisted leaching and selective separation process employing biphasic aqua regia-ionic liquid systems was developed herein. It was hypothesized that the combined technique can pulverize the WPCB sample, while simultaneously leaching Au(III) and Cu(II) from the WPCBs and affording selective separation using the ionic liquid (IL), i.e. [C₈mim][(CF₃SO₂)₂N]. The results show that the microwave treatment increased the Au(III) and Cu(II) leaching efficiency by 45.56% and 10.83%, respectively, compared to the control test without microwave treatment, and the leached Au(III) and Cu(II) ions present in the aqua regia phase were simultaneously transferred into the IL phase, leading to high selective separation efficiencies, i.e. extraction rates of 95.50% and 1.26% for Au(III) and Cu(II), respectively. In the final stage, the concentrated Au(III) was back-stripped using 0.01 M thiourea in 0.1 M HCl solution. The recovery of Au(III) ions from the IL phase was 96.74 ± 2.19%. Consequently, it was revealed that microwave treatment in the aqua regia-IL phases can efficiently lead to pulverization of WPCBs and leaching of Au(III) and Cu(II), followed by selective separation of Au(III) from the leachate by the IL.