Simple and environmentally friendly metal recovery from waste printed circuit boards by using deep eutectic solvents

Abstract

<p>Increased environmental awareness has necessitated the development of a simple and environmentally friendly method for metal recovery from waste <a href="https://www.sciencedirect.com/topics/engineering/printed-circuit-board" title="Learn more about printed circuit boards from ScienceDirect's AI-generated Topic Pages">printed circuit boards</a> (WPCBs). Deep <a href="https://www.sciencedirect.com/topics/engineering/eutectics" title="Learn more about eutectic from ScienceDirect's AI-generated Topic Pages">eutectic</a> solvents (DESs) are environmentally friendly and non-aqueous lixiviants that can leach <a href="https://www.sciencedirect.com/topics/earth-and-planetary-sciences/metal-oxide" title="Learn more about metal oxides from ScienceDirect's AI-generated Topic Pages">metal oxides</a> to replace mineral acids. In this study, three <a href="https://www.sciencedirect.com/topics/earth-and-planetary-sciences/choline" title="Learn more about choline from ScienceDirect's AI-generated Topic Pages">choline</a> chloride (ChCl)-based DESs were synthesized, using ethylene glycol, <a href="https://www.sciencedirect.com/topics/earth-and-planetary-sciences/oxalic-acid" title="Learn more about oxalic acid from ScienceDirect's AI-generated Topic Pages">oxalic acid</a> (OA), and glycolic acid (GA) as the <a href="https://www.sciencedirect.com/topics/earth-and-planetary-sciences/hydrogen-bond" title="Learn more about hydrogen bond from ScienceDirect's AI-generated Topic Pages">hydrogen bond</a> donors in the <a href="https://www.sciencedirect.com/topics/earth-and-planetary-sciences/eutectics" title="Learn more about eutectic from ScienceDirect's AI-generated Topic Pages">eutectic</a> mixtures. The time-dependent leaching yields and saturated loading capacities of the DESs to typical metal oxides and Ag were evaluated. Considering the leaching performances, a simple and environmentally friendly method for metal recovery from WPCBs was established, based on two-stage DES leaching processes. The research object was the mixed metal powder collected from the mechanical processing of WPCBs. The results indicated that 90.35% of Zn, 87.47% of Pb, and 16.77% of Cu were removed from the mixed metal powder after calcination by leaching of the ChCl-GA DES and precipitation of the oxalic acid solution. When the residue was subjected to ChCl-OA DES leaching, Cu was recovered by diluting ChCl-OA DES with water. Specifically, 74.93% of Cu was separated in the form of CuC₂O₄·2H₂O with a purity of >98 wt%. The Sn remaining in the aqueous solution was efficiently recovered by the addition of reduced Fe powder, and the recovery yield of Sn in the recovery product was 51.29%. Finally, the advantages of a simplified and environmentally friendly process framework, are highlighted by a comparison of the recovery strategy for WPCB proposed in this study with conventional pyro- and hydro-metallurgical approaches.</p>