Sustainable leaching of metals from waste printed circuit boards using efficient carboxylic acid-based deep eutectic solvents

Abstract

• Carboxylic acid-based DESs were used to leach Cu, Al, Fe, Sn, and Sc from WPCBs. • ChCl:TCA DES achieved the highest metal recovery under optimized conditions. • FT-IR analysis confirmed metal complexation with DES components. • Kinetic analysis showed a diffusion-controlled leaching mechanism. • The study offers a sustainable alternative for e-waste recycling. The exponential growth in electronic waste presents a substantial environmental and economic challenge due to the high content of valuable metals it contains. So, in this study, we investigated the use of carboxylic acid-based deep eutectic solvents (DESs) for the leaching of base metals (Cu, Al, Fe, Sn, and Sc) from waste printed circuit boards (WPCBs). The DESs used were prepared at a 1:2 M ratio from choline chloride (ChCl) used as hydrogen bond acceptor (HBA) with either chloroacetic acid (CAA), dichloroacetic acid (DCA), or trichloroacetic acid (TCA) as hydrogen bond donors (HBDs). The influence of the DES type on the leaching of the metals studied follows the order: ChCl:TCA > ChCl:DCA > ChCl:CAA. Specifically, ChCl:TCA DES displayed the best leaching efficiencies by achieving leaching efficiencies of 87.3 % for Cu, 85.3 % for Al, 89.9 % for Fe, 68.4 % for Sn, and 60.6 % for Sc at a temperature of 45 °C and contact time of 3.0 h in the presence of 1.0 M H 2 O 2 with the grain size of 212 µm under 500 rpm agitation and solid-to-liquid ratio of 1:10. Outstanding leaching efficiencies of 100.0 %, 98.5 %, 95.3 %, 91.9 %, and 82.6 % were obtained for Cu, Al, Fe, Sn, and Sc respectively when the temperature was raised to 65 °C and the grain size reduced to 106 µm. Furthermore, kinetic analysis involving both diffusion- and chemical reaction-controlled models, yielded activation energies below 40.0 kJmol −1 for all metals, suggesting a diffusion-controlled leaching mechanism.