Silver leaching from wasted printed circuit boards using choline chloride-based ternary deep eutectic solvents

In this study, we developed two TDES systems- choline chloride (ChCl)-glycerol (Gly)-malic acid (MA), labelled as TDES 1, and ChCl-ethylene glycol (EG)-citric acid (CA), as TDES 2, for silver leaching from wasted printed circuit boards (WPCBs). Viscosity, density, pH, and solubility measurements were conducted to observe the physical characteristics of TDES. Both TDES systems were polar and exhibited a pH of 2. Increasing the molar ratio of the hydrogen-bond acceptor (HBA) decreased the viscosity of the TDES, whereas increasing the molar ratio of the hydrogen-bond donor (HBD) increased the viscosity of the DES. Fourier-transform infrared spectroscopy (FTIR) analysis revealed hydrogen-bond interactions between components in TDES, indicated by shifts in the functional group wavenumbers. Differential scanning calorimetry (DSC) showed thermal transitions, including partial melting, cold crystallization, and secondary phase changes, confirming the formation of stable eutectic systems. TDES 1 (1:2:1 molar ratio) and TDES 2 (2:1:1 molar ratio) were used as lixiviants to extract silver from WPCBs. The optimum leaching temperature for both TDES was 120 °C, with a solid-to-liquid (S/L) ratio of 1/100. The optimum leaching duration was 6 h for TDES 1 and 9 h for TDES 2. Under optimum conditions, TDES 1 and TDES 2 achieved efficiencies of 98.36% and 94.82%, respectively, highlighting their effectiveness in recovering silver from PCB waste. Both TDES offer potential as efficient and environmentally sustainable solvents for the recovery of critical metals from electronic components. This approach supports better resource recovery and a circular economy for electronic waste management.