Effectiveness of acidic deep eutectic solvents in recovery of hazardous base metals from waste printed circuit boards

Traditional methods for metal recovery from printed circuit boards (PCBs) are often associated with high costs, toxicity, and environmental risks. This study explores the use of acidic deep eutectic solvents (DESs) as a green alternative for recovering Pb, Cr, Zn, and Ni from waste PCBs. Three DESs were prepared using choline chloride (ChCl) as a hydrogen bond acceptor (HBA) and paired with acetic acid (AA), chloroacetic acid (CAA), or dichloroacetic acid (DCA) as hydrogen bond donors (HBDs). The effect of DES nature on the recovery of the investigated metals follows the sequence ChCl:DCA > ChCl:CAA > ChCl:AA. The results revealed that the ChCl:DCA DES exhibited the highest recovery efficiency, achieving 89.5% for Pb, 55.2% for Cr, 80.5% for Zn, and 88.6% for Ni at 50 °C for 3 h in the presence of 1.0 M H₂O₂ and a stirring speed of 500.0 rpm. In addition, recovery efficiencies of 99.8%, 71.8%, 100.0%, and 84.9% were achieved for Pb, Cr, Zn, and Ni, respectively, when 40.0 wt% water was added to the ChCl:DCA DES. The shrinking core model (SCM) reveals that the recovery of Pb, Cr, Zn, and Ni from waste PCBs is governed by a diffusion-controlled mechanism. The activation energies were determined to be 19.8 kJ/mol for Pb, 32.4 kJ/mol for Cr, 14.3 kJ/mol for Zn, and 30.2 kJ/mol for Ni. This study offers a promising and highly sustainable alternative for the recovery of hazardous metals from waste PCBs, contributing to a benign environmental approach and process.