Conceptual Process Design and LCA Evaluation of Precious Metals Recovery from Waste PCBs

Abstract The present study explores the development and evaluation of precious metals (PM) recovery processes designed to extract silver (Ag), gold (Au), and palladium (Pd) from copper anode slimes (CAS) generated via the black copper route from waste printed circuit boards (PCBs). Two conceptual process flowsheets—Route 1 (conventional) and Route 2 (polar aprotic solvent)—were designed and simulated adopting established and novel metallurgical methods using FactSage™ and HSC Chemistry 10 software. Both routes employed leaching-precipitation techniques; however, Route 1 utilized conventional acid-salt precipitation methods, whereas Route 2 incorporated with a novel approach based on polar aprotic solvent leaching. The results showed that the simulated recovery rates for Ag, Au, and Pd were high across both processes, achieving 94.8%, 99.1–99.3%, and 99–99.2%, respectively. To evaluate the environmental impacts, a life cycle assessment (LCA) was conducted using openLCA, with the treatment of CAS in kg as the functional unit and a gate-to-gate system boundary. It was found that Route 1 had lower environmental impact potentials, yielding acidification potential (AP) of 0.52–0.93 kg SO₂ eq, eutrophication potential (EP) of 0.67–1.21 kg PO₄ 3 ⁻ eq, and global warming potential (GWP) of 61.83–110.4 kg CO₂ eq. Conversely, Route 2 exhibited higher AP (0.59–1.26 kg SO₂ eq), EP (0.7–1.33 kg PO₄ 3 ⁻ eq), and GWP (75.1–134.9 kg CO₂ eq), primarily due to the use of CuCl₂, DMF, and ethanol in the Au and Pd recovery steps. Furthermore, scenario analysis revealed that CAS with higher PM content resulted in greater environmental burdens compared to CAS with a higher proportion of base metals. This finding suggests that while PM recovery remains the primary objective, base metal removal entails a lower environmental cost. Additionally, it is important to mention that both routes are identical up to the Ag electrorefining stage, which emerged as the most impactful unit operation, contributing approximately 65% and 98% of the total environmental impacts in Route 1 and Route 2, respectively, primarily due to the high demand for silver nitrate. Overall, Route 1 demonstrated superior environmental performance while maintaining high recovery rates, making it a more sustainable option for industrial-scale CAS processing. These findings provide valuable insights for optimizing PM recovery strategies while minimizing environmental impacts in the circular economy framework. Graphical Abstract