Felipe Alejandro Garcia Paz

The impulse of the Fourth Industrial Revolution is triggering the demand for few specific metals. These include copper, silver, gold, and platinum group metals (PGMs), with important applications in renewable energies, green hydrogen, and electronic products. However, the continuous extraction of these metals is leading to a rapid decline in their ore grades and, consequently, increasing the environmental impact of extraction. Hence, obtaining metals from secondary sources, such as waste electrical and electronic equipment (WEEE), becomes imperative for both environmental sustainability and ensuring availability. This recovery entails few problems such as allocation due to the simultaneous production of several metals, the use of non-renewable resources, and the exergy destruction during the life cycle of the metals. Therefore, this work analyses the waste printed circuit boards (PCBs) recycling process by proposing different exergy-based cost allocations for the mentioned metals, disaggregating the exergy cost into non-renewable and renewable, and considering the complete life cycle of metals with the Circular Thermoeconomics methodology. The results show a significant saving of non-renewable energy by using renewable energies in primary extraction (67-87%), recycling (97.6-98.5%), and renewable energies in recycling (98.7%, 99.0%), compared to conventional primary extraction. However, when considering the entire life cycle, between 47% and 53% of the non-renewable exergy is destroyed during recycling. Therefore, delaying recycling as much as possible would be the most desirable option for maximizing the use of non-renewable resources, which nature cannot replace in a short time.

This study outlines a recycling initiative conducted at Rekular GmbH, focusing on the recycling of 100 refrigerators. The recycling process employed a combination of manual dismantling, depollution, and mechanical processing techniques. Manual dismantling followed a predefined protocol to extract various materials, while the mechanical and physical processes involved shredding, zigzag, magnetic, and eddy current separation (ECS) to liberate and separate different materials. The resulting ferrous, non-ferrous and polymer product fractions were analyzed and categorized, providing valuable insights into the quality of interim products in the refrigerator recycling process. Simulations were then performed using FactSage^TM version 8.2 and HSC Chemistry 10 version 10.3.7.1 software to simulate the recovery of metals from the ferrous and non-ferrous fractions using pyro metallurgical and hydrometallurgical methods. An electric arc furnace (EAF) was utilized for iron (Fe), while a re-smelter process for aluminium (Al), and the black copper route was simulated for copper (Cu) recovery. The recovery rates including metallurgical, mechanical, and physical processes are as follows: Fe (78%), Al (68.4%), and Cu (52.4%). In contrast, the recovery rates through metallurgical processes are as follows: Al (99%), Fe (79%), and Cu (88%). This discrepancy is attributed to losses of these elements resulting from incomplete liberation in mechanical processing. Additionally, a product/centric approach was applied and the recycling index reached 76% for recovery the Al, Cu, and Fe metals in a refrigerator recycling process. Turning to the environmental impact evaluation within the life cycle assessment (LCA), the process unit with the highest emissions per refrigerator in the recycling process was the use of nitrogen during the shredding process, accounting for 3.7 kg CO₂ eq/refrigerator. Subsequently, the consumption of medium voltage electricity from the German grid during mechanical and physical separations contributed to 0.6 kg CO₂ eq/refrigerator. The EAF, and electrolytic refining stages in the metallurgical recovery process also had a notable impact, generating 10.7 kg CO₂ eq/refrigerator.