Waste printed circuit boards (PCBs) account for about 3% of nearly 50Mt/year global E-waste generation [1]. They are constituted by a heterogeneous mixture of metals, ceramic and plastics. Among these fractions, the driving force for recycling waste PCBs is the recovery of metals (in particular Au). Because PCBs contain many base and precious metals (PMs), which concentrations are much higher than those found in the natural deposits, they are recognized as a respectable poly-metallic secondary urban mining. However, due to their heterogeneous composition and hazardous material contents, proper recycling methodology is still a challenging task.
Besides a huge informal sector for treatment of waste PCBs handled in several countries (mainly in China), in developed countries, the treatment of waste PCBs is carried out by physical recycling of metallic and non-metallic (NM) fractions by mechanical recycling and/or in smelters (via pyrometallurgy followed by hydrometallurgical refining) [1]. Even though physical recycling methods are relatively simple and environmentally sound, significant dust generation and PMs loss (about 40%) occur [1]. Although smelters offer the advantage to treat any form of scraps [2], pyrometallurgical processes present important drawbacks [loss of PMs, generation of hazardous emissions (namely dioxins plus flue dust containing metals). Since the energy costs are steadily rising and stricter environmental regulations will require large investments for smelters, hydrometallurgical routes for treatment of flue dusts are complex and generate sludges, all these facts stress the urgency of developing alternative metallurgical infrastructures at a small scale. Considering that, the strength of hydrometallurgy when compared with pyrometallurgy lies in the possibility to process low grade and chemically complex streams to obtain final products with low energy consumption, low or no gases emissions and high metals recovery rates [3], recycling waste PCBs should be based in hydrometallurgical processes.
Since Au is the key economic driver force for recycling PCBs, alternative hydrometallurgical strategies to the complex ones available now (see Literature review) should be based in efficient and simple processes. Recently, we developed a simple hydrometallurgical process for recycling Cu from wastes PCB with high yield and purity [4]. These results are encouraging. Moreover, our subsequent preliminary results (see Task 2) open the possibility of answering positively to this challenge. Based on this fact and the multidisciplinary expertise of this team, the main aim of this project is to develop a new sustainable and flexible (which adapts to different metal grades without compromising the purity of the final products) metallurgical process with lower carbon footprint for valorising all fractions (particular the one of highest economical value revenue) of waste PCBs and minimizing the amount of waste created (see Plan and Methods).