Recovery of pure lead and preparation of nano-copper from waste glass diodes via a clean and efficient technology of step-by-step vacuum evaporation-condensation

Waste glass diodes, generated vastly with discarded printed circuit boards, are rich in metal resources while carriers of hazardous heavy metals. They require proper treatment to recover metals and avoid heavy metal contamination, but relevant research is insufficient currently. Thus, an environmentally-friendly and efficient technology of step-by-step vacuum evaporation-condensation was proposed in this study to recover lead and prepare nano-copper particles. A heat transfer model was established to guide the evaporation process with the purpose of effective treatment and energy-saving. According to the model, metal materials and the heating equipment could reach the endpoint of the set temperature T1 almost simultaneously when T1 >= 600 degrees C. In the first step, 99.94% of lead was separated when evaporating at 800 degrees C for 1 h. Condensation products of pure lead were collected centrally, which eliminated the Pb contamination caused by its migration. The second step was optimized by the response surface methodology, and optimal operation parameters were determined as 1250 degrees C and 3 h. Under these conditions, 91.71% of copper was evaporated and transformed into nano-copper particles ranging from 20 nm to 200 nm. In short, this study firstly provided an effective approach for the treatment of waste glass diodes and their high-value-added reuse.