A novel method of preparing highly dispersed spherical lead nanoparticles from solders of waste printed circuit boards

• Vacuum separation and dynamic inert gas condensation were applied in this research.
• More than 98 wt% of Pb were separated from waste solders.
• Spherical Pb nanoparticles with high purity were successfully prepared.
• The formation mechanism of Pb nanoparticles was studied.

In this study, highly dispersed spherical lead (Pb) nanoparticles were prepared from Pb contained solders of waste printed circuit boards (WPCBs) by combining vacuum evaporation and forced flow inert gas condensation. With a relatively high vapor pressure, Pb could be easily separated from waste Pb/Sn solders by vacuum evaporation, while Sn still remained in the residues. Simultaneously, Pb nanoparticles were prepared by the dynamic inert gas condensation. Agglomeration and size inhomogeneity phenomena were eliminated to the maximum extent by sharp quenching using forced flow inert gas and optimizing operation parameters like dynamic nitrogen gas pressure, heating and condensation temperature and condensation distance away from the heater. Highly dispersed spherical Pb nanoparticles were prepared under the optimized conditions of 1223 K heating temperature, 1000 Pa dynamic nitrogen gas pressure, 413 K condensation temperature and 60 cm condensation distance away from the heater. The separation efficiency of Pb from waste solders could reach to higher than 98.2 wt% with the product purity of more than 98 wt% and the size distribution ranging from 20 to 100 nm. This work provides the theoretic foundation for recycling Pb with high added values from waste Pb/Sn solders or other Pb contained solid wastes.

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