Advanced utilization of copper in waste printed circuit boards: Synthesis of nano-copper assisted by physical enrichment.

The copper in the waste printed circuit boards (WPCBs) is cleanly recycled by physical methods and presented in the form of nano copper particles by hydrometallurgical, which provides environmental approach to the advanced utilization of metal copper. Copper in WPCBs was first pre-concentrated by gradient enrichment process including gravity separation, mechanical grinding and flotation. The leaching method was then used to dissolve copper from the flotation concentrate in ammoniacal/ammonium salt solutions. Subsequently, reduction treatment was conducted to synthesize nano-copper from leaching solution. The enrichment results of the clean physical separation process show that the grade of copper increased from 16.22% to -38.05% by gravity separation, and the grade of copper further increased to 72.62 % by flotation after dissociation, which avoids overgrinding of low value components. Copper nanoparticles can be prepared effectively, and the recovery of copper in the leaching process reaches 99 %. The particle size of copper nanoparticles obtained by ascorbic acid reduction is tens of nanometers, and the surface of copper nanoparticles is smooth and nearly spherical. The present study proposes an environmentally friendly process of preparing nano-copper from the copper in WPCBs.