Proposal of novel process to concentrate valuable metals and to remove impurity elements from wasted PCBs

Recycling of various metals involved in the electronic printed circuit boards (PCBs) is important. However, PCBs contain not only valuable metals, Cu and precious/rare metals, but also the elements, Al, Br, Sb, etc., which adversely affect the following non-ferrous metals smelting operation. Most of the conventional PCB recycling processes, involving crushing and physical separation, have not taken care on such elements. This study presents a knowledge of PCB recycling, to concentrate valuable metals and remove such impurity elements, by combining roasting, selective crushing and physical separation. It was determined that an appropriate roasting condition was approx. 300 C at air atmosphere to make brittle the resins composed of the PCB and to decompose flame retardants, Br and Sb. It was also found important to apply two-stage comminution, which involves cutting into the pieces of appropriate size in the first stage and liberating E-glass fiber from resin in the PCB without flocculating E-glass in the second stage. The subsequent physical separation process could concentrate of 38.9 wt% Cu with the recovery of 80.3 % and reduce Al by 64.7 %, Br by 75.1 % and Sn by 50.2 %.