Surface characteristic driven in waste printed circuit boards flotation: Floatability mechanism of resin and glass fiber in non-metallic component

Abstract

To alleviate the environmental crisis caused by electrical waste, green reverse flotation of waste printed circuit boards (WPCBs) has been an appealing approach. Unfortunately, whether the floatability of non-metallic particles (NMPs) is caused by resin or glass fiber has not been confirmed. The floatability of NMPs, glass fiber particles in NMPs, pure resin particles and pure glass fiber particles were studied to determine the contribution to the floatability of NMPs. Firstly, the surface morphology of NMPs was analyzed by SEM, the results show that glass fiber and resin are locked together, leading to confusion in the mechanism of flotation. FTIR results show that the hydrophobic functional groups in NMPs are mainly derived from resins. Secondly, the floatability of each sample was also characterized by contact angle (CA) and wrap angle. The results show that NMPs and pure resin particles have excellent floatability with CA of 77.31º and 85.19º, while pure glass fiber particles have strong hydrophilicity with CA of 0º. The wrap angles of pure resin particles and pure glass fiber particles are 245º and 76º, respectively. Furthermore, the flotation results show that accumulated float yield of pure resin reach 100% within 120 s. The cumulative yield of pure glass fiber particles and NMPs after combustion is 6.22% and 12.52%, respectively. This study reveals the flotation mechanism of NMPs in WPCBs, proves that resin is the cause of the floatability of NMPs, which provides a guidance for the subsequent efficient recycling of WPCBs.